Environmental Dermatology

Horse flies (Tabanidae) are hematophagous dipteran insects that feed on the blood of their hosts, including humans.¹ Their bites can cause minor cutaneous reactions (eg, urticaria) or, rarely, severe reactions such as anaphylaxis. They also are vectors of tularemia, which may manifest with cutaneous ulcers and systemic illness. In this article, we discuss identifying features of horse flies as well as clinical manifestations from bite reactions, symptomatic and emergency management, and strategies for prevention and control.

Morphology and Geographic Distribution

Horse flies, which can grow as large as 30 mm, can be identified by their brown or black bodies and characteristic large heads and proboscises, wing venation, large calypters, pulvilliform empodium between large pulvilli, and lack of bristles on the body.² Occasionally, their bodies may be gray, yellow, green, or blue, but this is less likely than in the other species of the Tabanidae family. Short hairs are present on the head and thorax. The eyes are large and often patterned, multicolored, and bright, though they also can exhibit shades of dark brown, gray, or black. There is variation in the appearance of male vs female horse flies: females have eyes that are widely spaced apart, while males have eyes that are closer together.² It is important to note the difference between male and female horseflies, as hematophagy is exhibited only by females.¹

Horse flies are found worldwide, with the exception of Hawaii, Greenland, and Iceland.^3,4 They are especially prevalent in warm and moist regions, as these conditions are optimal for breeding.^3-5 They tend to be active during the day and inactive at night due to a preference for sunlight and warmth.⁶ Due to this preference, horse flies’ seasonal activity depends on the climate; for many regions, activity persists from summer to early autumn.⁷

Clinical Manifestations and Treatment

Female horse flies use their mouthparts to pierce the host’s skin, inject saliva, and suck blood. The saliva contains anticoagulant properties. The bites are painful for the host, and various reactions can occur, including large urticarial wheals or papules at the site of the bite. Treatment for these minor cutaneous reactions is largely symptomatic. The bite site should be washed with soap and water; ice can be applied to help reduce inflammation.⁸ Oral antihistamines may be administered to reduce pruritus and treat urticaria. Topical steroids also can be prescribed for symptomatic relief. Acetaminophen and nonsteroidal anti-inflammatory drugs can be administered for pain control.⁸

While most cases of horse fly bites are minor, there have been reports of anaphylaxis.⁹ Horse fly bite–induced anaphylaxis can manifest as generalized itching, urticaria, and angioedema within minutes of being bitten. This may be followed by pharyngeal constriction, shortness of breath, nausea, vomiting, shivers, perspiration, and loss of consciousness.⁹ Anaphylaxis symptoms should be treated with immediate administration of intramuscular epinephrine.¹⁰

Pathogen Transmission, Prevention, and Control

Although horse flies have been found to carry numerous viruses, bacteria, and protozoa that affect other mammals, there is not enough evidence to suggest that they are vectors of transmission for humans for most diseases.^11,12 In particular, West Nile virus and Borrelia burgdorferi both have been found in horse flies, but there are no reports of transmission of these diseases to humans through their bites.¹²

Horse flies, their close cousins deer flies (specifically Chrysops discalis), and ticks are known vectors of Francisella tularensis.¹³ These bacteria cause tularemia, which can manifest with symptoms such as fever, headache, and malaise. Ulceroglandular tularemia is the most common manifestation, in which the patient develops a cutaneous ulceration at the site of the horse fly bite and exhibits associated tender regional lymphadenopathy.¹⁴ Exudative conjunctivitis, exudative pharyngitis, abdominal pain, diarrhea, vomiting, and severe bilateral pneumonia also are common symptoms. The most severe form of tularemia is systemic or typhoidal tularemia, which can manifest with fever, septic shock, and hepatosplenomegaly.¹⁴ The current treatment of choice for all forms of tularemia is intravenous gentamicin, with a recommended dosage of 5 mg/kg/d for 7 to 14 days; streptomycin is an acceptable alternative.^14-16 Ciprofloxacin is used less commonly and is reserved for milder disease. Incision and drainage of the affected lymph nodes also may be necessary.¹⁴ It is important to promptly identify and treat tularemia, as the mortality rate can be as high as 50% for untreated disease, especially in patients with systemic symptoms. Even after treatment, many patients exhibit residual scarring at the site of the ulcer, as well as lung, kidney, and muscle damage.¹⁴

It is advised to avoid contact with horse flies due to the range of symptom severity caused by their bites, but avoidance and control can be difficult. Malaise traps, consisting of a tent and polyester netting, can be used to capture the insects.¹⁷ Octenol has been shown to be effective for attracting horse flies and can be applied to the trap in order to increase its effectiveness.¹⁸ A Manitoba horse fly trap is a modified version of the Malaise trap that contains a suspended dark sphere to further attract horse flies.¹⁹ Patients also should be instructed to wear long-sleeved shirts and pants when outdoors in areas with horse flies to avoid contact, and application of DEET (N,N-diethylmeta-toluamide), picaridin, citronella, or geraniol-based repellents also can be effective in reducing exposure.²⁰

Final Thoughts

Horse flies are large, blood‑feeding dipteran insects whose bites usually produce painful local reactions. Although most bites are benign, they rarely can cause anaphylaxis, and certain Tabanidae insects can transmit Francisella tularensis; therefore, clinicians should consider the risk for tularemia infection in patients presenting with horse fly bites and start appropriate antibiotic therapy when indicated. Due to the risks, prevention of bites and reduction of contact with horse flies via protective clothing, repellents, and trapping methods is recommended. Patients should be advised on bite care and to seek urgent care for systemic symptoms or rapidly progressive local signs.

Horse flies (Tabanidae) are hematophagous dipteran insects that feed on the blood of their hosts, including humans.¹ Their bites can cause minor cutaneous reactions (eg, urticaria) or, rarely, severe reactions such as anaphylaxis. They also are vectors of tularemia, which may manifest with cutaneous ulcers and systemic illness. In this article, we discuss identifying features of horse flies as well as clinical manifestations from bite reactions, symptomatic and emergency management, and strategies for prevention and control.

Morphology and Geographic Distribution

Horse flies, which can grow as large as 30 mm, can be identified by their brown or black bodies and characteristic large heads and proboscises, wing venation, large calypters, pulvilliform empodium between large pulvilli, and lack of bristles on the body.² Occasionally, their bodies may be gray, yellow, green, or blue, but this is less likely than in the other species of the Tabanidae family. Short hairs are present on the head and thorax. The eyes are large and often patterned, multicolored, and bright, though they also can exhibit shades of dark brown, gray, or black. There is variation in the appearance of male vs female horse flies: females have eyes that are widely spaced apart, while males have eyes that are closer together.² It is important to note the difference between male and female horseflies, as hematophagy is exhibited only by females.¹

Horse flies are found worldwide, with the exception of Hawaii, Greenland, and Iceland.^3,4 They are especially prevalent in warm and moist regions, as these conditions are optimal for breeding.^3-5 They tend to be active during the day and inactive at night due to a preference for sunlight and warmth.⁶ Due to this preference, horse flies’ seasonal activity depends on the climate; for many regions, activity persists from summer to early autumn.⁷

Clinical Manifestations and Treatment

Female horse flies use their mouthparts to pierce the host’s skin, inject saliva, and suck blood. The saliva contains anticoagulant properties. The bites are painful for the host, and various reactions can occur, including large urticarial wheals or papules at the site of the bite. Treatment for these minor cutaneous reactions is largely symptomatic. The bite site should be washed with soap and water; ice can be applied to help reduce inflammation.⁸ Oral antihistamines may be administered to reduce pruritus and treat urticaria. Topical steroids also can be prescribed for symptomatic relief. Acetaminophen and nonsteroidal anti-inflammatory drugs can be administered for pain control.⁸

While most cases of horse fly bites are minor, there have been reports of anaphylaxis.⁹ Horse fly bite–induced anaphylaxis can manifest as generalized itching, urticaria, and angioedema within minutes of being bitten. This may be followed by pharyngeal constriction, shortness of breath, nausea, vomiting, shivers, perspiration, and loss of consciousness.⁹ Anaphylaxis symptoms should be treated with immediate administration of intramuscular epinephrine.¹⁰

Pathogen Transmission, Prevention, and Control

Although horse flies have been found to carry numerous viruses, bacteria, and protozoa that affect other mammals, there is not enough evidence to suggest that they are vectors of transmission for humans for most diseases.^11,12 In particular, West Nile virus and Borrelia burgdorferi both have been found in horse flies, but there are no reports of transmission of these diseases to humans through their bites.¹²

Horse flies, their close cousins deer flies (specifically Chrysops discalis), and ticks are known vectors of Francisella tularensis.¹³ These bacteria cause tularemia, which can manifest with symptoms such as fever, headache, and malaise. Ulceroglandular tularemia is the most common manifestation, in which the patient develops a cutaneous ulceration at the site of the horse fly bite and exhibits associated tender regional lymphadenopathy.¹⁴ Exudative conjunctivitis, exudative pharyngitis, abdominal pain, diarrhea, vomiting, and severe bilateral pneumonia also are common symptoms. The most severe form of tularemia is systemic or typhoidal tularemia, which can manifest with fever, septic shock, and hepatosplenomegaly.¹⁴ The current treatment of choice for all forms of tularemia is intravenous gentamicin, with a recommended dosage of 5 mg/kg/d for 7 to 14 days; streptomycin is an acceptable alternative.^14-16 Ciprofloxacin is used less commonly and is reserved for milder disease. Incision and drainage of the affected lymph nodes also may be necessary.¹⁴ It is important to promptly identify and treat tularemia, as the mortality rate can be as high as 50% for untreated disease, especially in patients with systemic symptoms. Even after treatment, many patients exhibit residual scarring at the site of the ulcer, as well as lung, kidney, and muscle damage.¹⁴

It is advised to avoid contact with horse flies due to the range of symptom severity caused by their bites, but avoidance and control can be difficult. Malaise traps, consisting of a tent and polyester netting, can be used to capture the insects.¹⁷ Octenol has been shown to be effective for attracting horse flies and can be applied to the trap in order to increase its effectiveness.¹⁸ A Manitoba horse fly trap is a modified version of the Malaise trap that contains a suspended dark sphere to further attract horse flies.¹⁹ Patients also should be instructed to wear long-sleeved shirts and pants when outdoors in areas with horse flies to avoid contact, and application of DEET (N,N-diethylmeta-toluamide), picaridin, citronella, or geraniol-based repellents also can be effective in reducing exposure.²⁰

Final Thoughts

Horse flies are large, blood‑feeding dipteran insects whose bites usually produce painful local reactions. Although most bites are benign, they rarely can cause anaphylaxis, and certain Tabanidae insects can transmit Francisella tularensis; therefore, clinicians should consider the risk for tularemia infection in patients presenting with horse fly bites and start appropriate antibiotic therapy when indicated. Due to the risks, prevention of bites and reduction of contact with horse flies via protective clothing, repellents, and trapping methods is recommended. Patients should be advised on bite care and to seek urgent care for systemic symptoms or rapidly progressive local signs.

Horse flies (Tabanidae) are hematophagous dipteran insects that feed on the blood of their hosts, including humans.¹ Their bites can cause minor cutaneous reactions (eg, urticaria) or, rarely, severe reactions such as anaphylaxis. They also are vectors of tularemia, which may manifest with cutaneous ulcers and systemic illness. In this article, we discuss identifying features of horse flies as well as clinical manifestations from bite reactions, symptomatic and emergency management, and strategies for prevention and control.

Morphology and Geographic Distribution

Horse flies, which can grow as large as 30 mm, can be identified by their brown or black bodies and characteristic large heads and proboscises, wing venation, large calypters, pulvilliform empodium between large pulvilli, and lack of bristles on the body.² Occasionally, their bodies may be gray, yellow, green, or blue, but this is less likely than in the other species of the Tabanidae family. Short hairs are present on the head and thorax. The eyes are large and often patterned, multicolored, and bright, though they also can exhibit shades of dark brown, gray, or black. There is variation in the appearance of male vs female horse flies: females have eyes that are widely spaced apart, while males have eyes that are closer together.² It is important to note the difference between male and female horseflies, as hematophagy is exhibited only by females.¹

Horse flies are found worldwide, with the exception of Hawaii, Greenland, and Iceland.^3,4 They are especially prevalent in warm and moist regions, as these conditions are optimal for breeding.^3-5 They tend to be active during the day and inactive at night due to a preference for sunlight and warmth.⁶ Due to this preference, horse flies’ seasonal activity depends on the climate; for many regions, activity persists from summer to early autumn.⁷

Clinical Manifestations and Treatment

Female horse flies use their mouthparts to pierce the host’s skin, inject saliva, and suck blood. The saliva contains anticoagulant properties. The bites are painful for the host, and various reactions can occur, including large urticarial wheals or papules at the site of the bite. Treatment for these minor cutaneous reactions is largely symptomatic. The bite site should be washed with soap and water; ice can be applied to help reduce inflammation.⁸ Oral antihistamines may be administered to reduce pruritus and treat urticaria. Topical steroids also can be prescribed for symptomatic relief. Acetaminophen and nonsteroidal anti-inflammatory drugs can be administered for pain control.⁸

While most cases of horse fly bites are minor, there have been reports of anaphylaxis.⁹ Horse fly bite–induced anaphylaxis can manifest as generalized itching, urticaria, and angioedema within minutes of being bitten. This may be followed by pharyngeal constriction, shortness of breath, nausea, vomiting, shivers, perspiration, and loss of consciousness.⁹ Anaphylaxis symptoms should be treated with immediate administration of intramuscular epinephrine.¹⁰

Pathogen Transmission, Prevention, and Control

Although horse flies have been found to carry numerous viruses, bacteria, and protozoa that affect other mammals, there is not enough evidence to suggest that they are vectors of transmission for humans for most diseases.^11,12 In particular, West Nile virus and Borrelia burgdorferi both have been found in horse flies, but there are no reports of transmission of these diseases to humans through their bites.¹²

Horse flies, their close cousins deer flies (specifically Chrysops discalis), and ticks are known vectors of Francisella tularensis.¹³ These bacteria cause tularemia, which can manifest with symptoms such as fever, headache, and malaise. Ulceroglandular tularemia is the most common manifestation, in which the patient develops a cutaneous ulceration at the site of the horse fly bite and exhibits associated tender regional lymphadenopathy.¹⁴ Exudative conjunctivitis, exudative pharyngitis, abdominal pain, diarrhea, vomiting, and severe bilateral pneumonia also are common symptoms. The most severe form of tularemia is systemic or typhoidal tularemia, which can manifest with fever, septic shock, and hepatosplenomegaly.¹⁴ The current treatment of choice for all forms of tularemia is intravenous gentamicin, with a recommended dosage of 5 mg/kg/d for 7 to 14 days; streptomycin is an acceptable alternative.^14-16 Ciprofloxacin is used less commonly and is reserved for milder disease. Incision and drainage of the affected lymph nodes also may be necessary.¹⁴ It is important to promptly identify and treat tularemia, as the mortality rate can be as high as 50% for untreated disease, especially in patients with systemic symptoms. Even after treatment, many patients exhibit residual scarring at the site of the ulcer, as well as lung, kidney, and muscle damage.¹⁴

It is advised to avoid contact with horse flies due to the range of symptom severity caused by their bites, but avoidance and control can be difficult. Malaise traps, consisting of a tent and polyester netting, can be used to capture the insects.¹⁷ Octenol has been shown to be effective for attracting horse flies and can be applied to the trap in order to increase its effectiveness.¹⁸ A Manitoba horse fly trap is a modified version of the Malaise trap that contains a suspended dark sphere to further attract horse flies.¹⁹ Patients also should be instructed to wear long-sleeved shirts and pants when outdoors in areas with horse flies to avoid contact, and application of DEET (N,N-diethylmeta-toluamide), picaridin, citronella, or geraniol-based repellents also can be effective in reducing exposure.²⁰

Final Thoughts

Horse flies are large, blood‑feeding dipteran insects whose bites usually produce painful local reactions. Although most bites are benign, they rarely can cause anaphylaxis, and certain Tabanidae insects can transmit Francisella tularensis; therefore, clinicians should consider the risk for tularemia infection in patients presenting with horse fly bites and start appropriate antibiotic therapy when indicated. Due to the risks, prevention of bites and reduction of contact with horse flies via protective clothing, repellents, and trapping methods is recommended. Patients should be advised on bite care and to seek urgent care for systemic symptoms or rapidly progressive local signs.

Triatome bugs cause painful bites and serve as vectors for Chagas disease. In this article, we will address diagnosis and vector identification.

Key Morphologic Features

Insects from the subfamily Triatominae are identifiable by their long legs and a shieldlike abdomen behind a platelike pronotum that covers the thorax. Their half-membranous wings overlap, covering the central abdomen but leaving the lateral portions visible. Tigerlike stripes are characteristically prominent on the visible portions of the lateral abdomen. The stalklike head has an articulated beaklike mouth that can be retracted and used to deliver a powerful bite (Figure 1).

Feeding Mechanisms and Host Reactions

Triatome bugs are blood-feeding arthropods that hide in cracks and crevices in domestic structures by day and feed at night. They are shy feeders, and laboratory colonies have been known to die rather than feed in daylight. They are particularly common in thatched or wattle-and-daub dwellings, where they can be present in great numbers and descend on sleeping inhabitants at night. Triatome bugs require regular blood meals throughout the 5 developmental nymph stages in order to undergo successful molting.

In the wild, triatome bugs feed on a range of animals with little specificity, but in domestic settings they feed largely on humans. Thermosensors in the antennae help them locate blood vessels under the skin, which they penetrate easily due to their long mouthparts. Like other blood-sucking arthropods, they release an anticoagulant that facilitates continuous blood flow while feeding, which accounts for many of the cutaneous reactions observed after the host sustains a triatomine bite.¹

Triatomine bugs have trouble feeding through clothing and seek out exposed skin, particularly the eyelids, producing the characteristic unilateral eyelid swelling known as the Romaña sign. Other bite reactions include purpura; macular erythema; and vesiculobullous, papular, and urticarial lesions (Figure 2).² Associated lymphangitis or lymphadenopathy may be noted, and anaphylaxis has been reported. Similar to those of cockroaches, triatome antigens have been associated with atopic dermatitis and asthma.³

Chagas Disease Risk and Transmission

Triatomine reduviids are the primary vector of Chagas disease, and the geographic range of both continues to expand, particularly in North America. The disease remains endemic in Latin America, with the highest incidence now reported in Brazil.⁴ An estimated 240,000 to 350,000 individuals in the United States are infected, primarily immigrants from Mexico, Central America, and South America; approximately 30% of those infected will develop cardiac and/or gastrointestinal complications.⁴ If left untreated, Chagas disease leads to autonomic ganglion destruction and subsequent gastrointestinal and cardiac complications, including megacolon, dilated cardiomyopathy, and heart failure.⁵

Trypanosoma cruzi, the microorganism responsible for Chagas disease, is spread to humans through triatomine fecal matter scratched into the bite wound.⁶ Triatomine bugs have a highly developed gastrocolic reflex and defecate liberally as they feed. Fecal volume is heavily dependent on species and sex, with fifth-stage female nymphs producing the highest volume of excrement and thereby acting as particularly adept disease vectors.⁶ Triatoma infestans and members of the genus Mepraia are key vectors of T cruzi.¹ In areas of South America where populations of T infestans are controlled through public health measures, Mepraia emerge as a largely uncontrolled disease vector.^1,7 While endemic to the southern United States and South America, T cruzi has spread to much of North America and Europe by way of Triatominae as naturalized or invasive species.⁸

There are 3 phases of Chagas disease: acute, indeterminate, and chronic. A chagoma is a localized erythematous swelling at the site of the bite. The acute phase often lacks systemic symptoms but may include fever, myalgia, and headache. The intermediate phase may include fatigue and recurrent fevers. The most serious manifestations occur in the chronic phase and include cardiomyopathy with signs of congestive heart failure, irregular heartbeat, cardiac arrest, abdominal pain, constipation, and dysphagia.

Deforestation has been identified as a driving factor in the spread of Chagas disease, as the disease vectors shift from wilderness areas and animal hosts to inhabited areas where humans are the most readily available food source. Triatome bugs in areas experiencing higher levels of development or forest harvesting are forced into human-populated areas. As a result, instances of Chagas disease are on the rise in these communities.⁷ Salvador, Bahia, Brazil, has been identified as one such target of increased vector presence due to heavy deforestation, and the hottest months were identified as having the greatest threat of vector exposure.⁹ Brazil became the leading geographic area for the disease partly because of heavy loss of forested land.¹⁰

Vector Control and Prevention Strategies

Elimination of cracks and crevices in walls; replacement of wattle and daub with stucco, plaster, and other solid building materials; and the use of insecticides with durability in the environment have been used to reduce triatome bug infestation in homes. However, highly persistent insecticides carry greater environmental risk and may drive resistance as declining concentrations select for resistant arthropods. Repellents have less environmental impact and play an important role in vector control. Citronella essential oil has been observed to repel several species of triatome bugs that are common in Arizona; specifically, the component alcohols geraniol and citronellol were found to be effective at inhibiting triatome feeding.¹¹

Early detection of Chagas disease is essential, as end-stage cardiomyopathy and megacolon are difficult to treat. Newly developed multiantigen testing has shown promising results, suggesting a potential for more accurate testing for Chagas disease.⁸ Geospatial tracking and mapping of T cruzi vectors now are employed to track seasonal vector changes and disease patterns.⁹ Researchers also have developed a dedicated dichotomous key for the identification of triatome bugs endemic in Brazil with the hope of better identification and mapping of disease vector presence and density.¹⁰ The key consists of a series of statements with 2 choices in each step. It uses observable features of the arthropod to lead users to the correct identification.

Final Thoughts

Identification of triatome bugs can help with public health efforts to control the spread of disease. Patients with unilateral eyelid swelling should be evaluated for possible bedbug or triatome exposure.

Triatome bugs cause painful bites and serve as vectors for Chagas disease. In this article, we will address diagnosis and vector identification.

Key Morphologic Features

Insects from the subfamily Triatominae are identifiable by their long legs and a shieldlike abdomen behind a platelike pronotum that covers the thorax. Their half-membranous wings overlap, covering the central abdomen but leaving the lateral portions visible. Tigerlike stripes are characteristically prominent on the visible portions of the lateral abdomen. The stalklike head has an articulated beaklike mouth that can be retracted and used to deliver a powerful bite (Figure 1).

Feeding Mechanisms and Host Reactions

Triatome bugs are blood-feeding arthropods that hide in cracks and crevices in domestic structures by day and feed at night. They are shy feeders, and laboratory colonies have been known to die rather than feed in daylight. They are particularly common in thatched or wattle-and-daub dwellings, where they can be present in great numbers and descend on sleeping inhabitants at night. Triatome bugs require regular blood meals throughout the 5 developmental nymph stages in order to undergo successful molting.

In the wild, triatome bugs feed on a range of animals with little specificity, but in domestic settings they feed largely on humans. Thermosensors in the antennae help them locate blood vessels under the skin, which they penetrate easily due to their long mouthparts. Like other blood-sucking arthropods, they release an anticoagulant that facilitates continuous blood flow while feeding, which accounts for many of the cutaneous reactions observed after the host sustains a triatomine bite.¹

Triatomine bugs have trouble feeding through clothing and seek out exposed skin, particularly the eyelids, producing the characteristic unilateral eyelid swelling known as the Romaña sign. Other bite reactions include purpura; macular erythema; and vesiculobullous, papular, and urticarial lesions (Figure 2).² Associated lymphangitis or lymphadenopathy may be noted, and anaphylaxis has been reported. Similar to those of cockroaches, triatome antigens have been associated with atopic dermatitis and asthma.³

Chagas Disease Risk and Transmission

Triatomine reduviids are the primary vector of Chagas disease, and the geographic range of both continues to expand, particularly in North America. The disease remains endemic in Latin America, with the highest incidence now reported in Brazil.⁴ An estimated 240,000 to 350,000 individuals in the United States are infected, primarily immigrants from Mexico, Central America, and South America; approximately 30% of those infected will develop cardiac and/or gastrointestinal complications.⁴ If left untreated, Chagas disease leads to autonomic ganglion destruction and subsequent gastrointestinal and cardiac complications, including megacolon, dilated cardiomyopathy, and heart failure.⁵

Trypanosoma cruzi, the microorganism responsible for Chagas disease, is spread to humans through triatomine fecal matter scratched into the bite wound.⁶ Triatomine bugs have a highly developed gastrocolic reflex and defecate liberally as they feed. Fecal volume is heavily dependent on species and sex, with fifth-stage female nymphs producing the highest volume of excrement and thereby acting as particularly adept disease vectors.⁶ Triatoma infestans and members of the genus Mepraia are key vectors of T cruzi.¹ In areas of South America where populations of T infestans are controlled through public health measures, Mepraia emerge as a largely uncontrolled disease vector.^1,7 While endemic to the southern United States and South America, T cruzi has spread to much of North America and Europe by way of Triatominae as naturalized or invasive species.⁸

There are 3 phases of Chagas disease: acute, indeterminate, and chronic. A chagoma is a localized erythematous swelling at the site of the bite. The acute phase often lacks systemic symptoms but may include fever, myalgia, and headache. The intermediate phase may include fatigue and recurrent fevers. The most serious manifestations occur in the chronic phase and include cardiomyopathy with signs of congestive heart failure, irregular heartbeat, cardiac arrest, abdominal pain, constipation, and dysphagia.

Deforestation has been identified as a driving factor in the spread of Chagas disease, as the disease vectors shift from wilderness areas and animal hosts to inhabited areas where humans are the most readily available food source. Triatome bugs in areas experiencing higher levels of development or forest harvesting are forced into human-populated areas. As a result, instances of Chagas disease are on the rise in these communities.⁷ Salvador, Bahia, Brazil, has been identified as one such target of increased vector presence due to heavy deforestation, and the hottest months were identified as having the greatest threat of vector exposure.⁹ Brazil became the leading geographic area for the disease partly because of heavy loss of forested land.¹⁰

Vector Control and Prevention Strategies

Elimination of cracks and crevices in walls; replacement of wattle and daub with stucco, plaster, and other solid building materials; and the use of insecticides with durability in the environment have been used to reduce triatome bug infestation in homes. However, highly persistent insecticides carry greater environmental risk and may drive resistance as declining concentrations select for resistant arthropods. Repellents have less environmental impact and play an important role in vector control. Citronella essential oil has been observed to repel several species of triatome bugs that are common in Arizona; specifically, the component alcohols geraniol and citronellol were found to be effective at inhibiting triatome feeding.¹¹

Early detection of Chagas disease is essential, as end-stage cardiomyopathy and megacolon are difficult to treat. Newly developed multiantigen testing has shown promising results, suggesting a potential for more accurate testing for Chagas disease.⁸ Geospatial tracking and mapping of T cruzi vectors now are employed to track seasonal vector changes and disease patterns.⁹ Researchers also have developed a dedicated dichotomous key for the identification of triatome bugs endemic in Brazil with the hope of better identification and mapping of disease vector presence and density.¹⁰ The key consists of a series of statements with 2 choices in each step. It uses observable features of the arthropod to lead users to the correct identification.

Final Thoughts

Identification of triatome bugs can help with public health efforts to control the spread of disease. Patients with unilateral eyelid swelling should be evaluated for possible bedbug or triatome exposure.

Triatome bugs cause painful bites and serve as vectors for Chagas disease. In this article, we will address diagnosis and vector identification.

Key Morphologic Features

Insects from the subfamily Triatominae are identifiable by their long legs and a shieldlike abdomen behind a platelike pronotum that covers the thorax. Their half-membranous wings overlap, covering the central abdomen but leaving the lateral portions visible. Tigerlike stripes are characteristically prominent on the visible portions of the lateral abdomen. The stalklike head has an articulated beaklike mouth that can be retracted and used to deliver a powerful bite (Figure 1).

Feeding Mechanisms and Host Reactions

Triatome bugs are blood-feeding arthropods that hide in cracks and crevices in domestic structures by day and feed at night. They are shy feeders, and laboratory colonies have been known to die rather than feed in daylight. They are particularly common in thatched or wattle-and-daub dwellings, where they can be present in great numbers and descend on sleeping inhabitants at night. Triatome bugs require regular blood meals throughout the 5 developmental nymph stages in order to undergo successful molting.

In the wild, triatome bugs feed on a range of animals with little specificity, but in domestic settings they feed largely on humans. Thermosensors in the antennae help them locate blood vessels under the skin, which they penetrate easily due to their long mouthparts. Like other blood-sucking arthropods, they release an anticoagulant that facilitates continuous blood flow while feeding, which accounts for many of the cutaneous reactions observed after the host sustains a triatomine bite.¹

Triatomine bugs have trouble feeding through clothing and seek out exposed skin, particularly the eyelids, producing the characteristic unilateral eyelid swelling known as the Romaña sign. Other bite reactions include purpura; macular erythema; and vesiculobullous, papular, and urticarial lesions (Figure 2).² Associated lymphangitis or lymphadenopathy may be noted, and anaphylaxis has been reported. Similar to those of cockroaches, triatome antigens have been associated with atopic dermatitis and asthma.³

Chagas Disease Risk and Transmission

Triatomine reduviids are the primary vector of Chagas disease, and the geographic range of both continues to expand, particularly in North America. The disease remains endemic in Latin America, with the highest incidence now reported in Brazil.⁴ An estimated 240,000 to 350,000 individuals in the United States are infected, primarily immigrants from Mexico, Central America, and South America; approximately 30% of those infected will develop cardiac and/or gastrointestinal complications.⁴ If left untreated, Chagas disease leads to autonomic ganglion destruction and subsequent gastrointestinal and cardiac complications, including megacolon, dilated cardiomyopathy, and heart failure.⁵

Trypanosoma cruzi, the microorganism responsible for Chagas disease, is spread to humans through triatomine fecal matter scratched into the bite wound.⁶ Triatomine bugs have a highly developed gastrocolic reflex and defecate liberally as they feed. Fecal volume is heavily dependent on species and sex, with fifth-stage female nymphs producing the highest volume of excrement and thereby acting as particularly adept disease vectors.⁶ Triatoma infestans and members of the genus Mepraia are key vectors of T cruzi.¹ In areas of South America where populations of T infestans are controlled through public health measures, Mepraia emerge as a largely uncontrolled disease vector.^1,7 While endemic to the southern United States and South America, T cruzi has spread to much of North America and Europe by way of Triatominae as naturalized or invasive species.⁸

There are 3 phases of Chagas disease: acute, indeterminate, and chronic. A chagoma is a localized erythematous swelling at the site of the bite. The acute phase often lacks systemic symptoms but may include fever, myalgia, and headache. The intermediate phase may include fatigue and recurrent fevers. The most serious manifestations occur in the chronic phase and include cardiomyopathy with signs of congestive heart failure, irregular heartbeat, cardiac arrest, abdominal pain, constipation, and dysphagia.

Deforestation has been identified as a driving factor in the spread of Chagas disease, as the disease vectors shift from wilderness areas and animal hosts to inhabited areas where humans are the most readily available food source. Triatome bugs in areas experiencing higher levels of development or forest harvesting are forced into human-populated areas. As a result, instances of Chagas disease are on the rise in these communities.⁷ Salvador, Bahia, Brazil, has been identified as one such target of increased vector presence due to heavy deforestation, and the hottest months were identified as having the greatest threat of vector exposure.⁹ Brazil became the leading geographic area for the disease partly because of heavy loss of forested land.¹⁰

Vector Control and Prevention Strategies

Elimination of cracks and crevices in walls; replacement of wattle and daub with stucco, plaster, and other solid building materials; and the use of insecticides with durability in the environment have been used to reduce triatome bug infestation in homes. However, highly persistent insecticides carry greater environmental risk and may drive resistance as declining concentrations select for resistant arthropods. Repellents have less environmental impact and play an important role in vector control. Citronella essential oil has been observed to repel several species of triatome bugs that are common in Arizona; specifically, the component alcohols geraniol and citronellol were found to be effective at inhibiting triatome feeding.¹¹

Early detection of Chagas disease is essential, as end-stage cardiomyopathy and megacolon are difficult to treat. Newly developed multiantigen testing has shown promising results, suggesting a potential for more accurate testing for Chagas disease.⁸ Geospatial tracking and mapping of T cruzi vectors now are employed to track seasonal vector changes and disease patterns.⁹ Researchers also have developed a dedicated dichotomous key for the identification of triatome bugs endemic in Brazil with the hope of better identification and mapping of disease vector presence and density.¹⁰ The key consists of a series of statements with 2 choices in each step. It uses observable features of the arthropod to lead users to the correct identification.

Final Thoughts

Identification of triatome bugs can help with public health efforts to control the spread of disease. Patients with unilateral eyelid swelling should be evaluated for possible bedbug or triatome exposure.

Chromoblastomycosis is a neglected tropical implantation mycosis caused by dematiaceous fungi that leads to substantial morbidity. This condition is diagnosed microscopically by visualizing the characteristic thick-walled, single, or multicellular clusters of pigmented fungal cells (also known as medlar bodies, muriform cells, or sclerotic bodies).¹ The main causative fungi varies by geographic region, but most commonly is caused by Cladophialophora carrionii, Fonsecaea species, Phialophora verrucosa species complex, and Rhinocladiella aquaspersa.^2-4 Standardized treatment guidelines have not been established, but itraconazole typically is considered first-line regardless of causative fungi.⁵ Terbinafine, other azoles, and topical immunomodulators, either as monotherapy or in combination, may be appropriate alternative or adjunctive options for refractory disease, although supporting data are limited.^6-9

Complications from chromoblastomycosis are common, particularly in long-standing, severe, or refractory disease. An analysis using billing codes in the United States found 14% (35/255) of hospitalized patients with chromoblastomycosis had lymphedema.¹⁰ In Mexico, 63% (32/51) of patients with chromoblastomycosis developed secondary bacterial infections.¹¹ Skin fibrosis and ankylosis also can occur and cause mobility issues and decreased quality of life. An infrequent but potentially life-threatening complication¹² is the development of squamous cell carcinoma (SCC) associated with chronic lesions, representing a preventable end-stage complication of delayed diagnosis and treatment (Figure).

In this review, we summarize reported epidemiology and clinical risk factors for SCC complicating chromoblastomycosis. We also discuss plausible inflammatory mechanisms of malignant transformation and propose pragmatic clinical and public health interventions, including decentralized microscopy-based diagnosis, timely antifungal access, and biopsy-triggered surveillance of chronically inflamed lesions, to reduce preventable morbidity.

Epidemiology and Risk Factors

The epidemiology of SCC developing from chromoblastomycosis is not well understood due to gaps in national and global surveillance. Some studies have found that 2% to 13% of patients with chromoblastomycosis developed SCC.^4,11,13-15 Based on case reports and case series, a symptom duration of more than 10 years appears to be the most substantial risk factor for the development of SCC rather than host immune status.^16-18 Severity, specifically the size of the injury, and vegetating lesions also have been suggested as risk factors for the development of SCC.¹⁶ Additionally, the appearance of new lesions (mainly ulcers not related to secondary infection) that appear during the healing phase should raise the suspicion of SCC and warrant a biopsy for evaluation.¹⁶

Pathophysiology

The exact mechanism of malignant transformation has not been elucidated, but histopathologic features suggest substantial epidermal proliferation. In some cases, this leads to pseudoepitheliomatous hyperplasia, a nonmalignant hyperproliferative state that is an important differential HPV to leishmaniasis and lupus vulgaris.¹⁹ The chronic inflammation from long-standing chromoblastomycosis likely contributes to the further malignant transformation to SCC.

Polymorphonuclear cells and activated macrophages seen in chronic inflammation can promote the release of enzymes and free radicals that has led to malignant transformation in vitro but has not been investigated specifically in chromoblastomycosis.¹⁶ Additionally, chronic inflammation and metabolic products of phagocytosis often are accompanied by excessive production of reactive oxygen and nitrogen species, which can damage DNA, lipoproteins, and cell membranes. Other potential contributors include the expression of cyclooxygenase 2 and release of arachidonic acid metabolites (eg, prostaglandins, leukotrienes), which can damage the cell and promote carcinogenesis. It is not clear whether similar mechanisms account for the development of SCCs in other chronic skin inflammations or infections such as cutaneous tuberculosis or Marjolin ulcers.²⁰

Clinical and Public Health Interventions

Squamous cell carcinoma arising in the setting of chromoblastomycosis warrants prompt oncologic evaluation and definitive surgical management, which may require extensive surgical excision and, in advanced disease, amputation.^14,17,18 Advanced malignant tumors can be difficult to manage and can result in death.^21,22 Additionally, clinicians should maintain a low threshold for biopsy in long-standing chromoblastomycosis, particularly when lesions demonstrate new ulceration, rapid growth, bleeding, pain, malodor, or failure to improve with appropriate antifungal therapy.¹⁶ Recurrent or new lesions after amputation may indicate persistent or recurrent infection and may require continued antifungal management alongside cancer care.¹⁶

Squamous cell carcinoma arising from chromoblastomycosis results after substantial diagnostic delays, allowing chronic inflammation to transform infection into malignancy. Separating benign inflammation-associated epidermal proliferation from transformation to SCC requires histopathologic skill. An assay based on increased expression of chromosome 15 open reading frame 48 (C15orf48), an immune regulatory protein, has been developed to aid in this distinction; however, it is not widely available.²³

Raising awareness of chromoblastomycosis among clinicians and communities, particularly in rural areas where the disease is more common, is critical to improve health care–seeking behaviors and expedite access to care pathways.² Furthermore, access and training on microscopy to diagnose chromoblastomycosis in decentralized areas can facilitate earlier diagnosis in primary health care settings rather than waiting for diagnosis in tertiary care settings, at which point disease usually is advanced. Global implementation of existing programs that use microscopy (eg, malaria in rural areas) can be partnered with frontline health worker cross-training on chromoblastomycosis diagnosis to improve appropriate identification of disease.²⁴ Finally, improving access to affordable antifungals, particularly itraconazole, is necessary along with further research into novel therapeutic strategies. Approaches that utilize local manufacturing and pooled procurement could help expand treatment availability in parallel with diagnostic improvement initiatives.²⁵

Final Thoughts

Squamous cell carcinoma resulting from chromoblastomycosis is a devastating complication, often leading to limb amputation. The true prevalence is unknown, but it occurs more commonly in long-standing disease without appropriate therapy. The appearance of new lesions or ulcers after initial improvement should increase suspicion and lead to biopsy and careful pathologic evaluation. Prevention of SCC requires increased clinical awareness, early diagnosis, and timely initiation of antifungal treatment. Enhanced surveillance among individuals with chromoblastomycosis would help to better understand its prevalence, associated risk factors, and impact on quality of life.

Chromoblastomycosis is a neglected tropical implantation mycosis caused by dematiaceous fungi that leads to substantial morbidity. This condition is diagnosed microscopically by visualizing the characteristic thick-walled, single, or multicellular clusters of pigmented fungal cells (also known as medlar bodies, muriform cells, or sclerotic bodies).¹ The main causative fungi varies by geographic region, but most commonly is caused by Cladophialophora carrionii, Fonsecaea species, Phialophora verrucosa species complex, and Rhinocladiella aquaspersa.^2-4 Standardized treatment guidelines have not been established, but itraconazole typically is considered first-line regardless of causative fungi.⁵ Terbinafine, other azoles, and topical immunomodulators, either as monotherapy or in combination, may be appropriate alternative or adjunctive options for refractory disease, although supporting data are limited.^6-9

Complications from chromoblastomycosis are common, particularly in long-standing, severe, or refractory disease. An analysis using billing codes in the United States found 14% (35/255) of hospitalized patients with chromoblastomycosis had lymphedema.¹⁰ In Mexico, 63% (32/51) of patients with chromoblastomycosis developed secondary bacterial infections.¹¹ Skin fibrosis and ankylosis also can occur and cause mobility issues and decreased quality of life. An infrequent but potentially life-threatening complication¹² is the development of squamous cell carcinoma (SCC) associated with chronic lesions, representing a preventable end-stage complication of delayed diagnosis and treatment (Figure).

In this review, we summarize reported epidemiology and clinical risk factors for SCC complicating chromoblastomycosis. We also discuss plausible inflammatory mechanisms of malignant transformation and propose pragmatic clinical and public health interventions, including decentralized microscopy-based diagnosis, timely antifungal access, and biopsy-triggered surveillance of chronically inflamed lesions, to reduce preventable morbidity.

Epidemiology and Risk Factors

The epidemiology of SCC developing from chromoblastomycosis is not well understood due to gaps in national and global surveillance. Some studies have found that 2% to 13% of patients with chromoblastomycosis developed SCC.^4,11,13-15 Based on case reports and case series, a symptom duration of more than 10 years appears to be the most substantial risk factor for the development of SCC rather than host immune status.^16-18 Severity, specifically the size of the injury, and vegetating lesions also have been suggested as risk factors for the development of SCC.¹⁶ Additionally, the appearance of new lesions (mainly ulcers not related to secondary infection) that appear during the healing phase should raise the suspicion of SCC and warrant a biopsy for evaluation.¹⁶

Pathophysiology

The exact mechanism of malignant transformation has not been elucidated, but histopathologic features suggest substantial epidermal proliferation. In some cases, this leads to pseudoepitheliomatous hyperplasia, a nonmalignant hyperproliferative state that is an important differential HPV to leishmaniasis and lupus vulgaris.¹⁹ The chronic inflammation from long-standing chromoblastomycosis likely contributes to the further malignant transformation to SCC.

Polymorphonuclear cells and activated macrophages seen in chronic inflammation can promote the release of enzymes and free radicals that has led to malignant transformation in vitro but has not been investigated specifically in chromoblastomycosis.¹⁶ Additionally, chronic inflammation and metabolic products of phagocytosis often are accompanied by excessive production of reactive oxygen and nitrogen species, which can damage DNA, lipoproteins, and cell membranes. Other potential contributors include the expression of cyclooxygenase 2 and release of arachidonic acid metabolites (eg, prostaglandins, leukotrienes), which can damage the cell and promote carcinogenesis. It is not clear whether similar mechanisms account for the development of SCCs in other chronic skin inflammations or infections such as cutaneous tuberculosis or Marjolin ulcers.²⁰

Clinical and Public Health Interventions

Squamous cell carcinoma arising in the setting of chromoblastomycosis warrants prompt oncologic evaluation and definitive surgical management, which may require extensive surgical excision and, in advanced disease, amputation.^14,17,18 Advanced malignant tumors can be difficult to manage and can result in death.^21,22 Additionally, clinicians should maintain a low threshold for biopsy in long-standing chromoblastomycosis, particularly when lesions demonstrate new ulceration, rapid growth, bleeding, pain, malodor, or failure to improve with appropriate antifungal therapy.¹⁶ Recurrent or new lesions after amputation may indicate persistent or recurrent infection and may require continued antifungal management alongside cancer care.¹⁶

Squamous cell carcinoma arising from chromoblastomycosis results after substantial diagnostic delays, allowing chronic inflammation to transform infection into malignancy. Separating benign inflammation-associated epidermal proliferation from transformation to SCC requires histopathologic skill. An assay based on increased expression of chromosome 15 open reading frame 48 (C15orf48), an immune regulatory protein, has been developed to aid in this distinction; however, it is not widely available.²³

Raising awareness of chromoblastomycosis among clinicians and communities, particularly in rural areas where the disease is more common, is critical to improve health care–seeking behaviors and expedite access to care pathways.² Furthermore, access and training on microscopy to diagnose chromoblastomycosis in decentralized areas can facilitate earlier diagnosis in primary health care settings rather than waiting for diagnosis in tertiary care settings, at which point disease usually is advanced. Global implementation of existing programs that use microscopy (eg, malaria in rural areas) can be partnered with frontline health worker cross-training on chromoblastomycosis diagnosis to improve appropriate identification of disease.²⁴ Finally, improving access to affordable antifungals, particularly itraconazole, is necessary along with further research into novel therapeutic strategies. Approaches that utilize local manufacturing and pooled procurement could help expand treatment availability in parallel with diagnostic improvement initiatives.²⁵

Final Thoughts

Squamous cell carcinoma resulting from chromoblastomycosis is a devastating complication, often leading to limb amputation. The true prevalence is unknown, but it occurs more commonly in long-standing disease without appropriate therapy. The appearance of new lesions or ulcers after initial improvement should increase suspicion and lead to biopsy and careful pathologic evaluation. Prevention of SCC requires increased clinical awareness, early diagnosis, and timely initiation of antifungal treatment. Enhanced surveillance among individuals with chromoblastomycosis would help to better understand its prevalence, associated risk factors, and impact on quality of life.

Chromoblastomycosis is a neglected tropical implantation mycosis caused by dematiaceous fungi that leads to substantial morbidity. This condition is diagnosed microscopically by visualizing the characteristic thick-walled, single, or multicellular clusters of pigmented fungal cells (also known as medlar bodies, muriform cells, or sclerotic bodies).¹ The main causative fungi varies by geographic region, but most commonly is caused by Cladophialophora carrionii, Fonsecaea species, Phialophora verrucosa species complex, and Rhinocladiella aquaspersa.^2-4 Standardized treatment guidelines have not been established, but itraconazole typically is considered first-line regardless of causative fungi.⁵ Terbinafine, other azoles, and topical immunomodulators, either as monotherapy or in combination, may be appropriate alternative or adjunctive options for refractory disease, although supporting data are limited.^6-9

Complications from chromoblastomycosis are common, particularly in long-standing, severe, or refractory disease. An analysis using billing codes in the United States found 14% (35/255) of hospitalized patients with chromoblastomycosis had lymphedema.¹⁰ In Mexico, 63% (32/51) of patients with chromoblastomycosis developed secondary bacterial infections.¹¹ Skin fibrosis and ankylosis also can occur and cause mobility issues and decreased quality of life. An infrequent but potentially life-threatening complication¹² is the development of squamous cell carcinoma (SCC) associated with chronic lesions, representing a preventable end-stage complication of delayed diagnosis and treatment (Figure).

In this review, we summarize reported epidemiology and clinical risk factors for SCC complicating chromoblastomycosis. We also discuss plausible inflammatory mechanisms of malignant transformation and propose pragmatic clinical and public health interventions, including decentralized microscopy-based diagnosis, timely antifungal access, and biopsy-triggered surveillance of chronically inflamed lesions, to reduce preventable morbidity.

Epidemiology and Risk Factors

The epidemiology of SCC developing from chromoblastomycosis is not well understood due to gaps in national and global surveillance. Some studies have found that 2% to 13% of patients with chromoblastomycosis developed SCC.^4,11,13-15 Based on case reports and case series, a symptom duration of more than 10 years appears to be the most substantial risk factor for the development of SCC rather than host immune status.^16-18 Severity, specifically the size of the injury, and vegetating lesions also have been suggested as risk factors for the development of SCC.¹⁶ Additionally, the appearance of new lesions (mainly ulcers not related to secondary infection) that appear during the healing phase should raise the suspicion of SCC and warrant a biopsy for evaluation.¹⁶

Pathophysiology

The exact mechanism of malignant transformation has not been elucidated, but histopathologic features suggest substantial epidermal proliferation. In some cases, this leads to pseudoepitheliomatous hyperplasia, a nonmalignant hyperproliferative state that is an important differential HPV to leishmaniasis and lupus vulgaris.¹⁹ The chronic inflammation from long-standing chromoblastomycosis likely contributes to the further malignant transformation to SCC.

Polymorphonuclear cells and activated macrophages seen in chronic inflammation can promote the release of enzymes and free radicals that has led to malignant transformation in vitro but has not been investigated specifically in chromoblastomycosis.¹⁶ Additionally, chronic inflammation and metabolic products of phagocytosis often are accompanied by excessive production of reactive oxygen and nitrogen species, which can damage DNA, lipoproteins, and cell membranes. Other potential contributors include the expression of cyclooxygenase 2 and release of arachidonic acid metabolites (eg, prostaglandins, leukotrienes), which can damage the cell and promote carcinogenesis. It is not clear whether similar mechanisms account for the development of SCCs in other chronic skin inflammations or infections such as cutaneous tuberculosis or Marjolin ulcers.²⁰

Clinical and Public Health Interventions

Squamous cell carcinoma arising in the setting of chromoblastomycosis warrants prompt oncologic evaluation and definitive surgical management, which may require extensive surgical excision and, in advanced disease, amputation.^14,17,18 Advanced malignant tumors can be difficult to manage and can result in death.^21,22 Additionally, clinicians should maintain a low threshold for biopsy in long-standing chromoblastomycosis, particularly when lesions demonstrate new ulceration, rapid growth, bleeding, pain, malodor, or failure to improve with appropriate antifungal therapy.¹⁶ Recurrent or new lesions after amputation may indicate persistent or recurrent infection and may require continued antifungal management alongside cancer care.¹⁶

Squamous cell carcinoma arising from chromoblastomycosis results after substantial diagnostic delays, allowing chronic inflammation to transform infection into malignancy. Separating benign inflammation-associated epidermal proliferation from transformation to SCC requires histopathologic skill. An assay based on increased expression of chromosome 15 open reading frame 48 (C15orf48), an immune regulatory protein, has been developed to aid in this distinction; however, it is not widely available.²³

Raising awareness of chromoblastomycosis among clinicians and communities, particularly in rural areas where the disease is more common, is critical to improve health care–seeking behaviors and expedite access to care pathways.² Furthermore, access and training on microscopy to diagnose chromoblastomycosis in decentralized areas can facilitate earlier diagnosis in primary health care settings rather than waiting for diagnosis in tertiary care settings, at which point disease usually is advanced. Global implementation of existing programs that use microscopy (eg, malaria in rural areas) can be partnered with frontline health worker cross-training on chromoblastomycosis diagnosis to improve appropriate identification of disease.²⁴ Finally, improving access to affordable antifungals, particularly itraconazole, is necessary along with further research into novel therapeutic strategies. Approaches that utilize local manufacturing and pooled procurement could help expand treatment availability in parallel with diagnostic improvement initiatives.²⁵

Final Thoughts

Squamous cell carcinoma resulting from chromoblastomycosis is a devastating complication, often leading to limb amputation. The true prevalence is unknown, but it occurs more commonly in long-standing disease without appropriate therapy. The appearance of new lesions or ulcers after initial improvement should increase suspicion and lead to biopsy and careful pathologic evaluation. Prevention of SCC requires increased clinical awareness, early diagnosis, and timely initiation of antifungal treatment. Enhanced surveillance among individuals with chromoblastomycosis would help to better understand its prevalence, associated risk factors, and impact on quality of life.

Photosensitivity refers to clinical manifestations arising from exposure to sunlight. Photodermatoses encompass a group of skin diseases caused by varying degrees of radiation exposure, including UV radiation and visible light. Photodermatoses can be categorized into 5 main types: primary, exogenous, photoexacerbated, metabolic, and genetic.¹ The clinical features of photodermatoses vary depending on the underlying cause but often include pruritic flares, wheals, or dermatitis on sun-exposed areas of the skin.² While photodermatoses typically are not life threatening, they can greatly impact patients’ quality of life. It is crucial to emphasize the importance of photoprotection and sunlight avoidance to patients as preventive measures against the manifestations of these skin diseases. Furthermore, we present a case of photocontact dermatitis (PCD) and discuss common causative agents, diagnostic mimickers, and treatment options.

Case Report

A 51-year-old woman with no relevant medical history presented to the dermatology clinic with a rash on the neck and under the eyes of 6 days’ duration. The rash was intermittently pruritic but otherwise asymptomatic. The patient reported that she had spent extensive time on the golf course the day of the rash onset and noted that a similar rash had occurred one other time 2 to 3 months prior, also following a prolonged period on the golf course. She had been using over-the-counter fexofenadine 180 mg and over-the-counter lidocaine spray for symptom relief.

Upon physical examination, erythematous patches were appreciated in a photodistributed pattern on the arms, legs, neck, face, and chest—areas that were not covered by clothing (Figures 1-3). Due to the distribution and morphology of the erythematous patches along with clinical course of onset following exposure to various environmental agents including pesticides, herbicides, oak, and pollen, a diagnosis of PCD was made. The patient was prescribed hydrocortisone cream 2.5%, fluticasone propionate cream 0.05%, and methylprednisolone in addition to the antihistamine. Improvement was noted after 3 days with complete resolution of the skin manifestations. She was counseled on wearing clothing with a universal protection factor rating of 50+ when on the golf course and when sun exposure is expected for an extended period of time.

Causative Agents

Photodermatoses are caused by antigenic substances that lead to photosensitization acquired by either contact or oral ingestion with subsequent sensitization to UV radiation. Halogenated salicylanilide, fenticlor, hexachlorophene, bithionol and, in rare cases, sunscreens, have been reported as triggers.³ In a study performed in 2010, sunscreens, antimicrobial agents, medications, fragrances, plants/plant derivatives, and pesticides were the most commonly reported offending agents listed from highest to lowest frequency. Of the antimicrobial agents, fenticlor, a topical antimicrobial and antifungal that is now mostly used in veterinary medicine, was the most common culprit, causing 60% of cases.^4,5

Clinical Manifestations

Clinical manifestations of photodermatoses vary depending upon the specific type of reaction. Examples of primary photodermatoses include polymorphous light eruption (PMLE) and solar urticaria. The cardinal symptoms of PMLE consist of severely pruritic skin lesions that can have macular, papular, papulovesicular, urticarial, multiformelike, and plaquelike variants that develop hours to days after sun exposure.³ Conversely, solar urticaria commonly develops more abruptly, with indurated plaques and wheals appearing on the arms and neck within 30 minutes of sun exposure. The lesions typically resolve within 24 hours.¹

Examples of the exogenous subtype include drug-induced photosensitivity, PCD, and pseudoporphyria, with the common clinical presentation of eruption following contact with the causative agent. Drug-induced photosensitivity primarily manifests as a severe sunburnlike rash commonly caused by systemic drugs such as tetracyclines. Photocontact dermatitis is limited to sun-exposed areas of the skin and is caused by a reactive irritant such as chemicals or topical creams. Pseudoporphyria, usually caused by nonsteroidal anti-inflammatory drugs, can manifest with skin fragility and subepidermal blisters.⁶

Photoexacerbated photodermatoses encompass a variety of conditions ranging from hyperpigmentation disorders such as melasma to autoimmune conditions such as systemic lupus erythematosus (SLE) and dermatomyositis (DM). Common clinical features of these diseases include photodistributed erythema, often involving the cheeks, upper back, and anterior neck. Photo-exposed areas of the dorsal hands also are commonplace for both SLE and DM. Clinical manifestations of PCD are limited to sun-exposed areas of the body, specifically those that come into contact with photoallergic triggers.³ Manifestations of PCD can include pruritic eczematous eruptions resembling those of contact dermatitis 1 to 2 days after sun exposure.¹

Photocontact dermatitis represents a specific sensitization via contact or oral ingestion acquired prior to sunlight exposure. It can be broken down into 2 distinct subtypes: photoallergic and photoirritant dermatitis, dependent on whether an allergic or irritant reaction is invoked.² Plants are known to be a common trigger of photoirritant reactions, while extrinsic triggers include psoralens and medications such as tetracycline antibiotics or sulfonamides. Photoallergic reactions commonly can be caused by topical application of sunscreen or medications, namely nonsteroidal anti-inflammatory drugs.² Clinical manifestations that may point to photoirritant dermatitis include a photodistributed eruption and classic morphology showing erythema and edema with bullae present in severe cases. These can be contrasted with the clinical manifestations of photoallergic reactions, which usually do not correlate to sun-exposed areas and consist of a monomorphous distribution pattern similar to that of eczema. Although there are distinguishing features of both subtypes of PCD, the overlapping clinical features can mimic those of solar urticaria, PMLE, cutaneous lupus erythematosus, and more systemic conditions such as SLE and DM.⁷

Systemic lupus erythematosus is associated with a broad range of cutaneous manifestations.⁸ Exposure to UV radiation is a common trigger for lupus and has the propensity to cause a malar (butterfly) rash that covers the cheeks and nasal bridge but classically spares the nasolabial folds. The rash may display confluent reddish-purple discoloration with papules and/or edema and typically is present at diagnosis in 40% to 52% of patients with SLE.⁸ Discoid lupus erythematosus, one of the most common cutaneous forms of lupus, manifests with various-sized coin-shaped plaques with adherent follicular hyperkeratosis and plugging. These lesions usually develop on the face, scalp, and ears but also may appear in non–sun-exposed areas.⁸ Dermatomyositis can manifest with photodistributed erythema affecting classic areas such as the upper back (shawl sign), anterior neck and upper chest (V-sign), and a malar rash similar to that seen in lupus, though DM classically does not spare the nasolabial folds.^8,9

Because SLE and DM manifest with photodistributed rashes, it can be difficult to distinguish them from the classic symptoms of photoirritant dermatitis.⁹ Thus, it is imperative that providers have a high clinical index of suspicion when dealing with patients of similar presentations, as the treatment regimens vastly differ. Approaching the patient with a thorough medical history review, review of systems, biopsy (including immunofluorescence), and appropriate laboratory workup may aid in excluding more complex differential diagnoses such as SLE and DM.

Metabolic and genetic photodermatoses are more rare but can include conditions such as porphyria cutanea tarda and xeroderma pigmentosum, both of which demonstrate fragile skin, slow wound healing, and bullae on photo-exposed skin.¹ Although the manifestations can be similar in these systemic conditions, they are caused by very different mechanisms. Porphyria cutanea tarda is caused by deficiencies in enzymes involved in the heme synthesis pathway, whereas xeroderma pigmentosum is caused by an alteration in DNA repair mechanisms.⁷

Prevalence and the Need for Standardized Testing

Most practicing dermatologists see cases of PCD due to its multiple causative agents; however, little is known about its overall prevalence. The incidence of PCD is fairly low in the general population, but this may be due to its clinical diagnosis, which excludes diagnostic testing such as phototesting and photopatch testing.¹⁰ While the incidence of photoallergic contact dermatitis also is fairly unknown, the inception of testing modalities has allowed statistics to be drawn. Research conducted in the United States has disclosed that the incidence of photoallergic contact dermatitis in individuals with a history of a prior photosensitivity eruption is approximately 10% to 20%.¹⁰ The development of guidelines and a registry for photopatch testing would aid in a greater understanding of the incidence of PCD and overall consistency of diagnosis.⁷ Regardless of this lack of consensus, these conditions can be properly managed and prevented if recognized clinically, while newer testing modalities would allow for confirmation of the diagnosis. It is important that any patient presenting with a history of photosensitivity be seen as a candidate for photopatch testing, especially today, as the general population is increasingly exposed to new chemicals entering the market and new social trends.^7,10

Diagnosis and Treatment

It is important to consider a detailed history, including the timing, location, duration, family history, and seasonal variation of suspected photodermatoses. A thorough skin examination that takes note of the specific areas affected, morphology, and involvement of the rash or lesions can be helpful.¹ Further diagnostic testing such as phototesting and photopatch testing can be employed and is especially important when distinguishing photoallergy from phototoxicity.¹¹ Phototesting involves exposing the patient’s skin to different doses of UVA, UVB, and visible light, followed by an immediate clinical reading of the results and then a delayed reading conducted after 24 hours.¹ Photopatch testing involves the application of 2 sets of identical photoallergens to prepped skin (typically cleansed with isopropyl alcohol), with one being irradiated with UVA after 24 hours and one serving as the control. A clinical assessment is conducted at 24 hours and repeated 7 days later.¹ In photodermatoses, a visible reaction can be appreciated on the treatment arm while the control arm remains clear. When both sides reveal a visible reaction, this is more indicative of a ­light-independent allergic contact dermatitis.¹

Photodermatoses occur only if there has been a specific sensitization, and therefore it is important to work with the patient to discover any new products that have been introduced into their regimen. Though many photosensitizers in personal care products (eg, antiseptics in soap and topical creams) have been discontinued, certain allergenic ingredients may remain.¹² It also is important to note that sensitization to a substance that previously was not a known allergen for a particular patient can occur later in life. Avoiding further sun exposure can rapidly improve the dermatitis, and it is possible for spontaneous remission without further intervention; however, as photoallergic reactions can cause severely pruritic skin lesions, the mainstay of symptomatic treatment consists of topical corticosteroids. Oral and topical antihistamines may help alleviate the pruritus but should not be heavily relied on as this can lead to medication resistance and diminishing efficacy.³ Use of short-term oral steroids also may be considered for rapid improvement of symptoms when the patient is in moderate distress and there are no contraindications. By identifying a temporal association between the introduction of new products and the emergence of dermatitis, it may be possible to identify the causative agent. The patient should promptly discontinue the suspected agent and remain under close observation by the clinician for any further eruptions, especially following additional sun exposure.

Prevention Strategies

In the case of PCD, prevention is key. As PCD indicates a photoallergy, it is important to inform patients that the allergy will persist for a lifetime, much like in contact dermatitis; therefore, the causative agent should be avoided indefinitely.³ Patients with PCD should make intentional efforts to read ingredient lists when purchasing new personal care products to ensure they do not contain the specific causative allergen if one has been identified. Further steps should be taken to ensure proper photoprotection, including use of dense clothing and sunscreen with UVA and UVB filters (broad spectrum).³ It has also been suggested that utilizing sunscreen with ectoin, an amino acid–derived molecule, may result in increased protection against UVA-induced photodermatoses.¹³

Final Thoughts

Photodermatoses are a group of skin diseases caused by exposure to UV radiation. Photocontact dermatitis/photoallergy is a form of allergic contact dermatitis that results from exposure to an allergen, whether topical, oral, or environmental. The allergen is activated by exposure to UV radiation to sensitize the allergic response, resulting in a rash characterized by confluent erythematous patches or plaques, papular vesicles, and rarely blisters.³ Photocontact dermatitis, although rare, is an important differential diagnosis to consider when the presenting rash is restricted to sun-exposed areas of the skin such as the arms, legs, neck, and face. Diagnosis remains a challenge; however, new testing modalities such as photopatch testing may open the door for further confirmation and aid in proper diagnosis leading to earlier treatment times for patients. It is recommended that the clinician and patient work together to identify the possible causative agent to prevent further eruptions.

Photosensitivity refers to clinical manifestations arising from exposure to sunlight. Photodermatoses encompass a group of skin diseases caused by varying degrees of radiation exposure, including UV radiation and visible light. Photodermatoses can be categorized into 5 main types: primary, exogenous, photoexacerbated, metabolic, and genetic.¹ The clinical features of photodermatoses vary depending on the underlying cause but often include pruritic flares, wheals, or dermatitis on sun-exposed areas of the skin.² While photodermatoses typically are not life threatening, they can greatly impact patients’ quality of life. It is crucial to emphasize the importance of photoprotection and sunlight avoidance to patients as preventive measures against the manifestations of these skin diseases. Furthermore, we present a case of photocontact dermatitis (PCD) and discuss common causative agents, diagnostic mimickers, and treatment options.

Case Report

A 51-year-old woman with no relevant medical history presented to the dermatology clinic with a rash on the neck and under the eyes of 6 days’ duration. The rash was intermittently pruritic but otherwise asymptomatic. The patient reported that she had spent extensive time on the golf course the day of the rash onset and noted that a similar rash had occurred one other time 2 to 3 months prior, also following a prolonged period on the golf course. She had been using over-the-counter fexofenadine 180 mg and over-the-counter lidocaine spray for symptom relief.

Upon physical examination, erythematous patches were appreciated in a photodistributed pattern on the arms, legs, neck, face, and chest—areas that were not covered by clothing (Figures 1-3). Due to the distribution and morphology of the erythematous patches along with clinical course of onset following exposure to various environmental agents including pesticides, herbicides, oak, and pollen, a diagnosis of PCD was made. The patient was prescribed hydrocortisone cream 2.5%, fluticasone propionate cream 0.05%, and methylprednisolone in addition to the antihistamine. Improvement was noted after 3 days with complete resolution of the skin manifestations. She was counseled on wearing clothing with a universal protection factor rating of 50+ when on the golf course and when sun exposure is expected for an extended period of time.

Causative Agents

Photodermatoses are caused by antigenic substances that lead to photosensitization acquired by either contact or oral ingestion with subsequent sensitization to UV radiation. Halogenated salicylanilide, fenticlor, hexachlorophene, bithionol and, in rare cases, sunscreens, have been reported as triggers.³ In a study performed in 2010, sunscreens, antimicrobial agents, medications, fragrances, plants/plant derivatives, and pesticides were the most commonly reported offending agents listed from highest to lowest frequency. Of the antimicrobial agents, fenticlor, a topical antimicrobial and antifungal that is now mostly used in veterinary medicine, was the most common culprit, causing 60% of cases.^4,5

Clinical Manifestations

Clinical manifestations of photodermatoses vary depending upon the specific type of reaction. Examples of primary photodermatoses include polymorphous light eruption (PMLE) and solar urticaria. The cardinal symptoms of PMLE consist of severely pruritic skin lesions that can have macular, papular, papulovesicular, urticarial, multiformelike, and plaquelike variants that develop hours to days after sun exposure.³ Conversely, solar urticaria commonly develops more abruptly, with indurated plaques and wheals appearing on the arms and neck within 30 minutes of sun exposure. The lesions typically resolve within 24 hours.¹

Examples of the exogenous subtype include drug-induced photosensitivity, PCD, and pseudoporphyria, with the common clinical presentation of eruption following contact with the causative agent. Drug-induced photosensitivity primarily manifests as a severe sunburnlike rash commonly caused by systemic drugs such as tetracyclines. Photocontact dermatitis is limited to sun-exposed areas of the skin and is caused by a reactive irritant such as chemicals or topical creams. Pseudoporphyria, usually caused by nonsteroidal anti-inflammatory drugs, can manifest with skin fragility and subepidermal blisters.⁶

Photoexacerbated photodermatoses encompass a variety of conditions ranging from hyperpigmentation disorders such as melasma to autoimmune conditions such as systemic lupus erythematosus (SLE) and dermatomyositis (DM). Common clinical features of these diseases include photodistributed erythema, often involving the cheeks, upper back, and anterior neck. Photo-exposed areas of the dorsal hands also are commonplace for both SLE and DM. Clinical manifestations of PCD are limited to sun-exposed areas of the body, specifically those that come into contact with photoallergic triggers.³ Manifestations of PCD can include pruritic eczematous eruptions resembling those of contact dermatitis 1 to 2 days after sun exposure.¹

Photocontact dermatitis represents a specific sensitization via contact or oral ingestion acquired prior to sunlight exposure. It can be broken down into 2 distinct subtypes: photoallergic and photoirritant dermatitis, dependent on whether an allergic or irritant reaction is invoked.² Plants are known to be a common trigger of photoirritant reactions, while extrinsic triggers include psoralens and medications such as tetracycline antibiotics or sulfonamides. Photoallergic reactions commonly can be caused by topical application of sunscreen or medications, namely nonsteroidal anti-inflammatory drugs.² Clinical manifestations that may point to photoirritant dermatitis include a photodistributed eruption and classic morphology showing erythema and edema with bullae present in severe cases. These can be contrasted with the clinical manifestations of photoallergic reactions, which usually do not correlate to sun-exposed areas and consist of a monomorphous distribution pattern similar to that of eczema. Although there are distinguishing features of both subtypes of PCD, the overlapping clinical features can mimic those of solar urticaria, PMLE, cutaneous lupus erythematosus, and more systemic conditions such as SLE and DM.⁷

Systemic lupus erythematosus is associated with a broad range of cutaneous manifestations.⁸ Exposure to UV radiation is a common trigger for lupus and has the propensity to cause a malar (butterfly) rash that covers the cheeks and nasal bridge but classically spares the nasolabial folds. The rash may display confluent reddish-purple discoloration with papules and/or edema and typically is present at diagnosis in 40% to 52% of patients with SLE.⁸ Discoid lupus erythematosus, one of the most common cutaneous forms of lupus, manifests with various-sized coin-shaped plaques with adherent follicular hyperkeratosis and plugging. These lesions usually develop on the face, scalp, and ears but also may appear in non–sun-exposed areas.⁸ Dermatomyositis can manifest with photodistributed erythema affecting classic areas such as the upper back (shawl sign), anterior neck and upper chest (V-sign), and a malar rash similar to that seen in lupus, though DM classically does not spare the nasolabial folds.^8,9

Because SLE and DM manifest with photodistributed rashes, it can be difficult to distinguish them from the classic symptoms of photoirritant dermatitis.⁹ Thus, it is imperative that providers have a high clinical index of suspicion when dealing with patients of similar presentations, as the treatment regimens vastly differ. Approaching the patient with a thorough medical history review, review of systems, biopsy (including immunofluorescence), and appropriate laboratory workup may aid in excluding more complex differential diagnoses such as SLE and DM.

Metabolic and genetic photodermatoses are more rare but can include conditions such as porphyria cutanea tarda and xeroderma pigmentosum, both of which demonstrate fragile skin, slow wound healing, and bullae on photo-exposed skin.¹ Although the manifestations can be similar in these systemic conditions, they are caused by very different mechanisms. Porphyria cutanea tarda is caused by deficiencies in enzymes involved in the heme synthesis pathway, whereas xeroderma pigmentosum is caused by an alteration in DNA repair mechanisms.⁷

Prevalence and the Need for Standardized Testing

Most practicing dermatologists see cases of PCD due to its multiple causative agents; however, little is known about its overall prevalence. The incidence of PCD is fairly low in the general population, but this may be due to its clinical diagnosis, which excludes diagnostic testing such as phototesting and photopatch testing.¹⁰ While the incidence of photoallergic contact dermatitis also is fairly unknown, the inception of testing modalities has allowed statistics to be drawn. Research conducted in the United States has disclosed that the incidence of photoallergic contact dermatitis in individuals with a history of a prior photosensitivity eruption is approximately 10% to 20%.¹⁰ The development of guidelines and a registry for photopatch testing would aid in a greater understanding of the incidence of PCD and overall consistency of diagnosis.⁷ Regardless of this lack of consensus, these conditions can be properly managed and prevented if recognized clinically, while newer testing modalities would allow for confirmation of the diagnosis. It is important that any patient presenting with a history of photosensitivity be seen as a candidate for photopatch testing, especially today, as the general population is increasingly exposed to new chemicals entering the market and new social trends.^7,10

Diagnosis and Treatment

It is important to consider a detailed history, including the timing, location, duration, family history, and seasonal variation of suspected photodermatoses. A thorough skin examination that takes note of the specific areas affected, morphology, and involvement of the rash or lesions can be helpful.¹ Further diagnostic testing such as phototesting and photopatch testing can be employed and is especially important when distinguishing photoallergy from phototoxicity.¹¹ Phototesting involves exposing the patient’s skin to different doses of UVA, UVB, and visible light, followed by an immediate clinical reading of the results and then a delayed reading conducted after 24 hours.¹ Photopatch testing involves the application of 2 sets of identical photoallergens to prepped skin (typically cleansed with isopropyl alcohol), with one being irradiated with UVA after 24 hours and one serving as the control. A clinical assessment is conducted at 24 hours and repeated 7 days later.¹ In photodermatoses, a visible reaction can be appreciated on the treatment arm while the control arm remains clear. When both sides reveal a visible reaction, this is more indicative of a ­light-independent allergic contact dermatitis.¹

Photodermatoses occur only if there has been a specific sensitization, and therefore it is important to work with the patient to discover any new products that have been introduced into their regimen. Though many photosensitizers in personal care products (eg, antiseptics in soap and topical creams) have been discontinued, certain allergenic ingredients may remain.¹² It also is important to note that sensitization to a substance that previously was not a known allergen for a particular patient can occur later in life. Avoiding further sun exposure can rapidly improve the dermatitis, and it is possible for spontaneous remission without further intervention; however, as photoallergic reactions can cause severely pruritic skin lesions, the mainstay of symptomatic treatment consists of topical corticosteroids. Oral and topical antihistamines may help alleviate the pruritus but should not be heavily relied on as this can lead to medication resistance and diminishing efficacy.³ Use of short-term oral steroids also may be considered for rapid improvement of symptoms when the patient is in moderate distress and there are no contraindications. By identifying a temporal association between the introduction of new products and the emergence of dermatitis, it may be possible to identify the causative agent. The patient should promptly discontinue the suspected agent and remain under close observation by the clinician for any further eruptions, especially following additional sun exposure.

Prevention Strategies

In the case of PCD, prevention is key. As PCD indicates a photoallergy, it is important to inform patients that the allergy will persist for a lifetime, much like in contact dermatitis; therefore, the causative agent should be avoided indefinitely.³ Patients with PCD should make intentional efforts to read ingredient lists when purchasing new personal care products to ensure they do not contain the specific causative allergen if one has been identified. Further steps should be taken to ensure proper photoprotection, including use of dense clothing and sunscreen with UVA and UVB filters (broad spectrum).³ It has also been suggested that utilizing sunscreen with ectoin, an amino acid–derived molecule, may result in increased protection against UVA-induced photodermatoses.¹³

Final Thoughts

Photodermatoses are a group of skin diseases caused by exposure to UV radiation. Photocontact dermatitis/photoallergy is a form of allergic contact dermatitis that results from exposure to an allergen, whether topical, oral, or environmental. The allergen is activated by exposure to UV radiation to sensitize the allergic response, resulting in a rash characterized by confluent erythematous patches or plaques, papular vesicles, and rarely blisters.³ Photocontact dermatitis, although rare, is an important differential diagnosis to consider when the presenting rash is restricted to sun-exposed areas of the skin such as the arms, legs, neck, and face. Diagnosis remains a challenge; however, new testing modalities such as photopatch testing may open the door for further confirmation and aid in proper diagnosis leading to earlier treatment times for patients. It is recommended that the clinician and patient work together to identify the possible causative agent to prevent further eruptions.

Photosensitivity refers to clinical manifestations arising from exposure to sunlight. Photodermatoses encompass a group of skin diseases caused by varying degrees of radiation exposure, including UV radiation and visible light. Photodermatoses can be categorized into 5 main types: primary, exogenous, photoexacerbated, metabolic, and genetic.¹ The clinical features of photodermatoses vary depending on the underlying cause but often include pruritic flares, wheals, or dermatitis on sun-exposed areas of the skin.² While photodermatoses typically are not life threatening, they can greatly impact patients’ quality of life. It is crucial to emphasize the importance of photoprotection and sunlight avoidance to patients as preventive measures against the manifestations of these skin diseases. Furthermore, we present a case of photocontact dermatitis (PCD) and discuss common causative agents, diagnostic mimickers, and treatment options.

Case Report

A 51-year-old woman with no relevant medical history presented to the dermatology clinic with a rash on the neck and under the eyes of 6 days’ duration. The rash was intermittently pruritic but otherwise asymptomatic. The patient reported that she had spent extensive time on the golf course the day of the rash onset and noted that a similar rash had occurred one other time 2 to 3 months prior, also following a prolonged period on the golf course. She had been using over-the-counter fexofenadine 180 mg and over-the-counter lidocaine spray for symptom relief.

Upon physical examination, erythematous patches were appreciated in a photodistributed pattern on the arms, legs, neck, face, and chest—areas that were not covered by clothing (Figures 1-3). Due to the distribution and morphology of the erythematous patches along with clinical course of onset following exposure to various environmental agents including pesticides, herbicides, oak, and pollen, a diagnosis of PCD was made. The patient was prescribed hydrocortisone cream 2.5%, fluticasone propionate cream 0.05%, and methylprednisolone in addition to the antihistamine. Improvement was noted after 3 days with complete resolution of the skin manifestations. She was counseled on wearing clothing with a universal protection factor rating of 50+ when on the golf course and when sun exposure is expected for an extended period of time.

Causative Agents

Photodermatoses are caused by antigenic substances that lead to photosensitization acquired by either contact or oral ingestion with subsequent sensitization to UV radiation. Halogenated salicylanilide, fenticlor, hexachlorophene, bithionol and, in rare cases, sunscreens, have been reported as triggers.³ In a study performed in 2010, sunscreens, antimicrobial agents, medications, fragrances, plants/plant derivatives, and pesticides were the most commonly reported offending agents listed from highest to lowest frequency. Of the antimicrobial agents, fenticlor, a topical antimicrobial and antifungal that is now mostly used in veterinary medicine, was the most common culprit, causing 60% of cases.^4,5

Clinical Manifestations

Clinical manifestations of photodermatoses vary depending upon the specific type of reaction. Examples of primary photodermatoses include polymorphous light eruption (PMLE) and solar urticaria. The cardinal symptoms of PMLE consist of severely pruritic skin lesions that can have macular, papular, papulovesicular, urticarial, multiformelike, and plaquelike variants that develop hours to days after sun exposure.³ Conversely, solar urticaria commonly develops more abruptly, with indurated plaques and wheals appearing on the arms and neck within 30 minutes of sun exposure. The lesions typically resolve within 24 hours.¹

Examples of the exogenous subtype include drug-induced photosensitivity, PCD, and pseudoporphyria, with the common clinical presentation of eruption following contact with the causative agent. Drug-induced photosensitivity primarily manifests as a severe sunburnlike rash commonly caused by systemic drugs such as tetracyclines. Photocontact dermatitis is limited to sun-exposed areas of the skin and is caused by a reactive irritant such as chemicals or topical creams. Pseudoporphyria, usually caused by nonsteroidal anti-inflammatory drugs, can manifest with skin fragility and subepidermal blisters.⁶

Photoexacerbated photodermatoses encompass a variety of conditions ranging from hyperpigmentation disorders such as melasma to autoimmune conditions such as systemic lupus erythematosus (SLE) and dermatomyositis (DM). Common clinical features of these diseases include photodistributed erythema, often involving the cheeks, upper back, and anterior neck. Photo-exposed areas of the dorsal hands also are commonplace for both SLE and DM. Clinical manifestations of PCD are limited to sun-exposed areas of the body, specifically those that come into contact with photoallergic triggers.³ Manifestations of PCD can include pruritic eczematous eruptions resembling those of contact dermatitis 1 to 2 days after sun exposure.¹

Photocontact dermatitis represents a specific sensitization via contact or oral ingestion acquired prior to sunlight exposure. It can be broken down into 2 distinct subtypes: photoallergic and photoirritant dermatitis, dependent on whether an allergic or irritant reaction is invoked.² Plants are known to be a common trigger of photoirritant reactions, while extrinsic triggers include psoralens and medications such as tetracycline antibiotics or sulfonamides. Photoallergic reactions commonly can be caused by topical application of sunscreen or medications, namely nonsteroidal anti-inflammatory drugs.² Clinical manifestations that may point to photoirritant dermatitis include a photodistributed eruption and classic morphology showing erythema and edema with bullae present in severe cases. These can be contrasted with the clinical manifestations of photoallergic reactions, which usually do not correlate to sun-exposed areas and consist of a monomorphous distribution pattern similar to that of eczema. Although there are distinguishing features of both subtypes of PCD, the overlapping clinical features can mimic those of solar urticaria, PMLE, cutaneous lupus erythematosus, and more systemic conditions such as SLE and DM.⁷

Systemic lupus erythematosus is associated with a broad range of cutaneous manifestations.⁸ Exposure to UV radiation is a common trigger for lupus and has the propensity to cause a malar (butterfly) rash that covers the cheeks and nasal bridge but classically spares the nasolabial folds. The rash may display confluent reddish-purple discoloration with papules and/or edema and typically is present at diagnosis in 40% to 52% of patients with SLE.⁸ Discoid lupus erythematosus, one of the most common cutaneous forms of lupus, manifests with various-sized coin-shaped plaques with adherent follicular hyperkeratosis and plugging. These lesions usually develop on the face, scalp, and ears but also may appear in non–sun-exposed areas.⁸ Dermatomyositis can manifest with photodistributed erythema affecting classic areas such as the upper back (shawl sign), anterior neck and upper chest (V-sign), and a malar rash similar to that seen in lupus, though DM classically does not spare the nasolabial folds.^8,9

Because SLE and DM manifest with photodistributed rashes, it can be difficult to distinguish them from the classic symptoms of photoirritant dermatitis.⁹ Thus, it is imperative that providers have a high clinical index of suspicion when dealing with patients of similar presentations, as the treatment regimens vastly differ. Approaching the patient with a thorough medical history review, review of systems, biopsy (including immunofluorescence), and appropriate laboratory workup may aid in excluding more complex differential diagnoses such as SLE and DM.

Metabolic and genetic photodermatoses are more rare but can include conditions such as porphyria cutanea tarda and xeroderma pigmentosum, both of which demonstrate fragile skin, slow wound healing, and bullae on photo-exposed skin.¹ Although the manifestations can be similar in these systemic conditions, they are caused by very different mechanisms. Porphyria cutanea tarda is caused by deficiencies in enzymes involved in the heme synthesis pathway, whereas xeroderma pigmentosum is caused by an alteration in DNA repair mechanisms.⁷

Prevalence and the Need for Standardized Testing

Most practicing dermatologists see cases of PCD due to its multiple causative agents; however, little is known about its overall prevalence. The incidence of PCD is fairly low in the general population, but this may be due to its clinical diagnosis, which excludes diagnostic testing such as phototesting and photopatch testing.¹⁰ While the incidence of photoallergic contact dermatitis also is fairly unknown, the inception of testing modalities has allowed statistics to be drawn. Research conducted in the United States has disclosed that the incidence of photoallergic contact dermatitis in individuals with a history of a prior photosensitivity eruption is approximately 10% to 20%.¹⁰ The development of guidelines and a registry for photopatch testing would aid in a greater understanding of the incidence of PCD and overall consistency of diagnosis.⁷ Regardless of this lack of consensus, these conditions can be properly managed and prevented if recognized clinically, while newer testing modalities would allow for confirmation of the diagnosis. It is important that any patient presenting with a history of photosensitivity be seen as a candidate for photopatch testing, especially today, as the general population is increasingly exposed to new chemicals entering the market and new social trends.^7,10

Diagnosis and Treatment

It is important to consider a detailed history, including the timing, location, duration, family history, and seasonal variation of suspected photodermatoses. A thorough skin examination that takes note of the specific areas affected, morphology, and involvement of the rash or lesions can be helpful.¹ Further diagnostic testing such as phototesting and photopatch testing can be employed and is especially important when distinguishing photoallergy from phototoxicity.¹¹ Phototesting involves exposing the patient’s skin to different doses of UVA, UVB, and visible light, followed by an immediate clinical reading of the results and then a delayed reading conducted after 24 hours.¹ Photopatch testing involves the application of 2 sets of identical photoallergens to prepped skin (typically cleansed with isopropyl alcohol), with one being irradiated with UVA after 24 hours and one serving as the control. A clinical assessment is conducted at 24 hours and repeated 7 days later.¹ In photodermatoses, a visible reaction can be appreciated on the treatment arm while the control arm remains clear. When both sides reveal a visible reaction, this is more indicative of a ­light-independent allergic contact dermatitis.¹

Photodermatoses occur only if there has been a specific sensitization, and therefore it is important to work with the patient to discover any new products that have been introduced into their regimen. Though many photosensitizers in personal care products (eg, antiseptics in soap and topical creams) have been discontinued, certain allergenic ingredients may remain.¹² It also is important to note that sensitization to a substance that previously was not a known allergen for a particular patient can occur later in life. Avoiding further sun exposure can rapidly improve the dermatitis, and it is possible for spontaneous remission without further intervention; however, as photoallergic reactions can cause severely pruritic skin lesions, the mainstay of symptomatic treatment consists of topical corticosteroids. Oral and topical antihistamines may help alleviate the pruritus but should not be heavily relied on as this can lead to medication resistance and diminishing efficacy.³ Use of short-term oral steroids also may be considered for rapid improvement of symptoms when the patient is in moderate distress and there are no contraindications. By identifying a temporal association between the introduction of new products and the emergence of dermatitis, it may be possible to identify the causative agent. The patient should promptly discontinue the suspected agent and remain under close observation by the clinician for any further eruptions, especially following additional sun exposure.

Prevention Strategies

In the case of PCD, prevention is key. As PCD indicates a photoallergy, it is important to inform patients that the allergy will persist for a lifetime, much like in contact dermatitis; therefore, the causative agent should be avoided indefinitely.³ Patients with PCD should make intentional efforts to read ingredient lists when purchasing new personal care products to ensure they do not contain the specific causative allergen if one has been identified. Further steps should be taken to ensure proper photoprotection, including use of dense clothing and sunscreen with UVA and UVB filters (broad spectrum).³ It has also been suggested that utilizing sunscreen with ectoin, an amino acid–derived molecule, may result in increased protection against UVA-induced photodermatoses.¹³

Final Thoughts

Photodermatoses are a group of skin diseases caused by exposure to UV radiation. Photocontact dermatitis/photoallergy is a form of allergic contact dermatitis that results from exposure to an allergen, whether topical, oral, or environmental. The allergen is activated by exposure to UV radiation to sensitize the allergic response, resulting in a rash characterized by confluent erythematous patches or plaques, papular vesicles, and rarely blisters.³ Photocontact dermatitis, although rare, is an important differential diagnosis to consider when the presenting rash is restricted to sun-exposed areas of the skin such as the arms, legs, neck, and face. Diagnosis remains a challenge; however, new testing modalities such as photopatch testing may open the door for further confirmation and aid in proper diagnosis leading to earlier treatment times for patients. It is recommended that the clinician and patient work together to identify the possible causative agent to prevent further eruptions.

Candida is a common commensal organism of human skin and mucous membranes. Candidiasis of the skin and nails is caused by overgrowth of Candida species due to excess skin moisture, skin barrier disruption, or immunosuppression. Candidiasis of the skin manifests as red, moist, itchy patches that develop particularly in skin folds. Nail involvement is associated with onycholysis (separation of the nail plate from the nail bed) and subungual debris.¹ Data on the prevalence of candidiasis of the skin and nails in the United States are scarce. In this study, we evaluated the prevalence, characteristics, and treatment practices of candidiasis of the skin and nails using data from 2 large US health insurance claims databases.

Methods

We used the 2023 Merative MarketScan Commercial, Medicare Supplemental, and Multi-State Medicaid Databases (https://www.merative.com/documents/­merative-marketscan-research-databases) to identify outpatients with the International Classification of Diseases, 10th Revision, Clinical Modification (ICD-10-CM) code B37.2 for candidiasis of the skin and nails. The Commercial and Medicare Supplemental databases include health insurance claims data submitted by large employers and health plans for more than 19 million patients throughout the United States, and the Multi-State Medicaid database includes similar data from more than 5 million patients across several geographically dispersed states. The index date for each patient corresponded with their first qualifying diagnosis of skin and nail candidiasis during January 1, 2023, to December 31, 2023. Inclusion in the study required continuous insurance enrollment from 30 days prior to 7 days after the index date, resulting in exclusion of 7% of commercial/Medicare patients and 8% of Medicaid patients. Prevalence per 1000 out­patients was calculated, with stratification by demographic characteristics.

We examined selected diagnoses made on or within 30 days before the index date, diagnostic testing performed within the 7 days before or after the index date after using specific Current Procedural Terminology codes, and outpatient antifungal and combination ­antifungal-corticosteroid prescriptions made within 7 days before or after the index date (Table). Race/­ethnicity data are unavailable in the commercial/Medicare database, and geographic data are unavailable in the Medicaid database.

Results

The prevalence of skin and nail candidiasis was 3.7 per 1000 commercial/Medicare outpatients and 7.8 per 1000 Medi­caid outpatients (eTable 1). Prevalence was highest among patients aged 0 to 3 years (commercial/Medicare, 30.3 per 1000; Medicaid, 43.6 per 1000), followed by patients 65 years or older (commercial/Medicare, 7.4 per 1000; Medicaid, 7.5 per 1000). Prevalence was higher among females compared with males (commercial/Medicare, 4.8 vs 2.4 per 1000, respectively; Medicaid, 8.8 vs 6.4 per 1000, respectively). Among Medicaid patients, prevalence was highest among those of other race, non-Hispanic (8.9 per 1000) and White non-­Hispanic patients (7.5 per 1000). In the commercial/Medicare dataset, prevalence was highest in patients residing in the Midwest (4.4 per 1000) and the South (4.0 per 1000).

Diaper dermatitis was listed as a concurrent diagnosis among 51% of patients aged 0 to 3 years in both datasets (eTable 2). Diabetes (commercial/Medicare, 32%; Medicaid, 36%) and immunosuppressive conditions (commercial/Medicare, 10%; Medicaid, 7%) were most frequent among patients aged 65 years or older. Obesity was most commonly listed as a concurrent diagnosis among patients aged 35 to 64 years (commercial/Medicare, 17%; Medicaid, 23%).

Patients aged 18 to 34 years had the highest rates of diagnostic testing in the 7 days before or after the index date (commercial/Medicare, 9%; Medicaid, 10%). Topical antifungal medications (primarily nystatin) were most frequently prescribed for patients aged 0 to 3 years ­(commercial/Medicare, 67%; Medicaid, 70%). Topical combination antifungal-corticosteroid medications were most frequently prescribed for patients aged 35 to 64 years in the commercial/Medicare dataset (16%) and for patients aged 18 to 34 years in the Medicaid dataset (8%). Topical onychomycosis treatments were prescribed for fewer than 1% of patients in both datasets. Oral antifungal medications were most frequently prescribed for patients aged 35 to 64 years in the commercial/Medicare dataset (26%) and for patients aged 18 to 34 years in the Medicaid dataset (24%). Fewer than 11% of patients across all age groups in both datasets were prescribed both topical and oral antifungal medications.

Comment

Our analysis provides preliminary insight into the prevalence of skin and nail candidiasis in the United States based on health insurance claims data. Higher prevalence of skin and nail candidiasis among patients with Medicaid compared with those with commercial/Medicare health insurance is consistent with previous studies showing increased rates of other superficial fungal infections (eg, dermatophytosis) among patients of lower socioeconomic status.² This finding could reflect differences in underlying health status or reduced access to health care, which could delay treatment or follow-up care and potentially lead to prolonged exposure to conditions favoring the development of candidiasis.

In both the commercial/Medicare health insurance and Medicaid datasets, prevalence of diagnosis codes for candidiasis of the skin and nails was highest among infants and toddlers. Diaper dermatitis also was observed in more than half of patients aged 0 to 3 years; this is a well-established risk factor for cutaneous candidiasis, as immature skin barrier function and prolonged exposure to moisture and occlusion facilitate fungal overgrowth.³ In adults, diabetes and obesity were among the most frequent comorbidities observed; both conditions are recognized risk factors for superficial candidiasis due to their impact on immune function and skin integrity.⁴

In both study cohorts, diagnostic testing in the 7 days before or after the index date was infrequent (≤10%), consistent with most cases being diagnosed clinically.⁵ Topical antifungals, especially nystatin, were most frequently prescribed for young children, while oral antifungals were more frequently prescribed for adults; nystatin is one of the most well-studied topical treatments for cutaneous candidiasis, and oral fluconazole is the primary systemic treatment for cutaneous candidiasis.¹ In our study, the ICD-10-CM code B37.2 appeared to be used primarily for diagnosis of skin rather than nail infections based on the low proportions of patients who received treatment that was onychomycosis specific.

Our study was limited by potential misclassification inherent to data based on diagnosis codes; incomplete capture of underlying conditions given the short continuous enrollment criteria; and lack of information about affected body site(s) and laboratory results, including data identifying the Candida species. A previous study found that Candida parapsilosis and Candida albicans were the most common species involved in candidiasis of the skin and nails and that one-third of isolates exhibited low sensitivity to commonly used antifungals.⁶ For nails, Candida species are sometimes contaminants rather than pathogens.

Conclusion

Our findings provide a baseline understanding of the epidemiology of candidiasis of the skin and nails in the United States. The growing threat of antifungal resistance, particularly among non-albicans Candida species, underscores the need for appropriate use of antifungals.⁷ Future epidemiologic studies about laboratory-confirmed candidiasis of the skin and nails to understand causative species and drug resistance would be useful, as would further investigation into disparities.

Candida is a common commensal organism of human skin and mucous membranes. Candidiasis of the skin and nails is caused by overgrowth of Candida species due to excess skin moisture, skin barrier disruption, or immunosuppression. Candidiasis of the skin manifests as red, moist, itchy patches that develop particularly in skin folds. Nail involvement is associated with onycholysis (separation of the nail plate from the nail bed) and subungual debris.¹ Data on the prevalence of candidiasis of the skin and nails in the United States are scarce. In this study, we evaluated the prevalence, characteristics, and treatment practices of candidiasis of the skin and nails using data from 2 large US health insurance claims databases.

Methods

We used the 2023 Merative MarketScan Commercial, Medicare Supplemental, and Multi-State Medicaid Databases (https://www.merative.com/documents/­merative-marketscan-research-databases) to identify outpatients with the International Classification of Diseases, 10th Revision, Clinical Modification (ICD-10-CM) code B37.2 for candidiasis of the skin and nails. The Commercial and Medicare Supplemental databases include health insurance claims data submitted by large employers and health plans for more than 19 million patients throughout the United States, and the Multi-State Medicaid database includes similar data from more than 5 million patients across several geographically dispersed states. The index date for each patient corresponded with their first qualifying diagnosis of skin and nail candidiasis during January 1, 2023, to December 31, 2023. Inclusion in the study required continuous insurance enrollment from 30 days prior to 7 days after the index date, resulting in exclusion of 7% of commercial/Medicare patients and 8% of Medicaid patients. Prevalence per 1000 out­patients was calculated, with stratification by demographic characteristics.

We examined selected diagnoses made on or within 30 days before the index date, diagnostic testing performed within the 7 days before or after the index date after using specific Current Procedural Terminology codes, and outpatient antifungal and combination ­antifungal-corticosteroid prescriptions made within 7 days before or after the index date (Table). Race/­ethnicity data are unavailable in the commercial/Medicare database, and geographic data are unavailable in the Medicaid database.

Results

The prevalence of skin and nail candidiasis was 3.7 per 1000 commercial/Medicare outpatients and 7.8 per 1000 Medi­caid outpatients (eTable 1). Prevalence was highest among patients aged 0 to 3 years (commercial/Medicare, 30.3 per 1000; Medicaid, 43.6 per 1000), followed by patients 65 years or older (commercial/Medicare, 7.4 per 1000; Medicaid, 7.5 per 1000). Prevalence was higher among females compared with males (commercial/Medicare, 4.8 vs 2.4 per 1000, respectively; Medicaid, 8.8 vs 6.4 per 1000, respectively). Among Medicaid patients, prevalence was highest among those of other race, non-Hispanic (8.9 per 1000) and White non-­Hispanic patients (7.5 per 1000). In the commercial/Medicare dataset, prevalence was highest in patients residing in the Midwest (4.4 per 1000) and the South (4.0 per 1000).

Diaper dermatitis was listed as a concurrent diagnosis among 51% of patients aged 0 to 3 years in both datasets (eTable 2). Diabetes (commercial/Medicare, 32%; Medicaid, 36%) and immunosuppressive conditions (commercial/Medicare, 10%; Medicaid, 7%) were most frequent among patients aged 65 years or older. Obesity was most commonly listed as a concurrent diagnosis among patients aged 35 to 64 years (commercial/Medicare, 17%; Medicaid, 23%).

Patients aged 18 to 34 years had the highest rates of diagnostic testing in the 7 days before or after the index date (commercial/Medicare, 9%; Medicaid, 10%). Topical antifungal medications (primarily nystatin) were most frequently prescribed for patients aged 0 to 3 years ­(commercial/Medicare, 67%; Medicaid, 70%). Topical combination antifungal-corticosteroid medications were most frequently prescribed for patients aged 35 to 64 years in the commercial/Medicare dataset (16%) and for patients aged 18 to 34 years in the Medicaid dataset (8%). Topical onychomycosis treatments were prescribed for fewer than 1% of patients in both datasets. Oral antifungal medications were most frequently prescribed for patients aged 35 to 64 years in the commercial/Medicare dataset (26%) and for patients aged 18 to 34 years in the Medicaid dataset (24%). Fewer than 11% of patients across all age groups in both datasets were prescribed both topical and oral antifungal medications.

Comment

Our analysis provides preliminary insight into the prevalence of skin and nail candidiasis in the United States based on health insurance claims data. Higher prevalence of skin and nail candidiasis among patients with Medicaid compared with those with commercial/Medicare health insurance is consistent with previous studies showing increased rates of other superficial fungal infections (eg, dermatophytosis) among patients of lower socioeconomic status.² This finding could reflect differences in underlying health status or reduced access to health care, which could delay treatment or follow-up care and potentially lead to prolonged exposure to conditions favoring the development of candidiasis.

In both the commercial/Medicare health insurance and Medicaid datasets, prevalence of diagnosis codes for candidiasis of the skin and nails was highest among infants and toddlers. Diaper dermatitis also was observed in more than half of patients aged 0 to 3 years; this is a well-established risk factor for cutaneous candidiasis, as immature skin barrier function and prolonged exposure to moisture and occlusion facilitate fungal overgrowth.³ In adults, diabetes and obesity were among the most frequent comorbidities observed; both conditions are recognized risk factors for superficial candidiasis due to their impact on immune function and skin integrity.⁴

In both study cohorts, diagnostic testing in the 7 days before or after the index date was infrequent (≤10%), consistent with most cases being diagnosed clinically.⁵ Topical antifungals, especially nystatin, were most frequently prescribed for young children, while oral antifungals were more frequently prescribed for adults; nystatin is one of the most well-studied topical treatments for cutaneous candidiasis, and oral fluconazole is the primary systemic treatment for cutaneous candidiasis.¹ In our study, the ICD-10-CM code B37.2 appeared to be used primarily for diagnosis of skin rather than nail infections based on the low proportions of patients who received treatment that was onychomycosis specific.

Our study was limited by potential misclassification inherent to data based on diagnosis codes; incomplete capture of underlying conditions given the short continuous enrollment criteria; and lack of information about affected body site(s) and laboratory results, including data identifying the Candida species. A previous study found that Candida parapsilosis and Candida albicans were the most common species involved in candidiasis of the skin and nails and that one-third of isolates exhibited low sensitivity to commonly used antifungals.⁶ For nails, Candida species are sometimes contaminants rather than pathogens.

Conclusion

Our findings provide a baseline understanding of the epidemiology of candidiasis of the skin and nails in the United States. The growing threat of antifungal resistance, particularly among non-albicans Candida species, underscores the need for appropriate use of antifungals.⁷ Future epidemiologic studies about laboratory-confirmed candidiasis of the skin and nails to understand causative species and drug resistance would be useful, as would further investigation into disparities.

Candida is a common commensal organism of human skin and mucous membranes. Candidiasis of the skin and nails is caused by overgrowth of Candida species due to excess skin moisture, skin barrier disruption, or immunosuppression. Candidiasis of the skin manifests as red, moist, itchy patches that develop particularly in skin folds. Nail involvement is associated with onycholysis (separation of the nail plate from the nail bed) and subungual debris.¹ Data on the prevalence of candidiasis of the skin and nails in the United States are scarce. In this study, we evaluated the prevalence, characteristics, and treatment practices of candidiasis of the skin and nails using data from 2 large US health insurance claims databases.

Methods

We used the 2023 Merative MarketScan Commercial, Medicare Supplemental, and Multi-State Medicaid Databases (https://www.merative.com/documents/­merative-marketscan-research-databases) to identify outpatients with the International Classification of Diseases, 10th Revision, Clinical Modification (ICD-10-CM) code B37.2 for candidiasis of the skin and nails. The Commercial and Medicare Supplemental databases include health insurance claims data submitted by large employers and health plans for more than 19 million patients throughout the United States, and the Multi-State Medicaid database includes similar data from more than 5 million patients across several geographically dispersed states. The index date for each patient corresponded with their first qualifying diagnosis of skin and nail candidiasis during January 1, 2023, to December 31, 2023. Inclusion in the study required continuous insurance enrollment from 30 days prior to 7 days after the index date, resulting in exclusion of 7% of commercial/Medicare patients and 8% of Medicaid patients. Prevalence per 1000 out­patients was calculated, with stratification by demographic characteristics.

We examined selected diagnoses made on or within 30 days before the index date, diagnostic testing performed within the 7 days before or after the index date after using specific Current Procedural Terminology codes, and outpatient antifungal and combination ­antifungal-corticosteroid prescriptions made within 7 days before or after the index date (Table). Race/­ethnicity data are unavailable in the commercial/Medicare database, and geographic data are unavailable in the Medicaid database.

Results

The prevalence of skin and nail candidiasis was 3.7 per 1000 commercial/Medicare outpatients and 7.8 per 1000 Medi­caid outpatients (eTable 1). Prevalence was highest among patients aged 0 to 3 years (commercial/Medicare, 30.3 per 1000; Medicaid, 43.6 per 1000), followed by patients 65 years or older (commercial/Medicare, 7.4 per 1000; Medicaid, 7.5 per 1000). Prevalence was higher among females compared with males (commercial/Medicare, 4.8 vs 2.4 per 1000, respectively; Medicaid, 8.8 vs 6.4 per 1000, respectively). Among Medicaid patients, prevalence was highest among those of other race, non-Hispanic (8.9 per 1000) and White non-­Hispanic patients (7.5 per 1000). In the commercial/Medicare dataset, prevalence was highest in patients residing in the Midwest (4.4 per 1000) and the South (4.0 per 1000).

Diaper dermatitis was listed as a concurrent diagnosis among 51% of patients aged 0 to 3 years in both datasets (eTable 2). Diabetes (commercial/Medicare, 32%; Medicaid, 36%) and immunosuppressive conditions (commercial/Medicare, 10%; Medicaid, 7%) were most frequent among patients aged 65 years or older. Obesity was most commonly listed as a concurrent diagnosis among patients aged 35 to 64 years (commercial/Medicare, 17%; Medicaid, 23%).

Patients aged 18 to 34 years had the highest rates of diagnostic testing in the 7 days before or after the index date (commercial/Medicare, 9%; Medicaid, 10%). Topical antifungal medications (primarily nystatin) were most frequently prescribed for patients aged 0 to 3 years ­(commercial/Medicare, 67%; Medicaid, 70%). Topical combination antifungal-corticosteroid medications were most frequently prescribed for patients aged 35 to 64 years in the commercial/Medicare dataset (16%) and for patients aged 18 to 34 years in the Medicaid dataset (8%). Topical onychomycosis treatments were prescribed for fewer than 1% of patients in both datasets. Oral antifungal medications were most frequently prescribed for patients aged 35 to 64 years in the commercial/Medicare dataset (26%) and for patients aged 18 to 34 years in the Medicaid dataset (24%). Fewer than 11% of patients across all age groups in both datasets were prescribed both topical and oral antifungal medications.

Comment

Our analysis provides preliminary insight into the prevalence of skin and nail candidiasis in the United States based on health insurance claims data. Higher prevalence of skin and nail candidiasis among patients with Medicaid compared with those with commercial/Medicare health insurance is consistent with previous studies showing increased rates of other superficial fungal infections (eg, dermatophytosis) among patients of lower socioeconomic status.² This finding could reflect differences in underlying health status or reduced access to health care, which could delay treatment or follow-up care and potentially lead to prolonged exposure to conditions favoring the development of candidiasis.

In both the commercial/Medicare health insurance and Medicaid datasets, prevalence of diagnosis codes for candidiasis of the skin and nails was highest among infants and toddlers. Diaper dermatitis also was observed in more than half of patients aged 0 to 3 years; this is a well-established risk factor for cutaneous candidiasis, as immature skin barrier function and prolonged exposure to moisture and occlusion facilitate fungal overgrowth.³ In adults, diabetes and obesity were among the most frequent comorbidities observed; both conditions are recognized risk factors for superficial candidiasis due to their impact on immune function and skin integrity.⁴

In both study cohorts, diagnostic testing in the 7 days before or after the index date was infrequent (≤10%), consistent with most cases being diagnosed clinically.⁵ Topical antifungals, especially nystatin, were most frequently prescribed for young children, while oral antifungals were more frequently prescribed for adults; nystatin is one of the most well-studied topical treatments for cutaneous candidiasis, and oral fluconazole is the primary systemic treatment for cutaneous candidiasis.¹ In our study, the ICD-10-CM code B37.2 appeared to be used primarily for diagnosis of skin rather than nail infections based on the low proportions of patients who received treatment that was onychomycosis specific.

Our study was limited by potential misclassification inherent to data based on diagnosis codes; incomplete capture of underlying conditions given the short continuous enrollment criteria; and lack of information about affected body site(s) and laboratory results, including data identifying the Candida species. A previous study found that Candida parapsilosis and Candida albicans were the most common species involved in candidiasis of the skin and nails and that one-third of isolates exhibited low sensitivity to commonly used antifungals.⁶ For nails, Candida species are sometimes contaminants rather than pathogens.

Conclusion

Our findings provide a baseline understanding of the epidemiology of candidiasis of the skin and nails in the United States. The growing threat of antifungal resistance, particularly among non-albicans Candida species, underscores the need for appropriate use of antifungals.⁷ Future epidemiologic studies about laboratory-confirmed candidiasis of the skin and nails to understand causative species and drug resistance would be useful, as would further investigation into disparities.

The genus of flowering plants commonly known as prickly pear cacti (Opuntia) or sabra are native to the Americas but are naturalized in many parts of the world, particularly southwest Asia and Sicily, Italy, where they are grown commercially and commonly are seen growing on rocky hillsides. (Figure 1). A prickly pear cactus has paddles that represent modified stems, and the spines are modified leaves (Figure 2). Its bright red or yellow flowers, dark-red fruit, low water requirement, and adaptability to poor-quality soil make it an attractive plant for landscaping and an important agricultural crop in many parts of the world, including the United States, Mexico, and Southern Europe. The prickly pear fruit is tasty but loaded with seeds and often is eaten fresh or used to make jam. The paddles are sometimes cut into strips, breaded or battered, and fried. The spines are easily embedded in skin and are an important cause of dermatitis.

Identifying Features

Opuntia species are found in both warm and temperate zones and grow well in arid climates. Like other cacti, they are distinguished by their water-hoarding stems and glochids (needlelike modified leaves). In prickly pears, the stems flatten to leaflike paddles that alternate in direction. Photosynthesis occurs in the stem tissues, while modified leaves (spines) are purely for defense against predators and unsuspecting humans. Opuntia species are easily identified by their broad flattened stems and dark-red fruits, both of which bear glochids (Figures 3-5).

Dermatologic Implications of Prickly Pear Injury

Prickly pear spines are very small, sharp, and difficult to see. They embed in the skin in great numbers when the plant or its fruit are handled by unsuspecting humans and have a tendency to burrow into soft tissue and underlying structures. It is very difficult to remove prickly pear spines with forceps, and attempts to do so often drive them deeper into the skin.¹ Better results are obtained by tape stripping or using water-activated cosmetic pore strips.

Cactus spine injuries may lead to mucoceles of the oral mucosa and sinuses, especially in individuals who attempt to bite into the fruit without first scorching the spines with a blow torch.² Inflammatory responses to the embedded spines are common and often result in prolonged erythematous inflammatory papules at sites of injury. Recalcitrant dermatitis and edema of underlying tissues typically occur near the point of entry of a prickly pear spine and extend to areas where the spine migrates.^3,4 Individuals who casually brush up against the plant may not be aware that they have been inoculated with the spines and may not relate the prior accidental contact with the onset of erythematous papules and edema that occurs days later. Biopsy may reveal the prickly pear spines or a granulomatous reaction pattern within the dermis. Linear patterns of necrosis surrounded by palisading histiocytes may be noted, representing the tract of the inoculation injury.

If identified in tissue, glochids are variably refractile and measure 40 to 70 µm in diameter. Glochids initiate a delayed-type hypersensitivity and foreign body response. A T-helper 1 cytokine signal is typical, and there may be a secondary influx of neutrophils, but tissue eosinophilia is uncommon. Systemic inflammation also has been reported, including eosinophilic cholangitis without biliary stricture⁵ and septic and aseptic arthritis near the site of leaf puncture and at distant sites.^6,7 Allergic contact dermatitis has been reported due to contact with the fruit of the plant and can be confirmed by patch testing.^8,9

Potential Medicinal Benefits

Prickly pear cacti have shown potential medicinal properties. While the spines may produce intense inflammation when embedded in the skin, extracts of the fruit and leaf juices have shown anti-inflammatory properties. Various vesicle and polysaccharide extracts of Opuntia cacti have been shown to reduce environmental and chemical stressors associated with open wounds.^10-12 Preclinical studies also have suggested that they could be helpful in speeding the wound-healing process when applied topically. Opuntia species also have shown promise in reducing hyperpigmentation after topical application.¹³ Preliminary data in animals also have suggested that oral administration of the fruit may slow kidney deterioration in patients with diabetes.¹⁴ Following tissue penetration by the spines, Opuntia extracts have demonstrated the ability to prevent calcium deposition in soft tissue.¹⁵ Similar preliminary data also have suggested that Opuntia extracts may reduce toxicity from cadmium, chromium, methotrexate, and acetaminophen.^16-19 Extracts from the peel of the red pitaya (Hylocereus polyrhizus), a closely related cactus, have been studied for their potential to prevent the advance of alcohol-associated liver disease, suggesting that studies evaluating the benefits of prickly pear cacti and related species may be worth pursuing.²⁰

Final Thoughts

Prickly pear cacti have the potential to act as both friend and foe. The flowers and fruit are beautiful, and the plant is well adapted to xeriscape gardens in areas under perpetual water restriction. The fruit and flesh are edible if handled properly, and prickly pear jam is delicious. While the spines are capable of inflicting local injury and migrating to internal sites, causing arthritis and other deep tissue injury, extracts of the fruit and stems have potential uses for their anti-inflammatory effects and ability to protect against toxic injury. Further studies are needed to evaluate the therapeutic potential of Opuntia and related species.

The genus of flowering plants commonly known as prickly pear cacti (Opuntia) or sabra are native to the Americas but are naturalized in many parts of the world, particularly southwest Asia and Sicily, Italy, where they are grown commercially and commonly are seen growing on rocky hillsides. (Figure 1). A prickly pear cactus has paddles that represent modified stems, and the spines are modified leaves (Figure 2). Its bright red or yellow flowers, dark-red fruit, low water requirement, and adaptability to poor-quality soil make it an attractive plant for landscaping and an important agricultural crop in many parts of the world, including the United States, Mexico, and Southern Europe. The prickly pear fruit is tasty but loaded with seeds and often is eaten fresh or used to make jam. The paddles are sometimes cut into strips, breaded or battered, and fried. The spines are easily embedded in skin and are an important cause of dermatitis.

Identifying Features

Opuntia species are found in both warm and temperate zones and grow well in arid climates. Like other cacti, they are distinguished by their water-hoarding stems and glochids (needlelike modified leaves). In prickly pears, the stems flatten to leaflike paddles that alternate in direction. Photosynthesis occurs in the stem tissues, while modified leaves (spines) are purely for defense against predators and unsuspecting humans. Opuntia species are easily identified by their broad flattened stems and dark-red fruits, both of which bear glochids (Figures 3-5).

Dermatologic Implications of Prickly Pear Injury

Prickly pear spines are very small, sharp, and difficult to see. They embed in the skin in great numbers when the plant or its fruit are handled by unsuspecting humans and have a tendency to burrow into soft tissue and underlying structures. It is very difficult to remove prickly pear spines with forceps, and attempts to do so often drive them deeper into the skin.¹ Better results are obtained by tape stripping or using water-activated cosmetic pore strips.

Cactus spine injuries may lead to mucoceles of the oral mucosa and sinuses, especially in individuals who attempt to bite into the fruit without first scorching the spines with a blow torch.² Inflammatory responses to the embedded spines are common and often result in prolonged erythematous inflammatory papules at sites of injury. Recalcitrant dermatitis and edema of underlying tissues typically occur near the point of entry of a prickly pear spine and extend to areas where the spine migrates.^3,4 Individuals who casually brush up against the plant may not be aware that they have been inoculated with the spines and may not relate the prior accidental contact with the onset of erythematous papules and edema that occurs days later. Biopsy may reveal the prickly pear spines or a granulomatous reaction pattern within the dermis. Linear patterns of necrosis surrounded by palisading histiocytes may be noted, representing the tract of the inoculation injury.

If identified in tissue, glochids are variably refractile and measure 40 to 70 µm in diameter. Glochids initiate a delayed-type hypersensitivity and foreign body response. A T-helper 1 cytokine signal is typical, and there may be a secondary influx of neutrophils, but tissue eosinophilia is uncommon. Systemic inflammation also has been reported, including eosinophilic cholangitis without biliary stricture⁵ and septic and aseptic arthritis near the site of leaf puncture and at distant sites.^6,7 Allergic contact dermatitis has been reported due to contact with the fruit of the plant and can be confirmed by patch testing.^8,9

Potential Medicinal Benefits

Prickly pear cacti have shown potential medicinal properties. While the spines may produce intense inflammation when embedded in the skin, extracts of the fruit and leaf juices have shown anti-inflammatory properties. Various vesicle and polysaccharide extracts of Opuntia cacti have been shown to reduce environmental and chemical stressors associated with open wounds.^10-12 Preclinical studies also have suggested that they could be helpful in speeding the wound-healing process when applied topically. Opuntia species also have shown promise in reducing hyperpigmentation after topical application.¹³ Preliminary data in animals also have suggested that oral administration of the fruit may slow kidney deterioration in patients with diabetes.¹⁴ Following tissue penetration by the spines, Opuntia extracts have demonstrated the ability to prevent calcium deposition in soft tissue.¹⁵ Similar preliminary data also have suggested that Opuntia extracts may reduce toxicity from cadmium, chromium, methotrexate, and acetaminophen.^16-19 Extracts from the peel of the red pitaya (Hylocereus polyrhizus), a closely related cactus, have been studied for their potential to prevent the advance of alcohol-associated liver disease, suggesting that studies evaluating the benefits of prickly pear cacti and related species may be worth pursuing.²⁰

Final Thoughts

Prickly pear cacti have the potential to act as both friend and foe. The flowers and fruit are beautiful, and the plant is well adapted to xeriscape gardens in areas under perpetual water restriction. The fruit and flesh are edible if handled properly, and prickly pear jam is delicious. While the spines are capable of inflicting local injury and migrating to internal sites, causing arthritis and other deep tissue injury, extracts of the fruit and stems have potential uses for their anti-inflammatory effects and ability to protect against toxic injury. Further studies are needed to evaluate the therapeutic potential of Opuntia and related species.

The genus of flowering plants commonly known as prickly pear cacti (Opuntia) or sabra are native to the Americas but are naturalized in many parts of the world, particularly southwest Asia and Sicily, Italy, where they are grown commercially and commonly are seen growing on rocky hillsides. (Figure 1). A prickly pear cactus has paddles that represent modified stems, and the spines are modified leaves (Figure 2). Its bright red or yellow flowers, dark-red fruit, low water requirement, and adaptability to poor-quality soil make it an attractive plant for landscaping and an important agricultural crop in many parts of the world, including the United States, Mexico, and Southern Europe. The prickly pear fruit is tasty but loaded with seeds and often is eaten fresh or used to make jam. The paddles are sometimes cut into strips, breaded or battered, and fried. The spines are easily embedded in skin and are an important cause of dermatitis.

Identifying Features

Opuntia species are found in both warm and temperate zones and grow well in arid climates. Like other cacti, they are distinguished by their water-hoarding stems and glochids (needlelike modified leaves). In prickly pears, the stems flatten to leaflike paddles that alternate in direction. Photosynthesis occurs in the stem tissues, while modified leaves (spines) are purely for defense against predators and unsuspecting humans. Opuntia species are easily identified by their broad flattened stems and dark-red fruits, both of which bear glochids (Figures 3-5).

Dermatologic Implications of Prickly Pear Injury

Prickly pear spines are very small, sharp, and difficult to see. They embed in the skin in great numbers when the plant or its fruit are handled by unsuspecting humans and have a tendency to burrow into soft tissue and underlying structures. It is very difficult to remove prickly pear spines with forceps, and attempts to do so often drive them deeper into the skin.¹ Better results are obtained by tape stripping or using water-activated cosmetic pore strips.

Cactus spine injuries may lead to mucoceles of the oral mucosa and sinuses, especially in individuals who attempt to bite into the fruit without first scorching the spines with a blow torch.² Inflammatory responses to the embedded spines are common and often result in prolonged erythematous inflammatory papules at sites of injury. Recalcitrant dermatitis and edema of underlying tissues typically occur near the point of entry of a prickly pear spine and extend to areas where the spine migrates.^3,4 Individuals who casually brush up against the plant may not be aware that they have been inoculated with the spines and may not relate the prior accidental contact with the onset of erythematous papules and edema that occurs days later. Biopsy may reveal the prickly pear spines or a granulomatous reaction pattern within the dermis. Linear patterns of necrosis surrounded by palisading histiocytes may be noted, representing the tract of the inoculation injury.

If identified in tissue, glochids are variably refractile and measure 40 to 70 µm in diameter. Glochids initiate a delayed-type hypersensitivity and foreign body response. A T-helper 1 cytokine signal is typical, and there may be a secondary influx of neutrophils, but tissue eosinophilia is uncommon. Systemic inflammation also has been reported, including eosinophilic cholangitis without biliary stricture⁵ and septic and aseptic arthritis near the site of leaf puncture and at distant sites.^6,7 Allergic contact dermatitis has been reported due to contact with the fruit of the plant and can be confirmed by patch testing.^8,9

Potential Medicinal Benefits

Prickly pear cacti have shown potential medicinal properties. While the spines may produce intense inflammation when embedded in the skin, extracts of the fruit and leaf juices have shown anti-inflammatory properties. Various vesicle and polysaccharide extracts of Opuntia cacti have been shown to reduce environmental and chemical stressors associated with open wounds.^10-12 Preclinical studies also have suggested that they could be helpful in speeding the wound-healing process when applied topically. Opuntia species also have shown promise in reducing hyperpigmentation after topical application.¹³ Preliminary data in animals also have suggested that oral administration of the fruit may slow kidney deterioration in patients with diabetes.¹⁴ Following tissue penetration by the spines, Opuntia extracts have demonstrated the ability to prevent calcium deposition in soft tissue.¹⁵ Similar preliminary data also have suggested that Opuntia extracts may reduce toxicity from cadmium, chromium, methotrexate, and acetaminophen.^16-19 Extracts from the peel of the red pitaya (Hylocereus polyrhizus), a closely related cactus, have been studied for their potential to prevent the advance of alcohol-associated liver disease, suggesting that studies evaluating the benefits of prickly pear cacti and related species may be worth pursuing.²⁰

Final Thoughts

Prickly pear cacti have the potential to act as both friend and foe. The flowers and fruit are beautiful, and the plant is well adapted to xeriscape gardens in areas under perpetual water restriction. The fruit and flesh are edible if handled properly, and prickly pear jam is delicious. While the spines are capable of inflicting local injury and migrating to internal sites, causing arthritis and other deep tissue injury, extracts of the fruit and stems have potential uses for their anti-inflammatory effects and ability to protect against toxic injury. Further studies are needed to evaluate the therapeutic potential of Opuntia and related species.

Sporotrichosis is an implantation mycosis that classically manifests as a localized skin and subcutaneous fungal infection but may disseminate to other parts of the body.¹ It is caused by several species within the Sporothrix genus² and is associated with varying clinical manifestations, geographic distributions, virulence profiles, and antifungal susceptibility patterns.^3,4 Transmission of the fungus can involve inoculation from wild or domestic animals (eg, cats).^5,6 Occupations such as landscaping and gardening or elements in the environment (eg, soil, plant fragments) also can be sources of exposure.^7,8

Sporotrichosis is recognized by the World Health Organization as a neglected tropical disease that warrants global advocacy to prevent infections and improve patient outcomes.^9,10 It carries substantial stigma and socioeconomic burden.^11,12 Diagnostics, species identification, and antifungal susceptibility testing often are limited, particularly in resource-limited settings.¹³ In this article, we outline steps to diagnose and manage sporotrichosis to improve care for affected patients globally.

Epidemiology

Sporotrichosis occurs worldwide but is most common in tropical and subtropical regions.^14,15 Outbreaks and clusters of sporotrichosis have been observed across North, Central, and South America as well as in southern Africa and Asia. The estimated annual incidence is 40,000 cases worldwide,^16-20 but global case counts likely are underestimated due to limited surveillance data and diagnostic capability.²¹

On the Asian subcontinent, Sporothrix globosa is the predominant causative species of sporotrichosis, typically via contaminated plant material²²; however, at least 1 outbreak has been associated with severe flooding.²³ In Africa, infections are most commonly caused by Sporothrix schenckii sensu stricto through a similar transmission route. Across Central America, S schenckii sensu stricto is the predominant causative species; however, Sporothrix brasiliensis is the predominant species in some countries in South America, particularly Brazil.²⁰   

Data describing the current geographic distribution and prevalence of sporotrichosis in the United States are limited. Historically, the disease was reported most commonly in Midwestern states and was associated with outbreaks related to handling Sphagnum moss.^24,25 Epidemiologic studies using health insurance data indicate an average annual incidence of 2.0 cases per million individuals in the United States, with a higher prevalence among women and a median age at diagnosis of 54 years.²⁶ A review of sporotrichosis-associated hospitalizations across the United States from 2000 to 2013 indicated an average hospitalization rate of 0.35 cases per 1 million individuals; rates were higher (0.45 cases per million) in the West and lower (0.15 per million) in the Northeast and in men (0.40 per million).²⁷ Type 2 diabetes, immune-mediated inflammatory disease, and chronic obstructive pulmonary disease are associated with an increased risk for infection and hospitalization.²⁷

Causative Organisms

Sporothrix species are thermally dimorphic fungi that can grow as mold in the environment and as yeast in human tissue. Sporothrix brasiliensis is the only thermodimorphic fungus known to be transmitted directly in its yeast form.²⁸ In other species, inoculation usually occurs after contact with contaminated soil or plant material during gardening, carpentry, or agricultural practices.⁷

Zoonotic transmission of sporotrichosis from animals to humans has been reported from a range of domestic and wild animals and birds but historically has been rare.^5,7,29,30 Recently, the importance of both cat-to-cat (epizootic) and cat-to-human (zoonotic) transmission of S brasiliensis has been recognized, with infection typically following traumatic inoculation after a scratch or bite; less frequently, transmission occurs due to exposure to respiratory droplets or contact with feline exudates.^5,29,31 Sporothrix brasiliensis is responsible for zoonotic epidemics in South America, primarily in Brazil. Transmission occurs among humans, cats, and canines, with felines serving as the primary vector.³² Transmission of this species is particularly common in stray and unneutered male cats that exhibit aggressive behaviors.³³ This species also is thought to be the most virulent Sporothrix species.²¹

Sporothrix brasiliensis can persist on nondisinfected inanimate surfaces, which suggests that fomite transmission can lead to human infection.³¹ The epidemiology of sporotrichosis has transformed in regions where S brasiliensis circulates, with epidemic spread resulting in thousands of cases, whereas in other areas without S brasilinesis, sporotrichosis predominantly occurs sporadically with rare clusters.^1,2,7,15

Sporotrichosis has been the subject of a taxonomic debate in the mycology community.²¹ Sporothrix schenckii sensu lato originally was believed to be the sole fungal pathogen causing sporotrichosis³⁴ but was later divided into S schenckii sensu stricto, Sporothrix globosa, and S brasiliensis.³⁵ More than 60 distinct species now have been described within the Sporothrix genus,^36,37 but the primary species causing human sporotrichosis include S schenckii sensu stricto, S brasiliensis, S globosa, Sporothrix mexicana, and Sporothrix luriei.³⁵ Both S schenckii and S brasiliensis have greater virulence than other Sporothrix species⁴; however, S schenckii causes infections that typically are localized and are milder, while S brasiliensis can lead to more atypical, severe, and disseminated infections^38,39 and can spread epidemically.

Clinical Manifestations

Sporotrichosis has 4 main clinical presentations: cutaneous lymphatic, fixed cutaneous, cutaneous or systemic disseminated, and extracutaneous.^40,41 The most common clinical manifestation is the cutaneous lymphatic form, which predominantly affects the hands and forearms in adults and the face in children.⁷ The primary lesion usually manifests as a unilateral papule, nodule, or pustule that may ulcerate (sporotrichotic chancre), but multiple sites of inoculation are possible. Subsequent lesions may appear in a linear distribution along a regional lymphatic path (sporotrichoid spread). Systemic symptoms and regional lymphadenopathy are uncommon and usually are mild.

The second most common clinical manifestation is the fixed cutaneous form, typically affecting the face, neck, trunk, or legs with a single papule, nodule, or verrucous lesion with no lymphangitic spread.⁷ Usually confined to the inoculation site, the primary lesion may be accompanied by satellite lesions and often presents a diagnostic challenge.

Disseminated sporotrichosis (either cutaneous or systemic) is rare. Disseminated cutaneous sporotrichosis manifests with multiple noncontiguous skin lesions caused by lymphatic and possible hematogenous spread. Lesions may include a combination of papules, pustules, follicular eruptions, crusted plaques, and ulcers that may mimic other systemic infections. Immunoreactive changes such as erythema nodosum, erythema multiforme, or arthritis may accompany skin lesions, most commonly with S brasiliensis infections. Nearly 10% of S brasiliensis infections involve the ocular adnexa, and Parinaud oculoglandular syndrome is commonly described in cases reported in Brazil.^42,43 Disseminated disease usually occurs in immunocompromised hosts; however, despite a focus on HIV co-infection,^8,44 prior epidemiologic research has suggested that diabetes and alcoholism are the most common predisposing factors.⁴⁵ Systemic disseminated sporotrichosis by definition affects at least 2 body systems, most commonly the central nervous system, lungs, and musculoskeletal system (including joints and bone marrow).⁴⁵

Extracutaneous sporotrichosis is rare and often is difficult to diagnose. Risk factors include chronic obstructive pulmonary disease, alcoholism, use of steroid medications, AIDS, solid organ transplantation, and use of tumor necrosis factor α inhibitors. It usually affects bony structures through hematogenous spread in immunocompromised hosts and is associated with a high risk for osteomyelitis due to delayed diagnosis.²

Clinical progression of sporotrichosis usually is slow, and lesions may persist for months or years if untreated. Sporotrichosis should always be considered for atypical, persistent, or treatment-resistant manifestations of nodular or ulcerated skin lesions in endemic regions or acute illness with these symptoms following exposure. Preventing secondary bacterial infection is an important consideration as it can exacerbate disease severity, extend the treatment duration, prolong hospitalization, and increase mortality risk.⁴⁶

Diagnosis

In regions endemic for S brasiliensis, it may be acceptable to commence treatment on clinical suspicion without a definitive diagnosis,²¹ but caution is necessary, as lesions easily can be mistaken for other conditions such as Mycobacterium marinum infections (sporotrichoid lesions) or cutaneous leishmaniasis. Limited availability of molecular diagnostic tools in routine clinical laboratories affects the diagnosis of sporotrichosis and species identification. Direct microscopy on a 10% to 30% potassium hydroxide wet mount has low diagnostic sensitivity and is not recommended⁴⁷; findings typically include cigar-shaped yeast cells (eFigure 1). Biopsy and histopathology also are useful, although in many infections (other than those due to S brasiliensis) there are very few detectable organisms in the tissue. Fluorescent staining of fungi with optical brighteners (eg, Calcofluor, Blankophor) is a useful technique with high sensitivity in clinical specimens on histopathologic and direct examination.⁴⁸

Fungal culture has higher sensitivity and specificity than microscopy and is the gold-standard approach for diagnosis of sporotrichosis (eFigure 2); however, culture cannot differentiate between Sporothrix species and may take more than a month to yield a positive result.⁷ No reliable serologic test for sporotrichosis has been validated, and a standardized antigen assay currently is unavailable.⁴⁹ Serology may be more useful for patients who present with systemic disease or have persistently negative culture results despite a high index of suspicion. 

A recent study evaluated the effectiveness of a lateral flow assay for detecting anti-Sporothrix antibodies, demonstrating the potential for its use as a rapid diagnostic test.⁵⁰ Investigating different molecular methods to increase the sensitivity and specificity of diagnosis and distinguish Sporothrix species has been a focus of recent research, with a preference for polymerase chain reaction (PCR)–based genotypic methods.^13,51 Recent advances in diagnostic testing include the development of multiplex PCR,⁵² culture-independent PCR techniques,⁵³ and matrix-assisted laser desorption/ionization–time of flight mass spectrometry,⁵⁴ each with varying clinical and practical applicability. Specialized testing can be beneficial for patients who have a poor therapeutic response to standard treatment, guide antifungal treatment choices, and identify epidemiologic disease and transmission patterns.²¹

Although rarely performed, antifungal susceptibility testing may be useful in guiding therapy to improve patient outcomes, particularly in the context of treatment failure, which has been documented with isolates exhibiting high minimal inhibitory concentrations (MICs) to first-line therapy and a poor clinical response.^55,56 Proposed mechanisms of resistance include increased cellular melanin ­production, which protects against oxidative stress and reduces antifungal activity.⁵⁶ Antifungal susceptibility profiles for therapeutics vary across Sporothrix species; for example, S brasiliensis generally shows lower MICs to itraconazole and terbinafine compared with S schenckii and S globosa, and S schenckii has shown a high MIC to itraconazole, as reflected in MIC distribution studies and epidemiologic cutoff values for antifungal agents.^55,57-59 However, specific breakpoints for different Sporothrix species have not been determined.⁶⁰ Robust clinical studies are needed to determine the correlation of in vitro MICs to clinical outcomes to assess the utility of antifungal susceptibility testing for Sporothrix species.

Management

Treatment of sporotrichosis is guided by clinical presentation, host immune status, and species identification. Management can be challenging in cases with an atypical or delayed diagnosis and limited access to molecular testing methods. Itraconazole is the first-line therapy for management of cutaneous sporotrichosis. It is regarded as safe, effective, well tolerated, and easily administered, with doses ranging from 100 mg in mild cases to 400 mg (with daily or twice-daily dosing).⁶¹ Treatment usually is for 3 to 6 months and should continue for 1 month after complete clinical resolution is achieved⁶²; however, some cases of S brasiliensis infection require longer treatment, and complex or disseminated cases may require therapy for up to 12 months.⁶¹ Itraconazole is contraindicated in pregnancy and has many drug interactions (through cytochrome P450 inhibition) that may preclude administration, particularly in elderly populations. Therapeutic drug monitoring is recommended for prolonged or high-dose therapy, with periodic liver function testing to reduce the risk for toxicity. Itraconazole should be administered with food, and concurrent use of antacids or proton pump inhibitors should be avoided.⁶¹

Oral terbinafine (250 mg daily) can be considered as an effective alternative to treat cutaneous disease.⁶³ Particularly in resource-limited settings, potassium iodide is an affordable and effective treatment for cutaneous sporotrichosis, administered as a saturated oral solution,⁶⁴ but due to adverse effects such as severe nausea, the daily dose should be increased slowly each day to ensure tolerance.

Amphotericin B is the treatment of choice for severe and treatment-resistant cases of sporotrichosis as well as for immunocompromised patients.^21,61 In patients with HIV, a longer treatment course is recommended with oversight from an infectious diseases specialist and usually is followed by a 12-month course of itraconazole after completion of initial therapy.⁶¹ Surgical excision infrequently is recommended but can be used in combination with another treatment modality and may be useful with a slow or incomplete response to medical therapy. Thermotherapy involves direct application of heat to cutaneous lesions and may be considered for small and localized lesions, particularly if antifungal agents are contraindicated or poorly tolerated.⁶¹ Public health measures include promoting case detection through practitioner education and patient awareness in endemic regions, as well as zoonotic control of infected animals to manage sporotrichosis.

Final Thoughts

Sporotrichosis is a fungal infection with growing public health significance. While the global disease burden is unknown, rising case numbers and geographic spread likely reflect a complex interaction between humans, the environment, and animals, exemplified by the spread of feline-associated infection due to S brasiliensis in South America.²⁸ Cases of S brasiliensis infection after importation of an affected cat have been detected outside South America, and clinicians should be alert for introduction to the United States. Strengthening genotypic and phenotypic diagnostic capabilities will allow species identification and guide treatment and management. Disease surveillance and operational research will inform public health approaches to control sporotrichosis worldwide.

Sporotrichosis is an implantation mycosis that classically manifests as a localized skin and subcutaneous fungal infection but may disseminate to other parts of the body.¹ It is caused by several species within the Sporothrix genus² and is associated with varying clinical manifestations, geographic distributions, virulence profiles, and antifungal susceptibility patterns.^3,4 Transmission of the fungus can involve inoculation from wild or domestic animals (eg, cats).^5,6 Occupations such as landscaping and gardening or elements in the environment (eg, soil, plant fragments) also can be sources of exposure.^7,8

Sporotrichosis is recognized by the World Health Organization as a neglected tropical disease that warrants global advocacy to prevent infections and improve patient outcomes.^9,10 It carries substantial stigma and socioeconomic burden.^11,12 Diagnostics, species identification, and antifungal susceptibility testing often are limited, particularly in resource-limited settings.¹³ In this article, we outline steps to diagnose and manage sporotrichosis to improve care for affected patients globally.

Epidemiology

Sporotrichosis occurs worldwide but is most common in tropical and subtropical regions.^14,15 Outbreaks and clusters of sporotrichosis have been observed across North, Central, and South America as well as in southern Africa and Asia. The estimated annual incidence is 40,000 cases worldwide,^16-20 but global case counts likely are underestimated due to limited surveillance data and diagnostic capability.²¹

On the Asian subcontinent, Sporothrix globosa is the predominant causative species of sporotrichosis, typically via contaminated plant material²²; however, at least 1 outbreak has been associated with severe flooding.²³ In Africa, infections are most commonly caused by Sporothrix schenckii sensu stricto through a similar transmission route. Across Central America, S schenckii sensu stricto is the predominant causative species; however, Sporothrix brasiliensis is the predominant species in some countries in South America, particularly Brazil.²⁰   

Data describing the current geographic distribution and prevalence of sporotrichosis in the United States are limited. Historically, the disease was reported most commonly in Midwestern states and was associated with outbreaks related to handling Sphagnum moss.^24,25 Epidemiologic studies using health insurance data indicate an average annual incidence of 2.0 cases per million individuals in the United States, with a higher prevalence among women and a median age at diagnosis of 54 years.²⁶ A review of sporotrichosis-associated hospitalizations across the United States from 2000 to 2013 indicated an average hospitalization rate of 0.35 cases per 1 million individuals; rates were higher (0.45 cases per million) in the West and lower (0.15 per million) in the Northeast and in men (0.40 per million).²⁷ Type 2 diabetes, immune-mediated inflammatory disease, and chronic obstructive pulmonary disease are associated with an increased risk for infection and hospitalization.²⁷

Causative Organisms

Sporothrix species are thermally dimorphic fungi that can grow as mold in the environment and as yeast in human tissue. Sporothrix brasiliensis is the only thermodimorphic fungus known to be transmitted directly in its yeast form.²⁸ In other species, inoculation usually occurs after contact with contaminated soil or plant material during gardening, carpentry, or agricultural practices.⁷

Zoonotic transmission of sporotrichosis from animals to humans has been reported from a range of domestic and wild animals and birds but historically has been rare.^5,7,29,30 Recently, the importance of both cat-to-cat (epizootic) and cat-to-human (zoonotic) transmission of S brasiliensis has been recognized, with infection typically following traumatic inoculation after a scratch or bite; less frequently, transmission occurs due to exposure to respiratory droplets or contact with feline exudates.^5,29,31 Sporothrix brasiliensis is responsible for zoonotic epidemics in South America, primarily in Brazil. Transmission occurs among humans, cats, and canines, with felines serving as the primary vector.³² Transmission of this species is particularly common in stray and unneutered male cats that exhibit aggressive behaviors.³³ This species also is thought to be the most virulent Sporothrix species.²¹

Sporothrix brasiliensis can persist on nondisinfected inanimate surfaces, which suggests that fomite transmission can lead to human infection.³¹ The epidemiology of sporotrichosis has transformed in regions where S brasiliensis circulates, with epidemic spread resulting in thousands of cases, whereas in other areas without S brasilinesis, sporotrichosis predominantly occurs sporadically with rare clusters.^1,2,7,15

Sporotrichosis has been the subject of a taxonomic debate in the mycology community.²¹ Sporothrix schenckii sensu lato originally was believed to be the sole fungal pathogen causing sporotrichosis³⁴ but was later divided into S schenckii sensu stricto, Sporothrix globosa, and S brasiliensis.³⁵ More than 60 distinct species now have been described within the Sporothrix genus,^36,37 but the primary species causing human sporotrichosis include S schenckii sensu stricto, S brasiliensis, S globosa, Sporothrix mexicana, and Sporothrix luriei.³⁵ Both S schenckii and S brasiliensis have greater virulence than other Sporothrix species⁴; however, S schenckii causes infections that typically are localized and are milder, while S brasiliensis can lead to more atypical, severe, and disseminated infections^38,39 and can spread epidemically.

Clinical Manifestations

Sporotrichosis has 4 main clinical presentations: cutaneous lymphatic, fixed cutaneous, cutaneous or systemic disseminated, and extracutaneous.^40,41 The most common clinical manifestation is the cutaneous lymphatic form, which predominantly affects the hands and forearms in adults and the face in children.⁷ The primary lesion usually manifests as a unilateral papule, nodule, or pustule that may ulcerate (sporotrichotic chancre), but multiple sites of inoculation are possible. Subsequent lesions may appear in a linear distribution along a regional lymphatic path (sporotrichoid spread). Systemic symptoms and regional lymphadenopathy are uncommon and usually are mild.

The second most common clinical manifestation is the fixed cutaneous form, typically affecting the face, neck, trunk, or legs with a single papule, nodule, or verrucous lesion with no lymphangitic spread.⁷ Usually confined to the inoculation site, the primary lesion may be accompanied by satellite lesions and often presents a diagnostic challenge.

Disseminated sporotrichosis (either cutaneous or systemic) is rare. Disseminated cutaneous sporotrichosis manifests with multiple noncontiguous skin lesions caused by lymphatic and possible hematogenous spread. Lesions may include a combination of papules, pustules, follicular eruptions, crusted plaques, and ulcers that may mimic other systemic infections. Immunoreactive changes such as erythema nodosum, erythema multiforme, or arthritis may accompany skin lesions, most commonly with S brasiliensis infections. Nearly 10% of S brasiliensis infections involve the ocular adnexa, and Parinaud oculoglandular syndrome is commonly described in cases reported in Brazil.^42,43 Disseminated disease usually occurs in immunocompromised hosts; however, despite a focus on HIV co-infection,^8,44 prior epidemiologic research has suggested that diabetes and alcoholism are the most common predisposing factors.⁴⁵ Systemic disseminated sporotrichosis by definition affects at least 2 body systems, most commonly the central nervous system, lungs, and musculoskeletal system (including joints and bone marrow).⁴⁵

Extracutaneous sporotrichosis is rare and often is difficult to diagnose. Risk factors include chronic obstructive pulmonary disease, alcoholism, use of steroid medications, AIDS, solid organ transplantation, and use of tumor necrosis factor α inhibitors. It usually affects bony structures through hematogenous spread in immunocompromised hosts and is associated with a high risk for osteomyelitis due to delayed diagnosis.²

Clinical progression of sporotrichosis usually is slow, and lesions may persist for months or years if untreated. Sporotrichosis should always be considered for atypical, persistent, or treatment-resistant manifestations of nodular or ulcerated skin lesions in endemic regions or acute illness with these symptoms following exposure. Preventing secondary bacterial infection is an important consideration as it can exacerbate disease severity, extend the treatment duration, prolong hospitalization, and increase mortality risk.⁴⁶

Diagnosis

In regions endemic for S brasiliensis, it may be acceptable to commence treatment on clinical suspicion without a definitive diagnosis,²¹ but caution is necessary, as lesions easily can be mistaken for other conditions such as Mycobacterium marinum infections (sporotrichoid lesions) or cutaneous leishmaniasis. Limited availability of molecular diagnostic tools in routine clinical laboratories affects the diagnosis of sporotrichosis and species identification. Direct microscopy on a 10% to 30% potassium hydroxide wet mount has low diagnostic sensitivity and is not recommended⁴⁷; findings typically include cigar-shaped yeast cells (eFigure 1). Biopsy and histopathology also are useful, although in many infections (other than those due to S brasiliensis) there are very few detectable organisms in the tissue. Fluorescent staining of fungi with optical brighteners (eg, Calcofluor, Blankophor) is a useful technique with high sensitivity in clinical specimens on histopathologic and direct examination.⁴⁸

Fungal culture has higher sensitivity and specificity than microscopy and is the gold-standard approach for diagnosis of sporotrichosis (eFigure 2); however, culture cannot differentiate between Sporothrix species and may take more than a month to yield a positive result.⁷ No reliable serologic test for sporotrichosis has been validated, and a standardized antigen assay currently is unavailable.⁴⁹ Serology may be more useful for patients who present with systemic disease or have persistently negative culture results despite a high index of suspicion. 

A recent study evaluated the effectiveness of a lateral flow assay for detecting anti-Sporothrix antibodies, demonstrating the potential for its use as a rapid diagnostic test.⁵⁰ Investigating different molecular methods to increase the sensitivity and specificity of diagnosis and distinguish Sporothrix species has been a focus of recent research, with a preference for polymerase chain reaction (PCR)–based genotypic methods.^13,51 Recent advances in diagnostic testing include the development of multiplex PCR,⁵² culture-independent PCR techniques,⁵³ and matrix-assisted laser desorption/ionization–time of flight mass spectrometry,⁵⁴ each with varying clinical and practical applicability. Specialized testing can be beneficial for patients who have a poor therapeutic response to standard treatment, guide antifungal treatment choices, and identify epidemiologic disease and transmission patterns.²¹

Although rarely performed, antifungal susceptibility testing may be useful in guiding therapy to improve patient outcomes, particularly in the context of treatment failure, which has been documented with isolates exhibiting high minimal inhibitory concentrations (MICs) to first-line therapy and a poor clinical response.^55,56 Proposed mechanisms of resistance include increased cellular melanin ­production, which protects against oxidative stress and reduces antifungal activity.⁵⁶ Antifungal susceptibility profiles for therapeutics vary across Sporothrix species; for example, S brasiliensis generally shows lower MICs to itraconazole and terbinafine compared with S schenckii and S globosa, and S schenckii has shown a high MIC to itraconazole, as reflected in MIC distribution studies and epidemiologic cutoff values for antifungal agents.^55,57-59 However, specific breakpoints for different Sporothrix species have not been determined.⁶⁰ Robust clinical studies are needed to determine the correlation of in vitro MICs to clinical outcomes to assess the utility of antifungal susceptibility testing for Sporothrix species.

Management

Treatment of sporotrichosis is guided by clinical presentation, host immune status, and species identification. Management can be challenging in cases with an atypical or delayed diagnosis and limited access to molecular testing methods. Itraconazole is the first-line therapy for management of cutaneous sporotrichosis. It is regarded as safe, effective, well tolerated, and easily administered, with doses ranging from 100 mg in mild cases to 400 mg (with daily or twice-daily dosing).⁶¹ Treatment usually is for 3 to 6 months and should continue for 1 month after complete clinical resolution is achieved⁶²; however, some cases of S brasiliensis infection require longer treatment, and complex or disseminated cases may require therapy for up to 12 months.⁶¹ Itraconazole is contraindicated in pregnancy and has many drug interactions (through cytochrome P450 inhibition) that may preclude administration, particularly in elderly populations. Therapeutic drug monitoring is recommended for prolonged or high-dose therapy, with periodic liver function testing to reduce the risk for toxicity. Itraconazole should be administered with food, and concurrent use of antacids or proton pump inhibitors should be avoided.⁶¹

Oral terbinafine (250 mg daily) can be considered as an effective alternative to treat cutaneous disease.⁶³ Particularly in resource-limited settings, potassium iodide is an affordable and effective treatment for cutaneous sporotrichosis, administered as a saturated oral solution,⁶⁴ but due to adverse effects such as severe nausea, the daily dose should be increased slowly each day to ensure tolerance.

Amphotericin B is the treatment of choice for severe and treatment-resistant cases of sporotrichosis as well as for immunocompromised patients.^21,61 In patients with HIV, a longer treatment course is recommended with oversight from an infectious diseases specialist and usually is followed by a 12-month course of itraconazole after completion of initial therapy.⁶¹ Surgical excision infrequently is recommended but can be used in combination with another treatment modality and may be useful with a slow or incomplete response to medical therapy. Thermotherapy involves direct application of heat to cutaneous lesions and may be considered for small and localized lesions, particularly if antifungal agents are contraindicated or poorly tolerated.⁶¹ Public health measures include promoting case detection through practitioner education and patient awareness in endemic regions, as well as zoonotic control of infected animals to manage sporotrichosis.

Final Thoughts

Sporotrichosis is a fungal infection with growing public health significance. While the global disease burden is unknown, rising case numbers and geographic spread likely reflect a complex interaction between humans, the environment, and animals, exemplified by the spread of feline-associated infection due to S brasiliensis in South America.²⁸ Cases of S brasiliensis infection after importation of an affected cat have been detected outside South America, and clinicians should be alert for introduction to the United States. Strengthening genotypic and phenotypic diagnostic capabilities will allow species identification and guide treatment and management. Disease surveillance and operational research will inform public health approaches to control sporotrichosis worldwide.

Sporotrichosis is an implantation mycosis that classically manifests as a localized skin and subcutaneous fungal infection but may disseminate to other parts of the body.¹ It is caused by several species within the Sporothrix genus² and is associated with varying clinical manifestations, geographic distributions, virulence profiles, and antifungal susceptibility patterns.^3,4 Transmission of the fungus can involve inoculation from wild or domestic animals (eg, cats).^5,6 Occupations such as landscaping and gardening or elements in the environment (eg, soil, plant fragments) also can be sources of exposure.^7,8

Sporotrichosis is recognized by the World Health Organization as a neglected tropical disease that warrants global advocacy to prevent infections and improve patient outcomes.^9,10 It carries substantial stigma and socioeconomic burden.^11,12 Diagnostics, species identification, and antifungal susceptibility testing often are limited, particularly in resource-limited settings.¹³ In this article, we outline steps to diagnose and manage sporotrichosis to improve care for affected patients globally.

Epidemiology

Sporotrichosis occurs worldwide but is most common in tropical and subtropical regions.^14,15 Outbreaks and clusters of sporotrichosis have been observed across North, Central, and South America as well as in southern Africa and Asia. The estimated annual incidence is 40,000 cases worldwide,^16-20 but global case counts likely are underestimated due to limited surveillance data and diagnostic capability.²¹

On the Asian subcontinent, Sporothrix globosa is the predominant causative species of sporotrichosis, typically via contaminated plant material²²; however, at least 1 outbreak has been associated with severe flooding.²³ In Africa, infections are most commonly caused by Sporothrix schenckii sensu stricto through a similar transmission route. Across Central America, S schenckii sensu stricto is the predominant causative species; however, Sporothrix brasiliensis is the predominant species in some countries in South America, particularly Brazil.²⁰   

Data describing the current geographic distribution and prevalence of sporotrichosis in the United States are limited. Historically, the disease was reported most commonly in Midwestern states and was associated with outbreaks related to handling Sphagnum moss.^24,25 Epidemiologic studies using health insurance data indicate an average annual incidence of 2.0 cases per million individuals in the United States, with a higher prevalence among women and a median age at diagnosis of 54 years.²⁶ A review of sporotrichosis-associated hospitalizations across the United States from 2000 to 2013 indicated an average hospitalization rate of 0.35 cases per 1 million individuals; rates were higher (0.45 cases per million) in the West and lower (0.15 per million) in the Northeast and in men (0.40 per million).²⁷ Type 2 diabetes, immune-mediated inflammatory disease, and chronic obstructive pulmonary disease are associated with an increased risk for infection and hospitalization.²⁷

Causative Organisms

Sporothrix species are thermally dimorphic fungi that can grow as mold in the environment and as yeast in human tissue. Sporothrix brasiliensis is the only thermodimorphic fungus known to be transmitted directly in its yeast form.²⁸ In other species, inoculation usually occurs after contact with contaminated soil or plant material during gardening, carpentry, or agricultural practices.⁷

Zoonotic transmission of sporotrichosis from animals to humans has been reported from a range of domestic and wild animals and birds but historically has been rare.^5,7,29,30 Recently, the importance of both cat-to-cat (epizootic) and cat-to-human (zoonotic) transmission of S brasiliensis has been recognized, with infection typically following traumatic inoculation after a scratch or bite; less frequently, transmission occurs due to exposure to respiratory droplets or contact with feline exudates.^5,29,31 Sporothrix brasiliensis is responsible for zoonotic epidemics in South America, primarily in Brazil. Transmission occurs among humans, cats, and canines, with felines serving as the primary vector.³² Transmission of this species is particularly common in stray and unneutered male cats that exhibit aggressive behaviors.³³ This species also is thought to be the most virulent Sporothrix species.²¹

Sporothrix brasiliensis can persist on nondisinfected inanimate surfaces, which suggests that fomite transmission can lead to human infection.³¹ The epidemiology of sporotrichosis has transformed in regions where S brasiliensis circulates, with epidemic spread resulting in thousands of cases, whereas in other areas without S brasilinesis, sporotrichosis predominantly occurs sporadically with rare clusters.^1,2,7,15

Sporotrichosis has been the subject of a taxonomic debate in the mycology community.²¹ Sporothrix schenckii sensu lato originally was believed to be the sole fungal pathogen causing sporotrichosis³⁴ but was later divided into S schenckii sensu stricto, Sporothrix globosa, and S brasiliensis.³⁵ More than 60 distinct species now have been described within the Sporothrix genus,^36,37 but the primary species causing human sporotrichosis include S schenckii sensu stricto, S brasiliensis, S globosa, Sporothrix mexicana, and Sporothrix luriei.³⁵ Both S schenckii and S brasiliensis have greater virulence than other Sporothrix species⁴; however, S schenckii causes infections that typically are localized and are milder, while S brasiliensis can lead to more atypical, severe, and disseminated infections^38,39 and can spread epidemically.

Clinical Manifestations

Sporotrichosis has 4 main clinical presentations: cutaneous lymphatic, fixed cutaneous, cutaneous or systemic disseminated, and extracutaneous.^40,41 The most common clinical manifestation is the cutaneous lymphatic form, which predominantly affects the hands and forearms in adults and the face in children.⁷ The primary lesion usually manifests as a unilateral papule, nodule, or pustule that may ulcerate (sporotrichotic chancre), but multiple sites of inoculation are possible. Subsequent lesions may appear in a linear distribution along a regional lymphatic path (sporotrichoid spread). Systemic symptoms and regional lymphadenopathy are uncommon and usually are mild.

The second most common clinical manifestation is the fixed cutaneous form, typically affecting the face, neck, trunk, or legs with a single papule, nodule, or verrucous lesion with no lymphangitic spread.⁷ Usually confined to the inoculation site, the primary lesion may be accompanied by satellite lesions and often presents a diagnostic challenge.

Disseminated sporotrichosis (either cutaneous or systemic) is rare. Disseminated cutaneous sporotrichosis manifests with multiple noncontiguous skin lesions caused by lymphatic and possible hematogenous spread. Lesions may include a combination of papules, pustules, follicular eruptions, crusted plaques, and ulcers that may mimic other systemic infections. Immunoreactive changes such as erythema nodosum, erythema multiforme, or arthritis may accompany skin lesions, most commonly with S brasiliensis infections. Nearly 10% of S brasiliensis infections involve the ocular adnexa, and Parinaud oculoglandular syndrome is commonly described in cases reported in Brazil.^42,43 Disseminated disease usually occurs in immunocompromised hosts; however, despite a focus on HIV co-infection,^8,44 prior epidemiologic research has suggested that diabetes and alcoholism are the most common predisposing factors.⁴⁵ Systemic disseminated sporotrichosis by definition affects at least 2 body systems, most commonly the central nervous system, lungs, and musculoskeletal system (including joints and bone marrow).⁴⁵

Extracutaneous sporotrichosis is rare and often is difficult to diagnose. Risk factors include chronic obstructive pulmonary disease, alcoholism, use of steroid medications, AIDS, solid organ transplantation, and use of tumor necrosis factor α inhibitors. It usually affects bony structures through hematogenous spread in immunocompromised hosts and is associated with a high risk for osteomyelitis due to delayed diagnosis.²

Clinical progression of sporotrichosis usually is slow, and lesions may persist for months or years if untreated. Sporotrichosis should always be considered for atypical, persistent, or treatment-resistant manifestations of nodular or ulcerated skin lesions in endemic regions or acute illness with these symptoms following exposure. Preventing secondary bacterial infection is an important consideration as it can exacerbate disease severity, extend the treatment duration, prolong hospitalization, and increase mortality risk.⁴⁶

Diagnosis

In regions endemic for S brasiliensis, it may be acceptable to commence treatment on clinical suspicion without a definitive diagnosis,²¹ but caution is necessary, as lesions easily can be mistaken for other conditions such as Mycobacterium marinum infections (sporotrichoid lesions) or cutaneous leishmaniasis. Limited availability of molecular diagnostic tools in routine clinical laboratories affects the diagnosis of sporotrichosis and species identification. Direct microscopy on a 10% to 30% potassium hydroxide wet mount has low diagnostic sensitivity and is not recommended⁴⁷; findings typically include cigar-shaped yeast cells (eFigure 1). Biopsy and histopathology also are useful, although in many infections (other than those due to S brasiliensis) there are very few detectable organisms in the tissue. Fluorescent staining of fungi with optical brighteners (eg, Calcofluor, Blankophor) is a useful technique with high sensitivity in clinical specimens on histopathologic and direct examination.⁴⁸

Fungal culture has higher sensitivity and specificity than microscopy and is the gold-standard approach for diagnosis of sporotrichosis (eFigure 2); however, culture cannot differentiate between Sporothrix species and may take more than a month to yield a positive result.⁷ No reliable serologic test for sporotrichosis has been validated, and a standardized antigen assay currently is unavailable.⁴⁹ Serology may be more useful for patients who present with systemic disease or have persistently negative culture results despite a high index of suspicion. 

A recent study evaluated the effectiveness of a lateral flow assay for detecting anti-Sporothrix antibodies, demonstrating the potential for its use as a rapid diagnostic test.⁵⁰ Investigating different molecular methods to increase the sensitivity and specificity of diagnosis and distinguish Sporothrix species has been a focus of recent research, with a preference for polymerase chain reaction (PCR)–based genotypic methods.^13,51 Recent advances in diagnostic testing include the development of multiplex PCR,⁵² culture-independent PCR techniques,⁵³ and matrix-assisted laser desorption/ionization–time of flight mass spectrometry,⁵⁴ each with varying clinical and practical applicability. Specialized testing can be beneficial for patients who have a poor therapeutic response to standard treatment, guide antifungal treatment choices, and identify epidemiologic disease and transmission patterns.²¹

Although rarely performed, antifungal susceptibility testing may be useful in guiding therapy to improve patient outcomes, particularly in the context of treatment failure, which has been documented with isolates exhibiting high minimal inhibitory concentrations (MICs) to first-line therapy and a poor clinical response.^55,56 Proposed mechanisms of resistance include increased cellular melanin ­production, which protects against oxidative stress and reduces antifungal activity.⁵⁶ Antifungal susceptibility profiles for therapeutics vary across Sporothrix species; for example, S brasiliensis generally shows lower MICs to itraconazole and terbinafine compared with S schenckii and S globosa, and S schenckii has shown a high MIC to itraconazole, as reflected in MIC distribution studies and epidemiologic cutoff values for antifungal agents.^55,57-59 However, specific breakpoints for different Sporothrix species have not been determined.⁶⁰ Robust clinical studies are needed to determine the correlation of in vitro MICs to clinical outcomes to assess the utility of antifungal susceptibility testing for Sporothrix species.

Management

Treatment of sporotrichosis is guided by clinical presentation, host immune status, and species identification. Management can be challenging in cases with an atypical or delayed diagnosis and limited access to molecular testing methods. Itraconazole is the first-line therapy for management of cutaneous sporotrichosis. It is regarded as safe, effective, well tolerated, and easily administered, with doses ranging from 100 mg in mild cases to 400 mg (with daily or twice-daily dosing).⁶¹ Treatment usually is for 3 to 6 months and should continue for 1 month after complete clinical resolution is achieved⁶²; however, some cases of S brasiliensis infection require longer treatment, and complex or disseminated cases may require therapy for up to 12 months.⁶¹ Itraconazole is contraindicated in pregnancy and has many drug interactions (through cytochrome P450 inhibition) that may preclude administration, particularly in elderly populations. Therapeutic drug monitoring is recommended for prolonged or high-dose therapy, with periodic liver function testing to reduce the risk for toxicity. Itraconazole should be administered with food, and concurrent use of antacids or proton pump inhibitors should be avoided.⁶¹

Oral terbinafine (250 mg daily) can be considered as an effective alternative to treat cutaneous disease.⁶³ Particularly in resource-limited settings, potassium iodide is an affordable and effective treatment for cutaneous sporotrichosis, administered as a saturated oral solution,⁶⁴ but due to adverse effects such as severe nausea, the daily dose should be increased slowly each day to ensure tolerance.

Amphotericin B is the treatment of choice for severe and treatment-resistant cases of sporotrichosis as well as for immunocompromised patients.^21,61 In patients with HIV, a longer treatment course is recommended with oversight from an infectious diseases specialist and usually is followed by a 12-month course of itraconazole after completion of initial therapy.⁶¹ Surgical excision infrequently is recommended but can be used in combination with another treatment modality and may be useful with a slow or incomplete response to medical therapy. Thermotherapy involves direct application of heat to cutaneous lesions and may be considered for small and localized lesions, particularly if antifungal agents are contraindicated or poorly tolerated.⁶¹ Public health measures include promoting case detection through practitioner education and patient awareness in endemic regions, as well as zoonotic control of infected animals to manage sporotrichosis.

Final Thoughts

Sporotrichosis is a fungal infection with growing public health significance. While the global disease burden is unknown, rising case numbers and geographic spread likely reflect a complex interaction between humans, the environment, and animals, exemplified by the spread of feline-associated infection due to S brasiliensis in South America.²⁸ Cases of S brasiliensis infection after importation of an affected cat have been detected outside South America, and clinicians should be alert for introduction to the United States. Strengthening genotypic and phenotypic diagnostic capabilities will allow species identification and guide treatment and management. Disease surveillance and operational research will inform public health approaches to control sporotrichosis worldwide.

Biting midges, commonly known as no-see-ums, are true flies (order Diptera) and members of the Ceratopogonidae family. Regionally, they are known as punkies in the Northeast, pinyon gnats in the Southwest, moose flies in Canada, and sand gnats in Georgia, among other names.¹ There are 6206 species found worldwide except for Antarctica.² The 3 genera of greatest importance to human and livestock health in the United States are Culicoides, Leptoconops, and Forcipomyia.¹ Forty-seven species of the genus Culicoides are known to be present in Florida.³ Species belonging to the genus Leptoconops also are present in coastal areas of southeast Florida as well as in the tropics, subtropics, and Caribbean.³ In the United States, biting midges primarily are a nuisance; the major medical issue associated with Culicoides insects are allergic reactions to their bites. Even though no-see-ums are not known to transmit disease in humans, they have an impact on other animal species in the United States as biting pests and vectors of disease-causing pathogens.¹ Biting midges pose quite a nuisance for the proper enjoyment of outdoor spaces in the southeastern United States.

Characteristics

Morphologically, no-see-ums are gray flies measuring 1 to 3 mm in length (eFigure 1). Adults have 2 wings with distinctive patterns, large compound eyes, a thorax that extends slightly over the head, an abdomen with 9 segments, and antennae with 15 segments (eFigure 2).^1,3,4 Females have modified mouth parts including mandibles that lacerate the skin during feeding, which is mainly on blood from vertebrate hosts (primarily mammals but also birds, reptiles, and amphibians).^1,4 They also can feed on invertebrate hosts. Both male and female no-see-ums feed on nectar, but adult females require a blood meal to develop their eggs.² Their life cycle progresses in stages from egg to larva to pupa to adult. Larval habitats include salt marshes, swamps, shores of streams and ponds, water-holding plants, rotting fruit, and saturated wood- and manure-enriched soil. Adults can live 2 to 7 weeks. They are weak fliers, particularly in windy conditions.¹

In Florida, no-see-ums are more active during the rainy months of May to October but are active year-round in the southeastern United States and the Gulf Coast from Florida to West Texas. They are active throughout the United States in the warmer months of June and July.⁵ Their peak feeding activity occurs at dawn and dusk, but different species of biting midges such as Leptoconops and Culicoides also can feed during daylight hours and at night, respectively.^1,6,7

Case Report

One of the authors (M.J.S.), a healthy 54-year-old man with no remarkable medical history or current use of medications, documented the natural progression of a no-see-um bite by sitting in an outdoor Florida space at 8:00 am armed with a dermatoscope and a smartphone camera. The initial sensation of the bite felt like a sting that progressed over a few minutes to itchiness; however, the culprit was not readily identifiable. Upon closer inspection, pinpoint black dots could be correlated with the location of discomfort on the exposed upper extremities. Upon dermoscopic examination, 2 biting midges were identified as well as multiple wheals at the bite sites, and they seemed unbothered by the polarized light of the dermatoscope while feeding (eFigure 3). They flew away after a few minutes of feeding. The site of the bite wound was readily identifiable on dermoscopy as a wheal with a pinpoint red dot at the center (eFigure 4). The wheal started to form during the act of feeding and lasted up to 2 hours before fading (eFigure 5). The itch quickly resolved within the hour if hydrocortisone 1% was used. If untreated and scratched, itching rarely could last longer than a day.

Clinical Manifestations

Although no-see-ums are not known to transmit disease in the United States, they are important biting pests that can affect tourism and prevent enjoyment of outdoor spaces and activities.² The bite reactions on the host can range from wheal-like lesions to papules measuring 2 to 3 mm (at times with overlying vesicles) to nodules up to 1 cm in diameter.⁸ In our reported case, the small wheals disappeared within hours, but pruritic papules have been described to last from weeks to months. Published histopathologic correlation of biopsied indurated papules within 3 days of bite occurrence have revealed a superficial infiltrate composed of lymphocytes and histiocytes, while eosinophils were found in the deeper dermis and subcutaneous fat. Within 2 weeks, as the lesions aged, the infiltrate contained a smaller percentage of eosinophils and predominantly was present in only the superficial dermis.⁸ Delayed-type hypersensitivity reactions including pustules and bullous lesions also have been described.^9,10 Host immune reaction to the saliva introduced during the bite dictates the severity of the response, and lesions may become secondarily infected due to scratching.¹¹

Management Recommendations

Management consists of cleaning the bite site with soap and water to prevent infection, applying cold compresses or ice packs to relieve the intense itch, and avoiding scratching.¹¹ Application of over-the-counter calamine lotion or hydrocortisone cream can relieve itch, and mid- to high-potency topical corticosteroids also can be prescribed for 1 to 2 weeks for more intense bite reactions in conjunction with oral antihistamines. Topical or oral antibiotics may be indicated if redness and swelling progress at the bite site or if breaks in the skin become secondarily infected.

Final Thoughts

Because of the wide-ranging habitats of no-see-ums, eradication programs using insecticides have been inefficient or environmentally suboptimal. Emptying all standing water in outdoor spaces will reduce the number of no-see-ums. Avoidance of the outdoors at dawn and dusk when no-see-ums are most active is helpful, as well as protecting exposed skin by wearing long-sleeved shirts and long pants when outside. Insect repellents containing DEET (N-N-diethyl-meta-toluamide) or picaridin can offer additional protection on the remaining exposed skin. Oil of lemon eucalyptus, or active compound p-menthane-3,8-diol, has been shown to be effective against no-see-ums. Use of DEET should be avoided in children younger than 2 years and p-menthane-3,8-diol in those younger than 3 years. Picaridin is safe for use in children.¹² Citronella oil is ineffective. Installing window and patio screens with a mesh size less than 16 can prevent no-see-ums from passing through the netting but will restrict air flow.³ Turning off porch lights also is helpful, as no-see-ums are attracted to light sources.⁶ Since no-see-ums are weak flyers, setting ceiling or window fans at high speeds can minimize exposure; similarly, being outdoors on a windy day may decrease the likelihood of being bitten. Ultimately, the best remedy for a bite is to prevent them from happening.

Biting midges, commonly known as no-see-ums, are true flies (order Diptera) and members of the Ceratopogonidae family. Regionally, they are known as punkies in the Northeast, pinyon gnats in the Southwest, moose flies in Canada, and sand gnats in Georgia, among other names.¹ There are 6206 species found worldwide except for Antarctica.² The 3 genera of greatest importance to human and livestock health in the United States are Culicoides, Leptoconops, and Forcipomyia.¹ Forty-seven species of the genus Culicoides are known to be present in Florida.³ Species belonging to the genus Leptoconops also are present in coastal areas of southeast Florida as well as in the tropics, subtropics, and Caribbean.³ In the United States, biting midges primarily are a nuisance; the major medical issue associated with Culicoides insects are allergic reactions to their bites. Even though no-see-ums are not known to transmit disease in humans, they have an impact on other animal species in the United States as biting pests and vectors of disease-causing pathogens.¹ Biting midges pose quite a nuisance for the proper enjoyment of outdoor spaces in the southeastern United States.

Characteristics

Morphologically, no-see-ums are gray flies measuring 1 to 3 mm in length (eFigure 1). Adults have 2 wings with distinctive patterns, large compound eyes, a thorax that extends slightly over the head, an abdomen with 9 segments, and antennae with 15 segments (eFigure 2).^1,3,4 Females have modified mouth parts including mandibles that lacerate the skin during feeding, which is mainly on blood from vertebrate hosts (primarily mammals but also birds, reptiles, and amphibians).^1,4 They also can feed on invertebrate hosts. Both male and female no-see-ums feed on nectar, but adult females require a blood meal to develop their eggs.² Their life cycle progresses in stages from egg to larva to pupa to adult. Larval habitats include salt marshes, swamps, shores of streams and ponds, water-holding plants, rotting fruit, and saturated wood- and manure-enriched soil. Adults can live 2 to 7 weeks. They are weak fliers, particularly in windy conditions.¹

In Florida, no-see-ums are more active during the rainy months of May to October but are active year-round in the southeastern United States and the Gulf Coast from Florida to West Texas. They are active throughout the United States in the warmer months of June and July.⁵ Their peak feeding activity occurs at dawn and dusk, but different species of biting midges such as Leptoconops and Culicoides also can feed during daylight hours and at night, respectively.^1,6,7

Case Report

One of the authors (M.J.S.), a healthy 54-year-old man with no remarkable medical history or current use of medications, documented the natural progression of a no-see-um bite by sitting in an outdoor Florida space at 8:00 am armed with a dermatoscope and a smartphone camera. The initial sensation of the bite felt like a sting that progressed over a few minutes to itchiness; however, the culprit was not readily identifiable. Upon closer inspection, pinpoint black dots could be correlated with the location of discomfort on the exposed upper extremities. Upon dermoscopic examination, 2 biting midges were identified as well as multiple wheals at the bite sites, and they seemed unbothered by the polarized light of the dermatoscope while feeding (eFigure 3). They flew away after a few minutes of feeding. The site of the bite wound was readily identifiable on dermoscopy as a wheal with a pinpoint red dot at the center (eFigure 4). The wheal started to form during the act of feeding and lasted up to 2 hours before fading (eFigure 5). The itch quickly resolved within the hour if hydrocortisone 1% was used. If untreated and scratched, itching rarely could last longer than a day.

Clinical Manifestations

Although no-see-ums are not known to transmit disease in the United States, they are important biting pests that can affect tourism and prevent enjoyment of outdoor spaces and activities.² The bite reactions on the host can range from wheal-like lesions to papules measuring 2 to 3 mm (at times with overlying vesicles) to nodules up to 1 cm in diameter.⁸ In our reported case, the small wheals disappeared within hours, but pruritic papules have been described to last from weeks to months. Published histopathologic correlation of biopsied indurated papules within 3 days of bite occurrence have revealed a superficial infiltrate composed of lymphocytes and histiocytes, while eosinophils were found in the deeper dermis and subcutaneous fat. Within 2 weeks, as the lesions aged, the infiltrate contained a smaller percentage of eosinophils and predominantly was present in only the superficial dermis.⁸ Delayed-type hypersensitivity reactions including pustules and bullous lesions also have been described.^9,10 Host immune reaction to the saliva introduced during the bite dictates the severity of the response, and lesions may become secondarily infected due to scratching.¹¹

Management Recommendations

Management consists of cleaning the bite site with soap and water to prevent infection, applying cold compresses or ice packs to relieve the intense itch, and avoiding scratching.¹¹ Application of over-the-counter calamine lotion or hydrocortisone cream can relieve itch, and mid- to high-potency topical corticosteroids also can be prescribed for 1 to 2 weeks for more intense bite reactions in conjunction with oral antihistamines. Topical or oral antibiotics may be indicated if redness and swelling progress at the bite site or if breaks in the skin become secondarily infected.

Final Thoughts

Because of the wide-ranging habitats of no-see-ums, eradication programs using insecticides have been inefficient or environmentally suboptimal. Emptying all standing water in outdoor spaces will reduce the number of no-see-ums. Avoidance of the outdoors at dawn and dusk when no-see-ums are most active is helpful, as well as protecting exposed skin by wearing long-sleeved shirts and long pants when outside. Insect repellents containing DEET (N-N-diethyl-meta-toluamide) or picaridin can offer additional protection on the remaining exposed skin. Oil of lemon eucalyptus, or active compound p-menthane-3,8-diol, has been shown to be effective against no-see-ums. Use of DEET should be avoided in children younger than 2 years and p-menthane-3,8-diol in those younger than 3 years. Picaridin is safe for use in children.¹² Citronella oil is ineffective. Installing window and patio screens with a mesh size less than 16 can prevent no-see-ums from passing through the netting but will restrict air flow.³ Turning off porch lights also is helpful, as no-see-ums are attracted to light sources.⁶ Since no-see-ums are weak flyers, setting ceiling or window fans at high speeds can minimize exposure; similarly, being outdoors on a windy day may decrease the likelihood of being bitten. Ultimately, the best remedy for a bite is to prevent them from happening.

Biting midges, commonly known as no-see-ums, are true flies (order Diptera) and members of the Ceratopogonidae family. Regionally, they are known as punkies in the Northeast, pinyon gnats in the Southwest, moose flies in Canada, and sand gnats in Georgia, among other names.¹ There are 6206 species found worldwide except for Antarctica.² The 3 genera of greatest importance to human and livestock health in the United States are Culicoides, Leptoconops, and Forcipomyia.¹ Forty-seven species of the genus Culicoides are known to be present in Florida.³ Species belonging to the genus Leptoconops also are present in coastal areas of southeast Florida as well as in the tropics, subtropics, and Caribbean.³ In the United States, biting midges primarily are a nuisance; the major medical issue associated with Culicoides insects are allergic reactions to their bites. Even though no-see-ums are not known to transmit disease in humans, they have an impact on other animal species in the United States as biting pests and vectors of disease-causing pathogens.¹ Biting midges pose quite a nuisance for the proper enjoyment of outdoor spaces in the southeastern United States.

Characteristics

Morphologically, no-see-ums are gray flies measuring 1 to 3 mm in length (eFigure 1). Adults have 2 wings with distinctive patterns, large compound eyes, a thorax that extends slightly over the head, an abdomen with 9 segments, and antennae with 15 segments (eFigure 2).^1,3,4 Females have modified mouth parts including mandibles that lacerate the skin during feeding, which is mainly on blood from vertebrate hosts (primarily mammals but also birds, reptiles, and amphibians).^1,4 They also can feed on invertebrate hosts. Both male and female no-see-ums feed on nectar, but adult females require a blood meal to develop their eggs.² Their life cycle progresses in stages from egg to larva to pupa to adult. Larval habitats include salt marshes, swamps, shores of streams and ponds, water-holding plants, rotting fruit, and saturated wood- and manure-enriched soil. Adults can live 2 to 7 weeks. They are weak fliers, particularly in windy conditions.¹

In Florida, no-see-ums are more active during the rainy months of May to October but are active year-round in the southeastern United States and the Gulf Coast from Florida to West Texas. They are active throughout the United States in the warmer months of June and July.⁵ Their peak feeding activity occurs at dawn and dusk, but different species of biting midges such as Leptoconops and Culicoides also can feed during daylight hours and at night, respectively.^1,6,7

Case Report

One of the authors (M.J.S.), a healthy 54-year-old man with no remarkable medical history or current use of medications, documented the natural progression of a no-see-um bite by sitting in an outdoor Florida space at 8:00 am armed with a dermatoscope and a smartphone camera. The initial sensation of the bite felt like a sting that progressed over a few minutes to itchiness; however, the culprit was not readily identifiable. Upon closer inspection, pinpoint black dots could be correlated with the location of discomfort on the exposed upper extremities. Upon dermoscopic examination, 2 biting midges were identified as well as multiple wheals at the bite sites, and they seemed unbothered by the polarized light of the dermatoscope while feeding (eFigure 3). They flew away after a few minutes of feeding. The site of the bite wound was readily identifiable on dermoscopy as a wheal with a pinpoint red dot at the center (eFigure 4). The wheal started to form during the act of feeding and lasted up to 2 hours before fading (eFigure 5). The itch quickly resolved within the hour if hydrocortisone 1% was used. If untreated and scratched, itching rarely could last longer than a day.

Clinical Manifestations

Although no-see-ums are not known to transmit disease in the United States, they are important biting pests that can affect tourism and prevent enjoyment of outdoor spaces and activities.² The bite reactions on the host can range from wheal-like lesions to papules measuring 2 to 3 mm (at times with overlying vesicles) to nodules up to 1 cm in diameter.⁸ In our reported case, the small wheals disappeared within hours, but pruritic papules have been described to last from weeks to months. Published histopathologic correlation of biopsied indurated papules within 3 days of bite occurrence have revealed a superficial infiltrate composed of lymphocytes and histiocytes, while eosinophils were found in the deeper dermis and subcutaneous fat. Within 2 weeks, as the lesions aged, the infiltrate contained a smaller percentage of eosinophils and predominantly was present in only the superficial dermis.⁸ Delayed-type hypersensitivity reactions including pustules and bullous lesions also have been described.^9,10 Host immune reaction to the saliva introduced during the bite dictates the severity of the response, and lesions may become secondarily infected due to scratching.¹¹

Management Recommendations

Management consists of cleaning the bite site with soap and water to prevent infection, applying cold compresses or ice packs to relieve the intense itch, and avoiding scratching.¹¹ Application of over-the-counter calamine lotion or hydrocortisone cream can relieve itch, and mid- to high-potency topical corticosteroids also can be prescribed for 1 to 2 weeks for more intense bite reactions in conjunction with oral antihistamines. Topical or oral antibiotics may be indicated if redness and swelling progress at the bite site or if breaks in the skin become secondarily infected.

Final Thoughts

Because of the wide-ranging habitats of no-see-ums, eradication programs using insecticides have been inefficient or environmentally suboptimal. Emptying all standing water in outdoor spaces will reduce the number of no-see-ums. Avoidance of the outdoors at dawn and dusk when no-see-ums are most active is helpful, as well as protecting exposed skin by wearing long-sleeved shirts and long pants when outside. Insect repellents containing DEET (N-N-diethyl-meta-toluamide) or picaridin can offer additional protection on the remaining exposed skin. Oil of lemon eucalyptus, or active compound p-menthane-3,8-diol, has been shown to be effective against no-see-ums. Use of DEET should be avoided in children younger than 2 years and p-menthane-3,8-diol in those younger than 3 years. Picaridin is safe for use in children.¹² Citronella oil is ineffective. Installing window and patio screens with a mesh size less than 16 can prevent no-see-ums from passing through the netting but will restrict air flow.³ Turning off porch lights also is helpful, as no-see-ums are attracted to light sources.⁶ Since no-see-ums are weak flyers, setting ceiling or window fans at high speeds can minimize exposure; similarly, being outdoors on a windy day may decrease the likelihood of being bitten. Ultimately, the best remedy for a bite is to prevent them from happening.

Cydnidae is a family of small to medium-sized shield bugs with spiny legs that commonly are known as burrowing bugs (or burrower bugs). The family Cydnidae includes more than 100 genera and approximately 600 species worldwide.¹ These insects are arthropods of the order Hemiptera (suborder: Heteroptera; superfamily: Pentatomoidae) and largely are concentrated in tropical and temperate regions. Approximately 145 species have been recorded in the Neotropical Region and have been included in the subfamilies Amnestinae, Cephalocteinae, and Sehirinae, in addition to Cydnidae.² Burrowing bugs are ovoid in shape and 2 to 20 mm in length and morphologically are well adapted for burrowing. Their life span is 100 to 300 days. Being phytophagous, they burrow to feed on plants and roots. Adult burrowing bugs have wings and can fly. They have specialized glands located in either the abdomen (nymph) or thorax (adult) that secrete odorous chemicals for self-protection.³ The secretions contain hydrocarbonates that function as repellents and danger signals, can cause paralysis in prey, and act as a chemoattractant for mates.^4-6 They also cause hyperpigmentation upon contact with the skin.

In this article, we present a series of cases from the same community to demonstrate the characteristic features of hyperpigmented macules caused by exposure to burrowing bugs. Dermatologists should be aware of this entity to prevent misdiagnosis and unnecessary investigations and treatment.

Case Series

A 36-year-old woman and 6 children (age range, 6-12 years) presented with a widespread, acute, brown-pigmented, macular eruption with lesions that increased in number over a 1-week period. All 7 patients resided in the same locality and were otherwise systemically healthy. Initially, the index case, a 7-year-old girl, was referred to our tertiary care center by a dermatologist with a provisional diagnosis of idiopathic macular eruptive pigmentation. The patient’s mother recalled noticing a tiny black insect on the child's scalp that left pigment on the skin when she crushed it between her fingers. The rest of the patients presented over the next few days: 3 of the children belonged to the same household as the index case, and there was history of all 6 children playing in the neighborhood park during late evening hours. The adult patient was the parent of one of the affected children. The lesions were associated with mild itching and tingling in 3 children but were asymptomatic in the other patients.

Clinical examination of the patients revealed multiple dark- to light-brown, discrete, irregularly shaped macules over the trunk, arms, and soles (eFigure 1). Dermoscopic examination of a pigmented macule showed an irregularly shaped, brownish, structureless area with accentuation of the pigment at skin creases and perieccrine pigmentation (eFigure 2). The pigmentation was unaffected by rubbing with alcohol or water. Clinicoepidemiologic parameters of the patients are summarized in the eTable.

One of the children’s parents conducted a geological examination of the ground in the neighborhood park during evening hours and found tiny burrowing bugs (eFigure 3). When crushed between the fingers, these insects left a similar brownish hyperpigmentation on the skin. The parents were counseled on the nature of the eruption, and the patients were kept under observation for 2 weeks. On follow-up after 5 days, the lesions showed markedly decreased intensity of hyperpigmentation, and no new lesions were observed in any of the 7 patients.

Comment

Pentatomoidae insects generally are benign and harmless to humans. There have been isolated reports of erythematous plaques caused by Antiteuchus mixtus and Edessa maculate.⁷ Malhotra et al⁸ reported the first known series of cases with Cydnidae insect–induced hyperpigmented macules. The reported patients presented with asymptomatic, brown, hyperpigmented macules over exposed sites such as the feet, neck, and chest. All the cases occurred during the monsoon season in tropical and temperate regions of the world, and the patients were characteristically clustered in similar geographic areas. The causative insect was identified as Chilocoris assmuthi Breddin, 1904, belonging to the family Cydnidae. When it was crushed between the fingers, the skin became hyperpigmented, confirming the role of the secretions from the insect in the etiology.⁸

A second case was described by Sonthalia,⁹ who also described the dermoscopic features of hyperpigmented macules caused by burrowing bugs. The lesions showed a stuck-on, clustered appearance of ovoid and bizarre pigmented clods, globules, and granules.⁹ Although the lesions occur mainly over exposed sites, pigmented macules occurring over unusual sites such as the abdomen and back also have been reported in association with burrowing bugs.¹⁰ Characteristically, the lesions initially are faint and darken with time and usually fade within a week. They can be rubbed off with acetone but persist when washed with soap and water. The fleeting nature of the pigmentation also has led to the term transient pseudo-lentigines sign to describe hyperpigmentation caused by burrowing bugs.¹¹

Soil and plants are burrowing bugs’ natural habitats, and the insects typically are seen in vegetation-rich, moist areas adjoining human dwellings (eg, parks, gardens), where clusters of cases can occur. These insects proliferate during the monsoon season in tropical and temperate areas, leading to more cases occurring during these months. 

Compared to prior reports,^8,9 a few of our patients had predominant trunk and neck involvement with an occasional tingling sensation or pruritus while the rest were asymptomatic. Dermoscopic features from our patients shared similar reported features of Cydnidae pigmentation.^4,5 The accentuation of pigment over skin creases seen on dermoscopy was due to accumulation of Cydnidae secretion at these sites. 

The differential diagnosis commonly includes idiopathic macular eruptive pigmentation, which is characterized by an asymptomatic progressive eruption of hyperpigmented macules over the trunk that persists from a few months up to 3 years. Other conditions in the differential include benign conditions such as acral benign melanocytic nevi, lentigines, pigmented purpuric dermatosis, and postinflammatory hyperpigmentation, as well as malignant conditions such as acral melanoma. Dermoscopy is a helpful, easy-to-use tool in differentiating these pigmentation disorders, obviating the need for an invasive investigation such as histopathologic analysis. Simultaneous involvement in a group of people living together or visiting the same place, abrupt onset, predominant involvement of the exposed sites, characteristic clinical and dermoscopic features, self-limiting course, and timing with the monsoon season should suggest a possibility of Cydnidae dermatitis/pigmentation, which can be confirmed by finding the causative bug in the affected locality.

Management

No specific treatment is required for the pigmentation caused by Cydnidae, as it is self-resolving. The macules can, however, be removed with acetone. Patients must be counseled regarding the benign and fleeting nature of this condition, as the abrupt onset may alarm them of a systemic disease. Affected patients should be advised against walking barefoot in areas where the insects can be found. Spraying insecticides in the affected locality also helps to reduce the presence of burrowing bugs.

Cydnidae is a family of small to medium-sized shield bugs with spiny legs that commonly are known as burrowing bugs (or burrower bugs). The family Cydnidae includes more than 100 genera and approximately 600 species worldwide.¹ These insects are arthropods of the order Hemiptera (suborder: Heteroptera; superfamily: Pentatomoidae) and largely are concentrated in tropical and temperate regions. Approximately 145 species have been recorded in the Neotropical Region and have been included in the subfamilies Amnestinae, Cephalocteinae, and Sehirinae, in addition to Cydnidae.² Burrowing bugs are ovoid in shape and 2 to 20 mm in length and morphologically are well adapted for burrowing. Their life span is 100 to 300 days. Being phytophagous, they burrow to feed on plants and roots. Adult burrowing bugs have wings and can fly. They have specialized glands located in either the abdomen (nymph) or thorax (adult) that secrete odorous chemicals for self-protection.³ The secretions contain hydrocarbonates that function as repellents and danger signals, can cause paralysis in prey, and act as a chemoattractant for mates.^4-6 They also cause hyperpigmentation upon contact with the skin.

In this article, we present a series of cases from the same community to demonstrate the characteristic features of hyperpigmented macules caused by exposure to burrowing bugs. Dermatologists should be aware of this entity to prevent misdiagnosis and unnecessary investigations and treatment.

Case Series

A 36-year-old woman and 6 children (age range, 6-12 years) presented with a widespread, acute, brown-pigmented, macular eruption with lesions that increased in number over a 1-week period. All 7 patients resided in the same locality and were otherwise systemically healthy. Initially, the index case, a 7-year-old girl, was referred to our tertiary care center by a dermatologist with a provisional diagnosis of idiopathic macular eruptive pigmentation. The patient’s mother recalled noticing a tiny black insect on the child's scalp that left pigment on the skin when she crushed it between her fingers. The rest of the patients presented over the next few days: 3 of the children belonged to the same household as the index case, and there was history of all 6 children playing in the neighborhood park during late evening hours. The adult patient was the parent of one of the affected children. The lesions were associated with mild itching and tingling in 3 children but were asymptomatic in the other patients.

Clinical examination of the patients revealed multiple dark- to light-brown, discrete, irregularly shaped macules over the trunk, arms, and soles (eFigure 1). Dermoscopic examination of a pigmented macule showed an irregularly shaped, brownish, structureless area with accentuation of the pigment at skin creases and perieccrine pigmentation (eFigure 2). The pigmentation was unaffected by rubbing with alcohol or water. Clinicoepidemiologic parameters of the patients are summarized in the eTable.

One of the children’s parents conducted a geological examination of the ground in the neighborhood park during evening hours and found tiny burrowing bugs (eFigure 3). When crushed between the fingers, these insects left a similar brownish hyperpigmentation on the skin. The parents were counseled on the nature of the eruption, and the patients were kept under observation for 2 weeks. On follow-up after 5 days, the lesions showed markedly decreased intensity of hyperpigmentation, and no new lesions were observed in any of the 7 patients.

Comment

Pentatomoidae insects generally are benign and harmless to humans. There have been isolated reports of erythematous plaques caused by Antiteuchus mixtus and Edessa maculate.⁷ Malhotra et al⁸ reported the first known series of cases with Cydnidae insect–induced hyperpigmented macules. The reported patients presented with asymptomatic, brown, hyperpigmented macules over exposed sites such as the feet, neck, and chest. All the cases occurred during the monsoon season in tropical and temperate regions of the world, and the patients were characteristically clustered in similar geographic areas. The causative insect was identified as Chilocoris assmuthi Breddin, 1904, belonging to the family Cydnidae. When it was crushed between the fingers, the skin became hyperpigmented, confirming the role of the secretions from the insect in the etiology.⁸

A second case was described by Sonthalia,⁹ who also described the dermoscopic features of hyperpigmented macules caused by burrowing bugs. The lesions showed a stuck-on, clustered appearance of ovoid and bizarre pigmented clods, globules, and granules.⁹ Although the lesions occur mainly over exposed sites, pigmented macules occurring over unusual sites such as the abdomen and back also have been reported in association with burrowing bugs.¹⁰ Characteristically, the lesions initially are faint and darken with time and usually fade within a week. They can be rubbed off with acetone but persist when washed with soap and water. The fleeting nature of the pigmentation also has led to the term transient pseudo-lentigines sign to describe hyperpigmentation caused by burrowing bugs.¹¹

Soil and plants are burrowing bugs’ natural habitats, and the insects typically are seen in vegetation-rich, moist areas adjoining human dwellings (eg, parks, gardens), where clusters of cases can occur. These insects proliferate during the monsoon season in tropical and temperate areas, leading to more cases occurring during these months. 

Compared to prior reports,^8,9 a few of our patients had predominant trunk and neck involvement with an occasional tingling sensation or pruritus while the rest were asymptomatic. Dermoscopic features from our patients shared similar reported features of Cydnidae pigmentation.^4,5 The accentuation of pigment over skin creases seen on dermoscopy was due to accumulation of Cydnidae secretion at these sites. 

The differential diagnosis commonly includes idiopathic macular eruptive pigmentation, which is characterized by an asymptomatic progressive eruption of hyperpigmented macules over the trunk that persists from a few months up to 3 years. Other conditions in the differential include benign conditions such as acral benign melanocytic nevi, lentigines, pigmented purpuric dermatosis, and postinflammatory hyperpigmentation, as well as malignant conditions such as acral melanoma. Dermoscopy is a helpful, easy-to-use tool in differentiating these pigmentation disorders, obviating the need for an invasive investigation such as histopathologic analysis. Simultaneous involvement in a group of people living together or visiting the same place, abrupt onset, predominant involvement of the exposed sites, characteristic clinical and dermoscopic features, self-limiting course, and timing with the monsoon season should suggest a possibility of Cydnidae dermatitis/pigmentation, which can be confirmed by finding the causative bug in the affected locality.

Management

No specific treatment is required for the pigmentation caused by Cydnidae, as it is self-resolving. The macules can, however, be removed with acetone. Patients must be counseled regarding the benign and fleeting nature of this condition, as the abrupt onset may alarm them of a systemic disease. Affected patients should be advised against walking barefoot in areas where the insects can be found. Spraying insecticides in the affected locality also helps to reduce the presence of burrowing bugs.

Cydnidae is a family of small to medium-sized shield bugs with spiny legs that commonly are known as burrowing bugs (or burrower bugs). The family Cydnidae includes more than 100 genera and approximately 600 species worldwide.¹ These insects are arthropods of the order Hemiptera (suborder: Heteroptera; superfamily: Pentatomoidae) and largely are concentrated in tropical and temperate regions. Approximately 145 species have been recorded in the Neotropical Region and have been included in the subfamilies Amnestinae, Cephalocteinae, and Sehirinae, in addition to Cydnidae.² Burrowing bugs are ovoid in shape and 2 to 20 mm in length and morphologically are well adapted for burrowing. Their life span is 100 to 300 days. Being phytophagous, they burrow to feed on plants and roots. Adult burrowing bugs have wings and can fly. They have specialized glands located in either the abdomen (nymph) or thorax (adult) that secrete odorous chemicals for self-protection.³ The secretions contain hydrocarbonates that function as repellents and danger signals, can cause paralysis in prey, and act as a chemoattractant for mates.^4-6 They also cause hyperpigmentation upon contact with the skin.

In this article, we present a series of cases from the same community to demonstrate the characteristic features of hyperpigmented macules caused by exposure to burrowing bugs. Dermatologists should be aware of this entity to prevent misdiagnosis and unnecessary investigations and treatment.

Case Series

A 36-year-old woman and 6 children (age range, 6-12 years) presented with a widespread, acute, brown-pigmented, macular eruption with lesions that increased in number over a 1-week period. All 7 patients resided in the same locality and were otherwise systemically healthy. Initially, the index case, a 7-year-old girl, was referred to our tertiary care center by a dermatologist with a provisional diagnosis of idiopathic macular eruptive pigmentation. The patient’s mother recalled noticing a tiny black insect on the child's scalp that left pigment on the skin when she crushed it between her fingers. The rest of the patients presented over the next few days: 3 of the children belonged to the same household as the index case, and there was history of all 6 children playing in the neighborhood park during late evening hours. The adult patient was the parent of one of the affected children. The lesions were associated with mild itching and tingling in 3 children but were asymptomatic in the other patients.

Clinical examination of the patients revealed multiple dark- to light-brown, discrete, irregularly shaped macules over the trunk, arms, and soles (eFigure 1). Dermoscopic examination of a pigmented macule showed an irregularly shaped, brownish, structureless area with accentuation of the pigment at skin creases and perieccrine pigmentation (eFigure 2). The pigmentation was unaffected by rubbing with alcohol or water. Clinicoepidemiologic parameters of the patients are summarized in the eTable.

One of the children’s parents conducted a geological examination of the ground in the neighborhood park during evening hours and found tiny burrowing bugs (eFigure 3). When crushed between the fingers, these insects left a similar brownish hyperpigmentation on the skin. The parents were counseled on the nature of the eruption, and the patients were kept under observation for 2 weeks. On follow-up after 5 days, the lesions showed markedly decreased intensity of hyperpigmentation, and no new lesions were observed in any of the 7 patients.

Comment

Pentatomoidae insects generally are benign and harmless to humans. There have been isolated reports of erythematous plaques caused by Antiteuchus mixtus and Edessa maculate.⁷ Malhotra et al⁸ reported the first known series of cases with Cydnidae insect–induced hyperpigmented macules. The reported patients presented with asymptomatic, brown, hyperpigmented macules over exposed sites such as the feet, neck, and chest. All the cases occurred during the monsoon season in tropical and temperate regions of the world, and the patients were characteristically clustered in similar geographic areas. The causative insect was identified as Chilocoris assmuthi Breddin, 1904, belonging to the family Cydnidae. When it was crushed between the fingers, the skin became hyperpigmented, confirming the role of the secretions from the insect in the etiology.⁸

A second case was described by Sonthalia,⁹ who also described the dermoscopic features of hyperpigmented macules caused by burrowing bugs. The lesions showed a stuck-on, clustered appearance of ovoid and bizarre pigmented clods, globules, and granules.⁹ Although the lesions occur mainly over exposed sites, pigmented macules occurring over unusual sites such as the abdomen and back also have been reported in association with burrowing bugs.¹⁰ Characteristically, the lesions initially are faint and darken with time and usually fade within a week. They can be rubbed off with acetone but persist when washed with soap and water. The fleeting nature of the pigmentation also has led to the term transient pseudo-lentigines sign to describe hyperpigmentation caused by burrowing bugs.¹¹

Soil and plants are burrowing bugs’ natural habitats, and the insects typically are seen in vegetation-rich, moist areas adjoining human dwellings (eg, parks, gardens), where clusters of cases can occur. These insects proliferate during the monsoon season in tropical and temperate areas, leading to more cases occurring during these months. 

Compared to prior reports,^8,9 a few of our patients had predominant trunk and neck involvement with an occasional tingling sensation or pruritus while the rest were asymptomatic. Dermoscopic features from our patients shared similar reported features of Cydnidae pigmentation.^4,5 The accentuation of pigment over skin creases seen on dermoscopy was due to accumulation of Cydnidae secretion at these sites. 

The differential diagnosis commonly includes idiopathic macular eruptive pigmentation, which is characterized by an asymptomatic progressive eruption of hyperpigmented macules over the trunk that persists from a few months up to 3 years. Other conditions in the differential include benign conditions such as acral benign melanocytic nevi, lentigines, pigmented purpuric dermatosis, and postinflammatory hyperpigmentation, as well as malignant conditions such as acral melanoma. Dermoscopy is a helpful, easy-to-use tool in differentiating these pigmentation disorders, obviating the need for an invasive investigation such as histopathologic analysis. Simultaneous involvement in a group of people living together or visiting the same place, abrupt onset, predominant involvement of the exposed sites, characteristic clinical and dermoscopic features, self-limiting course, and timing with the monsoon season should suggest a possibility of Cydnidae dermatitis/pigmentation, which can be confirmed by finding the causative bug in the affected locality.

Management

No specific treatment is required for the pigmentation caused by Cydnidae, as it is self-resolving. The macules can, however, be removed with acetone. Patients must be counseled regarding the benign and fleeting nature of this condition, as the abrupt onset may alarm them of a systemic disease. Affected patients should be advised against walking barefoot in areas where the insects can be found. Spraying insecticides in the affected locality also helps to reduce the presence of burrowing bugs.

Implantation mycoses such as chromoblastomycosis, subcutaneous phaeohyphomycosis, and mycetoma are a diverse group of fungal diseases that occur when a break in the skin allows the entry of the causative fungus. These diseases disproportionately affect individuals in low- and middle-income countries causing substantial disability, decreased quality of life, and severe social stigma.^1-3 Timely diagnosis and appropriate treatment are critical.

Chromoblastomycosis and mycetoma are designated as neglected tropical diseases, but research to improve their management is sparse, even compared to other neglected tropical diseases.^4,5 Since there are no global diagnostic and treatment guidelines to date, we outline steps to diagnose and manage chromoblastomycosis, subcutaneous phaeohyphomycosis, and mycetoma.

Chromoblastomycosis

Chromoblastomycosis is caused by dematiaceous fungi that typically affect the skin and subcutaneous tissue. Chromoblastomycosis is distinguished from subcutaneous phaeohyphomycosis by microscopically visualizing the characteristic thick-walled, single, or multicellular clusters of pigmented fungal cells (also known as medlar bodies, muriform cells, or sclerotic bodies).⁶ In phaeohyphomycosis, short hyphae and pseudohyphae plus some single cells typically are seen.

Epidemiology—Globally, the distribution and burden of chromoblastomycosis are relatively unknown. Infections are more common in tropical and subtropical areas but can be acquired anywhere. A literature review conducted in 2021 identified 7740 cases of chromo­blastomycosis, mostly reported in South America, Africa, Central America and Mexico, and Asia.⁷ Most of the patients were male, and the median age was 52 years. One study found an incidence of 14.7 per 1,000,000 patients in the United States for both chromoblastomycosis and phaeohyphomycotic abscesses (which included both skin and brain abscesses).⁸ Most patients were aged 65 years or older, with a higher incidence in males. Geographically, the incidence was highest in the Northeast followed by the South; patients in rural areas also had higher incidence of disease.⁸

Causative Organisms—Causative species cannot reliably distinguish between chromoblastomycosis and subcutaneous phaeohyphomycosis, as some species overlap. Cladophialophora carrionii, Fonsecaea species, Phialophora verrucosa species complex, and Rhinocladiella aquaspersa most commonly cause chromoblastomycosis.^9,10

Clinical Manifestations—Chromoblastomycosis initially manifests as a solitary erythematous macule at a site of trauma (often not recalled by the patient) that can evolve to a smooth pink papule and may progress to 1 of 5 morphologies: nodular, verrucous, tumorous, cicatricial, or plaque.⁶ Patients may present with more than one morphology, particularly in long-standing or advanced disease. Lesions commonly manifest on the arms and legs in otherwise healthy individuals in environments (eg, rural, agricultural) that have more opportunities for injury and exposure to the causative fungi. Affected individuals often have small black specks on the lesion surface that are visible with the naked eye.⁶

Diagnosis—Common differential diagnoses include cutaneous blastomycosis, fixed sporotrichosis, warty tuberculosis nocardiosis, cutaneous leishmaniasis, human papillomavirus (HPV) infection, podoconiosis, lymphatic filariasis, cutaneous tuberculosis, and psoriasis.⁶ Squamous cell carcinoma is both a differential diagnosis as well as a potential complication of the disease.¹¹

Potassium hydroxide preparation with skin scapings or a biopsy from the lesion has high sensitivity and quick turnaround times. There often is a background histopathologic reaction of pseudoepitheliomatous hyperplasia. Examining samples taken from areas with the visible small black dots on the skin surface can increase the likelihood of detecting fungal elements (Figure 1). Clinicians also may choose to obtain a 6- to 8-mm deep skin biopsy from the lesion and splice it in half, with one sample sent for histopathology and the other for culture (Figure 2). Skin scrapings can be sent for culture instead. In the case of verrucous lesions, biopsy is preferred if feasible. 

Treatment should not be delayed while awaiting the culture results if infection is otherwise confirmed by direct microscopy or histopathology. The treatment approach remains similar regardless of the causative species. If the culture results are positive, the causative genus can be identified by the microscopic morphology; however, molecular diagnostic tools are needed for accurate species identification.^12,13

Antifungal Susceptibility Testing—For most dematiaceous fungi, interpreting minimum inhibitory concentrations (MICs) is challenging due to a lack of data from multicenter studies. One report examined sequential isolates of Fonsecaea pedrosoi and demonstrated both high MIC values and clinical resistance to itraconazole in some cases, likely from treatment pressure.¹⁴ Clinical Laboratory Standards Institute–approved epidemiologic cutoff values (ECVs) are established for F pedrosoi for commonly used antifungals including itraconazole (0.5 µg/mL), terbinafine (0.25 µg/mL), and posaconazole (0.5 µg/mL).¹⁵ Clinicians may choose to obtain sequential isolates for any causative fungi in recalcitrant disease to monitor for increases in MIC.

Management—In early-stage disease, excision of the skin nodule may be curative, although concomitant treatment for several months with an antifungal is advised. If antifungals are needed, itraconazole is the most commonly prescribed agent, typically at a dose of 100 to 200 mg twice daily. Terbinafine also has been used first-line at a dose of 250 to 500 mg per day. Voriconazole and posaconazole also may be suitable options for first-line or for refractory disease treatment. Fluconazole does not have good activity against dematiaceous fungi and should be avoided.¹⁶ Topical antifungals will not reach the site of infection in adequate concentrations. Topical corticosteroids can make the disease worse and should be avoided. The duration of therapy usually is several months, but many patients require years of therapy until resolution of lesions. 

Clinicians can consider combination therapy with an antifungal and a topical immunomodulator such as imiquimod (applied topically 3 times per week); this combination can be considered in refractory disease and even upon initial diagnosis, especially in severe disease.^17,18 Nonpharmacologic interventions such as cryotherapy, heat, and light-based therapies have been used, but outcome data are scarce.^19-23

Subcutaneous Phaeohyphomycosis

Subcutaneous phaeohyphomycosis also is caused by dematiaceous fungi that typically affect the skin and subcutaneous tissue. Subcutaneous phaeohyphomycosis is distinguished from chromoblastomycosis by short hyphae and hyphal fragments usually seen microscopically instead of visualizing thick-walled, single, or multicellular clusters of pigmented fungal cells.⁶

Epidemiology—Globally, the burden and distribution of phaeohyphomycosis, including its cutaneous manifestations, are not well understood. Infections are more common in tropical and subtropical areas but can be acquired anywhere. Phaeohyphomycosis is a generic term used to describe infections caused by pigmented hyphal fungi that can manifest on the skin (subcutaneous phaeohyphomycosis) but also can affect deep structures including the brain (systemic phaeohyphomycosis).²⁴

Causative Organisms—Alternaria, Bipolaris, Cladosporium, Curvularia, Exophiala, and Exserohilum species most commonly cause subcutaneous phaeohyphomycosis. Alternaria infections manifesting with skin lesions often are referred to as cutaneous alternariosis.²⁵

Clinical Manifestations—The most common skin manifestation of phaeohyphomycosis is a subcutaneous cyst (cystic phaeohyphomycosis)(Figure 2). Subcutaneous phaeohyphomycosis also may manifest with nodules or plaques (Figure 3). Phaeohyphomycosis appears to occur more commonly in individuals who are immunosuppressed, those in whom T-cell function is affected, in congenital immunodeficiency states (eg, individuals with CARD9 mutations).²⁶

Diagnosis—Culture is the gold standard for confirming phaeohyphomycosis.²⁷ For cystic phaeohyphomycosis, clinicians can consider aspiration of the cyst for direct microscopic examination and culture. Histopathology may be utilized but can have lower sensitivity in showing dematiaceous hyphae and granulomatous inflammation; using the Masson-Fontana stain for melanin can be helpful. Molecular diagnostic tools including metagenomics applied directly to the tissue may be useful but are likely to have lower sensitivity than culture and require specialist diagnostic facilities.

Management—The approaches to managing chromoblastomycosis and subcutaneous phaeohyphomycosis are similar, though the preferred agents often differ. In early-stage disease, excision of the skin nodule may be curative, although concomitant treatment for several months with an antifungal is advised. In localized forms, itraconazole usually is used, but in those cases associated with immunodeficiency states, voriconazole may be necessary. Fluconazole does not have good activity against dematiaceous fungi and should be avoided.¹⁶ Topical antifungals will not reach the site of infection in adequate concentrations. Topical corticosteroids can make the disease worse and should be avoided. The duration of therapy may be substantially longer for chromoblastomycosis (months to years) compared to subcutaneous phaeohyphomycosis (weeks to months), although in immunocompromised individuals treatment may be even more prolonged.

Mycetoma

Mycetoma is caused by one of several different types of fungi (eumycetoma) and bacteria (actinomycetoma) that lead to progressively debilitating yet painless subcutaneous tumorlike lesions. The lesions usually manifest on the arms and legs but can occur anywhere.

Epidemiology—Little is known about the true global burden of mycetoma, but it occurs more frequently in low-income communities in rural areas.²⁸ A retrospective review identified 19,494 cases published from 1876 to 2019, with cases reported in 102 countries.²⁹ The countries with the highest numbers of cases are Sudan and Mexico, where there is more information on the distribution of the disease. Cases often are reported in what is known as the mycetoma belt (between latitudes 15° south and 30° north) but are increasingly identified outside this region.²⁸ Young men aged 20 to 40 years are most commonly affected.

In the United States, mycetoma is uncommon, but clinicians can encounter locally acquired and travel-associated cases; hence, taking a good travel history is essential. One study specifically evaluating eumycetoma found a prevalence of 5.2 per 1,000,000 patients.⁸ Women and those aged 65 years or older had a higher incidence. Incidence was similar across US regions, but a higher incidence was reported in nonrural areas.⁸

Causative Organisms—More than 60 different species of fungi can cause eumycetoma; most cases are caused by Madurella mycetomatis, Trematosphaeria grisea (formerly Madurella grisea); Pseudallescheria boydii species complex, and Falciformispora (formerly Leptosphaeria) senegalensis.³⁰ Actinomycetoma commonly is caused by Nocardia species (Nocardia brasiliensis, Nocardia asteroides, Nocardia otitidiscaviarum, Nocardia transvalensis, Nocardia harenae, and Nocardia takedensis), Streptomyces somaliensis, and Actinomadura species (Actinomadura madurae, Actinomadura pelletieri).³¹

Clinical Manifestations—Mycetoma is a chronic granulomatous disease with a progressive inflammatory reaction (Figures 4 and 5). Over the course of years, mycetoma progresses from small nodules to large, bone-invasive, mutilating lesions. Mycetoma manifests as a triad of painless firm subcutaneous masses, formation of multiple sinuses within the masses, and a purulent or seropurulent discharge containing sandlike visible particles (grains) that can be white, yellow, red, or black.²⁸ Lesions usually are painless in early disease and are slowly progressive. Large lesion size, bone destruction, secondary bacterial infections, and actinomycetoma may lead to higher likelihood of pain.³²

Diagnosis—Other conditions that could manifest with the same triad seen in mycetoma such as botryomycosis should be included in the differential. Other differential diagnoses include foreign body granuloma, filariasis, mycobacterial infection, skeletal tuberculosis, and yaws. 

Proper treatment requires an accurate diagnosis that distinguishes actinomycetoma from eumycetoma.³³ Culturing of grains obtained from deep lesion aspirates enables identification of the causative organism (Figure 6). The color of the grains may provide clues to their etiology: black grains are caused by fungus, red grains by a bacterium (A pelletieri), and pale (yellow or white) grains can be caused by either one.³¹Nocardia mycetoma grains are very small and usually cannot be appreciated with the naked eye. Histopathology of deep biopsy specimens (biopsy needle or surgical biopsy) stained with hematoxylin and eosin can diagnose actinomycetoma and eumycetoma. Punch biopsies often are not helpful, as the inflammatory mass is too deeply located. Deep surgical biopsy is preferred; however, species identification cannot be made without culture. Molecular tests for certain causative organisms of mycetoma have been developed but are not readily available.^34,35 Currently, no serologic tests can diagnose mycetoma reliably. Ultrasonography can be used to diagnose mycetoma and, with appropriate training, distinguish between actinomycetoma and eumycetoma; it also can be combined with needle aspiration for taking grain samples.³⁶

Treatment—Treatment of mycetoma depends on identification of the causal etiology and requires long-term and expensive drug regimens. It is not possible to determine the causative organism clinically. Actinomycetoma generally responds to medical treatment, and surgery rarely is needed. The current first-line treatment is co-trimoxazole (trimethoprim/sulfamethoxazole) in combination with amoxicillin and clavulanate acid or co-trimoxazole and amikacin for refractory disease; linezolid also may be a promising option for refractory disease.³⁷

Eumycetoma is less responsive to medical therapies, and recurrence is common. Current recommended therapy is itraconazole for 9 to 12 months; however, cure rates ranging from 26% to 75% in combination with surgery have been reported, and fungi often can still be cultured from lesions posttreatment.^38,39 Surgical excision often is used following 6 months of treatment with itraconazole to obtain better outcomes. Amputation may be required if the combination of antifungals and surgical excision fails. Fosravuconazole has shown promise in one clinical trial, but it is not approved in most countries, including the United States.³⁹

Final Thoughts

Chromoblastomycosis, subcutaneous phaeohyphomycosis, and mycetoma can cause devastating disease. Patients with these conditions often are unable to carry out daily activities and experience stigma and discrimination. Limited diagnostic and treatment options hamper the ability of clinicians to respond appropriately to suspect and confirmed disease. Effectively examining the skin is the starting point for diagnosing and managing these diseases and can help clinicians to care for patients and prevent severe disease.

Implantation mycoses such as chromoblastomycosis, subcutaneous phaeohyphomycosis, and mycetoma are a diverse group of fungal diseases that occur when a break in the skin allows the entry of the causative fungus. These diseases disproportionately affect individuals in low- and middle-income countries causing substantial disability, decreased quality of life, and severe social stigma.^1-3 Timely diagnosis and appropriate treatment are critical.

Chromoblastomycosis and mycetoma are designated as neglected tropical diseases, but research to improve their management is sparse, even compared to other neglected tropical diseases.^4,5 Since there are no global diagnostic and treatment guidelines to date, we outline steps to diagnose and manage chromoblastomycosis, subcutaneous phaeohyphomycosis, and mycetoma.

Chromoblastomycosis

Chromoblastomycosis is caused by dematiaceous fungi that typically affect the skin and subcutaneous tissue. Chromoblastomycosis is distinguished from subcutaneous phaeohyphomycosis by microscopically visualizing the characteristic thick-walled, single, or multicellular clusters of pigmented fungal cells (also known as medlar bodies, muriform cells, or sclerotic bodies).⁶ In phaeohyphomycosis, short hyphae and pseudohyphae plus some single cells typically are seen.

Epidemiology—Globally, the distribution and burden of chromoblastomycosis are relatively unknown. Infections are more common in tropical and subtropical areas but can be acquired anywhere. A literature review conducted in 2021 identified 7740 cases of chromo­blastomycosis, mostly reported in South America, Africa, Central America and Mexico, and Asia.⁷ Most of the patients were male, and the median age was 52 years. One study found an incidence of 14.7 per 1,000,000 patients in the United States for both chromoblastomycosis and phaeohyphomycotic abscesses (which included both skin and brain abscesses).⁸ Most patients were aged 65 years or older, with a higher incidence in males. Geographically, the incidence was highest in the Northeast followed by the South; patients in rural areas also had higher incidence of disease.⁸

Causative Organisms—Causative species cannot reliably distinguish between chromoblastomycosis and subcutaneous phaeohyphomycosis, as some species overlap. Cladophialophora carrionii, Fonsecaea species, Phialophora verrucosa species complex, and Rhinocladiella aquaspersa most commonly cause chromoblastomycosis.^9,10

Clinical Manifestations—Chromoblastomycosis initially manifests as a solitary erythematous macule at a site of trauma (often not recalled by the patient) that can evolve to a smooth pink papule and may progress to 1 of 5 morphologies: nodular, verrucous, tumorous, cicatricial, or plaque.⁶ Patients may present with more than one morphology, particularly in long-standing or advanced disease. Lesions commonly manifest on the arms and legs in otherwise healthy individuals in environments (eg, rural, agricultural) that have more opportunities for injury and exposure to the causative fungi. Affected individuals often have small black specks on the lesion surface that are visible with the naked eye.⁶

Diagnosis—Common differential diagnoses include cutaneous blastomycosis, fixed sporotrichosis, warty tuberculosis nocardiosis, cutaneous leishmaniasis, human papillomavirus (HPV) infection, podoconiosis, lymphatic filariasis, cutaneous tuberculosis, and psoriasis.⁶ Squamous cell carcinoma is both a differential diagnosis as well as a potential complication of the disease.¹¹

Potassium hydroxide preparation with skin scapings or a biopsy from the lesion has high sensitivity and quick turnaround times. There often is a background histopathologic reaction of pseudoepitheliomatous hyperplasia. Examining samples taken from areas with the visible small black dots on the skin surface can increase the likelihood of detecting fungal elements (Figure 1). Clinicians also may choose to obtain a 6- to 8-mm deep skin biopsy from the lesion and splice it in half, with one sample sent for histopathology and the other for culture (Figure 2). Skin scrapings can be sent for culture instead. In the case of verrucous lesions, biopsy is preferred if feasible. 

Treatment should not be delayed while awaiting the culture results if infection is otherwise confirmed by direct microscopy or histopathology. The treatment approach remains similar regardless of the causative species. If the culture results are positive, the causative genus can be identified by the microscopic morphology; however, molecular diagnostic tools are needed for accurate species identification.^12,13

Antifungal Susceptibility Testing—For most dematiaceous fungi, interpreting minimum inhibitory concentrations (MICs) is challenging due to a lack of data from multicenter studies. One report examined sequential isolates of Fonsecaea pedrosoi and demonstrated both high MIC values and clinical resistance to itraconazole in some cases, likely from treatment pressure.¹⁴ Clinical Laboratory Standards Institute–approved epidemiologic cutoff values (ECVs) are established for F pedrosoi for commonly used antifungals including itraconazole (0.5 µg/mL), terbinafine (0.25 µg/mL), and posaconazole (0.5 µg/mL).¹⁵ Clinicians may choose to obtain sequential isolates for any causative fungi in recalcitrant disease to monitor for increases in MIC.

Management—In early-stage disease, excision of the skin nodule may be curative, although concomitant treatment for several months with an antifungal is advised. If antifungals are needed, itraconazole is the most commonly prescribed agent, typically at a dose of 100 to 200 mg twice daily. Terbinafine also has been used first-line at a dose of 250 to 500 mg per day. Voriconazole and posaconazole also may be suitable options for first-line or for refractory disease treatment. Fluconazole does not have good activity against dematiaceous fungi and should be avoided.¹⁶ Topical antifungals will not reach the site of infection in adequate concentrations. Topical corticosteroids can make the disease worse and should be avoided. The duration of therapy usually is several months, but many patients require years of therapy until resolution of lesions. 

Clinicians can consider combination therapy with an antifungal and a topical immunomodulator such as imiquimod (applied topically 3 times per week); this combination can be considered in refractory disease and even upon initial diagnosis, especially in severe disease.^17,18 Nonpharmacologic interventions such as cryotherapy, heat, and light-based therapies have been used, but outcome data are scarce.^19-23

Subcutaneous Phaeohyphomycosis

Subcutaneous phaeohyphomycosis also is caused by dematiaceous fungi that typically affect the skin and subcutaneous tissue. Subcutaneous phaeohyphomycosis is distinguished from chromoblastomycosis by short hyphae and hyphal fragments usually seen microscopically instead of visualizing thick-walled, single, or multicellular clusters of pigmented fungal cells.⁶

Epidemiology—Globally, the burden and distribution of phaeohyphomycosis, including its cutaneous manifestations, are not well understood. Infections are more common in tropical and subtropical areas but can be acquired anywhere. Phaeohyphomycosis is a generic term used to describe infections caused by pigmented hyphal fungi that can manifest on the skin (subcutaneous phaeohyphomycosis) but also can affect deep structures including the brain (systemic phaeohyphomycosis).²⁴

Causative Organisms—Alternaria, Bipolaris, Cladosporium, Curvularia, Exophiala, and Exserohilum species most commonly cause subcutaneous phaeohyphomycosis. Alternaria infections manifesting with skin lesions often are referred to as cutaneous alternariosis.²⁵

Clinical Manifestations—The most common skin manifestation of phaeohyphomycosis is a subcutaneous cyst (cystic phaeohyphomycosis)(Figure 2). Subcutaneous phaeohyphomycosis also may manifest with nodules or plaques (Figure 3). Phaeohyphomycosis appears to occur more commonly in individuals who are immunosuppressed, those in whom T-cell function is affected, in congenital immunodeficiency states (eg, individuals with CARD9 mutations).²⁶

Diagnosis—Culture is the gold standard for confirming phaeohyphomycosis.²⁷ For cystic phaeohyphomycosis, clinicians can consider aspiration of the cyst for direct microscopic examination and culture. Histopathology may be utilized but can have lower sensitivity in showing dematiaceous hyphae and granulomatous inflammation; using the Masson-Fontana stain for melanin can be helpful. Molecular diagnostic tools including metagenomics applied directly to the tissue may be useful but are likely to have lower sensitivity than culture and require specialist diagnostic facilities.

Management—The approaches to managing chromoblastomycosis and subcutaneous phaeohyphomycosis are similar, though the preferred agents often differ. In early-stage disease, excision of the skin nodule may be curative, although concomitant treatment for several months with an antifungal is advised. In localized forms, itraconazole usually is used, but in those cases associated with immunodeficiency states, voriconazole may be necessary. Fluconazole does not have good activity against dematiaceous fungi and should be avoided.¹⁶ Topical antifungals will not reach the site of infection in adequate concentrations. Topical corticosteroids can make the disease worse and should be avoided. The duration of therapy may be substantially longer for chromoblastomycosis (months to years) compared to subcutaneous phaeohyphomycosis (weeks to months), although in immunocompromised individuals treatment may be even more prolonged.

Mycetoma

Mycetoma is caused by one of several different types of fungi (eumycetoma) and bacteria (actinomycetoma) that lead to progressively debilitating yet painless subcutaneous tumorlike lesions. The lesions usually manifest on the arms and legs but can occur anywhere.

Epidemiology—Little is known about the true global burden of mycetoma, but it occurs more frequently in low-income communities in rural areas.²⁸ A retrospective review identified 19,494 cases published from 1876 to 2019, with cases reported in 102 countries.²⁹ The countries with the highest numbers of cases are Sudan and Mexico, where there is more information on the distribution of the disease. Cases often are reported in what is known as the mycetoma belt (between latitudes 15° south and 30° north) but are increasingly identified outside this region.²⁸ Young men aged 20 to 40 years are most commonly affected.

In the United States, mycetoma is uncommon, but clinicians can encounter locally acquired and travel-associated cases; hence, taking a good travel history is essential. One study specifically evaluating eumycetoma found a prevalence of 5.2 per 1,000,000 patients.⁸ Women and those aged 65 years or older had a higher incidence. Incidence was similar across US regions, but a higher incidence was reported in nonrural areas.⁸

Causative Organisms—More than 60 different species of fungi can cause eumycetoma; most cases are caused by Madurella mycetomatis, Trematosphaeria grisea (formerly Madurella grisea); Pseudallescheria boydii species complex, and Falciformispora (formerly Leptosphaeria) senegalensis.³⁰ Actinomycetoma commonly is caused by Nocardia species (Nocardia brasiliensis, Nocardia asteroides, Nocardia otitidiscaviarum, Nocardia transvalensis, Nocardia harenae, and Nocardia takedensis), Streptomyces somaliensis, and Actinomadura species (Actinomadura madurae, Actinomadura pelletieri).³¹

Clinical Manifestations—Mycetoma is a chronic granulomatous disease with a progressive inflammatory reaction (Figures 4 and 5). Over the course of years, mycetoma progresses from small nodules to large, bone-invasive, mutilating lesions. Mycetoma manifests as a triad of painless firm subcutaneous masses, formation of multiple sinuses within the masses, and a purulent or seropurulent discharge containing sandlike visible particles (grains) that can be white, yellow, red, or black.²⁸ Lesions usually are painless in early disease and are slowly progressive. Large lesion size, bone destruction, secondary bacterial infections, and actinomycetoma may lead to higher likelihood of pain.³²

Diagnosis—Other conditions that could manifest with the same triad seen in mycetoma such as botryomycosis should be included in the differential. Other differential diagnoses include foreign body granuloma, filariasis, mycobacterial infection, skeletal tuberculosis, and yaws. 

Proper treatment requires an accurate diagnosis that distinguishes actinomycetoma from eumycetoma.³³ Culturing of grains obtained from deep lesion aspirates enables identification of the causative organism (Figure 6). The color of the grains may provide clues to their etiology: black grains are caused by fungus, red grains by a bacterium (A pelletieri), and pale (yellow or white) grains can be caused by either one.³¹Nocardia mycetoma grains are very small and usually cannot be appreciated with the naked eye. Histopathology of deep biopsy specimens (biopsy needle or surgical biopsy) stained with hematoxylin and eosin can diagnose actinomycetoma and eumycetoma. Punch biopsies often are not helpful, as the inflammatory mass is too deeply located. Deep surgical biopsy is preferred; however, species identification cannot be made without culture. Molecular tests for certain causative organisms of mycetoma have been developed but are not readily available.^34,35 Currently, no serologic tests can diagnose mycetoma reliably. Ultrasonography can be used to diagnose mycetoma and, with appropriate training, distinguish between actinomycetoma and eumycetoma; it also can be combined with needle aspiration for taking grain samples.³⁶

Treatment—Treatment of mycetoma depends on identification of the causal etiology and requires long-term and expensive drug regimens. It is not possible to determine the causative organism clinically. Actinomycetoma generally responds to medical treatment, and surgery rarely is needed. The current first-line treatment is co-trimoxazole (trimethoprim/sulfamethoxazole) in combination with amoxicillin and clavulanate acid or co-trimoxazole and amikacin for refractory disease; linezolid also may be a promising option for refractory disease.³⁷

Eumycetoma is less responsive to medical therapies, and recurrence is common. Current recommended therapy is itraconazole for 9 to 12 months; however, cure rates ranging from 26% to 75% in combination with surgery have been reported, and fungi often can still be cultured from lesions posttreatment.^38,39 Surgical excision often is used following 6 months of treatment with itraconazole to obtain better outcomes. Amputation may be required if the combination of antifungals and surgical excision fails. Fosravuconazole has shown promise in one clinical trial, but it is not approved in most countries, including the United States.³⁹

Final Thoughts

Chromoblastomycosis, subcutaneous phaeohyphomycosis, and mycetoma can cause devastating disease. Patients with these conditions often are unable to carry out daily activities and experience stigma and discrimination. Limited diagnostic and treatment options hamper the ability of clinicians to respond appropriately to suspect and confirmed disease. Effectively examining the skin is the starting point for diagnosing and managing these diseases and can help clinicians to care for patients and prevent severe disease.

Implantation mycoses such as chromoblastomycosis, subcutaneous phaeohyphomycosis, and mycetoma are a diverse group of fungal diseases that occur when a break in the skin allows the entry of the causative fungus. These diseases disproportionately affect individuals in low- and middle-income countries causing substantial disability, decreased quality of life, and severe social stigma.^1-3 Timely diagnosis and appropriate treatment are critical.

Chromoblastomycosis and mycetoma are designated as neglected tropical diseases, but research to improve their management is sparse, even compared to other neglected tropical diseases.^4,5 Since there are no global diagnostic and treatment guidelines to date, we outline steps to diagnose and manage chromoblastomycosis, subcutaneous phaeohyphomycosis, and mycetoma.

Chromoblastomycosis

Chromoblastomycosis is caused by dematiaceous fungi that typically affect the skin and subcutaneous tissue. Chromoblastomycosis is distinguished from subcutaneous phaeohyphomycosis by microscopically visualizing the characteristic thick-walled, single, or multicellular clusters of pigmented fungal cells (also known as medlar bodies, muriform cells, or sclerotic bodies).⁶ In phaeohyphomycosis, short hyphae and pseudohyphae plus some single cells typically are seen.

Epidemiology—Globally, the distribution and burden of chromoblastomycosis are relatively unknown. Infections are more common in tropical and subtropical areas but can be acquired anywhere. A literature review conducted in 2021 identified 7740 cases of chromo­blastomycosis, mostly reported in South America, Africa, Central America and Mexico, and Asia.⁷ Most of the patients were male, and the median age was 52 years. One study found an incidence of 14.7 per 1,000,000 patients in the United States for both chromoblastomycosis and phaeohyphomycotic abscesses (which included both skin and brain abscesses).⁸ Most patients were aged 65 years or older, with a higher incidence in males. Geographically, the incidence was highest in the Northeast followed by the South; patients in rural areas also had higher incidence of disease.⁸

Causative Organisms—Causative species cannot reliably distinguish between chromoblastomycosis and subcutaneous phaeohyphomycosis, as some species overlap. Cladophialophora carrionii, Fonsecaea species, Phialophora verrucosa species complex, and Rhinocladiella aquaspersa most commonly cause chromoblastomycosis.^9,10

Clinical Manifestations—Chromoblastomycosis initially manifests as a solitary erythematous macule at a site of trauma (often not recalled by the patient) that can evolve to a smooth pink papule and may progress to 1 of 5 morphologies: nodular, verrucous, tumorous, cicatricial, or plaque.⁶ Patients may present with more than one morphology, particularly in long-standing or advanced disease. Lesions commonly manifest on the arms and legs in otherwise healthy individuals in environments (eg, rural, agricultural) that have more opportunities for injury and exposure to the causative fungi. Affected individuals often have small black specks on the lesion surface that are visible with the naked eye.⁶

Diagnosis—Common differential diagnoses include cutaneous blastomycosis, fixed sporotrichosis, warty tuberculosis nocardiosis, cutaneous leishmaniasis, human papillomavirus (HPV) infection, podoconiosis, lymphatic filariasis, cutaneous tuberculosis, and psoriasis.⁶ Squamous cell carcinoma is both a differential diagnosis as well as a potential complication of the disease.¹¹

Potassium hydroxide preparation with skin scapings or a biopsy from the lesion has high sensitivity and quick turnaround times. There often is a background histopathologic reaction of pseudoepitheliomatous hyperplasia. Examining samples taken from areas with the visible small black dots on the skin surface can increase the likelihood of detecting fungal elements (Figure 1). Clinicians also may choose to obtain a 6- to 8-mm deep skin biopsy from the lesion and splice it in half, with one sample sent for histopathology and the other for culture (Figure 2). Skin scrapings can be sent for culture instead. In the case of verrucous lesions, biopsy is preferred if feasible. 

Treatment should not be delayed while awaiting the culture results if infection is otherwise confirmed by direct microscopy or histopathology. The treatment approach remains similar regardless of the causative species. If the culture results are positive, the causative genus can be identified by the microscopic morphology; however, molecular diagnostic tools are needed for accurate species identification.^12,13

Antifungal Susceptibility Testing—For most dematiaceous fungi, interpreting minimum inhibitory concentrations (MICs) is challenging due to a lack of data from multicenter studies. One report examined sequential isolates of Fonsecaea pedrosoi and demonstrated both high MIC values and clinical resistance to itraconazole in some cases, likely from treatment pressure.¹⁴ Clinical Laboratory Standards Institute–approved epidemiologic cutoff values (ECVs) are established for F pedrosoi for commonly used antifungals including itraconazole (0.5 µg/mL), terbinafine (0.25 µg/mL), and posaconazole (0.5 µg/mL).¹⁵ Clinicians may choose to obtain sequential isolates for any causative fungi in recalcitrant disease to monitor for increases in MIC.

Management—In early-stage disease, excision of the skin nodule may be curative, although concomitant treatment for several months with an antifungal is advised. If antifungals are needed, itraconazole is the most commonly prescribed agent, typically at a dose of 100 to 200 mg twice daily. Terbinafine also has been used first-line at a dose of 250 to 500 mg per day. Voriconazole and posaconazole also may be suitable options for first-line or for refractory disease treatment. Fluconazole does not have good activity against dematiaceous fungi and should be avoided.¹⁶ Topical antifungals will not reach the site of infection in adequate concentrations. Topical corticosteroids can make the disease worse and should be avoided. The duration of therapy usually is several months, but many patients require years of therapy until resolution of lesions. 

Clinicians can consider combination therapy with an antifungal and a topical immunomodulator such as imiquimod (applied topically 3 times per week); this combination can be considered in refractory disease and even upon initial diagnosis, especially in severe disease.^17,18 Nonpharmacologic interventions such as cryotherapy, heat, and light-based therapies have been used, but outcome data are scarce.^19-23

Subcutaneous Phaeohyphomycosis

Subcutaneous phaeohyphomycosis also is caused by dematiaceous fungi that typically affect the skin and subcutaneous tissue. Subcutaneous phaeohyphomycosis is distinguished from chromoblastomycosis by short hyphae and hyphal fragments usually seen microscopically instead of visualizing thick-walled, single, or multicellular clusters of pigmented fungal cells.⁶

Epidemiology—Globally, the burden and distribution of phaeohyphomycosis, including its cutaneous manifestations, are not well understood. Infections are more common in tropical and subtropical areas but can be acquired anywhere. Phaeohyphomycosis is a generic term used to describe infections caused by pigmented hyphal fungi that can manifest on the skin (subcutaneous phaeohyphomycosis) but also can affect deep structures including the brain (systemic phaeohyphomycosis).²⁴

Causative Organisms—Alternaria, Bipolaris, Cladosporium, Curvularia, Exophiala, and Exserohilum species most commonly cause subcutaneous phaeohyphomycosis. Alternaria infections manifesting with skin lesions often are referred to as cutaneous alternariosis.²⁵

Clinical Manifestations—The most common skin manifestation of phaeohyphomycosis is a subcutaneous cyst (cystic phaeohyphomycosis)(Figure 2). Subcutaneous phaeohyphomycosis also may manifest with nodules or plaques (Figure 3). Phaeohyphomycosis appears to occur more commonly in individuals who are immunosuppressed, those in whom T-cell function is affected, in congenital immunodeficiency states (eg, individuals with CARD9 mutations).²⁶

Diagnosis—Culture is the gold standard for confirming phaeohyphomycosis.²⁷ For cystic phaeohyphomycosis, clinicians can consider aspiration of the cyst for direct microscopic examination and culture. Histopathology may be utilized but can have lower sensitivity in showing dematiaceous hyphae and granulomatous inflammation; using the Masson-Fontana stain for melanin can be helpful. Molecular diagnostic tools including metagenomics applied directly to the tissue may be useful but are likely to have lower sensitivity than culture and require specialist diagnostic facilities.

Management—The approaches to managing chromoblastomycosis and subcutaneous phaeohyphomycosis are similar, though the preferred agents often differ. In early-stage disease, excision of the skin nodule may be curative, although concomitant treatment for several months with an antifungal is advised. In localized forms, itraconazole usually is used, but in those cases associated with immunodeficiency states, voriconazole may be necessary. Fluconazole does not have good activity against dematiaceous fungi and should be avoided.¹⁶ Topical antifungals will not reach the site of infection in adequate concentrations. Topical corticosteroids can make the disease worse and should be avoided. The duration of therapy may be substantially longer for chromoblastomycosis (months to years) compared to subcutaneous phaeohyphomycosis (weeks to months), although in immunocompromised individuals treatment may be even more prolonged.

Mycetoma

Mycetoma is caused by one of several different types of fungi (eumycetoma) and bacteria (actinomycetoma) that lead to progressively debilitating yet painless subcutaneous tumorlike lesions. The lesions usually manifest on the arms and legs but can occur anywhere.

Epidemiology—Little is known about the true global burden of mycetoma, but it occurs more frequently in low-income communities in rural areas.²⁸ A retrospective review identified 19,494 cases published from 1876 to 2019, with cases reported in 102 countries.²⁹ The countries with the highest numbers of cases are Sudan and Mexico, where there is more information on the distribution of the disease. Cases often are reported in what is known as the mycetoma belt (between latitudes 15° south and 30° north) but are increasingly identified outside this region.²⁸ Young men aged 20 to 40 years are most commonly affected.

In the United States, mycetoma is uncommon, but clinicians can encounter locally acquired and travel-associated cases; hence, taking a good travel history is essential. One study specifically evaluating eumycetoma found a prevalence of 5.2 per 1,000,000 patients.⁸ Women and those aged 65 years or older had a higher incidence. Incidence was similar across US regions, but a higher incidence was reported in nonrural areas.⁸

Causative Organisms—More than 60 different species of fungi can cause eumycetoma; most cases are caused by Madurella mycetomatis, Trematosphaeria grisea (formerly Madurella grisea); Pseudallescheria boydii species complex, and Falciformispora (formerly Leptosphaeria) senegalensis.³⁰ Actinomycetoma commonly is caused by Nocardia species (Nocardia brasiliensis, Nocardia asteroides, Nocardia otitidiscaviarum, Nocardia transvalensis, Nocardia harenae, and Nocardia takedensis), Streptomyces somaliensis, and Actinomadura species (Actinomadura madurae, Actinomadura pelletieri).³¹

Clinical Manifestations—Mycetoma is a chronic granulomatous disease with a progressive inflammatory reaction (Figures 4 and 5). Over the course of years, mycetoma progresses from small nodules to large, bone-invasive, mutilating lesions. Mycetoma manifests as a triad of painless firm subcutaneous masses, formation of multiple sinuses within the masses, and a purulent or seropurulent discharge containing sandlike visible particles (grains) that can be white, yellow, red, or black.²⁸ Lesions usually are painless in early disease and are slowly progressive. Large lesion size, bone destruction, secondary bacterial infections, and actinomycetoma may lead to higher likelihood of pain.³²

Diagnosis—Other conditions that could manifest with the same triad seen in mycetoma such as botryomycosis should be included in the differential. Other differential diagnoses include foreign body granuloma, filariasis, mycobacterial infection, skeletal tuberculosis, and yaws. 

Proper treatment requires an accurate diagnosis that distinguishes actinomycetoma from eumycetoma.³³ Culturing of grains obtained from deep lesion aspirates enables identification of the causative organism (Figure 6). The color of the grains may provide clues to their etiology: black grains are caused by fungus, red grains by a bacterium (A pelletieri), and pale (yellow or white) grains can be caused by either one.³¹Nocardia mycetoma grains are very small and usually cannot be appreciated with the naked eye. Histopathology of deep biopsy specimens (biopsy needle or surgical biopsy) stained with hematoxylin and eosin can diagnose actinomycetoma and eumycetoma. Punch biopsies often are not helpful, as the inflammatory mass is too deeply located. Deep surgical biopsy is preferred; however, species identification cannot be made without culture. Molecular tests for certain causative organisms of mycetoma have been developed but are not readily available.^34,35 Currently, no serologic tests can diagnose mycetoma reliably. Ultrasonography can be used to diagnose mycetoma and, with appropriate training, distinguish between actinomycetoma and eumycetoma; it also can be combined with needle aspiration for taking grain samples.³⁶

Treatment—Treatment of mycetoma depends on identification of the causal etiology and requires long-term and expensive drug regimens. It is not possible to determine the causative organism clinically. Actinomycetoma generally responds to medical treatment, and surgery rarely is needed. The current first-line treatment is co-trimoxazole (trimethoprim/sulfamethoxazole) in combination with amoxicillin and clavulanate acid or co-trimoxazole and amikacin for refractory disease; linezolid also may be a promising option for refractory disease.³⁷

Eumycetoma is less responsive to medical therapies, and recurrence is common. Current recommended therapy is itraconazole for 9 to 12 months; however, cure rates ranging from 26% to 75% in combination with surgery have been reported, and fungi often can still be cultured from lesions posttreatment.^38,39 Surgical excision often is used following 6 months of treatment with itraconazole to obtain better outcomes. Amputation may be required if the combination of antifungals and surgical excision fails. Fosravuconazole has shown promise in one clinical trial, but it is not approved in most countries, including the United States.³⁹

Final Thoughts

Chromoblastomycosis, subcutaneous phaeohyphomycosis, and mycetoma can cause devastating disease. Patients with these conditions often are unable to carry out daily activities and experience stigma and discrimination. Limited diagnostic and treatment options hamper the ability of clinicians to respond appropriately to suspect and confirmed disease. Effectively examining the skin is the starting point for diagnosing and managing these diseases and can help clinicians to care for patients and prevent severe disease.