Identifying Signs of Tinea Pedis: A Key to Understanding Clinical Variables

most common fungi.¹¹ Neoscytalidium spp are common fruit tree pathogen in the tropics, and geophilic transmission to human hosts in tropical and subtropical areas is thought to occur via contact with contaminated plants and soil.^10,12,13 Neoscytalidium spp are endemic to parts of Africa, Asia, the Caribbean, Central and South America, and several states in the U.S. Infection with Neoscytalidium spp results in chronic, treatment resistant tinea pedis, tinea manuum, and onychomycosis infection that is clinically indistinguishable from cases associated with dermatophytes.

While tinea pedis is predominantly a disease that affects adults, tinea pedis can occur in children and is associated with a distinct mycologic profile in children. T. tonsurans is implicated in pediatric tinea pedis cases, especially when patients have concurrent tinea capitis caused by this organism. Children can also be infected with the typical dermatophytes that affect adults via household contact with fomites.

Infection starts when the dermatophyte arthroconidia adheres to the superficial layer of the host’s epithelium, after which hyphae develop and penetrate deeper into the epithelium. T. rubrum can survive outside of the human host as an arthroconidia for only a short period of time, whereas E. floccosum can survive for years on fomites.¹⁴ Because sebaceous glands are absent on acral skin, and their secretions are thought to have antimicrobial properties, palms and soles are the primary sites of infection. Infection is limited to the stratum corneum, which is a keratin-rich structure. Keratin is a hard, densely packed protein. Dermatophyte growth is fueled by the ability of these organisms to degrade and use keratin via specialized enzymes: keratinase, cysteine dioxygenase, and a sulfite efflux pump.¹⁵ These enzymes represent a major virulence feature of dermatophytes.

Tinea pedis is a relatively new infection in the Western world, transported through global human migration in the end of the nineteenth century. T. rubrum, which is the most common cause of tinea pedis, is endemic to Southeast Asia, Western Africa, and parts of Australia.¹⁴ Interestingly, tinea pedis was not endemic in these areas at the time of its spread, probably due to the fact that people in these areas did not routinely wear occlusive footwear, which is a major risk factor for tinea pedis.

European colonization of regions with endemic T. rubrum is believed to be how tinea pedis was first introduced to Europe. Subsequently, T. rubrum infection spread throughout Europe. The first case of T. rubrum tinea pedis in the U.S. was documented in a World War 1 veteran in Birmingham Alabama.¹⁶ Once a rare disease, tinea pedis is now the most common dermatophyte infection.