The changing epidemiology and emerging patterns of dermatophyte species

The anthropophilic agents of tinea capitis are being eradicated from their historic areas in developed and developing nations. The one exception is T. tonsurans in the United States and Canada. In these nations, the infections are increasing among black children, probably because of hair style and hygiene habits. Elsewhere in the world, M. canis has become or is becoming the dominant agent of tinea capitis. Tinea corporis reflects either the dominant agent of tinea capitis or the sphere of T. rubrum. Trichophyton rubrum is the most common agent worldwide of crural and pedal disease and often tinea corporis. The other anthropophilic species, T. mentagrophytes var. interdigitale and E. floccosum, are also firmly established, but as a distant second and third. These five species account for most ringworm worldwide. Other species are of lowlevel infection, are rare, are locally endemic, or--in the case of some anthropophiles--are dying out. The only evidence of active evolution among the dermatophytes is seen in M. canis and T. mentagrophytes. In both, host-specific strains have emerged and will probably separate as species. This probably has happened already in the case of the variety interdigitale of T. mentagrophytes.