Epidemiology and ecology of onychomycosis.

The epidemiology and ecology of onychomycosis are complex and little understood. Most is known about tinea unguium, dermatophytic nail infection, and its causative agents. This is often categorised according to the precise locus on the nail of the infection. The principal infectious propagules are thought to be the arthroconidia or chlamydospores which form within the solid substratum of invaded nail tissue. The process of infecting new hosts appears to be facilitated by abrasion, moistening and scratching. The role of the non-dermatophyte yeast Candida as an agent of onychomycosis per se may have been overestimated. The range of interactions between dermatophytes and non-dermatophytes in nails is complex and poorly understood. There may be at least six distinct ecological categories of non-dermatophyte isolations from nails. It would be of clinical interest to know which species found in mixed infections were never able to advance beyond 'secondary colonisation', as they would not require specific treatment.