Dermatophytes are the most common cause for superficial mycoses in hair, nail and skin.
Dermatophytes can be divided into three groups: anthropophilic, zoophilic, and geophilic. Anthropophilic dermatophytes are passed from human to human and are the most common in the community. Zoophilic or animal acquired infections are usually sporadic. Infections with geophilic dermatophytes are most often acquired following a close association with soil or from an animal itself infected by soil contact. Infection is diagnosed by observing the presence of fungal hyphae in skin, hair or nail specimens. However, it is important to culture the material to determine the infecting genus and species. This is done to ensure selection of the most appropriate therapy and in order to trace its likely epidemiology.
Dermatophyte (otherwise known as ringworm) infections are usually referred to as tinea followed by the Latin name of the body area involved. The most common dermatophyte infections are tinea pedis in adults (athlete’s foot) which may also include tinea unguium (nail infection), and tinea capitis (scalp ringworm) in children.
Infection by dermatophytes is cutaneous and generally restricted to the non-living cornified layers in patients who are immunocompetent. This is because the dermatophyte group of fungi are generally unable to penetrate tissues which are not fully keratinised (i.e. deeper tissues and organs). However, reactions to such infections can range from mild to severe depending upon the host’s immune response, the virulence of the infecting species, the site of infection and environmental factors.
The dermatophyte group of fungi are classified in three genera: Epidermophyton species, Microsporum species and Trichophyton species.
Non-dermatophytes;
There are few non-dermatophyte moulds that can infect otherwise healthy skin and these include Scytalidium dimidiatum, Scytalidium hyalinum (a white variant of S. dimidiatum), Phaeoannellomyces werneckii and Piedraia hortae. Non-dermatophyte moulds, including those above, can infect nails damaged by physical trauma, disease or pre-existing infection with a dermatophyte. There are many non-dermatophyte moulds that have been implicated in nail infection, therefore isolation of a mould from a nail specimen should only be reported if certain strict criteria are met because contamination of nail samples with mould spores is common. A non-dermatophyte mould accounts for the diagnosis in less than 5% of infected nails.
