Dermatophytes are filamentous fungi that can cause skin lesions in humans and animals. The disease is called dermatophytosis. The fungi use keratin as a carbon source and colonise keratinised tissue, such as hair, skin or claws.
Dermatophytes are highly contagious. Infection is direct or indirect. Favourable factors are, for example, immunosuppression, reduced immune response (e.g. high age) or previous damage of the skin (e.g. by ectoparasites). Moreover, spores as form of propagation can remain infectious in the environment for years.
The clinical signs are diverse and dependent on the virulence of the fungal strain, the infection period and the immune status of the host. Typical patchy alopecia may be on the face, ears and front legs. Pruritus may be missing or may range from mild to severe. In case of skin diseases, dermatophytosis must always be considered in the differential diagnosis.
Especially guinea pigs from pet shops are (asymptomatic) carriers of Trichophyton benhamiae in 90% of the cases. Most zoonotically transmitted dermatophytoses in humans are now caused by this pathogen. Before introducing guinea pigs into a household, particularly if there are children or immunocompromised persons, the animals should be examined for dermatophytes.