An epizootic outbreak of ringworm in a guinea-pig colony caused by Trichophyton mentagrophytes.

The disease was characterized by loss of hair, initially occurring at the tip of the nose and spreading throughout the body. Lesions appeared as circular, scaley alopecia with occasional scarring. Although spread of the infection in the colony was random, the most severe infection occurred in an inbred line with light coat colour. The unusually high temperature and humidity, and the open type of outdoor management, appear to have contributed to the high incidence and severity of infection. Electron microscopic observation indicated that the organism multiplied in the keratin layer of the skin. The hyphae as well as chlamydospores were readily demonstrable by electron microscopy.