Natural pathogens of laboratory animals and their effects on research

The natural fungal pathogens of laboratory animals such as rabbits and guinea pigs are mainly dermatophyte species, most commonly Trichophyton mentagrophytes and also, less frequently Microsporum gypseum and M. canis. However, the incidences of infection and clinical disease are low in well-managed animal facilities. Young or immunocompromised rabbits are thought to be most susceptible. Dermatophytes infect the epidermis and adnexal structures, including hair follicles and shafts, usually on or around the head, and cause pruritis, patchy alopecia, erythema and crusting. Histopathological changes in the underlying skin occur and these changes could confound histological studies involving the skin. Yeast infections usually due to Candida spp. have been reported occasionally in laboratory animals. In this paper, the role of rodents in the evaluation of topical antifungal agents, dermatophytosis and two species of Candida, which are natural pathogens of laboratory animals, are discussed in relation to their effects on research. Pneumocystis carinii, an inhabitant of the respiratory tract of laboratory mice and rats, is a pathogen only under conditions of induced or inherent immunodeficiency. Infected mice and rats are likely to develop severe pneumocystosis following immunosuppression and will be rendered unsuitable for most experimental purposes.