Parasitic relationship between Microsporum canis and the cat.

Cats are often cited as reservoirs of M. canis but it is questionable whether M. canis is part of the resident flora of the cat's skin and hair or only a transient organism. Studies indicate that M. canis is most often isolated from cats at risk of infection or exposure from other infected cats or from a contaminated environment. Many more cats are culture-positive for M. canis than have dermatophytosis. Culture isolation alone is not an indication of dermatophytosis; the diagnosis of dermatophytosis requires microscopic evidence of infection as well as culture evidence of the presence of the dermatophyte. The cat's hair coat adopts the culture image of its surroundings. Diverse factors may influence the frequency of isolation of M. canis. Nevertheless, isolation of M. canis implies either active disease or fomite carriage and warrants aggressive investigation of the clinical situation.