Microsporum canis Infection in a Cat Breeder Family and an Investigation of Their Breeding Cats

Two pediatric cases of Microsporum canis infection that occurred in a cat breeder family and the isolation of dermatophytes from their 166 breeding cats are reported. The patients were a 16-month-old girl and her 26-month-old sister who both had tinea capitis. Their family consisted of six members: the sisters, their great-grandmother, grandmother, grandfather, and mother. Except for the two sisters, the family had no history of skin lesions. The grandmother had been a cat breeder for 20 years. We tested the cats using the hairbrush technique, and 56 of the 158 cats (35%) tested were positive for M. canis. In particular, cultures performed from 4 cats developed M. canis colonies that grew densely from all spikes on the hairbrush. On the basis of observations of the cultures, cutaneous infection was suspected when five or more colonies grew on a single plate medium (9 cats), whereas growth of fewer colonies was thought to suggest saprophytic colonization on cat hair. M. canis is known to be highly transmittable among cats, but 65% of the cats investigated remained negative. It was thus considered possible to prevent further spread of infection by practicing basic infection control and improving the environment.