Inability of two topical treatments to influence the course of experimentally induced dermatophytosis in cats.

An experimental model of dermatophytosis was used to compare the efficacy of 2 topical antifungal treatments against Microsporum canis infection in cats. Infection was established in 24 cats by topical application of 10(5) M canis macroconidia to the skin of the lateral part of the abdomen under an occlusive bandage. Three groups of 6 cats each then were treated twice weekly for 18 weeks with chlorhexidine shampoo and dip, detergent shampoo vehicle only, or glyceryl monolaurate shampoo. Six cats were left untreated as controls. The experimentally induced infections strongly resembled naturally developing infections of moderate to severe nature. Signs of infection peaked in severity at 5 weeks after inoculation, then gradually resolved over 7 to 16 additional weeks. Dermatophytes were consistently isolated on culture for at least 8 weeks of treatment. Mycologic cure (defined as lack of dermatophyte isolation on 3 successive weekly cultures) was attained in 8 cats at the end of 18 weeks of treatment. Infections appeared to resolve at equivalent rates in all groups of cats, including controls. Consistent or meaningful significant differences in variables such as lesion size, clinical sign score, or total infection score were not found between treated and control groups. Our study revealed that this topical treatment regimen with chlorhexidine or glyceryl monolaurate is ineffective against M canis infection in cats.