How to diagnose skin fungus in dogs and cats?

Abstract

BACKGROUND: Potential contagion and zoonotic risk make rapid diagnosis of dermatophytosis important amongst companion animals. HYPOTHESIS/OBJECTIVES: To compare the adhesive tape impression (ATI), trichogram, Wood's lamp (WL) examination and fungal culture for diagnosis of dermatophytosis, and the ATI and trichogram for ease of use. ANIMALS: Five dogs and 15 cats with consistent lesions, history and at least two positive dermatophyte test results. MATERIALS AND METHODS: After WL examination, one representative lesion per patient was sampled for ATI, trichogram and fungal culture. Microscopic detection of fungal elements on ATI and trichogram were objectively and subjectively compared. The ability of all tests to correctly detect dermatophytosis, and the ability of ATI and trichogram to detect fungal elements in >20 high-powered fields (HPF) were compared using Fisher's exact tests. RESULTS: ATI, trichogram, fungal culture and WL were positive in 100% (20 of 20), 90% (18 of 20), 95% (19 of 20) and 65% (13 of 20) of patients, respectively, with a significant difference between WL and ATI (p = 0.0499). Fungal culture revealed Microsporum. canis (n = 16), Nannizzia gypsea (n = 1), Trichophyton mentagrophytes (n = 1) and T. rubrum (n = 1). Fungal elements were detected in >20 HPF more frequently with ATI (18 of 20) than trichogram (11 of 20) (p = 0.017), and detection required careful scanning to distinguish from background debris more often with trichogram. Fungal elements were located with neutrophil clusters and keratinocyte rafts in addition to abnormal hair fragments more frequently on ATI. CONCLUSIONS AND CLINICAL RELEVANCE: ATI had the highest ability to correctly diagnose dermatophytosis, and increased ease of detecting fungal elements compared to trichogram.