Molecular diagnosis of dermatophyte infections in dogs

Dermatophytes are fungi that can be contagious and cause skin infections of mammals, including humans. The etiological diagnosis of dermatophytic infection is usually performed using a combination of in vitro-culture and microscopic methods. However, in vitro culture requires long incubation time and it is frequently complicated by the presence of opportunistic fungi (e.g., species of Alternaria, Cladosporium, Mucor, Penicillium, Scopularopsis, Rhizopus and Chrysosporium), which can be present on the animal hair coat. Recent studies have demonstrated that first and second internal transcribed spacers (ITS-1 and ITS-2, respectively) and the entire internal transcribed spacer region (ITS+) of nuclear ribosomal DNA as well as the chitin synthase 1 (chs1) gene are promising markers for selected species of dermatophytes. To date, the few studies attempting to specifically characterize dermatophytes from hair samples from dogs using PCR-based methodology relied on sequence-based analysis of selected genetic markers. The aim of the present study was to establish and evaluate a PCR-based approach employing genetic markers in nuclear DNA for the specific detection of dermatophytes on hair samples from dogs. Using 199 hair samples, we directly compared the test results of our one-step and nested-PCR assays with those based on conventional in vitro culture techniques (using the latter as the reference method). The one step-PCR showed a low sensibility (62.2%) and very high specificity (96.6%) for the testing of samples from dogs and allowed the differentiation of Microsporum canis from other dermatophytes. The nested-PCR achieved higher sensibility (89.2%) and specificity (95.7%) and allowed the differentiation of M. canis from Trichophyton interdigitale (zoophilic) and geophilic dermatophytes (i.e. Microsporum gypseum or Trichophyton terrestre). The results provide practical tools for diagnostic applications to support clinicians in initiating prompt and targeted chemotherapy of canine dermatophytoses