Diagnostic performance of molecular and conventional methods for identification of dermatophyte species from clinically infected Arabian horses in Egypt

Background: Rapid and accurate identification of dermatophytes is crucial for the effective control of disease outbreaks. Current methods based on culture and microscopic characteristics may require weeks before positive identification is made.
Objectives: To (i) identify the most common pathogenic dermatophytes affecting Arabian horses; (ii) compare the performance of direct microscopy (DM), culture, PCR using hair samples (PCR_hair) and PCR based on culture isolates (PCR_culture) for the diagnosis of dermatophytosis.
Methods: Samples of hair and crusts of skin lesions from Arabian horses were collected on a monthly basis by scraping skin of affected horses. Samples were divided into three portions: the first portion was used for microscopic examination, the second for culture and the third portion for PCR amplification of intergenic spacer (ITS) regions.
Results: Out of 200 horses examined, 70 (35%) showed cutaneous lesions characteristic of dermatophytosis. DM revealed that 70.4% were positive for fungal elements and 85.7% were culture positive. The identified species were Microsporum canis, Trichophyton verrucosum, T. mentagrophytes var. mentagrophytes and M. equinum. Among 25 selected samples, 64, 92, 91.3 and 52% were positive for dermatophytes, as determined by DM, culture, PCR_culture and PCR_hair, respectively.
Conclusions: The dermatophytes M. canis, T. verrucosum, T. mentagrophytes var. mentagrophytes and M. equinum were the most common cause of dermatophytosis in Arabian horses. Although the number of samples was small, the ITS-based PCR may be a useful diagnostic tool when combined with culture.