RT-qPCR for the diagnosis of dermatophilosis in horses.

Abstract

BACKGROUND: Dermatophilus congolensis causes a crusting dermatitis that affects horses. Diagnosis requires the identification of the organism with cytological evaluation of crust samples. This method can lack sensitivity in chronic cases. HYPOTHESIS/OBJECTIVES: To develop a probe-based real time quantitative polymerase chain reaction (RT-qPCR) test to assist with the diagnosis of dermatophilosis in horses. ANIMALS: Twenty six privately owned horses and seven horses from a research colony were used. METHODS: Crust samples, collected from 14 horses with suspected dermatophilosis and 12 horses with crusting skin disease not characteristic of dermatophilosis, were evaluated by cytological evaluation and RT-qPCR; the latter was also performed on hair samples collected from seven healthy horses. RESULTS: Cytological evaluation revealed organisms consistent with Dermatophilus congolensis from nine horses with suspected dermatophilosis, with only a few organisms seen from five samples. Cytological evaluation of all other crusts was negative for Dermatophilus. Other bacterial organisms were detected on cytological evaluation from 15 samples. RT-qPCR for Dermatophilus was positive from 11 crusts, whereas all other samples were negative. Two samples were cytologically negative but RT-qPCR positive for Dermatophilus. No samples were cytologically positive but RT-qPCR negative for Dermatophilus. CONCLUSION: Results of this study show that RT-qPCR may be a more sensitive and easier method than cytological evaluation for the diagnosis of dermatophilosis in horses.