How common is Dermatophilus congolensis in horses with pastern

Abstract

BACKGROUND: Dermatophilus congolensis is a facultative anaerobic actinomycete that causes papular to exudative dermatitis with crusting in horses. This organism is frequently implicated as a cause of pastern dermatitis, but few data are available validating the organism's association with this disease. HYPOTHESIS/OBJECTIVES: The aim of this study was to evaluate if D. congolensis is associated with pastern dermatitis in horses utilizing RT-qPCR. ANIMALS: Fifteen client-owned horses diagnosed with pastern dermatitis and eight client-owned unaffected control horses were utilized for this study. METHODS: A cross-sectional study was performed. History and physical examination findings were recorded, and samples were collected and tested for D. congolensis utilizing cytological evaluation and RT-qPCR. Dermatophyte culture and superficial skin scrapings were also performed. RESULTS: Ten of 15 horses with pastern dermatitis had feathered pasterns. Dermatophilus congolensis was identified by RT-qPCR from one nonfeathered horse but none with feathered pasterns. Cytological evaluation identified bacteria in all horses but failed to identify organisms resembling D. congolensis in any horse. Four of 15 horses, all feathered, were positive for Chorioptes mites. Fungal culture was negative for dermatophytes in all horses. All test results were negative for the eight control horses. CONCLUSIONS AND CLINICAL IMPORTANCE: Dermatophilus congolensis was uncommonly associated with pastern dermatitis in horses in this population. However, chorioptic mange was commonly associated with pastern dermatitis in feathered horses and represented an important differential diagnosis for this clinical presentation.