Pathology and diagnostic criteria of Clostridium difficile enteric infection in horses.

Clostridium difficile is commonly associated with diarrhea and colitis in humans and other mammals, including horses. To this date, the epidemiologic, microbiologic, clinical, and diagnostic aspects of C. difficile-associated disease (CDAD) in horses have been thoroughly described. However, reports describing the enteric pathology of this disease in horses are limited. This study presents a comprehensive description of the pathologic characteristics of CDAD in 21 horses and discusses the criteria for the diagnosis of the disease. Case selection was based on C. difficile A/B toxins detection (enzyme-linked immunosorbent assay) in intestinal content samples accompanied by compatible gross and microscopic enteric lesions. Grossly, multifocal, segmental, or diffuse hemorrhage; congestion; and/or marked gelatinous edema of the intestinal wall with abundant bloody or green watery contents were observed. Histologically, the most common lesion was severe necrotizing or necrohemorrhagic enteritis, colitis, or typhlocolitis, with mucosal and/or submucosal thrombosis and marked submucosal edema. The pathology of CDAD in horses is similar to that caused by other equine enteric pathogens; therefore, a definitive diagnosis requires detection of C. difficile A/B toxins in the intestinal contents.