Histiocytic Ulcerative Colitis in an American Staffordshire Terrier.

A 9-year-old female American Staffordshire terrier was presented to a veterinary hospital with diarrhoea, severe prostration, hypothermia, dehydration and anaemia. The dog died 6 days after the first consultation. At necropsy examination the serosa of the large intestine showed a granular appearance and the mucosa was thickened, ulcerated and red, with prominent folding. Histological examination revealed marked inflammatory infiltration of macrophages into the mucosa and submucosa of the large intestine. These cells stained positively by the periodic acid-Schiff reaction. Immunohistochemistry showed marked presence of intracytoplasmic Escherichia coli in the macrophages. Bacteriological examination of intestinal sections yielded E. coli growth and the isolate displayed atypical characteristics when compared with strains associated with previously published cases of histiocytic ulcerative colitis (HUC). The molecular characterization showed that the isolate harboured none of the genes associated with enterotoxigenic E. coli strains and harboured only a limited number of genes associated with extra-intestinal pathotypes. Adherent and invasive E. coli are unlikely to have been involved in the pathogenesis of HUC in the present case. HUC is a rare disease with a predisposition for boxer dogs; however, sporadic occurrence in other breeds may occur. This is the first reported case of HUC in an American Staffordshire terrier.