Naturally-occurring Tyzzer's disease (Bacillus piliformis infection) in horse foals
Harrington, D.D.
Veterinary Record 96(3): 59-63
1975
ISSN/ISBN: 0042-4900 PMID: 1119056 Document Number: 91087
Spontaneous Tyzzer's disease is described in two quarter horse foals which died suddenly with no clinical history of apparent illness. Significant gross findings included icterus, focal pale tan areas in the liver and catarrhal enterocolitis. Focal dark red lesions were present in the small intestine of one foal, and the mesenteric lymph nodes of another were enlarged and hyperaemic. Histologically, the liver showed multiple discrete and confluent foci of necrosis, fatty change, sinusoid congestion and haemorrhage. Bundles of intracytoplasmic bacilli were demonstrated in hepatocytes at the margin of liver lesions using special stains. Infiltration of the portal triads with inflammatory cells and biliary duct hyperplasia and degeneration were also observed. Lesions in the intestine were characterised by mucosal necrosis with inflammatory cell infiltration, increased mucus production, submucosal lymphois hyperplasia and, in one foal, submucosal haemorrhage. Necrosis of lymph follicles, congestion and haemorrhage were also present in the spleen and mesenteric lymph nodes.