Abstract
Yersiniosis, caused by Yersinia pseudotuberculosis, was diagnosed in 25 deer submitted to the Veterinary Diagnostic Laboratories of the Ontario Ministry of Agriculture and Food from 8 farms in Ontario, Canada, over the 4-year period of January 1990 to December 1993. The organism was cultured, usually in large numbers, from the intestines and, less frequently, mesenteric lymph nodes and/or the spleen of 13 red deer (Cervus elaphus), 6 elk (C. e. canadiensis), 4 fallow deer (Dama dama), and 2 red deer-elk hybrids. Outbreaks occurred almost exclusively in the fall (September-November) and affected recently weaned calves, 4–6 months old. Sudden death usually signalled the start of an outbreak. Outbreaks often occurred during inclement weather; usually a sudden cold snap, with or without rain, after a period of relatively mild fall weather. At necropsy, the animals were usually emaciated and dehydrated, and the perineum and tail were sometimes fecally stained. The small and large intestines were congested and filled with serofibrinous and/or seroanguineous fluid. Mesenteric lymph nodes were edematous and congested. Microabscesses surrounding large bacterial colonies in the lamina propria in the jejunum and ileum were typical lesions seen histologically. Peyer's patches were depleted and sometimes contained microabscesses. Purulent lymphadenitis associated with bacterial colonies was the prominent histologic lesion in mesenteric lymph nodes.