Johne's disease (paratuberculosis) was diagnosed in a 2-yr-old, male, free-ranging white-tailed deer (Odocoileus virginianus) from Fauquier County, Virginia, USA, based on histopathology and culture for Mycobacterium avium subspecies paratuberculosis. Clinical and pathologic findings included emaciation; loss of body fat; chronic diarrhea; severe, chronic, diffuse granulomatous colitis with intrahistiocytic acid-fast bacilli; moderate, chronic granulomatous lymphadenitis with intrahistiocytic acid-fast bacilli; as well as moderate chronic, multifocal, lymphoplasmacytic hepatitis. These findings are consistent with previous reports of Johne's disease in cervids. Subsequent targeted surveillance of 10 emaciated deer with diarrhea, as well as sampling of 72 asymptomatic deer for M. avium subsp. paratuberculosis using culture of multiple tissue types, as well as serology using an enzyme-linked immunosorbent assay (ELISA) optimized for cervid antibody detection, did not reveal any additional cases of infection in this geographic region. To date, this appears to be an isolated case of Johne's disease in a free-ranging white-tailed deer, and infection with the causative agent for Johne's disease appears to be an infrequent occurrence in deer from this region. The origin of infection was most likely domestic ruminants. This is the first report of clinical Johne's disease in a free-ranging white-tailed deer outside of the Florida Keys, USA. Stressors, such as high deer population density and low selenium levels, may have contributed to the development of clinical disease in this case and warrant further investigation.

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