Seroprevalence and risk factors of Brucella ovis in domestic sheep in Wyoming, USA

Authors: ELDERBROOK, MOLLY - University Of Wyoming; SCHUMAKER, BRANT - University Of Wyoming; CORNISH, TODD - University Of Wyoming; Peck, Dannele; SONDGEROTH, KERRY - University Of Wyoming

Submitted to: BMC Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2019
Publication Date: 7/16/2019
Citation: Elderbrook, M., Schumaker, B., Cornish, T., Peck, D.E., Sondgeroth, K. 2019. Seroprevalence and risk factors of Brucella ovis in domestic sheep in Wyoming, USA. BMC Veterinary Research. 15:246. https://doi.org/10.1186/s12917-019-1995-5.
DOI: https://doi.org/10.1186/s12917-019-1995-5

Interpretive Summary: Brucella ovis causes an infectious and sexually transmitted disease of domestic sheep. In rams, the disease causes genital lesions and inflammation of the epididymis (the coiled tube at the back of the testicle, which stores and carries sperm). In ewes, symptoms include infection and inflammation of the placenta in pregnant ewes, which may lead in rare cases to abortion or death of newborn lambs. This study collected and analyzed blood samples from domestic sheep across Wyoming, USA, to: 1) estimate the percent of animals and flocks with B. ovis antibodies in their blood (indicating they have been exposed to the disease in the past), and 2) describe risk factors associated with individual sheep or individual flocks having B. ovis antibodies. Blood samples were collected from sheep on eighteen, non-random, owner-selected operations and from operations that submitted samples to the Wyoming State Veterinary Laboratory (WSVL) for B. ovis antibody testing. An estimated 0.53% (95% CI: 0.21 – 1.01%; 22/2,423) of individual sheep tested positive for B. ovis antibodies. An estimated 22.47% (95% CI: 14.56 – 33.01%; 18/82) of flocks tested positive for B. ovis antibodies. Statistical analyses found that age and breed are risk factors associated with individual sheep testing positive for B. ovis antibodies. Risk factors associated with flocks testing positive for B. ovis antibodies included flock size and region of the state. Results suggest that a small proportion of individual sheep have been exposed to B. ovis, but many flocks contain at least one exposed animal. Results also indicate that each region of Wyoming contained at least one exposed animal. Disease spread could potentially be reduced by testing the disease status of individual sheep before deciding whether to introduce them into a flock.

Technical Abstract: Brucella ovis causes a sexually transmitted, infectious disease of domestic sheep characterized by genital lesions and epididymitis in rams, placentitis and rare abortions in ewes, and neonatal mortality in lambs. A prospective cross-sectional study was designed to 1) estimate animal and flock seroprevalence of B. ovis antibodies in sheep across Wyoming, USA, and 2) describe epidemiologic risk factors associated with seropositive sheep and flocks. Blood samples used to estimate seroprevalence were collected from sheep on eighteen, non-random, owner-selected operations and from operations that submitted sera to the Diagnostic Serology Lab at the Wyoming State Veterinary Laboratory (WSVL) for B. ovis antibody testing. Data regarding animals and flocks was collected during the time of sample collection and via questionnaire post collection. Estimated animal and flock seroprevalence was 0.53% (95% CI: 0.21 – 1.01%; 22/2,423) and 22.47% (95% CI: 14.56 – 33.01%; 18/82), respectively, and statistical analyses found the following risk factors to be associated with seropositive sheep and flocks: age, breed, region, and flock size. The results from this study suggest few sheep have been exposed to B. ovis, but many flocks contain at least one seropositive animal. The characteristics that vary between sheep and operations likely contribute to the introduction and persistence of B. ovis infection in the flock.