The Seroprevalence of <i>Chlamydia abortus</i> in Montana Domestic Rangeland Sheep Varies by Breed, Flock and Herding Practices

BACKGROUND: Ovine enzootic abortion (OEA) is a reproductive disease in domestic sheep characterized by late-term abortions occurring 2-3 weeks before term and leading to economic losses for sheep producers. OEA is caused by Chlamydia abortus, an obligate intracellular bacterium, which is primarily spread through intranasal transmission from infected aborted fetal contents and vaginal discharge. This method of transmission leads to rapid transmission within and between flocks each lambing season, with infected ewes aborting in the subsequent lambing season. OBJECTIVES: While there are surveys performed in other countries to determine the seroprevalence of C. abortus in domestic sheep populations, very few have been performed in the United States. We performed the first seroprevalence survey on C. abortus in Montana domestic rangeland sheep. METHODS: We collected serum samples from 781 domestic sheep from 17 flocks in Montana, which were used to determine the seroprevalence through indirect ELISA. RESULTS AND CONCLUSIONS: In total, 95 (12.6%) of the sheep tested had C. abortus anti-major outer membrane protein (anti-MOMP) antibodies. Seropositivity varied significantly by breed, flock, whether the animals were herded and whether the tested ewe had already lambed that season prior to sampling. These data provide insight into the impacts of OEA in Montana domestic rangeland sheep and will better inform local producers about whether additional treatments and preventative measures should be put in place.