Bighorn sheep may be at risk for TSEs

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A U.S. Geological Survey study indicates bighorn sheep may be susceptible to transmissible spongiform encephalopathies found in domestic and wild animals that share the sheep’s western U.S. habitat.

Bighorn sheep
(Photo by J. Peaco/U.S. National Park Service)

Results of in vitro prion protein conversion assays conducted by the Geological Survey’s National Wildlife Health Center suggest that bighorn sheep are likely vulnerable to scrapie and chronic wasting disease. The USGS study was published Aug. 9 in the journal BMC Veterinary Research.

“Bighorn sheep are economically and culturally important to the western U.S.,” said Christopher Johnson, PhD, a USGS scientist and senior study author. “Understanding future risks to the health of bighorn sheep is key to proper management of the species.”

Bighorn sheep populations in western North America are in decline as a result of habitat loss and, more recently, epidemics of fatal pneumonia thought to be transmitted by domestic sheep. It now appears prion diseases are another possible threat to this species.

Results of USGS laboratory testing revealed evidence that bighorn sheep could be vulnerable to CWD from either white-tailed deer or elk, and to scrapie from a domestic sheep. None of a small number of bighorn sheep tested in the study had evidence of infection, however.

“Our results do not mean that bighorns get, or will eventually get, prion diseases,” Dr. Johnson explained. “However, wildlife species like bighorn sheep are increasingly exposed to areas where CWD occurs as the disease expands to new geographical areas and increases in prevalence.”

The laboratory test results could be useful to wildlife managers because bighorn sheep habitats overlap with farms and ranches with scrapie-infected sheep and regions where CWD is common in deer, elk, and moose.

Further investigation of TSE transmissibility to bighorn sheep, including animal studies, is warranted, the study concludes, adding that the lack of reported TSEs in bighorn sheep may be attributable to other host factors or a lack of surveillance in this particular species.

“In vitro prion protein conversion suggests risk of bighorn sheep (Ovis canadensis) to transmissible spongiform encephalopathies,” is posted on the BMC Veterinary Research journal website.