Several California bighorn sheep in Oregon's John Day River have tested positive for Mycoplasma ovipneumoniae (M.ovi), a respiratory pathogen associated with pneumonia outbreaks in wild sheep. The detection marks the first known cases in the state's largest bighorn sheep herd, which has an estimated 1,000 individuals, the Oregon Department of Fish and Wildlife announced.
ODFW staff are conducting necropsies on dead animals, arranging testing at the Washington Animal Disease Diagnostic Laboratory, and surveying the canyon for additional sick sheep to determine the extent of the outbreak. There is currently no known vaccine or treatment for M.ovi.
Wildlife managers typically manage the disease by reducing or eliminating contact between bighorns and potential vectors such as domestic goats, sheep, and exotic aoudad (also known as barbary sheep).
"Many bighorn populations in the state have felt the impacts of pneumonia over the years. But the John Day bighorn herd has stood out as a stronghold for its size and health both in Oregon and across the West as until now we had not detected M.ovi in this herd. So, this is disappointing news," said Trent Gianella, an ODFW assistant wildlife biologist.
M.ovi outbreaks have previously devastated bighorn populations in Hells Canyon and the Owyhees. Different strains of the bacterium produce different outcomes — some infected herds experience short-term impacts while others face chronic disease lasting decades. Wildlife managers across the western United States have employed various strategies, including removing infected individuals or reducing herd densities to slow disease spread.
A growing population of aoudad in the John Day region presents an additional management challenge. Aoudad, which escaped from a private game ranch in central Oregon in the late 1970s, are known to be potential disease vectors to bighorn sheep.
ODFW will work with the Confederated Tribes of the Warm Springs and the Confederated Tribes of the Umatilla Indian Reservation to evaluate findings and develop management plans in coming months.