ODFW responding to detection of M.ovi in John Day River bighorn sheep herd

THE DALLES, Ore. – Several California bighorn sheep along the John Day River have recently tested positive for Mycoplasma ovipneumoniae (M. ovi), the respiratory pathogen associated with pneumonia outbreaks in wild sheep.

The detections mark the first known cases of M.ovi in the John Day River herd, the state's largest bighorn sheep herd with an estimated 1,000 individuals.

ODFW staff are now working to determine the extent of the outbreak and the strain of M.ovi involved by conducting necropsies on dead sheep, getting those samples tested at the Washington Animal Disease Diagnostic Laboratory (WADDL) and surveying the canyon for additional sick animals.

"Many bighorn populations in the state have felt the impacts of pneumonia over the years," said Trent Gianella, ODFW Assistant Wildlife Biologist in The Dalles. "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."

M. ovi outbreaks in Oregon have dramatically affected populations of bighorns in areas such as Hells Canyon and the Owyhees in the past. There is currently no known vaccine or treatment for M. ovi. Generally, the first step to managing the disease is to reduce or eliminate contact between bighorns and animals known to be potential vectors for introduction of the disease, such as domestic goats and sheep and exotic aoudad.

"As an agency we have had an exceptional collaborative relationship with landowners adjacent to the John Day canyon and have worked to ensure we collectively managed bighorns to reduce the risk of contact between potential disease vectors and wild sheep," said Gianella. "A newer challenge to that management goal is a growing herd of aoudad in the region." (Aoudad, aka barbary sheep, are an exotic species that came to central Oregon via a private game ranch in the late 1970s.)

Once M. ovi is detected in a bighorn population, wildlife managers initially monitor to determine the severity of the disease on the specific herd where it has been found. Like many diseases, different variations of the bacteria have different overall outcomes. With M. ovi, some infected herds may see short-term impacts while others may see longer-term chronic issues lasting for decades.

While there is no cure, wildlife managers across the west have enacted multiple actions to reduce the spread and longevity of disease outbreaks, such as removing infected individuals or reducing herd densities to slow the rate of spread. Local biologists will explore what options may be available for the John Day herd as more data on overall disease prevalence is collected.

ODFW will be working with key partners and the Confederated Tribes of the Warm Springs and Confederated Tribes of the Umatilla Indian Reservation in coming months to evaluate findings and develop plans to manage the disease and keep it from spreading to other herds.

For anyone recreating in the John Day River canyon this fall, please notify your local ODFW office should you encounter any dead or potentially sick bighorn sheep.