Cleman Mountain bighorn sheep tests positive for lethal bacteria

YAKIMA– The Washington Department of Fish and Wildlife announced today that a bighorn sheep from the Cleman Mountain herd tested positive for Mycoplasma ovipneumoniae last week.

Wildlife biologists received reports from a hunter in the area who saw a deceased lamb and lambs that were acting lethargic. Upon investigation, biologists found a dead lamb and were able to collect samples for testing. That test came back positive.

“The fact that this bacteria has been found in the Cleman Mountain herd is significant, and we have limited options for how to address this positive test,” said Mike Livingston, WDFW Region 3 Director. “We reviewed options such as lethal removal, testing, or increased monitoring. Because of the size of the herd and their range, we don’t believe that removing animals from the population is the best option at this time.”

In addition to increasing monitoring through this winter to spring 2021, WDFW will collect lungs and nasal swab samples from any animals harvested during this season’s remaining special permit hunts. More samples will help the department determine the extent of the disease outbreak in the Cleman Mountain herd.

The hunter who reported the sighting had also successfully harvested a ram, and biologists collected a sample from that animal as well – that sample tested negative for the bacteria.

The lethal bacteria that causes pneumonia in wild bighorn populations is usually fatal across a significant portion of the herd and can reduce the survival rate of lambs born to surviving animals for many years after the initial outbreak. There is no treatment for wild bighorn sheep, and no preventative vaccine.

The department hasn’t determined the source of the bacteria. However, there is no evidence that connects this situation to another incident reported last week in a herd located roughly 40 miles away.  

Past pneumonia outbreaks among bighorn sheep in Washington and other parts of the western United States have been linked to contact between wild sheep and domestic sheep or goats that carry Mycoplasma but are unaffected by the bacteria.

In 2013, state and federal wildlife managers removed the entire Tieton bighorn sheep herd to prevent the outbreak from spreading to the Cleman Mountain herd. The department is not considering similar actions because the nearest herd is the Yakima Canyon herd, where the pathogen is already established.

WDFW is the primary state agency tasked with preserving, protecting, and perpetuating fish, wildlife, and ecosystems, while providing sustainable fishing and hunting opportunities.