YAKIMA, Wash. (AP) — A bighorn sheep from the Cleman Mountain herd in central Washington state has tested positive for a lethal disease, the state Department of Fish and Wildlife said this week.

A hunter in the area saw a dead lamb and other 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 for the bacteria that causes pneumonia in wild bighorn populations, the agency said.

The department will monitor the herd and collect lung 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 bacteria is usually fatal across a significant portion of the herd, the agency said. There is no treatment for wild bighorn sheep, and no preventative vaccine.

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.