PINEDALE, Wyo. – Wildlife officials have determined the likely cause of a rare disease outbreak that has killed hundreds of pronghorn in a matter of weeks in western Wyoming.
The Wyoming Game and Fish Department estimated that approximately 200 so-called American antelope have died since mid-February, centered around the southern end of the Mesa south of Pinedale.
The pathogen causing the deaths is Mycoplasma bovis, according to preliminary lab results.
Wildlife officials said this pathogen should not be confused with Mycobacterium bovids, which causes tuberculosis in cattle. They are two unrelated bacteria that cause very different diseases. The source of infection and the ability to predict the duration and geographic distribution of the outbreak is currently unknown.
"While reported M. bovis outbreaks causing mortality in wildlife are rare, this is not the first occurrence of M. bovis being linked to pronghorn mortalities in Wyoming," Wyoming Game and Fish wildlife disease specialist Hank Edwards said.
The first reported cases of pneumonia in pronghorn occurred during the winters of 2019 and 2020 near Gillette, Wyoming, involving at least 460 animals, according to Edwards. Those outbreaks started at a similar time in mid-February and then tapered down by the beginning of April.
While officials continue to monitor for this disease across the state, the bacterium has not been reported to be associated with significant mortality in other wildlife populations in Wyoming besides the two reported areas.
In an effort to help reduce the prevalence of the pathogen on the landscape, some carcasses have been removed, and other dying pronghorn have been euthanized.
Wyoming Game and Fish also said the pathogen had not been shown to affect domestic pets such as horses, dogs or cats and is not considered a human health risk.