The Wyoming Game and Fish Department, in collaboration with the Wyoming State Veterinary Laboratory, is investigating a rare disease outbreak in pronghorn in western Wyoming. Game and Fish is estimating that approximately 200 animals have died since mid-February, centered around the southern end of the Mesa south of Pinedale. Preliminary lab results identify Mycoplasma bovis as the pathogen causing the mortalities.

Mycoplasma bovis should not be confused with Mycobacterium bovis that causes tuberculosis in cattle. They are two unrelated bacteria that cause very different diseases.

The source of infection of the M.bovis and the ability to predict the duration and the geographic distribution of this outbreak in pronghorn is unknown at this time.

“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,” said Wyoming Game and Fish Wildlife Disease Specialist Hank Edwards.

The first reported cases of pneumonia in pronghorn occurred during the winters of 2019 and 2020 near Gillette, involving at least 460 animals. Those outbreaks started at a similar time in mid-February and then tapered down by the beginning of April.

Game and Fish continues to monitor for this disease across the state. With the exception of the Gillette area, this bacteria has not been reported to be associated with significant mortality in other wildlife populations in Wyoming.

To date, this pathogen has not been shown to affect domestic pets such as horses, dogs or cats and is not considered a human health risk. Local Game and Fish personnel will periodically remove carcasses and euthanize dying pronghorn in relatively accessible areas when disturbance to other healthy wintering pronghorn is minimal to help reduce the prevalence of this pathogen on the landscape.