Hundreds of pronghorn are dropping dead in Wyoming, officials say. What’s the cause?

Mitchell Willetts
Thu, March 9, 2023

Hundreds of pronghorn antelope have suddenly died in western Wyoming, and wildlife officials say a rare disease is to blame.

In a matter of weeks, starting in mid-February, an estimated 200 pronghorn have died due to pneumonia brought on by Mycoplasma bovis, a disease typically associated with cattle, the state Game and Fish Department said in a March 8 news release.

Photos shared by the department show the animals apparently falling down dead, their bodies collapsed in the snow.

It’s rare to see M. bovis spreading among wildlife in Wyoming, officials said.

“This is a nasty, nasty pathogen,” Hank Edwards, WGFD wildlife disease specialist, told Field & Stream. “Whether it’s in domestic stock or otherwise, it’s just incredibly fatal — particularly in pronghorn. The pneumonia that they’re getting is substantial. It’s killing them pretty ... quickly.”

The deaths appear to be centered in a specific area south of the town of Pinedale, according to the release. However, the source of the outbreak is unknown, and it’s unclear if the pathogen could be more widespread.

“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,” Edwards said in the release.

The disease is not a direct threat to humans, but it can have a devastating impact in other ways, according to the National Institutes of Health, as Mycoplasma bovis infections “are responsible for substantial economic health and welfare problems worldwide.”

From 2019 to 2020, the disease killed nearly 500 pronghorn in the northeastern part of the state before the outbreak burned out during spring, Wyoming wildlife officials said.

“We were hoping that that outbreak was the last of it … but we were really surprised to see it pop up again on the other side of the state,” Edwards told Field & Stream.

Wildlife officials will continue monitoring across the state for signs of M. bovis, the release said.