Yellowstone National Park announced this week that a mule deer buck inside the park’s borders has tested positive for chronic wasting disease. The detection is a first for the park, which has previously managed to dodge the always-fatal disease despite its presence in the three states that neighbor Yellowstone.

In a Tuesday press release, the park said that the Wyoming Game and Fish Department tested the carcass of a radio-collared mule deer that died in the southeastern section of the park near Yellowstone Lake. The release notes that there’s “no effective strategy to eradicate [CWD] once it’s established” and its plan in the wake of the detection is to ramp up monitoring to determine how prevalent the disease is within the park.

CWD causes physiological and behavioral changes in infected cervids and ultimately leads to emaciation and death. It’s a transmissible, progressive neurological disease similar to mad cow disease, which jumped the species barrier in the mid-1990s, leading to the deaths of 176 Britons who developed a variant form of Creutzfeldt-Jakob Disease, a slow-acting degenerative brain disorder. 


FAQ: Chronic wasting disease in Montana

Though Chronic Wasting Disease infection rates statewide have stayed in the single digits, in some units up to 20% of deer tested are carrying the fatal neurodegenerative disease. Here’s how hunters can help slow CWD’s spread.

CWD is most common in white-tail and mule deer, but it has also been detected in elk and moose. It can be transmitted via contact between animals and their bodily fluids and excretions. The proteins that cause the disease are persistent in the environment once established in an area. Animals with later stages of chronic wasting disease appear sickly and malnourished.

Montana has hosted CWD dating back to at least 2017. It’s particularly widespread in the Libby and Dillon areas. Montana Fish, Wildlife and Parks has ramped up its surveillance efforts and instituted hunts aimed specifically at reducing the density of deer in those areas and obtaining more information about its prevalence. Since its initial detection in Montana six years ago, 3% of all animals tested for CWD have come back positive, though it appears that percentage is inching upward. Of the 2,437 animals tested so far this year, 85 have tested positive, or 3.5%. 

Orange dots represent positive detections of chronic wasting disease in Montana as of Nov. 13, 2023. Credit: FWP

In parts of Wyoming CWD has become so widespread that wildlife managers are concerned about population declines due to “extraordinarily high rates of CWD” in some regions of the state, central Wyoming in particular.

Although there is no known case of the disease being transmitted from cervids to humans, FWP and the federal Centers for Disease Control and Prevention advise hunters not to eat animals that test positive for CWD. FWP encourages hunters to collect samples from animals they’ve harvested and send them in for testing before consuming meat from their quarry.

As a result of the detection, Yellowstone National Park is updating its Chronic Wasting Disease Surveillance Plan with an estimated completion date of 2024. 

“Most wild animals in Yellowstone are healthy and thrive in their natural environment, but sometimes wildlife can get sick just like people,” according to the park’s release. 

Visitors who see sick or dead wildlife are encouraged to report the sighting to a park employee and avoid handling the animal.


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Amanda Eggert studied print journalism at the University of Montana. Prior to becoming a full-time journalist, Amanda spent four years working with the Forest Service as a wildland firefighter. After leaving the Forest Service in 2014, Amanda worked for Outside magazine as an editorial fellow before joining Outlaw Partners’ staff to lead coverage for Explore Big Sky newspaper and contribute writing and editing to Explore Yellowstone and Mountain Outlaw magazines. Prior to joining Montana Free Press’ staff in 2021 Amanda was a freelance writer, researcher and interviewer. In addition to writing...