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CWD is spreading in Montana. Will deer and elk populations decline as a result?

Author: Amanda Eggert, Montana Free Press Montana Free Press

In some Montana hunting districts, up to one-third of animals have contracted chronic wasting disease, the fatal, neurodegenerative disorder that’s driving down deer and elk populations in other western states.

This article was originally published in the Montana Free Press and is republished here courtesy of the Montana Free Press.

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For decades, wildlife managers in Wyoming, Colorado and Utah have been grappling with the spread of chronic wasting disease, a neurodegenerative disorder that sickens and ultimately kills ungulates such as deer, elk and moose over a period of months or years.

The disease is now well established in Montana, according to wildlife managers. Montana Fish, Wildlife and Parks told state lawmakers last month that the infection curve is climbing, particularly among white-tailed and mule deer. According to FWP’s analysis, the disorder, first detected in 2017, is spreading in the Treasure State.

“We now know that chronic wasting disease is found in 33% of hunt districts in Montana, it’s found in all susceptible species, and as of the end of our last hunting season, the data showed that our highest three-year prevalence was 39% in white-tailed deer and 23% in mule deer,” FWP wildlife biologist Bevin McCormick told lawmakers.

So, will we see a decline in Montana’s deer and elk populations?

McCormick said there isn’t enough data to conclude with certainty if CWD is contributing to the decline in eastern Montana mule deer populations, but that the state is doing its best to manage the disease by increasing monitoring efforts, expanding hunting opportunities where it has been found, and educating hunters on proper carcass disposal.

Even if it’s too early to tell if Montana hunters and other wildlife stakeholders should prepare for a sustained deer population decline, neighboring Wyoming’s experience with the disease offers a cautionary tale about what happens when the disorder becomes endemic, or consistently present, in a given region.

CWD is believed to have originated in the 1960s or 1970s from a U.S. Department of Agriculture facility in northern Colorado where scientists were researching a related disease called Scrapie that infects sheep and goats, according to the National Institutes of Health.

In a recent conversation with Montana Free Press, leading CWD researcher Peter Larsen described Wyoming and Colorado as the “epicenter” of CWD in the United States. That’s because the disease, which is caused by a highly transmissible misfolded protein called a prion, has been present there for decades.

Wildlife researchers in 2017 estimated that a 20% CWD infection rate among mule deer in southeastern Wyoming would lead to a 21% population decline. According to a related paper published the year prior, CWD-infected white-tailed deer were 4.5 times more likely to die in a given year than those without the disease. Under a worst-case scenario, chronic levels of CWD in that area of eastern Wyoming could lead to the “possible extinction” of that particular population within five decades, researchers concluded.

Larsen, who co-directs the Minnesota Center for Prion Research and Outreach, underscored that risk. He told MTFP that Montana wildlife managers and other stakeholders should prepare for a future with fewer ungulates and possibly CWD transmission to other species. That’s due, in part, to the fact that the disease often progresses slowly — it’s not uncommon for an animal to carry CWD for several years before succumbing to it — but disperses widely.

“CWD is spreading fast throughout the U.S., but we’re really only at the very beginning,” Larsen said. “The way this disease spreads and how those infections spread make it really difficult to manage.”

CWD is highly infectious, in part because the prions that cause it can continue to sicken animals long after the carrier has died. A study in Wisconsin has demonstrated that the prions that cause CWD, which an infected animal sheds in its bodily fluids and tissues, can persist in the environment for 16 years, Larsen said.

“In a late-stage white-tailed deer with CWD, there are enough prions in that brain to kill all deer in North America,” he added. “We’re starting to get worried about accumulation in the environment and other species coming into contact with it.”

As the disease becomes more widespread, the risk that it will jump the species barrier and infect other animals, such as mountain lions or coyotes, increases, Larsen said. While humans can’t contract CWD, the disease poses a “non-zero” risk to them, he said. “Some studies show there’s a really strong species barrier. Other studies show it’s not 100%, and there may actually be potential [for] crossover.”

Researchers trying to learn more about whether the prions become more or less infectious as they move through the food chain, according to Larson, are grappling with a “dynamic” situation. It’s possible, he said, that movement through an animal’s GI tract can change the prions’ shape in a way that increases the infection risk for other species.

“It’s really difficult to know whether or not predators are going to be an effective way to manage it,” Larsen continued. “I don’t think it hurts anything … but it’s still going to be spreading during that long incubation time.”

Asked about the most effective tools to limit the spread of CWD, Larsen responded, “hunting, hunting, hunting.” Culling is another management approach, though Missouri’s experience with that strategy has demonstrated that taking such an aggressive approach to CWD can invite controversy.

FWP spokesperson Greg Lemon said Montana’s approach centers on enlisting hunters to help with monitoring and hunting efforts.

“If we can keep prevalence low where it exists, we can hopefully limit the disease’s ability to spread to other herds that might not have CWD yet,” Lemon said. “And if we can do that with the help of hunters … then we can protect the herds and the hunting heritage that we value in Montana.”

Article Images

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Image 1 Caption: A healthy cow elk looks over its shoulder. Chronic wasting disease has been on the rise and is now found in 33% of hunt districts in Montana. Credit: NPS
Image 2 Caption: A sick and doomed elk infected with chronic wasting disease. While CWD is well established in Montana, leading CWD researcher Peter Larsen described Wyoming and Colorado as the “epicenter” of CWD in the United States. Credit: Wyoming Game and Fish Department
Image 4 Caption: Logo