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With CWD finally confirmed in Yellowstone National Park, Predators Could be Yellowstone's Salvation

Experts say first-ever CWD case in park was ‘only a matter of time,’ call for Wyoming to eliminate elk feedgrounds

A mule deer found near Yellowstone Lake is the first confirmed case of chronic wasting disease ever in Yellowstone National Park. The disease, also known as CWD, is always deadly to the cervids it infects, and experts have said it was "only a matter of time" before it was discovered in Yellowstone. Photo by Jim Peaco/NPS
A mule deer found near Yellowstone Lake is the first confirmed case of chronic wasting disease ever in Yellowstone National Park. The disease, also known as CWD, is always deadly to the cervids it infects, and experts have said it was "only a matter of time" before it was discovered in Yellowstone. Photo by Jim Peaco/NPS
by Laura Lundquist

The mule deer staggered as he tried to follow the timeless instinct telling him it was time to go. The aspen leaves were yellowing, nights getting longer. Other members of the Upper Shoshone herd had already started their 60-mile trek back through the Absaroka Mountains to their wintering grounds west of Cody, Wyoming. But even though he was only about four years old, his starved body wouldn’t work, and he was so thirsty. He had summered on the Promontory, a southern peninsula surrounded by Yellowstone Lake, but the water hadn’t been able to quench his thirst. Shaky legs splayed, he stood looking at the water, long ears drooping. Drool dripped from his mouth as he tried to focus. Finally, his legs buckled.

It was mid-October, and over in the Cody Office of Wyoming Game and Fish, biologist Tony Mong got an alarm, signifying that one of his collared deer had died. Disappointed, he noted that the young buck had been collared only seven months prior along with 30 other bucks near the North Fork of the Shoshone River. When he saw the collar’s location, he called Yellowstone National Park and drove toward Yellowstone Lake.

After hiking in, Mong found the buck where it fell. The body was emaciated but showed no signs of a predator attack. With a bad feeling, Mong pulled his knife and removed the lymph glands from near the deer’s head to send to the lab.

A few weeks later, the results came back: The buck had died of chronic wasting disease or CWD.

Since the late 1960s when it was first identified in in a captive deer at a Colorado Division of Wildlife facility, CWD has spread to infect wild deer and elk populations in 31 states and three Canadian provinces, according to the U.S. Geological Survey. So far, the spread is unstoppable, because CWD is caused by a deformed protein called a “prion,” which, unlike bacteria or viruses, is hard to detect or treat and can persist in the environment for years. And CWD is always deadly.
This USGS map below shows the distribution of CWD as of Oct. 15, 2023. The highly contagious fatal disease was discovered in a mule deer carcass in Yellowstone National Park on Nov. 14.
This USGS map below shows the distribution of CWD as of Oct. 15, 2023. The highly contagious fatal disease was discovered in a mule deer carcass in Yellowstone National Park on Nov. 14.
Once an animal picks up a prion—usually by direct contact with bodily fluids of other infected animals, their carcasses or even the surroundings—the prion begins to reshape critical proteins in the animal’s lymph and nervous systems, causing them to malfunction. The infection can last 18 to 24 months in deer, but it’s only in the later stages that the animal shows the obvious symptoms displayed by the muley buck.

“[The buck] was healthy when we caught it. Over the summer, GPS data shows at least one other deer in that area where we found him [dead],” Mong said. “But in Yellowstone, Grand Teton; a majority of our deer live in those areas. I wouldn’t be surprised if we do find some others, just based on the 10-15 percent [infection] rate that we have for CWD in this herd unit and the number of animals moving from the Cody area to the park for the summer. I think it’s inevitable that there are other individuals that probably have CWD that use the park. It’s just that this one had a collar and alerted us when it did die.”

Mong informed Yellowstone National Park, which sent out a press release on Nov. 14 announcing that the first known case of chronic wasting disease had been found in Yellowstone. It was a sad revelation for America’s first national park, where many visitors come specifically to see and photograph its abundant wildlife.
"The fact we see CWD pretty much all around the [Greater Yellowstone Ecosystem] shows you this is a situation where the toothpaste may out of the tube, and all we can do is hope to figure out how to slow the spread, not eliminate it.” – Dan Vermillion, former Montana Fish, Wildlife and Parks commissioner
It’s uncertain how the park will respond, beyond a stated push to increase monitoring of deer, elk and moose, and testing carcasses for CWD like Mong did with his deer. Yellowstone published a Chronic Wasting Disease Surveillance Plan in 2021 but removed it from its website this past week. When Mountain Journal requested a copy of the plan, Public Affairs Officer Morgan Warthin said in an email that they’d removed it because they’re revising it to include additional actions the park will take to manage the disease and will share it when it’s complete sometime in 2024.

The news attracted significant attention on social media, where some expressed despair while others said they were disappointed but not surprised.

Dan Vermillion, former Montana Fish, Wildlife and Parks commissioner, was in the latter camp, saying it was “only a matter of time.” During the dozen years he was on the commission, Vermillion watched CWD spread and worsen throughout Wyoming and over the Canadian border in Alberta and Saskatchewan. He wasn’t surprised with Montana’s first positive test in 2017, and he isn’t now with the Yellowstone case.

What does surprise him is that Wyoming insists on maintaining the elk feedgrounds south of Yellowstone and Grand Teton national parks. CWD spreads more quickly where elk or deer congregate, and elk gather on the feedgrounds in high densities during winter. Some of those elk migrate to other locations, so they could carry the disease with them.

Grand Teton National Park had its first CWD case in 2018 when a car struck and killed a buck mule deer that tested positive. According to a 2018 Wyoming Game and Fish release, biologists said it wasn’t a surprise based on finding infected mule deer to the south in Star Valley and Pinedale in 2017. Some muleys that summer in Grand Teton National Park and near some elk feedgrounds spend winters near Dubois and Cody, so migration aids the spread.

Vermillion hopes the attention on the Yellowstone deer will prompt Wyoming to reconsider the feedgrounds.

“When I was on the commission, we had really contentious meetings with the Wyoming Fish and Game commission and their director on this very issue,” Vermillion said. “We sent them a pretty stern letter asking them to stop feeding elk. They took great umbrage, but I think we were right. And I still do … The fact we see CWD pretty much all around the [Greater Yellowstone Ecosystem] shows you this is a situation where the toothpaste may out of the tube, and all we can do is hope to figure out how to slow the spread, not eliminate it.”
An elk, sick and doomed with CWD, shows symptoms of the deadly disease at a wildlife laboratory in Wyoming. Photo courtesy Wyoming Game and Fish Department
An elk, sick and doomed with CWD, shows symptoms of the deadly disease at a wildlife laboratory in Wyoming. Photo courtesy Wyoming Game and Fish Department
Washington State University pathology professor Margaret A. Wild agrees that Wyoming should reconsider their policy on feeding elk now that it’s certain that animals in Yellowstone have been exposed. However, it’s unlikely the Yellowstone deer was the first case; it just happened to be collared so its illness was identified. Wild should know. Not only does she study emerging infectious diseases like CWD, but she was the chief wildlife veterinarian for the National Park Service until 2018.
"A complete predator guild like Yellowstone has is one of the best things I can think of for chronic wasting disease management.” – Margaret A. Wild, pathology professor, Washington State University
However, Wild has hope for Yellowstone because, of all the national parks, it may have the one strength that could help its deer, elk and moose populations endure the disease: a healthy dose of predators.

“They’ve got wolves, they’ve got mountain lions. These predators can detect animals that are sick long before people can,” Wild said. “Some modeling we’ve done in the past, we showed that removal [of CWD-infected cervids] by hunters may help some. But what really helps is selective removal by predators. Assuming that predators can detect and remove animals earlier in the disease course, they can reduce the amount of time a deer or elk is transmitting the disease to other animals either directly or by putting feces, urine or saliva into the environment that their counterparts could encounter. So, a complete predator guild like Yellowstone has is one of the best things I can think of for chronic wasting disease management.”

Other parks aren’t so lucky. The USGS has found that CWD was the leading cause of death in the elk population in Wind Cave National Park south of Rapid City, South Dakota, with infection rates up to 24 percent. So, scientists are evaluating the effectiveness of reducing elk density on chronic wasting-disease mortality. But without predators around, that requires that people either haze or harvest elk.

Paul Cross, USGS research biologist at the Northern Rocky Mountain Science Center, and his team have done some of the computer modeling that shows predators can help in two ways. First, they keep densities of elk and deer down and they devour carcasses, so animals have fewer opportunities to come into contact. Second, they may be able to cull the sick individuals out of the herd early so they have less of a chance to spread the infection.
What does surprise Dan Vermillion is that Wyoming insists on maintaining the elk feedgrounds south of Yellowstone and Grand Teton national parks.
Their modeling shows that works. But they’ve yet to demonstrate the second hypothesis in real populations, partly because they don’t yet know when infected deer or elk become contagious. If deer or elk experience symptoms before they are contagious, predators could be the key to keeping infection rates down. Otherwise, predators play a smaller role.

“What we learned on a personal level from Covid-19 is it’s hard to control a disease when transmission occurs before symptoms appear,” Cross said. “So, this is a challenging question that will take us a long time to empirically answer. But national parks serve an important role in providing places to observe and study how ecosystems function. In this case, Yellowstone, Grand Teton—they’re critical in understanding how predators might serve to keep the herd healthy. We have a hard time learning that in other places.”

In the meantime, Mong said it will be up to the park and state biologists like him to remove animals showing obvious signs of CWD.

“Hopefully we can use this as an educational tool and get people on board for managing chronic wasting disease,” Mong said.

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Mountain Journal is the only nonprofit, public-interest journalism organization of its kind dedicated to covering the wildlife and wild lands of Greater Yellowstone. We take pride in our work, yet to keep bold, independent journalism free, we need your support. Please donate here. Thank you.

Laura Lundquist
About Laura Lundquist

Laura Lundquist earned a journalism degree from the University of Montana in 2010, and has since covered the environmental beat for newspapers in Twin Falls, Idaho and Bozeman, in addition to a year of court reporting in Hamilton. She's now a freelance environmental reporter with the Missoula Current Online Journal.
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