As chronic wasting disease spreads, wildlife managers plea for strategies that could work
By Christine Peterson
No one knew why the deer were losing weight, struggling to stand, and then keeling over, dead. So for years in the 1960s and 70s, researchers at a Colorado State University research facility recorded the mystery by collecting tiny slivers of the deer’s brains and filing them away.
Then one day a PhD student named Beth Williams unearthed those slides. Under a microscope, each sample appeared filled with holes, like the brain tissue had turned into Swiss cheese. Those holes, she realized, were similar to the ones veterinarians had already identified in sheep brains, and the always-fatal illness with no cure was coined chronic wasting disease (CWD).
As she and other researchers sounded the alarm, the strange new disease spread from Colorado to Wyoming, and then Nebraska and South Dakota, killing any deer or elk it infected. In 1996, Williams gave what now feels like a prophetic piece of advice about managing CWD: “You’ll have to be aggressive,” she said. “Remove all sources…and all potential movement. Cut wider and deeper than you ever think necessary. The deer will come back; but you’ll get one chance. If CWD gets widely established, you’ll have it for a very long time.”
In the decades since, states that followed her advice, like New York and Minnesota, have so far mostly kept the disease at bay. But in places like Wyoming and Wisconsin, which have largely lacked the will to cut as deep for as long as disease experts say is necessary, CWD has continued to spread. “There is apathy from both the wildlife managers but also the public,” says Brian Nesvik, director of the Wyoming Game and Fish Department. “Does this worry me? Absolutely.”
Today, CWD has become one of the thorniest wildlife diseases of our time, infecting deer, elk, reindeer, and moose in three-fifths of the US and portions of Canada, Norway, and even South Korea, with prevalence rates as high as 60 percent. Despite this, most experts and wildlife managers agree that it’s not too late to act. Try something, they say. Don’t just watch and wait.
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Chronic wasting disease, or transmissible spongiform encephalopathy as it’s known to scientists, is caused by the buildup of misfolded proteins called prions, which kill brain cells and leave holes in animals’ brains. Infected animals become lethargic and emaciated, wasting away until, inevitably, they die. Because it isn’t a bacteria or a virus, it can’t be treated with antibiotics or prevented with traditional vaccines.
The disease first spreads among animals largely through nose-to-nose contact. Once CWD is established in a population and animals shed prions onto the landscape, experts believe individuals can then contract the disease through infected soil or even, possibly, through prions clinging to blades of grass.
Researchers know that deer contract the disease at higher rates than elk, which contract the disease at higher rates than moose, though no one knows exactly why. Bucks seem to be infected twice as often as does, likely because they tend to move and socialize more.
Left unchecked on a landscape, it moves slowly—it took about 40 years for CWD to creep from southeast Wyoming to the western portions of the state. But humans have given it a lift by moving captive elk and deer between businesses that raise them for food or hunting opportunities. Saskatchewan imported the disease in a captive elk from South Dakota in the late 90s. South Korea then unknowingly imported an infected elk from Canada in 2001.
Because there is no cure, and infectious prions may linger on the landscape a long time, CWD researcher Krysten Schuler, a wildlife disease ecologist and director of the Cornell Wildlife Health Lab, says the best way to contain the disease is to limit possible sources of transmission. Stop treating deer and elk like livestock that can be shipped between captive facilities, particularly across state lines, she says. Explain to hunters that carcasses should go to landfills or carcass-disposal facilities and not get tossed on the side of a dirt road, where they could potentially infect nearby herds. Don’t transport brain or spinal tissue to new areas.
New York, where Schuler works, took this lesson to heart when it identified the disease in an infected deer from a captive deer facility that was made into chili for a local fire hall event in 2005. After the first discovery, officials found more positive deer at another captive facility, and ultimately paid to depopulate both businesses. Since then, they’ve worked on keeping the disease out by banning facilities from importing live deer or elk from out of state, prohibiting hunters from bringing intact carcasses in from other states, outlawing baiting and feeding to reduce gathering spots, and surveilling herds especially in high-risk areas. The state has even paid meat processors and taxidermists $10 and $20, respectively, to send in either a head or lymph node for testing.
The state is proof, Schuler says, that CWD can be isolated. “There’s an obligation to try and stop it and not just throw up our hands and say it’s going to be everywhere.”
Bryan Richards, the emerging disease coordinator at the USGS National Wildlife Health Center in Wisconsin, advocates for an even simpler approach: reduce the number of deer gathered in close quarters by thinning herds. It’s the same one Williams recommended almost 30 years ago.
When CWD popped up in Minnesota in 2011, wildlife managers used sharpshooters and a late-season deer hunt to try and reduce the spread. Since then, the state regularly culls several hundred deer from hot spots where infections pop up before the disease has a chance to spread. And the strategy has largely worked. Officials believe only one herd has established CWD, and rates hover around 1 percent.
But this aggressive response only seems to work with a public prepared for what trying to control CWD requires. Years before the CWD outbreak in Minnesota, the state culled whitetail deer in its successful fight against bovine tuberculosis, a disease that can sicken and kill both whitetail deer and cattle. Because of that, says Kelly Straka, head of fish and wildlife for the Minnesota Department of Natural Resources, hunters and the general public knew what to expect.
In contrast, when researchers in the rolling foothills of the Norwegian mountains discovered CWD variants in a herd of reindeer, the swift response was deeply unpopular. They essentially eliminated one population, killing more than 2,000 reindeer, says Atle Mysterud, a university of Oslo professor who has studied CWD for years. They’re monitoring the spread of CWD in another one.
That initial attack was met with uproar from the public, and Mysterud is not sure Norway will be so aggressive again. “We should have clearer goals. Current aim is ‘limit, if possible eradicate’ – but limit vs eradicate involve quite different actions.”
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In Wyoming, where CWD is established in many, but not all, deer and elk herds, the state has had to walk the line between limiting the spread and managing infected populations. “For the vast majority of the time, we didn’t engage in any meaningful statewide management,” says Justin Binfet, a wildlife biologist with the Wyoming Game and Fish Department. But now the state has a new CWD plan, which he hopes will help Wyoming turn a corner.
The plan, finalized in 2020, calls for reducing deer or elk densities at potential hot spots like center irrigation pivots or haystacks and directs Game and Fish to sample at least 200 buck mule deer and 200 elk out of each of the state’s herds every five years. It also says thinning herds or increasing buck hunting in some herds may be necessary to conserve the state’s abundant wildlife. But the latter has proved challenging to enact.
In 2022, a mule deer herd in the early stages of CWD infection lived tucked up along the east side of Wyoming’s Snowy Range. Rates of the disease in buck deer were around 8 percent, a far cry from the 40 percent or even 70 percent in mature bucks farther north.
Research in other herds showed that left unabated, prevalence would inevitably increase. It also showed that CWD spreads first in bucks and then into does. Cut down on the number of bucks, especially big, old bucks, which are prized by hunters but are more likely to carry the disease and spread it around, and potentially control the disease.
So Lee Knox, a Game and Fish biologist, made a plan. He held a series of public meetings explaining CWD research and gauging hunters’ thoughts on increasing buck harvest. At the time, the herd of almost 4,000 deer had about 40 bucks per 100 does. Many other Wyoming herds keep buck numbers around or under 30 bucks per 100 does, and states like Minnesota hold their herds often around 20.
He proposed, and many of hunters in those early meetings agreed, to offer 100 more buck tags spread across four hunt areas and allow hunters to look for them in November instead of exclusively during the first two weeks of October.
But before the concept could even make it to the Wyoming Game and Fish Commission the following spring, online hunting forums exploded. Game and Fish was trying to kill all of the area’s bucks, people said. In a deer population that is already struggling, increasing hunting would ruin opportunities to shoot big bucks in the future. The outrage reached such a fever pitch that the department pulled the proposal, saying it was just not the right time.
“You’ll hear people say the cure is worse than the disease, which is not true at all,” Knox says. “But the public wants a guarantee, and we can’t guarantee anything.” Two years later, CWD prevalence rates in the herd now hover around 15 percent.
The story illustrates the difficulty of trying to reduce CWD’s spread by increasing hunting in a state where mule deer are so prized they adorn license plates, and herds are struggling from drought, development, invasive species, and disease.
Game and Fish Director Nesvik doesn’t blame people. Increasing hunting or thinning herds is a hard pill to swallow when populations are already lower than people would like. Plus, he said, “the public can’t see the disease killing deer. They know there’s less deer, but they go to the things that are simpler to understand. They think, ‘Well, we know mountain lions eat deer, so mountain lions are the problem.’ I think that people are having a hard time believing that CWD is actually having an effect on the population.”
Wyoming officials are also quick to point out other differences between combatting CWD in New York and Minnesota and fighting it in the Cowboy State. The Midwest’s abundant deer stay relatively put, while deer and elk herds in the West migrate dozens if not hundreds of miles, which complicates efforts to slow the spread. Managing a landscape steeped in the disease, they say, is also very different than keeping the infectious prions out.
Once the disease has already taken root, even Schuler and Straka say there’s no reasonable way to get rid of it. At that point, entities are left to manage through monitoring the spread and trying to keep prevalence down. But if support for cutting deeply once to prevent CWD’s establishment was difficult to come by, the will to cull year after year just to maintain disease levels has been even more elusive.
Wyoming wildlife managers once dramatically increased hunting in a deer herd in Thermopolis but soon discovered CWD was already enmeshed in the area. After two years, the public’s appetite for keeping deer numbers low dropped, hunting returned to usual, and rates spiked.
In Wisconsin, where disease pathologists first detected CWD in three deer killed by hunters in the fall of 2001, wildlife managers took the arrival seriously. They made deer hunting essentially unlimited in many places, required hunters shoot a doe before they kill a buck in others, and department officials culled deer. But when they sampled more than 40,000 deer the following year, they found another 205 cases. The disease, it appeared, had already taken hold.
Six years later, the hunting public had had enough. They were willing to invest in a short-term solution, it appeared, but not one that could last forever.
“Ultimately, populations are managed by hunters, and hunters wield funding and influence,” says Richards with the USGS. “As long as agencies keep producing lots of deer and big deer, the influence hunters apply is positive. But if hunters are unhappy, then the legislature takes over.”
Hunters wanted to go to back to the good old days of hunting, when the forests and fields were full of big deer, before culling dropped the number of overall deer. So the state legislature ordered an analysis of the efforts, and upon learning the results were inconclusive told the Department of Natural Resources to stop. Hunting seasons returned to normal, deer numbers bounced back, and now, 20 years later in a state with two million whitetail deer, prevalence rates in some areas are over 50 percent.
Somewhat ironically, Richards has a paper coming out this year that looks back at those early efforts to contain the disease and found that they did, in fact, help curb the spread.
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Researchers and wildlife managers like Richards and Nesvik are frustrated by the general lack of willingness to do anything, the desire to just go back to the days before the disease gripped the landscape, before hard decisions like thinning herds needed to be made. Even in places where prevention has largely been successful, like Minnesota, “there can be a perspective of impending doom,” says Straka. “You can continue to do whatever you want, but the threat will be there.”
“It’s a wicked problem,” Richards says. “There’s no easy answer and no one group by themselves can manage the outcome.” But researchers agree that states need to work together, sharing infection data and comparing strategies to aggressively prevent the disease’s spread and keep prevalence down in infected populations.
That’s not likely to happen unless CWD spreads to humans or domestic livestock like cattle, Richards says. Or, adds Nesvik, if a study could show irrefutable proof that reducing densities in areas like Wyoming’s rolling sagebrush and rugged mountains works.
Schuler thinks by now the message should be clear. “The one constant with CWD is it always seems to get worse, but I don’t think people are really trying to make it better,” she says. “I think we need a groundswell of hunters and conservationists and the public to talk to their elected officials and say, ‘This is really important to me, and we need to do something about it.’ Because the status quo is we’re losing, and we’re losing pretty badly.”
Christine Peterson is a freelance journalist covering the environment, wildlife and outdoor recreation for local, regional and national publications from her home in Laramie, Wyoming.
