The return of wolves across the American West has raised howls from ranchers worried about theirlivestock, and hunters worried that wolves will make deer and elk more scarce during hunting season. Wolf boosters counter those arguments with data on how wolves improve the health of ecosystems by preventing overgrazing and overpopulation. But some scientists studying one of the worst scourges to afflict deer in North America—chronic wasting disease (CWD)—think wolves could have another benefit. It’s possible that the predators could help to chase down the disease and reduce its impact.
CWD is a prion disease—it results from a mutated protein that fails to fall apart when it should. Instead, the protein hangs around, gumming up the central nervous system and converting other proteins to its evil ways. As the infected proteins take over the brain, deer and elk eventually lose the ability to feed themselves, and then starve.
As prions build up in the brain and in tissues, infected deer begin to spread them around. “They shed them in saliva, urine, feces, so they can be transmitted from individual to individual,” explains Daniel Storm, a deer research scientist with the Wisconsin Department of Natural Resources (DNR). When a male shoves his nose into the nether regions of a female to find out if she’s ready to mate, “there's exposure to fluids there.” Bucks also do something called “scraping.” They find an overhanging branch and bite, lick, and rub their scent glands on it. It’s a way of saying “Buck wuz heer.” Storm and his colleagues have shown that bucks are three times more likely to get a CWD infection than does—a problem for any hunter in search of a good rack.
No one knows where CWD originated, but it’s spreading—in 29 states as of June 2022. It’s no longer legal to take any deer carcass across county lines in Wisconsin—one way authorities try to control the disease’s expansion.
An animal can be infected for months or even years with few outward signs of illness. The only way to tell is by examining the lymph nodes located around the deer’s jaw—something deer are obviously not volunteering to donate. Currently, says Daniel Storm, a deer research scientist with the DNR, it’s up to hunters to get their deer checked either by turning in the head to the DNR to get the animal’s lymph nodes analyzed or by having a taxidermist remove the lymph nodes for them. About 20,000 deer get analyzed every year in Wisconsin, he says. That seems like a high number—until you find out that hunters killed more than 300,000 deer in the state in 2021.
If an animal carcass turns out to have CWD, the CDC says you can’t eat the meat (though Storm notes that does not stop all hunters from doing so). An infected carcass can’t just be tossed somewhere into the back 40 either. Instead, hunters are encouraged to use deer dumpsters provided by the state. “I can look out my window and in our parking lot, there's a giant dumpster that people can come and drop their deer carcasses off,” Storm says. (When people go into wildlife management to be close to nature, this is probably not what they had in mind.)
The spread of CWD can probably be blamed on wildlife management practices that have resulted in a whole lot of deer, says Margaret Wild, a wildlife veterinarian at Washington State University. The more densely packed deer are, the more likely they are to get up close and personal with the bodily fluids of another infected deer. Even after death, their decaying bodies “create a little hotspot of prions,” Wild explains. Those proteins stick around “longer than things that we generally think of. … It’s not a virus. It's not a bacteria. It's not a parasite. It's just this protein.” It does degrade eventually, but until it does, every deer that comes to sniff the corpse might get a dangerous dose.
There’s no cure for CWD. Some states have tried to mitigate it by expanding hunting, trying to reduce deer and elk numbers and slow the spread. Some also call in sharpshooters to cull the populations. But “generally deer hunters don't like policies to have fewer deer,” Storm says.
It’s also not clear if hunting or culling is having an effect on CWD spread. Deer are shedding virus long before they look sick. Just reducing the overall number of deer in an area might help, but “it's still an open question as to how effective it would be,” Storm says.
Are four legs better than two?
But there are some predators more efficient than people. Wolves and mountain lions, Wild says, might be able to sense things in deer that hunters cannot. “It's a dementia-type disease,” Wild says. “These animals—ones I've seen in captivity—a year before they succumb to the disease, you'll catch them just kind of staring off into space and forgetting to do something,” Wild says. “They have these periods where they're just not as aware, not as vigilant as other animals.”
A hunter might miss that. Wild thinks a hungry predator wouldn’t. “Wolves are constantly testing their prey,” Wild says. “All it takes is minor missteps like that and a wolf, as acoursing predator, it's going to pick that up and remove those animals earlier in the disease course.” A studyof mountain lion kills published in Biology Letters showed that the big cats were more likely to take out mule deer infected with CWD than human hunters in the same area. Diseased moose and bison also appear to be more vulnerable to hunting wolves than their healthy brethren.
In a model published in the Journal of Wildlife Diseases, Wild and her colleagues found that wolves might be able to keep CWD levels lower in some deer populations than human hunters or sharpshooters. The model also showed that wolf and mountain lion predation might keep the overall deer population higher. If wolves could pick off infected deer half a year earlier on average than hunters could, notes Wild, infected deer would have six fewer months to spend walking around spreading CWD.
Predators may also help clear up the prions hanging out in the environment. In astudy published in mSphere, researchers fed two captive mountain lions ground meat from CWD-infected deer. When they tested the resulting lion poo (the things we do for science!) they found that less than 4 percent of the prions in the meat survived the journey through the big cats’ digestive tracts.
Correlations between wolves and areas with less CWD might be easy to find. Proving causation would be a lot harder. Testing the hypothesis would require tracking wolves in areas with CWD and testing their kills to see if they are more likely to be infected than the overall deer population. Researchers would need to compare their findings with areas where deer have CWD but no predators other than humans. And if predators could prevent CWD from even spreading to new areas, Storm says, would we even know? CWD would just never appear at all.
Finally, if wolves did help reduce CWD, would the wolf-haters even care? Storm worries that wolves are far too contentious for a little science to make a difference. But even if existing research isn’t enough to persuade the reluctant to introduce wolves into CWD-infected regions, it could be an argument to keep them on the landscape where they are already, says Wild. Wolves come with challenges, but “it's still a lot easier to manage wolves than it is to manage a disease.”