Carnivores and scavengers could help reduce CWD

Wyoming Game and Fish biologists and technicians have spent the last year and a half feeding four captive bobcats ground meat infected with chronic wasting disease. The study isn't to see if bobcats can contract the disease - it hasn't been shown to cross the species barrier to carnivores like big cats - the goal is to see what comes out the other end.

The results so far have been promising. Only 2% of the chronic wasting disease prions that go into a bobcat's mouth can be detected in the bobcat's poop. And that's day one. By day two there's less than 1%, and by day three there's none at all.

It might seem strange, but whether or not carnivores or scavengers like bobcats keep depositing infectious prions on the landscape may matter quite a bit.

"There's a lot of individuals that believe that carnivores and scavengers play a very large role in the movement of CWD prions in the environment," said Dr. Samantha Allen, the state's wildlife veterinarian. "I think that it shows that they're maybe not contributing as much as some folks would like to believe."

And some scavengers may even be removing some of the infectious prions from the landscape, she added, though many more questions still need answers.

A deadly disease

Chronic wasting disease is an always fatal illness in deer, elk and, to a much lesser degree, moose. It was first identified in captive deer in Colorado in 1967 and, years later, in wild deer in southeast Wyoming. It has since spread across large portions of the U.S., Canada and even South Korea.

It can cause population-level declines in deer and was recently discovered in Yellowstone National Park. A recent report showed dire consequences for elk on the state's feed grounds.

But the more questions researchers answer, the more questions pop up. One question that has loomed for many years is the role that predators and scavengers play in the spread of chronic wasting disease.

CWD prions, which are technically misfolded proteins, can't be killed like a bacteria or virus. They stay infectious in soil and can even be pulled into plants. At home, health officials say to treat any surfaces that could have come in contact with an infected animal with a solution of lye, bleach or heated to temperatures greater than 900 degrees Fahrenheit.

That means it's nearly impossible to get rid of prions once they've been deposited in nature by an infected animal or its decomposing carcass.

So researchers are starting to look at ways that nature may be able to clean up the disease on its own.

Studying scavengers

About a decade ago, researchers fed crows, and then a few years later another team fed coyotes, meat from animals infected with CWD. After analyzing poop from the two species, researchers found infectious prions and concluded that scavengers had the ability to spread the disease further around the landscape. But fast forward eight to 10 years, and testing technology has improved significantly.

In 2021, a team of researchers conducted a similar study on two captive mountain lions and found that while there were infectious prions in their poop, it was only about 3% of what they consumed. That meant 97% of the prions that went in could not be detected when they came out.

Researchers at the University of Wyoming and Game and Fish then wanted to know if the same applied to bobcats, an even more common wild feline scavenger. So in 2022, Madison Davis, a UW graduate student, began working with Game and Fish and veterinary staff at the Tom Thorne/Beth Williams Wildlife Research Center in Sybille Canyon to feed four captive bobcats CWD-infected meat.

The team ground up lymph nodes and brain tissue from infected deer and elk and mixed it into the bobcats' normal ground beef diet at the research station. Davis then collected fecal samples twice a day for a week after feeding and ran them through a series of tests.

She detected even fewer prions in the bobcat poop than in the lion scat study, with amounts sharply decreasing each day. As a result, Davis said, the amount they spread around the landscape outside of a perimeter where CWD already exists is likely minimal.

Nature's cleaning crew?

The results are certainly promising, said Joe Holbrook, an assistant professor at UW's Haub School of Environment and Natural Resources who studies carnivores. But more questions linger.

He and Game and Fish large carnivore biologist Justin Clapp are trying to figure out if scavengers like mountain lions or bobcats will actually consume deer that have died of CWD. Some anecdotes suggest they may avoid those carcasses.

But if, in fact, scavengers do consume deer and elk that have died of the disease, they could be acting as a kind of cleaning crew on the landscape. It's partly why Jennifer Malmberg, an adjunct UW veterinary sciences professor who led the project, decided to look at bobcats. 

People tend to tolerate a limited number of mountain lions because they kill and eat large animals like deer and elk as well as occasional livestock. But if researchers find bobcats help clean up the landscape, then perhaps more of the smaller cats would be allowed to flourish. 

No one knows for sure what happens on the insides of a lion or bobcat that seems to neutralize a prion that requires lye, bleach or high temperatures to destroy. Malmberg's best guess is the prions bind to something inside the cats that renders them no longer detectable.

If they can figure it out, Malmberg wonders if it's possible to replicate the process to help fight the disease. That's just another question to add to the list.

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