Possibility of wildlife-to-human crossover heightens concern about chronic wasting disease

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Every fall, millions of hunters across North America enter forests and grasslands to hunt deer. In winter, people eat venison steaks, sausages and burgers made from the animals.

These hunters, however, are not the only ones on the front lines of an American tradition. Infectious disease researchers say they are on the front lines of what could be a serious threat to public health: chronic wasting disease.

The neurological disease, which is contagious, rapidly spreading and always fatal, is caused by a misfolded protein called prion. It is currently only known to infect members of the cervid family – elk, deer, reindeer, caribou and moose.

Animal disease scientists are concerned about the rapid spread of CWD in deer. Recent research shows that a spillover barrier in humans is less robust than previously believed and that these disease-causing prions may become more capable of infecting humans.

The response to the threat is increasing. In 2023, a coalition of researchers “started working on a major initiative, bringing together 68 different global experts on different aspects of CWD, to see what the challenges are ahead if we see a spillover into humans and food production,” says Michael. Osterholm, an infectious disease specialist at the University of Minnesota and a leading authority on CWD.

“The bottom line message is we’re pretty unprepared,” Osterholm said. “If we saw a spillover now, we’d be off the hook. There’s no contingency plan for what to do or how to follow up.”

The team of experts is planning a potential outbreak, focusing on public health surveillance, lab capacity, prion disease diagnosis, livestock and wildlife surveillance, risk communication, and education and outreach.

Despite concerns, thousands of infected animals have been eaten by humans in recent years, yet there have been no known human cases of the disease.

Many hunters have wrestled with how seriously to take the threat of CWD. “The main opinion I encounter is that no one is infected with this disease,” says Steve Rinella, an author and founder of MeatEater, a media and lifestyle company focused on wild game hunting and cooking.

They think, “I’m not going to worry about it because it hasn’t crossed the species barrier,” Rinella said. “If a predator gets CWD, that will change dramatically.”

Other prion diseases, such as bovine spongiform encephalopathy, also known as mad cow disease, and Creutzfeldt-Jakob disease, have affected humans. Mad cows have claimed more than 200 lives, mostly in the UK and France. Some experts believe that Parkinson’s and Alzheimer’s may also be caused by prions.

First discovered in captive deer in Colorado in 1967, CWD has since spread widely. It has been found in animals in at least 32 states, four Canadian provinces and four other foreign countries. It was recently found for the first time in Yellowstone National Park.

Prions behave very differently from viruses and bacteria and are virtually impossible to eradicate. Experts call it a “disease from outer space,” says Matthew Dunphy, director of the Chronic Wasting Disease Alliance.

The symptoms are dire. The brain deteriorates to a spongy consistency. Sometimes nicknamed “zombie deer disease,” the condition causes infected animals to stumble, blink and stare blankly before dying. There is no treatment or vaccine. And it’s extremely difficult to eradicate, whether with disinfectants or high heat—it even survives autoclaving or medical sterilization.

Cooking does not kill prions, Osterholm said. Unfortunately, he said, “cooking concentrates the prions. It makes it more likely” that people will eat them, he said.

Although CWD is not known to be transmitted to humans or domestic animals, experts are very concerned about both possibilities, with Osterholm’s group receiving just over $1.5 million in funding for the study. CWD can infect more of an animal’s body than other prion diseases, such as mad cow disease, making it more likely to spread to people who eat venison — if it jumps to humans.

Researchers estimate that 7,000 to 15,000 infected animals are unwittingly eaten by hunting families, a number that grows each year as it spreads across the continent. Although wild game testing for CWD is available, it is cumbersome and the tests are not widely used in many places.

A major problem in determining whether CWD has affected humans is that it has a long latency. People who consume prions may not develop the disease until many years later – so, if someone does get sick, there may not be an apparent connection to eating deer.

Prions are extremely persistent in the environment. They can remain in the soil for many years and can even be taken up by plants.

Because the most likely route of spillover is through people who eat deer meat, rapid testing of deer and other cervid carcasses is where resistance is concentrated. Right now, a hunter can take a deer to a check station and a lymph node sample can be sent to a lab. It can take a week or more to get results, so most hunters skip it.

For example, Montana is famous for its deer hunting. CWD was first detected in the wild there in 2017 and has now spread across much of the state. Despite the warnings and free testing, Montana wildlife officials haven’t seen much concern among hunters. “We haven’t seen a reduction in deer hunting because of this,” said Brian Wakeling, game management bureau chief for the Montana Department of Fish, Wildlife and Parks. Montana hunters killed about 88,000 deer in 2022. Only 5,941 samples were taken and of these, 253 tested positive.

Experts believe that a rapid test would greatly increase the number of animals tested and help prevent spillover.

Because of the deer’s importance to Native Americans, several tribal nations in Minnesota are working with University of Minnesota experts on ways to monitor and manage the disease. “The threat and potential for the spread of CWD on any of our three reservations has the potential to negatively impact the Ojibwe’s culture and deer hunting tradition by providing deer meat to our membership,” said Doug McArthur, tribal biologist for the White Earth Nation. A statement announcing the program. (Other groups mentioned are the Leech Lake Band of the Ojibwe and the Red Lake Band of the Chippewa.) “Tribes must prepare plans to manage and mitigate the effects of CWD… to ensure time-honored and culturally significant harvesting practices. Deer are maintained for future generations.”

Peter Larsen is an assistant professor at the University of Minnesota College of Veterinary Medicine and co-director of the Minnesota Center for Prion Research and Outreach. The center was formed to study numerous aspects of prions as part of a push to move forward from potential spillovers. “Our goal is to learn everything we can about not only CWD, but other life-threatening diseases, including Parkinson’s and Alzheimer’s disease,” he said. “We are studying the biology and ecology” of misfolded proteins, he said. “How do prions move in the environment? How can we help reduce risk and improve animal health and welfare?”

Part of that mission is new technology to make testing faster and easier. Researchers have developed a way for hunters to conduct their own tests, although it can take weeks to get results. There is hope, within the next two years, of a test that will reduce waiting times to three to four hours.

“With all the doom and gloom surrounding CWD, we have real solutions that can help us fight this disease in new ways,” Larsen said. “There is some optimism.”

Kaiser Health NewsReprinted from this article khn.orgA national newsroom that produces in-depth journalism about health issues and is one of KFF’s core operating programs – the independent source for health policy research, polling and journalism.

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