In a scattershot pattern that now extends from coast to coast, continental US states have been announcing new hotspots of chronic wasting disease (CWD).
The contagious and always-fatal neurodegenerative disorder infects the cervid family that includes deer, elk, moose and, in higher latitudes, reindeer. There is no vaccine or treatment.
Described by scientists as a “slow-motion disaster in the making”, the infection’s presence in the wild began quietly, with a few free-ranging deer in Colorado and Wyoming in 1981. However, it has now reached wild and domestic game animal herds in 36 US states as well as parts of Canada, wild and domestic reindeer in Scandinavia and farmed deer and elk in South Korea.
In the media, CWD is often called “zombie deer disease” due to its symptoms, which include drooling, emaciation, disorientation, a vacant “staring” gaze and a lack of fear of people. As concerns about spillover to humans or other species grow, however, the moniker has irritated many scientists.
“It trivialises what we’re facing,” says epidemiologist Michael Osterholm. “It leaves readers with the false impression that this is nothing more than some strange fictional menace you’d find in the plot of a sci-fi film. Animals that get infected with CWD do not come back from the dead. CWD is a deathly serious public and wildlife health issue.”
Five years ago, Osterholm, the director of the Center for Infectious Disease Research and Policy at the University of Minnesota, delivered what he hoped would be a wake-up call before the Minnesota legislature, warning about “spillover” of CWD transmission from infected deer to humans eating game meat. Back then, some portrayed him as a scaremonger.
Today, as CWD spreads inexorably to more deer and elk, more people – probably tens of thousands each year – are consuming infected venison, and a growing number of scientists are echoing Osterholm’s concerns.
In January 2025, researchers published a report, Chronic Wasting Disease Spillover Preparedness and Response: Charting an Uncertain Future. A panel of 67 experts who study zoonotic diseases that can move back and forth between humans and animals concluded that spillover to humans “would trigger a national and global crisis” with “far-reaching effects on the food supply, economy, global trade and agriculture”, as well as potentially devastating effects on human health. The report concludes that the US is utterly unprepared to deal with spillover of CWD to people, and that there is no unifying international strategy to prevent CWD’s spread.
So far, there has not been a documented case of a human contracting CWD, but as with BSE (or mad cow disease) and its variant strain that killed people, long incubation times can mask the presence of disease. CWD, which is incurable, can be diagnosed only after a victim dies. Better surveillance to identify disease in people and game animals is more urgent than ever, experts say. Osterholm says the Trump administration’s proposed cuts to public health funding and research, and the US’s withdrawal from international institutions, such as the World Health Organization, could not be happening at a worse time.
The risk of a CWD spillover event is growing, the panel of experts say, and the risk is higher in states where big game hunting for the table remains a tradition. In a survey of US residents by the Centers for Disease Control and Prevention, 20% said they had hunted deer or elk, and more than 60% said they had eaten venison or elk meat.
Tens of thousands of people are probably eating contaminated game meat either because they do not think they are at risk or they are unaware of the threat. “Hunters sharing their venison with other families is a widespread practice,” Osterholm says. The Centers for Disease Control and Prevention advises people who suspect they have killed an animal infected with CWD not to eat it, and states advise any hunters taking animals from infected regions to get them tested. Many, however, do not.
The movement of meat around the country also raises concerns of environmental contamination. CWD is not caused by bacteria or a virus, but by “prions”: abnormal, transmissible pathogenic agents that are difficult to destroy. Prions have demonstrated an ability to remain activated in soils for many years, infecting animals that come in contact with contaminated areas where they have been shed via urination, defecation, saliva and decomposition when an animal dies. Analysis by the US Geological Survey has shown that numerous carcasses of hunted animals, many probably contaminated with CWD, are transported across state lines, accelerating the scope of prion dispersal.
In states where many thousands of deer and elk carcasses are disposed of, some in landfill, there is concern among epidemiologists and local public health officials that toxic waste sites for prions could be created.
Every autumn, Lloyd Dorsey has hunted elk and deer to put meat on the table, but now he is concerned about its safety. “Since CWD is now in elk and deer throughout Greater Yellowstone, the disease is on everybody’s mind,” he says. Dorsey has spent decades as a professional conservationist for the Sierra Club, based in Jackson Hole in Wyoming, and he has pressed the state and federal governments to shut down feedgrounds for deer – where cervids gather and disease can easily spread.
“Wyoming has wilfully chosen to ignore conservationists, scientists, disease experts and prominent wildlife managers who were all saying the same thing: stop the feeding,” he says.
Apart from the grave concerns about CWD reaching people, scientists describe it as “an existential threat” to wild cervid populations, which are central to American hunting traditions. Nowhere is there more at stake than in the region surrounding the country’s most famous nature preserve, Yellowstone.
A new study that tracked 1,000 adult white-tailed deer and fawns in south-west Wisconsin mirrors what research elsewhere suggests: over time infected animals die at rates that outpace natural reproduction, meaning some populations could disappear. No animals have demonstrated immunity to CWD and there is no vaccine.
If depopulating herds becomes necessary to reduce disease presence, it could have devastating consequences for people who rely on those animals and who have a connection to them.
Studies show that having healthy wild carnivores on a landscape can help weed out sick CWD-carrying elk and deer, but states in the northern Rockies have adopted policies aimed at dramatically reducing wolves, bears and mountain lions.
Other policies continue to contradict scientific advice. Wyoming has attracted national criticism for refusing to shutter nearly two dozen feedgrounds where tens of thousands of elk and deer gather in close confines every winter and are fed artificial forage to bolster their numbers.
One of the largest feedgrounds is operated by the federal government: the National Elk Refuge, where more than 8,000 elk cluster, and CWD has already been detected. Tom Roffe, former chief of animal health for the US Fish and Wildlife Service, which manages the refuge, and Bruce Smith, a former refuge senior biologist, have said Wyoming has created ripe conditions for an outbreak of the disease, with consequences that will negatively ripple throughout the region.
“This has been a slowly expanding epidemic with a growth curve playing out on a decades scale, but now we’re seeing the deepening consequences and they could be severe,” Roffe says. “Unfortunately, what’s happening with this disease was predictable and we’re living with the consequences of some decisions that were rooted in denial.”
Roffe and others say the best defence is having healthy landscapes where unnatural feeding of wildlife is unnecessary and where predators are not eliminated but allowed to carry out their role of eliminating sick animals.
“As Yellowstone has been for generations, it is the most amazing and best place to get wildlife conservation right,” Dorsey says. “It would be such a shame if we continued doing something as foolish as concentrating thousands of elk and deer, making them more vulnerable to catching and spreading this catastrophic disease, when we didn’t have to.”
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