Across North America, deer and elk are increasingly suffering from a devastating illness. They stumble, drool, and appear visibly emaciated. They lose their fear of humans, staring blankly as if their senses have abandoned them. This grim affliction, known colloquially as “zombie deer disease,” has experts deeply concerned — not just for wildlife, but potentially for human health as well.

Officially termed chronic wasting disease (CWD), the condition is neither a virus nor a bacterium. It’s but a prion disease; and if you’re not terrified of prions, you probably don’t know enough about them.

A ticking time bomb

Prions are infectious proteins that cause the body’s normal proteins to misfold, leading to severe neurological damage and eventual death. Prion diseases, also known as transmissible spongiform encephalopathies (TSEs), can affect both animals and humans. In humans, these diseases include Creutzfeldt-Jakob disease (CJD), which often appears spontaneously without a known cause, and variant Creutzfeldt-Jakob disease (vCJD), which emerged during the “mad cow disease” epidemic when people consumed contaminated beef.

Despite decades of research, prion diseases remain incurable and fatal. We have no idea how to fight back against them. Their unique biology poses enormous challenges for public health officials and scientists. This also makes it hard to assess the risk of them jumping to other species, including humans.

So, since CWD is spreading, researchers are understandably worried.

First identified in captive mule deer in Colorado in 1967, CWD has silently spread among deer, elk, and moose populations across North America.

Now, the disease may be reaching a dangerous critical point.

What began quietly over half a century ago has now exploded into a full-blown wildlife epidemic. By early 2025, the disease had been documented in wild and domestic herds across 36 U.S. states and several Canadian provinces. This spread to faraway places like Finland, Norway, and Sweden, and even in farmed animals in South Korea. In some places, infection rates among local deer populations are staggering. In southern Saskatchewan, for example, nearly 80% of male mule deer now carry CWD.

Why this disease is spreading

The first problem is that prions are remarkably durable. They’re not living entities, so they don’t really need to do anything to endure. Shed through bodily fluids — saliva, urine, feces — these prions persist in soils for years. They contaminate plants and water sources, creating invisible reservoirs of infection. Wildlife officials struggle to manage the disease, particularly as animals congregate at artificial feeding sites established by humans, which makes it easier to pass the disease from one animal to another.

In Wyoming, where elk gather by the thousands at winter feedgrounds, warnings from scientists like conservationist Lloyd Dorsey have gone unheeded. “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. Now, experts fear, the situation has reached a critical point and places like Wyoming have set up a perfect storm that can allow CWD to explode.

As infected deer roam further and wider, hunters across the United States unknowingly harvest infected animals, consuming the contaminated venison and sharing it with their communities. The Centers for Disease Control and Prevention (CDC) advises hunters to test deer from infected areas, but compliance remains low. Simply put, hunters don’t seem to listen to the warnings. To make matters even worse, CDC “disease detectors” were among the first to be fired by the Trump administration.

Could humans be next?

No confirmed cases of humans contracting CWD have yet been documented, but it’s a looming threat. The more we let diseases like this roam free, the more we risk an unwanted jump to humans.

In January 2025, a chilling report from the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota warned of an impending global crisis if CWD were to spill over to humans. Authored by a panel of 67 leading scientists and health experts, the report concludes the United States — and indeed the world — is woefully unprepared for such an event.

“Despite this, no contingency plans exist at a national or international level to address the possibility of spillover, which would trigger a national and global crisis.”

The report essentially piles on one bit of bad news after another.

“Currently, CWD management is in the domain of wildlife agencies. With no vaccine or treatment available, CWD management focuses on mitigating disease spread. Thus, CWD is likely to become endemic in more areas over time as the agent is introduced to new areas where cervids are present. Because cervids are widespread on every continent except Antarctica, CWD poses a significant global threat.”

The immediate concern is the disease jumping to a farm animal species. If that were to happen, we don’t even have a way to detect the disease.

“No single test can identify CWD transmission to a non-cervid species, clearly presenting a major diagnostic challenge. In theory, a combination of existing tests could be used, but data are not available on whether they could differentiate BSE or scrapie from CWD in
a novel animal host.”

Historical precedents for prion spillover do exist. In the 1980s and 1990s, the United Kingdom witnessed mad cow disease (bovine spongiform encephalopathy, BSE) jump to humans through contaminated beef, resulting in the fatal variant Creutzfeldt-Jakob Disease (vCJD).

“There is a risk of CWD spillover to other wildlife, non-cervid production animals, and humans. The risk of CWD spillover is not static and may be increasing as new strains emerge and exposure probabilities increase.”

“There is a pressing need to better understand evolving CWD prion strain characteristics and associated spillover risk,” the CIDRAP report concludes.

We urgently need to be prepared

We’re already seeing some concerning human cases. Two hunters in Texas who frequently consumed deer meat from a CWD-infected region died from Creutzfeldt-Jakob Disease (CJD). And, while a direct link to CWD wasn’t proven, this is a plausible connection.

“Physician recognition of prion diseases is limited because these illnesses are rare and have symptoms that overlap with other neurodegenerative diseases,” CIDRAP experts wrote. They recommend expanding surveillance programs, enhancing physician awareness, and establishing clear public health guidelines.

Amira Roess, an epidemiologist at George Mason University, underscores the importance of caution, especially among hunters. “Fortunately, the risk of prion disease from deer appears low if humans limit their contact with deer, especially their blood and nervous tissue. But this means that we must be very careful and vigilant,” she explains.

Scientists agree there’s still a window of opportunity to prevent a human outbreak, but time is running short. Better coordination between wildlife management, public health agencies, and scientists is urgently needed. CIDRAP’s extensive report calls for immediate action: comprehensive surveillance, sustained research, and rigorous public outreach to educate hunters and consumers.