Chronic wasting disease (CWD), often referred to as "zombie deer disease," has been steadily spreading through deer populations across North America for decades. This fatal neurological disease, a prion-based affliction similar to mad cow disease, causes infected animals to waste away, lose coordination, and display eerie, zombie-like symptoms. But could this deadly disease one day make the jump to humans?
While no human cases of CWD have been confirmed to date, growing concerns over its spread — and its potential to mutate — are drawing serious attention. Here’s what we know so far about CWD, how it spreads, and whether it poses a threat to human health.
What Is Zombie Deer Disease?
Chronic wasting disease is a prion disease — a rare, neurodegenerative disorder caused by misfolded proteins, called prions, that damage brain tissue. It affects members of the deer family (Cervidae), including deer, elk, and moose, and it’s always fatal. Animals infected with CWD eventually display symptoms such as severe weight loss, lack of coordination, teeth-grinding, drooling, and confusion, giving them an almost zombie-like appearance.
First identified in captive deer at a Colorado research facility in 1967, CWD wasn’t identified in wild deer until 1981. It has since been detected in 35 U.S. states, four Canadian provinces, and parts of South Korea and Europe, further raising concerns about its potential to infect other species — including humans.
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Symptoms of Chronic Wasting Disease in Deer
CWD symptoms often develop slowly, making the disease difficult, though not impossible, to detect in its early stages. Initially, infected deer may show no visible signs of illness, allowing them to continue spreading the disease undetected. Over time, though, the symptoms usually become unmistakable: staggering, confusion, walking in patterns, extreme weight loss, and an unusual lack of fear toward humans. CWD typically kills infected deer within two years of being infected, though larger animals like elk tend to survive 6 to 12 months longer.
Because CWD can remain dormant for long periods, infected animals can unknowingly shed prions through their saliva, urine, feces, and even decaying carcasses. These prions can linger in the environment for years, contaminating soil and water sources and spreading the disease to new animals.
What Causes Chronic Wasting Disease?
CWD is caused by infectious proteins called prions. Prions are unique in that they don’t contain DNA or RNA, unlike bacteria or viruses. Instead, they are misfolded proteins that cause other proteins in the brain to likewise misfold, ultimately leading to brain damage. Once these proteins accumulate in the brain, they create spongy holes in the tissue, resulting in severe neurological dysfunction.
Prions are also virtually indestructible. They resist extreme heat, radiation, and most sterilization techniques, which makes them highly infectious in environments. They spread through saliva, urine, feces, and even decaying carcasses of infected animals. Once prions are in the soil or water, they can remain infectious for years or possibly decades. And as more deer contract the disease, the likelihood of environmental contamination increases, posing an increased threat to other animal populations in the area.
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Can Humans Get Chronic Wasting Disease?
So far, there has been no confirmed case of CWD transmission to humans. However, experts remain cautious. A similar prion disease, bovine spongiform encephalopathy (BSE), or mad cow disease, was once thought unlikely to infect humans. That is, until it did, causing many to die of an always fatal condition called variant Creutzfeldt-Jakob disease (vCJD). Since mad cow disease was first seen in 1995, more than 140 people worldwide have died from vCJD as the result of consuming contaminated beef.
Despite the lack of human cases of CWD, laboratory studies may provide some cause for concern. Research has shown that CWD prions can be transmitted to some non-human primates, namely the squirrel monkey. In another study, genetically modified mice that carried human genes also developed CWD. At minimum, this suggests that further research on the topic of CWD is warranted.
To minimize risk, the Centers for Disease Control and Prevention (CDC) advises hunters in CWD-positive regions to test their game before consuming it. The CDC also recommends avoiding the consumption of meat from animals that test positive for CWD, especially the brain, spinal cord, and other nervous tissue where prions are most concentrated.
While there is currently no direct evidence that CWD can infect humans, scientists are keeping a close eye on its potential to mutate. Some researchers fear that as CWD spreads across wildlife populations, the increased number of infected animals could heighten the chances of a species jump. However, a recent NIH study found it unlikely that CWD will make the jump to humans.
Unfortunately, prion diseases are notoriously difficult to study and diagnose because of their long incubation periods — sometimes taking years or even decades before symptoms appear. But if CWD were to cross the species barrier, it could manifest in humans as a condition similar to variant Creutzfeldt-Jakob disease, causing brain degeneration, memory loss, motor dysfunction, and, ultimately, death.
Preventing Chronic Wasting Disease
Public health and wildlife agencies are taking the threat of CWD seriously, particularly in regions where the disease is most prevalent. The CDC and state wildlife agencies in regions affected by CWD are working to monitor and slow the spread of the disease through both surveillance and testing. In some areas, there are guidelines or even strict bans on moving carcasses out of infected zones, and certain states require mandatory testing of hunted deer.
For hunters that may contact an animal potentially infected with CWD, the CDC recommends precautions such as wearing gloves when handling carcasses, properly disposing of remains, and avoiding consumption of high-risk parts like the brain and spinal cord.
For now, the risk of zombie deer disease jumping to humans is hypothetical. But as with any potential emerging disease, staying vigilant is key. That’s why hunters, wildlife managers, and scientists will continue to work together to monitor CWD’s spread, as well as ensure that appropriate precautions are in place to protect both animals and people alike.
Just remember, until we know more about CWD, testing potentially infected meat and staying informed are your two best defenses against this growing wildlife epidemic.
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Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
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Jake Parks is a freelance writer and editor who specializes in covering science news. He has previously written for Astronomy magazine, Discover Magazine, The Ohio State University, the University of Wisconsin-Madison, and more.
