Here's What Experts Say About 'Zombie Deer Disease'

Chronic wasting disease, coined 'zombie deer disease' by some, is spreading among deer in the United States — triggering fears that it may eventually infect humans.

Chronic wasting disease (CWD) is a disorder that affects cervids, AKA deer, elk, reindeer, sika deer, and moose. It's caused by pathogenic agents called prions that induce abnormal folding of prion proteins in the brain. The disease is similar to other prion diseases, such as scrapie in sheep and mad cow disease in cattle.

An infected deer typically develops neurological symptoms as the disease destroys the animal's brain. These include weight loss (wasting), listlessness, and stumbling.

CWD is always fatal, and there are no vaccines to prevent the disease or cures that eliminate it once the animal is infected.

Still, deer and other cervids do not turn into 'zombies' when infected with CWD, and unlike mad cow disease, there have been no cases of CWD reported among humans.

However, recently, CWD data released by the National Wildlife Health Center set off alarms among news outlets and the public, resulting in sensational headlines warning the "zombie" disease may spread to people.

What the data shows

Overall, CWD has been detected in 32 states and four Canadian provinces in both free-ranging wild cervids and captive animals, such as deer housed in deer farms. Moreover, the numbers indicate that CWD has spread to places not known for the disease.

Bryan J. Richards, Emerging Disease Coordinator at the USGS National Wildlife Health Center, tells Healthnews, "The most recent geographic expansion includes detections in British Columbia, Canada, and the data I collate shows 44 'new' counties in the U.S. with their first detections in the 2023 sampling period — which for some states is not quite completed yet as they sample based on biological periods."

CWD Distribution: Image Courtesy of National Wildlife Health Center
CWD Distribution: Image Courtesy of National Wildlife Health Center

Can chronic wasting disease infect humans?

Prion diseases that have had spillover events from animals to humans include bovine spongiform encephalopathy (BSE) or mad cow disease. In the mid-1990s, people in the United Kingdom became infected with a version of the disease called the new variant Creutzfeldt-Jakob disease (nvCJD) from eating beef contaminated with nervous system tissue from infected cattle. Over 200 people were infected, and all died.

This is why the spread of CWD among deer has people worried about whether it has the potential to crossover to humans. But is CWD an actual risk for humans?

According to epidemiologist Michael T. Osterholm, Ph.D., Regents Professor, McKnight Presidential Endowed Chair in Public Health, and the director of the University of Minnesota's Center for Infectious Disease Research and Policy (CIDRAP), while there currently is no evidence of CWD transmission to humans, the true zoonotic potential is unknown.

Currently, the University's Infectious Disease Research and Policy is studying the possibility of CWD spreading to cows, pigs, and humans.

"Epidemiologic studies considering contact with CWD and human prion disease have not yet identified an association between this exposure and outcome," Osterholm tells Healthnews.

He says that scientists use animal models such as transgenic mice and non-human primates to replace humans when studying CWD. The results from these studies have been mixed, with several reporting cases where CWD spilled over to animal models, while others found no evidence of transmission.

Still, these studies also had limitations that further complicate the interpretation of results.

"When assessing the latest scientific publications on this topic, there is not sufficient evidence to confidently conclude 'yes' or 'no' to the question of CWD breaching the species barrier," Osterholm explains. "Nevertheless, given the continued spread of the disease among cervids, propagation of novel CWD prion strains, and increasing levels of human exposure to the CWD prion agent, we are in uncharted territory."

If it were to happen, Osterholm says it would likely transmit through consuming the meat from a CWD-infected animal.

"Unlike BSE, where prions were largely confined to the central nervous system tissues of infected cattle, CWD prions can be widely distributed throughout the body of an infected cervid — including the skeletal muscle," Osterholm notes.

According to Richards, there is no evidence that CWD has crossed over into a human host. Still, there is an increasing amount of human exposure via consumption of venison from either known positive deer or untested deer.

In a recent human dimensions report conducted by the Wisconsin Department of Natural Resources, the most common response of hunters when informed that their deer tested positive was that they were going to consume it anyway.

Richards

The impact on deer hunters

With so many unknowns about whether CWD could eventually be transmitted to humans, are avid hunters and people who consume cervid meat, AKA venison, concerned?

Gregg Walker, publisher of The Lakeland Times and The Northwoods River News, two newspapers in Northern Wisconsin, has been an avid deer hunter for 43 years. Walker founded the Northwoods Youth Deer Hunt Challenge — an event to foster young hunters — and currently sits on Oneida County's County Deer Advisory Council (CDA).

On three occasions, Walker testified about deer management issues before the Natural Resource Committees for the Wisconsin State Senate and Assembly.

Walker tells Healthnews that he hunts in CWD areas, consumes venison, and is not concerned about acquiring the disease from deer.

However, he does have concerns about how state officials are managing CWD in Wisconsin.

"I'm not 100% convinced that the management plan the Department of Natural Resources (DNR) is putting forth on CWD makes a whole lot of sense from a deer management perspective," Walker says.

Walker explains that to keep the spread of CWD low, the state will eliminate a significant number of deer when one tests positive in the area.

"When you look across the Midwest and to the West, you have states that have dealt with CWD for decades long before it became an issue in Wisconsin, and it seems to be a little different than we treat it here, where we just go in and massacre deer," Walker says. "The whole management plan from when they started to what it is today doesn't show any real results."

In his most recent testimony, Walker says statistics showed that 70 to 80% of deer hunters in Wisconsin do not trust the DNR.

"It's not all related to CWD, but it's the way the DNR has enacted and managed it that has raised concerns," Walker says.

Are chronic wasting disease numbers accurate?

Mistrust of how government agencies handle CWD was brought to the forefront in a 2023 lawsuit filed by James Kelly against the State of Tennessee, the Tennessee Wildlife Resources Agency (TWRA), and its Executive Director, Jason Maxedon. The suit alleges that the TWRA intentionally mishandled testing data.

According to a news report, Kelly, a wildlife biologist who led the TWRA's deer management program, claims the Agency fired him in 2022 after he questioned its CWD testing practices.

Kelly says state officials manipulated data and misled the public about the prevalence of CWD, resulting in overinflated numbers in several Tennessee counties.

The lawsuit has been moved from federal to state court.

Still, Richards says CWD rates among cervids are likely higher than the data shows.

"In the State of Wisconsin alone, there have been in excess of 1,000 positive hunter-harvested (wild) deer in each of the last five years, with the number exceeding 1,500 in 2023. Plus, in the highest prevalence areas of the state, typically less than 25% of the harvested deer are sampled (sampling is voluntary) so [the] true number of positives is likely substantially higher," Richards explains.

How to protect against chronic wasting disease

Venison, or deer, elk, and moose meat, is a leaner and lower-calorie alternative to beef. It's sometimes considered an ideal option for people with heart disease who want a low-cholesterol protein choice.

Still, with the unknowns surrounding CWD, what can people do to protect themselves?

Osterholm tells Healthnews, "The best way to protect yourself and your family is by getting your deer tested for CWD — particularly if it's in an area where the disease has already been detected — and not consuming the meat if a test comes back positive."

Richards notes that both the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) recommend that humans not consume tissues from any animal known to be positive for any Transmissible Spongiform Encephalopathy (TSE) prion disease, including CWD.

According to the Wisconsin Department of Resources, options for testing in that state include:

  • Self-service kiosks with kits for sampling.
  • Bringing the deer to a meat processor who can collect samples.
  • Obtaining at-home lymph node sampling kits.
  • Making an appointment for testing with local DNR staff.

Bottom line

While the latest data suggests that CWD is spreading throughout cervid populations in North America, it has not been transmitted to humans. Moreover, it is not a disease that turns infected animals into "zombies."

In the unlikely event that it does jump species and infects humans, people can avoid contracting the disease by having the deer tested and not eating infected meat.

Key takeaways:


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