Why Experts Say "Zombie Deer" Disease Can Spread Chronic Wasting to Humans

 "It's possible the number of human cases will be substantial." 

A few months ago, the “zombie deer disease” was largely the concern of deer hunters, deer activists, and anyone generally attuned to weird zombie-like diseases that abound in nature. But now, the disease is present in deer in 24 states and two Canadian provinces, and experts are warning it may be transmissible to humans — a potential risk that is too pressing to ignore.

The “zombie deer disease” is actually called “chronic wasting disease (CWD).” Though it doesn’t actually cause any outward zombification (rotting flesh, an urge to attack the living, etc), it causes the brain of an infected deer to waste away, taking on a spongy appearance that is always fatal. As a result, the deer rapidly lose weight, lose their coordination, and become aggressive — in other words, appear zombie-like.

As of now, there have been no recorded cases of CWD in humans. But in a meeting before Minnesota lawmakers on February 7, Michael Osterholm, Ph.D., director of the Center for Infectious Disease Research and Policy at the University of Minnesota, warned that we can’t rule out the possibility that we won’t see those cases in the future.

“It is probable that human cases of chronic wasting disease associated with consumption with contaminated meat will be documented in the years ahead,” said Osterholm. “It’s possible the number of human cases will be substantial, and will not be isolated events.”

chronic wasting disease deer
CWD is always fatal in deer and can also infect moose and elk. 

How CWD Might be Transmitted to Humans

The reason scientists like Osterholm are concerned is because CWD belongs to a class of diseases called transmissible spongiform encephalopathies (TSEs) or prion diseases. Normally, proteins in the brain are programmed to fold themselves into standard patterns. In these deer, the proteins in their brains are misfolded, which causes the dangerous and deadly effects of CWD. These proteins are misfolded because of the presence of other proteins in the brain called prions, which can cause otherwise healthy proteins to fold incorrectly.

During the presentation in Minnesota, Trevor Ames, DVM, and dean of the University of Minnesota’s college of Veterinary Medicine, noted that CWD-causing prions have been found in the saliva, urine, and feces of infected deer, but importantly, they’re also present in their organs and muscle tissue — parts that people might eat. Citing the Alliance for Public Wildlife’s 2017 report, Osterholm noted that humans eat between 7,000 and 15,000 deer with these CWD infections each year, putting them at risk for developing a similar disease.

CWD’s Link to Mad Cow Disease

As of now, scientists don’t know whether the prions that cause CWD in deer have a similar spongifying effect on human brains. They do know, however, about the history of prion diseases making the jump from animals to humans because of contaminated meat consumption. “Mad cow disease,” which infects cows, is also caused by prions and has been linked to the development of variant Creutzfeldt-Kakob disease in humans, a fatal condition that causes proteins to fold in strange ways in human brains. In the nineties, the spread of mad cow disease in the UK led to bans on imported British beef in the US and Europe. Nearly 4.4 million cattle were slaughtered (and not eaten) in an attempt to cull the disease before it could spread. Those cows, like the “zombie” deer, lost weight, became uncoordinated, and acted abnormally before they died.

Now, the USDA has monitoring systems in place to prevent the spread of prion diseases, and the World Health Organization warns that countries should take care to ensure that meat from animals infected with prion diseases (not just deer but cows and sheep, which have their own prion-based diseases) doesn’t end up in the food chain, where it may infect humans.

As far as CWD goes, we don’t know whether it can wreak havoc on humans, but Ames noted research suggesting it might. “It is not known if people can get infected with the disease. But there is some experimental evidence that has shown evidence of CWD prion transmission to primates and human cell lines, which raises concern,” Ames said at the meeting.

A lot of unanswered questions about zombie deer disease remain, but for now, the historical precedent set by mad cow disease and other prion diseases has prompted the CDC to warn people to steer clear of deer meat from infected animals.