“Zombie deer disease.” Gimme a break. One of the tackier headlines of all time. That said, Chronic Wasting Disease is real, and the possibility of CWD in humans may be getting closer to real.
I’ve been following the research on Chronic Wasting Disease (CWD) for many years, mostly as it pertains to CWD in humans. Given all the misinformation out there, I thought it time for a calmer voice. What follows below is what we know about CWD, and other similar ailments, as of September 2022.
Keep in mind I am not writing about CWD as it affects deer and other cervids, I am writing about how it may or may not affect humans eating venison. This is a cooking website, after all.
OK, number one thing you need to know is this: CWD has never been shown to affect human beings.
Chronic Wasting Disease has been known to science for more than 50 years, and millions and millions of pounds of deer meat has been eaten by millions and millions of people, and there has not been one verifiable case of CWD in humans. Not one.
Chronic Wasting Disease does indeed affect cervids, however. What’s a cervid? Anything with antlers. Keep in mind that pronghorns are not cervids, nor are bison or real antelope like oryx, nilgai or blackbucks — they are all bovids, like cattle. We’ll get to them in a moment.
So why are people flipping out about CWD in humans? Other than the fact that it is affecting the local deer herds in 30 states plus five Canadian provinces, there is a fear that it might somehow jump to humans.
Side note: When I first wrote this article in March 2019, it was only 25 states and 2 provinces, so Chronic Wasting Disease is spreading fast.
What is Chronic Wasting Disease?
Chronic Wasting Disease is believed to be caused by a prion. A prion is a misfolded, self-replicating protein that, when it does self-replicate, can massively mess up your brain.
Here’s a good explanation from a 2016 Nature article: “The protein can adopt malformed shapes that cause disease. Those proteins, which are resistant to degradation, bind and convert normal protein to their troublesome conformation. Over time, the diseased protein builds up and forms fibrils in the brain, causing neurodegeneration and ultimately death.” No bueno.
This sort of cellular mayhem happens to occur naturally in many animals: cattle, sheep, cats, minks, cervids, and yes, humans. Human prion diseases include fatal insomnia; kuru; Gerstmann-Straussler-Scheinker syndrome; as well as variant, hereditary and sporadic Creutzfeldt Jakob disease (CJD). Sporadic CJD is the most common human prion disease; your chances of getting it are about one in a million.
Incidentally, it’s generally not a good idea to eat human brains, as doing so is a cause of another prion disease known as kuru, so called for the illness’ name among a group of brain-eating cannibals in New Guinea, who are the only known people to have ever contracted it.
Mad Cow Disease
It’s BSE that has everyone jumpy. Of all the various prion ailments, BSE is the only one to have ever jumped the species barrier in real life. Some scientists think mad cow developed from scrapie, after cows ate scrapie-infected bone meal made from sheep bits. It was first detected in 1984 in the UK. This feeding practice was banned in 1988 – before the first human detection of the disease.
Somehow BSE jumped from cows to humans in Britain about 30 years ago, causing a new variant of CJD, contracted by eating infected meat. Fascinatingly, everyone who got vCJD from mad cow had the same genetic marker – although 40% of Caucasians happen to have that marker. (I could not find data on its prevalence among non-white people. A bit of scientific bigotry, there…) And almost all cases were young adults, most of whom showed symptoms by age 28.
All told, this new vCJD has thus far killed 232 humans. The peak of the “epidemic” was 31 cases in 1999 in the European Union, and there have been only 3 cases in the EU from 2010 to 2014. Keep in mind that millions of Britons were exposed to infected beef before it was all incinerated 20 years ago.
There have been 6 cases of BSE in cows in the US, the last in Florida in 2018. There have been only 4 human cases in the US, the last a Texas man in 2014.
Let me say this one more time: BSE is the only known prion illness to have jumped the species barrier in real life, and even then it affected a tiny number of people who fit a specific subset of the population.
Yes, I know, I wouldn’t want to be one of the unlucky few, either. But I just want to put all this in perspective.
CWD in Humans?
Still, you have the World Health Organization issuing a warning about Chronic Wasting Disease, not to mention local and national health institutes of both the United States and Canada. Why? In a word, uncertainty.
We’ve been eating scrapie-infected lamb and mutton for thousands of years, but no one has ever contracted scrapie. And a variant of BSE has been around probably forever; the Romans wrote about it. So what caused it to jump to humans? We’re still not sure.
Science has its full attention on this issue, and new data is emerging constantly. Scientists have done studies on how to detect a prion illness, how to cure it, what are the mechanisms for transmission both within a species and across species. There’s even one researcher who is convinced that prions aren’t the cause, but rather a bacteria. He’s been following this line of research since 1979, but so far he remains an outlier in CWD research.
It’s this fluidity that has everyone up in arms. People want easy answers, and with CWD there aren’t any.
Latest Studies on CWD in Humans
A September 2022 study by the University of Calgary shows that there could be a mechanism for CWD in humans to exist.
“This is the first study to show that the barrier for CWD prions to infect humans is not absolute and that there is an actual risk that it can transmit to humans,” said Dr. Sabine Gilch, one of the authors of the study.
The researchers took CWD isolates from infected deer and injected them into “humanized” mouse models. Over a period of years, the mice developed CWD. The mice also were found to shed infectious prions in feces. “The implication is that CWD in humans might be contagious and transmit from person to person,” Gilch said.
Furthermore, the study showed that CWD in humans might look different from CJD, the “normal” prion disease we can get. “When we look at humans, we usually see a typical signature,” Gilch said. “And in this mouse model we did not find that signature, which means if this ever happens with humans, it will not look like the prion diseases that we know. It might be significantly different from whatever we know so far.”
All this said, the researchers stressed that this does not prove that CWD in humans exists. It just shows that there is a pathway for it to do so.
Welcome to science, folks. Nothing gets settled until lots of other scientists can reproduce someone’s results. And since most prion diseases take years to develop symptoms, it makes doing that with CWD fiendishly hard.
Another fear factor is that scientists have been able to get prion diseases to jump species barriers in the lab, often using weird, inject-it-into-your-brain methods. Hell, they even got scrapie to jump this way. The takeaway from all these experiments isn’t that you’re going to die tomorrow from CWD, it’s that there is a way, in theory, for these prions to jump from deer to humans.
How that might happen in real life is what science is working on now. It happened with BSE, turning itself to vCJD. Exactly how isn’t known.
CWD vs. Mad Cow
Well, what if Chronic Wasting Disease jumps to cattle and gets into the food supply that way? It won’t. A 2018 study done by the USDA (among others) determined that cattle, living for years among infected deer and eating lots and lots of CWD infected brain material in their feed (what the British banned back in 1988), still didn’t get it.
And according to a 2017 article in the Journal of Virology, pigs eating dead, CWD-infected deer could act as a reservoir for the illness, although they wouldn’t get it. Interestingly, they don’t get BSE or anything like it even eating lots of infected beef. Other research suggests otherwise, however, so the jury is still out on this one.
Confounding, eh? The reason could be because of how a particular animal is built. A UC-San Diego researcher named Timothy Kurt looked at what makes up the prion, that malformed protein that is the cause of all this…
“Kurt looked at the role played by the 210 amino acids in the prion protein to figure out why CWD is transmitted to some species and not others. He found that when a species had a different amino acid in a key location, the diseased prion wouldn’t fit neatly into the healthy prion, like a zipper with teeth that don’t fit together. This, Kurt believes, is CWD’s species barrier. The amino acid sequence differed between humans and deer at a key location. A different study showed that a macaque’s amino acids matched the deer sequence in the same spot, but not the human one.”
This amino acid factor is real. For a prion to transfer across species, the “zipper” has to fit right. You can shoehorn it in the lab, but in natural conditions it won’t do it. The real fear is mutation.
Like scrapie, CWD could be an illness we could live alongside for millennia with no problems. Or, it could be like mad cow. We just don’t know.
Why You Should Care
So what does that all mean to you, the eater of venison?
Sadly, I can’t tell you what to do.
All data shows that you have nothing to fear from CWD. But the long incubation period of prion illnesses, the fact that CWD has been shown to mutate within deer populations, and the fact that BSE did somehow jump the species barrier all suggest caution on our part. In short, no one has gotten Chronic Wasting Disease, but no one wants to be Patient Zero, either.
And my old advice from seven years ago, that the prions, if present, would largely be in the spine and bones, is no longer accurate. Scientists recently have found CWD prions throughout the bodies of infected deer.
As scientist Sandra Pritzkow puts in in a 2022 article on the potential for CWD in humans: “The zoonotic potential of CWD remains a dangerous enigma.”
As of now, it looks like the safest course would be to get your deer tested for CWD if you are in a region where it is known to exist. Keep in mind that in most places where it does exist, CWD is still uncommon. There are a few places in Canada, Wisconsin, Nebraska, Colorado and Wyoming where the prevalence is high, however.
If your deer tests positive, it’s your call on eating it. Data says you’re fine. But you have to be comfortable with eating the animal. I am honestly not sure if I would or not, but I am leaning toward no.
Here is a map of where Chronic Wasting Disease has been found, both in wild and captive deer populations.
If you hunt deer in Colorado, here is how to get your deer tested.
Wyoming CWD testing information.
Utah CWD check stations and other data.
Minnesota test results by county.
Information and testing options for CWD in Illinois.
Data on CWD in New Mexico.
Virginia testing for CWD.
Maryland CWD information.
How to get your deer tested in Arkansas.
Tennessee CWD information and testing results.
Getting your deer tested in Missouri.