Scientific abstract scrutinizes two human deaths, but there’s no evidence CWD has jumped species barrier

I would wager that every deer hunter or reader of Outdoor News has heard of chronic wasting disease. Two obvious concerns about this always-fatal disease in deer and elk are:

1) Will it drastically reduce deer numbers? And 2) Can humans get a similar disease from eating infected venison?

Natural resources departments have devoted many hours and dollars to managing CWD in deer populations, but viral mass media reports last week regarding a scientific abstract placed new scrutiny on the worrisome Question No. 2.

The journal Neurology published the short abstract on April 9, 2024, by Jonathan Trout and colleagues from the University of Texas San Antonio Long School of Medicine entitled, “Two Hunters from the Same Lodge Afflicted with Sporadic CJD: Is Chronic Wasting Disease to Blame?”

Stories about the research blew up on viral news websites like The Daily Mail, and a syndicated version from Yahoo appeared on social media feeds across the country.

Skepticism of the rush to claim that zombie deer were infecting people immediately erupted within the scientific community. The National Deer Association issued a response last Thursday with the following headline, “NDA Urges Deer Hunters to Consider New CWD Report with Caution,” and calling the online Neurology report “sketchy.”

“Nothing about this new report changes current knowledge or guidance on CWD in deer. The evidence remains strong that CWD in deer and elk is not causing disease among hunters who consume infected animals. Because scientific certainty is not 100%, and prion diseases are still not fully understood, experts continue to recommend CWD testing of all deer harvested in known CWD areas, and avoiding consumption of CWD-positive venison to minimize risk.”

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Also, deer biologist and wildlife science coordinator for the Arizona Game and Fish Department, Jim Heffelfinger, wrote in an Instagram post last Thursday (his handle is cervidnut): “This is not a study and this is not a scientific paper. The whole thing is only 344 words and is simply a mention about two hunters that died of (Creutzfeldt-Jakob disease) and both of them ate deer from the same deer population. There is no evidence of CWD infecting hunters.”

But to be clear, the piece in question is an abstract; it was never billed as a peer-reviewed scientific paper, the gold standard in science.

So, the guilt here is in the media taking the information presented in the abstract at face value and treating it like a major research publication. It is not. An abstract should be considered as merely suggestive, not something definitive.

A CWD quick recap

CWD was first noticed in the mid-1960s in Colorado in captive mule deer that were penned with sheep. The disease has spread to at least 32 states and several Canadian provinces and has been the reason for bans on supplemental feeding.

It is part of a family of neurodegenerative diseases termed transmissible spongiform encephalopathies. TSEs include mad cow disease (technically bovine spongiform encephalopathy, or BSE), scrapie, and variant Creutzfeldt-Jakob disease (in humans), among others.

Basically, a naturally occurring protein, a prion, undergoes a change in its shape and becomes an infectious prion, and builds up by contact between infectious and normal proteins, eventually clogging the central nervous system and resulting in death.

Sporadic CJD, or Creutzfeldt Jakob disease, is a human equivalent of CWD. Unlike vCJD (the v stands for “variant”) that seems to come from eating beef with mad cow disease, sporadic CJD is thought to be generated from within the body, rather than obtained from an outside source (like infected beef).

Sporadic CJD is thought to occur naturally at a rate of about 1 per one million people worldwide, and the mean age at onset is 62. It’s a fatal disease, like CWD. But it could be triggered by eating a deer with CWD, at least in theory.

The Neurology report

Trout and colleagues report that in 2022, a 72-year-old man who frequently consumed venison from a deer herd with CWD developed symptoms consistent with sporadic CJD (rapid-on-set confusion and aggression), and rapidly went downhill, dying within a month of symptom onset.

An autopsy confirmed that he died of CJD. A friend of the deceased also died from CJD and was a frequent consumer of deer from the same population. The study does not identify where the deer that the hunters consumed were harvested. But these observations motivated Trout and colleagues to call attention to these cases given the potentially implications.

The authors wrote, “Although causation remains unproven, this cluster emphasizes the need for further investigation into the potential risks of consuming CWD-infected deer and its implications for public health.” It’s not clear that two is a cluster.

That is, people get CJD who have not consumed venison. We have a correlation, which, as we always say, doesn’t prove causation. There was a similar instance a few years ago in Wisconsin, where three hunters contacted a TSE and were frequent consumers of venison, but disease transfer from contaminated venison was ruled out.

Given the millions of deer that have been eaten, including many from CWD zones, and the few cases of CJD in venison consumers, it is possible that these isolated instances are just correlations – that is, these people unfortunately would have died from CJD whether or not they ate venison.

I hate to say time will tell, but given the potentially long incubation of TSEs (like vCJD from beef) before disease expression, it’s a fair statement as to what we know. It is also worth noting that only recently have we seen the frequency of CWD-positive deer get very high and only in some areas, so possibly exposure to infected deer is too recent to have led to many cases of a TSE in people.

It is unlikely that the deceased hunters ate deer that were obviously in the late near-death stages of CWD, when clinical signs are obvious – staggering, emaciated condition, drooling, no fear, etc. It’s more likely that if they did get sporadic CJD from deer – a big if here – they got it from deer that were CWD-positive but not far enough along in the course of infection to show the outward signs of the disease.

There has been other research on this topic. In a story for NDA last July, the group’s chief communication officer, Lindsay Thomas, wrote about data presented by Dr. Joe Abrams of the Centers for Disease Control in Atlanta. Speaking at the 4th International CWD Symposium held in Denver last summer, Abrams presented preliminary data from a survey of hunters in some of the oldest CWD outbreak areas in wild deer and/or elk in Colorado, Wyoming and Wisconsin.

The Colorado and Wyoming studies reviewed data went back 30 years and examined records for over 2 million hunters, including hundreds of thousands who hunted in CWD endemic areas. It is likely that over decades many thousands of these hunters knowingly or unknowingly ate venison from CWD-positive animals that were not showing outward signs of the disease.

NDA has a long story on Abrams’ study, but the overall results did not show hunters in those areas dying at higher rates of prion diseases than the general population.

We should be clear here too, that the NDA story profiles a talk at a conference, not a peer-reviewed scientific paper, which suggests caution in accepting its conclusions.

If we find more clustered cases of sporadic CJD in zones where deer have CWD and been eaten by those dying of CJD, it becomes likely that some outside influence is at work – there could be some thing in the water, or more likely, in the deer. It’s worth remaining vigilant.

Lindsay Thomas will join Outdoor News Managing Editor Rob Drieslein for an interview about this topic on this weekend’s Outdoor News Radio show and podcast.