Is deer meat safe for human consumption?
It’s a question that has taken on new life in this part of the world since chronic wasting disease (CWD) was discovered in whitetail deer in West Tennessee late last year.
While the disease — which is always fatal in deer and elk but hasn’t yet shown up in humans — is not present in East Tennessee, it is slowly creeping this direction. In fact, since it first appeared in captive mule deer in Fort Collins, Colo. in 1967, CWD has infected wild herds in 26 states and Canada. Tennessee became the 26th state when random tests of hunter-harvested deer revealed the disease in the southwest corner of the state in December. Since that time, the number of deer testing positive for CWD in West Tennessee has climbed to 91.
Michael Osterholm, director of the University of Minnesota’s Center for Infectious Disease Research & Prevention, made headlines two weeks ago when he testified to his state’s lawmakers that “it is probable that human cases of CWD associated with the consumption of contaminated meat will be documented in the years ahead. It is possible that the number of human cases will be substantial and will not be isolated events.”
Since CWD became a public health concern, it has been generally believed that it cannot make the leap to humans. That theory has been supported by some research, while other research has cast doubts. Health experts have quietly said for several years that it’s possible for CWD to infect humans. The U.S. Centers for Disease Control & Prevention (CDC) now recommends that hunters who kill a deer or elk from an area where CWD is known to be present “strongly consider” having their animal tested before eating the meat.
PRIONS & SPECIES BARRIERS
CWD is caused by prions — misfolded, infectious proteins — that accumulate in the brain and spinal column. It causes rapid cognitive decline once symptoms first appear. Rapid weight loss, a loss of fear of humans, and aggression can be symptoms. It’s sometimes referred to as a “zombie disease” because it causes deer and elk to behave like zombie animals.
CWD is one of several brain-wasting prion diseases that belong to a family known as transmissible spongiform encamphalopathies, or TSEs. There are several TSEs that are closely related — including mad cow disease in cattle, scrapie in sheep and Creutzfeldt-Jakob Disease (CJD) in humans — but it was once thought that the species barrier prevented the prion diseases from jumping from one species to another.
In fact, for several years after researchers learned in the late ‘70s that it was a prion disease that was killing captive deer and elk at several facilities in western states, it was believed that it was impossible for the disease to jump from cervids to other species.
Then, in the 1980s, mad cow disease showed up in the United Kingdom after cattle ate the bone meal of sheep that were infected with scrapie. The disease then made the jump to people through infected beef, causing a new variant of Creutzfeldt-Jakob, or vCJD.
So far, the same hasn’t happened with CWD. But officials aren’t ruling it out.
THE HUMAN CONNECTION
Creutzfeldt-Jakob Disease, the human form of the brain-wasting prion diseases, is horrifying. It starts with a decline of memory function, unexplained mood changes such as depression or anger, and progresses to include seizures and, eventually, coma and death. There is no cure, it is always fatal, and death usually occurs within six to 12 months after symptoms appear.
CJD is rare; it only occurs in about one to two people per million. Eighty-five percent of the time, it occurs sporadically, with no known cause. Its victims are usually older — the average age is 68 — who are otherwise healthy. The remaining 15 percent of cases are hereditary, caused by genetics.
The good news, for venison lovers, is that vCJD cases began to show up just a few years after mad cow disease appeared in the UK, and, even though CWD has been around many years longer than mad cow, there hasn’t been anyone infected with vCJD due to eating infected venison.
But that doesn’t mean the CDC hasn’t explored the possibility. In the 1990s, before CWD jumped the Mississippi River and came to the eastern U.S. for the first time, the CDC investigated the deaths of three deer hunters who had contracted CJD. The cases were alarming because the three hunters were less than 30 years old. The classical form of CJD typically shows up in people who are older than 60, while most of the victims of vCJD who had eaten tainted beef were in their 20s and 30s.
In the 2000s, the CDC investigated several other cases involving people who contracted CJD at a younger age, or who had other neurological symptoms that mimicked prion diseases. One case was particularly alarming: three men ate together at regular wild game feasts, then became sick and died. Two were suspected of having CJD. The third showed no signs of a prion disease, but suffered rapid neurological deterioration.
The CDC found that nearly all of the patients in those cases were hunters, or had eaten meat that someone else had hunted. But, in every case, the researchers determined that the meat the victims had eaten wasn’t from an area known to be infected with CWD, or found no biological connection between their illness and CWD.
Meanwhile, early research in lab rats determined that it was almost impossible for CWD to jump the species barrier; only rats that had prions injected directly into their brain became sick.
But that was before macaque monkeys entered the fray.
CAUSES FOR ALARM
In 2017, Canadian researchers announced that macaque monkeys in their labs had contracted CWD after eating meat from infected deer.
The study, conducted at the University of Calgary, was an eight-year project that saw 18 macaque monkeys — chosen because the macaque most closely resembles humans — exposed to CWD in several ways. Several had tissue from infected deer rubbed on their skin, to simulate contact a hunter might have while field-dressing a deer. Those monkeys did not contract the disease. Other monkeys had CWD prions injected directly into their brains. All of them contracted the disease.
Most alarmingly, five of the monkeys were fed meat from deer that were infected. They were given the human equivalent of a 7-ounce steak per month. Three of those monkeys contracted CWD — one by being fed the brain stem of an infected deer; the other two after being fed CWD-infected meat. It marked the first time research had found that the disease could be contracted orally by a different species.
“This study does not mean people will get CWD, but it means people need to be considering that possibility,” veterinarian Dave Clausen told reporters at the time.
There have been other red flags. Recently, the Milwaukee Journal-Sentinel examined the number of Wisconsinites being infected with Creutzfeldt-Jakob. The newspaper determined that the disease incidence had increased by 117 percent from 2002, when CWD first appeared in wild deer in Wisconsin.
The CDC downplayed the newspaper’s finding, saying there was no conclusive link between the increase of CJD cases in Wisconsin and the presence of the brain-wasting disease in deer. Nationwide, the number of CJD cases increased 85 percent during the same time period. The CDC said the increase is due to increased awareness of the disease, which can only be confirmed by brain autopsy after death, and an aging population.
Skeptics, who fear CWD will ultimately make the jump to humans, point out that it was originally thought humans could not contract a prion disease from infected cattle. Then cases of vCJD began to be linked to infected beef.
To date, vCJD has claimed the lives of 229 people around the world, including four in the U.S. Almost all of those cases — including the four in the U.S. — have been conclusively linked to contaminated beef that was eaten in the UK or in a country supplied by the UK’s beef industry.
CAUSES FOR CONFIDENCE
Not everyone buys the Canadian macaque study. In fact, a similar study in the U.S. contradicted it.
In 2018, the National Institutes of Health announced that researchers had conducted a 13-year study with macaques, and found no evidence that CWD crossed the species barrier. Some of the monkeys were injected with brain matter from CWD-infected deer and elk, while some were fed brain matter from diseased animals.
In neither case did the monkeys contract CWD.
At best, the two studies seem to contradict. But critics have emerged of the Canadian study. They point out that it was never peer-reviewed and was never presented in a scientific paper. Additionally, Dr. Don Davis — a retired associate professor at Texas A&M’s College of Veterinary Medicine, pointed out that while it was not reported in media recounts of the Canadian study, researchers actually fed the monkeys meat from CWD-infected deer and from CWD-infected monkeys — meaning it’s perhaps just as likely that the three macaque monkeys became sick through cannibalism rather than infected deer meat.
As for speculation that cases of CJD may be rising in states where CWD has been detected, a study of historical data by Colorado researchers seems to indicate just the opposite.
The researchers looked at data from the seven northern Colorado counties where CWD has occurred in free-ranging deer and elk for more than 25 years. Their conclusion: there was no significant difference in the proportion of CJD deaths between CWD-endemic areas and non-CWD endemic areas.
Critics of what they term CWD fear-mongering like to point out that the first cases of variant Creutzfeldt-Jakob began to appear in Europe some 10 years after mad cow disease first appeared. It’s an alarming incubation period. However, chronic wasting disease has been in the wild in America for much longer than that, and there have been no confirmed cases of the disease in humans.
AN INCONCLUSIVE CONCLUSION
So, is deer meat safe to eat? The answer, apparently, is probably…but not definitely. Millions of dollars have been spent on research with still no conclusive evidence that humans can or can’t contract CWD. Overwhelmingly, the body of evidence suggests that, yes, deer meat is safe to eat. But the CDC continues to recommend that hunters who are harvesting deer or elk in CWD-infected areas have their animals tested, even if they aren’t showing symptoms of illness.
In Tennessee, the state’s Wildlife Resources Agency points out that there is no scientific evidence that CWD can be naturally transmitted to humans, but urges as a general precaution several safeguards:
- Avoid shooting, handling or eating animals that appear sick. Instead, contact TWRA.
- Have your animal processed in the area in which it was harvested to minimize the risk of disease spread.
- Wear rubber or latex gloves when field dressing deer or elk.
- Don’t handle the brain, spinal cord, eyes, spleen, tonsils or lymph nodes any more than necessary.
- Thoroughly wash your hands, knives and other tools used to field dress the animal, and disinfect tools by soaking them for an hour in a solution of 50 percent bleach and 50 percent household water.
Additionally, TWRA recommends that all animals in the CWD Zone be tested for CWD. If the test comes back positive, the agency says, the meat should not be consumed. Outside the CWD Zone, TWRA will sample any deer that’s harvested if the hunter transports the deer to a freezer drop-off location. Since all of those drop-off locations are in West Tennessee, that isn’t feasible for hunters on the eastern side of the state. However, there are a number of labs that hunters can contact for testing. Among them are the State of Florida’s Bronson Animal Disease Lab. The lab requires hunters to ship retropharyngeal lymph nodes, tonsils and obex for testing. The fee is $25, and results are available in 10 days. For more information, phone 321-697-1400.