Can This Deer Disease Be Transmitted to Humans?

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July 25, 2017 | 24,242 views

Story at-a-glance

  • The Canadian Health Products and Food Branch (HPFB) issued an advisory in April 2017 warning of “potential human health risks from chronic wasting disease”
  • Three of five macaque monkeys fed CWD-infected white tail deer meat developed CWD over a three-year period
  • Two monkeys that had infected matter exposed to their brains also developed CWD

By Dr. Mercola

Chronic wasting disease (CWD) is a contagious neurological disease that is part of the transmissible spongiform encephalopathies (TSEs) disease family — the most notable member of which is bovine spongiform encephalopathy (BSE), also known as mad cow disease. Unlike BSE, which infects cattle, CWD affects deer, elk and moose.

"It causes a characteristic spongy degeneration of the brains of infected animals resulting in emaciation, abnormal behavior, loss of bodily functions and death," The Chronic Wasting Disease Alliance reports.1 The symptoms are similar to those of mad cow disease, scrapie (a similar disease found in sheep and goats) and Creutzfeldt-Jakob disease (CJD) in humans. The infectious agent thought to cause CWD and other TSEs is prions — an infectious type of protein known to cause neurodegeneration.

A human version of mad cow disease, known as variant Creutzfeldt-Jakob disease (vCJD), can be caused by eating beef contaminated with brain, spinal cord or other central nervous system tissue from infected cattle.2 This can occur in ground meat (including hot dogs, bologna, taco fillings and more), as it may become contaminated during the "extraction of the last bits of meat from cow carcasses," the Center for Food Safety stated.3

The question then, as CWD continues to spread across the U.S., is whether this disease may also jump to humans — and the Canadian government has recently issued a warning based on new research suggesting the answer is yes.

Canadian Government Warns Chronic Wasting Disease May Jump to Humans

The Canadian Health Products and Food Branch (HPFB) issued an advisory in April 2017 warning of "potential human health risks from chronic wasting disease." The disease has been detected in cervids (mammals belonging to the deer family) in 24 U.S. states and two Canadian provinces to date, including in farmed elk and wild mule deer. The advisory states:4

"While extensive disease surveillance in Canada and elsewhere has not provided any direct evidence that CWD has infected humans, the potential for CWD to be transmitted to humans cannot be excluded. In exercising precaution, HPFB continues to advocate that the most prudent approach is to consider that CWD has the potential to infect humans."

The warning came on the heels of a study led by a Canadian Food Inspection Agency (CFIA) scientist, which found CWD was transmitted to macaque monkeys, which are the nonhuman primate species most closely related to humans that are still allowed to be used in research, via "both the intracranial and oral routes of exposure." Further, both brain and muscle tissue from infected animals were capable of transmitting disease.

In the ongoing study of 18 macaques, three of five monkeys fed infected white tail deer meat developed CWD over a three-year period. Two monkeys that had infected matter exposed to their brains also developed CWD.5

Based on this and other data, including a systematic literature review that included a study showing CWD could be transmitted to squirrel monkeys,6 the HPFB warned that although CWD may be "readily" transmitted to humans, "the species barrier is not absolute." They also included a list of the many possible routes of exposure to CWD for humans, especially among those who rely on deer meat as a regular food source:7

"Canadians may be exposed to cervids, and materials derived from cervids through a variety of sources, and routes of exposure, including in their diet and through the use of natural health products that contain antler velvet.

There is also the potential for Canadians to be exposed to cervids through farming (including veterinary services), slaughter, velvet harvest, as well as through field dressing of hunted animals, preparing trophies and/or the use of cervid-derived materials (e.g., urine) as hunting lures.

While monitoring and control programs are in place to reduce the likelihood that animals known to be infected with CWD reach the marketplace, the possibility cannot be excluded that some of these sources of exposure may be derived from animals with CWD. Cervid meat (venison) is available in many of the same cuts and processed meat products as for other meat products.

While consumption survey estimates for the general Canadian population … indicate that overall venison consumption is quite low, there are known subpopulations, including rural and Indigenous populations that have higher dietary exposures to this food. In addition, populations that rely on cervids as an important source of protein are more likely to hunt and/or consume wild cervids."

Are Rising Cases of Creutzfeldt-Jakob Disease Due to CWD?

Meanwhile, cases of Creutzfeldt-Jakob disease have spiked 85 percent in the U.S. from 2002 to 2015, which is surprising since the natural variant of the disease is typically extremely rare. In Wisconsin, a 117 percent increase in cases was recorded since 2002 — all as rates of CWD continue to rise.8 Health officials have downplayed any connection, blaming it instead on an aging population and increased detection and conformation of Creutzfeldt-Jakob cases, but it cannot be ruled out.

Speaking to the Milwaukee Journal Sentinel, U.S. Centers for Disease Control and Prevention (CDC) spokesperson Christine Pearson said, "While no human cases of CWD have been reported to date, the new [macaque] study findings raise concerns that people who hunt or consume meat from infected animals could be at risk for CWD infection." In response, they recommend not eating meat from infected deer or elk and having meat tested if it came from an area where known cases are present.

It's not unheard of that a form of TSE could mutate into one that could infect humans. This is what happened with mad cow disease in cattle, which first began after cattle were fed food containing sheep parts infected with scrapie. The sheep disease mutated into a form that could infect cattle, which in turn mutated into a form that could infect humans. There's a good chance that hunters consuming venison may be coming into contact with infected deer, at least in Wisconsin.

And although the state offers free CWD testing to hunters, many do not take advantage of it. With cases of both CWD and Creutzfeldt-Jakob disease trending upward, the potential connection is unsettling to put it mildly, especially in light of the new research. The Journal Sentinel put it down in numbers:9

"[Wisconsin Department of Natural Resources (DNR)] figures show that tens of thousands of hunters are killing deer in areas where CWD is prevalent and are not submitting them for testing. In 2016, in a CWD-prone area that the DNR describes as the southern farmland zone, 442 deer tested positive for disease out of 3,760 samples. More than 65,000 deer were killed in that zone and were not tested, according to DNR figures."

CWD Is Fatal, Has No Cure and Spreads Like Wildfire Among Captive Animals

CWD-infected animals shed the infectious prions in saliva and urine, starting around three months after being infected. They remain contagious for the remainder of their life, contaminating land and water as they go along. According to some experts, the prions causing CWD are the most resistant disease agent currently known.

The Chronic Wasting Disease Alliance seconds this, noting, "The CWD infectious agent is smaller than most viral particles and does not evoke any detectable immune response or inflammatory reaction in the host animal. Based on experience with other TSE agents, the CWD infectious agent is assumed to be resistant to enzymes and chemicals that normally break down proteins, as well as resistant to heat and normal disinfecting procedures."10

The infectious agents in CWD also persist in the environment, which is why deer and elk raised in captivity (or concentrated via artificial feeding) have an increased likelihood of transmitting the disease among them.

The common denominator between mad cow disease and CWD is forcing natural herbivores to eat animal parts — a more or less routine practice in the concentrated animal feeding operation (CAFO) model. It's one more reason to avoid all meats from livestock raised in CAFOs and to be wary of supporting game farms.

The Alzheimer's Connection

While CWD and Creutzfeldt-Jakob disease may seem like more obscure diseases, the mention of Alzheimer's disease may hit closer to home. Alzheimer's disease has grown to be one of the most pressing and tragic public health issues facing the U.S. With no known cure and the number of people affected expected to triple by 2050, the Alzheimer's Association estimates that by mid-century someone in the U.S will develop Alzheimer's disease every 33 seconds.11

An infectious protein called TDP-43 behaves like the prions implicated in mad cow disease and CWD. Researchers have also found that this protein may play an important role in Alzheimer's disease,12 as it is correlated with shrinkage of the hippocampus, thereby causing memory loss. By examining the autopsied brains of more than 340 Alzheimer's patients, the researchers found that TDP-43 was present in nearly 200 of them.

Research presented at the 2014 Alzheimer's Association International Conference (AAIC) also revealed Alzheimer's patients with TDP-43 were 10 times more likely to have been cognitively impaired at death than those without it,13 and the possibility has been raised that humans might get infected with TDP-43 via contaminated meats. A 2005 study published in the journal Medical Hypotheses, stated:14

"In the opinion of experts, ample justification exists for considering a similar pathogenesis for Alzheimer's, Creutzfeldt-Jakob and the other spongiform encephalopathies such as Mad Cow disease. In fact, Creutzfeldt-Jakob and Alzheimer's often coexist and at this point are thought to differ merely by time-dependent physical changes. A recent study links up to 13 percent of all 'Alzheimer's' victims as really having Creutzfeldt-Jakob disease."

When it comes to CAFO meats, be it chicken, pork or beef, you're being exposed to any number of foreign proteins — and TDP-43 might be one of them. Variant Creutzfeldt-Jakob disease (vCJD) has a long incubation period, and few dementia-related deaths in the U.S. are ever investigated. An infected person usually starts having symptoms in their 60s.

As noted by the Centers for Food Safety, the symptoms of vCJD are similar to Alzheimer's, and include staggering, memory loss, impaired vision and dementia.15 As for CWD, if it has infected people, there's no way to know how it would present and whether it would have different or identical symptoms to other TSEs, like CJD.

Kurt Giles, a prion disease expert and associate professor of neurology at the University of California, San Francisco's Institute for Neurodegenerative Diseases, told the Journal Sentinel, "All I can say is that currently I don't know of any evidence of transmission of CWD to people, but that doesn't mean it can't happen in the future, or indeed has already happened but we can't detect it."

Until we have more answers on this emerging predicament, it makes sense to take abundant precautions, especially if you consume venison from areas with known CWD outbreaks.

[+]Sources and References [-]Sources and References

  • 1, 10 The Chronic Wasting Disease Alliance, FAQs
  • 2 WebMD The Basics of Mad Cow Disease
  • 3, 15 Center for Food Safety, Mad Cow Fact Sheet (PDF)
  • 4, 7 The Tyee April 26, 2017
  • 5 The Tyee June 24, 2017
  • 6 J. Virol. November 2005 vol. 79 no. 21 13794-13796
  • 8, 9 Journal Sentinel July 7, 2017
  • 11 Alzheimer’s Association, Facts and Figures
  • 12 Acta Neuropathol. 2014 Mar;127(3):441-50.
  • 13 Alzheimer's & Dementia September 2014 Volume 10, Issue 5, Pages 583–586
  • 14 Medical Hypotheses 2005;64(4):699-705