Macaque study heightens concerns about human susceptibility to CWD

Macaque monkeys contracted chronic wasting disease after eating meat from CWD-positive deer, according to Canadian researchers. 

The findings are the first known oral transmissions of the prion disease to a primate and have heightened concerns of human susceptibility to CWD.

“The assumption was for the longest time that chronic wasting disease was not a threat to human health,” said Stefanie Czub, prion researcher with the Canadian Food Inspection Agency, in remarks published June 24 in The Tyee, a Vancouver, B.C. magazine. "But with the new data it seems we need to revisit this view to some degree."

Czub is leading the project, which began in 2009 and is funded by Alberta Prion Research Institute at the University of Calgary.

Eighteen macaques, a type of monkey, have been exposed to CWD in various ways to study the zoonotic potential of the disease.

Three of five macaques that were fed infected white-tailed deer meat over a three-year period tested positive for CWD.

The meat fed to the macaques represented the human equivalent of eating a seven-ounce steak per month.

Macaques that had the CWD prion injected into their brains also contracted the disease.

Those that had infected material rubbed on their skin – designed to simulate contact a hunter might have while field dressing a deer – have not contracted the disease.

Czub presented the results May 25 in a talk titled "CWD Transmission into non-human Primates" at the Prion 2017 conference in Edinburgh, Scotland.

The finding of oral transmission of CWD to a primate through eating of infected meat is most troubling to scientists and conservationists.

"This study does not mean people will get CWD," said Dave Clausen of Amery, a veterinarian, deer hunter and former chairman of the Wisconsin Natural Resources Board. "But it means people need to be considering that possibility."

Wisconsin hunters and their family members likely have more contact with CWD each year than those in any other state or province. 

The contagious disease, caused by a misfolded prion, or protein, is found at prevalence rates exceeding 30% in parts of deer-rich southern Wisconsin.

Last year, 442 of 3,758 deer submitted for testing in the southern farmland zone were CWD-positive. But more than 10 times as many deer were killed in the zone and not tested, many of which likely carried the disease.

According to the Alliance for Public Wildlife, a Canadian-based wildlife conservation organization, hunting families in North America consume between 7,000 and 15,000 CWD-infected animals every year.

Chronic wasting disease is fatal to deer, elk and moose. Since it is a transmissible spongiform encephalopathy (TSE) and in the same family as two diseases known to be fatal to humans (mad cow disease and Creutzfeldt-Jakob) researchers and health officials have long wanted to know more about the potential for inter-species CWD spread.

Based on the macaque study, Health Canada issued an updated CWD risk advisory.

"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," the advisory states. "In exercising precaution, (Health Canada) continues to advocate that the most prudent approach is to consider that CWD has the potential to infect humans."

From the World Health Organization to the federal Centers for Disease Control to state agencies, health officials are united in their recommendations to avoid eating meat from a CWD-positive animal.

Since 2003, the Wisconsin Department of Health Services (DHS) has issued a warning against consuming CWD-positive venison. The Canadian research reinforces the agency's position, said Jennifer Miller, DHS communications specialist.

"The Wisconsin Department of Health Services is aware of the study involving macaques contracting chronic wasting disease after being fed meat from deer infected with CWD," said Miller. "The department will continue to encourage hunters to have deer tested that were harvested from areas of the state where CWD is known to exist."

Miller said the department will also continue to discourage the consumption of meat from deer harvested anywhere that showed signs of illness – for example, deer that appeared emaciated or that acted abnormally.

The agency's recommendation states "venison from deer harvested inside the CWD Management Zone should not be consumed or distributed to others until CWD test results on the sources deer are known to be negative."

The Wisconsin guideline says venison from multiple deer should be kept separate and labeled before freezing so any meat from a CWD-positive animal can be discarded.

"Some might call the recommendation overly cautious," James Kazmierczak, DHS state public health veterinarian, told the Milwaukee Journal Sentinel in a July 2015 interview. "But the CWD prion has been found in muscle tissue. So from a public health perspective, the safest path is to test your deer and not consume meat from a CWD-positive animal."

In its Deer Hunting 2016 Pamphlet, the Wisconsin Department of Natural Resources also advises hunters to not eat the eyes, brain, spinal cord, spleen, tonsils or lymph nodes of any deer; to wear rubber or latex gloves when field-dressing carcasses, and to bone out the meat from the animal.

The Canadian study will likely wrap up in 2018, Czub said.

The preliminary results have already caused many to take notice.

"Research on prion diseases is unveiling new findings all the time," Clausen said. "This latest news confirms its wiser than ever to get your deer tested and follow the precautions."