The federal government has quietly issued a warning that a progressive and fatal neurological disease affecting deer, elk, and moose populations in western Canada and the United States for decades might infect humans.
For years scientists thought that it highly unlikely that chronic wasting disease (CWD), a prion-caused disease related to Mad Cow, could be transferred to humans who eat venison. Prions are infectious, misfolded proteins.
But dramatic new research has challenged that thinking.
The Health Products and Food Branch of Health Canada now warns that the potential for CWD “to be transmitted to humans cannot be excluded.”
The advisory, issued on April 26, adds that “In exercising precaution, [the branch] continues to advocate that the most prudent approach is to consider that CWD has the potential to infect humans.”
The advisory says that Health Canada should continue “to recommend avoiding consumption of foods from known infected or any diseased animals, and taking precautions when handling cervid carcasses.” Cervids include deer, caribou, elk and moose.
In addition, the advisory says rural people who have higher exposures to cervids through hunting and diet, such as Canada’s First Nations, should receive additional warnings.
“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,” states the advisory.
Stefanie Czub, a prominent prion researcher with the Canadian Food Inspection Agency, told The Tyee that “The assumption was for the longest time that chronic wasting disease was not a threat to human health.”
“But with the new data it seems we need to revisit this view to some degree,” she said.
The new scientific findings are startling.
A long-term study led by Czub exposed 18 macaques to CWD in a variety of ways: by injecting infected material into the brain; through contact with skin; by feeding them infected meat; and intravenously.
The study, which is ongoing, was funded by the Alberta Prion Research Institute at the University of Calgary and began in 2009.
To date, three of five macaques fed a total of five kilograms of infected white tail deer meat over a three-year period tested positive for chronic wasting disease.
That’s the human equivalent of eating a seven-ounce steak per month.
“If someone consumed venison for his life, this portion would represent the equivalent amount,” explained Czub.
Two of three macaques fed deer meat developed the symptoms of the disease, including anxiety, ataxia and tremors.
One animal lost a third of its body weight in a six-month period.
Two macaques that had infected matter inserted into their brains via steel wire also developed the disease.
Incubation times ranged from 4.5 to 6.9 years.
Researchers chose macaques, an Old World monkey from Asia, for the costly experiments because they are genetically and evolutionarily close to humans. Experiments with other primates such as chimpanzees are now forbidden.
The implications of the study are profound. “No one should consume animal products with a known prion disease,” said Czub who presented her findings at a prion conference in Edinburgh, Scotland, last month.
According to the Alliance for Public Wildlife, a Canadian-based organization dedicated to ensuring the conservation of North America’s wildlife, hunting families are now consuming between 7,000 and 15,000 CWD-infected animals every year and that percentage is rising by 20 per cent a year.
Darrel Rowledge, an Alberta hunter, independent prion researcher*, and director of the Alliance for Public Wildlife applauded the health advisory, but described the commercial game farming industry that imported and spread the disease as a public policy disaster.
“Ninety infected game farms in Saskatchewan spread this new and emerging disease all over that province, and the level of testing there is still pathetic,” said Rowledge.
“Farming cervids caused this whole thing exactly as some of the world’s best scientists predicted.”
The study’s results surprised Rowledge because they clearly show that “the highest risk of infection comes from eating a CWD-infected meat; in this study even a modest amount was sufficient.”
And very few scientists thought that was possible, he explained.
Late symptoms of CWD in cervids are horrific. Infected animals often tremble on splayed legs and have trouble standing. They drool and eat continuously but continually waste away. Many are hyper excitable and nervous. Researchers call them “droopy droolers.”
Rowledge hopes that the study and advisory prompts regulators to get more serious about controlling the rapidly expanding crisis for North American wildlife.
“The government has to contain this epidemic. That begins with stopping the movement of live animals and products or equipment from game farms. It also means every animal killed by hunters has to be tested for CWD in areas that have been infected,” said Rowledge.
In addition regulators need to require that “not a single animal leaves a CWD-infected area.”
Animals testing negative should be processed, packaged and delivered to the hunters for free to ensure widespread compliance, added Rowledge.
Chronic wasting disease first emerged among captive deer at a wildlife research facility in Colorado in 1967. Researchers didn’t realize that the mysterious killer was caused by prions until 1978.
Since then the disease has spread via trucks as the game farm industry traded and sold elk and deer across North America.
Scientists confirmed the first case on a game farm in Saskatchewan in 1996 and later traced the origin of the outbreak to infected CWD animals from a U.S. game farm.
Alberta soon confirmed CWD infections on farms as well, and in 2004 wildlife experts confirmed repeated transfers of the highly infectious disease from commercial farms into wild deer and elk populations in Canada.
Since then the disease has spread like a boreal wildfire. The Alberta government reports that the disease, once confined to the southern Saskatchewan border area, has now spread into the Red Deer, Battle River and Vermillion River watersheds.
Alberta has now found infected white tail deer as far north as Fort Saskatchewan and infected elk on the Canadian military base in Suffield in southern Alberta.
In the U.S., the rapid spread of the disease via the game farm industry has stunned regulators and deer hunters alike.
Last year the Canadian Food and Inspection Agency reported six outbreaks of CWD on six different game farms in Alberta and Saskatchewan.
All farmed cervids slaughtered in abattoirs in Saskatchewan, Alberta, Manitoba and Yukon must be tested for the disease. The testing of deer killed by hunters remains voluntary and haphazard.
“But the notion that the game farming industry appropriately tests all their animals and products is fallacious and preposterous.” said Rowledge. “In the case of velvet and urine it is not even possible; tons of velvet antler from CWD-infected animals entered the food chain.” The velvet from deer antlers has a long history as popular and edible aphrodiasic, particulary in Asia.
The dramatic results of the macaques study have prompted widespread discussion among regulators in North America and Europe where Norway recently discovered cases of CWD in reindeer and moose.
“Everyone is taking the results extremely seriously, above all the regulators in Canada and the U.S.,” said Czub. “The Norwegians are extremely concerned too.”
Scientists and regulators are “revisiting how we deal with CWD in terms of regulations,” Czub said.
“The discussions have been quite intense where the study’s results have become available.”
* Clarification: A previous version of this story described Rowledge as a prion researcher, which he is, but Rowledge is an independent researcher as opposed to a professional scientist.