Chronic Wasting Disease (CWD) – a highly infectious, debilitating and fatal illness – is spreading throughout North American deer populations, an epidemiological event experts say could have serious conservation and environmental impacts, especially if it makes it into Canada’s North, where it could particularly affect First Nation communities.

First detected in deer at a research facility in the late 1960s and then in wild populations in Colorado in 1981, CWD has since been found in 26 states and is now considered endemic in eight. In Canada, it was first detected in Saskatchewan in 1996, and has since spread throughout that province and spilled over into Alberta, which confirmed it’s first case in December 2005 in a wild deer harvested near the Saskatchewan border. It has continued to spread in an ever-widening radius, with Manitoba reporting its first confirmed case of the illness in a wild-harvested deer in November 2021.

CWD belongs to a unusual class of pathogens called prions, which are neither viruses nor bacteria, but misfolded proteins, the same family of infectious agents which causes Bovine Spongiform Encephalitis (BSE), which affects cattle and scrapie, which sickens sheep and goats.

Sometimes referred to as “zombie disease” because of the way stricken animals stumble and drool, often gaining a hunched, uncoordinated posture and displaying behaviour abnormalities, such as losing their fear of humans, infected deer may take up to two years to start showing outward symptoms, says Dr. Margo Pybus, wildlife disease specialist with the Alberta government’s fish and wildlife division and researcher at the University of Alberta. CWD is spread through animal-to-animal contact, including saliva and urine, but deer can also pick it up from their environment, particularly in areas where CWD has become established and endemic.

The illness is not limited to deer, and can infect any cervid, such as moose and elk. Of greatest concern for Northern communities is its potential to infect caribou; the disease is moving not only east and west, but north, where it threatens to overlap with the southern ranges of the ungulate, a cultural touchstone and a dietary staple of many Northern First Nations.

To date, the disease has not been found in Northern cervid populations, although Yukon and the Northwest Territories both have surveillance programs in place similar to those used in other jurisdictions in Canada, such as hunter and road kill submission testing for CWD. Likewise, CWD has not been found in wild North American caribou populations at this time–however, as climate change alters the traditional ranges of some animals, the likelihood of spread between northern and southern populations increases.

Mule deer, for example, have been expanding their range from Northern British Columbia into Southern Yukon for some time, and are considered among the “most susceptible species,” says Kristenn Magnusson, a veterinarian with Yukon’s Animal Health Unit.

“Certainly the migration of a CWD-positive animal (into Yukon) is a concern,” says Magnusson, adding that mule deer populations in the territory fluctuate depending on environmental conditions and that their population density is “still quite low” in the region.

“The mechanism of spread to geographically isolated areas is not completely understood with CWD. One of the challenges that we face with a lot of wildlife disease surveillance is the movement of wildlife…we're often surprised by how far and wide animal ranges are.”

Migration of a sick animal, however, is not the only possible way for the disease to enter the territories, Magnusson says.

As an infectious pathogen, CWD packs an “insidious” double whammy, says Pybus; not only are sick animals infectious during the disease’s prolonged latent period, during which they interact with other deer and spread the contagion, they also excrete prions into the environment, where they remain active and capable of causing infection. This means that as the number of infected animals increases, the amount of pathogens present in the environment builds up, to such a degree that eventually the soil itself becomes a vector for transmission.

Because the prions remain infectious even after their host has died, an infected animal harvested outside the territories and brought home could also be a vector, says Magnusson–even lures and scents, which are often derived from deer urine, could possibly be carrying the pathogen.

“Illegal importation of parts from CWD-positive cervids could spread CWD into Yukon… and then certainly movement of (contaminated) feed and soil is another way CWD could conceivably be brought into (the territory),” Magnusson says.

Both Yukon and NWT have special import and testing requirements on harvested cervids brought in from outside the territories.

The government of the Northwest Territories did not respond to multiple requests for comment on this story.

The long-lived and highly stable nature of CWD prions is part of what makes its spread so concerning; once it’s in a wild environment, it’s really difficult to get rid of. To denature the protein and render it harmless, even in lab conditions, requires serious work, says neurologist Dr. Valerie Sims of the Centre for Prions and Protein Folding Diseases, such as soaking it in sodium hydroxide, a strong base, for up to an hour, the use of low pH acidic phenol compounds, or very high concentrations of bleach–none of which, obviously, is easily utilized or even practical in a natural setting, like grasslands or tundra.

From a conservation perspective, CWD is a threat to cervid populations in two ways, says Pybus. Firstly, there is the direct mortality–sick animals don’t get better. Secondly, it significantly reduces the reproductive years of an animal, creating a cumulative spiral of declining fecundity; if an animal is infected at four years of age, it dies at six, if infected at two years of age, it dies at four, and if infected while very young, it may make it to reach maturity at all. Along the way, those missing years mean missing offspring, which in turn, never being born, will themselves never have the opportunity to reproduce, curbing population replacement.

In Colorado and Wyoming–states where the CWD is endemic and has been perhaps the longest established–research has found CWD has caused a 19 per cent increase in deer mortality, on top of normal predation and environmental factors, Pybus says.

To date, CWD has not been found to infect humans, although the government of Canada recommends people not consume meat that has tested positive for CWD. Although a recent German study found that macaque monkeys fed meat containing the CWD prion eventually became infected, Sims says it’s important not to jump to doomsday-like conclusions; the study is still being peer reviewed, and maquques are still “non-human” primates.

“Well, how concerned should we be?” she asks. “I think everybody should have awareness of this disease–I don't believe in blocking information just to… prevent (people) from being afraid. At the same time, we can't sensationalize it, such that it drives fear and terror into everyone, because that also has significant health consequences.”

With that said, there are special concerns when it comes to Northern communities, she notes, particularly in part because they tend to have lower access to health care (and therefore would be less likely to have disease detected if it did develop) and in part because of their higher risk of exposure, particularly in regards to a traditional diet.

When a zoonotic disease–one that infects an animal species–crosses over into humans, this event is referred to as a spillover; most recent pandemics, including HIV, SARS and COVID-19 are thought to have originated in this way. In order for this to happen, you need a person and an infected animal to interact in such a way that the infection–in this case, the CWD prion–has the opportunity to enter a human host. The way that’s most likely to happen with CWD is through eating infected meat, especially because the prion isn’t destroyed by cooking, Sims says–you can char an elk burger or cook mule deer tenderloin until it’s shoe leather, but the prion remains intact and infective, at least to other cervids.

This is especially important to consider when you recall that, up until a month or two before they die, most infected animals don’t look sick, and unless it’s tested and comes back positive, there’s no way for a hunter to know if they’ve got an animal with CWD or not.

“What's difficult about (this) is we're trying to figure out what the risk is when there [are] still a lot of unknowns,” says Sims. “We're all dealing with theories and theoretical risks, because at no point has (CWD) actually (been known to) infect humans– and there are plenty of humans that have been eating CWD contaminated meat for decades now. And nothing has happened.”

What is important to think about, though, she says, is that the more times a zoonotic disease comes in contact with a human, the more chance there is of a spillover.

During the BSE outbreak (BSE is better known as “mad cow disease”) the disease was first identified in cattle in the 1980s, with human cases–in humans, BSE presents as the Alzheimer's-like variant Creutzfeldt-Jakob disease (vCJD) – stemming from consumption of infected meat first popping up in the 1990s. With BSE, the disease entered a mass food chain production system, with an estimated 2 million infected animals, making it unlikely that every single person who ate contaminated meat got sick; to date, there have been only 232 identified cases of vCJD (although unfortunately all cases have been fatal).

Basically, lots of people probably got exposed and most didn’t get sick but some did; there’s never been a “clear reason” why some people got vCJD and others didn’t, although individual genetics may have been a factor in susceptibility, Sims says.

This phenomena is particularly important to consider when you’re thinking about Northern communities, especially Indigenous ones, because they may be consuming more game meat, such as caribou or moose, as part of a traditional diet than southern populations.

A 2016 study of Inuvialuit and Inuit in four communities in the Northwest Territories and Nunavut found that caribou comprised 26 per cent of respondents' diets during the study period. That’s important regardless of the possibility for human infectivity or not–if CWD were to make into those caribou populations, causing them to decline, a culturally invaluable food source on which people rely for their subsistence would be under threat.

“Consuming caribou was… shown to exert positive impacts on dietary quality, as measured by calorie intake and dietary diversity,” the study found. “Communities with less access to employment, income and food stores are predicted to be constrained in their ability to obtain an adequate diet in the event of scarcity of caribou meat.”

“While there’s a lot that we don’t yet know (about CWD), there’s enough (information) to be concerned,” says Sims, adding that she thinks there needs to be an “open dialogue” between scientists and Northern communities, such as a yearly update targeted specifically to the Elders and leaders in those communities.

“We can't change the fact that this (CWD spreading) is happening, but we can help people understand it, and when people understand, it helps them make their own informed decisions,” says Sims. “They may be okay with a certain level of risk–we are always at risk of something when we just step out of the house.”

“If we can have a way to keep an open dialogue and communication going forward, that’s going to be the most important thing–so that if something happens, we can notify people.”