It attacks the brain. It has a 100 per cent fatality rate. And it has spread all across southern and central Alberta.
Fifteen years ago, chronic wasting disease was rare in the province’s deer populations, showing up in a small percentage of animals in a handful of locations, mostly along the Saskatchewan border.
In the most recent surveillance, some of those areas were seeing 50 to 85 per cent of mule deer infected, while the disease has exploded westward and northward through the province. Cases have shown up in the U.S. Rocky Mountains and, for the first time, were detected last year in British Columbia.
Researchers are now racing to come up with strategies to at least slow the spread of the disease in deer and reduce the chances of it spreading to more vulnerable caribou populations — or, worse, humans.
To make matters even more challenging: the disease mechanism is only beginning to be understood. This particular kind of illness is not caused by a virus or bacteria, but rather a bizarre pathogenic agent known as a prion.
Prions are a type of protein found naturally on the surface of cells and are particularly abundant in the brain. The purpose of these proteins is not well understood. But what scientists do know is that when harmless versions of the proteins end up folded in a certain way, they can trigger more of the proteins to similarly misfold, clump up and cause brain damage.
“Basically, these protein clumps accumulate in the brain,” said Sabine Gilch, a professor of veterinary medicine at the University of Calgary and Canada Research Chair in prion disease. “They cannot be degraded by the brain cells and eventually destroy the brain.”
The prions involved in chronic wasting disease can be shed in saliva, urine or feces, or from animal carcasses, which allows for transmission between animals. So far, the disease has been detected only in cervids — such as deer, elk and moose — but not other types of animals.
“We haven’t seen it in any other species,” said Debbie McKenzie, an emeritus professor of biological sciences with the University of Alberta, whose research focused on chronic wasting disease.
There is some lab-based experimental evidence that suggests the disease can be transmitted to other types of animals, she said, and the big fear is over the potential for transmission to humans — a scenario considered to be highly unlikely but not impossible.
“We have very little evidence in the lab that it can jump to humans,” McKenzie said.
“It is, however, always a concern.”
Memories of mad cow
She noted that, decades ago, it was believed that bovine spongiform encephalopathy (BSE), or mad cow disease, could not jump into humans.
But in the 1990s, human cases (known as variant Creutzfeldt-Jakob disease) started popping up, largely in the United Kingdom. Many cases were linked to the consumption of beef from prion-infected cows. Globally, more than 200 deaths from the disease have been reported since 1996.
While chronic wasting disease is not known to infect humans, the Government of Alberta advises that “persons should not knowingly consume meat of animals with the disease.”
Hunters who harvest deer can drop off the heads of the animals at numerous locations across the province to be tested for chronic wasting disease. Submission of deer heads is mandatory in some cases and voluntary in others, depending on the species of deer and where it was taken.
Mitigation measures
Chronic wasting disease has spread far in Alberta — and other parts of North America — that researchers are now focused on mitigating it, rather than eliminating it.
“I don’t think that we’re going to be able to easily eradicate the disease,” McKenzie said. “We can slow it down — we think.”
To that end, different jurisdictions have tried different methods, including the mass culling of deer, particularly male mule deer, which are the most likely to be infected.
That approach can be effective, McKenzie said, especially if it’s taken early in an area where the disease is relatively new. But it’s often unpopular.
“It’s difficult to convince people that you should decrease the deer population right now in this small area so that you can have a healthy population down the road,” McKenzie said.
“Illinois has been doing that fairly well for 20-plus years now and they’ve been able to maintain a fairly constant, low prevalence of CWD compared to Wisconsin, just across the border, which tried to manage the deer population and got a lot of pushback on it.”
Researchers across Western Canada — including Gilch, at the University of Calgary — are also working on potential vaccines that could help slow the spread of the disease.
“I think a lot of hope lies within the CWD vaccine area,” she said.
There are challenges, too, especially with distributing a vaccine to wild animals. Even attempting that may be several years away, Gilch said, but wildlife experts are already working with researchers to help develop methods for administering a vaccine orally through some type of feed material.
In the meantime, Gilch believes the disease will get worse.
“I might sound really pessimistic, but I don’t think that the spread will stop in the near future,” she said.
“I guess it will further march toward the west, the north, and the numbers will increase. I don’t see anything that would intervene in that spread at the moment, unfortunately.”
