CWD may have ability to jump to humans

Scientists are a cautious bunch, so when researchers go public with a warning that a disease in deer and their relatives could jump to humans, it reflects their level of concern.

Dr. Hermann Schaetzl is part of a team of researchers that for the last 15 years has been conducting a study on whether chronic wasting disease (CWD) can be transmitted to macaque monkeys, and ostensibly to humans.

The short answer? Yes, it can.

“We can’t say how often it will happen, only that it can happen,” he said.

The news is troubling for game ranchers, hunters, outfitters, and most importantly, people in rural and remote communities that depend on wild game for their daily meals.

Schaetzl is a professor of biology and immunology and head of the Calgary Prion Research Unit at the University of Calgary. He said results from the soon-to-be-published macaque study match those from another in mice also in the pipe.

“If two independent lines of study are coming to the same conclusion, we have to take it seriously.”

CWD affects cervids, the deer family. This includes elk, moose and caribou. It attacks the brain and nervous system, killing the animal.

Schaetzl said infection rates are “exploding” in Alberta. A few years ago, data from heads submitted for testing by hunters showed below one percent to two percent.

Today, it’s found in five percent of white-tailed deer and 15 to 18 percent of mule deer populations. Saskatchewan also has high levels of the disease.

While it was unknown whether CWD could affect humans, the farmed elk and deer industry took a major blow when it showed up in some animals in the mid-1990s. The market for elk antler velvet, for example, disappeared.

Since then, game farmers and hunters have participated in testing programs aimed at keeping the disease out of the human food supply. Now, Schaetzl said these and other efforts must be stepped up to meet the threat.

One of these efforts is aimed at developing a vaccine against the prion that causes CWD. While efforts have been slowly proceeding for at least a decade, Schaetzl said this changed with the COVID-19 pandemic. Governments and funding agencies saw the dramatic effect of concerted, worldwide vaccine development, and scientists saw the power of putting collaboration ahead of “publish first” competition.

“One of the amazing things about COVID is this appreciation of putting aside competition in science and appreciating that when we come together, and everybody brings their best ideas, that’s where you have the greatest chance of success,” said Scott Napper.

Napper is a senior research scientist with the Vaccine and Infectious Disease Organization (VIDO) and a professor in the College of Medicine at the University of Saskatchewan. He said that developing vaccines for prion diseases like CWD are much more tricky than those for viruses and bacteria, since prions are misfolded versions of proteins that occur naturally in the body.

“It’s almost as if it’s a part of your own body that’s turned against you,” he said.

This means a vaccine must trigger an immune response against something that is not clearly foreign, but only slightly different from what belongs there. Vaccines must be much more precisely targeted.

VIDO has been collaborating on CWD vaccine projects for more than 10 years, notably with prion disease expert Neil Cashman at the University of British Columbia. The group has expanded to include Schaetzl and others such as Holger Wille at the University of Alberta’s Centre for Prions and Protein Folding Diseases.

The collaborators have pooled their potential vaccine targets, called disease-specific epitopes, so they can be put into formulations as vaccine candidates and tested concurrently, dramatically decreasing development time.

Napper said the preference is testing that mimics real world conditions. This means oral formulations of the vaccine candidates rather than injected to make sure they can be deployed in the wild. These candidates are fed to the animals, which are then exposed to CWD.

“At the end of the day, unless it’s successful in the target species, under those circumstances, we haven’t accomplished what we need to do,” he said.

Unfortunately, the candidates so far haven’t hit the mark — one even accelerated onset of disease in an elk trial in Wyoming. But there are other candidates.

“You have to test them all, and eventually, hopefully, find something that works,” Napper said.

While the CWD problem is serious, Schaetzl said it’s important to keep it in perspective. The risk is not so much that humans will start getting sick in droves, but that it will endanger the health system, blood donation system, and the agriculture and food economy.

The most notorious prion disease, bovine spongiform encephalopathy (BSE), gives some idea as to how the discovery of even a single case of CWD in humans might play out.

According to the United States Food and Drug Administration, as of 2019 BSE had killed 232 people worldwide. Almost all of these deaths were in the United Kingdom where the disease was first discovered in the mid-1980s. But it had impact far beyond the relatively modest human death toll.

This included mass culls of livestock in the U.K. and heightened trade barriers. Discovery of a BSE-positive animal in 2003 in Alberta closed international borders to Canadian beef exports. Restrictions weren’t fully lifted until the spring of 2021.

Public health barriers also remain in place. Anyone who has lived in the U.K. during the BSE outbreak period cannot donate blood in Canada to this day. Schaetzl said this is not an unreasonable precaution, since prion diseases can take decades to develop symptoms.

Another critical element is food security for rural and remote people, particularly Indigenous communities, that rely on wild game to feed their families. These most vulnerable populations are also the hardest for public health agencies to serve with CWD testing services. This is essential, since the best preventive measure available is to test any animal for CWD before eating it.