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The science of Chronic Wasting Disease

Chronic Wasting Disease is making headlines this summer. From articles in the Tyee, to reporting from the Canadian Press, stories have appeared across the country with a discouraging message.
It is not as bad as the reporting would make you believe.
Genome Alberta supported by Genome Canada, the Government of Alberta, the Alberta Prion Research Institute, Western Economic Diversification, and a variety of other organizations, are making headway.

What is known?

Chronic wasting disease (CWD) is an infectious, contagious disease affecting deer, elk and moose (known as cervids). It is a prion disease which affects the brain when a normal protein is misfolded into an abnormal form, resulting in neurodegeneration. All prion diseases, including human Creutzfeldt-Jakob disease (CJD) and cattle Bovine Spongiform Encephalopathy (BSE, or ‘mad cow’) share long incubation periods which means that, for deer, it can take 2 years or more from the time an animal is infected until it dies from the disease. Diagnosis is difficult as animals tend to look and act healthy during infection, and conclusive tests can only be performed after the animal has died. Unlike BSE, there is no evidence of CWD transmission into the human population.
CWD was first identified in Colorado and Wyoming in the 1960s and recognized as a prion disease in the early 1980s. It has since spread to deer, elk and moose populations in 25 US states and 3 Canadian provinces, to South Korea via the import of elk from Canada and to reindeer and moose in Norway, Finland and Sweden. The geographic spread is due to both natural movements of deer, elk and moose as well as transport of undiagnosed animals to other regions, though the exact origin of CWD in Scandinavia has not been determined. Once animals in an area become exposed to CWD, prevalence increases over time up to 50% in some free-ranging populations and can be greater than 80% in captive populations. There is currently no treatment or vaccine available for CWD, and diagnosis relies on a brain sample from an infected animal.
Apart from the impact on the wildlife, CWD impacts people who rely on cervids for food and culture and hurts Canada’s reputation as a wildlife destination. Governments view the disease and its impact seriously, with the broader research and environmental groups encouraging increased action and funding.

What is being done?

Recognizing the importance of applied research in this area, Genome Canada, Genome Alberta, and the Government of Alberta have funded world-renowned researchers at the University of Alberta and the University of Calgary who are tackling the challenging aspects of CWD biology, spread, and detection in Canadian deer and elk.
Transmission of CWD may occur between animals or indirectly via the environment. Unlike many other prion diseases, such as BSE, the infectious agent is shed into the environment through saliva, feces and urine. Prions are exceedingly difficult to inactivate and can survive in the environment for 10 years or more. Our funded CWD researchers has found that these prions can bind soil, leaving them infectious but difficult to detect. Members of the team have been actively developing new methods for detecting environmental CWD as knowing which areas are contaminated will allow us to focus on mitigation of the environmental contamination. The team is also working on developing diagnostics techniques for living animals, using cutting-edge -omics technologies targeting disease-specific biomarkers (biological indicators of disease). This will allow wildlife management entities to remove and isolate infected animals and reduce potential spread.
While robust detection will allow us to monitor the spread of CWD, understanding the biology and variability of the prion is essential. Genome Canada/Genome Alberta funded researchers are characterizing CWD strains on their ability to infect and cause disease. Several strains have been identified with novel properties and are being experimentally tested to determine what species are susceptible to infection. This work will be instrumental in understanding how evolution of CWD could increase the host range (breadth of susceptible animals) and speed of disease progression.

Where do we go now?

Although there is currently no evidence of transmission into the human population, all harvested deer from areas where CWD has been identified should be tested and positive animals should not be consumed. As the prevalence of CWD continues to increase across numerous geographic areas, the potential for transmission into humans and other species who live in the same areas with CWD-infected deer also increases. With continued government support and community engagement, CWD research and education will improve wildlife management strategies and enhance food safety for hunter groups and indigenous populations who rely on these animals.

Related links:
Chronic Wasting Disease – Information for hunters
CFIA Chronic wasting disease (CWD) fact sheet

The science of Chronic Wasting Disease

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