UCalgary researchers investigate genetic variation which makes some caribou less susceptible to chronic wasting disease

With their distinctive tall, flat antlers and their appearance in the Arctic, boreal and mountainous regions of the country, caribou are one of Canada’s most recognizable species, but they are also considered to be one of Canada’s most threatened species.

One of the threats these animals face is chronic wasting diseases (CWD). However, a new study conducted by researchers from the University of Calgary Faculty of Veterinary Medicine (UCVM) has found a genetic variation that makes some caribou less susceptible to the deadly disease.

CWD is a prion disease that effects the cervid, or deer, family. Prion diseases are diseases of the brain that occur in humans and animals and are caused by infectious agents that consist only of a misshaped form of a protein that is made by the host itself in the brain.

“Under certain circumstances such as infection with such misshaped proteins, the host’s protein will clump together and accumulate in the brain,” explains Dr. Sabine Gilch, PhD, an associate professor at UCVM. “From there, the protein aggregates will destroy the brain cells and leave holes in the brain.”

Prion diseases like CWD and mad cow disease are infectious and can be transmitted from animal to animal, or in some cases even from animal to human.

In their new study published in the Proceedings of the National Academy of Sciences, Gilch and Dr. Maria Arifin, DVM, PhD, a postdoctoral fellow at UCVM, found some caribou carry a genetic variation — called a polymorphism — that makes them less susceptible to CWD.

Arifin used gene-targeted mouse models they have generated with collaborators from Sweden — with the mouse prion protein replaced with caribou prion protein — and injected different isolates of CWD into the model. This allowed her to test the susceptibility of the gene-targeted mice to a wide range of CWD strains.

“We did find that the mice that were homozygous for the polymorphism were not susceptible to clinical disease,” says Arifin. “This means they did not develop any clinical signs of CWD during the two years of our experiment.”

Arifin adds that if the mice were heterozygous, they were even more resistant to CWD than if they were homozygous, which was a new finding for chronic wasting disease.

Gilch does note that while the mice didn’t show clinical symptoms of CWD, like drastic weight loss, stumbling, and limb weakness, they did find that they were still carrying CWD prions in their spleens, brains, and feces.

“While they do not show clinical disease, they can still slowly propagate prions and transmit the disease as silent carriers,” says Gilch.

These findings will be helpful for caribou conservation efforts because, as of today, no caribou populations have shown signs of chronic wasting disease infections. However, Gilch says there has been overlap in habitats between caribou and species who have been detected with CWD, like the white-tailed deer, meaning the disease could spread to them soon.

“Species like the woodland caribou are already endangered and declining, so having to deal with CWD on top of all the problems they already face would not be helpful,” she says.   

Finding this polymorphism will also help with disease surveillance, as researchers will know to look for CWD in other tissues than the brain since caribou with that genetic resistance may not be showing clinical signs.

The study will also help inform the work being done by Gilch and her team as part of a National Sciences and Engineering Research Council of Canada Alliance Grant to mitigate the spread of CWD amongst deer populations.

For Gilch and Arifin, this publication represents a culmination of work and funding. Arifin has been mapping polymorphisms in caribou populations for several years. The project has received seed funding from UCalgary, won a Margaret Gunn Endowment for Animal Research award, and received additional funding from Genome Canada and Parks Canada.

“It started very small, but now it’s become a much larger study and project, and we are grateful for all the support we received to pursue this important work,” says Gilch.