Chronic wasting disease (CWD) is best known as a disease that affects wildlife such as deer and elk. However, a new study by researchers at the University of Calgary and their international collaborators examined whether the disease could potentially go beyond cervids (clawed herbivores) and infect other species.
There has never been a confirmed case of CWD in people. Still, scientists say the new findings highlight the importance of continued monitoring and research as the disease continues to spread to new areas.
CWD is a fatal neurological disease caused by infectious proteins called prions. It is becoming increasingly widespread in North America, including the expanding regions of Alberta.
Study examines potential for cross-species transmission
In research published in Scientific advancesThe researchers used controlled laboratory experiments to study the zoonotic potential of CWD. Most of the animals involved did not develop symptoms. However, the researchers detected small amounts of infectious prions in their tissues. When samples from those animals were transferred to other species, the recipients developed signs of chronic wasting disease.
“These findings show that even without obvious (clinical signs), infectious prions can still be present and transmissible,” says Dr. Samia Hannaoui, PhD, researcher and assistant professor at the University of Calgary Faculty of Veterinary Medicine (UCVM), and first author of the study.
Why prion diseases are difficult to predict
Prions differ from many other infectious agents because they can change as they move between hosts. Over time, this process can produce new strains with different characteristics.
“We are not dealing with a single, fixed agent,” says Hermann Schaetzl, MD, Dr. med, professor at UCVM and last author of the study. “Prion strains can evolve, and that evolution can influence disease behavior.”
According to researchers, this ability to change makes prion diseases especially difficult to predict and manage.
CWD presents another problem. Animals infected with the disease can release infectious prions into the environment long before symptoms become visible. Prions can be shed through urine and feces for months or even years, contaminating vegetation and soil.
“When clinical signs are detected, the animal has usually been contagious for a long time,” says Schaetzl. “That’s what makes this disease particularly difficult to control.”
What the findings mean for human risk
The researchers emphasize that their results do not point to an immediate threat to humans.
“Our findings do not indicate an immediate risk to humans, but they do suggest that the situation is more nuanced than previously thought,” Schaetzl says. “As CWD becomes more widespread, understanding these dynamics becomes increasingly important.”
Scientists also note that prion diseases have crossed species barriers in the past. A well-known example is bovine spongiform encephalopathy (BSE), commonly called “mad cow disease,” which was transmitted from cattle to humans.
Current evidence indicates that there is a strong barrier between CWD and humans. However, studies like this are designed to investigate whether prions could gradually adapt in ways that change how they spread or how the disease develops.
Rising prevalence raises concern
Although researchers consider the current risk to people to be low, they say the continued spread of CWD in wildlife makes disease surveillance and control efforts increasingly important.
“The more the disease spreads in animals, the more potential there is for exposure,” Schaetzl says. “Risk is linked to prevalence.”
UCalgary researchers are also working on possible ways to reduce transmission among cervid populations. Early vaccine studies using mouse models that mimicked infection in deer and elk have produced encouraging results. Vaccinated animals shed fewer infectious prions during the early and late stages of the disease and survived longer after exposure.
“If we can reduce spread, we may be able to reduce transmission,” Hannaoui says. “That could have important implications at the cervid population level.”
As chronic wasting disease continues to expand, researchers say it remains essential to better understand how prion diseases spread and evolve, including the possibility of silent or unusual infections. That knowledge could play an important role in protecting wildlife and supporting public health efforts in the future.