Chronic wasting disease (CWD) is best known as a disease affecting wildlife such as deer and elk. However, a new study from researchers at the University of Calgary and their international collaborators examined whether the disease could potentially move beyond cervid (hooved, plant-eating) animals and infect other species.
There has never been a confirmed case of CWD in people. Even so, scientists say the new findings highlight the importance of continued monitoring and research as the disease continues to spread into new areas.
CWD is a fatal neurological disease caused by infectious proteins called prions. It is becoming increasingly widespread across North America, including expanding regions of Alberta.
Study Examines Cross-Species Transmission Potential
In research published in Science Advances, investigators used controlled laboratory experiments to study the zoonotic potential of CWD. Most of the animals involved did not develop symptoms. However, 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 CWD.
“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 on 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 may produce new strains with different characteristics.
“We’re not dealing with a single, fixed agent,” says Dr. Hermann Schaetzl, MD, Dr. med, UCVM professor and last author on the study. “Prion strains can evolve, and that evolution can influence how the disease behaves.”
According to the researchers, this ability to change makes prion diseases especially challenging to forecast 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.
“By the time you see clinical signs, the animal has often been infectious for a long time,” says Schaetzl. “That’s what makes this disease particularly challenging 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 don’t indicate an immediate risk to humans, but they do suggest the situation is more nuanced than previously understood,” says Schaetzl. “As CWD becomes more widespread, understanding these dynamics becomes increasingly important.”
Scientists also note that prion diseases have crossed species barriers in the past. One well-known example is bovine spongiform encephalopathy (BSE), commonly called “mad cow disease,” which was transmitted from cattle to humans.
Current evidence indicates that a strong barrier exists between CWD and humans. Nevertheless, studies such as this are designed to investigate whether prions could gradually adapt in ways that change how they spread or how disease develops.
Growing Prevalence Raises Concerns
Although researchers consider the current risk to people low, they say the continued expansion of CWD in wildlife makes surveillance and disease control efforts increasingly important.
“The more the disease spreads in animals, the more opportunities there are for exposure,” says Schaetzl. “Risk is linked to prevalence.”
Researchers at UCalgary are also working on potential ways to reduce transmission among cervid populations. Early vaccine studies using mouse models that mimic infection in deer and elk have produced encouraging results. Vaccinated animals shed fewer infectious prions during both the early and later stages of disease and survived longer following exposure.
“If we can reduce shedding, we may be able to reduce transmission,” says Hannaoui. “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.