Chronic wasting disease (CWD) is most commonly known as a disease that affects wild animals such as deer and elk. But a new study by researchers at the University of Calgary and their international collaborators investigated whether the disease could spread beyond cervids (ungulates, plant-eating animals) to other species.
There are no confirmed cases of CWD in humans. Still, scientists say the new findings highlight the importance of continued surveillance and research as the disease continues to spread to new regions.
CWD is a fatal neurological disease caused by infectious proteins called prions. It is becoming increasingly widespread throughout North America, including in expanding areas of Alberta.
Research investigating the possibility of interspecies transmission
In a study published in scientific progressresearchers used a controlled laboratory experiment 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 these animals were transferred to other species, the recipients showed signs of CWD.
“These findings show that even in the absence of obvious (clinical signs), infectious prions are still present and can be transmitted,” says Samia Hannaoui, Ph.D., a researcher and assistant professor at the University of Calgary’s School of Veterinary Medicine (UCVM) and lead author of the study.
Why prion diseases are difficult to predict
Prions are different from many other infectious agents because they can change as they move between hosts. Over time, this process can generate new strains with different properties.
“We’re not dealing with a single, fixed agent,” says Hermann Schätzl, MD, professor at UCVM and last author of the study. “Prion strains can evolve, and that evolution can influence disease behavior.”
This changing ability makes prion diseases particularly difficult to predict and manage, researchers say.
CWD presents another problem. Animals infected with this disease can shed infectious prions into the environment long before symptoms appear. Prions can be excreted through urine and feces over months or even years, contaminating plants and soil.
“The animal is often infectious for a long time before clinical symptoms appear,” Schatzl says. “That’s what makes this disease particularly difficult to control.”
What the findings mean for human risk
The researchers stress that their results do not suggest an immediate threat to humans.
“While our findings do not indicate an immediate risk to humans, they do suggest that the situation is more nuanced than previously understood,” Schatzle says. “As CWD becomes more prevalent, understanding these dynamics will become increasingly important.”
Scientists also note that prion diseases have crossed species boundaries in the past. One well-known example is bovine spongiform encephalopathy (BSE), commonly referred to as “mad cow disease,” which is transmitted from cows to humans.
Current evidence indicates that a strong barrier exists between CWD and humans. Nevertheless, such studies aim to investigate whether prions can gradually adapt in ways that change the way they spread or cause disease.
Concerns grow over the spread of infectious diseases
Researchers believe the current risk to people is low, but say surveillance and disease control efforts are becoming increasingly important as CWD continues to spread in wildlife.
“The more a disease spreads among animals, the more opportunities there are for transmission,” Schoetzl says. “Risk is related to prevalence.”
Researchers at the University of California, Calgary are also working on ways to potentially reduce transmission between cervids. Early vaccine studies using mouse models that mimic infection in deer and elk have shown promising results. Vaccinated animals shed fewer infectious prions during both early and late stages of disease and survived longer after exposure.
“If we can reduce shedding, we may be able to reduce transmission,” Hanawi said. “That could have important implications at the deer population level.”
As chronic wasting disease continues to spread, researchers say it remains essential to better understand how prion diseases spread and evolve, including the possibility of silent or abnormal infections. That knowledge could play an important role in supporting wildlife conservation and public health efforts in the future.
