New study explores potential cross-species spread of chronic wasting disease

Chronic wasting disease (CWD) is generally associated with animals. But a new study by researchers from the University of Calgary and international collaborators explored the potential for CWD to spread from deer, elk and other cervid (hooved, plant-eating) animals to other species.

There has never been a confirmed case of CWD in humans. However, researchers say the findings reinforce the need for continued surveillance and research as the disease expands geographically.

Caused by infectious proteins known as prions, CWD, a fatal neurological illness, continues to spread across North America, including growing regions of Alberta.

In a newly published study in Science Advances, researchers from the University of Calgary and collaborators around the world explored the cross-species spread potential of CWD in controlled laboratory settings. While most animals remained asymptomatic, researchers detected low levels of prions in tissues transferred to samples of other species that developed symptoms 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.

An evolving and unpredictable disease

Prions are unusual infectious agents because they can change and adapt as they move between hosts, potentially giving rise to new strains with different biological properties.

“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.”

Researchers say this variability makes prion diseases especially difficult to predict and control.

CWD also spreads in ways that make containment challenging. Infected animals can carry and shed infectious prions into the environment for months or even years before showing symptoms, contaminating soil and vegetation through urine and feces.

“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 researchers know and what remains uncertain

“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.”

Researchers note that prion diseases have crossed species barriers before. The best-known example is bovine spongiform encephalopathy (BSE), or “mad cow disease,” which was transmitted from cattle to humans.

While current evidence suggests the barrier between CWD and humans is strong, experimental studies like this continue to explore whether prions could adapt over time in ways that alter transmission potential and disease manifestation.

Why spread matters

Although the risk to humans is considered low, researchers say increasing prevalence in wildlife raises the importance of ongoing monitoring and mitigation efforts.

“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 investigating ways to slow transmission in cervid populations. Recent vaccine studies in mouse models designed to mimic infection in deer and elk showed promising early results, with vaccinated animals shedding fewer infectious prions during early and late stages of disease and surviving longer after 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 CWD continues to spread, researchers say understanding how prion diseases behave, including the potential for silent or atypical infections, remains critical for protecting both wildlife and public health.