Chronic wasting disease (CWD) is commonly associated with animals. But a new study by researchers at the University of Calgary and international collaborators investigated the possibility that CWD can spread from deer, elk and other cervids (ungulates that eat plants) to other species.
There have never been any confirmed cases of CWD in humans. But researchers say the findings support the need for continued surveillance and research as the disease spreads geographically.
CWD, a deadly neurological disease caused by infectious proteins known as prions, continues to spread across North America, including growing regions of Alberta.
In a newly published study, scientific progress, Researchers at the University of Calgary and collaborators from around the world investigated the zoonotic potential of CWD in a controlled laboratory setting. Although most of the animals remained asymptomatic, the researchers detected low levels of prions in the animals’ tissues and transferred the samples to other species that developed symptoms of CWD.
These findings indicate that infectious prions are still present and can be transmitted even in the absence of obvious (clinical signs). ”
Dr. Samia Hannaoui, researcher and assistant professor at the University of Calgary School of Veterinary Medicine (UCVM) and lead author of the study
Evolving and unpredictable disease
Prions are unusual infectious agents because they can change and adapt as they move between hosts, giving rise to new strains with different biological 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.”
Researchers say this variability makes prion diseases particularly difficult to predict and control.
CWD also spreads in ways that make it difficult to contain. Infected animals can carry and release infectious prions into the environment for months or even years before showing symptoms, contaminating soil and plants through urine and feces.
“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 researchers know and what they don’t know
“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.”
Researchers note that prion diseases have crossed species boundaries before. The best-known example is bovine spongiform encephalopathy (BSE), or “mad cow disease,” which is transmitted from cows to humans.
Although current evidence suggests that the barrier between CWD and humans is strong, experimental studies such as this continue to explore whether prions can adapt over time in ways that alter their transmissibility and disease expression.
Why is diffusion important?
Although the risk to humans is considered low, researchers say the increasing prevalence in wildlife makes continued monitoring and mitigation efforts more important.
“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 Calgary are also investigating ways to slow the infection in deer. Recent vaccine studies in mouse models designed to mimic infection in deer and elk have shown promising initial 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,” Hanawi said. “That could have important implications at the deer population level.”
As CWD continues to spread, researchers say understanding how prion diseases behave, including the potential for asymptomatic and atypical transmission, remains important to protect both wildlife and public health.
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Reference magazines:
Hannaoui, S. Others. (2026). Limited transmission of cervid prions to nonhuman primates provides insight into the zoonotic potential of chronic wasting diseases. Science progresses. DOI: 10.1126/sciadv.aeb7613. https://www.science.org/doi/10.1126/sciadv.aeb7613
