Scientists found that chronic wasting disease may spread silently between species, revealing a hidden challenge in the fight against the fatal wildlife disease.
Chronic wasting disease (CWD) is best known as a disease affecting deer, elk, and other cervid (hooved, plant-eating) animals. Now, researchers at the University of Calgary and their international collaborators have taken a closer look at whether the disease could potentially move into other species.
Although no human case of CWD has ever been confirmed, scientists say the new findings highlight the importance of continued monitoring and research as the disease spreads into new areas.
CWD is a fatal neurological disease caused by infectious proteins called prions. It continues to expand across North America, including in growing areas of Alberta.
In a study published in Science Advances, researchers investigated the zoonotic potential of CWD under controlled laboratory conditions. Most of the animals involved in the experiments showed no signs of illness. However, researchers detected low levels of prions in their tissues. When those samples were transferred to other species, the recipient animals developed symptoms associated with 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.
How Prions Can Change Over Time
One reason prion diseases are so challenging to understand is that prions can change as they pass between hosts. Those changes may create new strains with different biological 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 difficult to predict and manage.
CWD is also hard to contain because infected animals can spread prions long before they appear sick. Deer and other cervids may release infectious prions into the environment through urine and feces for months or even years before symptoms develop. As a result, soil and vegetation can become contaminated long before an infection is detected.
“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 Humans
Researchers emphasize that the study does not point to an immediate threat to people.
“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 spread from cattle to humans.
Current evidence indicates that a strong barrier exists between CWD and humans. Even so, studies like this are designed to investigate whether prions might adapt over time in ways that could affect how they spread and how disease develops.
Why Monitoring Chronic Wasting Disease Matters
While experts consider the current risk to humans to be low, they say the continued growth of CWD in wildlife populations makes surveillance and mitigation 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 strategies to reduce transmission among cervids. Recent vaccine experiments using mouse models that mimic infection in deer and elk produced encouraging early results. Vaccinated animals released 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,” 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 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 populations and safeguarding public health.
Reference: “Limited transmission of cervid prions to nonhuman primates provides insights into the zoonotic potential of chronic wasting disease” by Samia Hannaoui, Sandra Pritzkow, Wiebke M. Jürgens-Wemheuer, Dirk Motzkus, Joo-Hee Wälzlein, Karla A. Schwenke, Yo-Ching Cheng, Hanaa Ahmed Hassan, Irina Zemlyankina, Kylee Drever, Michael Beekes, Walter J. Schulz-Schaeffer, Christiane Stahl-Hennig, Sabine Gilch, Claudio Soto, Stefanie Czub and Hermann M. Schätzl, 27 May 2026, Science Advances.
DOI: 10.1126/sciadv.aeb7613
Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.