New Study Reveals Silent Prion Transmission in Chronic Wasting Disease, Raising Cross-Species Concerns
核心洞察
Researchers at the University of Calgary found that infectious CWD prions can be present and transmissible in animals that show no clinical symptoms, challenging previous assumptions about disease spread.
The study published in Science Advances demonstrates that prion strains can evolve as they move between hosts, making CWD particularly difficult to forecast and manage.
While no immediate human risk is indicated, scientists emphasize that continued surveillance is critical as CWD expands across North America, including growing regions of Alberta.
A landmark study from the University of Calgary Faculty of Veterinary Medicine (搜索) (UCVM) has revealed that chronic wasting disease (搜索) (CWD) can spread silently through animal populations, with infectious prions detected in tissues of hosts that never developed clinical symptoms. The findings, published in Science Advances, underscore the complexity of prion diseases and raise important questions about cross-species transmission potential as CWD continues its geographic expansion across North America.
The research team, led by Dr. Samia Hannaoui, PhD, assistant professor at UCVM and first author on the study, and Dr. Hermann Schaetzl, MD, Dr. med, UCVM professor and senior author, conducted controlled laboratory experiments to investigate the zoonotic potential of CWD. While most animals in the study did not develop symptoms, researchers detected small amounts of infectious prions in their tissues. Critically, when samples from those asymptomatic 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," said Hannaoui.
The Challenge of Evolving Prion Strains
Unlike conventional infectious agents, prions possess a unique ability to change as they move between hosts, potentially producing new strains with different characteristics over time. "We're not dealing with a single, fixed agent," explained Schaetzl. "Prion strains can evolve, and that evolution can influence how the disease behaves." This inherent adaptability makes prion diseases especially challenging to forecast and manage from both a wildlife and public health perspective.
Compounding the problem, animals infected with CWD can shed infectious prions into the environment through urine and feces for months or even years before any symptoms become visible, contaminating vegetation and soil. "By the time you see clinical signs, the animal has often been infectious for a long time," Schaetzl noted. "That's what makes this disease particularly challenging to control."
Human Risk: Low but Nuanced
The researchers are careful to emphasize that their results do not signal 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," said Schaetzl. "As CWD becomes more widespread, understanding these dynamics becomes increasingly important."
To date, there have been no confirmed cases of CWD infecting people. However, the scientific community remains vigilant, particularly given the historical precedent of bovine spongiform encephalopathy (搜索) (BSE), or "mad cow disease," which crossed the species barrier from cattle to humans. The World Health Organization recommended as early as 1997 that agents of all known prion diseases be kept from entering the human food chain.
Current evidence indicates that a strong barrier exists between CWD and humans. Nevertheless, the UCVM study was designed to investigate whether prions could gradually adapt in ways that alter transmission patterns or disease development.
Growing Prevalence and the Case for Surveillance
CWD has now been reported in multiple regions of North America, including expanding areas of Alberta, as well as in Norway and South Korea. "The more the disease spreads in animals, the more opportunities there are for exposure," Schaetzl cautioned. "Risk is linked to prevalence."
The continued expansion of CWD in wildlife populations has intensified calls for robust surveillance and disease control efforts. Researchers at UCalgary are also pursuing proactive interventions, including early-stage vaccine studies using mouse models that mimic infection in deer and elk. These studies have yielded encouraging results: vaccinated animals shed fewer infectious prions during both early and later stages of disease and survived longer following exposure.
"If we can reduce shedding, we may be able to reduce transmission," said Hannaoui. "That could have important implications at the cervid population level."
As CWD continues to spread into new territories, the UCVM team stresses that understanding how prion diseases evolve—including the possibility of silent or atypical infections—will be essential for protecting wildlife and supporting future public health efforts.