Chronic Wasting Disease (CWD) is a neurological condition that affects cervids, the family of animals including deer, elk, and moose. This disease, which is spreading across North America and other parts of the world, raises serious questions about potential risks to human health. While no human case of a prion disease has been definitively linked to CWD exposure, scientific research continues to evaluate the possibility of the disease crossing the species barrier and infecting people.
Defining Chronic Wasting Disease and Prions
Chronic Wasting Disease is a neurodegenerative disorder affecting cervids, including deer, elk, and moose. The disease is caused by an infectious agent called a prion, which is an abnormally folded protein lacking any genetic material like DNA or RNA. These misfolded prions replicate by forcing normal, healthy prion proteins within the host’s body to change into the abnormal shape.
The accumulation of these prions in the central nervous system, particularly the brain and spinal cord, leads to characteristic microscopic holes in the tissue, a process called spongiform encephalopathy. Clinical signs in infected animals include chronic weight loss, behavioral changes, excessive salivation, and incoordination, which worsen over time. CWD prions are shed into the environment through bodily fluids like saliva, urine, and feces, and they can remain infectious in the soil for years, contributing to the disease’s spread among cervid populations.
Current Scientific Consensus on Human Transmission Risk
The primary concern is whether CWD prions can overcome the “species barrier” and infect humans, similar to how Bovine Spongiform Encephalopathy (BSE) transmitted to people. Major health organizations, including the Centers for Disease Control and Prevention (CDC), state that no human CWD infections have ever been reported. However, the possibility of transmission is considered a theoretical risk.
The species barrier is a natural defense mechanism where differences between the prion proteins of two species make transmission inefficient or impossible. Laboratory studies testing this barrier have produced mixed results. Some studies using transgenic mice engineered to express human prion protein failed to develop clinical disease after CWD exposure, suggesting a strong barrier exists. Conversely, other research suggests the barrier may not be absolute, as certain lines of humanized transgenic mice have shown susceptibility to CWD infection.
Studies in non-human primates have also demonstrated varying susceptibility: squirrel monkeys developed the disease after both intracerebral and oral exposure, while cynomolgus macaques have shown conflicting results. Epidemiological studies have not found a significantly increased risk of human prion disease in areas where CWD is endemic. Despite millions of people having consumed venison from CWD-endemic areas over decades, a definitive link between CWD and a human prion disease has not been established. Nevertheless, the long incubation period of prion diseases means that symptoms could take many years, potentially decades, to manifest, making long-term surveillance necessary.
Contextualizing Human Prion Diseases
CWD belongs to a family of fatal brain disorders called transmissible spongiform encephalopathies (TSEs). The most common human prion disease is Creutzfeldt-Jakob Disease (CJD), which affects about one to two people per million globally each year. Most CJD cases occur spontaneously, without a known cause, and are referred to as sporadic CJD.
The concern about CWD stems from the historical precedent of Variant Creutzfeldt-Jakob Disease (vCJD), which resulted from consuming beef contaminated with BSE prions. This demonstrated that an animal prion disease could cross the species barrier and cause a novel human illness. Unlike sporadic CJD, which typically affects older individuals, vCJD often presented in younger people and had distinct clinical and pathological features.
The potential outcome of a CWD transmission event would be a severe, untreatable, and progressive neurodegenerative disease for humans. The possibility that a human disease acquired from CWD could mimic a rare subtype of sporadic CJD makes its detection challenging through typical surveillance, driving public health recommendations to minimize exposure.
Practical Guidance for Minimizing Exposure
Minimizing exposure to CWD prions involves several practical steps for hunters and individuals who consume venison. The CDC recommends not shooting, handling, or consuming any animal that appears sick, lethargic, or is acting strangely. In areas where CWD is known to be present, hunters should consider having harvested deer or elk tested for the disease before consuming the meat.
Proper carcass handling is important because prions concentrate in specific tissues.
Carcass Handling Precautions
- Wear latex or rubber gloves when field dressing and processing a cervid.
- Avoid cutting through the brain, spinal cord, and bone.
- Minimize handling of high-risk tissues, including the eyes, spleen, and lymph nodes.
- Dispose of all high-risk parts properly, often by double-bagging and taking them to a landfill, rather than leaving them in the environment.
Prions are highly resistant to conventional sterilization, so cooking does not destroy the infectious agent. Instruments and surfaces used for processing should be thoroughly cleaned, then disinfected by soaking for an hour in a 50/50 solution of household chlorine bleach and water.