Chronic Wasting Disease (CWD) is a fatal neurological disorder impacting members of the cervid family, including white-tailed deer, mule deer, elk, and moose. This transmissible disease is progressive; visual signs develop slowly over 18 to 24 months before becoming obvious. The severe neurological damage in the late stages often results in a “zombie-like” appearance. CWD is always lethal once symptoms manifest.
The Pathology Behind Visible Symptoms
The visible symptoms of CWD result from microscopic damage within the animal’s central nervous system. CWD is a transmissible spongiform encephalopathy (TSE), caused by misfolded proteins called prions. These infectious prions are a corrupted form of normal proteins found in the brain and spinal cord. As prions accumulate, they induce normal proteins to change shape, leading to aggregation and a chain reaction of destruction.
This accumulation creates microscopic holes, or vacuoles, in the brain tissue, giving it a characteristic spongy appearance (spongiform). The progressive destruction of brain cells leads to a gradual loss of control over bodily functions. The earliest visible sign is chronic weight loss, or “wasting,” as the animal loses the ability to properly feed and digest nutrients. This severe emaciation is often accompanied by a rough, dull coat and a sickly appearance.
Neurological impairment in the brainstem, which controls basic functions like swallowing, results in excessive salivation or drooling (hypersalivation). The animal struggles to swallow, leading to a wet muzzle and a lowered head posture. Damage to the cerebellum and other movement-control centers causes ataxia, or a lack of coordination, manifesting as stumbling, tremors, and an inability to walk normally. Behavioral changes are also common, including listlessness, repetitive walking patterns, and a notable loss of wariness or fear of humans.
Transmission Routes and Current Geographic Range
CWD is transmitted through direct contact between animals and indirect exposure to a contaminated environment. Direct transmission occurs when healthy cervids interact with infected individuals via saliva, urine, and feces, which shed infectious prions. Prions are shed throughout the incubation period, often before clinical signs become apparent.
Prions are uniquely durable and can persist in the soil for years, causing indirect environmental transmission. They bind strongly to soil components and remain infectious even after an infected carcass decomposes. This environmental contamination creates a long-term reservoir of infectivity that animals encounter while grazing. The persistence of prions makes the disease difficult to manage once established.
The disease was first identified in captive deer in Colorado in 1967 and has since spread extensively across North America. As of late 2022, CWD had been detected in wild or captive cervid populations in at least 32 states and four Canadian provinces. Key endemic areas with higher prevalence include parts of Colorado, Wyoming, and Wisconsin. Surveillance efforts have also confirmed cases in other regions, including Norway, Finland, and South Korea, underscoring the disease’s global reach.
Guidance for Hunters and Public Safety
The Centers for Disease Control and Prevention (CDC) reports no human cases of CWD infection, but public health agencies advise caution to minimize potential risk. The infectious agent is a prion, and although the species barrier appears strong, transmission to humans is not completely ruled out. Hunters face the highest risk of exposure due to direct contact with cervid tissues.
Hunters operating in CWD-endemic areas should adhere to specific state wildlife agency precautions. It is recommended to have harvested deer or elk tested for the disease before consuming the meat. If an animal tests positive, the meat should not be eaten. Hunters should never shoot or handle any animal that appears sick or acts abnormally.
Proper handling of the carcass is necessary to avoid contact with the most infectious tissues. This involves wearing latex or rubber gloves when field-dressing the animal. Hunters should minimize cutting through the brain and spinal column. Tissues harboring the highest concentration of prions must be avoided, including:
- The eyes
- The spleen
- The tonsils
- The lymph nodes
- The brain and spinal column
Carcasses should be disposed of properly, often by leaving the spinal column and skull within the harvest area or following specific local regulations to prevent environmental contamination.
General public safety involves reporting any cervid exhibiting visible CWD symptoms to local wildlife officials immediately. This vigilance aids surveillance efforts and helps track the disease’s spread. Most states prohibit the transport of whole carcasses from CWD zones, requiring that only de-boned meat, clean hides, and cleaned skull plates or antlers be moved. Following these guidelines protects the public and local cervid populations from further exposure.