Chronic Wasting Disease (CWD) is a progressive, fatal neurological disorder affecting members of the cervid family, including deer, elk, and moose. It is caused by an abnormal, misfolded protein, known as a prion, which accumulates in the brain and spinal tissue. This accumulation causes damage that results in a spongy degeneration of the nervous system. CWD has a long incubation period during which the infected animal appears healthy. Understanding the observable signs of CWD helps the public identify potentially infected animals and report them to wildlife authorities.
Behavioral Signs of Infection
The earliest indicators of CWD are often subtle alterations in an animal’s behavior and demeanor. One of the most noticeable behavioral changes is a profound loss of awareness, often manifesting as a diminished flight response or an unusual lack of fear of humans. An infected deer might stand listlessly or appear “out of it,” showing reduced interaction with other animals in the herd.
The neurological damage also affects motor control and coordination, leading to specific changes in movement. Deer may exhibit ataxia, which is a stumbling gait or an exaggerated, wide-based posture, particularly in their hindquarters. Repetitive walking in set patterns or pacing can also be observed in animals with CWD.
In addition to movement issues, infected deer frequently hold their head and ears in a noticeably lowered or drooping position. They might also display tremors, especially of the head. Other behavioral cues include confusion, excessive nervousness, or withdrawal from the group.
Advanced Physical Manifestations
As CWD progresses into its later stages, the most definitive physical characteristic is severe, progressive weight loss. The animal becomes emaciated over time, eventually leading to a dramatically gaunt appearance despite continued eating. This loss of body condition is a hallmark of the advanced stage of the infection.
The neurological damage also impairs the animal’s ability to regulate basic bodily functions, leading to excessive fluid output and intake. Infected deer often exhibit polydipsia (excessive thirst) and polyuria (frequent urination). This increased need for water is often accompanied by excessive salivation or drooling, a symptom known as hypersalivation, which can coat the chin and neck.
Difficulty swallowing, or dysphagia, can result from the impaired neurological control of the throat muscles. This difficulty can sometimes lead to aspiration pneumonia, a common cause of death in CWD-infected animals. Furthermore, the deer’s coat may appear rough, dull, or shaggy, indicating a general decline in health and grooming behavior.
Spread of the Disease and Affected Areas
CWD is transmissible among cervids through the shedding of infectious prions from an infected animal’s bodily fluids. Prions are released into the environment through saliva, urine, feces, and blood. This shedding occurs even during the long incubation period before an animal shows any visible symptoms.
The prions are exceptionally hardy and can persist in the environment for years, particularly by binding to soil and plants. This environmental contamination means that deer can become infected indirectly by grazing on contaminated forage or drinking from shared water sources. The disease can also be spread through the decomposition of infected carcasses.
Geographically, CWD has a widespread distribution across North America, having been reported in free-ranging and captive cervids in more than half of the U.S. states and several Canadian provinces. While originally identified in the western United States, the disease has since been found in all four regions of the country. CWD has also been reported in parts of Europe, including Norway, Finland, and Sweden, as well as South Korea.
Reporting Suspected Cases and Safety Protocols
Anyone who encounters a deer displaying the behavioral or physical signs of CWD should immediately contact their local state wildlife management or conservation agency. Provide the authorities with the exact location and a description of the animal. The public should not attempt to approach, handle, or kill the sick animal. Field personnel are trained to collect the necessary tissue samples for definitive diagnosis after the animal has been humanely euthanized.
While there have been no confirmed cases of CWD transmission to humans, the Centers for Disease Control and Prevention (CDC) advises taking certain precautions due to the theoretical risk. Never consume meat from a deer or elk that appears sick or has tested positive for the disease. Hunters should wear rubber or latex gloves when field dressing an animal to minimize contact with tissues that concentrate prions.
Specific tissues, including the brain, spinal cord, eyes, tonsils, spleen, and lymph nodes, are known to harbor the highest concentrations of prions and should be avoided. Hunters are advised to bone out the meat and minimize handling of the skull or spinal column. Furthermore, regulations often require that hunters do not transport whole carcasses out of areas where CWD is known to exist to prevent environmental spread.