Chronic Wasting Disease (CWD) is a neurological illness that affects members of the deer family, known as cervids. This includes species such as white-tailed deer, mule deer, elk, and moose. It is a progressive and invariably fatal condition. This article explains the typical progression of CWD.
Understanding CWD Progression
After a deer contracts CWD, there is an extended period during which the animal shows no outward signs of illness. This is called the incubation period, which averages 18 to 24 months. Internally, abnormal proteins called prions accumulate and spread throughout the deer’s body. These prions primarily target the central nervous system, including the brain and spinal cord, as well as lymphoid tissues.
Visible Signs and Disease Course
As the disease progresses and prions cause more extensive damage to the brain and nervous system, clinical signs begin to emerge. The most consistent symptom is significant weight loss, often referred to as “wasting,” despite the deer continuing to eat. Behavioral changes become noticeable, such as listlessness, a lowered head, and reduced interaction with other animals. Neurological signs like stumbling, tremors, and a lack of coordination also develop, alongside increased thirst and urination, and excessive salivation. These symptoms gradually intensify, leading to severe debilitation.
Fatal Outcome and Timeline
CWD is fatal, with no known cure or vaccine. The timeline from initial infection to death can vary, but it typically spans many months to several years. While the incubation period usually lasts 18 to 24 months before symptoms appear, once symptoms manifest, deer commonly die within one to twelve months. Progressive neurological damage ultimately leads to the deer’s death, often through secondary complications. These complications can include aspiration pneumonia due to difficulty swallowing, starvation from the inability to forage effectively, dehydration, or increased vulnerability to predators and vehicle collisions due to impaired mobility and awareness.
Factors Influencing Disease Duration
Several factors influence how long a deer lives after becoming infected with CWD. The deer’s age at the time of infection can play a role, with younger deer potentially showing symptoms sooner. Genetic susceptibility also affects disease progression; some deer possess genetic variations that may prolong survival, though complete immunity has not been observed. Additionally, the species of cervid and the strain of the CWD prion can impact the disease’s duration and clinical presentation. While environmental factors do not directly alter the disease’s course, they can indirectly affect survival by exacerbating the deer’s compromised state, such as harsh weather or limited food resources.