Chronic Wasting Disease (CWD) is a transmissible neurological disease of deer and elk that produces small lesions in brains of infected animals. It is characterized by loss of body condition, behavioral abnormalities and death. CWD is classified as a transmissible spongiform encephalopathy (TSE), and is similar to mad cow disease in cattle and scrapie in sheep. Infectious agents of CWD are neither bacteria nor viruses, but are hypothesized to be prions. Prions are infectious proteins without associated nucleic acids.
No treatment is available for animals affected with CWD. Once clinical signs develop, CWD is invariably fatal. Affected animals that develop pneumonia may respond temporarily to treatment with antibiotics, but ultimately the outcome is still fatal. Similarly, no vaccine is available to prevent CWD infection in deer or elk. It follows that controlling CWD is problematic. Long incubation periods, subtle early clinical signs, absence of a reliable ante mortem diagnostic tests, extremely resistant infectious agent, possible environmental contamination, and incomplete understanding of transmission all constrain options for controlling or eradicating CWD.
Chronic wasting disease in free-ranging cervids occurs in contiguous areas of Wyoming, Colorado and Nebraska; this is considered the core endemic area for CWD. Distribution of CWD in free-ranging deer, elk, and moose has been determined primarily through necropsy and examination of tissues from animals showing clinical signs suggestive of CWD (clinically targeted surveillance); this is an efficient approach for detecting new foci of infection. Since 2000, CWD has been detected in free-ranging cervids in several additional states.