Chronic wasting disease (CWD) is a disease of the nervous system that results in distinctive brain lesions. CWD affects elk, white-tailed deer, and mule deer, but has not been documented in livestock or humans. The origins of the disease, as well as the modes of transmission, remain unknown. Infected deer and elk appear robust and healthy in the early stages of CWD; clinical signs might not show for years. Mortality typically occurs within months after the appearance of clinical signs. The route of transmission is unknown; likely routes include direct transmission between infected and noninfected animals and infected animals contaminating local environments.