Chronic wasting disease (CWD) is a neurodegenerative disease caused by a prion that affects cervids including deer, elk and moose. At one time, CWD was an obscure illness that seemed to occur only in a small geographic area in northeastern Colorado and southeastern Wyoming. However, this disease is now found in wild and/or farmed cervids in many other states in the U.S., where it appears to be slowly spreading, and in parts of Canada. South Korea reported outbreaks among captive cervids between 2004 and 2010, after importing infected animals from Canada, and Norway detected CWD in wild cervids in 2016.

Chronic wasting disease can be devastating in farmed herds. This disease is always fatal once the clinical signs appear, and most or all of the herd can eventually become infected. It is one of the most difficult prion diseases to control: CWD prions are transmitted from animal to animal, and they can also be spread from contaminated environments for up to two years or more. Thousands of captive or wild deer and elk have been killed in the U.S. and Canada in control efforts. In addition, there are concerns about any potential for CWD to affect other species, including humans. Cooking does not destroy prions, and ingestion of another prion, the agent that causes bovine spongiform encephalopathy (BSE), has been linked to a fatal human neurological disease. CWD prions have been found in muscle (meat), as well as other tissues of cervids, and could enter the food supply. The evidence so far suggests that CWD does not affect humans, livestock or wild predators of cervids; nevertheless, the possibility that it could be zoonotic has not been ruled out.