Prion diseases (transmissible spongiform encephalopathies) are rare diseases that affect the brains of people and animals. Creutzfeldt-Jakob disease is the most common human prion disease. Bovine Spongiform Encephalopathy (sometimes called Mad Cow Disease) is a prion disease that affects cows and has been linked to variant Creutzfeldt-Jakob disease in humans.

Animals such as deer, elk and moose can have a prion disease called Chronic Wasting Disease. No cases have been found in people so far, but there may be a small risk for people to get Chronic Wasting Disease from eating the meat of infected animals. Hunters harvesting game from a Game Management Unit where Chronic Wasting Disease has been found in more than five percent of animals should have the carcass tested before eating the meat.