Prions are the abnormal, pathogenic agents that are transmissible and are able to induce abnormal folding of specific normal cellular proteins. Prion disease is an umbrella term for a group of fatal and currently untreatable neurodegenerative diseases that not only affect humans, but also wild and captive animals. These diseases include Creutzfeldt-Jakob disease (CJD) in humans, bovine spongiform encephalopathy (BSE, or ‘mad cow disease’), and chronic wasting disease (CWD) affecting deer, elk and moose.