A transmissible, invariably fatal disease of adult sheep and goats characterized by degeneration of the central nervous system. It is one of the transmissible spongiform encephalopathies, a disease family which includes bovine spongiform encephalopathy (BSE) in cattle (commonly known as mad cow disease), chronic wasting disease in deer, and Kuru and variant Creutzfeldt-Jakob disease in humans. Scrapie was first discovered in European sheep in the early eighteenth century and is now present in many sheep populations worldwide, excluding Australia and New Zealand.