Abstract
The transmissible spongiform encephalopathies, or prion diseases, are neurodegenerative conditions that affect both humans and animals. They are transmissible experimentally both within and between mammalian species by inoculation with infected tissues and sometimes by ingestion in food. The diseases affecting humans have traditionally been classified as Creutzfeldt–Jakob disease, Gerstmann–Sträussler–Scheinker disease, and kuru. They are rare, affecting about one person per million worldwide per year. By contrast, the prototypic spongiform encephalopathy scrapie is a relatively common, naturally occurring disease of sheep and goats, recognized for well over 200 years and occurring in many countries. Although these diseases have long been of . . .