False-colour transmission electron micrograph of scrapie-associated fibrils (red) in an extract of fresh brain from an infected sheep. Scrapie is a form of transmissible, slow virus encephalopathy which affects sheep & goats. Human slow virus encephalopathies include Kuru, Creutzfeldt-Jakob disease, & Gerstmann-Straussler syndrome. The agents causing these diseases form a group of virus-like organisms called prions. The scrapie- associated fibrils are believed to be aggregations of the major proteins of the infectious agents themselves. Magnification: x36,700 at 6x4.5cm size, x24,000 at 35mm size.