Scrapie fibrils. Coloured transmission electron micrograph of fibrils associated with scrapie. This 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. Prions are small protein-particles which appear to be self- replicating but uniquely contain no nucleic acid. Scrapie-associated fibrils are believed to be aggregations of the major proteins of the infectious agents. Magnification:x58,000 at 6x6cm size. x200,000 at 8x10 inch size.