Scrapie and Creutzfeldt-Jakob disease prions.

Scrapie and Creutzfeldt-Jakob disease are caused by prions which can be distinguished from both viruses and viroids. Aggregates of prions are ultrastructurally and histochemically identical to amyloid. Extracellular collections of prions form amyloid plaques within scrapie-infected brain. Prion amyloid plaques seem analogous to viral inclusion bodies in that they are composed of causative pathogens and are not merely a consequence of the disease.