[Scrapie, still always a puzzling infection].

Scrapie belongs to the spongiform encephalopathies in man and animals. The nature of the infectious agent, an "unconventional virus", has not been elucidated so far. The agent starts to replicate in lymphoid tissue, reaches high titers in the brain and induces the formation of amyloid in this organ. After trials to purify the agent, the infectivity proved to be associated with a protein, which has therefore been called "prion", and with rod-like structures from brain tissue (scrapie-associated fibrils, SAF). This protein is considered to be a reaction product of the infection rather than the infectious agent itself.