Scrapie is a prion disease. Like BSE, it is caused by the transmission of protease-resistant prion proteins. Scrapie has an incubation period of 2 to 5 years. Incubation length may depend on the 'strain' of Scrapie. Scrapie is an acquired infection.
Infection can be from pasture where placental tissue carrying the agent is ingested.
The presence of multiple strains of scrapie indicate different initial causes, presumably sporadic or inherited. It appears unlikely or at least extremely unusual for scrapie to be transmitted to man either occupationally or by eating sheep meat. While scrapie is common in sheep, CJD is very rare in man.