Scrapie
Scrapie is a fatal, degenerative disease affecting the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies and is thought to be caused by a prion. Scrapie has been known since at least 1732 and does not appear to be transmissible to humans.
Scrapie is the oldest known TSE, and under natural conditions only sheep and goats are known to be affected by scrapie. Once infected, the animal remains infected for life. Transmission of the classical scrapie agent is not completely understood, and apparently healthy sheep infected with the agent can transmit disease. Sheep and goats are typically infected as young lambs or kids, though adult sheep and goats can become infected.