Scrapie is a fatal, degenerative disease that affects the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies (TSEs), which are related to bovine spongiform encephalopathy (BSE or "mad cow disease") and chronic wasting disease of deer. Like other spongiform encephalopathies, scrapie is caused by a prion. Scrapie has been known since the 18th century (1732) and does not appear to be transmissible to humans.
The name scrapie is derived from one of the clinical signs of the condition, wherein affected animals will compulsively scrape off their fleece against rocks, trees or fences. The disease apparently causes an itching sensation in the animals. Other clinical signs include excessive lip-smacking, altered gaits, and convulsive collapse.
Scrapie is infectious and transmissible among similar animals, and so one of the most common ways to contain scrapie (since it is incurable) is to quarantine and destroy those affected. However, scrapie tends to persist in flocks and can also arise apparently spontaneously in flocks that have not previously had cases of the disease. The mechanism of transmission between animals and other aspects of the biology of the disease are only poorly understood and these are active areas of research. Recent studies suggest that prions may be spread through urine and persist in the environment for decades.
Scrapie usually affects sheep around 3â€“5 years of age. There appears to be the potential for transmission at birth and from contact with placental tissues. There is no evidence that scrapie is infectious to humans.