Scrapie

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Scrapie (/ˈskreɪpi/) is a fatal, degenerative disease affecting the nervous systems of sheep and goats.^[1] It is one of several transmissible spongiform encephalopathies (TSEs), and as such it is thought to be caused by a prion.^[2][3] Scrapie has been known since at least 1732 and does not appear to be transmissible to humans.^[4][5] However, it has been found to be experimentally transmissible to humanised transgenic mice^[6] and non-human primates.^[7]

The name scrapie is derived from one of the clinical signs of the condition, wherein affected animals will compulsively scrape off their fleeces 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.^[8]

Scrapie is infectious and transmissible among conspecifics, so one of the most common ways to contain it (since it is incurable) is to quarantine and kill those affected. However, scrapie tends to persist in flocks and can also arise 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 are active areas of research. Recent studies suggest prions may be spread through urine and persist in the environment for decades.^[9]

Scrapie usually affects sheep around three to five years of age.^[10] The potential for transmission at birth and from contact with placental tissues is apparent.^[11]