Scrapie
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.
Scrapie
The prion gene that codes for the prion protein is highly conserved in most mammals, meaning the gene is similar and present in most species of mammals. Three locations on the prion protein gene have been identified as highly polymorphic and may have an effect on scrapie: codons 136, 154, and 171. Codon 154 has not shown any evidence of having a high effect on scrapie susceptibility, but is most likely having an effect on incubation time of the disease. Codons 136 and 171 are thought to control the incubation time as well as the susceptibility of the disease, and are the ones the USDA uses in its breeding standard. Codon 171 has been determined to be the major genetic factor in scrapie susceptibility.