Is scrapie solely a genetic disease?
The prion protein (PrP) genotypes of healthy adult Cheviot and Suffolk sheep from UK, Australia and New Zealand were examined. In 168 UK Cheviots the genotype at the highest risk of contracting scrapie (genotype 1) was not found but genotype 2 with a high risk was found in 14% and the genotype with the lowest risk (genotype 13) was found in 19%. In 54 Australian Cheviots two (4%) had genotype 1, 9% genotype 2 and 9% genotype 13. In 102 New Zealand Cheviots none had genotype 1, 17% genotype 2 and 21% genotype 13. In Suffolks the most susceptible genotype (genotype 6) was present in 13% of 69 from UK, 53% of 32 Australian, and 39% of 112 New Zealand sheep. The least susceptible genotype (genotype 13) was present in 33% of UK, 3% of Australian and 8% of New Zealand Suffolks. The presence of scrapie associated alleles in sheep from Australia and New Zealand, both countries free from the disease, is concluded to indicate that scrapie is not solely a genetic disease but requires an additional factor, probably an infectious agent. It is concluded that the rigorous quarantine measures adopted by Australia and New Zealand are justified.