Genetics Research Helps Scuttle Scrapie

Contagious, incurable and fatal, scrapie is the sheep industry’s chief disease priority, costing U.S. producers an estimated $20 million every year. Scrapie's name reflects the disease’s most distinctive symptom: an uncontrollable itching sensation that causes afflicted sheep to compulsively scrape their bodies against nearby objects.

In a diseased animal, abnormally folded prions—proteins that occur in all mammals—cause the naturally produced prions to fold abnormally as well. As the misfolded proteins amass, they cause neurological problems and death. Most sheep die one to six months after symptoms appear, although they may be infected for years without showing any signs.

Genetic predisposition to the disease is related to variations in amino acid sequences coded within each sheep’s DNA. Selective breeding for resistance could one day reduce the genetic risk of developing scrapie and may eventually eradicate it.

Drawing from a diverse group of U.S. sheep, Michael P. Heaton, a geneticist at the Roman L. Hruska U.S. Meat Animal Research Center (USMARC) in Clay Center, and his colleagues have resequenced the prion gene, identifying new genetic variation.

This achievement has improved commercially available genotyping tests and enhanced the national scrapie eradication program run by the U.S. Department of Agriculture's Animal and Plant Health Inspection Service. Essentially, this research is improving the speed, cost and quality of anti-scrapie breeding methods.

The scientists have identified and stored DNA from 15 common sheep breeds. This information is freely available to researchers and testing labs to facilitate diagnosis and eventual scrapie eradication.

In short, the ARS researchers have amassed a detailed body of knowledge allowing them to test sheep for scrapie susceptibility with great accuracy. With that information, breeders can select less-susceptible sheep and breed more scrapie-resistant flocks.

ARS is the USDA's chief scientific research agency.