Derivation of a scrapie-free sheep flock from the progeny of a flock affected by scrapie

Abstract

The Cheviot flock at the Institute for Animal Health's Neuropathogenesis Unit (NPU) has endemic scrapie, which affects primarily VRQ/VRQ sheep and at high frequency. A new flock with a full range of PrP genotypes, including the highly susceptible VRQ/VRQ, has been produced on a separate site, from animals in the NPU breeding flock, and it remains scrapie-free after eight years. In contrast, in a parallel flock at the NPU farm, scrapie has reappeared after five years, although the animals were kept in separate accommodation from the scrapie-affected sheep. During this time the NPU breeding flock continued to have scrapie cases. Although it is known that highly susceptible sheep can remain free of infection in a clean environment, this is the first report of the infection being removed successfully from the bloodlines of scrapie-affected sheep. The results confirm that scrapie is not a genetic disease dependent only on the PrP gene sequence, but requires both genetic susceptibility and an infectious agent.