A review of the epidemiology of scrapie in sheep.

The aim of this review is to summarise and evaluate the data available about the aetiology of scrapie in naturally affected sheep flocks, particularly data concerning the possible transmission of infection between related animals. The author examines data taken from various relevant studies carried out over the last thirty years. The main conclusions are that scrapie is an infectious disease with a genetic influence on the incubation period. The increased risk of disease in the offspring of affected animals is thought to be largely the result of increased genetic susceptibility, with a large proportion of the cases occurring in high-incidence flocks being the result of horizontal transmission of infection.