Transmission dynamics and mechanisms of endemicity of scrapie in the UK sheep population

Scrapie is a fatal neurological disease of sheep which is endemic in the United Kingdom. It is one of the family of transmissible spongiform encephalopathies (TSEs) that includes BSE. In this paper, we developed a micro-simulation model for scrapie in the UK sheep population, incorporating the genetic and structural diversity of the population and infectious contact between flocks through trading. The simulation was fitted to epidemiological data from a range of sources. We found a detection/reporting probability of 16% (95% CI 12-17) for animals dying of scrapie. Prevalence of infected animals in the population was about 0-15%. Infected individuals were found in 9% of flocks overall, rising to 60% in Shetland and 75% in Swaledale flocks. Mean values of R-0 for flocks varied with breed from 2.43 (Shetland) to 0.21 (Suffolk). We also examined the possible long-term persistence of scrapie in the UK flock in the absence of any intervention.