The transmission dynamics of the aetiological agent of scrapie in a sheep flock

We formulate and investigate the properties of a model framework to mimic t he transmission dynamics of the aetiological agent of scrapie in a sheep ho ck. We derive expressions for summary parameters that characterize transmis sion scenarios, notably the basic reproduction number R-0 and the mean gene ration time T-g. The timescale of epidemic outbreaks is expressed in terms of R-0 and cumulants of the generation time distribution. We discuss the re lative contributions to the overall rate of transmission of horizontal and vertical routes during invasion and in endemicity. Simplified models are us ed to obtain analytical insight into the characteristics of the endemic sta te. (C) 2000 Elsevier Science Inc. All rights reserved.