ABSTRACT
In this chapter we would like to show that the methodology associated with the profile likelihood approach is not restricted to clinical trials but can be used successfully in other areas. Here, we consider a quite typical situation arising in disease surveillance with data arising from an observational study framework. The following introduction to the issue and problems of scrapie follows closely the recent work of Del Rio Vilas et al. (2007). Scrapie is a fatal neurological disease affecting small ruminants belonging to the group of diseases known as transmissible spongiform encephalopathies (TSE) that among others include bovine spongiform encephalopathy (BSE) in cattle and CreutzfeldtJakob disease (CJD) in humans. BSE was first detected in 1986 and was shown to spread between cattle by contaminated concentrate, see Wilesmith et al. (1988). In 1996 it became evident and likely that BSE transmits to humans and gives variant CJD (Will et al. (1996)). Throughout Europe, scrapie has acquired increased interest because it is considered a potential threat to public health after the successful experimental transmission of BSE to sheep, see Foster et al. (2001) and the likely exposure of sheep to concentrate feed contaminated with the BSE agent, see Hunter (2003). In order to obtain better estimates of the scrapie prevalence throughout the EU, active surveillance for scrapie in small ruminants was introduced in 2002. The surveillance comprised both slaughtered and found-dead animals, namely the abattoir (AS) and fallen stock (FS) surveys respectively, with the target numbers calculated for each country based on the adult sheep and goat populations (European Commission (2001)).
