Scrapie, a naturally occurring neurodegenerative disease of sheep and sometimes goats, is a prototypic disease for the whole group of the subacute spongiform virus encephalopathies. Kuru was the first human disease of this type to be discovered in 1957 by Gajdusek and Zigas, and its discovery opened the whole field in the human biomedical sciences by the very realization of the fact that viruses may induce disease months or even decades after infections, and that these slow virus diseases are more compatible with classical degenerations of the nervous system than with inflammatory disorders...