11 Scrapie, Chronic Wasting Disease, and Transmissible Mink Encephalopathy

Scrapie in sheep and goats, transmissible mink encephalopathy (TME), and chronic wasting disease (CWD) of cervids are all caused by prions. These diseases are of great interest both with respect to issues of animal health as well as the safety of the human food supply. In contrast to bovine spongiform encephalopathy (BSE), many attempts to link the ingestion of scrapie prions to the development of Creutzfeldt-Jakob disease (CJD) have been unsuccessful (Chapter 13). The high frequency of CWD among cervids has raised the possibility of cervid prion transmission to cattle and sheep through grazing on shared grasslands. In addition, epidemiologic investigations continue to focus on the frequency of CJD in deer hunters. SCRAPIE Epidemiology Sheep, goats, and moufflon ( Ovis musimon ) (Wood et al. 1992) are susceptible to natural scrapie, and the disease occurs primarily in sheep of breeding age. Scrapie is an enzootic fatal neurodegenerative disorder caused by prions. The disease is also called tremblante (trembling) in France, traberkrankheit in Germany (trotting disease), or rida in Iceland (ataxia or tremor). Scrapie was the first spongiform encephalopathy for which transmissibility was demonstrated (Cuille and Chelle 1936). Epidemiological studies have been conducted on the potential risk of transmission of the scrapie agent to humans but have never supported a causal relationship (Chatelain et al. 1981). Scrapie was initially reported in Europe in 1732 in England and in 1759 in Germany. The etiology of scrapie was already a matter of debate at the beginning of the 19th century. Some authors considered that the...