10 Scrapie, Chronic Wasting Disease, and Transmissible Mink Encephalopathy

Transmissible spongiform encephalopathies (TSE) such as scrapie in sheep and goats, transmissible mink encephalopathy (TME), and chronic wasting disease (CWD) of cervids belong to a group of diseases that affect both humans and animals, known as prion diseases. They are associated with alterations in conformation of a neural cell-surface glycoprotein, the prion protein (PrP C ) that aggregates and accumulates in the brain of affected animals or humans. This abnormal form of PrP (PrP Sc , also called PrP-res) is thought to be an essential component of the infectious particle causing TSEs, named prion (Prusiner 1982). In mice, it has been shown that TSE development is dependent on the agent strain, the infectious dose, and the host genotype (Bruce et al. 1991). Recent data now indicate that development of scrapie in sheep, CWD, and TME follows the same rules. 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 of unknown etiology. 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 whose 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.