Classical and Atypical Scrapie in Sheep and Goats

Scrapie is a naturally occurring transmissible spongiform encephalopathy (TSE) in sheep, goats and mufflons almost world-wide and is known for about 250 years. It is characterized by the accumulation of an abnormal isoform (PrPSc) in the central nervous system which leads to progressive neurodegeneration and death. Scrapie represents the prototype of the so-called prion diseases. It is observed to date as two types, classical and atypical scrapie. The susceptibility to both types is modulated by polymorphisms of the prion gene. Whereas classical scrapie is clearly a naturally occurring transmissible disease, atypical scrapie may also be caused by the spontaneous misfolding of prion protein. This review gives an overview on the current knowledge of classical and atypical scrapie in sheep and goats with special emphasis on epidemiology, clinical and pathological signs, genetic susceptibilities, diagnosis and the characteristics of the most common scrapie strains.