Classical and Atypical Scrapie in Sheep and Goats

Scrapie is a naturally occurring transmissible spongiform encephalopathy (TSE) in sheep, goats and moufflons almost worldwide and is known for about 270 years. It is characterised by the accumulation of an abnormal isoform (PrPSc) of host-encoded prion protein (PrPC) 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 protein gene. Whereas classical scrapie is clearly a naturally occurring contagious disease, atypical scrapie is most probably non-contagious and caused by an age-related spontaneous misfolding of the 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 scrapie prion strains.