This suggests that although some sort of modification occurs on passage of classical scrapie into ARR/ARR sheep, such change does not result in the emergence of atypical scrapie or BSE and also reinforces the notion that the interaction between the infecting source and the Prnp genotype of the host has significant impact on the susceptibility to scrapie and on the disease phenotype [21]. This evidence concerns the gene PRNP and scrapie.