There are important differences between animal species in the distribution of the pathological prion protein isoform in TSEs; in field cases of BSE in cattle it is restricted to the central and enteric nervous systems (CNS and ENS, respectively), whereas in both natural scrapie and experimental sheep BSE abnormal PrP is also found in the lymphoreticular system (LRS) and the peripheral nervous system (PNS) [6]. This evidence concerns the gene PRNP and scrapie.