First, minute amounts of classical scrapie (Dawson, Langlade, UKA2 and SC21), BSE, atypical BSE (BSE-H and BSE-L), and CWD were subjected to serial rounds of rec-PMCA using ovine and cervine rec-PrP substrates complemented with PRNP−/− brain homogenate. This evidence concerns the gene PRNP and scrapie.