We then decided to evaluate the possible influence of these differences in PrPc levels in the central nervous system on TSE development, following the inoculation of 3 mouse-adapted strains (BSE, C506M3, 87V), 3 experimental small ruminants isolates (SSBP1, CH1641, BSEOVINE) and 22 small ruminant natural isolates collected by active surveillance of TSEs in sheep and goats (10 classical scrapie isolates, including 3 usual isolates as shown by PrPres molecular analysis and 7 “CH1641-like” isolates; 12 atypical scrapie isolates). The gene discussed is PRNP; the disease is scrapie.