PrPSc deposition in nervous tissues without lymphoid tissue involvement is frequently found in ARQ/ARQ Sarda breed sheep preclinically affected with natural scrapie

Summary. The pathogenesis of natural scrapie in Sarda breed sheep was investigated in 1050 asymptomatic and 49 sick sheep from scrapie-affected flocks. Central and peripheral nervous system, along with lymphoreticular system (LRS) tissues, were subjected to immunohistochemistry (IHC) and Western-blotting (WB) for detection of pathological isoform of the prion protein (PrP^Sc). A total of 69 of the 1050 clinically healthy sheep were found to be infected with scrapie, with PrP^Sc being detected in both the central nervous system (CNS) and enteric nervous system (ENS) plexuses of 60 of the sheep, while IHC and WB yielded evidence of (PrP^Sc) deposition only in lymphoid tissues of the remaining 9 clinically healthy sheep. PrP^Sc was also detected in the CNS, as well as in ENS plexuses from all of the 49 clinically affected sheep. Nevertheless, 18 of the 69 clinically healthy animals (26%, 17 ARQ/ARQ and 1 ARQ/AHQ sheep), along with 3 ARQ/ARQ sheep (6%) of the clinically affected group, showed no IHC or WB evidence of PrP^Sc in lymphoid tissues, but PrP^Sc could be still detected in their CNS and ENS plexuses. The study demonstrates dual CNS and ENS PrP^Sc deposition in Sarda sheep with scrapie, in spite of an apparent lack of lymphoid tissue involvement in a number of cases.