PrP(Sc) deposition in nervous tissues without lymphoid tissue involvement is frequently found in ARQ/ARQ Sarda breed sheep preclinically affected with natural scrapie.

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.