Transmission of atypical scrapie to homozygous ARQ sheep.

Two Cheviot ewes homozygous for the ALRQ (ALRQ) prion protein (PrP) genotype were exposed intracerebrally to brain pools prepared using four field cases of atypical scrapie from the United Kingdom. Animals were clinically normal until the end of the experiment, when they were culled 7 years post-inoculation. Limited accumulation of disease-associated PrP (PrP) was observed in the cerebellar molecular layer by immunohistochemistry, but not by western blot or enzyme-linked immunosorbent assay. In addition, PrP was partially localized in astrocytes and microglia, suggesting that these cells have a role in PrP processing, degradation or both. Our results indicate that atypical scrapie is transmissible to ALRQ sheep, but these animals act as clinically silent carriers with long incubation times.