Classical BSE prions emerge from asymptomatic pigs challenged with atypical/Nor98 scrapie

Abstract

Pigs are susceptible to infection with the classical bovine spongiform encephalopathy (C-BSE) agent following experimental inoculation, and PrP^Sc accumulation was detected in porcine tissues after the inoculation of certain scrapie and chronic wasting disease isolates. However, a robust transmission barrier has been described in this species and, although they were exposed to C-BSE agent in many European countries, no cases of natural transmissible spongiform encephalopathies (TSE) infections have been reported in pigs. Transmission of atypical scrapie to bovinized mice resulted in the emergence of C-BSE prions. Here, we conducted a study to determine if pigs are susceptible to atypical scrapie. To this end, 12, 8-9-month-old minipigs were intracerebrally inoculated with two atypical scrapie sources. Animals were euthanized between 22- and 72-months post inoculation without clinical signs of TSE. All pigs tested negative for PrP^Sc accumulation by enzyme immunoassay, immunohistochemistry, western blotting and bioassay in porcine PrP mice. Surprisingly, in vitro protein misfolding cyclic amplification demonstrated the presence of C-BSE prions in different brain areas from seven pigs inoculated with both atypical scrapie isolates. Our results suggest that pigs exposed to atypical scrapie prions could become a reservoir for C-BSE and corroborate that C-BSE prions emerge during interspecies passage of atypical scrapie.

Figure 1

PrP^res detected in PMCA reactions seeded with brain material (parietal cortex) from atypical scrapie inoculated pigs. Positive PMCA reactions show an identical glycoform pattern to that of cattle C-BSE prions and/or cattle C-BSE propagated in tgBov substrate (third line). Positive reactions were obtained from pigs inoculated with both original atypical scrapie isolates (PS152 isolate: P-1215 and P-1216; TOA3 isolate: P-1228). PMCA reactions seeded with brain homogenate from a TSE negative sheep and unseeded PMCA reactions are included as controls of the technique. PMCA reactions were subjected to 3 amplification rounds (15 s sonication, 14 min 50 s incubation at 39 °C) in a Qsonica700 sonicator and analyzed for PrP^res by western blot using the monoclonal anti-PrP antibodies Sha31 and 12B2. WB control = classical scrapie isolate.