No Evidence of Uptake or Propagation of Reindeer CWD Prions in Environmentally Exposed Sheep

Abstract Background: Chronic wasting disease (CWD) is a prion disease of cervids. In 2016, CWD was discovered for the first time in reindeer. The affected population was situated in Nordfjella mountain region in Norway. In an attempt to eradicate the disease, all reindeer in the region were culled during winter 2017-18. Because many sheep have their summer pasture in Nordfjella, concern exists about the potential cross-species transmission of CWD to sheep. In this study, global positioning system (GPS) data from sheep and reindeer from the relevant time frame were analyzed to determine spatial overlap. Samples of gut-associated lymphoid tissue (GALT) from 503 lambs and sheep having grazed in the region were analyzed for the presence of prions. The rectoanal mucosa-associated lymphoid tissue (RAMALT) from all animals and ileal Peyer's patch (IPP) from 37 of them, were examined by histology, immunohistochemistry (IHC), and enzyme-linked immunosorbent assay (ELISA). Results: GPS data showed a direct overlap in area use between an infected reindeer and some of the sampled sheep. Generally, the sampled sheep herding areas were used intensively by reindeer before culling. No prions were detected in the GALT of sheep. The mean lymphoid follicle number per sample was 22.6 for RAMALT and 37.5 for IPP. Conclusion: Despite evidence of close reindeer to sheep interaction and spatial overlap in Nordfjella, prions were not detected in the GALT of sheep.. We document that the easily accessible RAMALT tissue at the mucocutaneous border is well suitable for slaughterhouse screening of prions in sheep.