Applicability of current bovine spongiform encephalopathy (BSE) diagnostic procedures for chronic wasting disease (CWD)

Extended application of the rapid post-mortem test kit for bovine spongiform encephalopathy to chronic wasting disease

Chronic wasting disease (CWD) is a prion disease affecting cervid species primarily in the United States of America and Canada; however, it is now emerging in Scandinavian countries. Although CWD cases have not been reported in Japan, in case of a CWD outbreak, it is critical to prepare for testing a large number of specimens. In the present study, we showed that a rapid post-mortem test kit, which is used for bovine spongiform encephalopathy surveillance in Japan, is valid for CWD prion detection. This article is protected by copyright. All rights reserved.

Monitoring of chronic wasting disease using real-time quaking-induced conversion assay in Japan

There has been no report on Chronic wasting disease (CWD) cases in Japan to date; however, there is concern about the geographic spread of CWD. To clarify the CWD status in Japan, we conducted CWD monitoring using real-time quaking-induced conversion (RT-QuIC) assay which can detect the low level of CWD prions. A total of 690 obex samples collected from sika deer and Reeves's muntjac in Hokkaido and Honshu was tested for CWD prions. No CWD-positive cases were found, suggesting that CWD is nonexistent in Japan. Our results also indicate that RT-QuIC assay is useful for continuous monitoring of CWD. Furthermore, nucleotide sequence analysis of the PrP gene revealed sika deer in Japan harbor CWD susceptible allele.

Scientific opinion on chronic wasting disease (II)

The European Commission asked EFSA for a scientific opinion on chronic wasting disease in two parts. Part one, on surveillance, animal health risk-based measures and public health risks, was published in January 2017. This opinion (part two) addresses the remaining Terms of Reference, namely, 'are the conclusions and recommendations in the EFSA opinion of June 2004 on diagnostic methods for chronic wasting disease still valid? If not, an update should be provided', and 'update the conclusions of the 2010 EFSA opinion on the results of the European Union survey on chronic wasting disease in cervids, as regards its occurrence in the cervid population in the European Union'. Data on the performance of authorised rapid tests in North America are not comprehensive, and are more limited than those available for the tests approved for statutory transmissible spongiform encephalopathies surveillance applications in cattle and sheep. There are no data directly comparing available rapid test performances in cervids. The experience in Norway shows that the Bio-Rad TeSeE™ SAP test, immunohistochemistry and western blotting have detected reindeer, moose and red deer cases. It was shown that testing both brainstem and lymphoid tissue from each animal increases the surveillance sensitivity. Shortcomings in the previous EU survey limited the reliability of inferences that could be made about the potential disease occurrence in Europe. Subsequently, testing activity in Europe was low, until the detection of the disease in Norway, triggering substantial testing efforts in that country. Available data neither support nor refute the conclusion that chronic wasting disease does not occur widely in the EU and do not preclude the possibility that the disease was present in Europe before the survey was conducted. It appears plausible that chronic wasting disease could have become established in Norway more than a decade ago.

Tracing conformational transition of abnormal prion proteins during interspecies transmission by using novel antibodies

Conformational differences in abnormal prion proteins (PrP(Sc)) have been postulated to produce different prion phenotypes. During the interspecies transmission of prions, the conformation of PrP(Sc) may change with passage; however, little is known about the mechanism of PrP(Sc) transition. In this study, novel PrP(Sc)-specific monoclonal antibodies (mAbs) were developed that could detect the PrP(Sc) of mouse but not that of sheep. By using these mAbs, we attempted to examine PrP(Sc) accumulated in mice inoculated with sheep scrapie serially up to five passages. The presence of PrP(Sc) in the mice was confirmed at all passages; however, mAb-bound PrP(Sc) conformer was detected only from the third passage onward. The generated mAb enabled tracing of a particular conformer during adaptation in sheep-to-mice transmission of prion, suggesting that the conformational transition of PrP(Sc) was caused by propagation of this conformer. Such mAbs capable of discriminating conformational differences may allow us to address questions concerning PrP(Sc) conformation and strain diversity.