We have developed a West Nile virus (WNV) subgenomic replicon harboring the secreted alkaline phosphatase (SEAP) reporter gene instead of viral structural genes (designated repWNV/SEAP). The repWNV/SEAP allowed easy evaluation of viral replication efficiency by direct measurement of SEAP secretion in the cell culture medium in physical containment level 2 facilities. Furthermore, we validated the availability of this system using a known anti-flavivirus gene, mouse oligoadenylate synthetase 1b

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... Oas1b). The Oas1b-transfected cells were more resistant to repWNV/SEAP replication than the original cells. Thus, this system not only affords a useful tool for identification/evaluation of anti-flavivirus genes/drugs in terms of safety, ease of use and reliability, but should be able to reduce or replace the bioassay using laboratory animals.