A new competitive ELISA detects West Nile virus infection using monoclonal antibodies against the precursor-membrane protein of West Nile virus.

Precursor membrane protein (prM) is found in the envelope of immature West Nile virus (WNV) particles. Anti-prM antibodies are found in flavivirus-infected animal sera, and they are known as relatively virus species specific antibodies. However, there are no known reports of WNV-specific epitope blocking or competitive enzyme-linked immunosorbent assay (c-ELISA) that detect anti-prM antibodies. Two anti-WNV-prM monoclonal antibodies (SHW-29C2 and SHW-31B2) were generated, and c-ELISAs were developed using these monoclonal antibodies. The c-ELISAs were evaluated using WNV-infected chicken sera. Both c-ELISAs detected anti-prM antibodies in WNV-infected chicken sera and showed little cross-reactivity to antisera against Japanese encephalitis virus, St. Louis encephalitis virus, and Murray valley encephalitis virus. The average inhibition of chicken sera at 3 weeks post WNV infection was 61.6% in SHW-29C2-based c-ELISA and 71.8% in SHW-31B2-based c-ELISA. High correlation was seen between percent inhibition in the c-ELISAs and optical density values of an IgG indirect ELISA. Additionally, SHW-31B2-based c-ELISA detected antibodies against a wide variety of WNV strains. Detecting anti-PrM antibodies using c-ELISA could be useful for WNV serodiagnosis.