Comparison of ELISA and immunoassays for measurement of IgG and IgM antibody to West Nile virus in human sera against virus neutralisation.

Two commercial assays for the detection of IgG antibody to West Nile virus (WNV), an indirect enzyme-linked immunosorbent assay (I-ELISA) and indirect fluorescent antibody test (IFAT), were evaluated against the virus neutralisation test. Excellent agreement with the virus neutralisation was obtained with both tests, i.e., 99.5% by I-ELISA and 100% by IFAT. The well-known serological cross-reactivity within the family of the Flaviviridae was analysed using sera with known antibodies against dengue virus, tick borne encephalitis virus and yellow fever virus. IgM and/or IgG positive sera were examined for reactivity by WNV-ELISA and WNV-IFAT. While cross-reactivity between 0 and 18.2% was recorded with IgM positive sera, there was extensive cross-reactivity of 15.7-100% with IgG positive sera.