Reverse ELISA for the detection of anti West Nile virus IgG antibodies in humans.

We have developed a specific reverse ELISA to investigate the potential of the domain III of the West Nile virus envelope protein to detect virus-specific antibodies. For this purpose, the domain III antigen was expressed in Escherichia coli, refolded and directly labelled with peroxidase. By mixing serum samples with the enzyme-labelled antigen, immune complexes will form that are simultaneously recognized by rheumatoid factor coated microtiter plates. Specific antibodies to the domain III were found in 160 out of 206 sera of patients with neutralising antibodies to West Nile virus (77.6% sensitivity). The antigen differentiated reliably between sera of West Nile virus- and dengue virus-infected patients. In combination with indirect immunofluorescence, to exclude four false-positive samples, the specificity was 100% (280 samples). Assuming a prevalence rate of anti-West-Nile virus antibodies of 5%, the positive and negative predictive values were 93.3% and 98.8% respectively. These results indicate that the reverse ELISA using a specific portion of the envelope antigen of West Nile virus is especially suitable for studies on the prevalence of West Nile infections in affected countries.