Development of a new neutralization test for measles virus

Sero-epidemiological studies are required to identify populations susceptible to measles. The hemagglutination inhibition (HI) test is no longer sensitive enough to confirm immunity to measles, and at present the particle agglutination (PA) test and enzyme-linked immunosorbent assay (EIA) are employed. The most reliable method is the neutralization test (NT), but it is time-consuming and requires experience. To simplify the NT, a recombinant measles AIK-C virus expressing green fluorescence protein (GFP-MVAIK) was constructed and used as a challenge virus. Plaques and cytopathic effects were visualized under ultraviolet light and detected easily, and measuring the intensity of the fluorescence enabled a reduction in the time-consuming steps. Neutralizing antibody titers of a complete inhibition neutralization test were equivalent to those of a 90% plaque reduction neutralization test. Comparison of four methods, HI, PA, EIA and the complete inhibition neutralization test, showed that only the results of EIA correlated well with those of the complete inhibition neutralization test, but sera with borderline levels by EIA were sometimes negative by the complete inhibition neutralization assay.