Development of a fluorescent antibody virus neutralisation test (FAVN test) for the quantitation of rabies-neutralising antibody.

A microtest named the FAVN test (fluorescent antibody virus neutralisation test), which is an adaptation of the original rapid fluorescent focus inhibition test (RFFIT) has been developed and evaluated. One hundred percent specificity was estimated using 414 sera from dogs sampled in rabies-free areas or from non-vaccinated animals. The accuracy as determined by the agreement between observed and expected values using sera of known titres was satisfactory. Serum samples from unvaccinated and vaccinated dogs (using sera with titres near 0.5 IU/ml) were assayed for rabies antibody by the FAVN test, the RFFIT and the mouse neutralisation test (MNT): comparative results obtained on the same sera with the three tests showed good agreement. Furthermore, distinguishing negative sera from positive sera with low titres is much easier with the FAVN test than with the RFFIT.