Comparative evaluation of a simple indirect immunofluorescence test and mouse neutralization test for assaying rabies antibodies

In this study, we have developed and evaluated a simple indirect immunofluorescence test (IIFT) to detect rabies antibodies in a two-step immunofluorescence assay. One hundred and eighty five serum samples from people who had taken different rabies vaccines and 8 pairs of serum and CSF samples from confirmed paralytic rabies cases were tested by IIFT and results evaluated in comparison to standard mouse neutralization test (MNT). Though the titres of rabies antibodies obtained with IIFT were 2-4 times lesser in comparison to MNT, a significant correlation was seen between the two tests (R = 0.883). The specificity of this IIFT was found to be 97.9% and the sensitivity was 97.2%. These results indicate that this simple and rapid IIFT can be used to screen large number of serum samples to monitor sero-conversion after pre or post exposure vaccination and may also assist in rapid ante-mortem diagnosis of atypical human rabies.