Development and evaluation of a latex agglutination test for rabies antibodies

The presently recommended tests for estimation of rabies neutralising antibodies like Rapid Fluorescent Focus Inhibition test (RFFIT) and Mouse Neutralisation test (MNT) are laborious, time consuming and not cost-effective for routine use. Simple, rapid and economical tests need to be developed for routine use.

The main objective of the present study was to develop and evaluate a rapid Latex Agglutination Test (LAT) to detect rabies specific antibodies.

Latex beads were coated with purified rabies glycoprotein at a concentration of 1 mg/ml followed by coating with 0.3% bovine serum albumin (BSA). These sensitised beads were used to detect antiglycoprotein antibodies in sera of 152 people who had taken a course of post exposure rabies vaccination with different cell culture vaccines and whose antibody titers were pre determined by MNT. Sera from 52 normal healthy people without any detectable levels of rabies antibodies were included as controls. The test was carried out on glass slides by mixing 20 micro l of sensitised beads and 20 micro l serum.

Preliminary evaluation with rabbit serum of known potency indicated that for clear agglutination of sensitised beads, a minimum of 2 IU/ml of rabies antibody should be present in the serum samples. Visible agglutination was noticed in positive sera with a titer > or =2 IU/ml within 3-5 min after mixing. Seven Sera whose MNT titers were less than 2 IU/ml did not show agglutinati or n. None of the negative control sera showed agglutination. Thus the specificity of the test was 100% and sensitivity was 95.4%.

The LAT described here detects rabies specific antibodies > or =2 IU/ml and can be used to screen large number of sera from vaccinated people to know the protective status after vaccination. This simple and rapid test may be used routinely in antirabies treatment centres to monitor sero conversion in vaccinated people.