An evaluation of two commercially available ELISAs and one in-house reference laboratory ELISA for the determination of human anti-rabies virus antibodies.

The envelope glycoprotein G of rabies virus in vaccines induces the production of neutralizing antibodies important in the protection against the disease. The measurement of anti-envelope glycoprotein antibodies is a good predictor of the degree of humoral immunity in people during anti-rabies treatment or after vaccination. Several assays exist for the serological determination of antibody protection against rabies virus infection. Antibody neutralization by the rapid fluorescent focus inhibition test (RFFIT) or the fluorescent antibody virus neutralization (FAVN) test is currently the gold standard. Performance of the highly complex RFFIT and FAVN tests, however, requires specialized reference laboratories with expertise with this assay. Although not widely used, ELISA test kits are available and may be an additional option for testing that is more accessible. The aim of the present study was to evaluate available ELISA assays for the determination of anti-rabies antibodies. We compared the Bio-Rad Platelia Rabies II ELISA, DRG Rabies Virus IgG Ab ELISA and Focus Diagnostics Rabies Antibody Detection by ELISA to RFFIT. Bland-Altman plots comparing the Bio-Rad Platelia assay and the Focus Diagnostics assay to RFFIT showed a low degree of variability between the ELISA assays and RFFIT results except in samples with high RFFIT values. The agreement, sensitivity and specificity of Bio-Rad Platelia Rabies II ELISA when compared to RFFIT were 95.1 %, 94.1 % and 95.8 %, respectively. The DRG Rabies assay compared to RFFIT had an agreement of 77.7 %, a sensitivity of 86.7 % and a specificity of 69.4 %. The agreement, sensitivity and specificity of Focus Diagnostics Rabies Detection by ELISA when compared to RFFIT were 82.2 %, 91.7 % and 73.0 %, respectively. Overall, the Bio-Rad Platelia assay showed higher accuracy and specificity than either the DRG or Focus assays. All of these ELISAs, however, measure all antibody types and do not discriminate the neutralizing antibodies as measured by functional assays (RFFIT and FAVN) and cannot be relied upon to predict the neutralizing activity of the sera. The results of this study offer insight into the availability of alternative, less-complex methods to monitor rabies antibody titres in at-risk individuals following vaccination.