Serological Assays to Measure Rabies Antibody Response in Equine Serum Samples

Rabies is a neglected tropical zoonotic disease caused by rabies-virus (RV) infection and is responsible for almost 60,000 annual deaths globally, largely affecting the socio-economically disadvantaged population. Although fatality is preventable by immunization either before or after exposure with therapeutic antibodies, the high cost of prophylaxis or treatment limits their accessibility for the affected population. However, due to the almost 100% fatality rate in symptomatic individuals, almost 29 million annual vaccinations are performed, imposing high financial burden. Human transmission occurs principally through bites from infected dogs and although multiple mammalian species are permissive to RV, transmission from them or from symptomatic humans is rare. To overcome the limitations posed by the requirement of biosafety level-3 (BSL-3) containment for live virus culture, we established a replication-deficient vesicular stomatitis virus (VSV) pseudovirus expressing the Rabies-G (RV-G) protein and a multiplexed Luminex immunoassay for quantifying anti-rabies antibodies in equine sera. The purified pseudovirus exhibited robust luciferase activity and was able to infect multiple mammalian cell lines, although with variable efficiency. Using hyper-immunized equine serum, we observed a strong correlation (ρ > 0.9, p < 0.001) between binding antibody titers measured by the Luminex assay with neutralizing antibody titers determined using the pseudovirus-based neutralization assay. These assays provide a safe, quantitative, and BSL-2-compatible platform for rabies serological evaluation and vaccine testing.