Virus Neutralization Test for Detecting and Quantifying Serum-Neutralizing Antibodies to Epizootic Hemorrhagic Disease Virus (EHDV) (Serotypes 1, 2, and 4-8).

Abstract

The virus neutralization test (VNT) is a functional immunoassay which detects the presence and quantity of neutralizing antibodies. It is a highly sensitive and specific test. As with most neutralization assays, the EHDV VNT does not react with all virus-targeting antibodies, but specifically with those antibodies that bind to VP2, the outermost capsid structural protein of the virus. The interaction between VP2 and neutralizing antibodies can block EHDV cell binding, neutralizing its infectivity. The detection and quantification of neutralizing antibodies are indicative of how protected an animal is against reinfection. The EHD VNT can therefore be a useful tool to monitor the efficacy of a vaccination campaign. VP2 is also the main determinant of EHDV serotype specificity, and so EHDV-neutralizing antibodies which target VP2 are also serotype-specific. Throughdetecting and quantifying neutralizing antibodies, the VNT can discriminate the EHDV serotype responsible for an infection and provides insights into the time of infection. It is considered the gold standard test for identifying and quantifying antibodies against EHDV serotypes present in test serum samples. The assay is performed in vitro and is based on inhibition of virus infectivity in the presence of neutralizing antibodies. A neutralizing antibody titer is determined through the presence or absence of cytopathic effect in a cell monolayer. The VNT is a relatively inexpensive assay using standard laboratory equipment; however, to perform the assay, cell cultures, significant time, intensive labor, and technical skill are required.