Comparison of Enzyme-Linked Immunosorbent Assay-Based Techniques for the Detection of Antibody to Rift Valley Fever Virus in Thermochemically Inactivated Sheep Sera

Different enzyme-linked immunosorbent assay (ELISA)-based techniques for the detection of antibodies to Rift Valley fever virus (RVFV) have been developed in recent years, but their diagnostic sensitivity was not directly compared. In addition, their use might still be restricted to high biocontainment facilities when sera to be tested are collected from viremic individuals. In this study, we report on direct comparison of various ELISA forms for the detection of anti-RVFV antibody in preinactivated sera using a simple thermochemical treatment. Results in naive and treated sera from experimentally infected sheep demonstrate that inactivation method used had no adverse effect on ELISA readings, but the assays analyzed differ in their ability to detect the early humoral responses to infection with RVFV. The IgM-capture ELISA was slightly more sensitive than the IgG-sandwich ELISA to detect early humoral response after infection. The indirect IgG ELISA, using Protein G Horseradish Peroxidase, was less sensitive in detecting seroconversion than the IgG-sandwich ELISA, but this problem was alleviated when using anti-sheep IgG conjugated with Horseradish Peroxidase. The high concentration of viral antigen in sheep sera collected shortly after infection might contribute to false-positive results in the inhibition ELISA, but its ability to detect seroconversion was comparable to that of IgM-capture ELISA.