IgG-sandwich and IgM-capture enzyme-linked immunosorbent assay for the detection of antibody to Rift Valley fever virus in domestic ruminants.

The recent occurrence of the first confirmed outbreaks of Rift Valley fever in humans and livestock outside the African region, namely in the Kingdom of Saudi Arabia and Yemen, is of global medical and veterinary concern. Disadvantages of classical techniques for serological diagnosis of Rift Valley fever include health risk to laboratory personnel, restrictions for their use outside endemic areas and inability to distinguish between different classes of immunoglobulins. We report on the development and validation of sandwich and capture ELISAs (both based on inactivated antigen) for detection of IgG and IgM antibody to Rift Valley fever virus in bovine, caprine and ovine sera. Compared to virus neutralisation and haemagglutination-inhibition tests, the IgG sandwich ELISA was more sensitive in detection of the earliest immunological responses to infection or vaccination with Rift Valley fever virus. Its sensitivity and specificity derived from field data sets ranged in different ruminant species from 99.05 to 100% and from 99.1 to 99.9%, respectively. The specificity of IgM-capture ELISA varied between different species from 97.4 to 99.4%; its sensitivity was 100% in sheep tested 5-42 days post-infection. Our results in field-collected, experimental and post-vaccination sera demonstrate that these assays will be useful for epidemiological surveillance and control programmes, import/export veterinary certification, early diagnosis of infection, and for monitoring of immune response in vaccinated animals. As highly accurate and safe tests, they have the potential to replace traditional diagnostic methods, which pose biohazard risks limiting their use outside of endemic areas to high containment facilities.