Application of enzyme-linked immunosorbent assays for the diagnosis of emerging equine paramyxovirus infection

Enzyme-linked immunosorbent assays (ELISAs) for the diagnosis of infections with Nipah or Hendra viruses, developed by the Australian Animal Health Laboratory (AAHL), were evaluated for their diagnostic application in Japan. The original ELISA protocols for the two viruses differed, with the method for Nipah virus developed to detect antiviral antibody in swine sera and that for Hendra virus developed to detect the antibody in horse sera. However, preprocessing of horse sera was not necessary for the Nipah virus ELISA as there was no interfering nonspecific reactivity. Cross-reactivity between antibodies against the Nipah and Hendra viruses demonstrated a two times higher OD (450 nm) in a homologous reaction than in a heterologous reaction. While the diagnostic threshold of antibody levels in the Hendra virus ELISA was dependent on OD value, results were easily influenced by the concentration of virus antigen in the test sample. For the diagnosis of either virus infection in horses, more rigorous standards for diagnostic thresholds of antibody titers are recommended. This is a good application model for the diagnosis of these emerging diseases.