An indirect sandwich ELISA utilising F(ab')2 fragments for the detection of African horsesickness virus.

African horsesickness virus (AHSV), an important disease of equines is caused by an orbivirus. Because of the need to contain the spread of the disease, it is often essential to make a rapid diagnosis. For this purpose, an ELISA capable of detecting viral antigen in animal tissue and in cell culture fluid was developed. Immobilised F(ab')2 fragments prepared by digestion of AHSV-specific IgG with pepsin were used to trap virus from tissue homogenates or cell culture supernatant. After addition of intact IgG as detecting antibody, Staphylococcus aureus protein A labelled with horseradish peroxidase was added to allow visualisation of the reaction. Polyclonal antibodies directed against either whole AHSV or viral core particles were suitable as detecting antibodies. On the other hand, a monoclonal antibody that was specific for a major core protein, VP7, gave a much weaker signal in the ELISA. All known AHSV serotypes were recognised in the F(ab')2-ELISA by polyclonal antisera against either whole virus particles or viral cores. Immunoprecipitation of AHSV structural polypeptides showed that such antisera contained populations of antibodies directed against core proteins. The F(ab')2-ELISA has potential as a diagnostic technique for AHSV infections.