Laboratory confirmation of African horsesickness in the western Cape: application of a F(ab')2-based indirect ELISA.

Recently a suspected outbreak of African horsesickness in the Western Cape Province resulted in the deaths of four foals and one adult horse. Spleen samples from these animals were subjected to analysis by an enzyme-linked immunosorbent assay (ELISA) which uses F(ab')2 fragments of immunoglobulins to detect African horse sickness virus (AHSV) antigens. The results of the immunoassay were compared with those obtained by isolation followed by serotyping as is currently applied by the Reference Centre at the Veterinary Research Institute, Onderstepoort. Samples of spleen tissue from the four foals contained sufficient antigen to be readily detectable by ELISA. A marginally positive signal was obtained with the tissue from the adult horse. This sample was inoculated onto VERO cells and four days were allowed for viral multiplication. Subsequently, when the cell culture was assayed by F(ab')2-ELISA, a much higher absorbance value than that obtained with the original spleen sample resulted, thus confirming the presence of AHSV in the initial specimen. The F(ab')2-ELISA has potential to be used as an initial diagnostic test to screen for AHSV.