Expression of the major core antigen VP7 of African horsesickness virus by a recombinant baculovirus and its use as a group-specific diagnostic reagent.

The major core protein, VP7, of African horsesickness virus serotype 4 (AHSV-4), the aetiological agent of a recent outbreak of the disease in southern Europe, was expressed in insect cells infected with a recombinant baculovirus containing a cloned copy of the relevant AHSV gene (S7). Analyses of its biochemical and antigenic properties confirmed the authenticity of the protein expressed. The high-level expression of VP7 under the control of the strong polyhedrin promoter of Autographa californica nuclear polyhedrosis virus induced disc-shaped crystals in infected insect cells. This enabled us to purify the protein by a one-step ultracentrifugation procedure and to utilize it for the detection of antibodies raised in horses to various serotypes of AHSV. A serological relationship between AHSV and two other orbiviruses, bluetongue virus and epizootic haemorrhagic disease virus, was also demonstrated.