Abstract
African horse sickness (AHS) is an equine disease with a mortality of up to 90% for susceptible horses. The causative agent AHS virus (AHSV) is transmitted by species of Culicoides. AHSV serogroup within the genus Orbivirus of the Reoviridae family consists of nine serotypes that show no or very limited cross-neutralization. Of the seven structural proteins (VP1-VP7) of AHSV, VP2 is the serotype specific protein, and the major target for neutralizing antibodies. In this report, recombinant VP2 proteins of all nine serotypes were expressed individually by the baculovirus expression system and the immunogenicity of each was studied by immunization of guinea pigs with single VP2 as well as with cocktails of VP2 proteins. Homologous neutralizing antibodies measured by 50% plaque reduction assay showed varying degrees (from 37 to 1365) of titers for different VP2 proteins. A low cross-neutralizing antibody titer was found for genetically related AHSV serotypes. Immunization with VP2 cocktails containing equal amounts of each of the VP2 proteins also triggered neutralizing antibodies albeit to lower titers (4-117) to each of the serotypes in the cocktail. This study is a first step to develop a VP2 subunit vaccine for AHS and our results indicate that VP2 subunit vaccines are feasible individually or in a multi-serotype cocktail.
Highlights
African horse sickness virus (AHSV) is the causative agent of African horse sickness (AHS) which is lethal for up to 90% of infected domestic horses [1]
Recombinant VP2 proteins of nine AHSV serotypes were expressed in Sf9 cells using the baculovirus expression system with VP2 genes under the control of the polyhedron promoter
VP2 protein of orbiviruses is the major determinant of eliciting neutralizing antibodies (nAbs) and has been used as recombinant protein-based vaccine in previous studies [17,21,22,23,31]
Summary
African horse sickness virus (AHSV) is the causative agent of African horse sickness (AHS) which is lethal for up to 90% of infected domestic horses [1]. AHSV infections of zebras and donkeys are less severe and mostly cause mild clinical symptoms or an asymptomatic infection. These equids are carriers of AHSV, which is transmitted by Culicoides midges, in particular by C. imicola in endemic areas [1,2]. AHSV is endemic in tropical and sub-Saharan Africa, but sporadic cases and short-term epidemics in North Africa and Middle-East have been reported in the mid-20th century. In 1987, an outbreak of AHSV-4 on the Iberian Peninsula, which was extended for a few years in Spain and spread to Portugal and Morocco indicating that AHSV had overwintered and spread by European Culicoides midges [1,3]
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