Evaluation of a prototype sub-unit vaccine against equine arteritis virus comprising the entire ectodomain of the virus large envelope glycoprotein (G(L)): induction of virus-neutralizing antibody and assessment of protection in ponies

An Escherichia coli-expressed recombinant protein (6hisG(L)ecto) comprising the entire ectodomain (aa 18-122) of equine arteritis virus (EAV) glycopro tein G(L), the immunodominant viral antigen, induced higher neutralizing an tibody titres than other G(L)-derived polypeptides when compared in an immu nization study in ponies. The potential of the recombinant G(L) ectodomain to act as a subunit vaccine against EAV was evaluated further in three grou ps of four ponies vaccinated with doses of 35, 70 or 140 mug of protein. Al l vaccinated animals developed a virus-neutralizing antibody (VNAb) respons e with peak titres 1-2 weeks after the administration of a booster on week 5 (VNAb titres of 1.8-3.1), 13 (VNAb titres of 1.4-2.9) or 53 (VNAb titres of 1.2-2.3). Vaccinated and unvaccinated control ponies were infected with EAV at different times post-vaccination to obtain information about the deg ree of protection relative to the levels of pre-challenge VNAb. Vaccination conferred varying levels of protection, as indicated by reduced or absent pyrexia, viraemia and virus excretion from the nasopharynx. The degree of p rotection correlated well with the levels of pre-challenge VNAb and, in par ticular, with levels of virus excretion. These results provide the first ev idence that a sub-unit vaccine protects horses against EAV. The use of the subunit vaccine in combination with a differential diagnostic test based on other EAV antigens would enable serological discrimination between natural ly infected and vaccinated equines.