Glycoprotein G deletion mutants of equine herpesvirus 1 (EHV1; equine abortion virus) and EHV4 (equine rhinopneumonitis virus)

Glycoprotein G (gG) deletion mutants of EHV1 and EHV4, designated EHV1ΔgG and EHV4ΔgG, were constructed. The growth characteristics of the EHV1ΔgG mutants were similar to the parent virus. All of the EHV4ΔgG mutants grew more slowly in cell culture and produced plaques of different morphology including smaller size. The yields of both gG deletion mutant viruses in cell culture were similar to the parent viruses. Sequencing of the genes flanking gG, Southern blot, PCR and western blot analyses of the mutant viruses demonstrated that the deletions were as expected, except for EHV4ΔgG mutants, which in addition to deletion of gG contained unexpected deletions in the adjacent down stream gene ORF 71 (glycoprotein 2). Antisera to EHV1ΔgG and EHV4ΔgG neutralised the respective mutant and the parent viruses to the same titre and these antisera could be distinguished from antisera to the wild type viruses in a gG antibody detection ELISA. The mutant viruses may be useful as vaccine candidates and the deletion of gG may act as a marker to distinguish vaccinated from the naturally infected horses.