Responses of ponies to equid herpesvirus-1 Iscom vaccination and challenge with virus of the homologous strain

An experimental (Iscom) vaccine previously shown to protect hamsters from lethal challenge with equid herpesvirus-1 (Ehv-1), was tested in horses. Vaccination with Ehv-1 Iscoms induced serum antibodies to the major virus glycoproteins gp10, 13, 14, 17, 18 and 21/22a, whereas antibody responses to gp2 were weak or absent. High levels of virus neutralising antibody of long duration were induced, but did not prevent challenge infection with virus of the homologous strain. However, in the vaccinated ponies there was a significant reduction in clinical signs, nasal virus excretion and cell associated viraemia compared with age-matched unvaccinated controls. There was a strong correlation between pre-challenge levels of serum virus neutralising antibody and the duration and total amount of virus excreted from the nasopharynx.