Equine abortion (herpes) virus: evaluation of markers in a field vaccination trial.

Twelve mares were vaccinated with attenuated equine abortion virus (EAV) strain RAC-H. Two nonvaccinated mares served as controls. In at least three mares the vaccination appeared to coincide with a natural infection. This was indicated by characterization of the EAV isolated from nasal secretions of six vaccinated mares, a nonvaccinated control, and also from the lung, spleen, and liver of a fetus aborted by a vaccinated mare. The relative sensitivity of the isolated EAV to dithiothreitol was used to distinguish the RAC-H strain and wild-type virus. Of the 10 EAV isolates, four were recognized as being the vaccine strain while six were recognized as being wild-type strains. Three of the latter originated from two vaccinated mares and a nonvaccinated control, and three were recovered from the fetus. The ability of the EAV strains to form plaques in a cloned line of L cells proved to be unsuitable for use as a marker in this study.