Equine herpesvirus 1 infection in mares vaccinated with a live-virus rhinopneumonitis vaccine attenuated in cell culture.

Vaccination, in July and again in either November or December 1976, of 55 pregnant Standardbred mares with a live-virus rhinopneumonitis vaccine attenuated in cell culture failed to protect some mares from infection with equine herpesvirus 1. From 1976-12-08 to 1977-03-08, 33 mares foaled healthy foals, 16 mares foaled dead foals or live foals which died usually within 48 hours and six mares aborted. Gross and histological examinations and virus isolation studies confirmed that equine herpesvirus 1 caused 18 of the 22 neonatal deaths, stillbirths or abortions.