Serological and virological investigations of an equid herpesvirus 1 (EHV-1) abortion storm on a stud farm in 1985.

An extensive outbreak of EHV-1 abortions occurred on a stud farm in England in 1985. Of the 67 pregnant mares present on the stud farm, 31 were challenged with EHV-1, resulting in the loss of 22 fetuses or foals. Laboratory investigations revealed that the spread of the virus closely followed movement of apparently healthy mares (during the incubation period of the infection). During the outbreak mares were challenged 1-4 months before the expected foaling date. There was no relationship between the gestational age at the time of challenge and the subsequent outcome of infection in terms of abortion. The period between the estimated date of infection and abortion varied between 9 days and 4 months. Virus was isolated from the nasopharynx of 3 apparently healthy foals born during the outbreak.