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Reasons for Performing Study: A silent cycle of equine herpesvirus 1 infection has been described following epidemiological studies in unvaccinated mares and foals. In 1997, an inactivated whole virus EHV-1 and EHV-4 vaccine was released commercially in Australia and used on many stud farms. However, it was not known what effect vaccination might have on the cycle of infection of EHV-1., Objective: To investigate whether EHV-1 and EHV-4 could be detected in young foals from vaccinated mares., Methods: Nasal and blood samples were tested by PCR and ELISA after collection from 237 unvaccinated, unweaned foals and vaccinated and nonvaccinated mares during the breeding season of 2000., Results: EHV-1 and EHV-4 DNA was detected in nasal swab samples from foals as young as age 11 days., Conclusions: These results confirm that EHV-1 and EHV-4 circulate in vaccinated populations of mares and their unweaned, unvaccinated foals., Potential Relevance: The evidence that the cycle of EHV-1 and EHV-4 infection is continuing and that very young foals are becoming infected should assist stud farms in their management of the threat posed by these viruses.

Reasons for Performing Study: EHV-1 and EHV-4 abortion diagnosis is based upon detailed examination of the aborted fetus. However, in some cases, only the placenta is available for examination. Furthermore, the contribution of lesions in the placenta to pathogenesis and diagnosis of EHV-1 and EHV-4 abortion has been neglected., Objectives: To assess the utility of placental examination in equine herpesvirus-1 (EHV-1) and EHV-4 abortion diagnosis., Methods: Sections of allantochorion from 49 herpesvirus abortions were analysed by PCR, in situ hybridisation and immunostaining., Results: Virus-specific nested PCR confirmed the presence of viral DNA in 46 cases; 41 cases were EHV-1-positive and 5 EHV-4-positive. Microscopic changes were nonspecific. Examination of the PCR-positive sections of allantochorion revealed EHV-1 DNA by in situ hybridisation (ISH) in 21 cases and EHV-4 in 4 cases. In 2 samples, DNA of both viruses was present on PCR and ISH. Viral antigen was found by immunohistology in 15 cases. Regarding the localisation of virus in the placentae, both viral DNA and antigen of EHV-1 and EHV-4 were found in endothelial cells of chorionic villi and, occasionally, in trophoblast epithelium. In the stromal endothelium, only EHV-1 was found., Conclusions: The data indicate that examination of placentae is a useful diagnostic aid in EHV-1 and EHV-4 abortion diagnosis., Potential Relevance: Virological examination of the placenta should become standard practice in equine abortion investigations, particularly in those cases where the fetus is not available for examination.