Failure to detect equid herpesvirus type 1 DNA in Thoroughbred placentae and healthy new-born foals

Abstract

Equid alphaherpesvirus 1 (EHV-1) is an economically important virus, associated with respiratory infection, late gestation abortion, neonatal death and myeloencephalopathy in horses. The aim of the present study was to test the hypothesis that EHV-1 is present in the nasopharynx and placentae of neonatal foals in the absence of clinical signs of infection. This would suggest that vertical transmission of virus occurs in inter-epizootic periods: such information could inform foaling management and the potential eradication of the virus by vaccination. Samples were collected from animals resident on a single farm in the Western Cape Province, South Africa, which had not experienced a clinical outbreak of EHV-1 recently. Sterile swab samples from 71 post-partum Thoroughbred mares, their healthy full-term foals and fetal membranes were obtained and assayed for EHV-1 and EHV-4 nucleic acid using a duplex quantitative polymerase chain reaction (qPCR). The null hypothesis for this study was that EHV-1 was not present in the nasopharynx and placentae of new-born, viable and healthy foals. As no EHV-1 or EHV-4 nucleic acid was detected on a duplex EHV-1/EHV-4 qPCR assay from the mare and foal nasal and fetal membrane swabs, the null hypothesis was accepted. It was therefore concluded that there was no detectable EHV-1 and -4 DNA in this population at the time of sampling. It was speculated that this may have been due to the cyclical nature of EHV-1 infections. The inclusion of additional breeding seasons on additional farms would be valuable for future studies.