No abstract

BackgroundEquid alphaherpesvirus 1 (EHV-1) is one of the main infectious causative agents of abortion in mares and can also be associated with stillbirth, neonatal foal death, rhinopneumonitis in young horses and a neurological disorder called equine herpesvirus myeloencephalopathy (EHM). The neuropathogenicity of the virus was shown to be significantly higher in EHV-1 strains that carry a single nucleotide point (SNP) mutation in the ORF30, which encodes a catalytic subunit of viral DNA polymerase (ORF30 D752). Another gene, ORF68 is frequently used for phylogenetic analysis of EHV-1.Methods27 EHV-1 strains isolated from aborted equine fetuses in Poland, collected between 1993 and 2017, were subjected to PCR targeting the open reading frames (ORFs) 30 and 68 of the EHV-1 genome. PCR products obtained were sequenced and SNPs were analyzed and compared to sequences available in GenBank.ResultsNone of the analyzed sequences belonged to the ORF30 D752neuropathogenic genotype: all EHV-1 belonged to the non-neuropathogenic variant N752. On the basis of ORF68 sequences, the majority of EHV-1 sequences (76.9%) cannot be assigned to any of the known groups; only six sequences (23.1%) clustered within groups II and IV.ConclusionsEHV-1 strains obtained from abortion cases belong to the non-neuropathogenic genotype. Many EHV-1 ORF68 sequences have similar SNPs to those already described in Poland, but a clear geographical distribution was not observed. A single particular ORF68 sequence type was observed in strains isolated from 2001 onwards.Electronic supplementary materialThe online version of this article (10.1186/s12985-018-1093-5) contains supplementary material, which is available to authorized users.

The purpose of the present review was a comparison of the abortions caused by EAV and EHV-1 viruses over the 34 years. A total of 452 tissues samples from aborted fetuses (347) or foals (105) stillborn or newborn that died within 72 hours were investigated. The material for the examinations came from different farms located throughout Poland. The tissue homogenates were examined by using virus isolation test in RK-13 and Vero cell lines and the cytopathic agent was confirmed as EHV-1 by the direct fluorescent antibody test or as EAV by the indirect fluorescent antibody test. The study indicated that EAV was isolated (104 cases, 23%) almost as equally often as EHV-1 (116 cases, 25.6%). Both, equid herpesvirus-associated abortion and the abortion induced by EAV were characterized by cyclicity. The percentage of EAV and EHV-1 isolation alternately reduced and increased, but the increase of isolation of one virus was accompanied by the decrease of the other. The domination of one virus over the other occurred in cycles of a few years.

Summary Viral causes of abortion include equine viral arteritis (EVA) and infection with equine herpesviruses‐1 and ‐4 (EHV‐1 and EHV‐4). Transmission of equine arteritis virus (EAV) occurs through respiratory, venereal or transplacental routes. Horizontal respiratory transmission of EAV results from exposure to infective nasopharyngeal secretions from acutely infected horses. For this transmission to occur, direct and close contact between horses is necessary. Venereal infection is an efficient method of transmission, with seroconversion of 85 to 100% of seronegative mares bred to virus shedding stallions. Asymptomatic carrier stallions are the essential natural reservoir of equine arteritis virus. Equine herpesviruses‐1 and ‐4 infect a susceptible host, replicate and establish a lifelong latent infection without any associated clinical signs. Reactivation of latent infections can result from factors such as stress and intercurrent disease. The control of these diseases is by implementation of appropriate management and hygiene measures, supplemented by vaccination and, in the case of EVA, by the identification of persistently infected stallions, which can be removed from breeding or continue to be bred to if managed under controlled conditions to prevent the risk of an outbreak of the disease.

No abstract