Abstract
Multiple locus typing based on sequencing heterologous regions in 26 open reading frames (ORFs) of equine herpesvirus 1 (EHV-1) strains Ab4 and V592 was used to characterise 272 EHV-1 isolates from 238 outbreaks of abortion, respiratory or neurological disease over a 28-year period. The analysis grouped the 272 viruses into at least 10 of the 13 unique long region (UL) clades previously recognised. Viruses from the same outbreak had identical multi-locus profiles. Sequencing of the ORF68 region of EHV-1 isolates from 222 outbreaks established a divergence into seven groups and network analysis demonstrated that Irish genotypes were not geographically restricted but clustered with viruses from all over the world. Multi-locus analysis proved a more comprehensive method of strain typing than ORF68 sequencing. It was demonstrated that when interpreted in combination with epidemiological data, this type of analysis has a potential role in tracking virus between premises and therefore in the implementation of targeted control measures. Viruses from 31 of 238 outbreaks analysed had the proposed ORF30 G2254/D752 neuropathogenic marker. There was a statistically significant association between viruses of the G2254/D752 genotype and both neurological disease and hypervirulence as defined by outbreaks involving multiple abortion or neurological cases. The association of neurological disease in those with the G2254/D752 genotype was estimated as 27 times greater than in those with the A2254/N752 genotype.
Highlights
Equid alphaherpesvirus 1 (EHV-1) commonly known as equine herpesvirus 1, is the most economically and clinically significant equine herpesvirus [1]
Phylogenetic analysis was performed using an artificial peptide consisting of concatenated amino acids of unique long region (UL) and unique short (US) based on 31 non-synonymous substitutions between Ab4 and V592 and seven additional mutations identified by analysis of viruses characterised in this study and published sequences [34,35]
Our investigation established that genetic characterisation has the potential to be a useful aid in the management of EHV-1 outbreaks, based on identification of the G2254/D752 polymerase genotype, the UL clade assignation, and to a lesser extent, ORF68 sequencing
Summary
Equid alphaherpesvirus 1 (EHV-1) commonly known as equine herpesvirus 1, is the most economically and clinically significant equine herpesvirus [1]. The virus has a global distribution in horse populations, causing several clinical syndromes including mild to severe respiratory disease, abortion, neonatal foal death, chorioretinitis, and neurological disorders often referred to as equine herpesvirus myeloencephalopathy (EHM) [3,4,5,6]. The neurological form of the disease is less common than abortion or respiratory disease but can result in fatalities [6]. Pathogens 2019, 8, 7 respiratory epithelium by close contact with infectious animals and inhalation of virus, or in rare cases contaminated feed and water [7,8]. EHM results from the inflammatory response to infection of the vascular endothelium of arteries in the central nervous system (CNS), leading to local haemorrhage, thrombosis, and ischaemia [11].
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