Abstract
Equid herpesvirus type 1 (EHV-1) is a common viral infection associated with varied clinical outcomes including respiratory disease, abortion and neurological disease. We have characterized EHV-1 sequences (n = 38) obtained from cases of equine abortion in Poland between 1999 and 2016, based on sequencing of PCR products from open reading frames (ORF) 30 and 68 of the EHV-1 genome. The majority (81.6%) of sequences were not classified into any of the previously described groups based on the ORF68 sequence. The remaining sequences belonged to ORF68 group III (7.9%) or IV (10.5%). A haplotype network analysis did not show any obvious structure within networks of local Polish sequences, nor within a global network of 215 EHV-1 sequences when these networks were coloured based on the geographical origin of viruses or date of detection. Our data suggest that ORF68 does not provide a reliable molecular marker for epidemiological studies of EHV-1, at least in a global sense. Its usefulness to aid local investigations of individual outbreaks remains to be established. All but two Polish EHV-1 sequences belonged to the ORF30 N752 genotype. The two ORF30 D752 viruses were obtained from abortion cases in 2009 and 2010. Hence, abortion cases that occurred in Poland between 1999 and 2016 were caused predominantly by EHV-1 with the ORF30 N752 genotype, with no indication of an increase in the prevalence of the ORF30 D752 variant.
Highlights
Equid herpesvirus 1 (EHV-1) is a common pathogen of horses worldwide [1]
All of the viruses tested as part of the current study belonged to the ORF30 N752 variant genotype based on PCR-RFLP testing, which was confirmed by sequencing
Out of 38 Polish Equid herpesvirus type 1 (EHV-1) sequences analyzed in the current study, three (7.9%) belonged to group III, four (10.5%) belonged to group IV, and the remaining 31 (81.6%) were not classified within any of the groups originally described by Nugent and colleagues [12] (Fig. 2)
Summary
Equid herpesvirus 1 (EHV-1) is a common pathogen of horses worldwide [1]. Many EHV-1 infections are subclinical, but the virus can cause respiratory disease of varying severity, abortion, neonatal death or neurological disease [4]. The frequency of reports of neurological disease associated with EHV-1 infection (equine herpesvirus myeloencephalopathy, EHM) seems to have increased in some parts of the world over the past 10-15 years, causing concerns among horse owners and veterinarians [5]. A feature of EHV-1 that seems to be directly linked to its virulence is the ability of the virus to establish cell-associated viraemia [3, 5, 9]. Virulent variants of EHV-1 seem to be able to establish cell-associated viraemia of higher magnitude than variants of lower virulence [10, 11]
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