Genetic characterization of equine herpesvirus 1 isolates from abortion outbreaks in India

Abstract

Equine herpesvirus 1 (EHV1) is a common pathogen of horses that causes upper respiratory tract disease, abortion, neonatal death and neurological disease. The neurological form of disease is called equine herpesvirus myeloencephalopathy (EHM). During the past decade, the incidence of EHM has been on the rise in Europe, North America, Australia and Asia. Some EHV1 isolates causing EHM exhibit a single-nucleotide polymorphism (SNP) in the DNA polymerase gene (ORF30) at position 2254 (A to G). Further, based on polymorphism in the ORF68, EHV1 isolates have been classified into different groups. The aim of the present study was to estimate the genetic diversity of EHV1 and to determine the prevalence of the neuropathogenic genotype of EHV1 in India. Out of 133 clinical specimens from abortion cases in northern India, 56 were positive for EHV1 infection. Analysis of the A/G SNP by real-time PCR and sequence analysis revealed that 54 of 56 samples (96.43 %) were of the non-neuropathogenic genotype (A), while two (3.57 %) had the neuropathogenic marker (G). Sequence analysis of the polymorphic region of ORF68 of EHV1 isolates (n = 9) from India indicated that the Delhi/1998, Tohana-2/2013, Hisar-2/2014 and Hisar-15/1990 isolates belonged to group 4, while the Jind/1996, Rajasthan/1998, Delhi-3/2007 and Tohana-5/1996 isolates clustered within group 5. One isolate (Hisar-7/1990) exhibited SNPs at positions C and C, forming a separate group. Here, we report for the first time the detection of neuropathogenic genotypes of EHV1 in India and show that Indian EHV1 isolates cluster within groups 4 and 5.

Molecular Characterisation of Equine Herpesvirus 1 Isolates from Cases of Abortion, Respiratory and Neurological Disease in Ireland between 1990 and 2017

“…Since 2006, when it was first proposed by Nugent et al (2006) [21] that the ORF68 polymorphic region was a putative molecular marker for epidemiological studies, this region has been commonly used for genotyping of EHV-1 isolates in different countries: Australia [24], Ethiopia [31], Hungary [30], India [29], Japan [33], and Poland [32]. The study by Nugent et al (2006) [21] identified six major groups (1–6) and two unassigned groups based on analysis of 106 global isolates and proposed that certain strain groups were geographically restricted.…”

“…Cuxson et al (2014) classified 52 Australian isolates as group 2 or 3 and two as group 5 [24]. Ninety-one Ethiopian isolates were restricted to group 4 [31], eight Indian isolates clustered within groups 4 and 5 [29] and a Japanese isolate was classified as group 2 [33]. However, several of these studies also reported a small number of viruses that could not be classified within the original proposed groups [24,29,33].…”

“…The original hypothesis that ORF68 groups are geographically restricted is not supported by the results of our study or those of other investigators. For example, Nugent et al (2006) [21] found that all group 5 isolates came from outbreaks in North America; however, 9% (20/222) of Irish isolates belong to this group, which has been demonstrated to include viruses from Australia [24] and India [29]. Network analysis of Irish isolates with international strains showed that Irish isolates clustered within 7 nodes with isolates from the several different geographic regions.…”

“…Nugent et al (2006) [21] also proposed that a short region spanning approximately 600 bp of ORF68, which encodes virion protein U S 2 [28], was a primary strain marker for classifying EHV-1 field isolates into six groups [21]. However, there have been conflicting conclusions regarding the usefulness of this approach for molecular tracking of EHV-1 in other countries suggesting that it may not be an effective substitute for more detailed sequence analysis [24,29,30,31,32,33].…”

Equid alphaherpesvirus 1 from Italian Horses: Evaluation of the Variability of the ORF30, ORF33, ORF34 and ORF68 Genes

“…In particular, a region of about 600 bp in ORF68 was particularly polymorphic, and therefore it was tentatively adopted as a marker system for efficiently grouping the isolates into six groups [4]. This method was subsequently used for comparing isolates from different geographical regions [7,8,9,10,11,12]. Recently a Multi-locus analysis approach, based on sequencing heterologous regions in 26 open reading frames, proved a more comprehensive method of strain typing than only ORF68 sequencing.…”