Abstract
Equid alphaherpesvirus 1 (EHV-1) is an important pathogen of horses. It is spread worldwide and causes significant economic losses. The ORF33 gene has a conserved region that is often used as target in diagnostic PCR protocols. Single nucleotide point (SNP) mutations in ORF30 are usually used to distinguish between neuropathogenic and non-neuropathogenic genotypes. An ORF68 SNP-based scheme has been used for grouping different isolates. Recently, the highest number of variable sites in EHV-1 from the UK has been found in ORF34. In this study, EHV-1 positive samples from Italian horses with a history of abortion were investigated by amplifying and sequencing the ORF30, ORF33, ORF34 and ORF68 genes. Most animals were infected by the neuropathogenic type A2254G. A 118 bp deletion was found at nucleotide positions 701–818 of the ORF68 gene, making impossible to assign the samples to a known group. Sequencing of the ORF34 gene with a newly designed nested PCR showed new SNPs. Analysis of these sequences and of those obtained from genetic databases allowed the identification of at least 12 groups. These data add depth to the knowledge of EHV-1 genotypes circulating in Italy.
Highlights
Equid alphaherpesvirus 1 (EHV-1) is a DNA virus belonging to the genus Varicellovirus in the family Herpesviridae, subfamily Alphaherpesvirinae
Two out of 20 samples had adenine (A) in position 2254 of the ORF30 gene and 18 had guanine (G), showing that most animals were infected by the EHV-1 neuropathogenic variant N752
Limited data are available on Italian EHV-1 strains; only two sequences of the ORF30 gene are deposited in GenBank (HM125711.1 and HM125712.1) and three strains have been recently investigated by a multi-locus sequence analysis approach [12], sequences are not present in genetic databases
Summary
Equid alphaherpesvirus 1 (EHV-1) is a DNA virus belonging to the genus Varicellovirus in the family Herpesviridae, subfamily Alphaherpesvirinae. The ORF30 gene, which encodes the DNA polymerase gene, is considered a marker of pathogenicity because the potential to cause neuropathogenicity is significantly higher in EHV-1 strains that carry a single nucleotide point (SNP) mutation in this gene [4]. The A to G mutation at nucleotide position 2254 of ORF30 causes a substitution of asparagine (N) to aspartic acid (D) at amino acid position 752 in the catalytic subunit of the viral DNA polymerase. EHV-1 N752 is referred to as a non-neuropathogenic genotype, and D752 as a neuropathogenic genotype. This single amino acid mutation causes replication to a higher level and longer viremia in experimentally infected horses, when compared to animals infected with EHV-1 lacking this particular mutation [5,6]. Comparison between the genomic sequences of the neuropathogenic strain Ab4 and of the non-neuropathogenic
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