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

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.

Evaluation of the Variability of the ORF34, ORF68, and MLST Genes in EHV-1 from South Korea

“…In the present study, all isolates had an infrequent deletion of 118 (701–818) bp in the ORF68 gene, which was unclassified. The same results were obtained for the unassigned group in KyA, RacL11, and Italian isolates [ 16 , 29 ]. Although ORF68 sequences of the 12 EHV-1 isolates were very similar to KyA and Racl11, these have SNPs at A236C, G689T, and C690T compared to KyA and RacL11 ( Table 2 ).…”

“…Recently, similar studies were reported in other countries, and the prevalence of the neuropathogenic genotype was extremely low in Japan (2.7%), Australia (3%) and Argentina (7.4%) [ 23 ]. In particular, neuropathogenic cases were extremely rare in Korea [ 16 ]. Furthermore, this study found an additional SNP at G2968A (E990K) in seven samples by comparing with the reference strain Ab4.…”

“…Therefore, EHV-1 N752 is referred to as a non-neuropathogenic genotype, and D752 is a neuropathogenic genotype [ 14 ]. The ORF33 gene, encoding glycoprotein B (gB), possesses a conserved region frequently used as a target for diagnostic PCR protocols [ 15 , 16 ]. Recently, genetic studies include the determination of whole-genome sequences for two well-characterized strains, Ab4 and V592 [ 2 , 10 ].…”

“…However, there have been conflicting conclusions regarding the usefulness of this approach for molecular tracking of EHV-1 in other countries [ 15 ]. ORF34, which encodes the V32 protein, was the most variable in this viral collection and was also classified into distinct groups by SNPs in their genomes [ 10 ] and allowed the identification of at least 12 groups [ 16 ]. Recently, a multi-locus sequence typing (MLST) analysis approach, based on sequencing heterologous regions in 26 ORFs, which has diverged into 13 distinct UL clades, proved to be a more comprehensive method of strain typing than only ORF68 sequencing [ 15 ].…”

Special Issue “Equine Viruses”: Old “Friends” and New Foes?

“…This disease mostly occurs in southern African countries, but its transmission by Culicoides biting midges is of great concern in the current context of global warming and its consequence on displacement of vector populations. A communication from Preziuso et al [4] and an article from Sutton et al [5] specifically focused on EHV-1 strain characterization in order to better understand EHV circulation in Italy and France. While live attenuated and inactivated AHSV vaccines have played a role to reduce the impact and occurrence of AHS in affected areas, the number of AHSV serotypes in circulation and their lack of DIVA markers (differentiating infected from vaccinated animals) is a drawback that leads to the development of a new generation of vaccines, such as poxvirus-vectored or reverse genetics vaccines.…”