Phylogenetic characterisation of the GL sequences of equine arteritis virus isolated from semen of asymptomatic stallions and fatal cases of equine viral arteritis in Denmark

The recent European isolate (08P178) of equine arteritis virus causes inflammation but not arteritis in experimentally infected ponies

In the last two decades, outbreaks of equine viral arteritis (EVA) have been reported in Europe, but little is known about these European isolates of equine arteritis virus (EAV). EAV European strain (08P178, EU-1 clade) isolated from one of these recent outbreaks is able to cause clinical signs on experimental infection. The aim of the present study was to investigate the microscopical lesions induced by this isolate after experimental infection of ponies. Animals were killed at 3, 7, 14 and 28 days post infection (dpi). At 3 dpi, lesions were essentially restricted to the respiratory tract and intestines and were characterized by mild multifocal epithelial degeneration and associated mononuclear cell infiltration. Lesions were more severe at 7 dpi and by 14 dpi, respiratory lesions were even more severe and lymphoplasmacytic infiltrates extended to other organs. At 28 dpi, lesions were still present in the viscera. In all specimens the most prominent histological change was intraepithelial, subepithelial and perivascular lymphoplasmacytic infiltration, ranging from mild and multifocal to extensive and diffuse. No signs of arterial damage such as infarcts, haemorrhages or necrosis were found. In conclusion, infection of naïve animals with the European 08P178 strain of EAV is associated with inflammation, but not arteritis.

Validation of an improved competitive enzyme-linked immunosorbent assay to detect Equine arteritis virus antibody

The objective of the present study was to validate a previously described competitive enzyme-linked immunosorbent assay (cELISA) to detect antibody to Equine arteritis virus (EAV) based on GP5-specific nonneutralizing monoclonal antibody (mAb) 17B79 using the World Organization for Animal Health (OIE)–recommended protocol, which includes the following 5 in-house analyses. 1) The assay was calibrated with the OIE-designated reference serum panel for EAV; 2) repeatability was evaluated within and between assay runs; 3) analytical specificity was evaluated using sera specific to related viruses; 4) analytical sensitivity was evaluated with sera from horses vaccinated with an EAV modified live virus (MLV) vaccine; and 5) the duration of cELISA antibody detection following EAV vaccination was determined. The positive cELISA cutoff of ≥35% inhibition (%I) was confirmed by receiver operating characteristic plot analysis. Analytical sensitivity of the cELISA was comparable to the serum neutralization (SN) assay in that it detected EAV-specific antibody as early as 8 days postvaccination. The duration of EAV-specific antibody detected by cELISA was over 5 years after the last vaccination. This cELISA could detect EAV-specific antibody in serum samples collected from horses infected with various EAV strains. In the field trial performed by American Association of Veterinary Laboratory Diagnosticians–accredited state laboratories and OIE laboratory, the diagnostic specificity of the cELISA was 99.5% and the diagnostic sensitivity was 98.2%. The data using various serum panels also had consistently significant positive correlation between SN titers and cELISA %I results. The results further confirm that the EAV antibody cELISA is a reliable, simple alternative to the SN assay for detecting EAV-specific antibodies in equine sera.

Emergence of novel equine arteritis virus (EAV) variants during persistent infection in the stallion: origin of the 2007 French EAV outbreak was linked to an EAV strain present in the semen of a persistently infected carrier stallion

During the summer of 2007, an outbreak of equine viral arteritis (EVA) occurred in Normandy (France). After investigation, a link was suggested between an EAV carrier stallion (A) and the index premise of the outbreak. The full-length nucleotide sequence analysis of a study reference strain (F27) isolated from the lung of a foal revealed a 12,710 nucleotides EAV genome with unique molecular hallmarks in the 5'UTR leader sequence and the ORF1a sequence encoding the non-structural protein 2. The evolution of the viral population in the persistently infected Stallion A was then studied by cloning ORFs 3 and 5 of the EAV genome from four sequential semen samples which were collected between 2000 and 2007. Molecular analysis of the clones confirmed the likely implication of Stallion A in the origin of this outbreak through the yearly emergence of new variants genetically similar to the F27 strain.

Molecular epidemiology and genetic characterization of equine arteritis virus isolates associated with the 2006-2007 multi-state disease occurrence in the USA

In 2006-2007, equine viral arteritis (EVA) was confirmed for the first time in Quarter Horses in multiple states in the USA. The entire genome of an equine arteritis virus (EAV) isolate from the index premises in New Mexico was 12 731 nt in length and possessed a previously unrecorded unique 15 nt insertion in the nsp2-coding region in ORF1a and a 12 nt insertion in ORF3. Sequence analysis of additional isolates made during this disease occurrence revealed that all isolates from New Mexico, Utah, Kansas, Oklahoma and Idaho had 98.6-100.0 % (nsp2) and 97.8-100 % (ORF3) nucleotide identity and contained the unique insertions in nsp2 and ORF3, indicating that the EVA outbreaks in these states probably originated from the same strain of EAV. Sequence and phylogenetic analysis of several EAV isolates made following an EVA outbreak on another Quarter Horse farm in New Mexico in 2005 provided evidence that this outbreak may well have been the source of virus for the 2006-2007 occurrence of the disease. A virus isolate from an aborted fetus in Utah was shown to have a distinct neutralization phenotype compared with other isolates associated with the 2006-2007 EVA occurrence. Full-length genomic sequence analysis of 18 sequential isolates of EAV made from eight carrier stallions established that the virus evolved genetically during persistent infection, and the rate of genetic change varied between individual animals and the period of virus shedding.

Equine arteritis virus: a new isolate from the presumable first carrier stallion in Argentina and its genetic relationships among the four reported unique Argentinean strains

Equine arteritis virus (EAV) was isolated from a testicle of the presumable first stallion infected with EAV in Argentina. This virus isolate (named LT-LP-ARG) was confirmed by GP5-specific PCR and indirect immunofluorescence assays. The PCR product was sequenced, and the phylogenetic analysis revealed that the LT-LP-ARG strain of EAV forms a monophyletic group, together with other strains previously isolated in our laboratory (LP02 group). However, all Argentinean EAV strains belong to a polyphyletic group. We believe that the virus isolate presented in this report could be the origin of EAV infection in our country.

Equine viral arteritis: current status and prevention

Recently, there has been increased interest in equine viral arteritis (EVA) among veterinarians and horse owners. Outbreaks of the disease were identified initially in New Mexico, USA in 2006, and in the Normandy region of France in the summer of 2007. Both occurrences were associated with AI of cool-shipped semen. Each was linked to respiratory illness, neonatal death, abortion, development of carrier stallions, and cancellation of equestrian events. In light of the increased interest, this paper will present a brief case history, followed by a review addressing common concerns regarding EVA, current status, and control and prevention strategies, including vaccination, and recommended bio-security measures.

Comparison of different molecular methods for assessment of equine arteritis virus (EAV) infection: a novel one-step MGB real-time RT-PCR assay, PCR-ELISA and classical RT-PCR for detection of highly diverse sequences of Slovenian EAV variants

In the present study, a new one-step real-time reverse transcription-polymerase chain reaction (RT-PCR) strategy with minor-groove-binder (MGB) technology for the detection of EAV from 40 semen samples of Slovenian carrier stallions was tested. A novel MGB probe (EAVMGBpr) and a reverse primer (EAV-R) based on the multiple sequence alignment of 49 different EAV strain sequences of the highly conserved ORF7 (nucleocapsid gene) were designed. The performance of the assay was compared with different molecular detection methods. Three different primer pairs targeting the ORF1b and ORF7 were used, respectively. The real-time RT-PCR assay was at least 2 log(10) more sensitive than the classical RT-PCR and at least 1 log(10) more sensitive than the primer set used in the semi-nested PCR. The specificities of the amplification reactions were confirmed with biotinylated probes in the PCR-enzyme-linked immunosorbent assay (PCR-ELISA). Under the conditions described in our study, the sensitivity of the real-time RT-PCR was found to be superior to the PCR-ELISA assay. Thus, while the PCR-ELISA method was found to be both relatively demanding and time consuming, better sensitivity coupled with high specificity and speed of the assay makes the real-time RT-PCR a valuable tool for diagnosis of EAV infection.

Genetic variation and phylogenetic analysis of 22 French isolates of equine arteritis virus

Genetic variation and phylogenetic relationships among 22 French isolates of equine arteritis virus (EAV) obtained over four breeding seasons (2001-2004) were determined by sequencing open reading frames (ORFs) 2a-7. The ORFs 2a-7 of 22 isolates differed from the prototype virulent Bucyrus strain of EAV by between 14 (99.5% identity) and 328 (88.7% identity) nucleotides, and differed from each other by between 0 (100% identity) and 346 (88.1% identity) nucleotides, confirming genetic diversity among EAV strains circulating in France. Phylogenetic analysis based on the partial ORF5 sequences (nucleotides 11296-11813) of 22 French isolates and 216 additional EAV strains available in GenBank clustered the global isolates of EAV into two distinct groups: North American and European. The latter could be further divided into two large subgroups: European subgroup 1 (EU-1) and European subgroup 2 (EU-2). Phylogenetic analysis based on 100 EAV ORF3 sequences yielded similar results. Of the 22 French EAV isolates, the 11 isolates obtained before January 28, 2003 clustered with either the EU-1 (9 isolates) or EU-2 (2 isolates) subgroup. In contrast, by the criteria used in this study, the 11 isolates obtained after January 30, 2003 belong to the North American group, strongly suggesting that these strains were recently introduced into France.

Genetic typing of equine arteritis virus isolates from Argentina

We report the nucleotide sequence and genetic diversity of four Equine Arteritis Virus (EAV) ORF 5 and 6 from Argentina isolates, obtained from asymptomatic virus-shedding stallions. Nucleic acid recovered from the isolates were amplified by RT-PCR and sequenced. Nucleotide and deduced amino acid sequences from the Argentine isolates were compared with 17 sequences available from the GenBank. Phylogenetic analysis revealed that the Argentine isolates grouped together in a definite cluster near European strains. Despite the greater genetic variability among ORF 5 from different isolates and strains of EAV, phylogenetic trees based on ORF 5 and 6 are similar. Both trees showed that virus sequences from America and Europe segregate into distinct clades based on sequence analysis of either ORF 5 or 6. This study constitutes the first characterization of Argentine EAV isolates.

Extended Phylogeny of Equine Arteritis Virus: Division into New Subgroups

To determine a conclusive phylogeny, equine arteritis viruses from Italy, Austria, Hungary, Sweden, South Africa and other parts of the world were analysed by reverse-transcription polymerase chain reaction amplification and direct sequencing. The nucleotide sequences corresponding to the variable part of the large glycoprotein GP5, specified by open reading frame 5, were compared and added to a previously published phylogenetic tree in which a clear division between 'European' and 'American' type viruses had been established. Adding the sequences determined in this study and new sequences retrieved from GenBank revealed additional diversity and new subgroups.

Recovery of Swedish Equine arteritis viruses from semen by cell culture isolation and RNA transfection

Recovery of infectious Equine arteritis virus (EAV) from the semen of persistently infected Swedish stallions was attempted by classical cell culture isolation and by transfection of extracted total RNA. Whereas virus from semen samples stored for several months at -20 degrees C or from extended semen could only be recovered by transfection of extracted RNA, isolation in cell culture was achieved readily with fresh, unextended semen stored at -70 degrees C or directly used after sampling. In parallel, the viruses were examined in the variable region of the large glycoprotein GP5 by nested RT-PCR and direct nucleotide sequencing. The resulting sequences were placed into a large phylogenetic tree from this region, demonstrating that Swedish strains belonged to very diverse phylogenetic groups. This represents the first report of recovery of infectious EAV from archived semen samples by RNA transfection.

Study on the epidemiology of equine arteritis virus infection with different diagnostic techniques by investigating 96 cases of equine abortion in Hungary

The occurrence of equine arteritis virus (EAV) induced equine abortions was studied with different laboratory methods during a 3-year period. Tissue samples from 96 aborted equine foetuses or newborn foals were collected from 57 farms located in different parts of Hungary. Virus isolation, polymerase chain reaction (PCR), immunohistochemistry and serology were used for the detection of EAV infection. The overall seroprevalence of EAV infection in mares was 65%. EAV induced abortion was diagnosed in eight (8.3%) cases from six (10.5%) herds. Abortion was sporadic in all herds except for one, where epidemic abortion happened. Fetal serology in six (75%) cases, the virus isolation in one (12.5%) case whereas PCR in all of the four investigated cases were positive. The virus could be observed with immunohistochemistry in seven (87.5%) cases mostly in the spleen followed by other organs and the allantochorion. In conclusion, PCR and immunohistochemistry seem to be the most sensitive and useful tests for the diagnosis of EAV induced equine abortion.

A Novel Subgroup among Genotypes of Equine Arteritis Virus: Genetic Comparison of 40 Strains

The authors determined partial nucleic sequences of the variable regions of open-reading frame (ORF5) from 151 nucleotide to 668 nucleotide and deduced amino acid sequences of 518 nucleotide respectively of 20 equine arteritis virus (EAV) isolates. About 19 Hungarian and one Austrian EAV strains were subjected to sequence analysis, the further data of 20 EAV strains: six North American and 14 European were obtained from the GenBank. Comparative sequence analysis of the Hungarian EAV strains indicated that among the three variable regions the first has been affected mostly by point mutations. Genetic comparison of the Hungarian strains with other EAV isolates from western Europe and North America (including the Bucyrus reference strain) has been performed on the aforementioned genome region. Besides the already known genetic subgroups of EAV; phylogenetic analysis revealed a novel subgroup comprising mainly Hungarian strains. Compared with the Bucyrus virus, the overall sequence divergencies of the examined Hungarian strains ranged from 81.47 to 90.73% at nucleotide and from 84.88 to 91.86% at amino acid level. Epizootiological studies have shown that the significant part of the EAV strains having been existed in Hungary before and in 2000 belong to this unique cluster (II.D) which was not indicated in former phylogenetic studies. After 2000 new EAV strains emerged in Hungary, one of them causing abortions or neonatal death. The previously dominant 'Hungarian' EAV genotypes were replaced by these new strains belonging to North American and European subgroups (I.A, I.B, II.A, II.B). The anamnesis of these cases revealed connections with persistent virus shedder stallions, those were imported to the country after 2000 or have been infected abroad. One of these Hungarian stallions became the source of abortion storms in Hungarian studs.

Genetic characterization of equine arteritis virus during persistent infection of stallions

Equine arteritis virus (EAV) causes a persistent infection of the reproductive tract of carrier stallions. The authors determined the complete genome sequences of viruses (CW96 and CW01) that were present 5 years apart in the semen of a carrier stallion (CW). The CW96 and CW01 viruses respectively had only 85.6 % and 85.7 % nucleotide identity to the published sequence of EAV (EAV030). The CW96 and CW01 viruses had two 1 nt insertions and a single 1 nt deletion in the leader sequence, and a 3 nt coding insertion in ORF1a; thus their genomes included 12 708 nt as compared to the 12 704 nt in EAV030. Variation between viruses present in the semen of stallion CW and EAV030 was especially marked in the replicase gene (ORF1a and 1b), and the greatest variation occurred in the portion of ORF1a encoding the nsp2 protein. The ORFs 3 and 5, which respectively encode the GP3 and GP5 envelope proteins, showed greatest variation amongst ORFs encoding structural EAV proteins. Comparative sequence analyses of CW96 and CW01 indicated that ORFs 1a, 1b and 7 were highly conserved during persistent infection, whereas there was substantial variation in ORFs 3 and 5. Although the variation that occurs in ORF5 results in the emergence of novel phenotypic viral variants as determined by neutralization assay, all variants were neutralized by high-titre polyclonal equine antisera, suggesting that immune evasion is unlikely to be responsible for the establishment of persistent EAV infection of carrier stallions. Northern blot analyses of RNA extracted from cell culture propagated viruses isolated from 10 different persistently infected stallions failed to demonstrate any large genomic deletions, suggesting that defective interfering particles are also unlikely to be important in either the maintenance or clearance of persistent EAV infection of the reproductive tract of carrier stallions.