Detection of equine herpesvirus 1 genome 1B in Argentina

To determine the genomic variation of equine herpesviruses (EHVs) isolated in Argentina between 1979 and the first half of 2004, DNA sequences from all 69 strains isolated were analysed. Sixty strains were recovered from aborted fetuses, one from leucocyte-rich plasma from a horse with respiratory signs and eight from cases of neonatal disease. The DNA was extracted from rabbit kidney epithelial (RK13) cells infected with each strain and digested with three restriction endonucleases (BamHI, Bg/II and KpnI). Two strains could be differentiated using BamHI restriction and were assigned to the EHV-1 1B prototype group. Only one of these two strains was typed EHV-1 1B with Bg/II. DNA digestion with KpnI was ineffective. The results obtained in this study demonstrate that the EHV-1 1B genome has been present in Argentina since at least 1996. The finding of two strains with this electropherotype suggests that there is genomic heterogeneity among Argentinian isolates.

An Argentine equine herpesvirus strain with special restriction patterns protect mice challenged with a pathogenic strain

Equine herpesvirus 1 (EHV-1) was first isolated in Argentina in 1979. This strain SPv has special restriction patterns, but a previous study demonstrated that SPv did not modify its growth in cell culture. In addition, it showed low virulence in the mouse respiratory model consistently with results found in female BALB/C at different state of gestation. This study evaluates in a mouse respiratory model, if primary infection with SPv strain protects animals from subsequent challenge with a pathogenic strain. Body weight loss was not observed in mice intranasally inoculated with SPv strain and challenged with HH1 Japanese strain. The SPv primary infection does not completely prevent clinical presentation by HH1 infection but the SPv inoculated animals recovered more quickly, with less intense and less persistent histological lesions. The challenge infection caused a rapid and prolonged increase in anti-EHV-1 antibodies in the mice previously infected with SPv, along with a more rapid reduction of viral titres in lungs. In this work it was demonstrated that this EHV-1 strain constitute a good immunogen. These results show that this SPv strain could be considered to produce an EHV-1 vaccine.

Detection and quantification of equine herpesvirus-1 viremia and nasal shedding by real-time polymerase chain reaction

Equine herpesvirus-1 (EHV-1) infection is common in young horses throughout the world, resulting in respiratory disease, epidemic abortion, sporadic myelitis, or latent infections. To improve on conventional diagnostic tests for EHV-1, a real-time polymerase chain reaction (PCR) technique was developed, using primers and probes specific for the EHV-1 gB gene. Amplification efficiencies of 100% +/- 5% were obtained for DNA isolated from a plasmid, infected peripheral blood mononuclear cells (PBMCs), and nasal secretions from infected ponies. The dynamic range of the assay was 8 log10 dilutions, and the lower limit of detection was 6 DNA copies. Fifteen ponies, seronegative for EHV-1, were experimentally infected with EHV-1, and nasal samples were used to quantify shedding of virus by both virus isolation and real-time PCR analysis. Virus isolation identified nasal shedding of EHV-1 in 12/15 ponies on a total of 25 days; real-time PCR detected viral shedding in 15/15 ponies on 75 days. Viremia was quantified using PBMC DNA, subsequent to challenge infection in 3 additional ponies. Viremia was identified in 1/3 ponies on a single day by virus isolation; real-time PCR detected viremia in 3/3 ponies on 17 days. When real-time PCR was used to analyze PBMC DNA from 11 latently infected ponies (documented by nested PCR), EHV-1 was not detected. We conclude that real-time PCR is a sensitive and quantitative test for EHV-1 nasal shedding and viremia and provides a valuable tool for EHV-1 surveillance, diagnosis of clinical disease, and investigation of vaccine efficacy.

A molecular approach to the identification of cytotoxic T-lymphocyte epitopes within equine herpesvirus 1

Equine herpesvirus 1 (EHV-1) causes respiratory and neurological disease and abortion in horses. Animals with high frequencies of cytotoxic T lymphocytes (CTL) show reduced severity of respiratory disease and frequency of abortion, probably by CTL-mediated control of cell-associated viraemia. This study aimed to identify CTL epitopes restricted by selected major histocompatibility complex (MHC) class I alleles expressed in the equine leukocyte antigen (ELA) A3 haplotype. Effector CTL were induced from EHV-1-primed ponies and thoroughbreds with characterized MHC class I haplotypes and screened against P815 target cells transfected with selected EHV-1 genes and MHC class I genes. Targets that expressed EHV-1 gene 64 and the MHC B2 gene were lysed by effector CTL in a genetically restricted manner. There was no T-cell recognition of targets expressing either the MHC B2 gene and EHV-1 genes 2, 12, 14, 16, 35, 63 or 69, or the MHC C1 gene and EHV-1 genes 12, 14, 16 or 64. A vaccinia virus vector encoding gene 64 (NYVAC-64) was also investigated. Using lymphocytes from ELA-A3 horses, the recombinant NYVAC-64 virus induced effector CTL that lysed EHV-1-infected target cells; the recombinant virus also supplied a functional peptide that was expressed by target cells and recognized in an MHC-restricted fashion by CTL induced with EHV-1. This construct may therefore be used to determine the antigenicity of EHV-1 gene 64 for other MHC haplotypes. These techniques are broadly applicable to the identification of additional CTL target proteins and their presenting MHC alleles, not only for EHV-1, but for other equine viruses.

Initial characterization of 17 viruses harboring mutant forms of the immediate-early gene of equine herpesvirus 1

The sole immediate-early (IE) gene of equine herpesvirus 1 (EHV-1) encodes a major regulatory protein of 1487 amino acids (aa) capable of modulating gene expression from both early and late promoters and also of trans-repressing its own promoter. Using a specially designed recombination system and a library of IE linker-insertion, deletion, point, and nonsense mutant constructs that encode forms of the IE protein (IEP) harboring mutations within all five regions, 17 mutant viruses were generated and characterized. Ribonuclease protection analyses revealed that all 17 mutants synthesize the IE mRNA in RK-13 cells, whereas those that failed to replicate on non-complementing RK-13 cells displayed a defect in the transcription of either an important early gene (EICP0) and/or an essential late gene (glycoprotein D). Western blot analyses showed that the IEP was synthesized and detectable in cells infected with each mutant virus, including those mutants that failed to replicate on non-complementing RK-13 cells. Eleven of the 17 mutants were capable of growth on non-complementing RK-13 cells, whereas mutant viruses with deletions within the serine-rich tract (SRT), nucleus localization signal (NLS), or DNA-binding domain (DBD) were capable of growth only on the IEP-producing cell line (IE13.1). Lastly, temperature shift experiments revealed that mutant viruses containing deletions within the C-terminus (KyAn1029 and KyAn1411) or within the SRT (KyADeltaSRT2) of the IEP exhibited a temperature-sensitive phenotype in that these viruses, in contrast to the parent KyA, failed to replicate at 39 degrees C. Overall, these results indicate that the C-terminus of the IEP is not essential for IEP function in cell culture, but this region contains elements that enhance the function(s) of the IEP. The initial characterization of these 17 EHV-1 mutants has shown that sequences totaling at least 43% of the IEP are not essential for virus replication in cell culture.

Temporal detection of equine herpesvirus infections of a cohort of mares and their foals

The objectives of this study were to estimate the prevalence of equine herpesviruses (EHV) 1-5 in the nasal secretions (NS) of a cohort of 12 mares and their foals from birth to 6 months of age, estimate the prevalence of EHV-1-5 infection of peripheral blood mononuclear cells (PBMC) of selected foals, and investigate phylogenetic relationships amongst the various strains of EHV-2 and 5. Virus-specific PCR assays were used to detect EHV-1-5 in NS and PBMC. A homologous portion of the glycoprotein B (gB) gene of the various strains of EHV-2 and 5 was sequenced and compared. EHV-2, 4, and 5 were all detected in NS from the horses, but only EHV-4 was associated with respiratory disease (P=0.005). EHV-2 and 5 infections were both common, but foals shed EHV-2 in their NS earlier in life than EHV-5 (P=0.01). Latent EHV-2 and 5 infections were detected in the PBMC of 75 and 88%, respectively, of the foals at approximately 6 months of age. The strains of EHV-2 shed in the NS of individual horses were more genetically heterogeneous than the strains of EHV-5 (95.5-99.3% versus 98.8-99.3% nucleotide identity, respectively). One-month-old foals typically shed strains of EHV-2 that were identical to those infecting their dams whereas older foals often shed virus strains that were different from those of their dams. Although herpesvirus infections were ubiquitous in this cohort of horses, there were distinct clinical consequences and clear epidemiological differences between infections with the different viruses.

Cloning, expression, and functional characterization of the equine herpesvirus 1 DNA polymerase and its accessory subunit

We report the expression and characterization of the putative catalytic subunit (pORF30) and accessory protein (pORF18) of equine herpesvirus 1 DNA polymerase, which are encoded by open reading frames 30 and 18 and are homologous to herpes simplex virus type 1 UL30 and UL42, respectively. In vitro transcription-translation of open reading frames 30 and 18 generated proteins of 136 and 45 kDa, respectively. In vitro-expressed pORF30 possessed basal DNA polymerase activity that was stimulated by pORF18, as measured by DNA polymerase assays in vitro. Purified baculovirus-expressed pORF30 exhibited DNA polymerase activity similar to that of the in vitro-expressed protein, and baculovirus-expressed pORF18 could stimulate both nucleotide incorporation and long-chain DNA synthesis by pORF30 in a dose- and time-dependent manner. The salt optima for activity of both pORF30 and the holoenzyme were substantially different from those for other herpesvirus DNA polymerases. As demonstrated by yeast two-hybrid assays, pORF30 and pORF18 could physically interact, most likely with a 1:1 stoichiometry. Finally, by mutational analysis of the 1,220-residue pORF30, we demonstrated that the extreme C terminus of pORF30 is important for physical and functional interaction with the accessory protein, as reported for UL30 and other herpesvirus DNA polymerases. In addition, a C-proximal region of pORF30, corresponding to residues 1114 to 1172, is involved in binding to, and stimulation by, pORF18. Taken together, the results indicate that pORF30 and pORF18 are the equine herpesvirus 1 counterparts of herpes simplex virus type 1 UL30 and UL42 and share many, but not all, of their characteristics.

In vitro transposon mutagenesis of an equine herpesvirus 1 genome cloned as a bacterial artificial chromosome

The 150-kbp genome of the alphaherpesvirus equine herpesvirus 1 (EHV-1) strain HVS25A was cloned as a bacterial artificial chromosome (EHV-1 BAC), with mini F plasmid sequences inserted between genes 62 and 63. Transfection of EHV-1 BAC DNA purified from E. coli gave rise to progeny virus that had a similar growth rate and yield in mammalian cell culture to those of parental wild-type EHV-1. Using in vitro mutagenesis with a Mu transposon, a large library of EHV-1 BAC mutants was generated, and sequence analysis indicated that insertions were dispersed randomly across the EHV-1 genome. Following transfections of a pilot sample of mutant EHV-1 BAC DNAs into mammalian cells, no CPE was observable by light microscopy for mutants carrying insertions in genes for the major capsid protein, large tegument protein, glycoprotein K, catalytic subunit of DNA polymerase, or single-stranded DNA-binding protein. Mutants that were able to produce CPE similar to wild-type EHV-1 included those with interruptions in ORFs of several tegument proteins. Analysis of several glycoprotein gene mutants indicated that those carrying insertions near the start of genes encoding glycoproteins E and I were viable, but showed markedly diminished plaque areas. These results were supported by confocal microscopy of transfected or infected cultures. Electron microscopy of cells infected with a gE mutant revealed accumulations of particles within cytoplasmic vesicles, consistent with a partial obstruction of maturation. The transposon library is a resource for comprehensive functional analysis of the HVS25A genome, with multiple mutants available in any of the predicted genes of EHV-1.

The unique IR2 protein of equine herpesvirus 1 negatively regulates viral gene expression

The IR2 protein (IR2P) is a truncated form of the immediate-early protein (IEP) lacking the essential acidic transcriptional activation domain (TAD) and serine-rich tract and yet retaining binding domains for DNA and TFIIB and nuclear localization signal (NLS). Analysis of the IR2 promoter indicated that the IR2 promoter was upregulated by the EICP0P. The IR2P was first detected in the nucleus at 5 h postinfection in equine herpesvirus 1 (EHV-1)-infected HeLa and equine NBL6 cells. Transient-transfection assays revealed that (i) the IR2P by itself downregulated EHV-1 early promoters (EICP0, TK, EICP22, and EICP27) in a dose-dependent manner; (ii) the IR2P abrogated the IEP and the EICP27P (UL5) mediated transactivation of viral promoters in a dose-dependent manner; and (iii) the IR2P, like the IEP itself, also downregulated the IE promoter, indicating that the IEP TAD is not necessary to downregulate the IE promoter. In vitro interaction assays revealed that the IR2P interacts with TATA box-binding protein (TBP). The essential domain(s) of the IR2P that mediate negative regulation were mapped to amino acid residues 1 to 706, indicating that the DNA-binding domain and the NLS of the IR2P may be important for the downregulation. In transient-transfection and virus growth assays, the IR2P reduced EHV-1 production by 23-fold compared to virus titers achieved in cells transfected with the empty vector. Overall, these studies suggest that the IR2P downregulates viral gene expression by acting as a dominant-negative protein that blocks IEP-binding to viral promoters and/or squelching the limited supplies of TFIIB and TBP.

Application of polymerase chain reaction and virus isolation techniques for the detection of viruses in aborted and newborn foals

The occurrence of two important pathogens, equine herpesvirus 1 (EHV1) and equine arteritis virus (EAV) causing abortions, perinatal foal mortality and respiratory disease, was investigated by polymerase chain reaction (PCR) and virus isolation to demonstrate the presence of abortigenic viruses in samples from 248 horse fetuses in Hungary. We found 26 EHV1- and 4 EAV-positive aborted or prematurely born foals from 16 and 4 outbreaks, respectively, proving that despite the widely applied vaccination, EHV1 is a far more important cause of abortions in the studs than EAV. We compared the virus content of different organs of the fetuses by PCR and isolation to identify the organ most suitable for virus demonstration. Our investigations indicate that the quantity of both viruses is highest in the lungs; therefore, according to our observations, in positive cases the probability of detection is highest from lung samples of aborted or newborn foals. Both the PCR and the virus isolation results revealed that the liver, though widely used, is not the best organ to sample either for EHV1 or for EAV detection. From the analysis of the epidemiological data, we tried to estimate the importance of the two viruses in the Hungarian horse population.

Genetic Complexity of EHV-1 Defective Interfering Particles and Identification of Novel IR4/UL5 Hybrid Proteins Produced During Persistent Infection

This study examined the genetic complexity of three equine herpesvirus 1 (EHV-1) defective interfering particles (DIP) and found the DIP genomes to range from 5.9 kbp to 7.3 kbp in total size. Each DIP contains an identical 5' end ( approximately 1.9 kb) that harbors UL3 and UL4 genes that are 100% identical to those of the infectious virus. DIP2 and DIP3 contain a previously described unique IR4/UL5 (EICP22/EICP27) hybrid gene (Hyb1.0). The DIP1 genome, however, appears to be generated from a different recombination event which results in the formation of a new distinct hybrid ORF. The new ORF (Hyb2.0) is comprised of 684 bp from the 5' end of IR4 fused to 45 bp from the 3' terminus of UL5. In contrast to Hyb1.0, the UL5 sequences present in Hyb2.0 are not in-frame. Thus, the Hyb2.0 protein is comprised of 228 residues from IR4 linked to a sequence of 15 amino acids that result from a frameshifted reading of UL5 sequences. Western blot analysis confirmed that the Hyb2.0 ORF is expressed during persistent infection to produce a family of proteins that migrate at 36-42 kDa. Fluorescence microscopy revealed that both Hyb proteins display diffuse cytoplasmic localization patterns dissimilar to the nuclear localization patterns of both IR4 and UL5. Neither Hyb protein, however, disrupts the nuclear entry of the EHV-1 immediate-early, IR4, or UL5 proteins or cellular TATA box binding protein (TBP) previously shown to interact with both IR4 or UL5 in productive infection. DIP genomic segments ( approximately 3.5-5.0 kbp) downstream of the 100% conserved origin of replication are highly variable among the three DIP genomes and contain large areas of repetitive sequences. The possibility that the non-coding sequences play a role in viral interference and/or persistent infection remains to be determined.

Equine herpesvirus 1 glycoprotein D expressed in E. coli provides partial protection against equine herpesvirus infection in mice and elicits virus-neutralizing antibodies in the horse

The envelope glycoprotein D of EHV-1 (EHV-1 gD) is essential for virus infectivity and entry of virus into cells and is a potent inducer of virus-neutralizing antibody. In this study, truncated EHV-1 gD (gDt) was expressed with a C-terminal hexahistidine tag in E. coli using a pET vector. Western blot analysis using an anti-gD monoclonal antibody demonstrated the presence of gDt bands at 37.5, 36, 29.5 and 28 kDa. The immunogenicity and protective efficacy of partially purified gDt was compared with gD expressed in insect cells by a recombinant baculovirus (Bac gD) using a BALB/c mouse model of EHV-1 respiratory infection. The proteins were also compared in a prime-boost protocol following an initial inoculation with gD DNA. gDt elicited similar levels of gD-specific antibody and neutralizing antibody compared with Bac gD and also provided a similar level of protection against EHV-1 challenge in mice. Inoculation of horses with gDt elicited EHV-1 gD-specific antibodies including virus-neutralizing antibody, suggesting that despite the lack of glycosylation, E. coli may be a useful vehicle for large scale production of EHV-1 gD for vaccine studies.

Immune responses to commercial equine vaccines against equine herpesvirus-1, equine influenza virus, eastern equine encephalomyelitis, and tetanus

Horses are commonly vaccinated to protect against pathogens which are responsible for diseases which are endemic within the general horse population, such as equine influenza virus (EIV) and equine herpesvirus-1 (EHV-1), and against a variety of diseases which are less common but which lead to greater morbidity and mortality, such as eastern equine encephalomyelitis virus (EEE) and tetanus. This study consisted of two trials which investigated the antigenicity of commercially available vaccines licensed in the USA to protect against EIV, EHV-1 respiratory disease, EHV-1 abortion, EEE and tetanus in horses. Trial I was conducted to compare serological responses to vaccines produced by three manufacturers against EIV, EHV-1 (respiratory disease), EEE, and tetanus given as multivalent preparations or as multiple vaccine courses. Trial II compared vaccines from two manufacturers licensed to protect against EHV-1 abortion, and measured EHV-1-specific interferon-gamma (IFN-gamma) mRNA production in addition to serological evidence of antigenicity. In Trial I significant differences were found between the antigenicity of different commercial vaccines that should be considered in product selection. It was difficult to identify vaccines that generate significant immune responses to respiratory viruses. The most dramatic differences in vaccine performance occurred in the case of the tetanus antigen. In Trial II both vaccines generated significant antibody responses and showed evidence of EHV-1-specific IFN-gamma mRNA responses. Overall there were wide variations in vaccine response, and the vaccines with the best responses were not produced by a single manufacturer. Differences in vaccine performance may have resulted from differences in antigen load and adjuvant formulation.

Analysis of equid herpesvirus 1 strain variation reveals a point mutation of the DNA polymerase strongly associated with neuropathogenic versus nonneuropathogenic disease outbreaks

Equid herpesvirus 1 (EHV-1) can cause a wide spectrum of diseases ranging from inapparent respiratory infection to the induction of abortion and, in extreme cases, neurological disease resulting in paralysis and ultimately death. It has been suggested that distinct strains of EHV-1 that differ in pathogenic capacity circulate in the field. In order to investigate this hypothesis, it was necessary to identify genetic markers that allow subgroups of related strains to be identified. We have determined all of the genetic differences between a neuropathogenic strain (Ab4) and a nonneuropathogenic strain (V592) of EHV-1 and developed PCR/sequencing procedures enabling differentiation of EHV-1 strains circulating in the field. The results indicate the occurrence of several major genetic subgroups of EHV-1 among isolates recovered from outbreaks over the course of 30 years, consistent with the proposal that distinct strains of EHV-1 circulate in the field. Moreover, there is evidence that certain strain groups are geographically restricted, being recovered predominantly from outbreaks occurring in either North America or Europe. Significantly, variation of a single amino acid of the DNA polymerase is strongly associated with neurological versus nonneurological disease outbreaks. Strikingly, this variant amino acid occurs at a highly conserved position for herpesvirus DNA polymerases, suggesting an important functional role.

The alpha-TIF (VP16) homologue (ETIF) of equine herpesvirus 1 is essential for secondary envelopment and virus egress

The equine herpesvirus 1 (EHV-1) alpha-trans-inducing factor homologue (ETIF; VP16-E) is a 60-kDa virion component encoded by gene 12 (ORF12) that transactivates the immediate-early gene promoter. Here we report on the function of EHV-1 ETIF in the context of viral infection. An ETIF-null mutant from EHV-1 strain RacL11 (vL11deltaETIF) was constructed and analyzed. After transfection of vL11deltaETIF DNA into RK13 cells, no infectious virus could be reconstituted, and only single infected cells or small foci containing up to eight infected cells were detected. In contrast, after transfection of vL11deltaETIF DNA into a complementing cell line, infectious virus could be recovered, indicating the requirement of ETIF for productive virus infection. The growth defect of vL11deltaETIF could largely be restored by propagation on the complementing cell line, and growth on the complementing cell line resulted in incorporation of ETIF in mature and secreted virions. Low- and high-multiplicity infections of RK13 cells with phenotypically complemented vL11deltaETIF virus resulted in titers of virus progeny similar to those used for infection, suggesting that input ETIF from infection was recycled. Ultrastructural studies of vL11deltaETIF-infected cells demonstrated a marked defect in secondary envelopment at cytoplasmic membranes, resulting in very few enveloped virions in transport vesicles or extracellular space. Taken together, our results demonstrate that ETIF has an essential function in the replication cycle of EHV-1, and its main role appears to be in secondary envelopment.

Detection of equine herpesvirus type 1 by real time PCR

A real-time PCR assay was developed for detection and quantitation of equid herpesvirus type 1 (EHV-1). The sensitivity of the assay was compared with an established nested-PCR (n-PCR). The real-time PCR detected 1 copy of target DNA, with a sensitivity 1 log higher than gel-based n-PCR. The assay was able to detect specifically EHV-1 DNA in equine tissue samples and there was no cross-amplification of other horse herpesviruses. Real-time PCR was applied to determine EHV-1 load in tissue samples from equine aborted fetuses. The high sensitivity and reproducibility of the EHV-1-specific fluorogenic PCR assay, combined with the wide dynamic range and the high throughput, make this method suitable for diagnostic and research applications.

Use of DNA and recombinant canarypox viral (ALVAC) vectors for equine herpes virus vaccination

In this study, experimental canarypox virus (ALVAC) and plasmid DNA recombinant vaccines expressing the gB, gC and gD glycoproteins of EHV-1 were assessed for their ability to protect conventional ponies against a respiratory challenge with EHV-1. In addition, potential means of enhancing serological responses in horses to ALVAC and DNA vaccination were explored. These included co-administration of the antigen with conventional adjuvants, complexation with DMRIE-DOPE and co-expression of the antigen along with equine GM-CSF. Groups of EHV primed ponies were vaccinated twice intra-muscularly with one dose of the appropriate test vaccine at an interval of 5 weeks. Two to 3 weeks after the second vaccination, ponies were infected intra-nasally with the virulent Ab4 strain of EHV-1 after which they were observed clinically and sampled for virological investigations. The results demonstrated that DNA and ALVAC vaccination markedly reduced virus excretion after challenge in terms of duration and magnitude, but failed to protect against cell-associated viremia. Noteworthy was the almost complete absence of virus excretion in the group of ponies vaccinated with ALVAC-EHV in the presence of Carbopol adjuvant or DNA plasmid formulated with aluminium phosphate. The administration of the DNA vaccine in the presence of GM-CSF and formulated in DMRIE-DOPE and of the ALVAC vaccine in the presence of Carbopol adjuvant significantly improved virus neutralising antibody responses to EHV-1. These findings indicate that DNA and ALVAC vaccination is a promising approach for the immunological control of EHV-1 infection, but that more research is needed to identify the immunodominant protective antigens of EHV-1 and their interaction with the equine immune system.

Inoculation of mares and very young foals with EHV-1 glycoproteins D and B reduces virus shedding following respiratory challenge with EHV-1

We have previously demonstrated that intramuscular inoculation of EHV-1 glycoprotein D (gD) and glycoprotein B (gB) produced by a recombinant baculovirus and formulated with the adjuvant Iscomatrix elicited virus-neutralizing antibody and gD- and gB-specific ELISA antibody in adult horses. In this study, 14 mares and their very young foals were inoculated with a combination of baculovirus-expressed EHV-1 gD and EHV-1 gB (EHV-1 gDBr) and challenged with a respiratory strain of EHV-1. Following experimental challenge, inoculated mares and foals shed virus in nasal secretions on significantly fewer occasions compared to uninoculated mares and foals. Uninoculated foals born from inoculated mares were no more protected against experimental challenge than uninoculated foals born from uninoculated mares. The results suggest that it is indeed possible to induce partial protection in very young foals through vaccination, and while the inoculation did not prevent infection, it did reduce the frequency of viral shedding with the potential to thereby reduce the risk and prevalence of infection in a herd situation.

Cytokine responses to EHV-1 infection in immune and non-immune ponies

Protecting equids against equine herpesvirus-1 (EHV-1) infection remains an elusive goal. Repeated infection with EHV-1 leads to protective immunity against clinical respiratory disease, and a study was conducted to measure the regulatory cytokine response (IFN-gamma and IL-4) in repeatedly infected immune ponies compared to non-immune ponies. Two groups of four ponies were established. Group 1 ponies had previously been infected on two occasions, and most recently 7 months before this study. Group 2 ponies had no history no vaccination or challenge infection prior to this study. Both groups were subjected to an intranasal challenge infection with EHV-1, and blood samples were collected pre-infection, and at 7 and 21 days post-infection for preparation of PBMCs. At each time point, the in vitro responses of PBMCs to stimulation with EHV-1 were measured, including IFN-gamma and IL-4 mRNA production, and lymphoproliferation. Group 1 ponies showed no signs of clinical disease or viral shedding after challenge infection. Group 2 ponies experienced a biphasic pyrexia, mucopurulent nasal discharge, and nasal shedding of virus after infection. Group 1 ponies had an immune response characterized both before and subsequent to challenge infection by an IFN-gamma response to EHV-1 in the absence of an IL-4 response, and demonstrated increased EHV-1-specific lymphoproliferation post-infection. Group 2 ponies had limited cytokine or lymphoproliferative responses to EHV-1 pre-challenge, and demonstrated increases in both IFN-gamma and IL-4 responses post-challenge, but without any lymphoproliferative response. Protective immunity to EHV-1 infection was therefore characterized by a polarized IFN-gamma dependent immunoregulatory cytokine response.

Characterization of Equid Herpesvirus 1 (EHV-1) Related Viruses from Captive Crevy's Zebra and Blackbuck

Equid herpes virus 1 (EHV-1) related isolates from a captive blackbuck (strain Ro-1) and Grevy's zebra (strain T965) behaved similarly to EHV-1 and EHV-9 in respect to their host cell range. Restriction enzyme analysis and a phylogenetic tree confirmed that Ro-1 and T965 were identical and more closely related to EHV-1 than to EHV-9. Differences from EHV-1 became obvious firstly, by amino acid alignments revealing two unique substitutions in the gB protein of Ro-1 and T965. Secondly, an EHV-1 type-specific monoclonal antibody did not detect its antigen on Ro-1, T965 or EHV-9 infected cells by immunohistochemistry. The results support the view that Ro-1 and T965 isolates represent a distinct, previously unrecognized species of equid herpesviruses.

Molecular variability in different Indian isolates of equine herpesvirus-1

Three abortigenic Indian isolates of equine herpesvirus-1 (EHV-1) (Tohana, Hisar and Bikaner), along with two exotic abortigenic isolates (AB4 and V592) and another EHV-1 isolate (Jind) obtained from a case of perinatal foal mortality, were studied for variability. For this purpose, PCR and restriction endonuclease (RE) digestion techniques were used simultaneously as a DNA fingerprinting system. Nine different regions of EHV-1 virus were amplified by PCR using primer pairs specific for the regions and the products obtained from these regions were subsequently subjected to various restriction endonucleases to further assess the variability in the number of RE sites as well as in their positions. No difference was observed in all the four abortigenic isolates in terms of the size of different PCR products amplified by all the nine primer pairs, except for primer pairs 'E' and 'C'. PCR products obtained with primer pair E revealed that Tohana and Bikaner isolates were most similar while Hisar isolate was like V592 isolate. However, the PCR product obtained from Jind isolate had a size between the PCR products of Hisar and Tohan/Bikaner isolates. The primer pair 'C' used to amplify the region between 1151 to 3679 in 'Gene 1,2,3' clearly differentiated the EHV-1 isolate obtained from a case of perinatal foal mortality from isolates obtained from abortion cases. This primer pair needs to be exploited more extensively for use as a potential marker for differentiating the EHV-1 isolates, mainly the abortion cases from perinatal foal mortality ones. Restriction endonuclease studies done with PCR product of all the isolates with various primer pairs did not reveal any changes in the position or number of RE sites present in the products amplified, indicating no variation in different RE sites within the amplified PCR products. However, this study clarified that all the Indian isolates belonged to the IP group of EHV-1.

Natural recombinant between equine herpesviruses 1 and 4 in the ICP4 gene

Equine herpesvirus 1 (EHV-1) is a pathogen causing rhinopneumonia in young horses, abortion in mares, and myeloencephalitis in adult horses. Two types, EHV-1 P and EHV-1 B, have recently been dominant among 16 electropherotypes. EHV-1 P and EHV-1 B viruses were compared by long and accurate polymerase chain reaction (LA-PCR) and restriction fragment length polymorphism (RFLP) analysis. Differences in restriction sites were found to be focused in ORF64, which encodes the infected cell protein 4 (ICP4), and downstream of the ICP4 gene. The 3 ' -end and downstream of ICP4 gene of EHV-1 B were found to be replaced by the corresponding region of EHV-4, indicating that EHV-1 B is a naturally occurring recombinant virus between progenitors of EHV-1 P and EHV-4. This is the first report showing a natural interspecies recombinant in alphaherpesviruses.

Detection of equine herpesvirus type 1 using a real-time polymerase chain reaction

Equid herpesvirus 1 (EHV1) is a major disease of equids worldwide causing considerable losses to the horse industry. A variety of techniques, including PCR have been used to diagnose EHV1. Some of these PCRs were used in combination with other techniques such as restriction enzyme analysis (REA) or hybridisation, making them cumbersome for routine diagnostic testing and increasing the chances of cross-contamination. Furthermore, they involve the use of suspected carcinogens such as ethidium bromide and ultraviolet light. In this paper, we describe a real-time PCR, which uses minor groove-binding probe (MGB) technology for the diagnosis of EHV1. This technique does not require post-PCR manipulations thereby reducing the risk of cross-contamination. Most importantly, the technique is specific; it was able to differentiate EHV1 from the closely related member of the Alphaherpesvirinae, equid herpesvirus 4 (EHV4). It was not reactive with common opportunistic pathogens such as Escherichia coli, Klebsiella oxytoca, Pseudomonas aeruginosa and Enterobacter agglomerans often involved in abortion. Similarly, it did not react with equine pathogens such as Streptococcus equi, Streptococcus equisimilis, Streptococcus zooepidemicus, Taylorella equigenitalis and Rhodococcus equi, which also cause abortion. The results obtained with this technique agreed with results from published PCR methods. The assay was sensitive enough to detect EHV1 sequences in paraffin-embedded tissues and clinical samples. When compared to virus isolation, the test was more sensitive. This test will be useful for the routine diagnosis of EHV1 based on its specificity, sensitivity, ease of performance and rapidity.

Glycoprotein G deletion mutants of equine herpesvirus 1 (EHV1; equine abortion virus) and EHV4 (equine rhinopneumonitis virus)

Glycoprotein G (gG) deletion mutants of EHV1 and EHV4, designated EHV1DeltagG and EHV4DeltagG, were constructed. The growth characteristics of the EHV1DeltagG mutants were similar to the parent virus. All of the EHV4DeltagG mutants grew more slowly in cell culture and produced plaques of different morphology including smaller size. The yields of both gG deletion mutant viruses in cell culture were similar to the parent viruses. Sequencing of the genes flanking gG, Southern blot, PCR and western blot analyses of the mutant viruses demonstrated that the deletions were as expected, except for EHV4DeltagG mutants, which in addition to deletion of gG contained unexpected deletions in the adjacent down stream gene ORF 71 (glycoprotein 2). Antisera to EHV1DeltagG and EHV4DeltagG neutralised the respective mutant and the parent viruses to the same titre and these antisera could be distinguished from antisera to the wild type viruses in a gG antibody detection ELISA. The mutant viruses may be useful as vaccine candidates and the deletion of gG may act as a marker to distinguish vaccinated from the naturally infected horses.

Isolation of equine herpesvirus-1 lacking glycoprotein C from a dead neonatal foal in Japan

We isolated a variant equine herpesvirus-1 (EHV-1), strain 5089, from the lung of a dead neonatal foal in Japan and characterized the biological nature of the virus. The virus spread in cultured cells mainly by cell-to-cell infection, unlike wild-type EHV-1, which spreads efficiently as a cell-free virus. The virus titer in cultured supernatant and the intracellular virus titer were low compared to those of wild-type EHV-1. Heparin treatment of the virus had no effect on viral infectivity in cell culture. Glycoprotein C (gC) was not detected by Western blotting and fluorescent antibody tests in 5089 virions and 5089-infected cells, respectively. RT-PCR analysis revealed that the expression level of 5089 gC mRNA was reduced considerably compared to that of wild-type EHV-1. Sequencing analysis of the 5089 gC coding region showed a point mutation in the promoter region of the gC open reading frame. However, the mutation did not affect the promoter activity. These results suggested that the lack of gC in 5089 virions might be one of the reasons for spread of the virus by cell-to-cell infection and that gC mRNA expression might not be activated efficiently due to factors other than the mutation in the gC promoter region.