The effect of equine herpesvirus type 4 on type-I interferon signaling molecules.

Equine herpesvirus type 4 (EHV-4) is mildly pathogenic but is a common cause of respiratory disease in horses worldwide. We previously demonstrated that unlike EHV-1, EHV-4 is not a potent inducer of type-I IFN and does not suppress that IFN response, especially during late infection, when compared to EHV-1 infection in equine endothelial cells (EECs). Here, we investigated the impact of EHV-4 infection in EECs on type-I IFN signaling molecules at 3, 6, and 12 hpi. Findings from our study revealed that EHV-4 did not induce nor suppress TLR3 and TLR4 expression in EECs at all the studied time points. EHV-4 was able to induce variable amounts of IRF7 and IRF9 in EECs with no evidence of suppressive effect on these important transcription factors of IFN-α/ß induction. Intriguingly, EHV-4 did interfere with the phosphorylation of STAT1/STAT2 at 3 hpi and 6 hpi, less so at 12 hpi. An active EHV-4 viral gene expression was required for the suppressive effect of EHV-4 on STAT1/STAT2 phosphorylation during early infection. One or more early viral genes of EHV-4 are involved in the suppression of STAT1/STAT2 phosphorylation observed during early time points in EHV-4-infected EECs. The inability of EHV-4 to significantly down-regulate key molecules of type-I IFN signaling may be related to the lower severity of pathogenesis when compared with EHV-1. Harnessing this knowledge may prove useful in controlling future outbreaks of the disease.

Concurrent vaccination against equine influenza and equine herpesvirus - a practical approach.

BACKGROUND: There is a lack of information concerning concurrent administration of vaccines against equine influenza virus (EIV) and equine herpesvirus 1 and 4 (EHV-1/4). OBJECTIVES: The primary objective of this study was to determine the impact of the concurrent use of EIV and EHV-1/4 vaccines in Thoroughbred racehorses on their humoral immune response to EIV. METHODS: This study was carried out on a population of 30 horses using an inactivated whole-virus EIV vaccine and an inactivated EHV-1/4 vaccine. Horses were randomly allocated to vaccination group A or B. Horses in group A were vaccinated against EIV and EHV-1/4 2 weeks apart. Horses in group B were vaccinated against EIV and EHV-1/4 on the same day. Whole-blood samples were collected on the day of vaccination and 2 weeks and 6 weeks post-vaccination. Antibody levels against EIV and EHV-1/4 were measured using the single radial haemolysis and serum neutralisation test, respectively. RESULTS: The pattern of EIV antibody response post-vaccination was similar for both groups. Highest EIV antibody levels were recorded 2 weeks post-vaccination, and a significant decrease in antibody level was observed 4 weeks later. Horses in group B demonstrated a significantly higher EIV antibody response post-vaccination. Overall, there was no significant difference in EHV-1/4 antibody response between the two groups post-vaccination. CONCLUSION: In this study, concurrent vaccination against EIV and EHV-1/4 increased the response to EIV and did not compromise the humoral immune response to EHV-1/4.

Virological and serological investigation of Equid herpesvirus 1 infection in New Zealand.

Infection with equid herpesvirus 1 (EHV-1) may be asymptomatic, or may result in respiratory disease, abortion, neonatal death, or neurological disease. The aim of this study was to estimate the prevalence of EHV-1 infection, including differentiation between genotypes with aspartic acid (D) and asparagine (N) at position 752 of the DNA polymerase sequence, within a selected population of New Zealand horses. The second aim was to determine the predictive value of serology for detection of latently infected horses. Retropharyngeal lymph nodes (RLN) and trigeminal ganglia (TG) were dissected from 52 horses at slaughter and tested for the presence of EHV-1 DNA using magnetic bead, sequence-capture enrichment followed by nested PCR. Sera were tested for EHV-1 antibody using type-specific glycoprotein G ELISA. Overall, 17/52 horses tested positive for EHV-1 DNA. All but one positive PCR results were obtained from RLN samples. Fifteen of the EHV-1 positive horses harboured EHV-1 with N752 genotype, one of which was additionally infected with the D752 genotypes of the virus. Our data comprise the first detection of EHV-1 with D752 genotype in New Zealand and suggest that the "neurovirulent" variant of EHV-1 had been present in New Zealand for at least two years before the first reported outbreak of EHM. All sampled horses tested positive for EHV-4 antibody, and 11/52 tested positive for EHV-1 antibody. The strength of agreement between results of EHV-1 PCR and EHV-1 serology was "fair" (Kappa 0.259, 95% CI: -0.022-0.539), which was likely a reflection of low levels of both EHV-1 antibody in sera and EHV-1 DNA in tissues tested.

Successful control of winter pyrexias caused by equine herpesvirus type 1 in Japanese training centers by achieving high vaccination coverage.

Equine herpesvirus type 1 (EHV-1) is a major cause of winter pyrexia in racehorses in two training centers (Ritto and Miho) in Japan. Until the epizootic period of 2008-2009, a vaccination program using a killed EHV-1 vaccine targeted only susceptible 3-year-old horses with low antibody levels to EHV-1 antigens. However, because the protective effect was not satisfactory, in 2009-2010 the vaccination program was altered to target all 3-year-old horses. To evaluate the vaccine's efficacy, we investigated the number of horses with pyrexia due to EHV-1 or equine herpesvirus type 4 (EHV-4) infection or both and examined the vaccination coverage in the 3-year-old population and in the whole population before and after changes in the program. The mean (± standard deviation [SD]) estimated numbers of horses infected with EHV-1 or EHV-4 or both, among pyretic horses from 1999-2000 to 2008-2009 were 105 ± 47 at Ritto and 66 ± 44 at Miho. Although the estimated number of infected horses did not change greatly in the first period of the current program, it decreased from the second period, with means (±SD) of 21 ± 12 at Ritto and 14 ± 15 at Miho from 2010-2011 to 2012-2013. Vaccination coverage in the 3-year-old population was 99.4% at Ritto and 99.8% at Miho in the first period, and similar values were maintained thereafter. Coverage in the whole population increased more gradually than that in the 3-year-old population. The results suggest that EHV-1 epizootics can be suppressed by maintaining high vaccination coverage, not only in the 3-year-old population but also in the whole population.

Development of a peptide ELISA for discrimination between serological responses to equine herpesvirus type 1 and 4.

A peptide-based enzyme-linked immunosorbent assay (ELISA) for discrimination between serological responses to equine herpesvirus type 1 (EHV-1) and 4 (EHV-4) was developed. Three and four peptides for EHV-1 and EHV-4, respectively, were designed and studied initially in the ELISA using sera from foals infected experimentally. The most promising peptide pair, derived from EHV-1 glycoprotein E and EHV-4 glycoprotein G, was evaluated further using acute and convalescent sera from horses infected experimentally and naturally as well as a panel of horse field sera. Ten pre- and post-vaccination serum pairs were similarly tested in the type-specific ELISA. The peptide ELISA was able to identify horses which had been infected with EHV-1 or EHV-4 as derived from the results using acute and convalescent sera collected from natural outbreaks. When applied to a set of field samples, the assay proved robust with respect to determining the EHV-1 and EHV-4 antibody status. Also, the peptide ELISA was able to detect type-specific seroconversion for EHV-1 in vaccinated animals. With further validation, the EHV-1/EHV-4 peptide ELISA described in this study could serve as a reliable and cost-effective alternative to current methods for serological EHV-1 and EHV-4 diagnosis.

Equine herpesviruses type 1 (EHV-1) and 4 (EHV-4)--masters of co-evolution and a constant threat to equids and beyond.

The equine herpesviruses type 1 (EHV-1) and 4 (EHV-4) are ubiquitous pathogens that affect horse populations on all continents. Despite widespread vaccination, EHV-1 and EHV-4 infections remain a permanent risk. While the two viruses share a high degree of genetic and antigenic similarity, they differ significantly in host range and pathogenicity. Compared to EHV-4, which mainly infects horses and causes respiratory disease, EHV-1 has a broader host range and can result in respiratory disease, abortions, neonatal death, and equine herpesvirusmyeloencephalopathy (EHM). Recent studies have elucidated a number of mechanisms that may, at least partly, explain the differential pathogenic potential of the two viruses. While both EHV-1 and EHV-4 can escape host immune responses and establish latent infection, there are differences with respect to virus entry and their ability to interfere with the innate immune response. Understanding the virus' repertoire of immunomodulatory mechanisms may lead the way to develop more efficient vaccines.

The role of secreted glycoprotein G of equine herpesvirus type 1 and type 4 (EHV-1 and EHV-4) in immune modulation and virulence.

Equine herpesvirus type 1 and 4 (EHV-1 and EHV-4) are important pathogens of horses worldwide. Infection with EHV-4 usually remains restricted to the upper respiratory tract, whereas infection with EHV-1 can generalize after leukocyte-associated viremia. Here we examined whether differences in the immunomodulatory glycoprotein G (gG) between the two viruses determine EHV-1's ability to cause systemic infection. To this end, mutant viruses were constructed based on the neurovirulent EHV-1 strain OH-03, in which the entire gG gene or parts thereof were exchanged with EHV-4 gG sequences. In vitro chemotaxis assays showed that supernatants of cells infected with the various gG mutant viruses interfered to variable degrees with neutrophil migration. More specifically, supernatants of cells infected with the gG deletion virus (vOH-ΔgG1) or OH-03 expressing EHV-4 gG (vOH-gG4) were unable to interfere with chemotaxis. Re-insertion of the predicted chemokine-binding region of EHV-1 gG in the vOH-gG4 mutant (vOH-gG4hyp1) did not completely restore the ability to inhibit neutrophil migration, whereas insertion of the hypervariable region of EHV-4 gG into vOH-03 (vOH-gG1hyp4) did not lead to a complete loss of chemokine-binding function. Very similar results were obtained in an in vivo study where the amount of neutrophils present in bronchioalveolar lavages (BALs) of mice infected with the different mutants was analyzed by flow cytometry. Taken together, our results show that, in a virus background, the hypervariable region is not solely responsible for the immunomodulatory potential of EHV-1 gG.

Serological responses and clinical outcome after vaccination of mares and foals with equine herpesvirus type 1 and 4 (EHV-1 and EHV-4) vaccines.

Equine herpesvirus type 1 and type 4 (EHV-1 and EHV-4) cause infections of horses worldwide. While both EHV-1 and EHV-4 cause respiratory disease, abortion and myeloencephalopathy are observed after infection with EHV-1 in the vast majority of cases. Disease control is achieved by hygiene measures that include immunization with either inactivated or modified live virus (MLV) vaccine preparations. We here compared the efficacy of commercially available vaccines, an EHV-1/EHV-4 inactivated combination and an MLV vaccine, with respect to induction of humoral responses and protection of clinical disease (abortion) in pregnant mares and foals on a large stud with a total of approximately 3500 horses. The MLV vaccine was administered twice during pregnancy (months 5 and 8 of gestation) to 383 mares (49.4%), while the inactivated vaccine was administered three times (months 5, 7, and 9) to 392 mares (50.6%). From the vaccinated mares, 192 (MLV) and 150 (inactivated) were randomly selected for serological analyses. There was no significant difference between the groups with respect to magnitude or duration of the humoral responses as assessed by serum neutralization assays (median range from 1:42 to 1:130) and probing for EHV-1-specific IgG isotypes, although neutralizing responses were higher in animals vaccinated with the MLV preparation at all time points sampled. The total number of abortions in the study population was 55/775 (7.1%), 9 of which were attributed to EHV-1. Seven of the abortions were in the inactivated and two in the MLV vaccine group (p=0.16). When foals of vaccinated mares were followed up, a dramatic drop of serum neutralizing titers (median below 1:8) was observed in all groups, indicating that the half-life of maternally derived antibody is less than 4 weeks.

Equine herpesvirus type 4 UL56 and UL49.5 proteins downregulate cell surface major histocompatibility complex class I expression independently of each other.

Major histocompatibility complex class I (MHC-I) molecules are critically important in the host defense against various pathogens through presentation of viral peptides to cytotoxic T lymphocytes (CTLs), a process resulting in the destruction of virus-infected cells. Herpesviruses interfere with CTL-mediated elimination of infected cells by various mechanisms, including inhibition of peptide transport and loading, perturbation of MHC-I trafficking, and rerouting and proteolysis of cell surface MHC-I. In this study, we show that equine herpesvirus type 4 (EHV-4) modulates MHC-I cell surface expression through two different mechanisms. First, EHV-4 can lead to a significant downregulation of MHC-I expression at the cell surface through the product of ORF1, a protein expressed with early kinetics from a gene that is homologous to herpes simplex virus 1 UL56. The EHV-4 UL56 protein reduces cell surface MHC-I as early as 4 h after infection. Second, EHV-4 can interfere with MHC-I antigen presentation, starting at 6 h after infection, by inhibition of the transporter associated with antigen processing (TAP) through its UL49.5 protein. Although pUL49.5 has no immediate effect on overall surface MHC-I levels in infected cells, it blocks the supply of antigenic peptides to the endoplasmic reticulum (ER) and transport of peptide-loaded MHC-I to the cell surface. Taken together, our results show that EHV-4 encodes at least two viral immune evasion proteins: pUL56 reduces MHC-I molecules on the cell surface at early times after infection, and pUL49.5 interferes with MHC-I antigen presentation by blocking peptide transport in the ER.

Immunological correlates of vaccination and infection for equine herpesvirus 1.

Equine herpesvirus 1 (EHV-1) induces a variety of disease manifestations, including respiratory disease, abortions, and myeloencephalopathy. Several vaccines are commercially available but could not previously be distinguished by serologic testing from infection with EHV-1 (or the closely related EHV-4). Currently available vaccines are not reliably protective against the severe manifestations of the disease, including fatal myeloencephalopathy. We determined immunological parameters that can differentiate vaccinated from previously infected animals by comparing humoral and cellular EHV-1-specific responses in clinically healthy horses 10 months after vaccination. Forty-seven horses with known histories of vaccination and infection were studied, including a group of horses that survived a severe neurological outbreak 5 years prior to vaccination. Results of serum virus neutralization (SN), serum IgG isotyping, and cytokine profiling of lymphocyte subsets were compared. IgG4/7 levels strongly correlated with virus neutralization (P < 0.0001). IgG1/3 and SN values distinguished vaccinated/outbreak-exposed (vacc/outbreak) horses from vaccinated horses (P < 0.05). EHV-1-specific gamma interferon (IFN-γ)-producing CD4(+) (but not CD8(+)) T-cell numbers were also increased in vacc/outbreak horses, which distinguished them from vaccinated horses (P < 0.01). IFN-α secretion was similar between all groups and independent of previous exposure or vaccination. Our data suggest that IgG isotype responses to EHV-1 are more diverse under field conditions than is revealed by experimental studies and that the current modified-live virus (MLV) vaccine induces a more restricted IgG isotype response than does natural exposure to EHV-1. Since these parameters can be assessed in a high-throughput manner, they may prove useful in screening future vaccine candidates and assessing levels of protection.

Induction of a Th-1-biased IgG subclass response against equine herpesvirus type 1 in horses previously infected with type 4 virus.

An immunoglobulin G (IgG) subclass response against equine herpesvirus type 1 (EHV-1) infection was investigated in horses that were naïve to EHV-1/4 and those that had previously been exposed to EHV-4. The IgG subclass response was determined by an ELISA using EHV-1-specific recombinant gG protein as an antigen. In most horses naïve to EHV-1/4, IgGa, IgGb, and IgG(T) were induced after experimental infection with EHV-1. In contrast, a subclass response dominated by IgGa and IgGb, with no apparent increase in IgG(T), was observed after EHV-1 infection in horses previously infected with EHV-4. Horses naturally infected with EHV-1 in the field showed similar responses. These results indicated that pre-infection with EHV-4 induced a Th-1-biased IgG subclass response against subsequent EHV-1 infection.

Pathogenic potential of equine alphaherpesviruses: the importance of the mononuclear cell compartment in disease outcome.

Equid herpesviruses types 1 and 4 (EHV-1 and EHV-4) are closely related pathogens of horses. While both viruses can infect the upper respiratory tract, EHV-1 regularly causes systemic infection, which is only rarely observed in the case of EHV-4. Little is known about the molecular basis for this striking difference in pathogenic potential. Recently, we have started a systematic analysis of differences in the amino acid sequences of proteins involved in virus replication, more specifically entry and egress, as well as proteins involved in immune evasion. Here, we summarize our findings relevant to glycoproteins D and G (gD and gG), which share a high degree of similarity between the viruses, yet exhibit important differences. We found that both these glycoproteins appear to be involved in the conquest of the mononuclear cell compartment. While gD is involved in infection of peripheral blood mononuclear cells through an RSD motif present in EHV-1 but not EHV-4, gG is implicated in thwarting innate responses by sequestration of chemokines. Again, the activity is only present in EHV-1, more specifically in a short stretch of variable amino acids in the extracellular domain of gG. The differences in the two glycoproteins of EHV-1 and EHV-4 are discussed, as is their role in pathogenesis. In addition, hypotheses are proposed related to the other equid respiratory alphaherpesviruses, EHV-8 and EHV-9, based on the amino acid sequences of gD and gG.

Clinical, serological and molecular investigations of EHV-1 and EHV-4 in 15 unweaned thoroughbred foals.

Fifteen unweaned thoroughbred foals, born on a stud farm to vaccinated mares, were clinically monitored during their first six months of life and repeatedly tested for equine herpesvirus type 1 (EHV-1) and equine herpesvirus type 4 (EHV-4). Nasopharyngeal swabs and blood samples were collected and screened respectively by PCR and seroneutralisation to detect the presence of the virus, explore its role as a possible cause of respiratory disease, and to assess the efficiency of the pcr for the diagnosis of this disease. The foals were divided into three groups on the basis of their clinical signs and whether they had seroconverted to EHV-1 and/or EHV-4: first, foals with no clinical signs of disease that had not seroconverted; secondly, foals with clinical signs that had seroconverted, and thirdly, foals with clinical signs that had not seroconverted. The results indicated that the viruses circulated on the stud farm despite stringent vaccination regimens against them, and confirmed their association with respiratory disease. The absence of significantly different pcr results among the three groups of foals showed that the pcr was effective in confirming the circulation of the viruses on the premises without being particularly helpful as a diagnostic tool.

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.

Equine herpesviruses 1 (EHV-1) and 4 (EHV-4)--epidemiology, disease and immunoprophylaxis: a brief review.

This review concentrates on the epidemiology, latency and pathogenesis of, and the approaches taken to control infection of horses by equine herpesvirus types 1 (EHV-1) and 4 (EHV-4). Although both viruses may cause febrile rhinopneumonitis, EHV-1 is the main cause of abortions, paresis and neonatal foal deaths. The lesion central to these three conditions is necrotising vasculitis and thrombosis resulting from lytic infection of endothelial cells lining blood capillaries. The initiation of infection in these lesions is likely to be by reactivated EHV-1 from latently infected leukocytes. However, host factors responsible for reactivation remain poorly understood. While vaccine development against these important viruses of equines involving classical and modern approaches has been ongoing for over five decades, progress, compared to other alpha herpesviruses of veterinary importance affecting cattle and pigs, has been slow. However recent data with a live temperature sensitive EHV-1 vaccine show promise.

Comparison of antibody detection assays for the diagnosis of equine herpesvirus 1 and 4 infections in horses.

OBJECTIVE: To compare methods of detecting equine herpesvirus type 1 (EHV1)- and EHV4-specific antibodies in horse sera. SAMPLE POPULATION: 33 acute and convalescent serum samples from experimentally or naturally infected horses after confirmed EHV1 or EHV4 infection. PROCEDURE: For each sample, serum antibody titers against EHV1 and EHV4 were determined by use of virus neutralization (VN) and complement fixation (CF) assays. The ELISA absorbance values for each serum sample were determined against the EHV1 and EHV4 recombinant ELISA antigens. Values obtained for acute and convalescent sera in each assay were compared. RESULTS: Following experimental infection of foals, EHV1 or EHV4 antibodies that were specific for the inoculating virus were detected only by use of the ELISA. Results of VN and CF assays indicated that the foals seroconverted to EHV1 and EHV4 following infection with EHV4 only. After EHV1-induced abortion, myeloencephalitis, or respiratory tract disease, the VN and CF assay results revealed seroconversion to EHV1 and EHV4, whereas results of the ELISA revealed seroconversion to EHV1 only. Similarly, after confirmed EHV4-induced respiratory tract disease, increases in EHV4-specific antibodies were detected only by use of the ELISA with no indication of an increase in EHV1 antibodies. The CF and, to a lesser degree, VN assays revealed that seroconversion to EHV1 and EHV4 occurred between the time of obtaining acute and convalescent serum samples. CONCLUSIONS AND CLINICAL RELEVANCE: The EHV1/EHV4 type-specific antibody ELISA clearly identifies horses that have been infected with EHV1 or EHV4 by use of acute and convalescent sera. Results of VN and CF assays indicate that cross-reactive antibodies greatly limit their use.

Identification of another B-cell epitope in the type-specific region of equine herpesvirus 4 glycoprotein G.

Recently, a novel 12-mer B-cell epitope, MKNNPIYSEGSL, in the type-specific region of equine herpesvirus 1 (EHV-1) glycoprotein G (gG) was identified and used as an antigen for enzyme-linked immunosorbent assay (Maeda et al., J. Clin. Microbiol. 42:1095-1098, 2004). Although our prototype strain, TH20p, possesses two repeat sequences containing the B-cell epitope, the EHV-4 NS80567 strain has two repeat sequences that are not identical. One repeat sequence stretch contained the B-cell epitope, while the other contained the 11-mer, MKNNPVYSESL (underlining indicates a different amino acid). In this study, heterogeneity of the type-specific region was compared among Japanese EHV-4 isolates. The 11-mer peptide, MKNNPVYSESL, specifically reacted with sera from horses naturally infected with EHV-4 but not with sera from horses experimentally infected with EHV-4 TH20p. The 11-mer peptide may be another B-cell epitope in the type-specific region.

Evidence that use of an inactivated equine herpesvirus vaccine induces serum cytotoxicity affecting the equine arteritis virus neutralisation test.

Several laboratories worldwide have recently experienced problems related to serum cytotoxicity with the equine arteritis virus (EAV) neutralisation test (VN) when using Office International des Epizooties (OIE) reference laboratory prescribed rabbit kidney (RK-13) indicator cells. Cytotoxicity can be mistaken for viral cytopathic effect and has led to increasing difficulties in test interpretation, consequently causing disruption to both equine breeding and disease surveillance. Results from experimental and field-derived data suggest that this serum cytotoxicity is associated with use of a tissue-culture-derived equine herpesvirus vaccine, probably manifested through a vaccine-induced anti-cellular antibody response directed against RK-13 cells. Two alternative EAV VN methods were shown to significantly reduce the effects of cytotoxicity (from 73 to <5% prevalence) among vaccinated horses but did not completely eliminate the problem. Use of ELISA-based tests, which are not affected by serum cytotoxicity but which are not currently recognised as international standards, should be evaluated as a useful backup in screening equine sera for EAV VN antibodies.

Use of the meridian test for the detection of equine herpesvirus type 1 infection in horses with decreased performance.

OBJECTIVE: To evaluate use of the acupuncture meridian test for detection of recent or recently reactivated equine herpesvirus type 1 (EHV-1) infection in horses with decreased performance. DESIGN: Case-control study. ANIMALS: 40 horses. PROCEDURE: Physical and neurologic examinations were performed, and acupuncture points on the bladder meridian were tested for sensitivity reactions in case and control horses. Polymerase chain reaction assays were performed to determine whether EHV-1 or equine herpesvirus type 4 (EHV-4) DNA could be detected in peripheral blood mononuclear cells. Complement fixation (CF) tests for detection of antibodies against EHV-1 and EHV-4 and virus neutralization (VN) tests for detection of antibodies against EHV-1 were performed on paired serum samples obtained 3 weeks apart. RESULTS: There was a significant difference in skin sensitivity in the cervical, sacral, and gluteal regions and flank between case and control horses. By use of the meridian test, all case horses were sensitive to manipulation of all acupuncture points believed to be associated with EHV infections, whereas only a few control horses were sensitive at an occasional point. Equine herpesvirus type 1 or EHV-4 viremia was not detected in any horses. Mean +/- SDVN antibody titers against EHV-1 were not significantly different between the 2 groups. Mean +/- SD CF antibody titers against EHV-1 obtained 3 weeks after the initial samples were higher in case horses than control horses; however, unequivocal seroconversion was not detected. CONCLUSIONS AND CLINICAL RELEVANCE: Results of the meridian test in case horses were associated with sensitivity reactions similar to those detected by physical and neurologic examinations; however, an unequivocal association with EHV-1 or EHV-4 infection was not detected.

Efficacy of a live equine herpesvirus-1 (EHV-1) strain C147 vaccine in foals with maternally-derived antibody: protection against EHV-1 infection.

REASONS FOR PERFORMING STUDY: Currently, there is no recommended immunoprophylaxis against febrile respiratory diseases due to equine herpesvirus-1 (EHV-1) and -4 (EHV-4) in horses below age 5-6 months. This is because of interference by maternally-derived antibody (MDA) of vaccines. OBJECTIVE: Unweaned equine foals are an important reservoir of EHV-1 transmission; therefore, we experimentally assessed the efficacy of a live EHV-1 vaccine in foals age 1.4-3.5 months with MDA. METHODS: Following vaccination and challenge, parameters assessed were virus shedding in nasal mucus, leucocyte-associated viraemia, circulating virus neutralising antibody activity and clinical reactions. RESULTS: Controlled challenge showed that a single intranasal dose of the vaccine afforded partial but significant protection against febrile respiratory disease, virus shedding and viraemia due to EHV-1 infection, despite virus-neutralising MDA. CONCLUSIONS AND POTENTIAL RELEVANCE: The prospective vaccine would be a significant step forward in reducing the incidence of the disease caused by EHV-1 infection.