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

Studying longitudinal neutralising antibody levels against Equid herpesvirus 1 in experimentally infected horses using a novel pseudotype based assay

Infection with equid herpesvirus 1 (EHV-1), a DNA virus of the Herpesviridae family represents a significant welfare issue in horses and a great impact on the equine industry. During EHV-1 infection, entry of the virus into different cell types is complex due to the presence of twelve glycoproteins (GPs) on the viral envelope. To investigate virus entry mechanisms, specific combinations of GPs were pseudotyped onto lentiviral vectors. Pseudotyped virus (PV) particles bearing gB, gD, gH and gL were able to transduce several target cell lines (HEK293T/17, RK13, CHO-K1, FHK-Tcl3, MDCK I & II), demonstrating that these four EHV-1 glycoproteins are both essential and sufficient for cell entry. The successful generation of an EHV-1 PV permitted development of a PV neutralisation assay (PVNA). The efficacy of the PVNA was tested by measuring the level of neutralising serum antibodies from EHV-1 experimentally infected horses (n = 52) sampled in a longitudinal manner. The same sera were assessed using a conventional EHV-1 virus neutralisation (VN) assay, exhibiting a strong correlation (r = 0.82) between the two assays. Furthermore, PVs routinely require -80 °C for long term storage and a dry ice cold-chain during transport, which can impede dissemination and utilisation in other stakeholder laboratories. Consequently, lyophilisation of EHV-1 PVs was conducted to address this issue. PVs were lyophilised and pellets either reconstituted immediately or stored under various temperature conditions for different time periods. The recovery and functionality of these lyophilised PVs was compared with standard frozen aliquots in titration and neutralisation tests. Results indicated that lyophilisation could be used to stably preserve such complex herpesvirus pseudotypes, even after weeks of storage at room temperature, and that reconstituted EHV-1 PVs could be successfully employed in antibody neutralisation tests.

An Outbreak of Equine Herpesvirus-4 in an Ecological Donkey Milk Farm in Romania

Equine herpesviruses are important pathogens causing significant economic loss in equine and asinine populations. EHV-1/4 strains are mainly associated with respiratory distress. The aim of this study is to report the first EHV 4-associated respiratory disease in donkeys in Romania. Thirty-seven of three hundred jennies in an ecological donkey farm in southwest Romania started initially showing signs of severe upper respiratory tract disease, with ten concomitant late abortions/neonatal deaths and three neurological cases. There were nine fatalities. Pathological examination was performed, and samples were collected for Real-Time PCR analysis and histology. In addition, serum samples from 28 individuals with respiratory symptoms were collected and tested using indirect ELISA. RT-PCR identified the EHV-4 strain. Acute, diffuse necrotizing bronchointerstitial pneumonia with occasional intraepithelial intranuclear viral inclusion bodies was identified. Additionally, EHV-1/4-specific antibodies were found in 15 of the 28 sampled animals. Few studies on donkeys and herpesviruses have been published, and this is the first reported case of EHV-4 outbreak in Romania. There is a need for more extensive seroprevalence studies as, currently, the status of EHV-4 infection in donkeys in Romania is unknown.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): infection with Equine Herpesvirus-1

Equine Herpesvirus-1 infection has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of: Article 7 on disease profile and impacts, Article 5 on the eligibility of the disease to be listed, Article 9 for the categorisation of the disease according to disease prevention and control measures as in Annex IV and Article 8 on the list of animal species related to Equine Herpesvirus-1 infection. The assessment has been performed following a methodology composed of information collection and compilation, and expert judgement on each criterion at individual and collective level. The outcome is the median of the probability ranges provided by the experts, which indicates whether the criterion is fulfilled (66-100%) or not (0-33%), or whether there is uncertainty about fulfilment (33-66%). For the questions where no consensus was reached, the different supporting views are reported. According to the assessment performed, Equine Herpesvirus-1 infection can be considered eligible to be listed for Union intervention according to Article 5 of the Animal Health Law with 33-90% certainty. According to the criteria as in Annex IV of the AHL related to Article 9 of the AHL for the categorisation of diseases according to the level of prevention and control, it was assessed with less than 1% certainty that EHV-1 fulfils the criteria as in Section 1 (category A), 1-5% for the criteria as in Section 2 (category B), 10-66% for the criteria as in Section 3 (category C), 66-90% for the criteria as in Section 4 (category D) and 33-90% for the criteria as in Section 5 (category E). The animal species to be listed for EHV-1 infection according to Article 8(3) criteria are the species belonging to the families of Equidae, Bovidae, Camelidae, Caviidae, Cervidae, Cricetidae, Felidae, Giraffidae, Leporidae, Muridae, Rhinocerontidae, Tapiridae and Ursidae.

Seroprevalence of Equine Herpesvirus 1 (EHV-1) and Equine Herpesvirus 4 (EHV-4) in the Northern Moroccan Horse Populations

Simple Summary

This work aims to evaluate the seroprevalence of equine EHV-1/4 in horse populations in the north of Morocco and to measure the antibody titers in vaccinated horses, under field conditions, with monovalent EHV-1 vaccines. Overall, 12.8% unvaccinated, and 21.8% vaccinated horses were positive for EHV-1. All samples were positive for EHV-4 when tested with the type-specific ELISA. The virus neutralization test showed low antibody titers in samples from vaccinated horses. Our study demonstrated that EHV-1 and EHV-4 are endemic in the horse populations in the north of Morocco and highlighted the necessity of reevaluating the vaccines and the vaccination protocol used.

Abstract

This study reports the first equine herpesvirus-1 (EHV-1) and equine herpesvirus-4 (EHV-4) seroprevalence investigation in horse populations of Morocco in 24 years. It also aims to determine antibody titers in horses vaccinated under field conditions with a monovalent EHV-1 vaccine. Blood samples were collected from 405 horses, including 163 unvaccinated and 242 vaccinated animals. They were tested using a commercial type-specific enzyme-linked immunosorbent assay (ELISA) and a virus neutralization test (VNT). Overall, 12.8% unvaccinated, and 21.8% vaccinated horses were positive for EHV-1. All samples were positive for EHV-4 when tested with the type-specific ELISA. In the vaccinated group, the VNT revealed a mean antibody titer of 1:49 for EHV-1 and 1:45 for EHV-4. The present study demonstrates that EHV-1 and EHV-4 are endemic in the horse populations in the north of Morocco, with prevalence differences between regions. Furthermore, horses vaccinated with a monovalent EHV-1 vaccine had low antibodies titers. This study highlights the necessity to establish and/or support efficient biosecurity strategies based on sound management of horses and characterize further and potentially improve the efficiency of the EHV vaccines and vaccination protocol used in the field.

Equid Herpesvirus 8 Isolated From an Adult Donkey in Israel

We report the isolation of Equid herpesvirus 8 from a rescued donkey that suffered severe postcastration complications. Despite intensive treatment, the donkey deteriorated and was euthanized. Postmortem virologic analysis revealed the isolation of a herpesvirus that is closely related to herpesviruses reported from donkeys and horses in Australia, China, and Ireland, causing respiratory disease in donkeys and abortion in mares. To our knowledge, this is the first report of this equid herpesvirus in Israel. The potential significance of this herpesvirus to the equid population in Israel needs further investigation.

Seroprevalence of equine herpes virus-1 in endemic area of Egypt with risk factors assessment

Although equine herpesvirus-1 (EHV-1) infection occurs throughout the world; causing various health problems within horse population such as respiratory disease, abortion and myeloencephalopathy, there is information shortage concerning the epidemiological situation of EHVs in Egypt. This paper is the first study of EHV-1 prevalence rate in Monufia province (as a model for other pro­vinces). During 2015, two hundred and seventy serum samples from EHV non-vaccinated horses were randomly collected from 9 centres of Monufia province. The indirect ELISA was used to detect the prevalence rate of the disease while assessment of the associated risk factors was conducted using univariate and multivariate logistic regression models. The results showed that EHV-1 infection was widespread among horses at Monufia province (apparent prevalence rate 64% and true prevalence rate 28%) and posed risk for the health of other equines in the region. Results of risk factors identification showed that horses > 5 years of age were at significant risk of getting EHV-1 infection than < 1-year-old horses (OR: 5; P<0.02), while males were twice more prone than females of getting the EHV-1 infection (OR: 2 and P<0.03). There was a significant effect of different localities on the prevalence of EHV-1 infection. The obtained results could be extrapolated to the different districts and governorates of Egypt because of the similarity of the husbandry system of equines all over Egypt.

Respiratory Disorders of the Donkey

Donkeys suffer from the same respiratory diseases as horses; however, owing to their nonathletic nature many conditions can present in a more advanced state before becoming clinically apparent. Anatomically, their respiratory tract is similar to the horse, with certain species-specific differences that are important to be aware of. Often donkeys do not receive the same level of routine care as horses, so many are not vaccinated against respiratory pathogens such as influenza or herpesviruses. Donkeys can act as a reservoir for certain infectious and parasitic respiratory diseases and the interpretation of diagnostic tests needs to be carried out with caution.

Seroprevalence and factors associated with equine herpesvirus type 1 and 4 in Spanish Purebred horses in Spain

Equine herpesvirus type 1 (EHV-1) and type 4 (EHV-4) have a worldwide distribution and cause respiratory disease, abortion, neonatal death and myeloencephalopathy in susceptible horses. Given the scarcity of serological EHV-1/EHV-4 data in Spain, the objective of this cross-sectional study was to estimate the seroprevalence of EHV-1/EHV-4 and to identify potential horse-level and stud farm-level factors associated with EHV-1/EHV-4 in the breeding Spanish Purebred (SP) horse population in central Spain. Serum samples from 334 SP unvaccinated horses, collected between September 2011 and November 2013 at 30 stud farms, were tested using a commercially available EHV-1/EHV-4 antibody ELISA and seroneutralisation as the World Organisation for Animal Health reference confirmation test. Data on factors putatively associated with seropositivity to EHV-1/EHV-4 were collected via a questionnaire and examined using logistic regression analysis. EHV-1/EHV-4 seroprevalence in the SP breeding population in central Spain, standardised for the sex distribution of the reference horse population, was 53.9 per cent (95 per cent confidence interval 44.0 per cent to 63.8 per cent). Increasing age, southern location of the stud farm, temperate climate during the summer, and a smaller surface area used for breeding activities in the farm were associated with increased odds for EHV-1/EHV-4 seropositivity, whereas EHV-1/EHV-4 vaccination of other resident horses and separation of breeding mares from youngsters were protective factors.

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.

A review of equid herpesvirus 1 for the veterinary practitioner. Part A: clinical presentation, diagnosis and treatment

Equid herpesvirus (EHV) type 1 is a common pathogen of horses with worldwide distribution. Although severe tracheobronchitis has been described in some field outbreaks of EHV-1 respiratory disease, many EHV-1 infections occur asymptomatically or are accompanied only by signs of mild respiratory disease. However, EHV-1 infection can also result in outcomes other than respiratory disease such as abortion, neonatal death or neurological disease. This review provides an overview of the diagnosis, treatment and prognosis for EHV-1-associated diseases, with an emphasis on neurological presentations of EHV-1 infection.

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.

Clinical observations and management of a severe equine herpesvirus type 1 outbreak with abortion and encephalomyelitis

Latent equine herpesvirus type 1 (EHV-1) infection is common in horse populations worldwide and estimated to reach a prevalence nearing 90% in some areas. The virus causes acute outbreaks of disease that are characterized by abortion and sporadic cases of myeloencephalopathy (EHM), both severe threats to equine facilities. Different strains vary in their abortigenic and neuropathogenic potential and the simultaneous occurrence of EHM and abortion is rare. In this report, we present clinical observations collected during an EHV-1 outbreak caused by a so-called “neuropathogenic” EHV-1 G₂₂₅₄/D₇₅₂ polymerase (Pol) variant, which has become more prevalent in recent years and is less frequently associated with abortions. In this outbreak with 61 clinically affected horses, 6/7 pregnant mares aborted and 8 horses developed EHM. Three abortions occurred after development of EHM symptoms. Virus detection was performed by nested PCR targeting gB from nasal swabs (11 positive), blood serum (6 positive) and peripheral blood mononuclear cells (9 positive) of a total of 42 horses sampled. All 6 fetuses tested positive for EHV-1 by PCR and 4 by virus isolation. Paired serum neutralization test (SNT) on day 12 and 28 after the index case showed a significant (≥ 4-fold) increase in twelve horses (n = 42; 28.6%). This outbreak with abortions and EHM cases on a single equine facility provided a unique opportunity for the documentation of clinical disease progression as well as diagnostic procedures.

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.

Experimental infection with neuropathogenic equid herpesvirus type 1 (EHV-1) in adult horses

Equid herpesvirus type 1 (EHV-1)-associated myeloencephalopathy (EHM) may follow an infection with the virus in horses. This study tested three hypotheses: (1) a large inhaled dose of a neuropathogenic EHV-1 strain would induce a cell-associated viraemia in all infected horses; (2) neurological disease will only occur in viraemic horses, and (3) the cerebrospinal fluid (CSF) composition following EHV-1 viraemia will be an indicator for EHM. Four EHV-1 seronegative horses were inoculated with EHV-1 by inhalation. Three developed clinical signs of neurological disease, which were mild in two horses and lacking typical EHM histopathological findings, but moderately severe in the third horse. This latter animal was the only one found to be viraemic, with xanthochromic CSF and spinal cord histopathology findings characteristic of EHM. This study showed that cell-associated viraemia was not guaranteed, despite a large-dose inoculation with EHV-1, yet viraemia was probably a pre-requisite for subsequent development of EHM. The histopathological changes used to confirm EHM may be predicted from CSF analysis.

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.

Detection of equine herpesviruses in aborted foetuses by consensus PCR

The major role of EHV-1 in equine abortion is widely reported in the literature but the contribution of EHV-2, EHV-3, EHV-4 or EHV-5 remains less well documented. The objective of this study is to evaluate the contribution of these five different EHVs to equine abortion in a variety of biological tissues using a consensus polymerase chain reaction (PCR). The test was validated for specificity and sensitivity in horses before screening specimens from 407 foetuses, stillbirths and premature foals collected over a 2.5-year interval. Positive results obtained with this assay were compared to other EHV type-specific PCR or by sequencing. EHV-1 was identified as the major cause of abortion in French mares (59/407 cases). However, there was evidence to suggest some variation in the potential of EHV-1 strains to induce abortion. Indeed, DNA samples from EHV-2 (in three cases) and EHV-5 (in one case) inferred a role of these viruses in abortion. The presence of viral DNA from EHV-3 or EHV-4 strains was not detected in the specimens studied. The data obtained suggest that the consensus herpesvirus PCR is an efficient screening tool. In association with a specific PCR, the test provides a rapid identification of the type of herpesvirus involved in abortion and is useful for routine diagnostic tests as it allows the identification of herpesviruses other than the EHV-1 strain.