Equine Herpesvirus-1 Infection Research Articles

Updated ACVIM consensus statement on equine herpesvirus-1.

Equine herpesvirus-1 (EHV-1) is a highly prevalent and frequently pathogenic infection of equids. The most serious clinical consequences of infection are abortion and equine herpesvirus myeloencephalopathy (EHM). The previous consensus statement was published in 2009 and considered pathogenesis, strain variation, epidemiology, diagnostic testing, vaccination, outbreak prevention and control, and treatment. A recent survey of American College of Veterinary Internal Medicine large animal diplomates identified the need for a revision to this original consensus statement. This updated consensus statement is underpinned by 4 systematic reviews that addressed key questions concerning vaccination, pharmaceutical treatment, pathogenesis, and diagnostic testing. Evidence for successful vaccination against, or effective treatment of EHV-1 infection was limited, and improvements in experimental design and reporting of results are needed in future studies of this important disease. This consensus statement also updates the topics considered previously in 2009.

Investigation of the presence of equine herpesvirus-1 (EHV-1) in tissue samples of aborted foals by histopathological, immunohistochemical, and Real-Time PCR techniques

Equine herpesvirus-1 (EHV-1) is a cause of pneumonia, encephalitis, and abortion in horses. Abortions occur alive or dead in the last trimester of pregnancy. The aim of this study is to investigate the incidence of EHV-1 infections in the tissue samples of aborted stillborn and live-born foals and the foals which died soon after birth and compare and correlate the conventional histopathologic diagnosis with IHC and Real-Time PCR. For this purpose, tissue samples (lung, liver, spleen, kidney, placenta, and brain) of 38 foals from Istanbul, Kocaeli, Bursa, and Eskişehir provinces of Turkey between August 2009 and March 2011 were examined Real-Time PCR revealed 52.6 % positivity (20/38), whereas 39.4 % (15/38) positivity was achieved with IHC, which indicated a correlation between these two diagnostic methods. In histopathological evaluation, the inclusion body was found in at least one of the tissue sections belonging to the lung, spleen, and mostly liver of 20 foals (52.6%). Tissue samples of the foals found to be positive by IHC and PCR revealed histopathologic findings compatible with the characteristics of the disease.

Viremia and nasal shedding for the diagnosis of equine herpesvirus-1 infection in domesticated horses.

Equine herpesvirus type 1 (EHV-1) infection is associated with upper respiratory disease, EHM, abortions, and neonatal death. Are nasal secretions a more sensitive biological sample compared to blood for the detection of EHV-1 infection? How long is EHV-1 detectable after primary infection by PCR? MedLine and Web of Science searches identified original peer-reviewed reports evaluating nasal shedding and viremia using virus isolation methods or PCR published in English before October 9, 2023. Sixty experimental and 20 observational studies met inclusion criteria. EHV-1 detection frequency by qPCR in nasal secretions and blood from naturally-infected horses with fever and respiratory signs were 15% and 9%, respectively; qPCR detection rates in nasal secretions and blood from horses with suspected EHM were 94% and 70%, respectively. In experimental studies the sensitivity of qPCR matched or exceeded that seen for virus isolation from either nasal secretions or blood. Detection of nasal shedding typically occurred within 2 days after EHV-1 inoculation with a detection period of 3 to 7 days. Viremia lasted 2 to 7 days and was usually detected ≥1 days after positive identification of EHV-1 in nasal secretions. Nasal shedding and viremia decreased over time and remained detectable in some horses for several weeks after inoculation. Under experimental conditions, blood and nasal secretions have similar sensitivity for the detection of EHV-1 when horses are sampled on multiple consecutive days. In contrast, in observational studies detection of EHV-1 in nasal secretions was consistently more successful.

Detection of equine herpesvirus-1 (EHV-1) in urine samples during outbreaks of equine herpesvirus myeloencephalopathy.

Real-time PCR is the diagnostic technique of choice for the diagnosis and control of equine herpesvirus-1 (EHV-1) in an outbreak setting. The presence of EHV-1 in nasal swabs (NS), whole blood, brain and spinal cord samples has been extensively described; however, there are no reports on the excretion of EHV-1 in urine, its DNA detection patterns, and the role of urine in viral spread during an outbreak. To determine the presence of EHV-1 DNA in urine during natural infection and to compare the DNA detection patterns of EHV-1 in urine, buffy coat (BC) and NS. Descriptive study of natural infection. Urine and whole blood/NS samples were collected at different time points during the hospitalisation of 21 horses involved in two EHV-1 myeloencephalopathy outbreaks in 2021 and 2023 in Spain. Quantitative real-time PCR was performed to compare the viral DNA load between BC-urine samples in 2021 and NS-urine samples in 2023. Sex, age, breed, presence of neurological signs, EHV-1 vaccination status and treatment data were recorded for all horses. A total of 18 hospitalised horses during the 2021 and 2023 outbreaks were positive for EHV-1, and viral DNA was detected in urine samples from a total of 11 horses in both outbreaks. Compared with BC samples, DNA presence was detected in urine samples for longer duration and with slightly higher concentration; however, compared with NS, detection of EHV-1 in urine was similar in duration with lower DNA concentrations. Limited sample size, different sampling times and protocols (BC vs. NS) in two natural infection outbreak settings. EHV-1 was detected in the urine from naturally infected horses. Urine should be considered as complimentary to blood and NS in diagnosis of EHV-1 infection.

Equine Herpesvirus-1 Outbreak During a Show-Jumping Competition: A Clinical and Epidemiological Study.

A total of 752 horses were involved in the CES Valencia Spring Tour 2021. Due to an equine herpesvirus-1 (EHV-1) outbreak, the competition was cancelled and the site was locked down. The objective of this study was to describe epidemiological, clinical, diagnostic, and outcome data of the 160 horses remaining in Valencia. Clinical and quantitative polymerase chain reaction (qPCR) data were analysed for 60 horses in a retrospective case-control observational study. The risk of developing clinical manifestations was explored using a logistic regression approach. EHV-1 was detected by qPCR, genotyped as A2254 (ORF30) and isolated on cell culture. From the 60 horses, 50 (83.3%) showed fever, 30 horses (50%) showed no further signs and 20 (40%) showed neurological signs, with eight horses (16%) hospitalised, of which two died (3%). Stallions and geldings were six times more likely to develop EHV-1 infection compared to mares. Horses older than 9 years, or housed in the middle of the tent were more likely to develop EHV-1 myeloencephalopathy (EHM). These data show that for EHV-1 infection, the risk factor was male sex. For EHM the risk factors were age > 9-year old and location in the middle of the tent. These data highlight the crucial role of stable design, position, and ventilation in EHV-outbreaks. It also showed that PCR testing of the horses was important to manage the quarantine.

Investigation of the EHV-1 Genotype (N752, D752, and H752) in Swabs Collected From Equids With Respiratory and Neurological Disease and Abortion From the United States (2019-2022).

Contemporary data on equine herpesvirus-1 (EHV-1) genotype (non-neuropathogenic or N752, neuropathogenic or D752 and new variant or H752) in clinically diseased equids is important in order to determine the frequency of these genotypes and their association with disease expression. A total of 297 EHV-1 qPCR-positive swabs collected from 2019 to 2022 from horses with respiratory disease (EHV-1), neurological disease (equine herpesvirus-1 myeloencephalopathy [EHM]) and abortion were tested for the three different EHV-1 genotypes (N752, D752 and H752) using qPCR allelic discrimination assays. All submissions originated from the United States and included 257 EHV-1 cases, 35 EHM cases and 5 cases of abortion. EHV-1 qPCR-positive cases were predominantly seen during winter and spring. N752 was the predominant genotype detected in EHV-1 cases (87.5%), EHM cases (74.3%) and abortions (80%). D752 was detected less frequently in EHV-1 cases (9.3%) and EHM cases (25.7%), while H752 was only detected in EHV-1 cases (3.1%). While the N752 genotype has remained the predominant genotype affecting horses with respiratory disease and abortion, it has also become a leading genotype in cases of EHM, when compared to historical data. The new H752 genotype, first reported in the United States in 2021, has remained confined to a cluster of geographically and temporally related outbreaks and the data showed no emerging spread of H752 since it was first reported. While the monitoring of EHV-1 genotypes is important from a diagnostic and epidemiological standpoint, it may also help establish medical interventions and preventive protocols to reduce the risk of severe complications associated with EHV-1 infection.

Clinical impact, diagnosis and control of Equine Herpesvirus-1 infection in Europe.

Equine herpesvirus‐1 (EHV‐1) can affect the entire equine sector in EU, and the large outbreak reported in 2021 in Spain drew attention to the needs of the European Commission for scientific advice for the assessment of EHV‐1 infection within the framework of Animal Health Law. EHV‐1 is considered endemic in the EU; its main risk is linked to the characteristic of producing latent life‐long infections. These can reactivate producing clinical disease, which can include respiratory, abortive and possibly fatal neurological forms. From the epidemiological and genomic viewpoint, there are no specific neuropathogenic EHV‐1 strains; the respiratory, reproductive and neurological signs are not found to be strain‐specific. This was also the case of the virus that caused the outbreak in Valencia (Spain) in 2021, which was genetically closely related to other viruses circulating before in Europe, and did not present the so‐called neuropathogenic genotype. The outbreak reported in Valencia was followed by wide geographic spread of the virus possibly due to a delay in diagnosis and late application of biosecurity measures. The recommended and most sensitive diagnostic test for detecting EHV‐1 is PCR performed on swabs collected according to the type of clinical signs. Serological assays on paired blood samples can help to detect a recent infection, while no diagnostic methods are available to detect EHV‐1 latent infections. Safe movements of horses can be ensured at premovement phase by testing and issuing health certificates, and by isolating animals upon arrival at new premises with regular health monitoring. In case of suspicion, movements should be forbidden and EHV‐1 infection early detected/confirmed by validated diagnostic tools. During outbreaks, no movements should be allowed until 21 days after the detection of the last case. In general, vaccination against EHV‐1 should be promoted, although this offers limited protection against the neurological form of the disease.

Viremia in Equine Herpes Virus-1 infection and a possible link to Transient Protective Immunity

Equine herpes virus (EHV-1) causes respiratory infections in equine, and results in abortion, paresis, neonatal death, and retinopathy and the virus may become latent following initial infection. Virus entry is via the respiratory route, and the virus replicates in the host in ciliated and non-ciliated epithelial cells of the respiratory tract and in Type 1 and Type 2 pneumocytes in the lung parenchyma. After viral replication in the respiratory system, the virus can become disseminated to other parts of body via viraemic cells. The virus also can cross the placenta which leads to abortion of live or dead fetuses without premonitory signs. Infected horses show transient immunity after natural or experimental infection and immune responses to EHV-1, but the immunoprotective status begins to decline after a few months of active infection. Due to the transient immune response, recovered horses are not immunoprotected and thus are prone to subsequent re-infection. Immunity is not long lived after experimental or natural infection, and as a result the development of an effective vaccine has remained a challenge. In this study viraemic cells were studied in a murine EHV-1 infection model. Mice were infected intranasally and viraemic cells were studied on days three and five which occurs during the peak of the infection. The results of this study may help to identify the nature of viraemic cells and their role in the transient immune response to infection. Buffy coat cells and lungs were removed and stained with a fluorescent antibody test for EHV-1 antigen, and lung specimens were subjected to transmission electron microscopy. Both techniques confirmed the presence of viraemic cells in lung tissues. These viraemic cells were further stained for EHV-1 antigen, and for CD4 or CD8 biomarkers and results are discussed re: pathogenesis of EHV-1 infection, identification of viraemic cells in a murine model and possible link of viraemia to transient immune responses in EHV-1 infection, which demonstrate the validity of this murine model for the investigation of the cytopathologic mechanism and sequelae of EHV manifestation in this model.

Proteomic analysis of the secretome of equine herpesvirus-1 infected rabbit kidney cells

Herpesviruses are the main cause of abortions and respiratory or neurological disorders in horses. Various disease patterns are suspected to be associated with the A2254G point mutation in the DNA polymerase sequence (ORF30) of the herpesvirus genome, although the importance of this link is still under debate. Based on a label-free quantitative proteomic analysis, the differences in the secretion of some host proteins between rabbit kidney cells infected with A2254 and cells of the same line infected with G2254 equine herpesvirus 1 (EHV-1) strains were identified. In both groups, downregulation of proteins involved in insulin growth factor and extracellular matrix pathway regulation was observed. Among 12 proteins with increased secretion, 8 were regulated only in G2254 EHV-1 infection. Those were endoplasmic reticulum chaperones with calcium binding properties, related to unfolded protein response and mitochondria. It was presumed that the secretion of proteins such as calreticulin, Hspa5 or endoplasmin may contribute to the pathogenesis of EHV-1 infection.

Application of equine herpesvirus-1 vaccine inactivated by both formaldehyde and binary ethylenimine in equine.

Background and Aim:Equine herpesvirus-1 infection in horses causes a wide range of manifestations affecting the respiratory tract. The virus can cause serious economic losses through sporadic abortion in pregnant mares, perinatal death, respiratory disease in young foals. This study was designed to prepare inactivated equine herpesvirus-1 (EHV-1) vaccine using both 0.005 M binary ethylenimine (BEI) and 0.0006% formaldehyde (FA) to decrease the use of BEI and provide a good immunological response. The efficacy, safety, and duration of immunity of the prepared inactivated EHV-1 vaccine were evaluated.Materials and Methods:The prepared FA/BEI-inactivated EHV-1 vaccine was adjuvanted with Alhydrogel and then evaluated by inoculation into guinea pigs, followed by comparison with the commercial inactivated EHV-1 vaccine. These two vaccines were evaluated by testing the safety and immunogenicity in horses classified into two groups. Group A was vaccinated with two doses of the prepared vaccine at a 4-week interval, while Group B was vaccinated with two doses of the commercial vaccine only. Anti-EHV-1 antibodies were detected in horse serum using enzyme-linked immunosorbent assay (ELISA) and virus neutralizing test (VNT).Results:Regarding the time required to inactivate EHV-1 vaccine, this was decreased using 0.005 M BEI and 0.0006% FA from 24 to 8 h. ELISA in Group A horses demonstrated a significant increase in EHV-1 antibody titer at 2 weeks after the booster dose compared with that for the pre-booster one, from 485 to 855 antibody titer, which then peaked at 1240 in the 3rd month post-vaccination; after that, it began to decline gradually until the 6th month. Meanwhile, in Group B, the ELISA reading increased from 420 to 790 and then peaked at 1215. The VNT mean in Group A increased from 1.1 to 2.5 within 2 weeks after administration of the booster dose, while in Group B it increased from 0.8 to 2.1. Moreover, ELISA in Group A pigs indicated mean antibody titers at the 3rd week post-inoculation of 576 for Group A and 554 for Group B.Conclusion:The inactivated EHV-1 vaccine, with fewer chemicals, was prepared in a shorter time. It is safe and also more potent to protect horses for up to 6 months against EHV-1 infection than the commercially produced vaccine.

Investigation of The Usefulness of Serum Amyloid A in Characterizing Selected Disease Forms of Equine Herpesvirus-1 Infection

The objective of this study was to study the SAA response of horses with various forms of EHV-1 infection. Archived serum samples from 153 horses with various disease forms of EHV-1 infection (48 healthy non-infected horses, 48 subclinically infected horses, 40 horses with respiratory EHV-1 infection and 17 horses with neurological EHV-1 infection) were available for SAA testing. SAA values ranged from 0 to 31 µg/mL (median 0 µg/mL) in healthy horses, from 0 to 2,416 µg/mL (median 8.5 µg/mL) in subclinically infected horses, from 0 to 3,000 µg/mL (median 597 µg/mL) in horse with respiratory EHV-1 infection and from 0 to 1,640 µg/mL (median 58 µg/mL) in horse with neurological EHV-1 disease. Infected horses had significantly higher SAA values compared to healthy, non-infected horses. While SAA was elevated in the majority of horses with evidence of EHV-1 infection, a single point in time SAA test was unable to consistently support infection in horses with subclinical disease

A Live-Attenuated Equine Influenza Vaccine Stimulates Innate Immunity in Equine Respiratory Epithelial Cell Cultures That Could Provide Protection From Equine Herpesvirus 1.

Equine herpesvirus 1 (EHV-1) ubiquitously infects horses worldwide and causes respiratory disease, abortion, and equine herpesvirus myeloencephalopathy. Protection against EHV-1 disease is elusive due to establishment of latency and immune-modulatory features of the virus. These include the modulation of interferons, cytokines, chemokines, antigen presentation, and cellular immunity. Because the modulation of immunity likely occurs at the site of first infection—the respiratory epithelium, we hypothesized that the mucosal influenza vaccine Flu Avert® I.N. (Flu Avert), which is known to stimulate strong antiviral responses, will enhance antiviral innate immunity, and that these responses would also provide protection from EHV-1 infection. To test our hypothesis, primary equine respiratory epithelial cells (ERECs) were treated with Flu Avert, and innate immunity was evaluated for 10 days following treatment. The timing of Flu Avert treatment was also evaluated for optimal effectiveness to reduce EHV-1 replication by modulating early immune responses to EHV-1. The induction of interferons, cytokine and chemokine mRNA expression, and protein secretion was evaluated by high-throughput qPCR and multiplex protein analysis. Intracellular and extracellular EHV-1 titers were determined by qPCR. Flu Avert treatment resulted in the modulation of IL-8, CCL2, and CXCL9 starting at days 5 and 6 post-treatment. Coinciding with the timing of optimal chemokine induction, our data also suggested the same timing for reduction of EHV-1 replication. In combination, our results suggest that Flu Avert may be effective at counteracting some of the immune-modulatory properties of EHV-1 at the airway epithelium and the peak for this response occurs 5–8 days post-Flu Avert treatment. Future in vivo studies are needed to investigate Flu Avert as a prophylactic in situations where EHV-1 exposure may occur.

ANCHOR-tagged equine herpesvirus 1: A new tool for monitoring viral infection and discovering new antiviral compounds

Equine herpesvirus 1 (EHV-1) is a causative agent of respiratory disorders, abortion and myeloencephalopathy in horses and has an important impact on equine health and economy. Several bacterial artificial chromosomes have already been developed and enabled identification and functional characterization of EHV-1 genes. Unfortunately, little is known about its replication. Here, the ANCHOR system was inserted by targeted homologous recombination into the equine herpesvirus genome. This insertion led to the conversion of EHV-1 DNA to auto-fluorescent spots easily detectable by fluorescence microscopy, and enabled production of an auto-fluorescent EHV-1 ANCHORGFP with tropism and replication kinetic like the parental strain. High resolution imaging allowed first visualization of EHV-1 replication from apparition of first viral genome to large replicative centers, in single cells or inside syncytia. Combined with high content microscopy, EHV-1 ANCHORGFP leads to identification of auranofin and azacytidine-5 as new potential antivirals to treat EHV-1 infection.

Transcriptomic Profiling of Equine and Viral Genes in Peripheral Blood Mononuclear Cells in Horses during Equine Herpesvirus 1 Infection.

Equine herpesvirus 1 (EHV-1) affects horses worldwide and causes respiratory disease, abortions, and equine herpesvirus myeloencephalopathy (EHM). Following infection, a cell-associated viremia is established in the peripheral blood mononuclear cells (PBMCs). This viremia is essential for transport of EHV-1 to secondary infection sites where subsequent immunopathology results in diseases such as abortion or EHM. Because of the central role of PBMCs in EHV-1 pathogenesis, our goal was to establish a gene expression analysis of host and equine herpesvirus genes during EHV-1 viremia using RNA sequencing. When comparing transcriptomes of PBMCs during peak viremia to those prior to EHV-1 infection, we found 51 differentially expressed equine genes (48 upregulated and 3 downregulated). After gene ontology analysis, processes such as the interferon defense response, response to chemokines, the complement protein activation cascade, cell adhesion, and coagulation were overrepresented during viremia. Additionally, transcripts for EHV-1, EHV-2, and EHV-5 were identified in pre- and post-EHV-1-infection samples. Looking at micro RNAs (miRNAs), 278 known equine miRNAs and 855 potentially novel equine miRNAs were identified in addition to 57 and 41 potentially novel miRNAs that mapped to the EHV-2 and EHV-5 genomes, respectively. Of those, 1 EHV-5 and 4 equine miRNAs were differentially expressed in PBMCs during viremia. In conclusion, this work expands our current knowledge about the role of PBMCs during EHV-1 viremia and will inform the focus on future experiments to identify host and viral factors that contribute to clinical EHM.

Susceptibility of rat immortalized neuronal cell line Rn33B expressing equine major histocompatibility class 1 to equine herpesvirus-1 infection is differentiation dependent.

Equine herpesvirus-1 (EHV-1), which causes encephalomyelitis in horses, shows endotheliotropism in the central nervous system of horses, and generally does not infect neurons. However, little is known about the mechanism underlying the resistance of neuron to EHV-1, due to the lack of convenient cell culture systems. In this study, we examined EHV-1 infection in immortalized Rn33B rat neuronal cells, which differentiate into neurons when cultured under nonpermissive conditions. Because murine cell lines are resistant to EHV-1 infections due to the lack of functional entry receptors for EHV-1, we used an Rn33B-derived cell line that stably expresses the equine MHC class 1 molecule, which acts as EHV-1 entry receptor (Rn33B-A68B2M cells). EHV-1 infected undifferentiated Rn33B-A68B2M cells more efficiently than differentiated cells, resulting in the production of progeny virus in the former but not in the latter. By contrast, both differentiated and undifferentiated cells infected with herpes simplex virus-1 produced infectious viral progeny. While EHV-1 infection induced stronger expression of IFN alpha gene in differentiated cells than in undifferentiated cells, downstream IFN responses, including phosphorylation of STAT1 (signal transducer and activator of transcription 1) and expression of IFN-stimulated genes, were not activated regardless of whether cells were differentiated or not. These results suggest that neuronal differentiation of RN33B-A68B2M cells reduced their susceptibility to EHV-1, which is not due to different IFN responses. This culture system may be useful as an in vitro model for studying neuron-specific resistance to EHV-1, by investigating viral and host factors responsible for the difference in susceptibility between differentiated and undifferentiated cells.

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.

Advances in vaccine strategies against equine herpesvirus-1

Equine herpesvirus-1 (EHV-1) is the ubiquitous viral pathogen causing respiratory infections, abortion in pregnant mares, neurological disorders, and neonatal foal deaths in horses worldwide. Once infected, horse remains a carrier for whole life due to typical nature of latency associated with EHV1 infection. Vaccination is the only option for effective control of the disease. Over the past few decades several vaccines including inactivated, subunit, live, and DNA vaccines have been developed to combat the disease. Despite limitation of all the vaccines, vaccination remains the prime option to fight against EHV-1 infection in horses. Till date, no vaccine showed potentiality to protect the neurological form of infections in horses. There is desperate necessity to search for improved new generation EHV-1 vaccines such as mRNA based vaccine that may stimulate not only humoral immunity but also systemic cellular immunity in the horses. This review highlights the state-of-the-art knowledge regarding vaccines studied in the past to prevent EHV-1 infection along with new directions need to be adopted to prevent EHV-1 infection and outbreak in horses in future.

Equine Herpesvirus-1 Infection, Clinical Features, Treatment and Control

Equine Herpesvirus-1 Infection, Clinical Features, Treatment and Control

Equine herpesvirus-1 genotype did not significantly affect clinical signs and disease outcome in 65 horses diagnosed with equine herpesvirus-1 myeloencephalopathy

The objective of this study was to determine if the genotype of equine herpesvirus-1 (EHV-1) impacted clinical disease and outcome of horses with laboratory confirmed equine herpesvirus myeloencephalopathy (EHM). Medical records from 65 horses diagnosed with EHM from 2011 to 2019 were reviewed for signalment, presence and severity of clinical signs (lethargy, fever, ataxia, urinary incontinence) and outcome. Horses were further grouped based on the EHV-1 genotype into neuropathic (D752) or non-neuropathic (N752) EHV-1 infection. Between the two EHV-1 genotype groups, age and sex distributions were similar, although breed distribution was different (Quarter Horses and Saddlebreds were overrepresented and Warmbloods were underrepresented in the EHV-1 D752 group compared to the EHV-1 N752 group; P = 0.009). Lethargy, fever, ataxia and outcome were not significantly different between the two EHV-1 genotype groups (P > 0.05). However, urinary incontinence was significantly more frequently reported in horses infected with the D752 genotype of EHV-1 (P=0.04). Contrary to previous studies, the present study showed no difference in frequency of genotype (D752 or N752) among 65 horses with EHM and, with the exception of urinary incontinence, no difference in clinical disease or outcome related to the EHV-1 genotype.

Molecular Surveillance of EHV-1 Strains Circulating in France during and after the Major 2009 Outbreak in Normandy Involving Respiratory Infection, Neurological Disorder, and Abortion.

Equine herpesvirus 1 (EHV-1) is an Alphaherpesvirus infecting not only horses but also other equid and non-equid mammals. It can cause respiratory distress, stillbirth and neonatal death, abortion, and neurological disease. The different forms of disease induced by EHV-1 infection can have dramatic consequences on the equine industry, and thus the virus represents a great challenge for the equine and scientific community. This report describes the progress of a major EHV-1 outbreak that took place in Normandy in 2009, during which the three forms of disease were observed. A collection of EHV-1 strains isolated in France and Belgium from 2012 to 2018 were subsequently genetically analysed in order to characterise EHV-1 strain circulation. The open reading frame 30 (ORF30) non-neuropathogenic associated mutation A2254 was the most represented among 148 samples analysed in this study. ORF30 was also sequenced for 14 strains and compared to previously published sequences. Finally, a more global phylogenetic approach was performed based on a recently described Multilocus Sequence Typing (MLST) method. French and Belgian strains were clustered with known strains isolated in United Kingdom and Ireland, with no correlation between the phylogeny and the time of collection or location. This new MLST approach could be a tool to help understand epidemics in stud farms.