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Background: Recent identification of viruses considered responsible for Theiler’s disease (acute hepatitis) in horses include equine parvovirus-hepatitis (EqPV-H) and the most likely of several flaviviruses, equine hepacivirus (EqHV). Both of these viruses have now been detected in North America, Asia, and Europe. Objectives: To determine the prevalence of EqPV-H and EqHV in French and Australian horses and to analyse their respective phylogenetic relationships. Study design: Cross-sectional. Methods: Clinically documented sera from 188 Australian horses and 259 French horses collected between 2016-2019 were analysed. qPCRs validated according to the NF47-600 standard were used to detect EqPV-H and EqHV in sera. Sequencing for phylogenetic analysis was performed on two NS1 fragments (516 nt and 587 nt) for EqPV-H and one NS5B fragment (308 nt) for EqHV. A phylogenic network was built using a Median Joining Network algorithm. Results: 1) EqPV-H: 12/259 (4.6%) and 6/188 (3.2%) samples from French and Australian horses were positive, respectively. Viral loads ranged from 2.3e05 to 6.5e05 copies genome/ml. 2) EqHV: 5/259 (1.9%) and 21/188 (11.2%) samples from French and Australian horses were positive, respectively. Viral loads ranged from 6.1e04 to 1.4e08 copies genome/ml. Both EqPV-H (587 nt fragment) and EqHV phylogenetic analyses showed that Australian strains were clustered, while overall distribution was more heterogenous in French horses. Main limitations: The study population is built by accessing laboratory submissions and potentially biased. The 516 nt NS1 fragment could not be sequenced. Conclusions: This is the first report of EqPV-H detection in both Australian and French horses. The EqPV-H prevalence was similar between the two countries (p-value=0.6) although phylogenetic differences were observed between the two populations. This is also the first reported detection of EqHV in Australian horses, with a higher prevalence when compared with French horses.

International audience; Background: Equine coital exanthema (ECE) is an acute viral infection of horses caused by equid herpesvirus-3 (EHV-3). The presence of the virus and its economic impact is well described in different countries such as Argentina or Japan. However, even though it is included in the HBLB code of practice (UK) and in the list of diseases monitored by the RESPE (FR), only a few studies have been performed in Europe.Objectives: To determine the circulation of EHV-3 in France and measure the efficacy of new antiviral compounds against EHV-3.Study design: Retrospective field study and in vitro experiments.Methods: 71 field samples from suspected ECE cases, and collected between 2010 and 2021, were analysed by qPCR (DNA polymerase gene) and phylogenetic analysis (gG gene) was performed on 10 positive samples. Antiviral compounds (aciclovir, ganciclovir, valganciclovir, decitabine, idoxuridine, pritelivir, cidofovir, aphidicolin, vidarabine) previously described with antiviral properties against EHV-1, were evaluated using Real-Time Cell Analysis (RTCA) on equine dermal cells with the reference strain EHV-3 VR3522, cytopathic effect monitoring (microscopy) and viral load quantification (qPCR).Results: 16/71 (22%) suspected ECE cases were confirmed positive by PCR with 0 to 3 cases per year. French strains were clustered into two of the three observed phylogenic groups, but there was no correlation between the phylogeny and the time of collection or location. Aphidicolin was the most effective compound with an EC50 value of 2.43±0.02 µM (RTCA) and 1.63±0.48 µM (qPCR). Pritelivir and cidofovir were less potent molecules against EHV-3 (EC50 >50 µM).Main limitation: Antiviral compounds were tested against the reference strain only.Conclusions: This study demonstrates for the first time the presence of EHV-3 over a twelve-year period in France. In vitro studies show the antiviral efficacy of aphidicolin.

Background: Equid herpesvirus-1 (EHV-1) is one of the most important horse pathogens, which induces respiratory disease, myeloencephalopathy, abortion or still-birth. The measurement of EHV-1 neutralising (EHV-1-VN) antibodies using a neutralisation assay (NA) gives an indication of the immune response of horses in the field. Objectives: To develop a real time neutralisation assay (RTNA) using the xCELLigence® technology for the measurement of EHV-1-VN antibodies in serums from EHV-1 experimentally infected or vaccinated horses. Study design: Assay development and field trial. Methods: The RTNA based on E. Derm cells was developed using serums (n=48) taken daily (from Days 0 to 18 post-infection) from ponies experimentally infected with a field EHV-1 strain. This method was further evaluated using field serums (n=63) taken during an EHV-1/-4 vaccination campaign. RTNA results were compared to those obtained with the conventional EHV-1 NA on RK13 cells. Two-fold serial dilutions of serums were incubated with a defined concentration of the KyD EHV-1 strain before infection of E. Derm cells. The normalised cell index was monitored pre- and post-infection using the xCELLigence® technology. Conventional NA was performed using the same experimental methodology on RK13 cells and cytopathic effects were measured 72 hours post-infection. Results: Serum titres which induced 50% of EHV-1 neutralisation (NT50) were determined using a dose-response approach. The increase of the EHV-1 NT50 was similar to the increase in titre measured with the conventional NA (R²=0.79). Seroconversion was detected between Days 0 and 18 post-infection for all infected ponies with both methods. The NT50 values measured for EHV-1/-4 vaccinated horse serums were also positively correlated with conventional NA titres (R²=0.83). Main limitations: EHV-1/-4 cross-reactivity will require further investigation. Each assay used different cells. Conclusion: While the conventional NA is time consuming, requires subjective measurements and provides semi-quantitative discrete ranked titres (e.g. 4, 8 etc.), the EHV-1-VN RTNA is an automated, sensitive and objective measurement that reports continuous titres.

International audience; Equine herpesvirus 1 isolates from a 2021 outbreak of neurologic disease in Europe have a mutation, A713G, in open reading frame 11 not detected in 249 other sequences from equine herpesvirus 1 isolates. This single-nucleotide polymorphism could help identify horses infected with the virus strain linked to this outbreak.

International audience; Background: Equine herpesvirus type-1 (EHV-1) is an important threat to the equine industry, as illustrated by the ongoing outbreak of neurological disease that was initially reported during a large equestrian event in Valencia, Spain in 2021. Horses returning from this event to their training yards have contributed to the spread of the virus to nine other European countries and to Qatar.Objectives: To design a “tracking” marker in order to specifically follow the dissemination of the Valencia strain, in EHV-1 infected horses with no known epidemiological link with the Valencia outbreak.Study design: Strain isolation and genome sequences’ comparison.Methods: 67 nasopharyngeal swab samples from horses stationed in Valencia were analysed by EHV-1 qPCR and a rapid A/G/C2254 (ORF30) typing test. Positive samples were used for strain isolation in vitro, and Multilocus Sequence Typing (MLST).Results: 19/67 (28%) samples were EHV-1 positive (all 19 typed as A2254). Two strains (FR/Valencia1/2021 and FR/Valencia2/2021) were successfully isolated and characterised by MLST as belonging to clade 10. Analysis of the MLST ORF sequences revealed a mutation at position 713 of the ORF11 (A713G) in FR/Valencia1/2021 and FR/Valencia2/2021, when compared with reference strains Ab4 and V592. This A713G mutation was not present in 104 ORF11 sequences obtained from Genbank (strains from the UK, USA, China, Australia, Belgium, New-Zealand, Japan or India), or 131 and 14 ORF11 sequences from strains isolated in Ireland or France, respectively. This marker allowed subsequent confirmation of suspicious epidemiological links in EHV-1 cases.Main limitation: The limited number of ORF11 sequences available in some countries.Conclusions: Although the existence of this mutation in other field strains cannot be excluded, its absence in the 249 ORF11 sequences analysed, suggests that this SNP constitutes an interesting epidemiological marker to identify horses infected with the EHV-1 strain which was associated with the outbreak in Valencia.

International audience; Data presented in this article are associated with the research article “Identification of antiviral compounds against equid herpesvirus-1 using real-time cell assay screening: efficacy of decitabine and valganciclovir alone and in combination” [1]. These data correspond to the in vitro screening of 2,891 potential antiviral compounds against equid herpesvirus-1 (EHV-1) based on impedance measurements using the xCELLigence® RTCA MP System. This dataset includes compounds from three different libraries: i) 1,199 compounds from the Prestwick® Chemical Library, which contains mostly US Food and Drug Administration approved drugs (Prestwick® Chemical, Illkirch, France); ii) 1,651 compounds from the Centre d'Etudes et de Recherche sur le Médicament de Normandie (CERMN, Caen, France); iii) 41 compounds (called herein in-house antiviral library) selected for their effects against different human viruses. Compounds effective against EHV-1 were selected using the area under normalised curves (AUCn) and the time required for the Cell Index to decrease by 50% after virus infection (CIT50). The full dataset from the screen is made publicly available for further analyses.

Equid herpesvirus 1 is one of the most common viral pathogens in the horse population and is associated with respiratory disease, abortion and still-birth, neonatal death and neurological disease. A single point mutation in the DNA polymerase gene (ORF30: A2254G, N752D) has been widely associated with neuropathogenicity of strains, although this association has not been exclusive. This study describes the fortuitous isolation of a strain carrying a new genotype C2254 (H752) from an outbreak in France that lasted several weeks in 2018 and involved 82 horses, two of which showed neurological signs of disease. The strain was characterised as UL clade 10 using the equid herpesvirus 1 (EHV-1) multi-locus sequence typing (MLST) classification but has not been identified or isolated since 2018. The retrospective screening of EHV-1 strains collected between 2016 and 2018 did not reveal the presence of the C2254 mutation. When cultured in vitro, the C2254 EHV-1 strain induced a typical EHV-1 syncytium and cytopathic effect but no significant difference was observed when compared with A2254 and G2254 EHV-1 strains. An experimental infection was carried out on four Welsh mountain ponies to confirm the infectious nature of the C2254 strain. A rapid onset of marked respiratory disease lasting at least 2 weeks, with significant virus shedding and cell-associated viraemia, was observed. Finally, an in vitro antiviral assay using impedance measurement and viral load quantification was performed with three antiviral molecules (ganciclovir (GCV), aciclovir (ACV) and aphidicolin (APD)) on the newly isolated C2254 strain and two other A/G2254 field strains. The three strains showed similar sensitivity to ganciclovir and aphidicolin but both C2254 and A2254 strains were more sensitive to aciclovir than the G2254 strain, based on viral load measurement.

International audience; Equid herpesvirus-1 infections cause respiratory, neurological and reproductive syndromes. Despite preventive treatments with vaccines, resurgence of EHV-1 infection still constitutes a major threat to equine industry. However, no antiviral compound is available to treat infected horses. In this study, 2891 compounds were screened against EHV-1 using impedance measurement. 22 compounds have been found to be effective in vitro against EHV-1. Valganciclovir, ganciclovir, decitabine, aphidicolin, idoxuridine and pritelivir (BAY 57-1293) are the most effective compounds identified, and their antiviral potency was further assessed on E. Derm, RK13 and EEK cells and against 3 different field strains of EHV-1 (ORF30 2254 A/G/C). We also provide evidences of synergistic interactions between valganciclovir and decitabine in our in vitro antiviral assay as determined by MacSynergy II, isobologramm and Chou-Talalay methods. Finally, we showed that deoxycytidine reverts the antiviral effect of decitabine, thus supporting some competition at the level of nucleoside phosphorylation by deoxycytidine kinase and/or DNA synthesis. Deoxycitidine analogues, like decitabine, is a family of compounds identified for the first time with promising antiviral efficacy against herpesviruses.

International audience; Respiratory infections are still a major concern in pigs. Amongst the involved viruses, the porcine reproductive and respiratory syndrome virus (PRRSV) and the swine influenza type A virus (swIAV) have a major impact. These viruses frequently encounter and dual infections are reported. We analyzed here the molecular interactions between viruses and porcine tracheal epithelial cells as well as lung tissue. PRRSV-1 species do not infect porcine respiratory epithelial cells. However, PRRSV-1, when inoculated simultaneously or shortly before swIAV, was able to inhibit swIAV H1N2 infection, modulate the interferon response and alter signaling protein phosphorylations (ERK, AKT, AMPK, and JAK2), in our conditions. SwIAV inhibition was also observed, although at a lower level, by inactivated PRRSV-1, whereas acid wash treatment inactivating non-penetrated viruses suppressed the interference effect. PRRSV-1 and swIAV may interact at several stages, before their attachment to the cells, when they attach to their receptors, and later on. In conclusion, we showed for the first time that PRRSV can alter the relation between swIAV and its main target cells, opening the doors to further studies on the interplay between viruses. Consequences of these peculiar interactions on viral infections and vaccinations using modified live vaccines require further investigations.

International audience; Equid alpha-herpesviruses (EHV) are responsible for different diseases in equine population. EHV-1 causes respiratory diseases, abortions and nervous disorders, EHV-4 causes respiratory diseases and sporadic abortion, while EHV-3 is responsible of equine coital exanthema. In view of the lack of efficacy of vaccines against EHV-1 and EHV-4 and in the absence of vaccines against EHV-3, the use of antiviral treatment is of great interest. In this study, we documented the interest of the Real-Time Cell Analysis (RTCA) technology to monitor the cytopathic effects induced by these viruses on equine dermal cells, and established the efficacy of this method to evaluate the antiviral effect of aciclovir (ACV) and ganciclovir (GCV). In addition, the RTCA technology has also been found appropriate for the high-throughput screening of small molecules against EHV, allowing the identification of spironolactone as a novel antiviral against EHV.

International audience; (1) Background: Equine hepacivirus (EqHV), also referred to as non-primate hepacivirus (NPHV), infects horses—and dogs in some instances—and is closely related to hepatitis C virus (HCV) that has infected up to 3% of the world’s human population, causing an epidemic of liver cirrhosis and cancer. EqHV also chronically infects the liver of horses, but does not appear to cause serious liver damages. Previous studies have been looking to identify route(s) of EqHV transmission to and between horses. (2) Methods: In this retrospective study, we sought to evaluate the prevalence of vertical transmission taking place in utero with measuring by quantitative RT-PCR the amounts of EqHV genome in samples from 394 dead foals or fetuses, paired with the allantochorion whenever available. (3) Results: Detection of EqHV in three foals most likely resulted from a vertical transmission from the mares to the fetuses, consistent with the in utero transmission hypothesis. In support of this observation, the presence of EqHV genome was found for the first time in two of the allantochorions. (4) Conclusions: As seemingly benign viruses could turn deadly (e.g., Zika flavivirus) and EqHV happens to have infected a significant proportion of the world’s horse herds, EqHV infectious cycle should be further clarified.

International audience; Like hepatitis C virus (HCV) in humans, the newly identified equine hepacivirus (NPHV) displays a predominating liver tropism that may evolve into chronic infections. The genomes of the two viruses share several organizational and functional features and are phylogenetically closest amongst the Hepacivirus genus. A limited amount of data is available regarding the spread of hepacivirus infections in horses. In this study, we asked whether in a more representative sample the prevalence and distribution of NPHV infections in France would resemble that reported so far in other countries. A total of 1033 horses sera from stud farms throughout France were analysed by qRT-PCR to determine the prevalence of ongoing NPHV infections and viral loads; in positive samples, partial sequences of NPHV’s genome (50UTR, NS3 and NS5B genes) were determined. Serum concentrations of biliary acids, glutamate dehydrogenase (GLDH) and L-gamma-glutamyl transferase (c-GT) were measured for most horses. We detected NPHV infections in 6.2% of the horses, a prevalence that reached 8.3% in thoroughbreds and was significantly higher than in other breeds. The presence of circulating virus was neither significantly associated with biological disturbances nor with clinical hepatic impairment. Our phylogenetic analysis was based on both neighbour- joining and maximum-likelihood approaches. Its result shows that, like almost everywhere else in the world so far, two major groups of NPHV strains infect French domestic horses. Based on genetic distances, we propose a classification into two separate NPHV subtypes. Viral loads in the serum of horses infected by the main subtype were, in average, four times higher than in those infected by the second subtype. We hypothesize that amino acid substitutions in the palm domain of NS5B between NPHV subtypes could underlie viral phenotypes that explain this result.

International audience; An episode of acute equine respiratory infection was reported in western Algeria (Tiaret province) between February and March 2011, affecting a large population of horses. Nasal swabs (n=100) were taken from horses aged between 1 and 27 years, presenting with cough and mucopurulent nasal discharge. The prevalence of equine respiratory virus infections was examined using quantitative polymerase chain reaction (qPCR). One, or more, of four equine respiratory viruses were detected in the nasal swabs of 90 of 100 horses (90%) and the detection rate of equine herpesvirus type 1 (EHV-1), equine herpesvirus type 4 (EHV-4), equine herpesvirus type 2 (EHV-2) and equine herpesvirus type 5 (EHV-5) were 2%, 14%, 90% and 75%, respectively. Equine influenza virus and equine arteritis virus were not detected in any samples. Among the 90 infected horses, 70 were coinfected with EHV-2 and EHV-5 and 14 others were co-infected with EHV-4, EHV-2 and EHV-5. The present study shows a positivity rate of 97.3% for EHV-5 in young horses aged

International audience; Equid gammaherpesviruses-2 and -5 are involved in respiratory problems, with potential clinical man-ifestations such as nasal discharge, pharyngitis and swollen lymph nodes. These viruses are sometimesassociated with a poor-performance syndrome, which may result in a significant and negative economicimpact for the horse industry. The aim of the present study was to develop and validate quantitative PCRmethods for the detection and quantitation of EHV-2 and EHV-5 in equine respiratory fluids. Two dis-tinct tests were characterised: (a) for the qPCR alone and (b) for the whole method (extraction and qPCR)according to the standard model AFNOR XP U47-600-2 (viz., specificity, quantifiable sensibility, linearity,accuracy, range of application, trueness, precision, repeatability and precision of reproducibility). EHV-2and EHV-5 detection were performed on nasal swabs collected from 172 horses, all of which exhibitedclinical signs of respiratory disease. The data revealed a high rate of EHV-2/EHV-5 co-detection that wascorrelated significantly with age. Viral load of EHV-2 was significantly higher in young horses whereasviral load of EHV-5 was not significantly different with age.

International audience; In virology, different conventional methods are commonly used for virus titration and infectivity studies. Most of them are based on direct examination of viral cytopathic effect, which is time consuming, tedious and requires an endpoint reading. The RTCA xCELLigence system (ACEA Biosciences) has been developed to follow cellular events and their dynamics in real time using a micro-electrical biosensor technology. The aim of this study was to evaluate the feasibility of using this biosensor technology to measure the effect of different equid herpesviruses on equine dermal cell cultures, with or without antiviral acyclovir treatment. Cells were infected with EHV-1 (VR700), EHV-4 (VR2230), EHV-2 (VR701) or EHV-3 (VR352). The viral effects were monitored by 3 different methods: impedance measurements (RTCA), cytopathic effects recording (microscopy) and viral load quantification (qPCR). The RTCA technology showed a dose dependent drop of the cellular index induced by specific impedance variations measured during growth of each virus tested. These results correlated with the cytopathic effect induced by the different herpesvirus species, as well as viral loads measured by qPCR. For example, after 3 days of incubation with EHV-1, RTCA results showed an increase of the cellular index from 0% (infection without antiviral) to 45% and 100% in presence of Acyclovir (10μl/mL and 100 μg/mL, respectively). These results are correlated with the decreased of viral load measured in the presence of Acyclovir: 1010 genome copies/mL with EHV-1 only, 106 copies/mL with EHV-1 + Acyclovir 10 μg/ mL and 105 copies/mL with EHV-1 + Acyclovir 100 μg/ mL. In conclusion, the cellular impedance monitoring system is a new real-time method to monitor cell growth and viral proliferation in cell cultures. This technology is well adapted for high-throughput screening of antiviral molecules. In fact, the xCELLigence system enables continuous impedance measurement and quantification of cell adhesion, proliferation, cell death and detachment during viral infection.

At least five equine herpesviruses are known to infect horses : three alpha herpesviruses (equine herpesvirus-1, -3 and -4) and two gamma herpesviruses (equine herpesvirus-2 and -5). Equine herpesvirus-1 is responsible for three clinical presentations : respiratory, abortigenic and neurological. This latter, widely known as EHV-1 associated, myeloencephalopathy has been thoroughly investigated over the past years. Most of the studies focused on the relation between the presence of a mutation in ORF 30 coding for DNA polymerase and the expression of the paralytic (neurological) form. Even if this mutation seems to play a role, other factors related to the host and the environment are certainly involved in the development of the disease. Equine herpesvirus-4 is better known as the rhinopneumonia virus and is responsible for a large part of respiratory disorders in young foals. Equine herpesvirus-3 is responsible for equine coital exanthema, whose transmission through the respiratory tract is now proven. Equine herpesvirus-2 and -5 are associated with subclinical respiratory diseases in equine athletes, even though their pathogenic role has yet to be clarified as they were detected in all continents only relatively recently. The development of molecular genetic tools lead to major progress in the detection of these viruses, but the differentiation between latent and infectious forms is still unresolved. Although studies are currently performed on the typing of strains responsible for different clinical presentations involving equine herpesviruses as well as in other equine viruses (influenza, equine viral arteritis), there is no international consensus on a phylogenic tree for any of the 5 equine herpesviruses. Further studies are definitely required to monitor and characterise the different strains of EHV., Au moins cinq herpèsvirus équins peuvent infecter le cheval : trois alpha-herpèsvirus (les herpèsvirus 1, 3 et 4) et deux gamma-herpèsvirus (les herpèsvirus équins 2 et 5). L’herpèsvirus équin 1 est responsable de trois formes cliniques : une forme respiratoire, une forme abortive et une forme neurologique. Cette dernière, plus connue sous le nom de myéloencéphalopathie à HVE-1, a fait l’objet de nombreuses études ces dernières années. La plupart des travaux ont porté sur la relation entre la présence d’une mutation dans l’ORF 30 codant l’ADN polymérase et l’expression de la forme paralytique. Si cette mutation semble jouer un rôle, d’autres facteurs liés à l’hôte et à l’environnement participent certainement au développement de la maladie. L’herpèsvirus équin 4 est plus connu sous le nom de virus de la rhinopneumonie et est responsable d’une part importante des affections respiratoires chez les jeunes poulains. L’herpèsvirus équin 3 est responsable de l’exanthème coïtal équin et l’on sait aujourd’hui qu’il peut se transmettre par les voies respiratoires. Les herpèsvirus équins 2 et 5 sont associés aux maladies respiratoires subcliniques du cheval athlète même si leur rôle reste à préciser, leur découverte sur l’ensemble des continents étant relativement récente. Le développement des outils de génétique moléculaire a permis de faire des progrès importants dans la détection de ces virus même si un challenge demeure : différencier les formes latentes des formes infectieuses. Si comme pour d’autres virus équins (ex : grippe, artérite virale équine), des travaux sont réalisés pour typer les différentes souches responsables de différentes formes d’expression de la maladie, il n’existe toujours pas de consensus international sur un arbre phylogénique pour aucun de ces cinq herpèsvirus équins. Le suivi et la caractérisation des différentes souches d’HVEs sont très certainement l’autre défi de demain., Pronost Stéphane, Hue Érika, Legrand Loïc, Pitel Pierre-Hugues, Fortier Guillaume. Herpèsviroses des équidés: intérêts et limites des outils de génétique moléculaire. In: Bulletin de l'Académie Vétérinaire de France tome 164 n°4, 2011. pp. 305-316.

International audience; The protocol describes a quantitative RT-PCR method for the detection and quantification of EHV-2 in equine respiratory fluids according to the NF U47-600 norm. After the development and first validation step, two distinct characterization steps were performed according to the AFNOR norm: (a) characterization of the qRT-PCR assay alone and (b) characterization of the whole analytical method. The validation of the whole analytical method included the portrayal of all steps between the extraction of nucleic acids and the final PCR analysis. Validation of the whole method is very important for virus detection by qRT-PCR in order to get an accurate determination of the viral genome load. Since the extraction step is the primary source of loss of biological material, it may be considered the main source of error of quantification between one protocol and another. For this reason, the AFNOR norm NF-U-47-600 recommends including the range of plasmid dilution before the extraction step. In addition, the limits of quantification depend on the source from which the virus is extracted. Viral genome load results, which are expressed in international units (IU), are easier to use in order to compare results between different laboratories. This new method of characterization of qRT-PCR should facilitate the harmonization of data presentation and interpretation between laboratories.

International audience; Horses are usually infected during the first months of life by several equine herpesviruses, such as EHV-1, EHV-4 or EHV-2. The persistence of these respiratory viruses through establishment of latency, often characterised by an absence of clinical signs, represents a real risk to the horse population. Reactivation of latent EHV could cause disease in both carriers and naive animals in contact. A better understanding of the immune response to EHV infection is necessary to improve our methods of prevention and decrease the risk of transmission. The objectives of this study were 1/ to characterise the cytokine gene expression profile of PBMC after in vitro EHV infection (EHV-1, EHV-4 and EHV-2) and 2/ To determine the efficacy of the inactivated Parapoxvirus ovis (iPPVO), a known immunomodulator in horses , against these same viruses. PBMC were isolated from 3 horses and infected in vitro with EHV-1, EHV-4 or EHV-2, in the presence or absence of iPPVO. In vitro culture of PBMC with EHV-1, EHV-4, EHV-2 and iPPVO induced a significant increase of IFN-α, IFN-β and IFN-γ gene expression. Moreover, EHV-2 induced a significant increase of IL-1β, IL-6 and TNF-α mRNA. The presence of iPPVO induced an earlier and stronger expression of IFN-α, IFN-β and IFN-γ during EHV infection. The presence of iPPVO reduced also the inflammatory response induced by EHV-2. In conclusion, this study suggests that the presence of iPPVO potentiates the development of the immune response during infection EHV in vitro.

International audience; Equine herpesviruses (EHV) infect horses early during life and the persistence of these viruses through establishment of latency represents a real risk. A better understanding of the immune response to EHV infection is necessary to improve our methods of prevention and decrease the risk of transmission. The objectives of this study were to characterise the cytokine gene expression profile of peripheral blood mononuclear cells (PBMC) after in vitro EHV-1, EHV-4, and EHV-2 infection and to determine the efficacy of inactivated Parapoxvirus ovis (iPPVO) against these 3 viruses. PBMC were isolated from 3 horses and infected in vitro with EHV-1, EHV-4, or EHV-2 in the presence or absence of iPPVO. In vitro culture of PBMC with EHV-1, EHV-4, and iPPVO induced a significant increase of IFN-α, IFN-β, and IFN-γ gene expression. EHV-4 also triggered a significant increase of IL-6 and TNF-α mRNA. EHV-2 triggered a significant increase of IFN-α, IFN-β, IFN-γ, IL-1β, IL-6, and TNF-α mRNA. The presence of iPPVO induced an earlier and stronger expression of IFN-α, IFN-β, and IFN-γ mRNA during EHV infection and reduced the inflammatory response induced by EHV-2. In conclusion, this study suggests that the presence of iPPVO potentiates the development of the immune response to in vitro EHV infection.