Equine rhinitis A virus (ERAV) and equine rhinitis B virus (ERBV) are major respiratory pathogens of horses with a global distribution. The aim of this study was to evaluate, for the first time in Algeria, the seroprevalence of ERAV antibodies, and to investigate a wide range of equine viruses (EIV, EHV-1, EHV-4, ERAV and ERBV). A total of 298 serum samples were collected between May 2022 and October 2023, from 11 provinces. Serological analysis for the presence of ERAV was performed using the complement fixation test (CFT). Our results revealed that 16.8% (50/298) samples tested positive for antibodies to ERAV. In parallel, 23 nasal swabs (NS) collected during this period were analyzed by RT-PCR for the detection of ERAV and ERBV. In addition, 74 different sample materials (50 NS, 21 fecal samples, and 3 urine samples), were taken from horses presenting with cough and mucopurulent nasal discharge, between November 2023 and June 2025. The prevalence of equine respiratory virus infections was examined using polymerase chain reaction (PCR). One, or more, of five equine respiratory viruses were detected in the nasal swabs of 3 of 72 horses (4.2%) and the detection rate of equine herpesvirus type 4 (EHV-4) and ERBV were 4.2% and 2.8%, respectively. Unfortunately, viruses could not be sequenced due to low viral load i.e. they had high Cycle Threshold (Ct) values. Equine herpesvirus type 1 (EHV-1), equine influenza virus (EIV) and ERAV were not detected in any samples. Among the three infected horses, two were co-infected with EHV-4 and ERBV. ERAV seroprevalence possibly varied according to sampling period. This study is the first to report the circulation of ERAV and ERBV in the Algerian horse population. Further studies are necessary to isolate and obtain molecular characterisation of ERAV and ERBV from horses in Algeria. Detailed research on epidemiological risk factors for ERVs infections in horses is essential to support and improve diagnosis, prevention and control strategies against these viruses.

Equine herpesvirus-1 and -4 are contagious viruses causing respiratory disease and reproductive losses in horses. This study aimed to determine the prevalence of EHV-1 and EHV-4 in eight Turkish stud farms using RT-PCR analysis of nasal secretions, uterine fluids and aborted foal tissues. Deep nasal swabs were collected from 443 horses showing acute-onset fever and/or clinical signs of respiratory disease. Additionally, uterine swabs and tissue samples (lung, liver, spleen, thymus, kidney, heart) were obtained from 152 abortion cases. Among symptomatic horses, EHV-1 DNA was found in 2 cases (0.45%), while EHV-4 DNA was detected in 67 (15.1%). One horse (0.23%) was positive for both viruses. From abortion-related samples, EHV-1 DNA was identified in 2 cases (1.32%), while no EHV-4 DNA was found. In 4,915 asymptomatic horses, 13 (0.26%) carried EHV-4; none were positive for EHV-1. Overall, active infection rates were 0.67% for EHV-1 and 11.26% for EHV-4. The low prevalence observed in this study suggests minimal active circulation of EHV-1 and EHV-4 in this large, semi-enclosed and well-managed equine population maintained under strict biosecurity and extensive vaccination programs. Although these findings do not reflect national or regional prevalence, they provide valuable epidemiological insight into the effectiveness of consistent vaccination, quarantine measures and PCR-based surveillance in limiting herpesvirus circulation. Overall, the results contribute to improved understanding, surveillance and control strategies for equine herpesviruses in Türkiye.

We report near-complete genome sequences of equine herpesvirus (EHV) 1, 3, and 4 from the USA. Hybrid assemblies combining Illumina and Oxford Nanopore reads yielded high-quality genomes, enhancing understanding of EHV diversity and evolution in the USA.

Equine Coital Exanthema (ECE) is a contagious venereal disease caused by Equid alphaherpesvirus 3 (EHV‑3). Although ECE is self-limiting, it causes significant economic losses to the global equine industry due to the temporary segregation of affected mares and stallions from breeding activities. This report describes the epidemiological, clinical, histological, and molecular findings from an outbreak of ECE in Uruguayan horses. Seven days following the introduction of a stallion, five mares developed extensive papular and vesicular dermatitis in the vaginal and perineal regions. The stallion exhibited minimal preputial mucosal ulcerative lesions. Histological examination of skin biopsies from three affected mares revealed ulcerative dermatitis with intranuclear eosinophilic inclusion bodies in keratinocytes. Molecular confirmation of EHV‑3 infection was achieved by qPCR analysis of perineal skin samples from a mare with typical ECE lesions.

Equine herpesvirus type 1 (EHV-1) is an important viral pathogen in horses, associated with diverse clinical manifestations including fever, upper and lower respiratory disease, neurological signs, ocular disease, and abortion. Currently, EHV-1 variants (genotypes) are classified based on a single nucleotide polymorphism mutation of the open reading frame 30 (ORF30). The aim of this retrospective study was to evaluate the EHV-1 genotypes present in horses with various clinical presentations, including respiratory disease, abortion, and neurological disease, at a referral center in the province of Ontario. Equine herpesvirus type 1 was detected in 11.7% of the tested horses, with clinical presentations including abortion (21%), myeloencephalopathy (64%), fever (11%), pneumonia (3.5%), and asymptomatic cases (3.5%). The neuropathogenic strain was more commonly present in horses with abortions and fevers. Equine herpesvirus myeloencephalopathy was associated with the non-neuropathogenic strain in 50% of the cases and the neuropathogenic strain in 44% of the cases. However, in 6% of the cases, the viral genotype was unknown. These findings highlighted that this is a multifactorial problem and clinical disease may not be solely attributed to viral genome. This variability reinforced the need for continued research into the behavior and epidemiology of EHV-1.

Characterization and component analysis of gM vesicles

Equine herpesvirus type 1 (EHV-1) is a high morbidity and mortality virus that impacts horse populations worldwide. As a respiratory virus, it enters through the upper respiratory tract (URT), where mucosal immunity plays a crucial role in preventing severe disease. In this study, flow cytometry was used to characterize the nasal leukocyte population during EHV-1 infection, and RNA sequencing of nasal secretions was employed to assess transcriptional markers of the mucosal immune response. Horses with distinct immune statuses were compared at four stages: pre-infection, early (day 1 and 3 post-infection [pi]), mid (days 8 and 10pi) and late (day 18pi) infection. Non-immune horses (n = 4), developed clinical signs, shed virus, and established viremia, whereas, immune horses (n = 4), possessing pre-existing immunity, showed no disease or detectable virus after EHV-1 infection. This comparison revealed differential expression of various T cell associated markers based on pre-existing immunity. In immune horses, upregulation of fewer genes occurred during early infection only, while in non-immune horses, a large number of genes were upregulated during mid and late infection. Collectively, these findings highlight a key role for mucosal T cells in mediating viral clearance and restoring homeostasis.

Nucleolar proteins nucleolin and nucleophosmin 1 differentially relocalize during equid alphaherpesvirus 1 (EHV1) infection.

Various bacterial and viral pathogens have been identified in cases of interstitial pneumonia in foals within the first month of life. A potential association has been suggested between equid gammaherpesvirus 5 (EqGHV5, equine herpesvirus 5; family Orthoherpesviridae, taxon species Percavirus equidgamma5) and interstitial pneumonia in foals; however, direct histologic evidence has been limited. We examined 2 neonates-12-d- and 24-d-old-with acute respiratory distress and poor response to treatment. Postmortem examination revealed interstitial pneumonia with diffuse alveolar damage and intranuclear inclusion bodies in alveolar macrophages, suggesting viral infection. EqGHV5 was identified in lung tissues by PCR and visualized in alveolar macrophages using in situ hybridization (ISH). No other bacterial or viral pathogens were detected in these cases. The consistent histologic lesions, inclusion bodies, and PCR and ISH data support a potential causal role of EqGHV5 in foal interstitial pneumonia. Additionally, we retrospectively investigated 23 cases of interstitial pneumonia (2-89-d-old foals) diagnosed in Hokkaido, Japan, between 2015 and 2020. We did not detect EqGHV5 in these 23 cases by PCR or ISH. Further studies are required to investigate the relationship between EqGHV5 and interstitial pneumonia in foals.

Infection with Streptococcus equi subspecies equi (S. equi) is characterised by acute disease, with about 10% of infected animals remaining persistently infected. Clinically, infection with S. equi cannot readily be distinguished from infection caused by other respiratory pathogens, including Streptococcus equi subspecies zooepidemicus (S. zooepidemicus), equine influenza virus, and equine herpes virus. Screening protocols, with appropriate quarantining facilities, are important to detect horses infected with S. equi and avoid strangles outbreaks. Virulent strains of S. zooepidemicus can also cause strangles-like presentations. To evaluate the effectiveness of the screening process implemented at a UK welfare centre to prevent the introduction of strangles and strangles-like presentations. Retrospective cross-sectional study. Clinical records of 626 equids admitted to a UK welfare centre between 2017 and 2021 and from horses that developed respiratory signs after admission were reviewed. The screening protocol, which included a clinical examination, paired serology samples (iELISA) taken 6 weeks apart, and bilateral guttural pouch endoscopy to identify abnormalities such as chondroids with lavage for qPCR and culture analysis for S. equi (and often S. zooepidemicus) was implemented during this time. There were 34 screening-positive equids. Of these, 24 (3.8%) were qPCR-positive for S. equi, 8 were qPCR/culture positive for S. zooepidemicus, and 2 were qPCR/culture negative but had chondroids. Bilateral guttural pouch endoscopy, with qPCR analysis of lavage material, was an effective method of screening equids. There were no cases of strangles or strangles-like presentations within the main herds after screening and admission of new horses. Variation in the level of detail of clinical records. The screening process resulted in the identification of screening-positive equids and maintained a strangles-free herd. Further research is required to elucidate the significance of S. zooepidemicus infection in the guttural pouch.

Umbilical cord torsion (UCT) is the most frequent pathology of the equine umbilical cord (UC) and a prominent cause of abortion, yet objective data on its features remain limited. This study compared UCT with clinically normal pregnancies (CNP) to (i) identify gross and histological features of the UC and fetal membranes, (ii) determine whether UCT is associated with fetal growth restriction, and (iii) rule out infectious aetiologies. Gross and histological features of the UC, chorioallantois and amnion were compared between groups. Fetal weight and crown-rump length were analysed relative to gestational age. Inflammatory infiltrates were evaluated and PCR screened chorioallantoic tissue for equine herpesviruses, Chlamydia psittaci, Coxiella burnetii and Leptospira spp. Alternating reddening and blanching on the amniotic UC was observed in all UCT cases and absent from CNP (p<0.001). Less specific, yet significant, features included amniotic UC stretch marks, membrane congestion, increased visibility of UC stromal vasculature, villous mineralisation, and karyorrhexis. The UCT cords were longer (total length 81.1cm 95% CI 77.7-84.6 vs. 54.2cm 95% CI 49.5-59.0, p<0.001), with a larger intraamniotic portion (p=0.04). Fetal weight did not differ significantly between groups (p=0.08), but crown-rump length was reduced in UCT (p=0.01). No significant inflammatory infiltrates were detected, and all screened samples tested negative for equine herpesviruses, C. burnetii and C. psittaci. This study defines UCT by reproducible gross and histological features and introduces a diagnostic matrix for improved assessment of risk factors and mechanisms of UCT abortion.

Here we discuss three veterinary alphaherpesviruses-pseudorabies virus, equid alphaherpesvirus 1, and bovine alphaherpesvirus 1-that were instrumental in uncovering the true extent of transcriptome complexity through long-read RNA sequencing, which earlier short-read approaches could not resolve. We focus on three major transcriptomic features whose discovery and characterization relied heavily on these viral models: (i) widespread transcriptional overlaps that complicate read assignment and may drive transcriptional interference; (ii) diverse transcript isoforms arising from alternative 5' and 3' transcript termini, as well as splicing; and (iii) non-coding RNAs clustered near replication origins that illuminate potential replication-transcription interactions on a shared nuclear template. Long-read viromics in these veterinary systems has additionally served as a stringent benchmark for transcript callers and annotation pipelines, because the extreme density of overlaps and co-terminal transcript families exposes errors that often go unnoticed in typical mammalian transcriptomes. This has made veterinary herpesvirus datasets disproportionately influential in shaping best practices for full-length isoform calling, transcript end mapping, and artifact-robust cDNA library handling. We also discuss animal gammaherpesviruses as proxies for human gammaherpesviruses, allowing experimental investigation of viral programs difficult to study in human infection. Finally, we describe pseudorabies virus applications as a retrograde transneuronal tracer.

Equine herpesvirus type 1 is a major pathogen of horses, which must be detected quickly and effectively to isolate infected animals and prevent transmission to healthy horses. Laboratory diagnosis depends on a combination of serology and molecular biology, making it challenging to establish a definitive field test. The aim of this study was to use recombinase technology for the field detection of this virus, thereby enabling a point-of-care test. Glycoprotein E (gE), one of the primary targets for detecting animal herpesviruses, was chosen for isothermal amplification with a specific recombinase kit. Several primer, time, and temperature combinations were tested. The optimal amplification conditions were 41°C for 25 minutes. This combination proved effective for amplifying the gE fragment (226 bp), even when the template DNA was diluted 100-fold. These parameters were subsequently applied in the point-of-care assay, which used a lateral flow detection device and produced comparable results, with a limit of detection ranging from 5 × 10² to 10¹ viral copies. The point-of-care test was compared to a real-time PCR method reported in the literature for field samples with known positivity/negativity. There was perfect agreement with negative samples (34/34), and 18 of 26 positives were accurately diagnosed. The assay identified EHV-1 DNA in 11/12 highly positive samples (with a low Ct in real-time PCR) and 7/14 weakly positive samples (Ct more than 26). The overall diagnostic specificity was 100%, and the sensitivity was 69.2%, which increased to 91.7% when highly positive samples were used. This work represents the first application of this technology for EHV-1 detection. Although viral load affects accuracy, this device has the potential to be used in the field, as it requires no specialized equipment and yields results rapidly.

IntroductionEquine herpesvirus type 1 (EHV-1) is a major veterinary pathogen causing significant economic losses in the livestock industry. Despite its impact, effective vaccines and targeted antiviral strategies remain limited, largely due to an incomplete understanding of host factors regulating viral replication and pathogenesis.MethodsTo systematically identify host genes essential for EHV-1 infection, we established a BHK-21 cell line stably expressing Cas9 and performed a genome-wide CRISPR/Cas9 knockout screen using a pooled lentiviral single-guide RNA library. Significantly enriched candidate genes from positive selection were validated by generating knockout cell lines. Viral replication and protein expression were assessed using quantitative polymerase chain reaction and Western blot analysis. Pathway enrichment and protein interaction network analyses were subsequently conducted.ResultsGenome-wide CRISPR/Cas9 screening identified multiple host factors critical for EHV-1 replication. Pathway enrichment analysis revealed that these genes were involved in key cellular signaling and regulatory networks associated with viral infection. Functional validation demonstrated that knockout of selected host genes significantly suppressed EHV-1 replication and viral protein synthesis.DiscussionThese findings highlight essential host determinants required for EHV-1 replication and suggest that targeting host factors may represent a promising strategy for antiviral intervention. This study provides a foundation for the development of host-directed immunotherapeutic and antiviral approaches against EHV-1 infection.

Comparative transcriptomics offers a powerful approach to elucidate host-virus interactions across related pathogens, yet systematic evaluations across species-matched cellular systems remain limited. We performed a cross-species RNA sequencing analysis of respective species' cells infected with three alphaherpesviruses-herpes simplex virus 1 (HSV-1), bovine alphaherpesvirus 1 (BHV-1), and equid alphaherpesvirus 1 (EHV-1)-to dissect conserved and virus-specific transcriptional responses. We show that certain orthologous genes and orthologous pathways are differentially regulated upon infection among the three species like pathways related to translation rRNA processing and TNF-alpha signalling. We find that the earliest sampled timepoint of infection, 2 h post infection (hpi), shows the most commonly enriched pathways among the three species compared to later timepoints. At 6 h and 9 h post infection, BHV-1- and EHV-1 infections have more in common with each other in terms of enriched pathways than with HSV-1 infections. Moreover, we provide a comprehensive analysis of temporal viral gene expression for all three herpesviruses. Together, these findings provide a comparative framework for understanding alphaherpevirus-host interactions and reveal both conserved core responses and species-specific transcriptional signatures. This work establishes a foundation for identifying broadly acting antiviral targets as well as virus-specific vulnerabilities that may inform host-directed therapies and cross-species disease management.

Equine alphaherpesvirus-1 (EHV-1) is a highly contagious virus that can cause the neurological form, equine herpesvirus myeloencephalopathy (EHM). Understanding transmission-related risk factors is crucial for improving prevention strategies and guiding effective control measures. In this study, we collected data from 63 horses that had previously participated in the February 2022 winter horse show season at the Desert International Horse Park (DIHP) (26 cases and 37 controls) to identify host and management factors associated with EHV-1 infection and/or EHM development during the February 2022 outbreak at the DIHP in Thermal, California. Risk factors were evaluated using multivariable logistic regression and a random forest model with conditional permutation importance. Greater age was associated with higher odds of becoming a case (OR = 1.33; 95%CI: 1.04-1.69, p-value: 0.01). Compared with hunters, jumpers had greater odds of developing EHV-1 and/or EHM (OR = 7.37; 95%CI: 1.57-34.61, p-value: 0.01). Sharing a barn was also strongly associated with EHV-1 and/or EHM case status (OR = 7.37; 95%CI: 1.79-30.29, p-value: <0.01). The machine-learning-based rankings were concordant with the regression estimates. Age, main activity, and sharing a barn were the most influential risk factors associated with elevated odds of developing EHV-1 and/or EHM. These results highlight specific demographic and management-related risk factors that could inform targeted prevention strategies.

Horse breeding is a fundamental component of economic and social development in many countries. Maintaining high fertility rates and ensuring the birth of healthy foals is crucial for the sustainability of the equine industry. However, both infectious and non-infectious factors contribute significantly to reproductive losses, including miscarriages, stillbirths, and postpartum fetal deaths. Infectious agents such as bacteria, viruses, fungi, and parasites play a significant role, while non-infectious causes include stress, transportation, hormonal imbalances, and uterine torsion. Early and accurate diagnosis of these factors is critical for effective treatment and prevention. In this context, the implementation of comprehensive preventive strategies, such as routine vaccination (e.g., against equine herpesvirus), isolation of pregnant mares, regular veterinary checkups, ongoing monitoring, and appropriate nutritional management, is crucial. This review aims to inform breeders and veterinarians about the underlying causes of miscarriage, infertility, and foal deaths in horses and to emphasize the importance of preventive medicine in reducing these risks.

Equine herpesvirus-1 (EHV-1) is ubiquitous in the horse population, but prevalence estimates have ranged from 3 to 88% depending on the population and method of sampling. No prevalence studies have been carried out in Ontario, Canada. The objective of this study was to measure the prevalence of EHV-1 shedding in healthy broodmares in Ontario. A total of 381 mares from 42 farms in Ontario were sampled, including pregnant and barren broodmares. Samples were collected from the nose, vagina, and blood of each mare up to 6 times from December 2016 through October 2017 using a cross-sectional study design. The EHV-1 glycoprotein B (gB) copy number was measured using droplet digital polymerase chain reaction (ddPCR). A survey was completed at time of sampling regarding signalment, pregnancy status, and vaccination. Overall, 85% of the mares sampled were positive for EHV-1 from at least one site, on at least one occasion. Samples were positive 8.1%, 15.8%, and 17.2% of the time from the nose, vagina, and white blood cells, respectively. Pregnant mares had increased odds of shedding virus from the nose [odds ratio (OR) = 1.50, 95% confidence interval (CI): 1.03 to 2.18, P = 0.037]. Vaccination only reduced the odds of virus presence in blood (OR = 0.70, 95% CI: 0.49 to 0.99, P = 0.043). Advanced gestation appeared to also have a sparing effect on virus presence in blood (OR = 0.89, 95% CI: 0.85 to 0.93, P < 0.001). Most mares in Ontario were positive for EHV-1 despite being healthy and vaccinated, although the amount of viral DNA detected was extremely low. In addition, the vagina was identified as a source of viral shedding.

Equine meningoencephalomyelitis is an important cause of morbidity and mortality and is associated with a wide variety of infectious etiologies. Because of the lack of large retrospective studies, the prevalence and incidence of these diseases are unknown. Here we describe 171 cases of meningoencephalomyelitis in horses submitted to the Section of Anatomic Pathology at the New York State Animal Health Diagnostic Center (Cornell University, Ithaca, NY, USA) from 1996-2023. Neuroinflammatory disease was identified in 5.4% of submitted horses with a wide breed, age, and sex distribution. A parasitic cause was identified in 32 (19%) cases, with protozoa in 18 (11%) cases and metazoa in 14 (8%) cases. A viral cause was identified in 31 (18%) cases, corresponding to infection by equid alphaherpesvirus 1 (EqAHV1; 12 of 31, 39%), eastern equine encephalitis virus (10 of 31; 32%), West Nile virus (5 of 31; 16%), and rabies virus (4 of 31; 13%), followed by 14 bacterial (8%) cases and 7 fungal (4%) cases. Of the remaining 87 of 171 (51%) cases, 20 (23%) had some histologic features, although not conclusive, of protozoal disease, and 8 (9%) of EqAHV1 infection. However, 59 (68%) cases did not have any neuropathologic changes that would support a definitive diagnosis. Although we found the expected causes of equine meningoencephalomyelitis in our study, the large number of cases with unknown etiologic diagnoses highlights the challenges of definitively proving causes of neuroinflammation in the horse and supports the need for improved ante- and postmortem testing.

A novel G-quadruplex aptamer with high affinity for the specific detection of equine herpesvirus type 1: Comprehensive biophysical and analytical characterization.