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.

Equine herpesvirus-9 (EHV-9), equine herpesvirus-1 (EHV-1) and zebra-borne EHV-1 are members of the family Herpesviridae and cause encephalitis and rhinopneumonitis in a range of animal species. The aim of this study was to characterize and compare the rhinopneumonitis induced by experimental intranasal inoculation of groups of hamsters with EHV-9, EHV-1 strain Ab4p or zebra-borne EHV-1 viruses. Animals inoculated with EHV-9 had earlier and more severe neurological and respiratory signs than those inoculated with EHV-1 strain Ab4p or zebra-borne EHV-1. At 4-5 days post inoculation (dpi), hamsters inoculated with EHV-9 had significantly increased expression of open reading fame (ORF) 30, the viral gene encoding the DNA polymerase, in lung tissue. ORF 30 expression at these time points was higher in the hamsters infected with EHV-9 than in those inoculated with the other two viruses. Severe, mild or very mild rhinitis was seen in animals inoculated with EHV-1 strain Ab4p, EHV-9 and zebra-borne EHV-1, respectively. Viral antigen was detected in olfactory receptor neurons, inflammatory cells and desquamated epithelial cells in animals in all groups until 5 dpi. Tracheitis was also seen in all three virus-infected groups with viral antigen detected in tracheal epithelium. Inoculated hamsters developed interstitial pneumonia of increasing severity over the course of the experiment. Bronchopneumonia and vasculitis were also seen in all three infected groups. These results confirm that, in addition to their neurotropism, EHV-9 and zebra-borne EHV-1 are pneumotropic viruses. EHV-1 strain Ab4p caused more severe upper respiratory tract disease, but no significant differences were detected in the severity of pneumonia induced by each virus.

Equine abortion is a cause of severe economic loss to the equine industry. Equine herpesvirus 1 is considered a primary cause of infectious abortion in horses, however other infectious agents can also cause abortion. Abortions due to zoonotic pathogens have implications for both human and animal health. We determined the prevalence of Coxiella burnetii, Leptospira spp. and Toxoplasma gondii in 600 aborted equine foetal tissues that were submitted to our diagnostic laboratories at the University of Melbourne from 1994 to 2019. Using qPCR we found that the prevalence of C. burnetii was 4%. The highest annual incidence of C. burnetii was observed between 1997-2003 and 2016-2018. The prevalence of C. burnetii in Victoria and New South Wales was 3% and 6% respectively. All the samples tested negative for Leptospira spp. and Toxoplasma gondii DNA. Equine herpesvirus 1 DNA was detected at a prevalence of 3%. This study has provided evidence for the presence of C. burnetii in equine aborted foetal tissues in Australia, but the role of C. burnetii as potential cause of abortion in Australia requires further investigation. C. burnetii is a zoonotic disease agent that causes the disease \'Q fever\' in humans. We recommend that appropriate protective measures should be considered when handling material associated with equine abortions to reduce the risk of becoming infected with C. burnetii.

BACKGROUND: Equid herpesvirus (EHV-1) infections in horses can lead to equine herpesvirus myeloencephalopathy (EHM), characterised by neurological clinical signs. The sporadic occurrence of the disease in horse herds suggests a host genetic component. A recent study reported an association between the occurrence of EHM and genetic markers on horse chromosome 6 (ECA6).
OBJECTIVE: To investigate the association of EHM with genetic host factors, especially with reference to the association reported for ECA6.
METHODS: Genome-wide association study (GWAS) was conducted based on 94 horses that had EHV-1 infections and comparing the 27 developing clinical EHM to the 67 which did not.
METHODS: DNA samples were tested from 94 horses for 382,529 single nucleotide polymorphisms (SNPs) with the Affymetrix Axiom 670K SNP array to identify possible associations with EHM. The data analysis included tests for basic, additive, dominant and recessive modes of inheritance, haplotype associations and runs of homozygosity (ROH).
RESULTS: Results from this study did not identify significant SNPs, haplotypes or ROH associations with the development of EHM following EHV-1 infections and excluded the involvement of a recessive genetic factor in the susceptibility to develop EHM.
CONCLUSIONS: Sample size and complex phenotype.
CONCLUSIONS: The results exclude the involvement of a recessive genetic factor in the susceptibility to develop clinically apparent EHM but do not have the power to exclude the involvement of other, complex host genetic factors. Furthermore, there was no association between development of EHM and genes on equine chromosome 6, as previously reported.

Equine herpesvirus type 1 (EHV-1)-induced myeloencephalopathy (EHM) is a neurologic disease of horses that represents one outcome of infection. The neurologic form of disease occurs in a subset of infected horses when virus-induced endothelial cell damage triggers vasculitis and subsequent ischemic insult to the central nervous system. EHM causes considerable animal suffering and economic loss for the horse industry. Virus polymorphisms have been previously associated with disease outcome but cannot fully explain why only some horses develop EHM. This study investigated the role of host genetics in EHM. DNA samples were collected from 129 horses infected with EHV-1 (61 that developed EHM and 68 in which disease resolved without the development of neurologic signs) during natural outbreaks or experimental infections. A genome-wide association study (GWAS) was performed to investigate host genetic variations associated with EHM. Genotyping was performed using the Illumina SNP50 and SNP70 arrays and a custom Sequenom array. Mixed linear model (MLM) analysis using a recessive model identified one marker that surpassed the threshold for genome-wide significance (P<0.001) after Bonferroni correction. The marker (BIEC2_946397) is in an intron of the tetraspanin 9 (TSPAN9) gene, which is expressed in endothelial cells and platelets. The GWAS identified a region in the horse genome that is associated with EHM in the sample population and thus warrants further exploration. Understanding the contribution of host genetic variation to the development of EHM will enhance our knowledge of disease pathophysiology, and lead to improved strategies for treating individual cases and managing outbreaks.

Equine herpesvirus 5 (EHV-5) infection is associated with pulmonary fibrosis in horses, but further studies on EHV-5 persistence in equine cells are needed to fully understand viral and host contributions to disease pathogenesis. Our aim was to develop a quantitative PCR (qPCR) assay to measure EHV-5 viral copy number in equine cell cultures, blood lymphocytes, and nasal swabs of horses. Furthermore, we used a recently developed equine primary respiratory cell culture system to study EHV-5 pathogenesis at the respiratory tract. PCR primers and a probe were designed to target gene E11 of the EHV-5 genome. Sensitivity and repeatability were established, and specificity was verified by testing multiple isolates of EHV-5, as well as DNA from other equine herpesviruses. Four-week old fully differentiated (mature), newly seeded (immature) primary equine respiratory epithelial cell (ERECs), and equine dermal cell cultures were inoculated with EHV-5 and the cells and supernatants collected daily for 14days. Blood lymphocytes and nasal swabs were collected from horses experimentally infected with equine herpesvirus 1 (EHV-1). The qPCR assay detected EHV-5 at stable concentrations throughout 14days in inoculated mature EREC and equine dermal cell cultures (peaking at 202 and 5861 viral genomes per 106 cellular β actin, respectively). EHV-5 copies detected in the immature EREC cultures increased over 14days and reached levels greater than 10,000 viral genomes per 106 cellular β actin. Moreover, EHV-5 was detected in the lymphocytes of 76% of horses and in the nasal swabs of 84% of horses experimentally infected with EHV-1 pre-inoculation with EHV-1. Post-inoculation with EHV-1, EHV-5 was detected in lymphocytes of 52% of horses while EHV-5 levels in nasal swabs were not significantly different from pre-inoculation levels. In conclusion, qPCR was a reliable technique to investigate viral load in in vivo and in vitro samples, and EHV-5 replication in equine epithelial cells may be influenced by cellular stages of differentiation.

Diagnosis of equine herpesvirus-1 associated myeloencephalopathy (EHM) can be troublesome, but early recognition and knowledge of risk factors are essential for prevention and control. The objectives for this study are to (1) describe EHM in France, (2) improve clinical recognition, (3) identify risk factors. Through epidemiosurveillance of acute neurological cases (all considered to be potentially infectious cases) in France (2008-2011), 26 EHM cases were identified and 29 EHM negative control cases. EHM cases were described and compared to controls with univariate, multivariate and classification and regression tree analysis. EHM cases had a 46% fatality rate and were frequently isolated cases. Most showed ataxia, paresis and a cauda equina syndrome, yet presence of other neurological signs was variable. Statistical analysis identified the following variables to be significantly associated to EHM compared to controls: introduction of a new horse to the herd, cauda equina syndrome, larger herd size, saddle horses and month of occurrence. The presence of many isolated cases, and less typical and variable clinical presentations emphasize the difficulty in diagnosing EHM. Nevertheless, history and clinical examination of acute neurological cases can be valuable in recognizing EHM early as well in order to select those cases that need further laboratory testing and infection control measures. Moreover, with a different study format and geographic location, risk factors were found to be similar to previous studies, therefore strengthening their significance to the spread of EHM.

The purpose of the present review was a comparison of the abortions caused by EAV and EHV-1 viruses over the 34 years. A total of 452 tissues samples from aborted fetuses (347) or foals (105) stillborn or newborn that died within 72 hours were investigated. The material for the examinations came from different farms located throughout Poland. The tissue homogenates were examined by using virus isolation test in RK-13 and Vero cell lines and the cytopathic agent was confirmed as EHV-1 by the direct fluorescent antibody test or as EAV by the indirect fluorescent antibody test. The study indicated that EAV was isolated (104 cases, 23%) almost as equally often as EHV-1 (116 cases, 25.6%). Both, equid herpes virus-associated abortion and the abortion induced by EAV were characterized by cyclicity. The percentage of EAV and EHV-1 isolation alternately reduced and increased, but the increase of isolation of one virus was accompanied by the decrease of the other. The domination of one virus over the other occurred in cycles of a few years.

BACKGROUND: A large multistate outbreak of equine herpesvirus myeloencephalopathy (EHM) occurred in May 2011 among horses that participated in a competitive event.
OBJECTIVE: To identify EHM risk factors among horses with a common exposure venue.
METHODS: A total of 123 horses: 19 horses with EHM, 14 equine herpesvirus-1 cases with no reported neurologic signs, and 90 control horses.
METHODS: EHM case survey data were compared with data from EHV-1 cases with no neurologic signs and healthy controls using univariable and multivariable methods.
RESULTS: Significant factors associated with higher risk for EHM compared with EHV-1 cases with no neurologic signs were (1) greater number of biosecurity risks at the event, (2) female sex, (3) increasing number of classes competed in at the event, and (4) an interaction between sex and number of classes competed in. In the EHM versus controls comparison, in addition to sex and biosecurity risks, factors associated with higher EHM risk included EHV-1 vaccination in the 5 weeks before the event and increasing number of events attended in April 2011; zinc dietary supplementation was associated with decreased risk. An interaction between sex and the number of events attended in April 2011 also was significant.
CONCLUSIONS: Findings from this study suggest that dietary zinc supplementation may be associated with decreased risk of EHM. Several factors were associated with increased risk of EHM. Additional investigations of factors associated with risk of EHM are warranted to evaluate the importance of these factors in this complex disease of horses.

Equid herpesvirus 1 (EHV-1) infection has a significant economic impact on equine production, causing abortion, respiratory disease, neonatal death and neurological disorders. The identification of specific EHV-1 genes related to virulence and pathogenicity has been the aim of several research groups. The purpose of the present study was to analyze different genomic regions of Argentinean EHV-1 strains and to determine their possible relationship with virulence or clinical signs. Twenty-five EHV-1 Argentinean isolates recovered from different clinical cases between 1979 and 2007 and two reference strains were amplified and sequenced. The sequence alignments were carried out using Clustal X version 1.92 and the putative amino acid sequences were deduced using Bio-Edit version 7.05. Minor changes were observed. No changes that could be involved in the different virulence in the mouse model of three EHV-1 Argentinean strains were found. No genetic variants were observed. The genomic regions analyzed are unsuitable for differentiation between abortigenic strains and those isolated from neonatal deaths.