Detection and identification of equine herpesvirus-1 and -4 by polymerase chain reaction

Retrospective study on equine viral abortions in Poland between 1999 and 2022

Introduction

Loss of pregnancy in mares is a major cause of economic and emotional impact for horse breeders. It can have many different infectious and noninfectious causes. The aim of this study was identification of the main viral causes of abortion in mares in Poland based on tissue samples from 180 aborted foetuses submitted for testing between 1999 and 2022.

Material and Methods

Tissues of aborted foetuses collected from different horse studs throughout Poland were tested for the presence of equine herpesvirus types 1 and 4 (EHV-1/-4) and if negative, for equine arteritis virus (EAV). The examination was performed using a PCR/reverse transcriptase PCR (1999-2012) and a quantitative PCR (2013-2022).

Results

The cause of abortion was determined to be EHV-1 in 49.4% of cases (n = 89), whereas no EHV-4- or EAV-positive cases were found. The proportion of abortions due to EHV-1 differed between regions, with the highest percentage in the Lubelskie and Wielkopolskie provinces.

Conclusion

The results of the study indicate that EHV-1 is the most important viral infectious agent causing abortions in mares in Poland.

First molecular detection of Equine Herpesvirus type 3 (EHV-3) in Chile

Equine coital rash (ECE) is a highly contagious benign infection that induces lesions on external genitals, and it is caused by the equine herpesvirus type 3 (EHV-3). Although the disease is globally distributed, its presence in Chile has not been documented from a genetic point of view. Here, we performed polymerase chain reaction screenings for EHV-3 in lesions of external genitals in four horses belonging to a riding station at Bulnes, Ñuble Region, Chile. We sequenced a fragment of the glycoprotein G (gG) gene from three horses with clinical signs of ECE. The sequences were identical between them and 99.7% similar to a haplotype of EHV-3 detected in Brazil, and phylogenetically related with homologue from Japan, Russia and Brazil. Our results show the presence of EHV-3 for the first time in horses with ECE in Chile.

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

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

Molecular Detection and Genetic Characteristics of Equine Herpesvirus in Korea

Respiratory diseases cause significant economic losses (especially in the horse racing industry). The present study describes the detection and genetic characteristics of equine herpesvirus (EHV) from a total of 1497 samples from clinically healthy horses in Korea, including 926 blood samples, 187 lung tissues, and 384 nasal swabs. EHV-2 and EHV-5 were detected in 386 (41.7%; 95% CI: 38.5–44.9) and 201 (21.7%; 95% CI: 19.1–24.4) blood samples, respectively, and in 25 (13.4%; 95% CI: 8.5–18.2) and 35 (18.7%; 95% CI: 13.1–24.3) lung tissues, respectively. EHV-1 and EHV-4 were not detected in either blood or lung tissues. EHV-1, EHV-2, and EHV-5 were detected in 46 (12.0%; 95% CI: 8.7–15.2), 21 (5.5%; 95% CI: 3.2–7.7), and 43 (11.2%; 95% CI: 8.0–14.4) nasal swabs, respectively. EHV-4 was not detected in nasal swabs. Co-infection with EHV-2 and EHV-5 was detected in 11.6% (107/926) of the blood samples and 6.4% (12/187) of lung tissues. In nasal swabs, co-infection with EHV-1, EHV-2, and EHV-5 was detected in 0.8% (3/384) of samples. Phylogenetic analysis of the glycoprotein B gene showed that EHV-1, EHV-2, and EHV-5 strains demonstrated significant genetic diversity in Korea, with a nucleotide sequence identity among them that ranged from 95.7% to 100% for EHV-1, 96.2–100% for EHV-2, and 93.8–99.3% for EHV-5. These results are the first phylogenetic analyses of EHV-1 in Korea in nasal swabs from a nationwide population of clinically healthy horses. Both EHV-2 and EHV-5 from blood, lung tissues, and nasal swabs were also detected.

EHV-1: A Constant Threat to the Horse Industry

Equine herpesvirus-1 (EHV-1) is one of the most important and prevalent viral pathogens of horses and a major threat to the equine industry throughout most of the world. EHV-1 primarily causes respiratory disease but viral spread to distant organs enables the development of more severe sequelae; abortion and neurologic disease. The virus can also undergo latency during which viral genes are minimally expressed, and reactivate to produce lytic infection at any time. Recently, there has been a trend of increasing numbers of outbreaks of a devastating form of EHV-1, equine herpesviral myeloencephalopathy. This review presents detailed information on EHV-1, from the discovery of the virus to latest developments on treatment and control of the diseases it causes. We also provide updates on recent EHV-1 research with particular emphasis on viral biology which enables pathogenesis in the natural host. The information presented herein will be useful in understanding EHV-1 and formulating policies that would help limit the spread of EHV-1 within horse populations.

Genetic characterization of equid herpesvirus type 1 from cases of abortion in Poland

Equid herpesvirus type 1 (EHV-1) is a common viral infection associated with varied clinical outcomes including respiratory disease, abortion and neurological disease. We have characterized EHV-1 sequences (n = 38) obtained from cases of equine abortion in Poland between 1999 and 2016, based on sequencing of PCR products from open reading frames (ORF) 30 and 68 of the EHV-1 genome. The majority (81.6%) of sequences were not classified into any of the previously described groups based on the ORF68 sequence. The remaining sequences belonged to ORF68 group III (7.9%) or IV (10.5%). A haplotype network analysis did not show any obvious structure within networks of local Polish sequences, nor within a global network of 215 EHV-1 sequences when these networks were coloured based on the geographical origin of viruses or date of detection. Our data suggest that ORF68 does not provide a reliable molecular marker for epidemiological studies of EHV-1, at least in a global sense. Its usefulness to aid local investigations of individual outbreaks remains to be established. All but two Polish EHV-1 sequences belonged to the ORF30 N₇₅₂ genotype. The two ORF30 D₇₅₂ viruses were obtained from abortion cases in 2009 and 2010. Hence, abortion cases that occurred in Poland between 1999 and 2016 were caused predominantly by EHV-1 with the ORF30 N₇₅₂ genotype, with no indication of an increase in the prevalence of the ORF30 D₇₅₂ variant.

Detection of Equine Herpesvirus (EHV) -1, -2, -4 and -5 in Ethiopian Equids with and without Respiratory Problems and Genetic Characterization of EHV-2 and EHV-5 Strains

Infections with equine herpesviruses (EHVs) are widespread in equine populations worldwide. Whereas both EHV-1 and EHV-4 produce well-documented respiratory syndromes in equids, the contribution of EHV-2 and EHV-5 to disease of the respiratory tract is still enigmatic. This study describes the detection and genetic characterization of EHVs from equids with and without clinical respiratory disease. Virus-specific PCRs were used to detect EHV-1, -2, -4 and -5. From the total of 160 equids with respiratory disease, EHV-5 was detected at the highest prevalence (23.1%), followed by EHV-2 (20.0%), EHV-4 (8.1%) and EHV-1 (7.5%). Concurrent infections with EHV-2 and EHV-5 were recorded from nine (5.2%) diseased horses. Of the total of 111 clinically healthy equids, EHV-1 and EHV-4 were never detected whereas EHV-2 and EHV-5 were found in 8 (7.2%) and 18 (16.2%) horses, respectively. A significantly higher proportion of EHV-2-infected equids was observed in the respiratory disease group (32/160, 20.0%; P = 0.005) compared to those without disease (8/111; 7.2%). EHV-2-positive equids were three times more likely to display clinical signs of respiratory disease than EHV-2-negative equids (OR 3.22, 95% CI: 1.42-7.28). For EHV-5, the observed difference was not statistically significant (P = 0.166). The phylogenetic analysis of the gB gene revealed that the Ethiopian EHV-2 and EHV-5 strains had a remarkable genetic diversity, with a nucleotide sequence identity among each other that ranged from 94.0 to 99.4% and 95.1 to 100%, respectively. Moreover, the nucleotide sequence identity of EHV-2 and EHV-5 with isolates from other countries acquired from GenBank ranged from 92.9 to 99.1% and 95.1 to 99.5%, respectively. Our results suggest that besides EHV-1 and EHV-4, EHV-2 is likely to be an important contributor either to induce or predispose equids to respiratory disease. However, more work is needed to better understand the contribution of EHV-2 in the establishment of respiratory disease.

A SEROLOGIC AND POLYMERASE CHAIN REACTION SURVEY OF EQUINE HERPESVIRUS IN BURCHELL'S ZEBRAS (EQUUS QUAGGA), HARTMANN'S MOUNTAIN ZEBRAS (EQUUS ZEBRA HARTMANNAE), AND THOMSON'S GAZELLES (EUDORCAS THOMSONII) IN A MIXED SPECIES SAVANNAH EXHIBIT

Reports of equine herpesvirus (EHV) 1 and EHV-9 causing clinical disease in a wide range of species have been well documented in the literature. It is thought that zebras are the natural hosts of EHV-9 both in the wild and in captive collections. Concerns about potential interspecies transmission of EHV-1 and EHV-9 in a mixed species savannah exhibit prompted serologic and polymerase chain reaction surveys. Eighteen Burchell's zebras ( Equus quagga ), 11 Hartmann's mountain zebras ( Equus zebra hartmannae), and 14 Thomson's gazelles ( Eudorcas thomsonii ) cohabitating the same exhibit were examined for EHV-1 virus neutralization titers, and evidence of virus via EHV 1-5 polymerase chain reactions. None of the animals had previous exposure to vaccination with EHV-1 or EHV-4. All tested zebras had positive EHV-1 titers, ranging from 4 to 384. All zebras and Thomson's gazelles had negative polymerase chain reaction results for all targeted equine herpesviruses. EHV-9-specific assays are not available but EHV-1, EHV-4, and EHV-9 cross-react serologically. Positive serology results indicate a potential latent equine herpesvirus in the zebra population, which prompted initiation of an equine herpesvirus vaccine protocol, changes in pregnant zebra mare management, and equine herpesvirus polymerase chain reaction screening prior to shipment to or from the study site.

Identification of Pathogenic Leptospira Strains in Tissues of a Premature Foal by Use of Polymerase Chain Reaction Analysis

Studies were carried out to determine the cause of death in a prematurely born Thoroughbred foal that died 24 hours after birth. Necropsy revealed gross lesions suggestive of septicemia. A commercial Leptospira polymerase chain reaction (PCR) assay designed to specifically amplify the hemolysis-associated protein 1 ( hap1) gene present only in pathogenic Leptospira strains detected the presence of Leptospira DNA in various tissues of the foal. Histologic examination of lung, liver, kidney, and myocardium revealed numerous spirochetes in Warthin–Starry-stained tissue sections. Results of PCR analysis and histologic examination suggested a leptospiral infection in the newborn foal. At the moment of death, the infection coexisted with a streptococcal-associated aspiration bronchopneumonia and postpartum septicemia. These findings indicate that the PCR assay based on the amplification of the hap1 gene represents a useful tool for specific detection of pathogenic leptospira in field samples taken from horses.

Equine Herpesvirus-1 Myeloencephalopathy, an Emerging Threat of Working Equids in Ethiopia

Although equine herpesvirus myeloencephalopathy (EHM) is a sporadic and relatively uncommon manifestation of equine herpesvirus-1 (EHV-1), it has the potential for causing devastating outbreaks in horses. Up till now, there were no reported EHM outbreaks in donkeys and mules. This study describes the isolation and molecular characterization of EHV-1 from clinically EHM-affected horses (n = 6), mules (n = 3) and donkeys (n = 82) in Ethiopia during outbreaks from May 2011 to December 2013. The incidence of EHM cases was higher from April to mid-June. EHM in donkeys was more severe and death without clinical signs of paralysis, and recumbency was frequently observed. The main age of affected equines ranged from 7 to 10 years (n = 51; 56.0%), and females (n = 58; 63.7%) were more affected than males. The incidence of neuropathogenic (D₇₅₂ ) and non-neuropathogenic (N₇₅₂ ) variants of EHV-1 from EHM-affected equines in Ethiopia was assessed by sequencing the DNA polymerase gene (ORF30) of the EHV-1 isolates. The results indicated that from the total of 91 clinically affected equines, 90 (98.9%) of them had an ORF30 D₇₅₂ genotype. An ORF30 N₇₅₂ variant was only found in one donkey. Analysis of ORF68 as grouping marker for geographical differences showed that the Ethiopian EHV-1 isolates belong to geographical group 4. Due to the fatal nature of EHV-1 in donkeys, it would be interesting to examine the pathogenesis of EHM in this species. At present, there is no vaccine available in Ethiopia, and therefore, outbreaks of EHV-1 should be controlled by proper management adaptations. In addition, it is important to test the efficacy of the commercial vaccines not only in horses, but also in donkeys and mules.

Detection of the neuropathogenic variant of equine herpesvirus 1 associated with abortions in mares in Poland

BACKGROUND

The incidence of reported cases of equine herpesvirus myeloencephalopathy (EHM) caused by infection with neuropathogenic strains of equine herpesvirus 1 (EHV-1) has markedly increased over the last decade in many Western countries. The purpose of this study was to estimate the prevalence of the neuropathogenic (G2254) and non-neuropathogenic (A2254) variants of EHV-1 among isolates associated with abortions in Polish stud farms.

RESULTS

The results of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and sequencing were consistent, and showed that two out of 64 abortions (3.1%) were induced by the neuropathogenic genotype G2254. All remaining 18 EHV-1 positive abortion cases (28.1%) were caused by the non-neuropathogenic genotype A2254.

CONCLUSIONS

Most of the abortions in mares in Poland from 1999 to 2012 were associated with non-neuropathogenic strains of EHV-1. However, the presented data indicate that the neuropathogenic genotype of the virus is also present in Polish stud farms. Such a presence suggests that the future emergence of EHM in Poland is probable.

Development of a single-tube duplex EvaGreen real-time PCR for the detection and identification of EHV-1 and EHV-4

The objective of this study was to develop a novel EvaGreen (EG) based real-time PCR technique for the simultaneous detection of Equine herpesvirus 1 (EHV-1) and Equine herpesvirus 4 (EHV-4) genomes from equine nasal swabs. Viral genomes were identified based on their specific melting temperatures (T m), which are 88.0 and 84.4 °C for EHV-1 and EHV-4, respectively. The detection limitation of this method was 50 copies/μl or 0.15 pg/μl for EHV-1 and 5 copies/μl or 2.5 fg/μl for EHV-4. This assay was 50-1,000 times more sensitive than the SYBR Green (SG)-based assay using the same primer pairs and as sensitive as the TaqMan-MGB probe-based assay. The validity of the real-time PCR assays was confirmed by testing 13 clinical samples. When all results of the EG, SG, and TaqMan probe-based singleplex and duplex real-time PCRs were considered together, a total of 84.6 % (11/13) horses and donkeys were positive for at least one virus. EHV-1 and EHV-4 coexisted in 81.8 % (9/11) horses. Overall, we report that the EvaGreen duplex real-time PCR is an economical and alternative diagnostic method for the rapid differentiation of EHV-1 and EHV-4 in nasal swabs.

Growth and Virulence Alterations of Equine Herpesvirus 1 by Insertion of a Green Fluorescent Protein Gene in the Intergenic Region between ORFs 62 and 63

Nucleotide sequences of the intergenic region between ORF 62 and ORF 63 of equine herpesvirus 1 (EHV-1) isolates were analyzed. The sequences of this region consisted of variable and conserved domains among EHV-1 isolates. An EHV-1 mutant, Ab4-GFP, was constructed by inserting a green fluorescent protein (GFP) expression cassette flanked by lox P at both ends into the intergenic region between ORF 62 and ORF 63. Another mutant, Ab4-loxP, which contains one lox P site, was constructed by excision of the GFP cassette from the Ab4-GFP virus genome by cre enzyme. The recombinant Ab4-GFP formed smaller plaques than the wild type in MDBK cells. Virus production also decreased for Ab4-GFP in multistep growth analyses. Virulence of Ab4-GFP in both mice and hamsters was weaker than that of the wild type. Ab4-loxP exhibited properties similar to those of the wild type. These results suggest that the intergenic region between ORF 62 and ORF 63 plays various roles in the virus growth.

Shuni virus as cause of neurologic disease in horses

To determine which agents cause neurologic disease in horses, we conducted reverse transcription PCR on isolates from of a horse with encephalitis and 111 other horses with acute disease. Shuni virus was found in 7 horses, 5 of which had neurologic signs. Testing for lesser known viruses should be considered for horses with unexplained illness.

Two outbreaks of neuropathogenic equine herpesvirus type 1 with breed-dependent clinical signs

Equine herpesvirus type 1 (EHV-1) is a worldwide spread pathogen of horses. It can cause abortion, respiratory and neurological disease and consequentially significant economic losses in equine industries. During 2009, two outbreaks of EHV-1 were confirmed in two stud farms in Eastern Croatia. The first outbreak occurred in February following the import of 12 horses from USA, serologically negative to EHV-1 before transport. Four mares aborted in the late stage of pregnancy and one perinatal death was recorded. Other six mares showed clinical signs of myeloencephalopathy with fatal end in four. One month later, the second EHV-1 outbreak was confirmed in stud farm about 100 km further with 17 abortions, three perinatal deaths and one mild neurological case. Epidemiological data showed that the disease was probably introduced in the first stud farm during international transport. The second outbreak started with the introduction of clinically healthy stallion from the first stud farm. Molecular characterisation and phylogenetic analysis confirmed that, despite different clinical signs, the identical virus caused both outbreaks. Both horse populations were free from EHV-1 infection before the outbreak and had not been vaccinated. Significant difference in clinical signs could be explained by different breed-related risk factors.

Neuropathogenic and non-neuropathogenic variants of equine herpesvirus 1 in France

Equine herpesvirus 1 (EHV-1) is a common pathogen of the horse which may induce mild respiratory distress, abortion, neonatal death and neurological disease. A single nucleotide polymorphism in the EHV-1 DNA polymerase (ORF30 A(2254) to G(2254)) has been associated with clinical signs of Equine herpes myeloencephalopathy (EHM). The aim of this work was to analyze the ORF30 genomic region among a panel of EHV-1 DNA extract in order to estimate the prevalence of the EHV-1 neuropathogenic genotype in France. Samples coming from cases associated with EHM, horses with respiratory symptoms and aborted mares, each obtained between 2002 and 2009, were investigated. DNA was directly extracted from biological samples and allelic discrimination was performed using real-time PCR. Thirty of the 125 analysed horses (24%) presented the G(2254) genotype of ORF 30. Among them, 7/16 were provided by EHM cases, 1/24 by respiratory cases and 22/85 by abortion cases. Concerning EHM, the 7 G(2254) genotype of ORF30 were all isolated in 2009 during two outbreaks where mortality was observed. Regarding the 22 G(2254) genotype of ORF 30, 17 were identified in foetuses on which EHV-1 was detected by PCR, without any certainty of viral implication in the abortion. These findings clearly suggest that other factors need to be considered for a better understanding of the impact of DNA polymerase genotype upon EHV-1 neuropathogenic phenotype.

Loop-mediated isothermal amplification assays for detection of Equid herpesvirus 1 and 4 and differentiating a gene-deleted candidate vaccine strain from wild-type Equid herpesvirus 1 strains

Loop-mediated isothermal amplification (LAMP) is a novel method for the rapid and sensitive detection of DNA without the need for expensive equipment. In the present study, LAMP assays were developed for the specific detection of Equid herpesvirus 1 and 4 (EHV-1 and EHV-4, respectively) and for the differentiation of glycoprotein E (gE)-deleted EHV-1 (DeltagE) strain, a candidate strain for a live vaccine, from field EHV-1 strains. Specific primer sets were designed for the gC and gE genes of EHV-1 and for the gC gene of EHV-4. The analytical sensitivities of the LAMP assays were compared with those of polymerase chain reaction (PCR). The detection limits of LAMP for EHV-1 gC and gE and PCR for EHV-1 gC were 1 plaque-forming unit (PFU)/tube, and those of LAMP and PCR for EHV-4 gC were 0.1 PFU/tube. The DeltagE strain could be differentiated from wild-type EHV-1 strains based on the reactivity in the LAMP for EHV-1 gC in combination with the LAMP for EHV-1 gE. The analytical specificities of the LAMP for EHV-1 and EHV-4 were examined by using several equine pathogens, and no cross-reactions were observed. The LAMP detection abilities for EHV-1 and EHV-4 on nasal swab samples collected from experimentally infected horses were in good agreement with that of PCR for EHV-1 and EHV-4, respectively. The LAMP assays developed in the current study were sensitive and specific for EHV-1 and EHV-4, and should provide a valuable alternative to PCR for use in clinical laboratories in the field.

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

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

Equine herpesvirus-1 myeloencephalopathy: a review of recent developments

Equine herpes myeloencephalopathy (EHM), although a relatively uncommon manifestation of equine herpesvirus-1 (EHV-1) infection, can cause devastating losses on individual farms or boarding stables. Although outbreaks of EHM have been recognized for centuries in domestic horse populations, many aspects of this disease remained poorly characterized. In recent years, an improved understanding of EHM has emerged from experimental studies and from data collected during field outbreaks at riding schools, racetracks and veterinary hospitals throughout North America and Europe. These outbreaks have highlighted the contagious nature of EHV-1 and have prompted a re-evaluation of diagnostic procedures, treatment modalities, preventative measures and biosecurity protocols for the disease. This review concentrates on these and other selected, clinically relevant aspects of EHM.

Detection of equine herpesviruses in aborted foetuses by consensus PCR

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

Potential risk of equine herpes virus 1 (EHV-1) transmission by equine embryo transfer

The objective of this study was to determine whether the 10 wash cycles proposed by the International Embryo Transfer Society (IETS) for bovine embryos efficiently decontaminated equine embryos exposed to equine herpes virus 1 (EHV-1) in vitro. Donor mares and stallions were individually screened and shown to be negative for the virus by PCR detection of EHV-1 DNA in blood leukocytes, semen, and uterine lavages in which embryos were recovered. Twenty embryos were recovered and randomly assigned to one of two groups: 10 embryos were exposed for 24h to infectious EHV-1 at 10(6)TCID(50)/ml, and 10 embryos were used as negative controls. Exposed embryos were washed in accordance with IETS recommendations for ruminant and porcine embryos, before being incubated for 24 h with semiconfluent rabbit kidney (RK13) cells to detect any cytopathic effects (CPE), and finally tested for the presence of EHV-1 viral DNA by PCR. The embryo washing media were also assayed for the virus on RK 13 cells and by PCR. Control embryos were neither exposed to the virus nor washed. EHV-1 was not found in the control embryos, or in the last five washes of the exposed embryos. However, the virus was detected in 7/10 of the embryos exposed to EHV-1 for 24h, as well as in the first five washes of the embryos. The gradual disappearance of EHV-1 from the 10 successive wash solutions from the exposed embryos and the detection of viral DNA in 7/10 washed embryos by PCR, demonstrated that the washing procedure was unable to remove EHV-1 and suggested that EHV-1 could be attached to the acellular layer surrounding embryos (zona pellucida or capsule) or had penetrated the embryo.

Detection of respiratory herpesviruses in foals and adult horses determined by nested multiplex PCR

A nested multiplex PCR was developed as a rapid (<12h), sensitive test for the simultaneous identification of equine herpesviruses (EHV1, EHV4, EHV2 and EHV5) in clinical samples from horses. Peripheral blood and nasal swab (NS) samples from 205 weanling Thoroughbred foals on 6 different studs over 3 consecutive seasons and from 92 adult horses without clinical signs of respiratory disease were examined using direct multiplex PCR of clinical samples (direct PCR) and conventional cell culture with differentiation of EHV in cell cultures by multiplex PCR. Multiplex PCR proved a sensitive and specific technique for the detection of EHV in cell culture and clinical samples. The technique described appeared equally sensitive as one using a single set of primers for individual EHV but reduced labour and reagent costs. Cell cultures showing cytopathic effect (CPE) were always positive for EHV on PCR. EHV were also detected by multiplex PCR in 11 samples which failed to show CPE. By a combination of multiplex PCR and cell culture or direct multiplex PCR, the presence of up to three EHV in the same sample was detected. Overall, EHV5 was detected by direct multiplex PCR of peripheral blood mononuclear cells (PBMC) and/or NS samples from 78% of foals and 47% of adult horses. Repeated sampling or cell culture in combination with multiplex PCR and with the incorporation of IL-2 in culture medium increased the sensitivity for detection of EHV in PBMC and demonstrated that EHV5 DNA could be identified in PBMC from 89% of foals and 100% of adult horses. EHV2 was identified from approximately 30% of foals, but was more frequently identified in samples from 17 foals with mild respiratory disease and was isolated infrequently from adult horses. EHV1 and EHV4 were identified uncommonly in any population in the current study.

Advanced Techniques in the Diagnosis and Management of Infectious Pulmonary Diseases in Horses

Techniques for novel approaches to the diagnosis and management of equine pulmonary disease continue to be developed and used in clinical practice. Diagnostic techniques involving immunoassays and nucleic acid-based tests not only decrease the time in which results become available but increase the sensitivity and specificity of test results. These assays do not substitute for careful clinical evaluation but can shorten the time to a confirmed accurate diagnosis, and thus allow for early initiation of therapeutic strategies and prevention protocols. With further understanding of the molecular biology and immunology of equine pulmonary disease, diagnostic and management techniques should become further refined.

Detection of equine herpesvirus type 1 by real time PCR

A real-time PCR assay was developed for detection and quantitation of equid herpesvirus type 1 (EHV-1). The sensitivity of the assay was compared with an established nested-PCR (n-PCR). The real-time PCR detected 1 copy of target DNA, with a sensitivity 1 log higher than gel-based n-PCR. The assay was able to detect specifically EHV-1 DNA in equine tissue samples and there was no cross-amplification of other horse herpesviruses. Real-time PCR was applied to determine EHV-1 load in tissue samples from equine aborted fetuses. The high sensitivity and reproducibility of the EHV-1-specific fluorogenic PCR assay, combined with the wide dynamic range and the high throughput, make this method suitable for diagnostic and research applications.

Detection of equine herpesvirus type 1 using a real-time polymerase chain reaction

Equid herpesvirus 1 (EHV1) is a major disease of equids worldwide causing considerable losses to the horse industry. A variety of techniques, including PCR have been used to diagnose EHV1. Some of these PCRs were used in combination with other techniques such as restriction enzyme analysis (REA) or hybridisation, making them cumbersome for routine diagnostic testing and increasing the chances of cross-contamination. Furthermore, they involve the use of suspected carcinogens such as ethidium bromide and ultraviolet light. In this paper, we describe a real-time PCR, which uses minor groove-binding probe (MGB) technology for the diagnosis of EHV1. This technique does not require post-PCR manipulations thereby reducing the risk of cross-contamination. Most importantly, the technique is specific; it was able to differentiate EHV1 from the closely related member of the Alphaherpesvirinae, equid herpesvirus 4 (EHV4). It was not reactive with common opportunistic pathogens such as Escherichia coli, Klebsiella oxytoca, Pseudomonas aeruginosa and Enterobacter agglomerans often involved in abortion. Similarly, it did not react with equine pathogens such as Streptococcus equi, Streptococcus equisimilis, Streptococcus zooepidemicus, Taylorella equigenitalis and Rhodococcus equi, which also cause abortion. The results obtained with this technique agreed with results from published PCR methods. The assay was sensitive enough to detect EHV1 sequences in paraffin-embedded tissues and clinical samples. When compared to virus isolation, the test was more sensitive. This test will be useful for the routine diagnosis of EHV1 based on its specificity, sensitivity, ease of performance and rapidity.

Genomic diversity among equine herpesvirus-4 field isolates

Infection with equine herpesvirus-4 (EHV-4) is a major cause of respiratory tract disease, equine rhinopneumonitis, in horses. Although the full sequence of EHV-4 has been reported, genomic differences among EHV-4 field isolates have not yet been characterized. In this study, the genomic diversity between 23 Japanese EHV-4 isolates was analyzed by digestion with restriction endonucleases (BamHI, BgIII, EcoRI, SacI, and SalI) and polymerase chain reaction (PCR). The restriction endonuclease digestion patterns of the EHV-4 field isolates showed distinct differences which included mobility shifts of some fragments as well as loss and/or gain of fragments. Two EHV-4 genes containing repeat sequences, ORFs 24 and 71, were amplified by PCR and the amplified fragments were compared among the field isolates. The sizes of the amplified fragments varied among epizootiologically unrelated isolates, while the fragments of related isolates had the same size. The observed genomic diversity among EHV-4 field isolates may be a useful tool for epidemiological study of equine rhinopneumonitis by EHV-4 infection.

Isolation of equine herpesvirus-1 lacking glycoprotein C from a dead neonatal foal in Japan

We isolated a variant equine herpesvirus-1 (EHV-1), strain 5089, from the lung of a dead neonatal foal in Japan and characterized the biological nature of the virus. The virus spread in cultured cells mainly by cell-to-cell infection, unlike wild-type EHV-1, which spreads efficiently as a cell-free virus. The virus titer in cultured supernatant and the intracellular virus titer were low compared to those of wild-type EHV-1. Heparin treatment of the virus had no effect on viral infectivity in cell culture. Glycoprotein C (gC) was not detected by Western blotting and fluorescent antibody tests in 5089 virions and 5089-infected cells, respectively. RT-PCR analysis revealed that the expression level of 5089 gC mRNA was reduced considerably compared to that of wild-type EHV-1. Sequencing analysis of the 5089 gC coding region showed a point mutation in the promoter region of the gC open reading frame. However, the mutation did not affect the promoter activity. These results suggested that the lack of gC in 5089 virions might be one of the reasons for spread of the virus by cell-to-cell infection and that gC mRNA expression might not be activated efficiently due to factors other than the mutation in the gC promoter region.

Isolation and partial characterization of equine herpesvirus type 1 in Czechia

Equine herpesvirus type 1 was determined as the etiological cause of an abortion storm in Czechia in 2003 after the virus strain was isolated from aborted fetus and identified by serological means and by PCR technique. Cloning and sequencing of the glycoprotein D confirmed the identity of the isolates and showed molecular relationships to known EHV-1 strains. Comparison of glycoprotein D sequences with corresponding sequence of EHV-1 reference strains (Kentucky-A and Ab1) revealed high nucleotide homology. The Czech isolate of EHV-1 virus does not differ significantly from the Ab1 strain regarding the glycoprotein D gene and does not bear the frameshift in the 3' terminus which occurs in the Kentucky-A strain.

Equine herpesvirus 1 and 4

Equine herpesvirus infections in horses remain a significant cause of abortion and neurologic disease. These viruses are also responsible for mild signs of respiratory disease. The ability to establish latent infections with periodic reactivation or transmission to other horses is an important feature of these herpesviruses. One of the most unique aspects of this report is the description of horses demonstrating neurologic signs serving as the source of infection for other horses. Accurate diagnosis and better means of protection for horses remain problems facing veterinarians and horse owners.

Investigation of Neospora sp. antibodies in aborted mares from Normandy, France

Neospora caninum, an apicomplexan protozoan parasite, is recognized as a major cause of abortion in cattle while limited information is presently available on association between equine Neospora infections and abortions. The aim of the present study was to document prevalence of antibodies against Neospora sp. in aborted mares as a clue to the role of N. caninum in mare reproductive failure in Normandy, France. Using an agglutination test, the number of animals with elevated (>80) anti-Neospora sp. antibody titer was higher in a group of 54 aborted mares than in randomly chosen groups of 45 mares and 76 horses sampled for equine arteritis virus and Fasciola hepatica antibodies, respectively (P<0.001). N. caninum DNA was found in 3/91 fetal brains, 2/77 fetal hearts, and 1/1 placenta, and present in both brains and hearts of two fetuses. In 13 cases for which both mare serum and fetus were available, no fetal N. caninum amplification product was present while a large variation of maternal antibody titers was found. Data prompt at additional surveys of association between equine reproductive failure and Neospora sp. infection.

Growth of recombinant equine herpesvirus 1 (EHV-1) replaced with passage-induced mutant gene 1 and gene 71 derived from an attenuated EHV-1 in cell cultures and in the lungs of mice

The relationship of passage-induced mutant genes 1 and 71 of an attenuated equine herpesvirus 1 (EHV-1) with virulence was analysed by constructing nine recombinant EHV-1 viruses by homologous recombination. Gene 1 or/and gene 71 of a virulent EHV-1 strain, HH1, was replaced by a mutant gene 1 or/and 71 of an attenuated HH1 strain, BK343, respectively. The beta-galactosidase gene of Escherichia coli was inserted within the gene 1 or 71 coding sequence of HH1 to inactivate the genes. Virus replications of these recombinant viruses in cell cultures were similar, but release of the gene 71-inactivated virus from infected cells was delayed compared to that of the other viruses. Plaque sizes of the recombinant viruses were similar to those of HH1, but those of BK343 were significantly smaller, indicating an effect of some unknown factor(s) on viral cell-to-cell spread. The growth abilities of the recombinant viruses with a mutant gene 1 or/and 71 in lungs of mice were similar to those of HH1, but those of gene 71-inactivated viruses were reduced to the level of BK343 and the titers were about 100-times lower than those of the other recombinant viruses. These results indicate that the mutant genes 1 and 71 of BK343 might not confer an attenuated nature to EHV-1.

The development of a competitive PCR-ELISA for the detection of equine herpesvirus-1

Equine herpesvirus-1 (EHV-1) infection is of significant animal welfare and economic importance. Yet, no standardised molecular techniques are available for diagnosis or confirmation of viral infection. The purpose of this study was to develop a standardised and quantitative assay system for the reliable detection of EHV-1 infection which was capable of eliminating the likelihood of false negative results. A region within the EHV-1 glycoprotein B gene was amplified by polymerase chain reaction (PCR), cloned and subjected to site-directed mutagenesis to generate a control plasmid, amplifiable by identical primers to wild type EHV-1, yet capable of detection by an alternate dinitrophenylated oligonucleotide probe in a PCR-ELISA system. A competitive PCR-ELISA system which can control for the presence of PCR inhibitors and which is capable of detecting 63 genome equivalents of EHV-1 has been developed. EHV-1 presence in infected equine tissue and cell culture material was demonstrated using this system. The entire assay can be completed within one working day and facilitates multiple sample analysis. The availability of a robust, competitive PCR-ELISA system for the detection of EHV-1 will facilitate the rapid and sensitive detection of EHV-1 and offers the potential for eliminating the occurrence of abortion storms in stud farms.

Detection and isolation of equine herpesviruses 1 and 4 from horses in Normandy: an autopsy study of tissue distribution in relation to vaccination status

Equine herpesviruses type 1 and 4 (EHV-1 and EHV-4) are ubiquitous in the equine population. One of their main properties is their ability to establish life-long latent infections in their hosts even in those with natural or vaccine-induced immunity. However, effect of vaccination status on prevalence and tissue tropism was not established. In this study, EHV-1 and EHV-4 were detected by polymerase chain reaction and by classical virus isolation from neural, epithelial and lymphoid tissues collected from unvaccinated (33) or vaccinated (23) horses. The percentage of EHV-1- and EHV-4-positive horses between vaccinates and unvaccinates was similar. Both viruses were detected in all tissues of both groups; in particular, lymph nodes draining the respiratory tract, nasal epithelium and nervous ganglia [i.e. trigeminal ganglia (TG)], which represent the main positive sites for EHV-1 and EHV-4. In vaccinated animals, the nervous ganglia (i.e. TG) were less frequently positive than in unvaccinated animals. Detection of positive TG was strongly correlated to the presence of EHV-1 in nasal epithelium.

Identification of equine herpesviruses 1 and 4 by polymerase chain reaction

OBJECTIVE

To develop and validate specific, sensitive and rapid (< 8 hour) diagnostic tests using polymerase chain reaction (PCR) for the diagnosis of abortion and respiratory disease caused by equine herpesvirus 1 (EHV1; equine abortion virus) and EHV4 (equine rhinopneumonitis virus).

DESIGN

Primer sets based on nucleotide sequences encoding glycoprotein H (gH) of EHV1 and gB of EHV4 were designed and used in single round and second round (seminested) PCRs, and in a multiplex PCR for the diagnosis of EHV1 and EHV4 infections.

METHODS

Oligonucleotide primers were designed for each virus, PCR conditions were defined and the specificity and sensitivity of the assays were determined. The tests were applied to tissue samples from aborted equine foetuses and to nasopharyngeal swabs from horses with acute febrile respiratory disease.

RESULTS

Individual single round and a second round (seminested) EHV1 and EHV4 PCRs were specific in that EHV1 primers amplified all (n = 30) EHV1 isolates and did not amplify EHV4. Similarly EHV4 primers amplified all (n = 6) EHV4 isolates and did not amplify EHV1. Both PCRs were sensitive in that the first round EHV1 PCR detected 1220 molecules of EHV1 plasmid DNA and the first round EHV4 PCR detected 7280 molecules of EHV4 plasmid DNA. The EHV1 second round PCR was 100 times more sensitive in that it detected 12 molecules of EHV1 DNA and the EHV4 second round PCR was 1000 times more sensitive in that it detected 8 molecules of EHV4 DNA. There was a high correlation between detection of EHV1 by virus isolation and PCR when tissue samples from 71 aborted foetuses were examined; all samples positive by virus isolation were positive by PCR. Similarly the EHV4 PCR was at least as sensitive as virus isolation when applied to nasaopharyngeal swabs from horses with respiratory disease in that all samples positive by virus isolation were also positive by PCR.

CONCLUSION

Individual single round and second round (seminested) PCRs and a seminested multiplex PCR were developed that enabled reliable, rapid detection of EHV1 and EHV4 in aborted foetal tissues and nasopharyngeal swab samples.

A polymerase chain reaction for detection of equine herpesvirus-1 in routine diagnostic submissions of tissues from aborted foetuses

Equine herpesvirus 1 (EHV-1) is the causative agent of abortion, perinatal foal mortality, neurological and acute respiratory diseases in horses. Conventional laboratory diagnosis involving viral isolation from aborted foetuses is laborious and lengthy and requires processing of samples within 24 h of collection, which is problematic for samples that come from long distances. The aim of this study was to develop a polymerase chain reaction (PCR) assay useful in Argentina to detect DNA sequences of EHV-1 in different tissues from aborted equine foetuses with variable quality of preservation and without the use of conventional DNA fenolic extraction. Several DNA extraction protocols and primers were evaluated. The amplification method was standardized and its specificity was analysed using 38 foetal samples of variable quality of preservation. Of the 38 different foetal tissues, nine livers, six spleens and two lungs in good preservation and eight livers, one spleen and four lungs in a poor state of preservation were positive for PCR. EHV-1 was recovered only from the nine livers, five spleens and two lungs in good preservation. No virus was isolated from the samples that were poorly preserved. Viral isolation was confirmed by cytopathic effect and indirect immunofluorescence. The specificity of the PCR results was confirmed by the restriction endonuclease digestion of PCR products and hybridization.

Fatal nonneurological EHV-1 infection in a yearling filly

A case of fatal nonneurological equine herpesvirus 1 (EHV-1) infection in a yearling filly is described. Gross lesions included extensive pulmonary edema, prominent laryngeal lymphoid follicles, and congestion and edema of the dorsal third ventricle choroid plexus. Histologically, there was vasculitis, hemorrhage, and edema in the lungs and dorsal third ventricle choroid plexus as well as mild intestinal crypt necrosis with occasional intranuclear inclusion bodies. The perivascular and vascular inflammatory infiltrates were comprised mainly of T lymphocytes and macrophages. EHV-1 antigen was identified within the nucleus and cytoplasm of endothelial cells, dendritic-like cells of the pharyngeal lymphoid follicles, pharyngeal glandular epithelium, crypt enterocytes, and monocytes. Attempted virus isolation was negative. Weak seroconversion for EHV-1 was observed. Herpesvirus-like particles were identified within pharyngeal endothelial cells by transmission electron microscopy. Polymerase chain reaction amplified 369 and 188 base-pair fragments specific for EHV-1. The scarcity of pathognomonic viral inclusions and lesions in this case suggests that this disease may not be recognized, particularly in situations when ancillary laboratory procedures are limited.

Diagnosis and prevention of equine infectious diseases: present status, potential, and challenges for the future

The frequent transfers of horses, whether on a permanent or temporary basis, make strict control of infectious diseases essential. Such control needs a reliable and rapid means to accurately diagnose the relevant diseases. Indirect diagnosis based on antibody detection remains certainly the best method to secure the epidemiologic surveillance of the diseases at regional, national, or even world level, while direct diagnosis is the only way to diagnose a new outbreak. New diagnostic methods resulting from advances in biochemistry, molecular biology, and immunology are now available. As far as antibody detection is concerned, the new methods are mainly based on immunoassays, especially ELISAs. Regarding the identification of the pathogens, while isolation is still of importance, much progress has been made with immunocapture tests including capture ELISA based on monoclonal antibodies. DNA probes and amplification tests such as PCR or RT-PCR are representing a real breakthrough. Factors common to all of these tests are specificity, sensitivity, rapid implementation, and quick results. Such tests are, however, often still at the development stage. They absolutely need to be validated under multicentric evaluations prior to being used on a larger scale. At the same time there is an obvious need for the standardization of the reagents used. The technical and economic impact of a false (either positive or negative) diagnosis justifies such an harmonization which could effectively be achieved worldwide under the aegis of the Office International des Epizooties (OIE), which is itself the primary source of disease information. Vaccines are also essential for the control of equine infectious diseases. Most vaccines used in the prevention of viral or bacterial diseases are inactivated adjuvanted vaccines, which may cause unacceptable side effects. Also, their efficacy can sometimes be questioned. Subunit vaccines, when available, represent significant advances especially with regards to safety. Greater progress is expected from the use of new technologies taking advantage of recent developments in molecular biology (recombinant DNA technology) and in immunology (immunomodulators). Significant results have been obtained with subunit vaccines or with live vectored vaccines using recombinant DNA technology. Good results are on the way to be achieved with genetic (or naked-DNA) vaccines. It is therefore possible to expect the availability of a new generation of vaccines in the rather short term. Such vaccines will not only be safer and more efficacious, but they will also make it possible to differentiate vaccinated from infected animals, which will contribute to better control of the infection. Whatever the quality of the vaccines of the future may be, vaccination alone will never be sufficient to control infectious diseases. It is therefore essential to keep on making the animal owners and their veterinarians aware of the importance of the management and the hygiene in the diseases control and to organize them under "Common Codes of Practice."

Diagnosis and sero-epizootiology of equine herpesvirus type 1 and type 4 infections in Japan using a type-specific ELISA

Recently, a type-specific ELISA using equine herpesvirus type 1 (EHV-1) and type 4 (EHV-4) glycoprotein Gs (gGs) was developed by Crabb and Studdert [1993]. To investigate the dissemination of EHV-1 and -4 among horses in Japan, we applied their ELISA as suitable for discriminating between EHV-1 and -4 infections serologically. Type-specificity of the ELISA was confirmed by using paired sera of infected horses with either EHV-1 or -4. Application of the ELISA to sera collected before and after the winter season of 1995-1996 from 80 racehorses revealed that 30 horses showed significant antibody responses against EHV-1 and 9 against EHV-4, respectively. The results indicated that this ELISA using paired sera is useful for a diagnosis and an epizootiological study on EHV-1 and -4 infections.