Evidence for absence of equine arteritis virus in the horse population of New Zealand

AIM: To summarise investigation and laboratory data collected between 2001 and 2011 to provide evidence that equine arteritis virus is not present in the horse population of New Zealand.

METHODS: Analysis was carried out on results from laboratory tests carried out at the Ministry for Primary Industries Animal Health Laboratory (AHL) for equine arteritis virus from horses tested prior to being imported or exported, testing of stallions as part of the New Zealand equine viral arteritis (EVA) control scheme and testing as part of transboundary animal disease (TAD) investigations for exclusion of EVA. Horse breeds were categorised as Thoroughbred, Standardbred or other.

RESULTS: A total of 7,157 EVA serological test records (from import and export testing, EVA control scheme testing and TAD investigations) were available for analysis between 2005 and 2011. For the three breed categories a seroprevalence of ≤1.6% at the 95% confidence level was determined for each category. Between 2001 and 2011, as part of the EVA control scheme, the EVA status of 465 stallions was determined to be negative. During 2005–2011 EVA was excluded from 84 TAD investigations.

CONCLUSIONS: There was no evidence of equine arteritis virus being present in the general horse population outside of carrier stallions managed under the EVA control scheme.

CLINICAL RELEVANCE: Equine arteritis virus is absent from the general horse population of New Zealand.     

Review of two viral agents of economic importance to the equine industry (equine herpesvirus-1, and equine arteritis virus)

Equine herpesvirus type-1 (EHV-1) and equine arteritis virus (EAV) are infectious agents that cause serious health risks to horse populations and are disbursed worldwide, which can lead to significant financial losses. In addition to being responsible for abortion and neonatal death, these viruses are associated with respiratory illness. Although previous research and reviews have been written on these viruses, both viruses still affect horse populations around the world and the vaccines currently available are not completely protective, especially against EHV-1 and equine herpes myeloencephalopathy (EHM). Moreover, EAV is considered a threat to the $102 billion equine industry in the United States. As a result, these viruses represent a huge threat to the horse industry and efforts geared towards preventing the outbreak of the disease are strongly encouraged. For this reason, updates about these viruses are necessary and require more and more discussion on the nature and characteristics of these viruses to know how to overcome them. Prevention and control of abortion and neonatal foal death caused by each of the two viruses depend on appropriate management strategies coupled with prophylactic vaccination. This review presents the latest detailed information on EHV-1 and EAV from several aspects such as transmission, clinical signs, pathogenesis, latest developments on the treatment of the diseases, vaccination, and finally challenges and future perspectives. The information presented herein will be useful in understanding EHV-1 and EAV and formulating policies that can help to limit the spread of these viruses within horse populations.     

Interstate Equine Semen and Embryo Shipment Regulations in the United States and Their Implications on Control of Disease Transmission

Outbreaks of both equine viral arteritis and contagious equine metritis (CEM) in the United States have occurred in recent years. Shipped semen has been implicated in disease transmission and rapid spread. A survey was performed of state regulations regarding testing for equine arteritis virus (EAV) and CEM before interstate semen or embryo shipment. Results demonstrated lack of any requirements in 31 states. Four states had regulations regarding EAV; 17 required a Certificate of Veterinary Inspection (CVI) to accompany a semen or embryo shipment. Ten states required a negative equine infectious anemia test, primarily as a requirement of a CVI versus because of risk of dissemination of disease. No states required CEM testing. A comparison of state department of agriculture or veterinary medical association Web sites and direct communication with state veterinarians or their offices demonstrated contradictory information in six states. The lack of uniform regulations concerning CEM and EAV testing for shipped semen and embryos, and the threat they pose to the equine breeding industry and horse health, should be alarming to veterinarians and horse owners. Routine testing of animals before shipment of semen or embryos and veterinary involvement in collection and breeding activities are appropriate and necessary to help prevent future outbreaks and protect equine health.     

Identification of equine herpesvirus 3 (equine coital exanthema virus), equine gammaherpesviruses 2 and 5, equine adenoviruses 1 and 2, equine arteritis virus and equine rhinitis A virus by polymerase chain reaction

OBJECTIVE: To develop rapid (< 8 hour) tests using polymerase chain reaction (PCR) for the diagnosis of equine herpesvirus 3 (EHV3; equine coital exanthema virus), equine gammaherpesviruses 2 (EHV2) and EHV5, equine adenovirus 1 (EAdV1), EAdV2, equine arteritis virus (EAV), equine rhinitis A virus (ERAV; formerly equine rhinovirus 1) DESIGN: Either single round or second round (seminested) PCRs were developed and validated. METHODS: Oligonucleotide primers were designed that were specific for each virus, PCR conditions were defined and the specificity and sensitivity of the assays were determined. The application of the tests was validated using a number of independent virus isolates for most of the viruses studied. The PCRs were applied directly to clinical samples where samples were available. RESULTS: We developed a single round PCR for the diagnosis of EHV3, a seminested PCR for EHV2 and single round PCRs for EHV5, EAdV1, EAdV2 and RT-PCRs for EAV and ERAV. The PCR primer sets for each virus were designed and shown to be highly specific (did not amplify any recognised non-target template) and sensitive (detection of minimal amounts of virus) and, where multiple virus isolates were available all isolates were detected. CONCLUSION: The development and validation of a comprehensive panel of PCR diagnostic tests, predominantly for viruses causing equine respiratory disease, that can be completed within 8 hours from receipt of clinical samples, provides a major advance in the rapid diagnosis or exclusion diagnosis of these endemic equine virus diseases in Australia.     

Abortogenic viruses in horses

Viral causes of abortion include equine viral arteritis (EVA) and infection with equine herpesviruses‐1 and ‐4 (EHV‐1 and EHV‐4). Transmission of equine arteritis virus (EAV) occurs through respiratory, venereal or transplacental routes. Horizontal respiratory transmission of EAV results from exposure to infective nasopharyngeal secretions from acutely infected horses. For this transmission to occur, direct and close contact between horses is necessary. Venereal infection is an efficient method of transmission, with seroconversion of 85 to 100% of seronegative mares bred to virus shedding stallions. Asymptomatic carrier stallions are the essential natural reservoir of equine arteritis virus. Equine herpesviruses‐1 and ‐4 infect a susceptible host, replicate and establish a lifelong latent infection without any associated clinical signs. Reactivation of latent infections can result from factors such as stress and intercurrent disease. The control of these diseases is by implementation of appropriate management and hygiene measures, supplemented by vaccination and, in the case of EVA, by the identification of persistently infected stallions, which can be removed from breeding or continue to be bred to if managed under controlled conditions to prevent the risk of an outbreak of the disease.     

Viruses associated with outbreaks of equine respiratory disease in New Zealand

AIM: To identify viruses associated with respiratory disease in young horses in New Zealand.

METHODS: Nasal swabs and blood samples were collected from 45 foals or horses from five separate outbreaks of respiratory disease that occurred in New Zealand in 1996, and from 37 yearlings at the time of the annual yearling sales in January that same year. Virus isolation from nasal swabs and peripheral blood leukocytes (PBL) was undertaken and serum samples were tested for antibodies against equine herpesviruses (EHV-1, EHV-2, EHV-4 and EHV-5), equine rhinitis-A virus (ERAV), equine rhinitis-B virus (ERBV), equine adenovirus 1 (EAdV-1), equine arteritis virus (EAV), reovirus 3 and parainfluenza virus type 3 (PIV3).

RESULTS: Viruses were isolated from 24/94 (26%) nasal swab samples and from 77/80 (96%) PBL samples collected from both healthy horses and horses showing clinical signs of respiratory disease. All isolates were identified as EHV-2, EHV-4, EHV-5 or untyped EHV. Of the horses and foals tested, 59/82 (72%) were positive for EHV-1 and/or EHV-4 serum neutralising (SN) antibody on at least one sampling occasion, 52/82 (63%) for EHV-1-specific antibody tested by enzyme-linked immunosorbent assay (ELISA), 10/80 (13%) for ERAV SN antibody, 60/80 (75%) for ERBV SN antibody, and 42/80 (53%) for haemagglutination inhibition (HI) antibody to EAdV-1. None of the 64 serum samples tested were positive for antibodies to EAV, reovirus 3 or PIV3. Evidence of infection with all viruses tested was detected in both healthy horses and in horses showing clinical signs of respiratory disease. Recent EHV-2 infection was associated with the development of signs of respiratory disease among yearlings [relative risk (RR)=2.67, 95% CI=1.59-4.47, p=0.017].

CONCLUSIONS: Of the equine respiratory viruses detected in horses in New Zealand during this study, EHV-2 was most likely to be associated with respiratory disease. However, factors other than viral infection are probably important in the development of clinical signs of disease.     

Pathology of maternal genital tract, placenta, and fetus in equine viral arteritis

Six pregnant mares were given equine viral arteritis virus intravenously. Tissues from genital tracts, placentae, and fetuses were examined by light and electron microscopy to study the mechanism of abortion. Four mares which died with acute disease had diffuse vacuolation of endometrial epithelium and systemic necrotizing vasculitis. Two of these mares had dead fetuses and two had live fetuses; virus was isolated from tissues of one live fetus. Placentae of mares dying from acute disease did not have lesions attributable to infection; virus was isolated from two of these placentae. One of the two mares which recovered from clinical disease aborted a dead fetus eight days after inoculation. The mare had severe necrotizing myometritis and virus was isolated from maternal ovaries and from fetal tissues. The fetus did not have lesions attributable to arteritis virus. These results suggest that although fetal death may occur in utero during acute equine viral arteritis, abortion probably is due to lesions in the uterus of the mare.     

定量检测马动脉炎病毒方法的建立

为建立快速、敏感、准确的马动脉炎病毒检测方法,笔者选取病毒基因组中高度保守的ORF7序列设计引物和TaqMan探针,分别使用马动脉炎病毒的总RNA和含有选定检测序列的克隆标准品进行一步法实时定量RT-PCR,绘制扩增曲线,两曲线斜率之差小于0.1,证明两者的扩增效率相同,可用选定检测序列的克隆标准品对马动脉炎病毒进行定量检测。     

Status of equine viral arteritis in Kentucky, 1985

Clinical cases of equine arteritis virus infection have not been diagnosed in Kentucky since 1984, and there has been no indication that any of the horses involved in the 1984 epizootic have since been responsible for spread of the disease to horses in other states or other countries. Cases of abortion caused by naturally acquired infection with this virus have not been confirmed in 1984 or 1985. Neither field nor vaccine strains of equine arteritis virus have been shown to induce teratologic abnormalities or the carrier state in foals born to infected or vaccinated mares. The carrier stallion appears to have played a major epidemiologic role in the dissemination and perpetuation of the virus. A commercial modified live equine viral arteritis vaccine was found to be safe and efficacious for stallions and mares. The disease can be controlled by immunizing the stallion population and by restricting the breeding of equine arteritis virus-shedding stallions to vaccinated or seropositive mares, followed by an appropriate period of isolation from other nonvaccinated Equidae.     

Equine arteritis virus: an overview.

The causative agent of the respiratory disease equine viral arteritis is a small, single-stranded RNA virus with a genome organization and replication strategy related to that of coronaviruses and toroviruses. Clinical signs of infection in horses vary widely and severe infection can lead to pregnant mares aborting. Infected horses generally make good recoveries but stallions may become semen shedders of equine arteritis virus (EAV). These carrier stallions play an important role in the dissemination and perpetuation of EAV. Laboratory tests exist to detect virus and the equine immune response to infection. However, vaccines are not currently licensed in the UK to combat viral arteritis, the incidence of which may increase due to changes in European legislation.     

Equine viral arteritis

Equine viral arteritis is reviewed with specific reference to clinical features, etiology, transmission, diagnosis, epidemiology, and current methods for the control of this disease. There is evidence of variation in pathogenicity among strains of equine arteritis virus. Virus transmission occurs primarily by the respiratory and venereal routes during the acute phase of the infection. The long-term carrier stallion appears to play a major epidemiological role in dissemination and perpetuation of the virus. Unlike the stallion, the carrier state has yet to be demonstrated in the mare or foal. A commercial modifiedlive equine arteritis virus vaccine has been shown to be safe and efficacious for stallions and mares. The disease can be controlled by identification and isolation of carrier stallions, immunization of seronegative stallions, and by restricting the breeding of equine arteritis virus-shedding stallions to equine arteritis virus vaccinated or seropositive mares.     

A survey of respiratory viruses in New Zealand horses

AIMS: To determine which viruses circulate among selected populations of New Zealand horses and whether or not viral infections were associated with development of respiratory disease.

METHODS: Nasal swabs were collected from 33 healthy horses and 52 horses with respiratory disease and tested by virus isolation and/or PCR for the presence of equine herpesviruses (EHV) and equine rhinitis viruses.

RESULTS: Herpesviruses were the only viruses detected in nasal swab samples. When both the results of nasal swab PCR and virus isolation were considered together, a total of 41/52 (79%) horses with respiratory disease and 2/32 (6%) healthy horses were positive for at least one virus. As such, rates of virus detection were significantly higher (p<0.001) in samples from horses with respiratory disease than from healthy horses. More than half of the virus-positive horses were infected with multiple viruses. Infection with EHV-5 was most common (28 horses), followed by EHV-2 (27 horses), EHV-4 (21 horses) and EHV-1 (3 horses).

CONCLUSIONS: Herpesviruses were more commonly detected in nasal swabs from horses with respiratory disease than from healthy horses suggesting their aetiological involvement in the development of clinical signs among sampled horses. Further investigation to elucidate the exact relationships between these viruses and respiratory disease in horses is warranted.

CLINICAL RELEVANCE: Equine respiratory disease has been recognised as an important cause of wastage for the equine industry worldwide. It is likely multifactorial, involving complex interactions between different microorganisms, the environment and the host. Ability to control, or minimise, the adverse effects of equine respiratory disease is critically dependent on our understanding of microbial agents involved in these interactions. The results of the present study update our knowledge on the equine respiratory viruses currently circulating among selected populations of horses in New Zealand.     

马病毒性动脉炎诊断技术研究进展

马病毒性动脉炎(EVA)是马属动物之间通过呼吸道或生殖器官传播的传染病,是危害养马业及赛马比赛的重要疾病之一,应用各种诊断技术对该病做出准确的诊断是预防和控制该病的前提.EVA的诊断技术包括检测病毒,检测血清抗体,涉及的技术和方法包括病毒的分离及中和试验、血凝及血凝抑制试验、免疫荧光试验以及酶联免疫吸附试验等.每种诊断技术都有其各自的优势和局限性,应根据目的及工作条件等综合情况予以选择,论文就各种诊断技术的原理、方法及特点进行了概述和比较,并对今后的应用前景和发展趋势进行了展望.     

Viruses associated with respiratory disease of horses in New Zealand: an update

Viruses causing or associated with respiratory disease in horses worldwide are reviewed. Results are presented from a serological survey of 121 New Zealand foals and horses that had been affected by respiratory disease, determining the prevalence of antibodies in this country to the major viruses associated with similar disease overseas. To date there is no evidence of equine influenza virus in New Zealand. Both equine herpesvirus type 1 and 2 have been frequently isolated and show high serological prevalences. Serological evidence of equine rhinovirus type 1 and type 2 is presented with a prevalence of 12.3% and 41.2% respectively observed in foal sera, and 37.7% and 84.9% in adult horse sera. Antibody reacting to equine viral arteritis virus antigen was detected in 3/121 test sera. Equine adenovirus has been isolated on occasions and has shown a 39% serological prevalence in one study reviewed. Progress in New Zealand equine virus research is discussed.     

Equine disease surveillance, April to June 2010

Recent outbreaks of equine infectious anaemia and equine viral arteritis in the UK. Update on the equine infectious anaemia situation in Europe. West Nile virus reported in several Mediterranean countries. Current and future approaches to equine viral arteritis control in the UK. These are among matters discussed in the quarterly equine disease surveillance report for April to June 2010, prepared by Defra, the Animal Health Trust and the British Equine Veterinary Association.     

An Outbreak of Type A2 Influenza Among Horses

The clinical diagnosis of equine influenza was first based on the spectacular contagiousness of the disease, the general clinical resemblances to human influenza and the almost complete absence of complications usually observed in infectious viral arteritis, viral rhinopneumonitis or in other respiratory infections of the horses. The specific viral etiology of the epizootic was ascertained through the isolation of a type A influenza virus and further substantiated by evaluation of the immunological response of the sick horses, as demonstrated by complement fixation and hemagglutination-inhibition tests, using normal and convalescent sera.     

马动脉炎病毒大囊膜糖蛋白真核表达载体的构建与瞬时表达

将马动脉炎病毒大囊膜糖蛋白基因GL插入真核表达载体pVAX1中构建真核表达载体pVAX1-GL，酶切和测序结果表明构建是正确的，用脂质体转染试剂将其转染BHK-21细胞并通过问接免疫荧光试验检测其在体外的表达情况，结果在转染的细胞表面观察到绿色荧光，证明基因得到了表达，而对照则无绿色荧光，本研究为马动脉炎基因疫苗的研究奠定了基础。