EPIZOOTIOLOGY OF BLUETONGUE: THE SITUATION IN THE UNITED STATES OF AMERICA

Bluetongue was first reported in the United States in 1948 in sheep in Texas. The virus has now been isolated from sheep in 19 States. When the disease first occurs in a flock, the morbidity may reach 50 to 75% and mortality 20 to 50%. In subsequent years, the morbidity may be only 1 to 2% with very few deaths. Difference in breed susceptibility has not been observed. Natural bluetongue infection has not been observed in Angora or dairy goats. Bluetongue virus was first isolated from cattle, in Oregon, in 1959. The virus has now been isolated from cattle in 13 States. In cattle, the disease is usually inapparent but can cause mild to severe clinical disease and neonatal losses. Natural clinical bluetongue has also been reported in bighorn sheep, exotic ruminants in a zoo, mule deer, and white-tailed deer. Serological evidence of exposure to the virus has also been found in other species of ruminants in the wild. Inoculation of virulent bluetongue virus, vaccine virus, or natural disease can cause congenital deformities and neonatal losses in calves, lambs, and white-tailed deer fawns. Culicoides is considered the important insect vector of bluetongue. The virus has also been isolated from sheep keds and cattle lice. U.S. field strains of the virus fit into four serologic groups. No cross reactions were found between bluetongue and epizootic haemorrhagic disease of deer viruses. Cattle are considered significant virus reservoirs. It is necessary to use washed erythrocytes, rather than whole blood, and to inoculate susceptible sheep, rather than embryonated chicken eggs, to detect longer-term viraemia in cattle.     

Neurological diseases of ruminant livestock in Australia. IV: viral infections

Most viral infections that affect the central nervous system of ruminants are exotic to Australia. As such, this review focuses on viruses of importance in Australian ruminants, including Akabane virus and the ruminant pestiviruses, bovine viral diarrhoea virus and border disease virus, as well as bluetongue virus. Each virus is discussed in terms of pathogenesis, clinical signs and diagnosis.     

Will bluetongue come on the wind to the United Kingdom in 2007?

In 2006, over 2000 cases of bluetongue were recorded in northern Europe. The disease, which has been more typically associated with Mediterranean areas, is believed to have become established hundreds of kilometres to the north of its traditional area, probably as a consequence of the hottest summer/autumn period since records began. In this special article, John Gloster and colleagues describe the meteorological conditions surrounding the 2006 outbreak, and investigate the possibility of bluetongue virus (BTV) spreading on the wind to the UK in 2007. For this to happen there would need to be a source of windborne virus, together with a susceptible population of ruminants in the vicinity of the coast. Evidence from outbreaks in the Mediterranean Basin suggests that long-distance transport of BTV-infected vectors has already occurred, at least in that region. The overall likelihood of this occurring in northern Europe depends critically on whether the virus overwinters on the near continent; this will not be known until around May 2007. The 2006 outbreak has highlighted the importance of understanding the impact of climate change on animal disease.     

Bovine infection with bluetongue virus with special emphasis on European serotype 8

Bluetongue virus (BTV) is an arthropod-borne virus infecting domestic and wild ruminants. Infection in cattle is commonly asymptomatic and characterised by a long viraemia. Associated with the emergence and the recrudescence of BTV serotype 8 (BTV-8) in Northern and Central Europe, remarkable differences have been noticed in the transmission and in the clinical expression of the disease, with cattle showing clinical illness and reproductive disorders such as abortion, stillbirth and fetal abnormalities. Several investigations have already indicated the putative ability of the European BTV-8 strain to cross the bovine placenta and to cause congenital infections. The current epidemiological and pathological findings present an unusual picture of the disease in affected bovines.     

Epizootic heamorragic disease

Epizootic haemorrhagic disease (EHD) is an infectious non-contagious viral disease transmitted by insects of the genus Culicoides which affects wild and domestic ruminants. The causative agent, the epizootic haemorrhagic disease virus (EHDV), belongs to the family Reoviridae, genus Orbivirus and shares many morphological and structural characteristics with the other members of the genus such as bluetongue, African horse sickness and equine encephalosis viruses. In recent years EHD outbreaks have been reported in countries bordering the European Union. They caused disease in cattle and severe repercussion on the livestock industry of the affected countries. In the light of recent European bluetongue epizootic these events pose an increasing threat to the European Union. This review includes the most recent information regarding the virus and the disease as well as tools for its diagnosis and control. It is our conviction that more attention should be drawn to both EHDV and the disease itself in order to fulfil all these gaps and not to be unprepared in case future possible incursions.     

Evidence for the presence of bluetongue virus in Kosovo between 2001 and 2004

In 2001, clinical cases of bluetongue were observed in Kosovo, and in that year and in 2003 and 2004, serum samples were collected from cattle and small ruminants and tested for antibodies to bluetongue virus. The results provide evidence that bluetongue virus was not present in Kosovo before the summer of 2001, but that the virus circulated subclinically among the cattle and sheep populations of Kosovo in 2002, 2003 and 2004.     

Vaccines for bluetongue

Isolation of 8 serotypes of bluetongue virus (BTV) in Australia has led to widespread debate on how to prepare for an outbreak of bluetongue disease and the type of vaccine best suited to control bluetongue in Australia. This article describes the vaccine options under consideration by research workers and animal health administrators. The most widely discussed options are live attenuated virus, killed virus and virus-like particles (VLP) generated by recombinant baculoviruses. Attenuated virus vaccines are cheap and easy to produce and are administered in a single dose. They replicate in sheep without causing significant clinical effects and provide protection against challenge with virulent virus of the same serotype. The possibility that insects could acquire vaccine virus by feeding on vaccinated animals and transmit it to sheep or cattle cannot be eliminated. This poses a risk because attenuated viruses are teratogenic if ewes are infected in the first half of pregnancy. In addition, vaccine virus replication in insects and ruminants may lead to a reversion to virulence. Killed virus vaccines have been shown to be efficacious in small laboratory trials and cannot be transmitted to other animals in the field, but are significantly more expensive to produce than attenuated viruses and require at least 2 doses with adjuvant to elicit an immune response. More work is needed to properly assess their effectiveness and determine their cost of production. Recombinant VLP contain the 4 major structural proteins of BTV but no nucleic acid. VLP are relatively easy to isolate, but it is unlikely that the purification methods currently used in laboratories will be adapted for use commercially. Despite the enthusiasm of recent years, little commercial progress appears to have been made. Although scientific research in Australia and overseas has provided a number of options for development of bluetongue vaccines, the decisions on which to use in an outbreak are complex and will require, not only consideration of factors discussed here, but also agreement from industry and government.     

Attenuation of a strain of rinderpest virus: potential homologous live vaccine

Peste des petits ruminants (PPR) is a highly contagious disease of small ruminants frequently associated with severe mortality in these hosts. In countries where it occurs, PPR represents an important constraint to the improved productivity of sheep and goats. Until now the only way to combat this plague has been the use of heterologous rinderpest vaccine; all attempts to develop a homologous vaccine have ended in failure. The present communication describes the attenuation of the Nigerian strain PPRV Nig 75/1 by serial passage in Vero cells. The avirulent virus obtained has the same characteristics as Plowright and Ferris' rinderpest vaccine. The virus is advanced as a potential homologous vaccine against PPR.     

Serological survey of ruminants in some Caribbean and South American countries for type-specific antibody to bluetongue and epizootic haemorrhagic disease viruses

The results of a serological survey of ruminant livestock in some countries of the Caribbean and South America for type-specific antibody to bluetongue virus are reported. Using the microneutralisation test with the international serotypes 1 to 22 of bluetongue virus, antibodies to several types were detected. Analysis of the data indicated that in 1981-82 bluetongue virus types 6, 14 and 17, or viruses closely related to them, were infecting ruminants in this region of the world. Antibody to the related virus of epizootic haemorrhagic disease (serotype 1) was also detected in cattle. The difficulty in interpreting the epidemiological significance of data generated by a serological survey of this kind is discussed.     

Bivens arm virus: a new rhabdovirus isolated from Culicoides insignis in Florida and related to Tibrogargan virus of Australia

During field studies in 1981 on the transmission of bluetongue viruses in ruminants in Florida, a virus was isolated from Culicoides insignis collected near water buffalo (Bubalus bubalis) recently imported from Trinidad. Electron microscopy showed that this isolate, for which the name Bivens Arm virus is proposed, has rhabdovirus morphology. Serologic comparisons were made with recognized rhabdoviruses from terrestrial vertebrates and hematophagous arthropods. Indirect fluorescent antibody, complement fixation and neutralization tests indicated antigenic reactivity between Bivens Arm virus and two rhabdoviruses found only in Australia, Tibrogargan and Coastal Plains viruses. The Australian isolates cause subclinical infections in cattle and water buffalo and are believed to be transmitted by Culicoides. Initially, it was thought that Bivens Arm virus may have been introduced to Florida with the water buffalo from Trinidad, but a serologic survey of cattle serum, collected before the importation of the buffalo revealed antibody to the virus in cattle on farms located in diverse areas of Florida.     

Porcine circovirus 2 replication in colostrum-deprived piglets following experimental infection and immune stimulation using a modified live vaccine against porcine respiratory and reproductive syndrome virus

Porcine circovirus type 2 (PCV2) infection is now recognized as the major factor in the development of post-weaning multisystemic wasting syndrome (PMWS). Although Koch's postulates have been fulfilled for PCV2 and PMWS, the severe clinical expression of the disease observed in field cases has been difficult to reproduce experimentally. Some studies have demonstrated that immune stimulation associated with the use of some commercially available swine vaccines may trigger progression of PCV2 infection to disease and lesions characteristic of PMWS. Here we describe the effects on PCV2 infection in an experimental model following the use of a commercially available modified live vaccine to porcine respiratory and reproductive syndrome virus (PRRSV). Although none of the piglets infected with PCV2 developed clinical PMWS, the severity of microscopical lesions and the PCV2 antigen load associated with these lesions were higher in the PRRSV-vaccinated piglets compared with those detected in the PCV2 only infected animals.     

First molecular study of Canine herpesvirus-1 in reproductive specimens of adult dogs in southeast of Iran

Canine herpesvirus-1 (CHV-1) is recognized to be enzootic in the dog population with a widespread distribution. This pathogen leads to a lethal generalized illness in newborn puppies and is associated with reproductive disorders. CHV-1 should be considered as an important pathogen of neonatal death and infertility; so, it appears to pose a threat for breeding kennels. Although serologic data point to the circulation of CHV-1 among dogs of Iran are available, no definitive diagnosis has been conducted based on the molecular assay. So, this research was done to detect the prevalence of CHV-1 in dogs of Kerman. In this study, the presence of CHV-1 in vaginal specimens and biopsies of the uterus of dogs referring to the Veterinary Hospital of Shahid Bahonar University of Kerman was determined. Fifteen uterine samples and seven vaginal samples were included in group of the pregnant dogs. Moreover, thirteen uterine samples and twenty vaginal samples were related to the dogs displaying suspicious clinical signs such as reproductive disorders. Samples were collected and evaluated using real-time PCR. Viral DNA was detected in 21 samples from a total of 140 (15 %) collected samples which were related to 14 uterine samples (20 %) and 7 (10 %) vaginal specimens. The association of this virus with age, breed, housing, pregnancy and reproductive disorders was not significant. Five positive reproductive samples were belonged to the dogs with a history of reproductive disorders including pyometra, metritis, stillbirths, vaginitis and vaginal prolapse. This study is the first molecular detection of CHV-1 in reproductive samples of dogs in Iran. Considering the significant prevalence of this virus, it is necessary to carry out management measures in controlling and preventing this disease. Tracing CHV-1 requires further research on this virus in dogs of this region.     

Susceptibility of in vitro produced hatched bovine blastocysts to infection with bluetongue virus serotype 8

ABSTRACT: Bluetongue virus serotype 8 (BTV-8), which caused an epidemic in ruminants in central Western Europe in 2006 and 2007, seems to differ from other bluetongue serotypes in that it can spread transplacentally and has been associated with an increased incidence of abortion and other reproductive problems. For these reasons, and also because BTV-8 is threatening to spread to other parts of the world, there is a need for more information on the consequences of infection during pregnancy. The aim of the present study was to investigate whether hatched (i.e. zona pellucida-free) in vitro produced bovine blastocysts at 8-9 days post insemination are susceptible to BTV-8 and whether such infection induces cell death as indicated by apoptosis. Exposure of hatched in vitro produced bovine blastocysts for 1 h to a medium containing 103.8 or 104.9 TCID50 of the virus resulted in active viral replication in between 25 and 100% of the cells at 72 h post exposure. The infected blastocysts also showed growth arrest as evidenced by lower total cell numbers and a significant level of cellular apoptosis. We conclude from this in vitro study that some of the reproductive problems that are reported when cattle herds are infected with BTV-8 may be attributed to direct infection of blastocysts and other early-stage embryos in utero.     

Experimental inoculation of late term pregnant sows with a field isolate of porcine reproductive and respiratory syndrome vaccine-derived virus.

The use of a live attenuated porcine reproductive and respiratory syndrome virus (PRRSV) vaccine in piglets has been associated with reproductive disorders in non-vaccinated sows. Vaccine-derived virus (VDV) has been isolated from foetuses, stillborn pigs, and dead piglets, indicating that the live vaccine spread from vaccinated piglets to non-vaccinated sows, and that the virus might be implicated in the severe reproductive problems observed. In the present study, one such VDV isolate was used to experimentally infect pregnant sows in the last trimester. The chosen isolate, which had more than 99.6% identity to the attenuated vaccine virus, originated from the lungs of a stillborn pig from a swine herd with a sudden high level of stillborn pigs and increased piglet mortality in the nursing period. Intranasal inoculation of sows with the virus isolate resulted in congenital infection, foetal death, and preweaning pig mortality. As such, the present study showed that vaccine-derived PRRSV can cause disease in swine consistent with PRRS.     

Bluetongue: history, global epidemiology, and pathogenesis

Bluetongue is an arthropod-transmitted viral disease of ruminants and certain other animals that was recognized and described more than 100 years ago in southern Africa. Bluetongue virus (BTV) infection of ruminants and vector Culicoides insects is enzootic throughout tropical and temperate regions of the world; however, there have been drastic recent regional alterations in the global distribution of BTV infection, particularly in Europe since 1998. Multiple novel BTV serotypes also have been detected since 1998 in the south-eastern United States, apparently encroaching from the adjacent Caribbean ecosystem, and novel serotypes of BTV have been identified recently in other historically enzootic regions of the world, including the Middle East and Australia. It has been proposed, but certainly not proven, that global climate change is responsible for these events. BTV infection of ruminants is often subclinical, but outbreaks of severe disease occur with regular frequency especially at the upper and lower limits of the virus' global range where infection is highly seasonal - occurring in the late summer and autumn. Bluetongue disease results from vascular injury, likely through a process analogous to that of human hemorrhagic viral fevers in which production of vasoactive mediators from virus-infected macrophages and dendritic cells results in enhanced endothelial paracellular permeability with subsequent vascular leakage and hypovolemic shock.     

A new bluetongue virus serotype isolated in Kenya.

An apparently new strain of bluetongue virus was first isolated in Kenya in 1965 and since, has been obtained on 7 further occasions from diseased sheep during clinical outbreaks of disease. It proved to be serologically different from the 16 bluetongue virus strains then held at this laboratory. The virus was modified by passage in embryonated hens eggs to produce a live virus strain suitable for inclusion in a polyvalent vaccine. Recent neutralisation tests, carried out with 24 guinea pig immune sera prepared at Pirbright against the currently known World serotypes, have confirmed the earlier results and show that it is different from any of the existing serotypes.     

鹿流行性出血病病毒双抗夹心ELISA方法的建立

为建立鹿流行性出血病病毒(EHDV)病原学检测方法,用纯化的抗EHDV特异性单克隆抗体包被ELISA板,用兔抗EHDV IgG作为夹心抗体,IgG作为夹心抗体建立EHDV双抗夹心ELISA方法,并对该方法的特异性和敏感性进行了试验.用ELISA分别检测EHDV、蓝舌病病毒(BTV)、水疱性口炎病毒(VSV)、赤羽病病毒...     

蓝舌病在全球的分布概况

蓝舌病为OIE规定的需通报疫病，我国将其列为一类动物疫病。该病已经给全球大部分流行地区造成巨大经济损失。我国于1979年首次证明该病存在，且在我国流行初期即造成大量易感动物死亡，给我国畜牧业带来了重大经济损失。但蓝舌病在我国仍属冷门研究方向，我国到底分离鉴定出多少个血清型的蓝舌病病毒，该病在我国的分布范围到底有多广？许多畜牧兽医工作者对这些问题并不是非常清楚。特别是在近年来鲜有蓝舌病引起动物发病死亡报道的前提下，人们对蓝舌病的重视程度进一步降低。本文对蓝舌病在全球的流行概况进行简要阐述，同时，对蓝舌病在我国40年的流行情况进行回顾，希望该病在我国能够得到足够的重视。     

小反刍兽疫研究现状

小反刍兽疫(Peste des petits ruminants,PPR)是由小反刍兽疫病毒(Peste des petits ruminants virus,PPRV)引起的一种主要感染小反刍动物的急性、接触性传染病,发病率、死亡率高.近年来,小反刍兽疫(PPR)呈扩散的趋势,成为重要的跨国动物传染病之一,我国周边国家频繁器发该病.2007年7月25日暴发于西藏自治区日土县的我国首例小反刍尊疫疫情,更是对我国如何做好该病的防控工作提出了新的要求和挑战.为了增强广大兽医工作者和相关人士对本病的认识,文中就小反刍兽疫的病原学、流行病学、临床症状、病理特征以及诊断方法等方面的研究现状进行了综述.