Bluetongue virus serotype 8-associated congenital hydranencephaly in calves

North American Arboviruses and White-Tailed Deer (Odocoileus virginianus): Associated Diseases and Role in Transmission

Background: Arboviral disease is of increasing concern to human and animal health professionals as emerging and re-emerging arboviruses are more frequently recognized. Wildlife species are known to play a role in the transmission and maintenance of arboviruses and infections can result in morbidity and mortality in wildlife hosts. Materials and Methods: In this review, we detail existing evidence of white-tailed deer (Odocoileus virginianus) as an important host to a diverse collection of arboviruses and evaluate the utility of this species as a resource to better understand the epidemiology of related viral diseases. Results: Relevant veterinary and zoonotic viral pathogens endemic to North America include epizootic hemorrhagic disease virus, bluetongue virus, orthobunyaviruses, vesicular stomatitis virus, Eastern equine encephalitis virus, West Nile virus, and Powassan virus. Exotic viral pathogens that may infect white-tailed deer are also identified with an emphasis on zoonotic disease risks. The utility of this species is attributed to the high degree of contact with humans and domestic livestock and evidence of preferential feeding by various insect vectors. Conclusions: There is mounting evidence that white-tailed deer are a useful, widely available source of information regarding arboviral circulation, and that surveillance and monitoring of deer populations would be of value to the understanding of certain viral transmission dynamics, with implications for improving human and domestic animal health.

Vaccination as a Strategy to Prevent Bluetongue Virus Vertical Transmission

Bluetongue virus (BTV) produces an economically important disease in ruminants of compulsory notification to the OIE. BTV is typically transmitted by the bite of Culicoides spp., however, some BTV strains can be transmitted vertically, and this is associated with fetus malformations and abortions. The viral factors associated with the virus potency to cross the placental barrier are not well defined. The potency of vertical transmission is retained and sometimes even increased in live attenuated BTV vaccine strains. Because BTV possesses a segmented genome, the possibility of reassortment of vaccination strains with wild-type virus could even favor the transmission of this phenotype. In the present review, we will describe the non-vector-based BTV infection routes and discuss the experimental vaccination strategies that offer advantages over this drawback of some live attenuated BTV vaccines.

A Duplex Fluorescent Microsphere Immunoassay for Detection of Bluetongue and Epizootic Hemorrhagic Disease Virus Antibodies in Cattle Sera

Bluetongue virus (BTV) causes internationally reportable hemorrhagic disease in cattle, sheep, and white-tailed deer. The closely related, and often co-circulating, epizootic hemorrhagic disease virus causes a clinically similar devastating disease in white-tailed deer, with increasing levels of disease in cattle in the past 10 years. Transmitted by Culicoides biting midges, together, they constitute constant disease threats to the livelihood of livestock owners. In cattle, serious economic impacts result from decreased animal production, but most significantly from trade regulations. For effective disease surveillance and accurate trade regulation implementation, rapid, sensitive assays that can detect exposure of cattle to BTV and/or EHDV are needed. We describe the development and validation of a duplex fluorescent microsphere immunoassay (FMIA) to simultaneously detect and differentiate antibodies to BTV and EHDV in a single bovine serum sample. Performance of the duplex FMIA for detection and differentiation of BTV and EHDV serogroup antibodies was comparable, with higher sensitivity than commercially available single-plex competitive enzyme-linked immunosorbent assays (cELISA) for detection of each virus antibody separately. The FMIA adds to the currently available diagnostic tools for hemorrhagic orbiviral diseases in cattle as a sensitive, specific assay, with the benefits of serogroup differentiation in a single serum sample, and multiplexing flexibility in a high-throughput platform.

Transmission of Bluetongue Virus Serotype 8 by Artificial Insemination with Frozen-Thawed Semen from Naturally Infected Bulls

Transmission of bluetongue (BT) virus serotype 8 (BTV-8) via artificial insemination of contaminated frozen semen from naturally infected bulls was investigated in two independent experiments. Healthy, BT negative heifers were hormonally synchronized and artificially inseminated at oestrus. In total, six groups of three heifers received semen from four batches derived from three bulls naturally infected with BTV-8. Each experiment included one control heifer that was not inseminated and that remained BT negative throughout. BTV viraemia and seroconversion were determined in 8 out of 18 inseminated heifers, and BTV was isolated from five of these animals. These eight heifers only displayed mild clinical signs of BT, if any at all, but six of them experienced pregnancy loss between weeks four and eight of gestation, and five of them became BT PCR and antibody positive. The other two infected heifers gave birth at term to two healthy and BT negative calves. The BT viral load varied among the semen batches used and this had a significant impact on the infection rate, the time of onset of viraemia post artificial insemination, and the gestational stage at which pregnancy loss occurred. These results, which confirm unusual features of BTV-8 infection, should not be extrapolated to infection with other BTV strains without thorough evaluation. This study also adds weight to the hypothesis that the re-emergence of BTV-8 in France in 2015 may be attributable to the use of contaminated bovine semen.

Clinical cases of Bluetongue serotype 8 in calves in France in the 2018-2019 winter

Bluetongue virus serotype 8 (BTV-8) caused an epizootic in Europe in 2006/09. Transplacental transmission of BTV-8 was demonstrated leading to abortions, congenital malformations or nervous clinical signs in newborn calves. BTV-8 re-emerged in France in 2015. Although the re-emergent strain is nearly genetically identical to the one that had circulated in 2006/2009, it has caused very few clinical cases. However, from mid-December 2018 to April 2019, cases of calves with congenital malformations or displaying nervous clinical signs occurred in some departments (French administrative unit) in mainland France. Blood samples from these animals were sent to local laboratories, and the positive ones were confirmed at the French Bluetongue reference laboratory (BT-NRL). Out of 580 samples found positive at the local laboratories, 544 were confirmed as RT-PCR BTV-8 positive. The 36 samples found positive in the local laboratories and negative in the BT-NRL were all at the limit of RT-PCR detection. Hundred eighty-eight of the confirmed samples were also tested for the presence of Schmallenberg virus (SBV) and bovine virus diarrhoea virus (BVDV) infection: 4 were found positive for BVDV and none for SBV. The main clinical signs recorded for 244 calves, for which a reporting form was completed by veterinarians, included nervous clinical signs (81%), amaurosis (72%) and decrease/ no suckling reflex (40%). Hydranencephaly and microphthalmia were reported in 19 calves out of 27 in which a necropsy was practiced after death or euthanasia. These results indicate that the re-emergent strain of BTV-8 can cross the transplacental barrier and cause congenital malformations or nervous clinical signs in calves.

Failure to Remove Bluetongue Serotype 8 Virus (BTV-8) From in vitro Produced and in vivo Derived Bovine Embryos and Subsequent Transmission of BTV-8 to Recipient Cows After Embryo Transfer

The behavior of BTV-8 in cattle is different from most other serotypes not only with regards to clinical signs but certainly with respect to virus transmission (transplacental, contact). Therefore, the possibility of virus transmission by means of embryo transfer was examined by in vitro exposure of in vitro produced and in vivo derived bovine blastocysts to BTV-8 followed by different washing protocols, including longer exposure times (up to 120 s) to 0.25% trypsin at room temperature or at 37°C. None of the washing protocols used was successful in removing the viral genome completely from the in vitro produced and in vivo derived embryos as was demonstrated by real-time PCR. Moreover, BTV-8 virus was transmitted to recipient cows after embryo transfer of in vivo derived BTV8-exposed embryos, which had been subjected to routine decontamination as recommended by IETS, consisting of 5 washes in PBS followed by a double treatment of 0.25% trypsin for 45s at 37°C, and an additional 5 washes in PBS with 2% FCS. This study clearly demonstrates the necessity of vigorous application of the directives for screening of potential donors and the collected embryos, especially in regions with BTV-8, to prevent transmission of the disease.

Reliable and Standardized Animal Models to Study the Pathogenesis of Bluetongue and Schmallenberg Viruses in Ruminant Natural Host Species with Special Emphasis on Placental Crossing

Starting in 2006, bluetongue virus serotype 8 (BTV8) was responsible for a major epizootic in Western and Northern Europe. The magnitude and spread of the disease were surprisingly high and the control of BTV improved significantly with the marketing of BTV8 inactivated vaccines in 2008. During late summer of 2011, a first cluster of reduced milk yield, fever, and diarrhoea was reported in the Netherlands. Congenital malformations appeared in March 2012 and Schmallenberg virus (SBV) was identified, becoming one of the very few orthobunyaviruses distributed in Europe. At the start of both epizootics, little was known about the pathogenesis and epidemiology of these viruses in the European context and most assumptions were extrapolated based on other related viruses and/or other regions of the World. Standardized and repeatable models potentially mimicking clinical signs observed in the field are required to study the pathogenesis of these infections, and to clarify their ability to cross the placental barrier. This review presents some of the latest experimental designs for infectious disease challenges with BTV or SBV. Infectious doses, routes of infection, inoculum preparation, and origin are discussed. Particular emphasis is given to the placental crossing associated with these two viruses.

Review of Diagnostic Procedures and Approaches to Infectious Causes of Reproductive Failures of Cattle in Australia and New Zealand

Infectious causes of reproductive failure in cattle are important in Australia and New Zealand, where strict biosecurity protocols are in place to prevent the introduction and spread of new diseases. Neospora caninum ranks highly as an important cause of reproductive wastage along with fungal and bacterial infections. Brucella, a leading cause of abortion elsewhere in the world, is foreign, following successful programs to control and eradicate the disease. Leptospirosis in cattle is largely controlled by vaccination, while Campylobacter and Tritrichomonas infections occur at low rates. In both countries, Bovine Viral Diarrhea virus (BVDV) infection rates as the second most economically important disease of cattle and one that also has an effect on reproduction. Effective disease control strategies require rapid diagnoses at diagnostic laboratories. To facilitate this process, this review will discuss the infectious causes of reproductive losses present in both countries, their clinical presentation and an effective pathway to a diagnosis.

Emergence of bluetongue virus serotype 4 in mainland France in November 2017

In November 2017, a 15-day-old calf located in France (Haute-Savoie department) was found positive for bluetongue virus (BTV) RNA by RT-PCR. Laboratory investigations allowed the isolation and identification of the serotype: BTV-4. The analysis of the full viral genome showed that all the 10 genome segments were closely related to BTV-4 strains involved in a large BT outbreak in the Balkan Peninsula, in Italy since 2014 and in Corsica since the end of October 2016. These results together with epidemiological data suggest that BTV-4 has been introduced to mainland France from Corsica or Italy where BTV-4 outbreaks have been reported in summer and autumn 2016. This is the first report of the introduction of BTV-4 in mainland France.

Teratogenic bluetongue and related orbivirus infections in pregnant ruminant livestock: timing and pathogen genetics are critical

Congenital infections of domestic animals with viruses in several families, including Bunyaviridae, Flaviridae, Parvoviridae, and Reoviridae, are the cause of naturally occurring teratogenic central nervous system and/or musculoskeletal defects (arthrogryposis) in domestic animals. Congenital infections of ruminant livestock with bluetongue virus (BTV) and some related members of the genus Orbivirus (family Reoviridae) have clearly shown the critical role of gestational age at infection in determining outcome. Specifically, fetuses infected prior to mid-gestation that survive congenital BTV infection are born with cavitating central nervous system defects that range from severe hydranencephaly to cerebral cysts (porencephaly). Generally, the younger the fetus (in terms of gestational age) at infection, the more severe the teratogenic lesion at birth. Age-dependent virus infection and destruction of neuronal and/or glial cell precursors that populate the developing central nervous system are responsible for these naturally occurring virus-induced congenital defects of animals, thus lesions are most severe when progenitor cells are infected prior to their normal migration during embryogenesis. Whereas congenital infection is characteristic of certain BTV strains, notably live-attenuated (modified-live) vaccine viruses that have been passaged in embryonating eggs, transplacental transmission is not characteristic of many field strains of the virus and much remains to be determined regarding the genetic determinants of transplacental transmission of individual virus strains.

Ring trial 2016 for Bluetongue virus detection by real-time RT-PCR in France

Since the unexpected emergence of BTV‐8 in Northern Europe and the incursion of BTV‐8 and 1 in France in 2006–2007, molecular diagnosis has considerably evolved. Several real‐time RT‐PCR (rtRT‐PCR) methods have been developed and published, and are currently being used in many countries across Europe for BTV detection and typing. In France, the national reference laboratory (NRL) for orbiviruses develops and validates ‘ready‐to‐use’ kits with private companies for viral RNA detection. The regional laboratories network that was set up to deal with a heavy demand for analyses has used these available kits. From 2007, ring tests were organized to monitor the performance of the French laboratories. This study presents the results of 63 regional laboratories in the ring trial organized in 2016. Blood samples were sent to the laboratories. Participants were asked to use the rtRT‐PCR methods in place in their laboratory, for detection of all BTV serotypes and specifically BTV‐8. The French regional laboratories are able to detect and genotype BTV in affected animals. Despite the use of several methods (i.e. RNA extraction and different commercial rtRT‐PCRs), the network is homogeneous. The ring trial demonstrated that the French regional veterinary laboratories have reliable and robust BTV diagnostic tools for BTV genome detection.

A Review of Knowledge Gaps and Tools for Orbivirus Research

Although recognized as causing emerging and re-emerging disease outbreaks worldwide since the late 1800 s, there has been growing interest in the United States and Europe in recent years in orbiviruses, their insect vectors, and the diseases they cause in domestic livestock and wildlife. This is due, in part, to the emergence of bluetongue (BT) in northern Europe in 2006-2007 resulting in a devastating outbreak, as well as severe BT outbreaks in sheep and epizootic hemorrhagic disease (EHD) outbreaks in deer and cattle in the United States. Of notable concern is the isolation of as many as 10 new BT virus (BTV) serotypes in the United States since 1999 and their associated unknowns, such as route of introduction, virulence to mammals, and indigenous competent vectors. This review, based on a gap analysis workshop composed of international experts on orbiviruses conducted in 2013, gives a global perspective of current basic virological understanding of orbiviruses, with particular attention to BTV and the closely related epizootic hemorrhagic disease virus (EHDV), and identifies a multitude of basic virology research gaps, critical for predicting and preventing outbreaks.

Sequence analysis and evaluation of the NS3/A gene region of bluetongue virus isolates from South Africa

Phylogenetic networks and sequence analysis allow a more accurate understanding of the serotypes, genetic relationships and epidemiology of viruses. Based on gene sequences of the conserved segment 10 (NS3), bluetongue virus (BTV) can be divided into five topotypes. In this molecular epidemiology study, segment 10 sequence data of 11 isolates obtained from the Virology Section of the Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, were analyzed and compared to sequence data of worldwide BTV strains available in the GenBank database. The consensus nucleotide sequences of NS3/A showed intermediate levels of variation, with the nucleotide sequence identity ranging from 79.72 % to 100 %. All 11 strains demonstrated conserved amino acid characteristics. Phylogenetic networks were used to identify BTV topotypes. The phylogeny obtained from the nucleotide sequence data of the NS3/A-encoding gene presented three major and two minor topotypes. The clustering of strains from different geographical areas into the same group indicated spatial spread of the segment 10 genes, either through gene reassortment or through the introduction of new strains from other geographical areas via trade. The effect of reassortment and genetic drift on BTV and the importance of correct serotyping to identify viral strains are highlighted.

Re-Emergence of Bluetongue Virus Serotype 8 in France, 2015

At the end of August 2015, a ram located in central France (department of Allier) showed clinical signs suggestive of BTV (Bluetongue virus) infection. However, none of the other animals located in the herd showed any signs of the Bluetongue disease. Laboratory analyses identified the virus as BTV serotype 8. The viro and sero prevalence intraherd were 2.4% and 8.6% in sheep and 18.3% and 42.9% in cattle, respectively. Phylogenetic studies showed that the sequences of this strain are closely related to another BTV-8 strain that has circulated in France in 2006-2008. The origin of the outbreak is unclear but it may be assumed that the BTV-8 has probably circulated at very low prevalence (possibly in livestock or wildlife) since its first emergence in 2007-2008.

Virus-induced congenital malformations in cattle

Diagnosing the cause of bovine congenital malformations (BCMs) is challenging for bovine veterinary practitioners and laboratory diagnosticians as many known as well as a large number of not-yet reported syndromes exist. Foetal infection with certain viruses, including bovine virus diarrhea virus (BVDV), Schmallenberg virus (SBV), blue tongue virus (BTV), Akabane virus (AKAV), or Aino virus (AV), is associated with a range of congenital malformations. It is tempting for veterinary practitioners to diagnose such infections based only on the morphology of the defective offspring. However, diagnosing a virus as a cause of BCMs usually requires laboratory examination and even in such cases, interpretation of findings may be challenging due to lack of experience regarding genetic defects causing similar lesions, even in cases where virus or congenital antibodies are present. Intrauterine infection of the foetus during the susceptible periods of development, i.e. around gestation days 60-180, by BVDV, SBV, BTV, AKAV and AV may cause malformations in the central nervous system, especially in the brain. Brain lesions typically consist of hydranencephaly, porencephaly, hydrocephalus and cerebellar hypoplasia, which in case of SBV, AKAV and AV infections may be associated by malformation of the axial and appendicular skeleton, e.g. arthrogryposis multiplex congenita. Doming of the calvarium is present in some, but not all, cases. None of these lesions are pathognomonic so diagnosing a viral cause based on gross lesions is uncertain. Several genetic defects share morphology with virus induced congenital malformations, so expert advice should be sought when BCMs are encountered.

Schmallenberg virus infection of ruminants: challenges and opportunities for veterinarians

In 2011, European ruminant flocks were infected by Schmallenberg virus (SBV) leading to transient disease in adult cattle but abortions and congenital deformities in calves, lambs, and goat kids. SBV belonging to the Simbu serogroup (family Bunyaviridae and genus Orthobunyavirus) was first discovered in the same region where bluetongue virus serotype 8 (BTV-8) emerged 5 years before. Both viruses are transmitted by biting midges (Culicoides spp.) and share several similarities. This paper describes the current knowledge of temporal and geographical spread, molecular virology, transmission and susceptible species, clinical signs, diagnosis, prevention and control, impact on ruminant health, and productivity of SBV infection in Europe, and compares SBV infection with BTV-8 infection in ruminants.

Ovine and Bovine Congenital Abnormalities Associated With Intrauterine Infection With Schmallenberg Virus

In December 2011, a previously unknown congenital syndrome of arthrogryposis and hydranencephaly in sheep and cattle appeared in the Netherlands as an emerging epizootic due to Schmallenberg virus (SBV). Gross lesions in 102 lambs and 204 calves included porencephaly, hydranencephaly, cerebellar dysplasia and dysplasia of the brainstem and spinal cord, a flattened skull with brachygnathia inferior, arthrogryposis, and vertebral column malformations. Microscopic lesions in the central nervous system showed rarefaction and cavitation in the white matter, as well as degeneration, necrosis, and loss of neurons in the gray matter. Brain and spinal cord lesions were more severe in lambs than in calves. Ovine and bovine cases examined early in the outbreak showed encephalomyelitis. SBV infection was confirmed by real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) in brain samples in 46 of 102 lambs (45%) and in 32 of 204 calves (16%). Immunohistochemistry, performed on tissue samples from 18 RT-qPCR-positive lambs, confirmed the presence of bunyaviral antigen in neurons of the brain in 16 cases. SBV antibodies were detected by enzyme-linked immunosorbent assay in fetal blood in 56 of 61 sampled ovine cases (92%). In a virus neutralization test, all tested dams of affected newborns, 46 ewes and 190 cows, were seropositive. Compared with other teratogenic viral infections, the pathogenesis and lesions of SBV in sheep and cattle fetuses are similar to those of other ruminant orthobunyaviruses. However, the loss of spinal ventral motor neurons and their tracts, resulting in micromyelia, distinguishes SBV infection from other viral central nervous system lesions in newborn ruminants.

Laboratory diagnosis of ruminant abortion in Europe

Abortion in ruminants is a major cause of economic loss worldwide, and the management and control of outbreaks is important in limiting their spread, and in preventing zoonotic infections. Given that rapid and accurate laboratory diagnosis is central to controlling abortion outbreaks, the submission of tissue samples to laboratories offering the most appropriate tests is essential. Direct antigen and/or DNA detection methods are the currently preferred methods of reaching an aetiological diagnosis, and ideally these results are confirmed by the demonstration of corresponding macroscopic and/or histopathological lesions in the fetus and/or the placenta. However, the costs of laboratory examinations may be considerable and, even under optimal conditions, the percentage of aetiological diagnoses reached can be relatively low. This review focuses on the most commonly occurring and important abortifacient pathogens of ruminant species in Europe highlighting their epizootic and zoonotic potential. The performance characteristics of the various diagnostic methods used, including their specific advantages and limitations, are discussed.

Full-Genome Sequencing of Four Bluetongue Virus Serotype 11 Viruses

Recently, a contamination incident was described in which the challenge inoculum used in a bluetongue virus serotype 8 (BTV-8) vaccination trial was contaminated with a BTV-11 virus that was closely related to the Belgian BTV-11 virus from 2008. This study reports the first complete genome sequences of four BTV-11 viruses: the BTV-11 contaminant, BTV-11 reference strain, BTV-11 vaccine strain and a recently isolated BTV-11 field strain from Martinique. Full-genome analysis showed that these viruses belong to serotype 11/nucleotype A and cluster together with other western topotype bluetongue viruses. Detailed comparisons of the genomes further indicated that the contaminant was derived from the BTV-11 reference strain, as they were distinguished by a single synonymous nucleotide substitution. The previously reported partial sequence of genome segment 2 of the Belgian BTV-11 was found to be identical to that of the BTV-11 vaccine strain, indicating that it most likely was the BTV-11 vaccine strain. These findings also suggest that the BTV-11 contaminant and the Belgian BTV-11 are not the same viruses. Finally, comparison of the reference and vaccine strain did not allow determining the amino acid substitutions that contribute to the attenuated phenotype.

Pulmonary artery haemorrhage in newborn calves following bluetongue virus serotype 8 experimental infections of pregnant heifers

The emergence of bluetongue disease (BT) among livestock in Europe in 2006 raised many questions including the occurrence and epidemiological significance of foetal infections in cattle. To clarify these aspects, vaccinated and unvaccinated pregnant heifers were sequentially infected twice in an isolation facility (biosafety level 3) with a northern European outbreak strain of Bluetongue virus serotype 8 (BTV-8). The study was terminated 2 months after calving with necropsy of the dams and their offspring. The cattle were monitored throughout the study by clinical scoring and for the presence of circulating neutralising antibodies, and after calving for the presence of infectious virus and viral RNA in blood and milk. Four calves, one born from a vaccinated dam and three from non-vaccinated ones, that were infected at 120 days of gestation had obvious haemorrhage of the pulmonary artery at necropsy. Although haemorrhage of the pulmonary artery is highly characteristic of BT, viral RNA was not detected in any of these calves. Furthermore, although none of the calves born from heifers infected prior to mid-gestation had teratogenic BTV typical brain lesions, some had lesions at birth suggestive of in utero BTV infection. Despite the lack of viral RNA detection, the presence of haemorrhage of the pulmonary artery deserves to be reported as a new observation in the context of the multiple investigations having as main subject the BTV placental crossing in cattle.

Evidence of transplacental transmission of bluetongue virus serotype 8 in goats

During the incursion of bluetongue virus (BTV) serotype 8 in Europe, an increase in the number of abortions in ruminants was observed. Transplacental transmission of BTV-8 in cattle and sheep, with subsequent foetal infection, is a feature of this specific bluetongue serotype. In this study, BTV-8 ability to cross the placental barrier at the beginning of the second third of pregnancy and at the end of pregnancy was investigated in goats in two separate experiments. In the first experiment, nine goats were experimentally infected with BTV-8 at 61 days of pregnancy. Foetuses were collected 21 dpi. BTV-8 was evidenced by real time RT-PCR and by viral isolation using blood from the umbilical cord and the spleens of 3 out of the 13 foetuses. All dams were viraemic (viral isolation) at the moment of sampling of the foetuses. Significant macroscopic or histological lesions could not be observed in foetuses or in their infected dams (notably at the placenta level). In the second experiment, 10 goats were infected with BTV-8 at 135 days of pregnancy. Kids were born by caesarean section at the programmed day of birth (15 dpi). BTV-8 could not be detected by rt-RT-PCR in blood or spleen samples from the kids. This study showed for the first time that BTV-8 transplacental transmission can occur in goats that have been infected at 61 days of pregnancy, with infectious virus recovered from the caprine foetuses. The observed transmission rate was quite high (33%) at this stage of pregnancy. However, it was not possible to demonstrate the existence of BTV-8 transplacental transmission when infection occurred at the end of the goat pregnancy.

Transplacental transmission of BTV-8 in sheep: BTV viraemia, antibody responses and vaccine efficacy in lambs infected in utero

Bluetongue virus (BTV) is an insect vector transmitted virus which causes an economically important disease in ruminants. BTV infection during pregnancy can result in infection of the foetus, which may lead to the birth of persistently infected or immunotolerant offspring. Since persistently infected animals continuously produce large amounts of virus they could be a source of infection for the insect vector. This could significantly influence the epidemiology of the virus and hence might require additional measures to control a BTV outbreak. Therefore, we investigated the potential of BTV-8 to induce persistent infection or immunotolerance in lambs in an experimental setting. Infection of eighteen 70-75 days pregnant ewes with wild type BTV-8 led to the birth of 25 out of 44 BTV RNA positive lambs (foetal infected, FI). All 23 FI lambs born alive also had anti BTV antibodies at birth; infectious virus could be recovered from 5 out of 25 FI lambs. Viral RNA loads decreased rapidly after birth; 19 out of 20 FI lambs that remained in the experiment until week 14 after birth, were RNA negative at that time. Since persistence of BTV-8 infection could not be demonstrated, we investigated whether foetal infection had an effect on protection against a field virus infection and on efficacy of vaccination. To this end, 5 FI lambs and 5 foetal non-infected (FNI) lambs were vaccinated with the inactivated Bovilis(®) BTV-8 vaccine, five months after birth. Three weeks after the vaccination, all lambs were infected with wild type BTV-8. The foetal infection did not interfere with vaccination efficacy. In contrast, foetal BTV-8 infection induced an immune response which afforded protection against BTV challenge comparable to the level of protection induced by vaccination.

Immunophenotyping of inflammatory cells associated with Schmallenberg virus infection of the central nervous system of ruminants

Schmallenberg virus (SBV) is a recently discovered Bunyavirus associated mainly with abortions, stillbirths and malformations of the skeletal and central nervous system (CNS) in newborn ruminants. In this study, a detailed immunophenotyping of the inflammatory cells of the CNS of affected animals was carried out in order to increase our understanding of SBV pathogenesis. A total of 82 SBV-polymerase chain reaction (PCR) positive neonatal ruminants (46 sheep lambs, 34 calves and 2 goat kids) were investigated for the presence of inflammation in the brain and spinal cord. The study focused on 15 out of 82 animals (18.3%) showing inflammation in the CNS. All 15 neonates displayed lymphohistiocytic meningoencephalomyelitis affecting most frequently the mesencephalon and the parietal and temporal lobes. The majority of infiltrating cells were CD3-positive T cells, followed by CD79α-positive B cells and CD68-positive microglia/macrophages. Malformations like por- and hydranencephaly, frequently found in the temporal lobe, showed associated demyelination and axonal loss. SBV antigen was detected in 37 out of 82 (45.1%) neonatal brains by immunohistochemistry. In particular, SBV antigen was found in 93.3% (14 out of 15 ruminants) and 32.8% (22 out of 67 ruminants) of animals with and without encephalitis, respectively. Highest amounts of virus-protein expression levels were found in the temporal lobe. Our findings suggest that: (i) different brain regions display differential susceptibility to SBV infection; (ii) inflammatory cells in the CNS are found only in a minority of virus infected animals; (iii) malformations occur in association with and without inflammation in the CNS; and (iv) viral antigen is strongly associated with the presence of inflammation in naturally infected animals. Further studies are required to explore the cell tropism and pathogenesis of SBV infection in ruminants.

Transplacental infection in goats experimentally infected with a European strain of bluetongue virus serotype 8

The capability of the recently emerged European strain of bluetongue virus serotype 8 (BTV-8) to cross the ruminant placenta has been established in experimental and field studies in both sheep and cattle. Seroprevalence rates in goats in North-Western Europe were high during the recent outbreak of BTV-8; however the capability of the virus to infect goats through the transplacental route has not been established. In the present study, four Saanen goats were inoculated with the European strain of BTV-8 at 62 days of gestation; this resulted in mild clinical signs, however gross lesions observed post mortem were more severe. Viral RNA was detected by real-time RT-PCR in blood and tissue samples from three fetuses harvested from two goats at 43 days post infection. Conventional RT-PCR and genome sequencing targeting viral segment 2 confirmed infection of brain tissue with BTV-8 in two of these fetuses. In total, five of six fetuses demonstrated lesions that may have been associated with transplacental infection with BTV. Infected fetuses did not demonstrate neurological lesions. Low viral RNA concentrations in fetal blood and tissue further suggest that the infected fetuses would probably not have been born viraemic. The implications of these findings with regards to the epidemiology and overwintering of BTV-8 in Europe remains unclear.

Bluetongue: a historical and epidemiological perspective with the emphasis on South Africa

Bluetongue (BT) is a non-contagious, infectious, arthropod transmitted viral disease of domestic and wild ruminants that is caused by the bluetongue virus (BTV), the prototype member of the Orbivirus genus in the family Reoviridae. Bluetongue was first described in South Africa, where it has probably been endemic in wild ruminants since antiquity. Since its discovery BT has had a major impact on sheep breeders in the country and has therefore been a key focus of research at the Onderstepoort Veterinary Research Institute in Pretoria, South Africa. Several key discoveries were made at this Institute, including the demonstration that the aetiological agent of BT was a dsRNA virus that is transmitted by Culicoides midges and that multiple BTV serotypes circulate in nature. It is currently recognized that BT is endemic throughout most of South Africa and 22 of the 26 known serotypes have been detected in the region. Multiple serotypes circulate each vector season with the occurrence of different serotypes depending largely on herd-immunity. Indigenous sheep breeds, cattle and wild ruminants are frequently infected but rarely demonstrate clinical signs, whereas improved European sheep breeds are most susceptible. The immunization of susceptible sheep remains the most effective and practical control measure against BT. In order to protect sheep against multiple circulating serotypes, three pentavalent attenuated vaccines have been developed. Despite the proven efficacy of these vaccines in protecting sheep against the disease, several disadvantages are associated with their use in the field.

Bluetongue virus genetic and phenotypic diversity: towards identifying the molecular determinants that influence virulence and transmission potential

Bluetongue virus (BTV) is the prototype member of the Orbivirus genus in the family Reoviridae and is the aetiological agent of the arthropod transmitted disease bluetongue (BT) that affects both ruminant and camelid species. The disease is of significant global importance due to its economic impact and effect on animal welfare. Bluetongue virus, a dsRNA virus, evolves through a process of quasispecies evolution that is driven by genetic drift and shift as well as intragenic recombination. Quasispecies evolution coupled with founder effect and evolutionary selective pressures has over time led to the establishment of genetically distinct strains of the virus in different epidemiological systems throughout the world. Bluetongue virus field strains may differ substantially from each other with regards to their phenotypic properties (i.e. virulence and/or transmission potential). The intrinsic molecular determinants that influence the phenotype of BTV have not clearly been characterized. It is currently unclear what contribution each of the viral genome segments have in determining the phenotypic properties of the virus and it is also unknown how genetic variability in the individual viral genes and their functional domains relate to differences in phenotype. In order to understand how genetic variation in particular viral genes could potentially influence the phenotypic properties of the virus; a closer understanding of the BTV virion, its encoded proteins and the evolutionary mechanisms that shape the diversity of the virus is required. This review provides a synopsis of these issues and highlights some of the studies that have been conducted on BTV and the closely related African horse sickness virus (AHSV) that have contributed to ongoing attempts to identify the molecular determinants that influence the virus' phenotype. Different strategies that can be used to generate BTV mutants in vitro and methods through which the causality between particular genetic modifications and changes in phenotype may be determined are also described. Finally examples are highlighted where a clear understanding of the molecular determinants that influence the phenotype of the virus may have contributed to risk assessment and mitigation strategies during recent outbreaks of BT in Europe.

Longitudinal study on morbidity and mortality in white veal calves in Belgium

Background

Mortality and morbidity are hardly documented in the white veal industry, despite high levels of antimicrobial drug use and resistance. The objective of the present study was to determine the causes and epidemiology of morbidity and mortality in dairy, beef and crossbred white veal production. A total of 5853 calves, housed in 15 production cohorts, were followed during one production cycle. Causes of mortality were determined by necropsy. Morbidity was daily recorded by the producers.

Results

The total mortality risk was 5,3% and was significantly higher in beef veal production compared to dairy or crossbreds. The main causes of mortality were pneumonia (1.3% of the calves at risk), ruminal disorders (0.7%), idiopathic peritonitis (0.5%), enterotoxaemia (0.5%) and enteritis (0.4%). Belgian Blue beef calves were more likely to die from pneumonia, enterotoxaemia and arthritis. Detection of bovine viral diarrhea virus at necropsy was associated with chronic pneumonia and pleuritis. Of the calves, 25.4% was treated individually and the morbidity rate was 1.66 cases per 1000 calf days at risk. The incidence rate of respiratory disease, diarrhea, arthritis and otitis was 0.95, 0.30, 0.11 and 0.07 cases per 1000 calf days at risk respectively. Morbidity peaked in the first three weeks after arrival and gradually declined towards the end of the production cycle.

Conclusions

The present study provided insights into the causes and epidemiology of morbidity and mortality in white veal calves in Belgium, housed in the most frequent housing system in Europe. The necropsy findings, identified risk periods and differences between production systems can guide both veterinarians and producers towards the most profitable and ethical preventive and therapeutic protocols.

Congenital hydranencephaly and cerebellar hypoplasia in water buffalo in southern Brazil

Seven cases of hydranencephaly and cerebellar hypoplasia in a water buffalo herd are described. The herd of 133 females was divided for mating into 4 groups and mated with different bulls. The disease was observed in the offspring of 5 cows from only 1 group over a period of 6 years. These cows had all mated with the same bull during that period. All affected calves were unable to suckle, showed intention tremors, involuntary movements of the ears, depression, and blindness. Some calves were recumbent and others showed wide-based stance and inability to walk. At necropsy, all affected calves had similar lesions consisting of hydranencephaly and cerebellar hypoplasia. Histologically, the cavities were surrounded by normal-looking nervous tissue. The occurrence of the disease in the offspring of only 1 out of 6 bulls in different years, the similar lesions in all 7 calves affected, and the negative serology and immunohistochemistry for Bovine virus diarrhea virus and Bluetongue virus highly suggest that the disease is hereditary.

Bluetongue virus serotype 8: abortion and transplacental transmission in cattle in the Burgundy region, France, 2008-2009

During the incursion of bluetongue virus (BTV) serotype 8 in France in 2007, an increase in the number of abortions in cattle was observed, but the cause was not clearly established. A survey of all the reported cases of abortion in cattle from November 2008 to April 2009 was conducted in the Nièvre district (Burgundy region) to determine the percentage of abortions as a result of BTV-8 and to study factors that could have played a role in BTV-8 transplacental transmission. BTV-8 was present in 16% of the fetuses or newborn calves that died within 48 h, from 780 dams. Dams inseminated before the BTV epizootic peak recorded from July to September 2008 were more likely to have BTV-positive abortions (OR=5.7, P<0.001) and those vaccinated in May or June 2008 were less likely to have BTV-positive abortions (OR=0.3, P=0.01 and OR=0.4, P=0.001, respectively). The gestational month was not a predictor of BTV abortion. In blood or spleen, fetuses/calves from RT-PCR-positive dams had significantly higher RNA concentrations than fetuses/calves from RT-PCR-negative dams. Of the 128 dams that had BTV-positive fetuses or calves, 60% were RT-PCR-negative. BTV-8-positive fetuses/calves were significantly more frequent (n=42 vs n=21, P=0.082) amongst those showing clinical signs or lesions suggestive of cerebral damage.

Determinants of bluetongue virus virulence in murine models of disease

Bluetongue is a major infectious disease of ruminants that is caused by bluetongue virus (BTV). In this study, we analyzed virulence and genetic differences of (i) three BTV field strains from Italy maintained at either a low (L strains) or high (H strains) passage number in cell culture and (ii) three South African "reference" wild-type strains and their corresponding live attenuated vaccine strains. The Italian BTV L strains, in general, were lethal for both newborn NIH-Swiss mice inoculated intracerebrally and adult type I interferon receptor-deficient (IFNAR(-/-)) mice, while the virulence of the H strains was attenuated significantly in both experimental models. Similarly, the South African vaccine strains were not pathogenic for IFNAR(-/-) mice, while the corresponding wild-type strains were virulent. Thus, attenuation of the virulence of the BTV strains used in this study is not mediated by the presence of an intact interferon system. No clear distinction in virulence was observed for the South African BTV strains in newborn NIH-Swiss mice. Full genomic sequencing revealed relatively few amino acid substitutions, scattered in several different viral proteins, for the strains found to be attenuated in mice compared to the pathogenic related strains. However, only the genome segments encoding VP1, VP2, and NS2 consistently showed nonsynonymous changes between all virulent and attenuated strain pairs. This study established an experimental platform for investigating the determinants of BTV virulence. Future studies using reverse genetics will allow researchers to precisely map and "weight" the relative influences of the various genome segments and viral proteins on BTV virulence.

Dystocia and fetotomy associated with cerebral aplasia in a greater one-horned rhinoceros (Rhinoceros unicornis)

The captive greater one-horned rhinoceros population consists of 176 animals. Since 1971, a total of 226 calves were born into this captive population. However, 24% of the offspring born were either stillborn or did not survive the first 3 months. The causes for this high rate of stillbirth and neonate mortality have not yet been documented. Here, we report on the veterinary management of a dystocia and foetotomy resulting from a malpositioned greater one-horned rhinoceros foetus. The dead foetus presented with a forelimb flexed at the shoulder joint, with all other joints extended. The foetus was dissected into five parts and extracted during two anaesthesias on two consecutive days. The dam recovered fully and came into oestrous 31 days after surgery. Post-mortem and CT examination of the malformed foetal head revealed cranioschisis with cerebral aplasia and cerebellar hypoplasia. The cerebral aplasia presented here and in other recent cases suggests that neural tube defects and cranial malformations may be associated with more captive rhinoceros stillbirths than previously considered. Epidemiologic studies of these phenomena and possible nutritional deficiencies or hereditary defects are warranted.

Full genome characterisation of bluetongue virus serotype 6 from the Netherlands 2008 and comparison to other field and vaccine strains

In mid September 2008, clinical signs of bluetongue (particularly coronitis) were observed in cows on three different farms in eastern Netherlands (Luttenberg, Heeten, and Barchem), two of which had been vaccinated with an inactivated BTV-8 vaccine (during May-June 2008). Bluetongue virus (BTV) infection was also detected on a fourth farm (Oldenzaal) in the same area while testing for export. BTV RNA was subsequently identified by real time RT-PCR targeting genome-segment (Seg-) 10, in blood samples from each farm. The virus was isolated from the Heeten sample (IAH "dsRNA virus reference collection" [dsRNA-VRC] isolate number NET2008/05) and typed as BTV-6 by RT-PCR targeting Seg-2. Sequencing confirmed the virus type, showing an identical Seg-2 sequence to that of the South African BTV-6 live-vaccine-strain. Although most of the other genome segments also showed very high levels of identity to the BTV-6 vaccine (99.7 to 100%), Seg-10 showed greatest identity (98.4%) to the BTV-2 vaccine (RSAvvv2/02), indicating that NET2008/05 had acquired a different Seg-10 by reassortment. Although Seg-7 from NET2008/05 was also most closely related to the BTV-6 vaccine (99.7/100% nt/aa identity), the Seg-7 sequence derived from the blood sample of the same animal (NET2008/06) was identical to that of the Netherlands BTV-8 (NET2006/04 and NET2007/01). This indicates that the blood contained two different Seg-7 sequences, one of which (from the BTV-6 vaccine) was selected during virus isolation in cell-culture. The predominance of the BTV-8 Seg-7 in the blood sample suggests that the virus was in the process of reassorting with the northern field strain of BTV-8. Two genome segments of the virus showed significant differences from the BTV-6 vaccine, indicating that they had been acquired by reassortment event with BTV-8, and another unknown parental-strain. However, the route by which BTV-6 and BTV-8 entered northern Europe was not established.

Emergence of bluetongue serotypes in Europe, part 2: the occurrence of a BTV-11 strain in Belgium

An EDTA-blood sample from a cow without clinical signs, which gave early birth to a newborn calf that died soon after delivery, was shown to be positive for bluetongue virus (BTV)-RNA using a group-specific real-time RT-PCR (RT-qPCR). In-house serotype-specific RT-qPCR assays for bluetongue virus serotype 1 (BTV-1), -6 and -8 all gave negative results. Subsequent assays were carried out using conventional (gel-based) RT-PCR primers for all 25 BTV serotypes and only two primer sets, both specific for BTV-11, gave bands of the expected size. The cDNAs generated were sequenced and comparisons of the genome segment 2 sequence with that of the modified 'live' vaccine strain of BTV-11 from South Africa showed 100% identity. A survey of all ruminants in a 1-km area around the first positive farm using a BTV-11 serotype-specific RT-qPCR revealed five other holdings with in total nine BTV-11 positive animals. A cross-sectional monitoring of dairy cattle in Belgium showed an overall prevalence of 3.8% on herd level and 0.2% on animal level. A BTV-11 has been introduced into the Belgian cattle herd during the 2008 vector season. The source of the infection and the way by which the virus was introduced are unknown.

Transplacental transmission of bluetongue virus 8 in cattle, UK

To determine whether transplacental transmission could explain overwintering of bluetongue virus in the United Kingdom, we studied calves born to dams naturally infected during pregnancy in 2007–08. Approximately 33% were infected transplacentally; some had compromised health. In all infected calves, viral load decreased after birth; no evidence of persistent infection was found.

The impact of naturally-occurring, trans-placental bluetongue virus serotype-8 infection on reproductive performance in sheep

Infection with bluetongue virus serotype (BTV)-8 occurred in ruminants in 2006 in Central-Western Europe. The trans-placental passage of this virus has been demonstrated in naturally- and experimentally-infected cattle and in experimentally-infected sheep. Trans-placental transmission is potentially important in the 'over-wintering' of this virus and its subsequent impact on reproductive performance. This epidemiological study was carried out on a sheep flock in Belgium that had experienced a severe outbreak of BTV-8 infection, and where the seroprevalence had increased from 1.3% to 88% between January and November 2007. In total, 476 lambs and 26 aborted fetuses from 300 ewes, lambing at four distinct time periods, were investigated between November 2007 and May 2008. The following evidence suggested that BTV-8 infection occurred in utero: (1) positive PCR results from splenic tissue from aborted fetuses (n=4); (2) fetal malformations suggestive of BTV infection (n=10); (3) positive PCR results from red blood cells in-lambs (n=7), and (4) the presence of antibody at birth in viable lambs prior to the intake of colostrum (n=9). The evidence provided by this investigation strongly suggests that trans-placental BTV-8 infection occurs in naturally-infected sheep and the impact of infection on the reproductive performance of such a naïve flock was considerable, with up to 25% of ewes aborting and with flock fertility reduced by 50%. The contribution of in utero-infected lambs to the over-wintering of BTV appears limited.

Bluetongue vaccines

Once thought largely restricted to India and Africa, the insect-borne livestock pathogen Bluetongue virus is now present on every continent with the exception of Antarctica. Outbreaks of the disease caused by the virus in Europe over the last decade, and the resulting impact on trade and agriculture, have focussed attention on the production of safe and effective vaccines. The determinants of protection for bluetongue are well defined but the variability of the virus, which exists as 24 immunologically distinct serotypes, means that even regions where large numbers of animals have been vaccinated remain at risk from new outbreaks of the virus.