Bluetongue virus detection by two real-time RT-qPCRs targeting two different genomic segments

Comparison of the neuropathology induced by two West Nile virus strains

Some strains of West Nile virus (WNV) are neuroinvasive and may induce fatal encephalitis/meningitis in a variety of animal species including humans. Whether, however, there is a strain-specific signature in the brain is as yet unknown. Here we investigated the neuropathogenesis induced by two phylogenetically distant WNV strains of lineage 1, WNV_IS98 and WNV_KUN35 911. While four-week old C57Bl/6J mice were susceptible to both strains and succumbed rapidly after intraperitoneal inoculation, differences were observed in virulence and clinical disease. WNV_KUN35 911, the less virulent strain as judged by determination of LD₅₀, induced typical signs of encephalitis. Such signs were not observed in WNV_IS98-infected mice, although they died more rapidly. Histological examination of brain sections also revealed differences, as the level of apoptosis and inflammation was higher in WNV_KUN35 911- than WNV_IS98-infected mice. Moreover, staining for cleaved caspase 3 showed that the two WNV strains induced apoptotic death through different molecular mechanisms in one particular brain area. Finally, the two strains showed similar tropism in cortex, striatum, brainstem, and cerebellum but a different one in hippocampus. In summary, our data show that, upon peripheral administration, WNV_IS98 and WNV_KUN35 911 strains induce partially distinct lesions and tissue tropism in the brain. They suggest that the virulence of a WNV strain is not necessarily correlated with the severity of apoptotic and inflammatory lesions in the brain.

No evidence for replication of a field strain of bluetongue virus serotype 1 in the blood of domestic dogs

The potential role of domestic dogs in the long-distance transmission of bluetongue virus (BTV) is currently unproven. This study set out, through an experimental infection study, to investigate whether domestic dogs mount a viraemia post-infection with a field strain of BTV serotype 1. All six experimentally infected dogs seroconverted within 14 days and viral RNA was detected in the blood of the dogs, albeit at significantly lower levels than that seen in domestic ruminants. There was no clear evidence for viral replication in the dogs as no increase in viral RNA was observed in, and it was not possible isolate virus from, the blood of the dogs. There was however evidence for a persistence of viral RNA in the blood of the dogs, which may be evidence for a low level of replication or could be indicative of persistence of the viral inoculum.

Rapid spread of Schmallenberg virus-infected biting midges (Culicoides spp.) across Denmark in 2012

Detection of Schmallenberg virus RNA, using real-time RT-PCR, in biting midges (Culicoides spp.) caught at 48 locations in 2011 and four well-separated farms during 2012 in Denmark, revealed a remarkably rapid spread of virus-infected midges across the country. During 2012, some 213 pools of obsoletus group midges (10 specimens per pool) were examined, and of these, 35 of the 174 parous pools were Schmallenberg virus RNA positive and 11 of them were positive in the heads. Culicoides species-specific PCRs identified both C. obsoletus and C. dewulfi as vectors of Schmallenberg virus.

Development of a pan-Simbu real-time reverse transcriptase PCR for the detection of Simbu serogroup viruses and comparison with SBV diagnostic PCR systems

Background

Schmallenberg virus (SBV), a novel orthobunyavirus of the Simbu serogroup, was first identified in October 2011 in dairy cattle in Germany, where it caused fever, diarrhea and a drop in milk yield. Since then, SBV additionally has been detected in adult sheep and goats. Although symptoms of acute infection were not observed, infection during a vulnerable phase of pregnancy caused congenital malformations and stillbirths. In view of the current situation and the possible emergence of further Simbu serogroup members, a pan-Simbu real-time reverse transcriptase (RT) PCR system for the reliable detection of Simbu serogroup viruses should be developed.

Methods

In this study a pan-Simbu real-time RT-PCR system was established and compared to several SBV real-time RT-PCR assays. All PCR-systems were tested using a panel of different Simbu serogroup viruses as well as several field samples from diseased cattle, sheep and goats originating from all over Germany. Several pan-Simbu real-time RT-PCR products were sequenced via Sanger sequencing. Furthermore, in silico analyses were performed to investigate suitability for the detection of further orthobunyaviruses.

Results

All tested members of the Simbu serogroup (n = 14) as well as most of the field samples were successfully detected by the pan-Simbu real-time RT-PCR system. The comparison of this intercalating dye assay with different TaqMan probe-based assays developed for SBV diagnostics confirmed the functionality of the pan-Simbu assay for screening purposes. However, the SBV-TaqMan-assay SBV-S3 delivered the highest analytical sensitivity of less than ten copies per reaction for duplex systems including an internal control. In addition, for confirmation of SBV-genome detection the highly specific SBV-M1 assay was established.

Conclusion

The pan-Simbu real-time RT-PCR system was able to detect all tested members of the Simbu serogroup, most of the SBV field samples as well as three tested Bunyamwera serogroup viruses with a suitable sensitivity. According to in silico analyses, this system seems to be able to detect a broad orthobunyavirus spectrum. As an additional feature of the pan-Simbu real-time RT-PCR system, subsequent species classification via sequencing is feasible. Regarding SBV diagnostics, the performance of the S-segment targeting SBV-S3 assay was superior with respect to the analytical sensitivity.

The use of infrared thermography as a non-invasive method for fever detection in sheep infected with bluetongue virus

Fever, which is closely linked to viraemia, is considered to be both the main and the earliest clinical sign in sheep infected with bluetongue virus (BTV). The aim of this study was to evaluate the potential use of infrared thermography (IRT) for early detection of fever in sheep experimentally infected with bluetongue virus serotype 1 (BTV-1) and serotype 8 (BTV-8). This would reduce animal stress during experimental assays and assist in the development of a screening method for the identification of fever in animals suspected of being infected with BTV. Rectal and infrared eye temperatures were collected before and after BTV inoculation. The two temperature measures were positively correlated (r=0.504, P<0.05). The highest correlation between rectal and infrared temperatures was observed when temperatures were above physiological levels. IRT discriminated between febrile and non-febrile sheep with a sensitivity of 85% and specificity of 97%. The results showed that eye temperature measured using IRT was a useful non-invasive method for the assessment of fever in sheep infected with BTV under experimental conditions. Further research is required to evaluate the use of IRT under field conditions to identify potentially infected animals in bluetongue surveillance programmes.

Bluetongue virus with mutated genome segment 10 to differentiate infected from vaccinated animals: a genetic DIVA approach

Bluetongue virus (BTV) includes 24 serotypes and recently even more serotypes are proposed. Mass vaccination campaigns highlight the need for differential diagnostics in vaccinated populations. Bluetongue disease is routinely diagnosed by serological and virological tests by which differentiation infected from vaccinated animals (DIVA principle) is not possible. Real time PCR tests preferably detect all BTV serotypes (panBTV PCR tests). These PCR tests operate as frontline test to detect new BTV incursions. However, highly sensitive panBTV PCR tests can also detect currently applied inactivated and modified-live vaccines. Here, BTV with eight silent mutations in segment 10 (Seg-10) was generated by reverse genetics. This BTV mutant is not detected by a Seg-10 panBTV PCR test (genetic DIVA). Thus, inactivated BT vaccine with this mutated Seg-10 will avoid false positive PCR results post vaccination, whereas BTV infected animals can be positively diagnosed with the accompanying Seg-10 panBTV PCR test (DIVA-test) far beyond the infectious period.

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.

Evaluation of the immunogenicity of an experimental subunit vaccine that allows differentiation between infected and vaccinated animals against bluetongue virus serotype 8 in cattle

Bluetongue virus (BTV), the causative agent of bluetongue in ruminants, is an emerging virus in northern Europe. The 2006 outbreak of BTV serotype 8 (BTV-8) in Europe was marked by an unusual teratogenic effect and a high frequency of clinical signs in cattle. Conventional control strategies targeting small ruminants were therefore extended to include cattle. Since cattle were not routinely vaccinated before 2006, the immune responses to BTV have not been studied extensively in this species. With the aims of developing a subunit vaccine against BTV-8 for differentiation between infected and vaccinated animals based on viral protein 7 (VP7) antibody detection and of improving the current understanding of the immunogenicity of BTV proteins in cattle, the immune responses induced by recombinant VP2 (BTV-8) and nonstructural protein 1 (NS1) and NS2 (BTV-2) were studied. Cows were immunized twice (with a 3-week interval) with the experimental vaccine, a commercial inactivated vaccine, or a placebo. The two vaccines induced similar neutralizing antibody responses to BTV-8. Furthermore, the antibody responses detected against VP2, NS1, and NS2 were strongest in the animals immunized with the experimental vaccine, and for the first time, a serotype cross-reactive antibody response to NS2 was shown in cattle vaccinated with the commercial vaccine. The two vaccines evoked measurable T cell responses against NS1, thereby supporting a bovine cross-reactive T cell response. Finally, VP7 seroconversion was observed after vaccination with the commercial vaccine, as in natural infections, but not after vaccination with the experimental vaccine, indicating that the experimental vaccine may allow the differentiation of vaccinated animals from infected animals regardless of BTV serotype. The experimental vaccine will be further evaluated during a virulent challenge in a high-containment facility.

Epidemiology, molecular virology and diagnostics of Schmallenberg virus, an emerging orthobunyavirus in Europe

After the unexpected emergence of Bluetongue virus serotype 8 (BTV-8) in northern Europe in 2006, another arbovirus, Schmallenberg virus (SBV), emerged in Europe in 2011 causing a new economically important disease in ruminants. The virus, belonging to the Orthobunyavirus genus in the Bunyaviridae family, was first detected in Germany, in The Netherlands and in Belgium in 2011 and soon after in the United Kingdom, France, Italy, Luxembourg, Spain, Denmark and Switzerland. This review describes the current knowledge on the emergence, epidemiology, clinical signs, molecular virology and diagnosis of SBV infection.

Clinical bovine piroplasmosis caused by Babesia occultans in Italy

A clinical outbreak of bovine piroplasmosis was reported in Italy. The etiological agent was characterized as Babesia occultans, a parasite regarded as apathogenic and never detected before in continental Europe. This report paves the way for further studies to assess the occurrence of this tick-transmitted protozoan in other European regions.

Bluetongue dynamics in French wildlife: exploring the driving forces

Bluetongue (BT) was monitored in wildlife in France during two consecutive years corresponding to contrasting incidence rates in livestock: in 2008 at the peak of domestic outbreaks and in 2009 when very few outbreaks were observed. The disease status of 2 798 ruminants comprising 837 red deer (Cervus elaphus) was explored using ELISA test on serum and real-time RT-PCR test on blood or spleen. A large proportion of red deer were seropositive and positive to RT-PCR in 2008, but also in 2009 (seroprevalence: 47.1% and 24.3%), suggesting that red deer could maintain infection when domestic incidence was negligible. By contrast, low seroprevalence (<3%) and few RT-PCR positive results were observed in other wild ruminant species, which rather appeared thus as dead-end hosts. The risk factors of bluetongue circulation during the periods of high (2008) and low (2009) domestic incidence were explored in red deer using logistic mixed models. In this species, prevalence has been mainly influenced by the initial peak of BT in livestock, but also by environmental factor such as elevation and edge density between forest and pastures. Surprisingly, cattle density has a negative influence on prevalence in red deer, possibly due to the protective effect of cattle regarding midges' bites and/or to still unexplained factors dealing with the host/midge interface. To our knowledge, this study is the first attempt at measuring the effect of landscape and wildlife/domestic interface on BT prevalence in wildlife in Europe.

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.

Region of difference 4 in alpine Mycobacterium caprae isolates indicates three variants

The lack of complete genome sequence information for Mycobacterium caprae complicates a robust differentiation of M. caprae and Mycobacterium bovis. In this study, the presence or absence of M. caprae-specific single nucleotide polymorphisms in lepA and gyrB genes was assessed. The region of difference 4 (RD4) was analyzed for the identification and characterization of M. caprae. Molecular characteristics were evaluated in 12 recent M. caprae isolates from livestock and wildlife collected over a 3-year period in Bavaria, Germany. Conventional PCR strategies, sequence analysis of PCR fragments, and data from a next-generation sequencing approach together with variable-number tandem-repeat genotyping were utilized. Single nucleotide polymorphisms in the lepA and gyrB genes indicating the presence of M. caprae were detected in all the isolates. At least three different RD4 variants were found for Alpine M. caprae isolates. The results demonstrate that the RD4 region is rather heterogeneous in M. caprae genomes. As assumed by others, the presence of RD4 is critical for PCR-based differentiation of M. caprae from M. bovis, but in addition, the observed variability of RD4 allows the identification of M. caprae genotypes and may be indicative of a geographical-type appearance.

Single-tube multiplexed molecular detection of endemic porcine viruses in combination with background screening for transboundary diseases

Detection of several pathogens with multiplexed real-time quantitative PCR (qPCR) assays in a one-step setup allows the simultaneous detection of two endemic porcine and four different selected transboundary viruses. Reverse transcription (RT)-qPCR systems for the detection of porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2), two of the most economically important pathogens of swine worldwide, were combined with a screening system for diseases notifiable to the World Organization of Animal Health, namely, classical and African swine fever, foot-and-mouth disease, and Aujeszky's disease. Background screening was implemented using the identical fluorophore for all four different RT-qPCR assays. The novel multiplex RT-qPCR system was validated with a large panel of different body fluids and tissues from pigs and other animal species. Both reference samples and clinical specimens were used for a complete evaluation. It could be demonstrated that a highly sensitive and specific parallel detection of the different viruses was possible. The assays for the notifiable diseases were even not affected by the simultaneous amplification of very high loads of PRRSV- and PCV2-specific sequences. The novel broad-spectrum multiplex assay allows in a unique form the routine investigation for endemic porcine pathogens with exclusion diagnostics of the most important transboundary diseases in samples from pigs with unspecific clinical signs, such as fever or hemorrhages. The new system could significantly improve early detection of the most important notifiable diseases of swine and could lead to a new approach in syndromic surveillance.

Diagnosis of Schmallenberg virus infection in malformed lambs and calves and first indications for virus clearance in the fetus

Since mid-December 2011, samples from malformed lambs and calves are sent to CODA-CERVA in Belgium for diagnosis of Schmallenberg virus (SBV), a novel Orthobunyavirus that was first detected by researchers of the Friedrich-Loeffler-Institut (FLI, Germany) in German cattle in autumn 2011 and was later shown to be involved in congenital malformations in lambs, goat kids and calves. Surprisingly, by making use of real time RT-PCR (rRT-PCR) assays developed by the FLI, presence of SBV RNA could only be confirmed in part of the SBV suspected newborns examined. To investigate possible causes for non-confirmation by rRT-PCR, a comparative analysis between different organs and tissues (cerebrum, cerebellum, brain stem, spinal cord, thymus, spleen, lymph nodes, meconium) originating from respectively 90 and 81 malformed lambs and calves was undertaken. Furthermore, thoracic fluids of respectively 55 malformed lambs and calves were examined by a virus neutralization test (VNT) to evaluate the presence of neutralizing anti-SBV antibodies in these animals. Our results show that among the different organs tested by rRT-PCR, brain stem material is the most appropriate tissue for SBV detection while it could also be detected in all other tissues but to a more variable degree. The VNT test showed that 95% of the malformed lambs were positive for anti-SBV neutralizing antibodies while this was only the case for 44% of malformed calves. These immunological data suggest that a humoral immune response could assist in the clearance of SBV from the fetus during gestation and that SBV specific antibody testing should be considered together with rRT-PCR analysis for confirmation of SBV infection.

Sustained high-throughput polymerase chain reaction diagnostics during the European epidemic of Bluetongue virus serotype 8

A real-time reverse transcription polymerase chain reaction assay (PCR test) based on genome segment 10 of Bluetongue virus (BTV) was developed. The PCR test consists of robotized viral RNA isolation from blood samples and an all-in-one method including initial denaturation of genomic double-stranded RNA, reverse transcription polymerase chain reaction (RT-PCR), and real-time detection and analysis. Reference strains of the 24 recognized BTV serotypes, isolates from different years, and geographic origins were detected. Other orbiviruses such as African horse sickness virus, Epizootic hemorrhagic disease virus, and Equine encephalosis virus were not detected. Experimentally infected animals were PCR positive from 2 days postinoculation, which was earlier than fever, other clinical signs, or seroconversion. The diagnostic sensitivity and specificity were very close to or even 100%. The PCR test played a key role in the detection of BTV serotype 8 in August 2006 in The Netherlands. The outbreak in a completely naive ruminant population allowed for further evaluation of the PCR test with field samples. In 2006, the correlation between enzyme-linked immunosorbent assay and PCR results was estimated to be 95%. In the following years, the PCR test was used for diagnosis of diseased animals, for testing of healthy animals for trade purposes, and for detection of BTV RNA in different species of the insect vector, Culicoides. In the autumn of 2008, BTV serotype 6 unexpectedly emerged in northwest Europe and was also detected with the PCR test developed in the current study. The performance in routine use over 5 years has been recorded and evaluated.

Bluetongue virus serotype 26: infection kinetics, pathogenesis and possible contact transmission in goats

The aim of this study was to assess the pathogenicity and infection kinetics of Bluetongue virus serotype 26 (BTV-26) in goats. Out of a group of six goats housed in insect free accommodation, five were experimentally infected with BTV-26 and one was kept uninfected as an in-contact control. Samples taken throughout the study were used to determine the kinetics of infection using a pan specific BTV real time RT-PCR assay and a group specific ELISA. The five infected goats did not show clinical signs of BTV, however high levels of viral RNA were detected and virus was isolated from the blood of all 5 goats. Antibodies against BTV were first detected between 7 and 11 dpi in all 5 experimentally infected goats. Interestingly at 21 dpi viral RNA was detected in, and virus was isolated from, the blood of the in-contact control goat, which also seroconverted. These results suggest that BTV-26 replicates to high levels in goats, causing no obvious clinical disease, suggesting that goats may be the natural host for this virus. Preliminary evidence also indicates that BTV-26 may be spread by contact transmission between goats, however a more detailed study is required in order to confirm this observation.

Novel virostatic agents against bluetongue virus

Bluetongue virus (BTV), a member in the family Reoviridae, is a re-emerging animal disease infecting cattle and sheep. With its recent outbreaks in Europe, there is a pressing need for efficacious antivirals. We presented here the identification and characterization of a novel virostatic molecule against BTV, an aminothiophenecarboxylic acid derivative named compound 003 (C003). The virostatic efficacy of C003 could be improved via chemical modification, leading to a de novo synthesized compound 052 (C052). The 50% effective concentrations (EC(50)) of C003 and C052 were determined at 1.76 ± 0.73 µM and 0.27 ± 0.12 µM, respectively. The 50% cytotoxicity concentration (CC(50)) of C003 was over 100 µM and the CC(50) of C052 was at 82.69 µM. Accordingly, the 50% selective index (SI(50)) of C003 and C052 against BTV was over 57 and 306, respectively. The inhibitory effect of C003/C052 on BTV-induced apoptosis was also confirmed via the inhibition of caspase-3/-7 activation post BTV infection. C003/C052 could inhibit BTV induced CPE even when added as late as 24 h.p.i., indicating that they might act at late stage of viral life-cycle. C003/C052 could reduce over two-logs of both the progeny virus production and the number of genomic viral RNA copies. Interestingly, both the activation of host autophagy and viral protein expression were inhibited post BTV infection when cells were treated with C003 and C052, suggesting that C003/C052 might act as virostatic agents via inhibiting host autophagy activation. Although further investigations might be needed to pin down the exact mechanism of C003/C052, our finding suggested that these compounds might be potent lead compounds with potential novel mechanism of action against BTV.

Application of quantitative real-time polymerase chain reaction for the diagnosis of toxoplasmosis and enzootic abortion of ewes

Toxoplasma gondii and Chlamydophila abortus are the 2 most common infectious causes of ovine abortion worldwide. These obligate intracellular pathogens are associated with severe placentitis leading to abortion or stillbirth in pregnant ewes, and resulting in significant economic losses. The objectives of the current study were the development, validation, and application of a duplex real-time polymerase chain reaction (PCR) assay capable of quantifying the burden of infection by T. gondii and C. abortus in material submitted for diagnostic purposes. The validation was carried out using samples from ewes experimentally infected with these organisms. Based on the numbers of genome copies detected, an arbitrary cutoff level was established to correlate with significant pathological changes sufficient to give rise to abortion. When the PCR assay was applied to samples from 66 Irish farms with naturally occurring outbreaks of ovine abortion, toxoplasmosis and enzootic abortion of ewes (EAE) accounted for 14% and 20% of the farms, respectively, while on 6% of the farms, there was evidence of dual infection. When standard diagnostic techniques including histopathological examination, serological analysis, chlamydial antigen detection, and bacteriological culture, were used on samples from the same farms, toxoplasmosis was diagnosed in 17% of farms, and EAE in 12%; dual infection was diagnosed on 3% of the farms. In general, good agreement was found between the PCR and the standard methods. The duplex real-time PCR assay developed in this study has proved to be a very sensitive and rapid tool that might provide a valuable addition to the methods currently available for routine diagnosis of ovine abortions.

Detection and typing of highly pathogenic porcine reproductive and respiratory syndrome virus by multiplex real-time rt-PCR

Porcine reproductive and respiratory syndrome (PRRS) causes economic losses in the pig industry worldwide, and PRRS viruses (PRRSV) are classified into the two distinct genotypes “North American (NA, type 2)” and “European (EU, type 1)”. In 2006, a highly pathogenic NA strain of PRRSV (HP-PRRSV), characterized by high fever as well as high morbidity and mortality, emerged in swine farms in China. Therefore, a real-time reverse transcription polymerase chain reaction (RT-qPCR) assay specific for HP-PRRSV was developed and combined with type 1- and type 2-specific RT-qPCR systems. Furthermore, an internal control, based on a heterologous RNA, was successfully introduced. This final multiplex PRRSV RT-qPCR, detecting and typing PRRSV, had an analytical sensitivity of less than 200 copies per µl for the type 1-assay and 20 copies per µl for the type 2- and HP assays and a high diagnostic sensitivity. A panel of reference strains and field isolates was reliably detected and samples from an animal trial with a Chinese HP-PRRS strain were used for test validation. The new multiplex PRRSV RT-qPCR system allows for the first time the highly sensitive detection and rapid differentiation of PRRSV of both genotypes as well as the direct detection of HP-PRRSV.

Protection of Spanish Ibex (Capra pyrenaica) against Bluetongue virus serotypes 1 and 8 in a subclinical experimental infection

Many wild ruminants such as Spanish ibex (Capra pyrenaica) are susceptible to Bluetongue virus (BTV) infection, which causes disease mainly in domestic sheep and cattle. Outbreaks involving either BTV serotypes 1 (BTV-1) and 8 (BTV-8) are currently challenging Europe. Inclusion of wildlife vaccination among BTV control measures should be considered in certain species. In the present study, four out of fifteen seronegative Spanish ibexes were immunized with a single dose of inactivated vaccine against BTV-1, four against BTV-8 and seven ibexes were non vaccinated controls. Seven ibexes (four vaccinated and three controls) were inoculated with each BTV serotype. Antibody and IFN-gamma responses were evaluated until 28 days after inoculation (dpi). The vaccinated ibexes showed significant (P<0.05) neutralizing antibody levels after vaccination compared to non vaccinated ibexes. The non vaccinated ibexes remained seronegative until challenge and showed neutralizing antibodies from 7 dpi. BTV RNA was detected in the blood of non vaccinated ibexes from 2 to the end of the study (28 dpi) and in target tissue samples obtained at necropsy (8 and 28 dpi). BTV-1 was successfully isolated on cell culture from blood and target tissues of non vaccinated ibexes. Clinical signs were unapparent and no gross lesions were found at necropsy. Our results show for the first time that Spanish ibex is susceptible and asymptomatic to BTV infection and also that a single dose of vaccine prevents viraemia against BTV-1 and BTV-8 replication.

Clinical pattern characterization of cattle naturally infected by BTV-8

Forty-one cattle from seven Belgian farms and two French farms confirmed as infected with bluetongue virus serotype 8 (BTV-8) were monitored from the onset of clinical signs to describe the disease pattern and estimate the duration of blood RT-qPCR and competitiveELISA positivity under field conditions. On each visit, blood samples were taken, and a standardized clinical form was filled in for each animal. A clinical score was calculated for every week until the end of clinical signs. A classification and regression tree (CART) analysis was conducted to determine the most important clinical signs every week for the first 7 weeks. The highest scores were recorded within 2 weeks of clinical onset. The first recorded clinical signs were quite obviously visible (lethargy, conjunctivitis, lesions of nasal mucosa, nasal discharge). Skin lesions, a drop in milk production and weight loss appeared later in the course of the disease. A biphasic pattern regarding nasal lesions was noticed: the first peak concerned mainly congestive and ulcerative lesions, whereas the second peak mainly concerned crusty lesions. The median time estimated by survival analysis to obtain negative RT-qPCR results from the onset of clinical signs was 195 days (range 166-213 days) in the 23 cattle included in the analysis. Serological results remained strongly positive until the end of the study. These results should ensure more accurate detection of an emerging infectious disease and are of prime importance in improving the modelling of BTV-8 persistence in Europe.

Characterization of the immune response induced by a commercially available inactivated bluetongue virus serotype 1 vaccine in sheep

The protective immune response generated by a commercial monovalent inactivated vaccine against bluetongue virus serotype 1 (BTV1) was studied. Five sheep were vaccinated, boost-vaccinated, and then challenged against BTV1 ALG/2006. RT-PCR did not detect viremia at any time during the experiment. Except a temperature increase observed after the initial and boost vaccinations, no clinical signs or lesions were observed. A specific and protective antibody response checked by ELISA was induced after vaccination and boost vaccination. This specific antibody response was associated with a significant increase in B lymphocytes confirmed by flow cytometry, while significant increases were not observed in T lymphocyte subpopulations (CD4⁺, CD8⁺, and WC1⁺), CD25⁺ regulatory cells, or CD14⁺ monocytes. After challenge with BTV1, the antibody response was much higher than during the boost vaccination period, and it was associated with a significant increase in B lymphocytes, CD14⁺ monocytes, CD25⁺ regulatory cells, and CD8⁺ cytotoxic T lymphocytes.

Epizootic hemorrhagic disease virus serotype 7 in European cattle and sheep: diagnostic considerations and effect of previous BTV exposure

Epizootic hemorrhagic disease virus (EHDV), an arthropod-borne orbivirus (family Reoviridae), is an emerging pathogen of wild and domestic ruminants that is closely related to bluetongue virus (BTV). The present study examines the outcome of an experimental EHDV-7 infection of Holstein cattle and East Frisian sheep. Apart from naïve animals that had not been exposed to BTV, it included animals that had been experimentally infected with either BTV-6 or BTV-8 two months earlier. In addition, EHDV-infected cattle were subsequently challenged with BTV-8. Samples were tested with commercially available ELISA and real-time RT-PCR kits and a custom NS3-specific real-time RT-PCR assay. Virus isolation was attempted in Vero, C6/36 and KC cells (from Culicoides variipennis), embryonated chicken eggs and type I interferon receptor-deficient IFNAR(-/-) mice. EHDV-7 productively infected Holstein cattle, but caused no clinical signs. The inoculation of East Frisian sheep, on the other hand, apparently did not lead to a productive infection. The commercial diagnostic kits performed adequately. KC cells proved to be the most sensitive means of virus isolation, but viremia was shorter than 2 weeks in most animals. No interference between EHDV and BTV infection was observed; therefore the pre-existing immunity to some BTV serotypes in Europe is not expected to protect against a possible introduction of EHDV, in spite of the close relation between the viruses.

Multiserotype protection elicited by a combinatorial prime-boost vaccination strategy against bluetongue virus

Bluetongue virus (BTV) belongs to the genus Orbivirus within the family Reoviridae. The development of vector-based vaccines expressing conserved protective antigens results in increased immune activation and could reduce the number of multiserotype vaccinations required, therefore providing a cost-effective product. Recent recombinant DNA technology has allowed the development of novel strategies to develop marker and safe vaccines against BTV. We have now engineered naked DNAs and recombinant modified vaccinia virus Ankara (rMVA) expressing VP2, VP7 and NS1 proteins from BTV-4. IFNAR^(−/−) mice inoculated with DNA/rMVA-VP2,-VP7-NS1 in an heterologous prime boost vaccination strategy generated significant levels of antibodies specific of VP2, VP7, and NS1, including those with neutralizing activity against BTV-4. In addition, vaccination stimulated specific CD8⁺ T cell responses against these three BTV proteins. Importantly, the vaccine combination expressing NS1, VP2 and VP7 proteins of BTV-4, elicited sterile protection against a lethal dose of homologous BTV-4 infection. Remarkably, the vaccine induced cross-protection against lethal doses of heterologous BTV-8 and BTV-1 suggesting that the DNA/rMVA-VP2,-VP7,-NS1 marker vaccine is a promising multiserotype vaccine against BTV.

An equine herpesvirus type 1 (EHV-1) expressing VP2 and VP5 of serotype 8 bluetongue virus (BTV-8) induces protection in a murine infection model

Bluetongue virus (BTV) can infect most species of domestic and wild ruminants causing substantial morbidity and mortality and, consequently, high economic losses. In 2006, an epizootic of BTV serotype 8 (BTV-8) started in northern Europe that caused significant disease in cattle and sheep before comprehensive vaccination was introduced two years later. Here, we evaluate the potential of equine herpesvirus type 1 (EHV-1), an alphaherpesvirus, as a novel vectored DIVA (differentiating infected from vaccinated animals) vaccine expressing VP2 of BTV-8 alone or in combination with VP5. The EHV-1 recombinant viruses stably expressed the transgenes and grew with kinetics that were identical to those of parental virus in vitro. After immunization of mice, a BTV-8-specific neutralizing antibody response was elicited. In a challenge experiment using a lethal dose of BTV-8, 100% of interferon-receptor-deficient (IFNAR(-/-)) mice vaccinated with the recombinant EHV-1 carrying both VP2 and VP5, but not VP2 alone, survived. VP7 was not included in the vectored vaccines and was successfully used as a DIVA marker. In summary, we show that EHV-1 expressing BTV-8 VP2 and VP5 is capable of eliciting a protective immune response that is distinguishable from that after infection and as such may be an alternative for BTV vaccination strategies in which DIVA compatibility is of importance.

Molecular diagnosis of African Swine Fever by a new real-time PCR using universal probe library

A highly sensitive and specific real-time PCR method was developed for the reliable and rapid detection of African swine fever virus (ASFV). The method uses a commercial Universal Probe Library (UPL) probe combined with a specifically designed primer set to amplify an ASFV DNA fragment within the VP72 coding genome region. The detection range of the optimized UPL PCR technique was confirmed by analysis of a large panel (n = 46) of ASFV isolates, belonging to 19 of the 22 viral p72 genotypes described. No amplification signal was observed when closely clinically related viruses, such as classical swine fever, or other porcine pathogens were tested by this assay. The detection limit of the UPL PCR method was established below 18 DNA copies. Validation experiments using an extensive collection of field porcine and tick samples (n = 260), coming from Eastern and Western African regions affected by ASF, demonstrated that the UPL PCR technique was able to detect over 10% more positive samples than the real-time TaqMan PCR test recommended in the OIE manual, confirming its superior diagnostic sensitivity. Clinical material collected during experimental infections with different ASFV p72 genotypes was useful for assuring both the capacity of the UPL PCR for an early viral DNA detection and the competence of the technique to be applied in any ASF diagnostic target sample. The reliability and robustness of the UPL PCR was finally verified with a panel of ASFV-infected clinical samples which was repeatedly tested at different times. Additionally, an internal control PCR assay was also developed and standardized using UPL probes within the endogenous β-actin gene. Finally, the complete study offers a new validated real-time PCR technique, by means of a standardized commercial probe, providing a simple, rapid and affordable test, which is ready for application in the routine diagnosis of ASF.

Rapid molecular detection methods for arboviruses of livestock of importance to northern Europe

Arthropod-borne viruses (arboviruses) have been responsible for some of the most explosive epidemics of emerging infectious diseases over the past decade. Their impact on both human and livestock populations has been dramatic. The early detection either through surveillance or diagnosis of virus will be a critical feature in responding and resolving the emergence of such epidemics in the future. Although some of the most important emerging arboviruses are human pathogens, this paper aims to highlight those diseases that primarily affect livestock, although many are zoonotic and some occasionally cause human mortality. This paper also highlights the molecular detection methods specific to each virus and identifies those emerging diseases for which a rapid detection methods are not yet developed.

Bluetongue virus serotype 26: infection kinetics and pathogenesis in Dorset Poll sheep

Bluetongue virus serotype 26 (BTV-26) has recently been isolated from sheep in Kuwait. The aim of this study was to assess the pathogenicity and infection kinetics of BTV-26 in Dorset Poll sheep. Six sheep were experimentally infected with BTV-26 and samples taken throughout the study were used to determine the kinetics of infection using a pan specific BTV real time RT-PCR assay and two group specific ELISAs. Five of the six sheep showed mild clinical signs characteristic of bluetongue including conjunctivitis, reddening of the mouth mucosal membranes, slight oedema of the face and nasal discharge. Viral RNA was detected in 5 of the 6 sheep by real time RT-PCR, however the levels of viral RNA detected in the samples were lower and of shorter duration than seen with other field strains of BTV. Virus was isolated from the blood of infected animals at the peak of viraemia at around 9 dpi. Antibodies against BTV were first detected by 7 dpi using the early detection BTV ELISA and a little later (7-14 dpi) using a BTV specific competitive ELISA. Four of the five remaining sheep developed neutralising antibodies to BTV-26, measured by a serum neutralisation test (SNT), with titres (log(10)) ranging from 1.40 to 2.08.

Complete genome characterisation of a novel 26th bluetongue virus serotype from Kuwait

Bluetongue virus is the "type" species of the genus Orbivirus, family Reoviridae. Twenty four distinct bluetongue virus (BTV) serotypes have been recognized for decades, any of which is thought to be capable of causing "bluetongue" (BT), an insect-borne disease of ruminants. However, two further BTV serotypes, BTV-25 (Toggenburg orbivirus, from Switzerland) and BTV-26 (from Kuwait) have recently been identified in goats and sheep, respectively. The BTV genome is composed of ten segments of linear dsRNA, encoding 7 virus-structural proteins (VP1 to VP7) and four distinct non-structural (NS) proteins (NS1 to NS4). We report the entire BTV-26 genome sequence (isolate KUW2010/02) and comparisons to other orbiviruses. Highest identity levels were consistently detected with other BTV strains, identifying KUW2010/02 as BTV. The outer-core protein and major BTV serogroup-specific antigen "VP7" showed 98% aa sequence identity with BTV-25, indicating a common ancestry. However, higher level of variation in the nucleotide sequence of Seg-7 (81.2% identity) suggests strong conservation pressures on the protein of these two strains, and that they diverged a long time ago. Comparisons of Seg-2, encoding major outer-capsid component and cell-attachment protein "VP2" identified KUW2010/02 as 26th BTV, within a 12th Seg-2 nucleotype [nucleotype L]. Comparisons of Seg-6, encoding the smaller outer capsid protein VP5, also showed levels of nt/aa variation consistent with identification of KUW2010/02 as BTV-26 (within a 9th Seg-6 nucleotype - nucleotype I). Sequence data for Seg-2 of KUW2010/02 were used to design four sets of oligonucleotide primers for use in BTV-26, type-specific RT-PCR assays. Analyses of other more conserved genome segments placed KUW2010/02 and BTV-25/SWI2008/01 closer to each other than to other "eastern" or "western" BTV strains, but as representatives of two novel and distinct geographic groups (topotypes). Our analyses indicate that all of the BTV genome segments have evolved under strong purifying selection.

Characterization of protection afforded by a bivalent virus-like particle vaccine against bluetongue virus serotypes 1 and 4 in sheep

Background

Bluetongue virus (BTV) is an economically important, arthropod borne, emerging pathogen in Europe, causing disease mainly in sheep and cattle. Routine vaccination for bluetongue would require the ability to distinguish between vaccinated and infected individuals (DIVA). Current vaccines are effective but are not DIVA. Virus-like particles (VLPs) are highly immunogenic structural mimics of virus particles, that only contain a subset of the proteins present in a natural infection. VLPs therefore offer the potential for the development of DIVA compatible bluetongue vaccines.

Methodology/Principal Findings

Merino sheep were vaccinated with either monovalent BTV-1 VLPs or a bivalent mixture of BTV-1 VLPs and BTV-4 VLPs, and challenged with virulent BTV-1 or BTV-4. Animals were monitored for clinical signs, antibody responses, and viral RNA. 19/20 animals vaccinated with BTV-1 VLPs either alone or in combination with BTV-4 VLPs developed neutralizing antibodies to BTV-1, and group specific antibodies to BTV VP7. The one animal that showed no detectable neutralizing antibodies, or group specific antibodies, had detectable viral RNA following challenge but did not display any clinical signs on challenge with virulent BTV-1. In contrast, all control animals' demonstrated classical clinical signs for bluetongue on challenge with the same virus. Six animals were vaccinated with bivalent vaccine and challenged with virulent BTV-4, two of these animals had detectable viral levels of viral RNA, and one of these showed clinical signs consistent with BTV infection and died.

Conclusions

There is good evidence that BTV-1 VLPs delivered as monovalent or bivalent immunogen protect from bluetongue disease on challenge with virulent BTV-1. However, it is possible that there is some interference in protective response for BTV-4 in the bivalent BTV-1 and BTV-4 VLP vaccine. This raises the question of whether all combinations of bivalent BTV vaccines are possible, or if immunodominance of particular serotypes could interfere with vaccine efficacy.

Generation of replication-defective virus-based vaccines that confer full protection in sheep against virulent bluetongue virus challenge

The reverse genetics technology for bluetongue virus (BTV) has been used in combination with complementing cell lines to recover defective BTV-1 mutants. To generate a potential disabled infectious single cycle (DISC) vaccine strain, we used a reverse genetics system to rescue defective virus strains with large deletions in an essential BTV gene that encodes the VP6 protein (segment S9) of the internal core. Four VP6-deficient BTV-1 mutants were generated by using a complementing cell line that provided the VP6 protein in trans. Characterization of the growth properties of mutant viruses showed that each mutant has the necessary characteristics for a potential vaccine strain: (i) viral protein expression in noncomplementing mammalian cells, (ii) no infectious virus generated in noncomplementing cells, and (iii) efficient replication in the complementing VP6 cell line. Further, a defective BTV-8 strain was made by reassorting the two RNA segments that encode the two outer capsid proteins (VP2 and VP5) of a highly pathogenic BTV-8 with the remaining eight RNA segments of one of the BTV-1 DISC viruses. The protective capabilities of BTV-1 and BTV-8 DISC viruses were assessed in sheep by challenge with specific virulent strains using several assay systems. The data obtained from these studies demonstrated that the DISC viruses are highly protective and could offer a promising alternative to the currently available attenuated and killed virus vaccines and are also compliant as DIVA (differentiating infected from vaccinated animals) vaccines.

Novel bluetongue virus serotype from Kuwait

Sheep and goats sampled in Kuwait during February 2010 were seropositive for bluetongue virus (BTV). BTV isolate KUW2010/02, from 1 of only 2 sheep that also tested positive for BTV by real-time reverse transcription-PCR, caused mild clinical signs in sheep. Nucleotide sequencing identified KUW2010/02 as a novel BTV serotype.

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.

Experimental infection of South American camelids with bluetongue virus serotype 8

Bluetongue (BT) is an infectious, non-contagious disease of wild and domestic ruminants. It is caused by bluetongue virus (BTV) and transmitted by Culicoides biting midges. Since 1998, BT has been emerging throughout Europe, threatening not only the naïve ruminant population. Historically, South American camelids (SAC) were considered to be resistant to BT disease. However, recent fatalities related to BTV in captive SAC have raised questions about their role in BTV epidemiology. Data on the susceptibility of SAC to experimental infection with BTV serotype 8 (BTV-8) were collected in an animal experiment. Three alpacas (Vicugna pacos) and three llamas (Lama glama) were experimentally infected with BTV-8. They displayed very mild clinical signs. Seroconversion was first measured 6-8 days after infection (dpi) by ELISA, and neutralising antibodies appeared 10-13 dpi. BTV-8 RNA levels in blood were very low, and quickly cleared after seroconversion. However, spleens collected post-mortem were still positive for BTV RNA, over 71 days after the last detection in blood samples. Virus isolation was only possible from blood samples of two alpacas by inoculation of highly sensitive interferon alpha/beta receptor-deficient (IFNAR(-/-)) mice. An in vitro experiment demonstrated that significantly lower amounts of BTV-8 adsorb to SAC blood cells than to bovine blood cells. Although this experiment showed that SAC are generally susceptible to a BTV-8 infection, it indicates that these species play a negligible role in BTV epidemiology.

Role of wild ruminants in the epidemiology of bluetongue virus serotypes 1, 4 and 8 in Spain

Although the importance of wild ruminants as potential reservoirs of bluetongue virus (BTV) has been suggested, the role played by these species in the epidemiology of BT in Europe is still unclear. We carried out a serologic and virologic survey to assess the role of wild ruminants in the transmission and maintenance of BTV in Andalusia (southern Spain) between 2006 and 2010.

A total of 473 out of 1339 (35.3%) wild ruminants analyzed showed antibodies against BTV by both ELISA and serum neutralization test (SNT). The presence of neutralizing antibodies to BTV-1 and BTV-4 were detected in the four species analyzed (red deer, roe deer, fallow deer and mouflon), while seropositivity against BTV-8 was found in red deer, fallow deer and mouflon but not in roe deer. Statistically significant differences were found among species, ages and sampling regions. BTV RNA was detected in twenty-one out of 1013 wild ruminants (2.1%) tested. BTV-1 and BTV-4 RNA were confirmed in red deer and mouflon by specific rRT-PCR.

BTV-1 and BTV-4 seropositive and RNA positive wild ruminants, including juveniles and sub-adults, were detected years after the last outbreak was reported in livestock. In addition, between the 2008/2009 and the 2010/2011 hunting seasons, the seroprevalence against BTV-1, BTV-4 and BTV-8 increased in the majority of provinces, and these serotypes were detected in many areas where BTV outbreaks were not reported in domestic ruminants. The results indicate that wild ruminants seem to be implicated in the dissemination and persistence of BTV in Spain.