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

Orbivirus NS4 Proteins Play Multiple Roles to Dampen Cellular Responses

Non-structural protein 4 (NS4) of insect-borne and tick-borne orbiviruses is encoded by genome segment 9, from a secondary open reading frame. Though a protein dispensable for bluetongue virus (BTV) replication, it has been shown to counter the interferon response in cells infected with BTV or African horse sickness virus. We further explored the functional role(s) of NS4 proteins of BTV and the tick-borne Great Island virus (GIV). We show that NS4 of BTV or GIV helps an E3L deletion mutant of vaccinia virus to replicate efficiently in interferon-treated cells, further confirming the role of NS4 as an interferon antagonist. Our results indicate that ectopically expressed NS4 of BTV localised with caspase 3 within the nucleus and was found in a protein complex with active caspase 3 in a pull-down assay. Previous studies have shown that pro-apoptotic caspases (including caspase 3) suppress type I interferon response by cleaving mediators involved in interferon signalling. Our data suggest that orbivirus NS4 plays a role in modulating the apoptotic process and/or regulating the interferon response in mammalian cells, thus acting as a virulence factor in pathogenesis.

Uncovering the Underlying Mechanisms Blocking Replication of Bluetongue Virus Serotype 26 (BTV-26) in Culicoides Cells

At least 12 serotypes of 'atypical' bluetongue virus (BTV-25 to BTV-36) have been identified to date. These atypical serotypes fail to infect/replicate in Culicoides-derived cell lines and/or adult Culicoides vectors and hence can no longer be transmitted by these vectors. They appear to be horizontally transmitted from infected to in-contact ruminants, although the route(s) of infection remain to be identified. Viral genome segments 1, 2 and 3 (Seg-1, Seg2 and Seg-3) of BTV-26 were identified as involved in blocking virus replication in KC cells. We have developed Culicoides-specific expression plasmids, which we used in transfected insect cells to assess the stability of viral mRNAs and protein expression from full-length open reading frames of Seg-1, -2 and -3 of BTV-1 (a Culicoides-vectored BTV) or BTV-26. Our results indicate that the blocked replication of BTV-26 in KC cells is not due to an RNAi response, which would lead to rapid degradation of viral mRNAs. A combination of degradation/poor expression and/or modification of the proteins encoded by these segments appears to drive the failure of BTV-26 core/whole virus-particles to assemble and replicate effectively in Culicoides cells.

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.

Identification of the Genome Segments of Bluetongue Virus Type 26/Type 1 Reassortants Influencing Horizontal Transmission in a Mouse Model

Bluetongue virus serotypes 1 to 24 are transmitted primarily by infected Culicoides midges, in which they also replicate. However, “atypical” BTV serotypes (BTV-25, -26, -27 and -28) have recently been identified that do not infect and replicate in adult Culicoides, or a Culicoides derived cell line (KC cells). These atypical viruses are transmitted horizontally by direct contact between infected and susceptible hosts (primarily small ruminants) causing only mild clinical signs, although the exact transmission mechanisms involved have yet to be determined. We used reverse genetics to generate a strain of BTV-1 (BTV-1 RG_C7) which is less virulent, infecting IFNAR^(−/−) mice without killing them. Reassortant viruses were also engineered, using the BTV-1 RG_C7 genetic backbone, containing individual genome segments derived from BTV-26. These reassortant viruses were used to explore the genetic control of horizontal transmission (HT) in the IFNAR^(−/−) mouse model. Previous studies showed that genome segments 1, 2 and 3 restrict infection of Culicoides cells, along with a minor role for segment 7. The current study demonstrates that genome segments 2, 5 and 10 of BTV-26 (coding for proteins VP2, NS1 and NS3/NS3a/NS5, respectively) are individually sufficient to promote HT.

Pentavalent Disabled Infectious Single Animal (DISA)/DIVA Vaccine Provides Protection in Sheep and Cattle against Different Serotypes of Bluetongue Virus

Bluetongue (BT) is a midge-borne OIE-notifiable disease of ruminants caused by the bluetongue virus (BTV). There are at least 29 BTV serotypes as determined by serum neutralization tests and genetic analyses of genome segment 2 encoding serotype immunodominant VP2 protein. Large parts of the world are endemic for multiple serotypes. The most effective control measure of BT is vaccination. Conventionally live-attenuated and inactivated BT vaccines are available but have their specific pros and cons and are not DIVA compatible. The prototype Disabled Infectious Single Animal (DISA)/DIVA vaccine based on knockout of NS3/NS3a protein of live-attenuated BTV, shortly named DISA8, fulfills all criteria for modern veterinary vaccines of sheep. Recently, DISA8 with an internal in-frame deletion of 72 amino acid codons in NS3/NS3a showed a similar ideal vaccine profile in cattle. Here, the DISA/DIVA vaccine platform was applied for other serotypes, and pentavalent DISA/DIVA vaccine for “European” serotypes 1, 2, 3, 4, 8 was studied in sheep and cattle. Protection was demonstrated for two serotypes, and neutralization Ab titers indicate protection against other included serotypes. The DISA/DIVA vaccine platform is flexible in use and generates monovalent and multivalent DISA vaccines to combat specific field situations with respect to Bluetongue.

Bluetongue and Epizootic Hemorrhagic Disease in the United States of America at the Wildlife-Livestock Interface

Bluetongue (BT) and epizootic hemorrhagic disease (EHD) cases have increased worldwide, causing significant economic loss to ruminant livestock production and detrimental effects to susceptible wildlife populations. In recent decades, hemorrhagic disease cases have been reported over expanding geographic areas in the United States. Effective BT and EHD prevention and control strategies for livestock and monitoring of these diseases in wildlife populations depend on an accurate understanding of the distribution of BT and EHD viruses in domestic and wild ruminants and their vectors, the Culicoides biting midges that transmit them. However, national maps showing the distribution of BT and EHD viruses and the presence of Culicoides vectors are incomplete or not available at all. Thus, efforts to accurately describe the potential risk of these viruses on ruminant populations are obstructed by the lack of systematic and routine surveillance of their hosts and vectors. In this review, we: (1) outline animal health impacts of BT and EHD in the USA; (2) describe current knowledge of the distribution and abundance of BT and EHD and their vectors in the USA; and (3) highlight the importance of disease (BT and EHD) and vector surveillance for ruminant populations.

The Bluetongue Disabled Infectious Single Animal (DISA) Vaccine Platform Based on Deletion NS3/NS3a Protein Is Safe and Protective in Cattle and Enables DIVA

The bluetongue virus (BTV) is transmitted by Culicoides biting midges and causes bluetongue (BT), an OIE-notifiable disease of ruminants. At least 29 BTV serotypes are described as determined by the outer shell proteins VP2 and VP5. Vaccination is the most effective control measure. Inactivated and live-attenuated vaccines (LAVs) are currently available. These vaccines have their specific pros and cons, and both are not DIVA vaccines. The BT Disabled Infectious Single Animal (DISA) vaccine platform is based on LAV without nonessential NS3/NS3a expression and is applicable for many serotypes by the exchange of outer shell proteins. The DISA vaccine is effective and completely safe. Further, transmission of the DISA vaccine by midges is blocked (DISA principle). Finally, the DISA vaccine enables DIVA because of a lack of antibodies against the immunogenic NS3/NS3a protein (DIVA principle). The deletion of 72 amino acids (72aa) in NS3/NS3a is sufficient to block virus propagation in midges. Here, we show that a prototype DISA vaccine based on LAV with the 72aa deletion enables DIVA, is completely safe and induces a long-lasting serotype-specific protection in cattle. In conclusion, the in-frame deletion of 72-aa codons in the BT DISA/DIVA vaccine platform is sufficient to fulfil all the criteria for modern veterinary vaccines.

Novel putative bluetongue virus serotype 29 isolated from inapparently infected goat in Xinjiang of China

Bluetongue virus (BTV) is the 'type' species of the genus Orbivirus causing bluetongue (BT) in sheep, bovine and other ruminants. Twenty-four serotypes and several atypical serotypes of BTV were identified worldwide. In present study, a novel strain of BTV (V196/XJ/2014) was isolated from an asymptomatic sentinel goat in Yuli County, Xinjiang of China. Serotype identification of this isolate exhibited uniform negative results by serotype-specific conventional RT-PCR and real-time RT-PCR for BTV-1 to BTV-27, and virus neutralization tests using reference sera of BTV-1 to BTV-24. Genomic analysis showed V196/XJ/2014 grouped with atypical serotypes of BTV-25 to BTV-28, BTV-X/XJ1407, BTV-X/ITL2015 and BTV-Y/TUN2017, while segment 2 and VP2 protein of V196/XJ/2014 shared <63.4%/61.4% nucleic acids and amino acids sequence identities with other recognized BTV serotypes and its segment 2 formed a separate 'nucleotype' in phylogenetic tree. These results indicated V196/XJ/2014 does not belong to any reported serotypes of BTV. Further studies of infectivity and pathogenicity showed that goats infected with V196/XJ/2014 did not exhibit observed clinical symptoms, but high level of virus amplification and homologous neutralization antibodies were detected post-infection. Our studies suggested a novel putative serotype of BTV-29 was isolated in Xinjiang of China, which expands our knowledge about the diversity of BTV.

Putative Novel Atypical BTV Serotype '36' Identified in Small Ruminants in Switzerland

We identified a putative novel atypical BTV serotype '36' in Swiss goat flocks. In the initial flock clinical signs consisting of multifocal purulent dermatitis, facial oedema and fever were observed. Following BTV detection by RT-qPCR, serotyping identified BTV-25 and also a putative novel BTV serotype in several of the affected goats. We successfully propagated the so-called "BTV-36-CH2019" strain in cell culture, developed a specific RT-qPCR targeting Segment 2, and generated the full genome by high-throughput sequencing. Furthermore, we experimentally infected goats with BTV-36-CH2019. Regularly, EDTA blood, serum and diverse swab samples were collected. Throughout the experiment, neither fever nor clinical disease was observed in any of the inoculated goats. Four goats developed BTV viremia, whereas one inoculated goat and the two contact animals remained negative. No viral RNA was detected in the swab samples collected from nose, mouth, eye, and rectum, and thus the experimental infection of goats using this novel BTV serotype delivered no indications for any clinical symptoms or vector-free virus transmission pathways. The subclinical infection of the four goats is in accordance with the reports for other atypical BTVs. However, the clinical signs of the initial goat flock did most likely not result from infection with the novel BTV-36-CH0219.

Putative Novel Serotypes '33' and '35' in Clinically Healthy Small Ruminants in Mongolia Expand the Group of Atypical BTV

Between 2015 and 2018, we identified the presence of three so-far-unknown Bluetongue virus (BTV) strains (BTV-MNG1/2018, BTV-MNG2/2016, and BTV-MNG3/2016) circulating in clinical healthy sheep and goats in Mongolia. Virus isolation from EDTA blood samples of BTV-MNG1/2018 and BTV-MNG3/2016 was successful on the mammalian cell line BSR using blood collected from surveillance. After experimental inoculation of goats with BTV-MNG2/2016 positive blood as inoculum, we observed viraemia in one goat and with the EDTA blood of the experimental inoculation, the propagation of BTV-MNG2/2016 in cell culture was successful on mammalian cell line BSR as well. However, virus isolation experiments for BTV-MNG2/2016 on KC cells were unsuccessful. Furthermore, we generated the complete coding sequence of all three novel Mongolian strains. For atypical BTV, serotyping via the traditional serum neutralization assay is not trivial. We therefore sorted the ‘putative novel atypical serotypes’ according to their segment-2 sequence identities and their time point of sampling. Hence, the BTV-MNG1/2018 isolate forms the ‘putative novel atypical serotype’ 33, the BTV-MNG3/2016 the ‘putative novel atypical serotype’ 35, whereas the BTV-MNG2/2016 strain belongs to the same putative novel atypical serotype ‘30’ as BTV-XJ1407 from China.

Inhibition of Orbivirus Replication by Aurintricarboxylic Acid

Bluetongue virus (BTV) and African horse sickness virus (AHSV) are vector-borne viruses belonging to the Orbivirus genus, which are transmitted between hosts primarily by biting midges of the genus Culicoides. With recent BTV and AHSV outbreaks causing epidemics and important economy losses, there is a pressing need for efficacious drugs to treat and control the spread of these infections. The polyanionic aromatic compound aurintricarboxylic acid (ATA) has been shown to have a broad-spectrum antiviral activity. Here, we evaluated ATA as a potential antiviral compound against Orbivirus infections in both mammalian and insect cells. Notably, ATA was able to prevent the replication of BTV and AHSV in both cell types in a time- and concentration-dependent manner. In addition, we evaluated the effect of ATA in vivo using a mouse model of infection. ATA did not protect mice against a lethal challenge with BTV or AHSV, most probably due to the in vivo effect of ATA on immune system regulation. Overall, these results demonstrate that ATA has inhibitory activity against Orbivirus replication in vitro, but further in vivo analysis will be required before considering it as a potential therapy for future clinical evaluation.

Isolation and Cultivation of a New Isolate of BTV-25 and Presumptive Evidence for a Potential Persistent Infection in Healthy Goats

Recently, several so-called “atypical” Bluetongue virus (BTV) serotypes were discovered, including BTV-25 (Toggenburg virus), in Switzerland. Most “atypical” BTV were identified in small ruminants without clinical signs. In 2018, two goats from a holding in Germany tested positive for BTV-25 genome by RT-qPCR prior to export. After experimental inoculation of the two goats with the BTV-25 positive field blood samples for generation of reference materials, viremia could be observed in one animal. For the first time, the BTV-25-related virus was isolated in cell culture from EDTA-blood and the full genome of isolate “BTV-25-GER2018” could be generated. BTV-25-GER2018 was only incompletely neutralized by ELISA-positive sera. We could monitor the BTV-25 occurrence in the respective affected goat flock of approximately 120 goats over several years. EDTA blood samples were screened with RT-qPCR using a newly developed BTV-25 specific assay. For serological surveillance, serum samples were screened using a commercial cELISA. BTV-25-GER2018 was detected over 4.5 years in the goat flock with intermittent PCR-positivity in some animals, and with or without concomitantly detected antibodies since 2015. We could demonstrate the viral persistence of BTV-25-GER2018 in goats for up to 4.5 years, and the first BTV-25 isolate is now available for further characterization.

Ecological Dynamics Impacting Bluetongue Virus Transmission in North America

Bluetongue virus (BTV) is an arbovirus transmitted to domestic and wild ruminants by certain species of Culicoides midges. The disease resulting from infection with BTV is economically important and can influence international trade and movement of livestock, the economics of livestock production, and animal welfare. Recent changes in the epidemiology of Culicoides-transmitted viruses, notably the emergence of exotic BTV genotypes in Europe, have demonstrated the devastating economic consequences of BTV epizootics and the complex nature of transmission across host-vector landscapes. Incursions of novel BTV serotypes into historically enzootic countries or regions, including the southeastern United States (US), Israel, Australia, and South America, have also occurred, suggesting diverse pathways for the transmission of these viruses. The abundance of BTV strains and multiple reassortant viruses circulating in Europe and the US in recent years demonstrates considerable genetic diversity of BTV strains and implies a history of reassortment events within the respective regions. While a great deal of emphasis is rightly placed on understanding the epidemiology and emergence of BTV beyond its natural ecosystem, the ecological contexts in which BTV maintains an enzootic cycle may also be of great significance. This review focuses on describing our current knowledge of ecological factors driving BTV transmission in North America. Information presented in this review can help inform future studies that may elucidate factors that are relevant to longstanding and emerging challenges associated with prevention of this disease.

Comparative Evaluation of T-Cell Immune Response to BTV Infection in Sheep Vaccinated with Pentavalent BTV Vaccine When Compared to Un-Vaccinated Animals

Recent invasion of multiple bluetongue virus serotypes (BTV) in different regions of the world necessitates urgent development of efficient vaccine that is directed against multiple BTV serotypes. In this experimental study, cell mediated immune response and protective efficacy of binary ethylenimine (BEI) inactivated Montanide^™ ISA 206 adjuvanted pentavalent (BTV-1, 2, 10, 16 and 23) vaccine was evaluated in sheep and direct challenge with homologous BTV serotypes in their respective group. Significant (P < 0.05) up-regulation of mRNA transcripts of IFN-α, IL-2, IL-6, IL-12, IFN-γ and TNF-α in PBMCs of vaccinated animals as compared to control (un-vaccinated) animals at certain time points was observed. On the other hand, there was a significant increase in mean ± SD percentage of CD8⁺ T cells after 7 days post challenge (DPC) but, the mean ± SD percentage of CD4⁺ T-cell population slightly declined at 7 DPC and enhanced after 14 DPC. Significant differences (P < 0.05) of CD8⁺ and CD4⁺T cells population was also observed between vaccinated and unvaccinated sheep. The vaccine also significantly (P < 0.05) reduced BTV RNA load in PBMCs of vaccinated animals than unvaccinated animals following challenge. There were no significant difference (P > 0.05) in cytokine induction, BTV RNA load and CD8⁺ and CD4⁺cell count among BTV-1, 2, 10, 16 and 23 serotype challenges except significant increase in mean ± SD percentage of CD8⁺ in BTV-2 group. These findings put forwarded that binary ethylenimine inactivated montanide adjuvanted pentavalent bluetongue vaccine has stimulated cell mediated immune response and most importantly reduced the severity of BTV-1, 2, 10, 16 and 23 infections following challenge in respective group.

Prospects of Next-Generation Vaccines for Bluetongue

Bluetongue (BT) is a haemorrhagic disease of wild and domestic ruminants with a huge economic worldwide impact on livestock. The disease is caused by BT-virus transmitted by Culicoides biting midges and disease control without vaccination is hardly possible. Vaccination is the most feasible and cost-effective way to minimize economic losses. Marketed BT vaccines are successfully used in different parts of the world. Inactivated BT vaccines are efficacious and safe but relatively expensive, whereas live-attenuated vaccines are efficacious and cheap but are unsafe because of under-attenuation, onward spread, reversion to virulence, and reassortment events. Both manufactured BT vaccines do not enable differentiating infected from vaccinated animals (DIVA) and protection is limited to the respective serotype. The ideal BT vaccine is a licensed, affordable, completely safe DIVA vaccine, that induces quick, lifelong, broad protection in all susceptible ruminant species. Promising vaccine candidates show improvement for one or more of these main vaccine standards. BTV protein vaccines and viral vector vaccines have DIVA potential depending on the selected BTV antigens, but are less effective and likely more costly per protected animal than current vaccines. Several vaccine platforms based on replicating BTV are applied for many serotypes by exchange of serotype dominant outer shell proteins. These platforms based on one BTV backbone result in attenuation or abortive virus replication and prevent disease by and spread of vaccine virus as well as reversion to virulence. These replicating BT vaccines induce humoral and T-cell mediated immune responses to all viral proteins except to one, which could enable DIVA tests. Most of these replicating vaccines can be produced similarly as currently marketed BT vaccines. All replicating vaccine platforms developed by reverse genetics are classified as genetic modified organisms. This implies extensive and expensive safety trails in target ruminant species, and acceptance by the community could be hindered. Nonetheless, several experimental BT vaccines show very promising improvements and could compete with marketed vaccines regarding their vaccine profile, but none of these next generation BT vaccines have been licensed yet.

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.

Replication kinetics and cellular tropism of emerging reoviruses in sheep and swine respiratory ex vivo organ cultures

Ex vivo organ cultures (EVOCs) are extensively used to study the cellular tropism and infectivity of different pathogens. In this study, we used ovine and porcine respiratory EVOCs to investigate the replication kinetics and cellular tropism of selected emerging reoviruses namely Pteropine orthoreovirus, an emerging bat-borne zoonotic respiratory virus, and atypical Bluetongue virus (BTV) serotypes which, unlike classical serotypes, do not cause Bluetongue, a major OIE-listed disease of ruminants. BTV failed to replicate in ovine EVOCs. Instead, PRV showed slight replication in porcine lower respiratory EVOCs and a more sustained replication in all ovine respiratory tissues. By confocal laser scanning microscopy, PRV was demonstrated to infect bronchiolar and type I pneumocytes of ovine tissues. Overall, respiratory EVOCs from different animal species, eventually obtained at slaughterhouse, are a useful tool for testing and preliminarily characterize novel and emerging viruses addressing the essential in vivo animal work. Further experiments are, indeed, warranted in order to characterize the pathogenesis and transmission of these emerging reoviruses.

Molecular typing of Bluetongue virus using the nCounter® analysis system platform

Bluetongue virus (BTV) is a segmented double-stranded RNA virus, existing in multiple serotypes, belonging to the genus Orbivirus of the family Reoviridae. BTV causes Bluetongue (BT), a major OIE-listed disease of ruminants. Identification of BTV serotype is accomplished using multiple typing assays and tends to be executed based on the known epidemiological situation within a given country. Samples containing multiple serotypes, particularly those containing novel introductions, may therefore be missed. The aim of this work was to optimize the nCounter® Analysis System Microarray platform (NanoString technologies), that would simultaneously identify all BTV serotypes and co-infections in analyzed samples. Probes were designed according to all Seg-2 sequences, coding for VP2 proteins which determine serotype specificity, available on line. A specific BTV CodeSet of probes was optimized. Experiments were performed with 30 BTV isolates and with 46 field samples previously shown to be infected with BTV by classical molecular assays. All BTV isolates were correctly identified and the expected BTV serotype was recognized in 35 field samples with C_T values between 22.0-33.0. In turn, it was unable to identify 11 samples with C_T values between 29.0-38.0. Although specificity of the assay needs to be further investigated against a larger panel of BTVs collected worldwide, RNA loads, which are normally detected in blood samples during the acute phase of infection, are within the range of C_T values detectable by the BTV CodeSet. We propose the NanoString RNA microarray as a first-line molecular diagnostic tool for identification and typing of BTV. Once identification of the index cases is performed, diagnosis of the following samples may be performed by specific, more sensitive and cheaper PCR-based tools.

Bluetongue and epizootic hemorrhagic disease viruses: recent developments with these globally re-emerging arboviral infections of ruminants

Bluetongue (BT) and epizootic hemorrhagic disease (EHD) are globally re-emerging diseases of domestic and wild ruminants, respectively caused by BT virus (BTV) and EHD virus. Both viruses are transmitted by hematophagous midges; however, newly recognized BTV serotypes may be transmitted horizontally without requirement for any biological vector. The global range of these viruses and/or their associated diseases have changed remarkably in recent years, most notably with the invasion of Europe by multiple serotypes of BTV since 1998. Although not zoonoses, the unanticipated emergence of BT and EHD in several different areas of the world provides a uniquely sobering and unambiguous reminder of the potential consequences of climate change on the distribution and severity of vector-borne diseases. Recent experiences with these viruses have also emphasized the need for effective, DIVA-compatible vaccines to combat anticipated future incursions, as existing vaccines have serious inherent deficiencies.

Exploiting serological data to understand the epidemiology of bluetongue virus serotypes circulating in Libya

The epidemiological patterns of Bluetongue (BT) in North Africa and Mediterranean Basin (MB) dramatically changed by emergence of subsequent episodes of novel bluetongue virus (BTV) serotypes with highly pathogenic indexes and socio-economic impacts. The objective of the study was to investigate the sero-prevalence and serotype distribution of BTV in Libya. During 2015-2016, a total of 826 serum samples were collected from domestic ruminants in Libya. All sera were assayed by competitive enzyme-linked immunosorbent assays (c-ELISA). C-Elisa-positive samples (43.3%; 173/400) were further analyzed by virus neutralization assay to identify BTV serotypes and determine the antibody titre of positive samples. An overall BTV sero-prevalence was 48.4% (95% CI: 45.0%-51.8%). Neutralizing antibodies were detected against the following BTV serotypes namely: BTV-1, BTV-2, BTV-3, BTV-4, BTV-9 and BTV-26. While BTV-1, BTV-2, BTV-4 and BTV-9 circulation was unsurprising as they have been responsible of the last year outbreaks in Northern African Countries, the detection of BTV-3 and BTV-26 was definitely new and concerning for the animal health of the countries facing the Mediterranean Basin. It is crucial that European and Northern African authorities collaborate in organizing common surveillance programmes to early detect novel strains or emerging serotypes in order to set up proper preventive measures, and, in case, develop specific vaccines and plan coordinated vaccination campaigns.

Evaluating the most appropriate pooling ratio for EDTA blood samples to detect Bluetongue virus using real-time RT-PCR

The control of Bluetongue virus (BTV) presents a significant challenge to European Union (EU) member states as trade restrictions are placed on animals imported from BTV-affected countries. BTV surveillance programs are costly to maintain, thus, pooling of EDTA blood samples is used to reduce costs and increase throughput. We investigated different pooling ratios (1:2, 1:5, 1:10 and 1:20) for EDTA blood samples to detect a single BTV positive animal. A published real-time RT-PCR assay (Hofmann et al., 2008) and a commercial assay (ThermoFisher VetMax™ BTV NS3 kit) were used to analyse BTV RNA extracted from pooled EDTA blood samples. The detection rate was low for the onset of infection sample (0-2 days post infection (dpi); C_T 36) irrespective of the pooling ratio. Both assays could reliably detect a single BTV-positive animal at early viraemia (3-6 dpi; C_T 33) when pooled, however, detection rate diminished with increasing pooling ratio. A statistical model indicated that pooling samples up to 1:20, is suitable to detect a single BTV positive animal at peak viraemia (7-12 dpi) or late infection (13-30 dpi) with a probability of detection of >80% and >94% using the Hofmann et al. (2008) and VetMAX assays, respectively. Using the assays highlighted in our study, pooling at ratios of 1:20 would be technically suitable in BTV-endemic countries for surveillance purposes. As peak viraemia occurs between 7-12 days post infection, a 1:10 pooling ratio is appropriate for post-import testing when animals are sampled within a similar time frame post-import.

One after the other: A novel Bluetongue virus strain related to Toggenburg virus detected in the Piedmont region (North-western Italy), extends the panel of novel atypical BTV strains

In this rapid communication, a novel atypical bluetongue virus (BTV) strain detected in goats in the Piedmont region (north-western Italy) is described. This strain, BTV-Z ITA2017, is most related in Seg-2/VP-2 (83.8% nt/82.7% aa) to strain TOV of BTV-25. Reactive antisera of goats positive by cELISA for BTV antibodies failed to neutralize a chimeric virus expressing the outermost protein of TOV. Infected animals displayed low levels of RNAemia and absence of clinical signs consistent with bluetongue infection, a scenario described in animals infected with atypical BTV strains.

A comprehensive study on seroprevalence of bluetongue virus in Haryana state of India

AIM

The aim of present study was to determine seroprevalence of bluetongue virus (BTV) in Haryana state of India.

MATERIALS AND METHODS

A total of 803 serum samples, 408 of cattle and 395 of buffalo origin, respectively, were collected from different villages of Haryana. Sampling was done randomly to obtain unbiased results. The samples were evaluated by a competitive enzyme-linked immunosorbent assay for the presence of BTV antibodies.

RESULTS

Overall seroprevalence of BTV antibody in cattle and buffaloes for all 21 districts of Haryana state was found to be 75.49% and 92.91%, respectively. The prevalence of BTV in different agroclimatic zones ranged between 72-77% and 90-94% for cattle and buffalo, respectively. In buffaloes, the BTV seroprevalence was comparatively higher than in cattle.

CONCLUSION

The study showed that BTV is circulating in cattle and buffalo populations in the Northern part of India.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): bluetongue

A specific concept of strain was developed in order to classify the BTV serotypes ever reported in Europe based on their properties of animal health impact: the genotype, morbidity, mortality, speed of spread, period and geographical area of occurrence were considered as classification parameters. According to this methodology the strain groups identified were (i) the BTV strains belonging to serotypes BTV‐1–24, (ii) some strains of serotypes BTV‐16 and (iii) small ruminant‐adapted strains belonging to serotypes BTV‐25, ‐27, ‐30. Those strain groups were assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7, Article 5 on the eligibility of bluetongue to be listed, Article 9 for the categorisation according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to bluetongue. The assessment has been performed following a methodology composed of information collection, expert judgement at individual and collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. The strain group BTV (1–24) can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL, while the strain group BTV‐25–30 and BTV‐16 cannot. The strain group BTV‐1–24 meets the criteria as in Sections 2 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (b) and (e) of Article 9(1) of the AHL. The animal species that can be considered to be listed for BTV‐1–24 according to Article 8(3) are several species of Bovidae, Cervidae and Camelidae as susceptible species; domestic cattle, sheep and red deer as reservoir hosts, midges insect of genus Culicoides spp. as vector species.

Novel putative Bluetongue virus in healthy goats from Sardinia, Italy

In recent years, novel Bluetongue virus (BTV) serotypes have been isolated and/or sequenced by researchers within the field. During Bluetongue surveillance activities, we identified a putative novel BTV serotype in healthy goats from Sardinia, Italy. RNAs purified from blood and serum samples were positive for BTV by a generic real time RT-PCR and c-ELISA, respectively, whereas genotyping and serotyping were unsuccessful. By NGS, the whole genome sequence was obtained from two blood samples (BTV-X ITL2015 strains 34200 and 33531). Overall, Seg 2 of BTV-X ITL2015 shows the highest identity (75.3-75.5% nt/77.4-78.1% aa) with recently isolated BTV-27s from Corsica and with the last discovered BTV XJ1407 from China (75.9% nt /78.2% aa), whereas it is less related with BTV-25 from Switzerland (73.0% nt/75.0% aa) and BTV-26 from Kuwait (62.0% nt/60.5% aa). A specific RT-qPCR targeting Seg 2 of BTV-X ITL2015 was assessed in this study. Considering the Seg 2/VP2 identity of BTV-X ITL2015 with BTV-25, 26, 27s and BTV XJ1407 and that serum of BTV-X ITL2015 infected goats failed to neutralize all tested extant serotypes, we propose the existence of a novel BTV serotype circulating in goats in Sardinia. Isolation was so far unsuccessful thus hampering proper antigenic characterization.

Bluetongue Virus: From BTV-1 to BTV-27

Bluetongue virus (BTV) is the type species of genus Orbivirus within family Reoviridae. Bluetongue virus is transmitted between its ruminant hosts by the bite of Culicoides spp. midges. Severe BT cases are characterized by symptoms including hemorrhagic fever, particularly in sheep, loss of productivity, and death. To date, 27 BTV serotypes have been documented. These include novel isolates of atypical BTV, which have been almost fully characterized using deep sequencing technologies and do not rely on Culicoides vectors for their transmission among hosts. Due to its high economic impact, BT is an Office International des Epizooties (OIE) listed disease that is strictly controlled in international commercial exchanges. During the 20th century, BTV has been endemic in subtropical regions. In the last 15 years, novel strains of nine "typical" BTV serotypes (1, 2, 4, 6, 8, 9, 11, 14, and 16) invaded Europe, some of which caused disease in naive sheep and unexpectedly in bovine herds (particularly serotype 8). Over the past few years, three novel "atypical" serotypes (25-27) were characterized during sequencing studies of animal samples from Switzerland, Kuwait, and France, respectively. Classical serotype-specific inactivated vaccines, although expensive, were very successful in controlling outbreaks as shown with the northern European BTV-8 outbreak which started in the summer of 2006. Technological jumps in deep sequencing methodologies made rapid full characterizations of BTV genome from isolates/tissues feasible. Next-generation sequencing (NGS) approaches are powerful tools to study the variability of BTV genomes on a fine scale. This paper provides information on how NGS impacted our knowledge of the BTV genome.

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.

Bluetongue virus surveillance in the Islamic Republic of Mauritania: Is serotype 26 circulating among cattle and dromedaries?

In March 2013, EDTA-blood and serum samples were collected from 119 cattle and 159 dromedaries at the slaughterhouse of Nouakchott, the capital city of the Islamic Republic of Mauritania. Serum samples were screened for the presence of Bluetongue (BT) antibodies by competitive ELISA (cELISA). Positive samples were then tested by serum-neutralization (SN) to determine BTV serotype. RNA from blood samples was first tested by a genus-specific quantitative RT-PCR assay which is able to detect all 27 existing BTV serotypes (RT-qPCR1-27). Positive samples were further screened by a RT-qPCR assay which, instead, is able to detect the classical 24 BTV serotypes only (RT-qPCR1-24). Of the 278 serum samples tested, 177 (mean=63.7%; 95% CI: 57.9%-69.1%) resulted positive by cELISA. Of these, 69 were from cattle (mean=58.0%; 95% CI: 49.0%-66.5%) and 108 from dromedaries (mean=67.9%; 95% CI: 60.3%-74.7%). BTV-26 neutralizing antibodies were by far the most frequently found as they were detected in 146 animals with titres ranging from 1:10 to 1:80. Out of 278 blood samples, 25 (mean=9.0%; 95% CI: 6.2%-12.9%) were found positive for BTV by RT-qPCR1-27, 20 (mean=16.8%; 95% CI: 11.2%-24.6%) were from cattle and 5 (mean=3.1%; 95% CI: 1.4%-7.1%) from dromedaries. When tested by RT-qPCR1-24 the 25 BTV positive samples were negative. Unfortunately, no genetic information by molecular typing or by next generation sequencing has been obtained as for the very low levels of RNA in the blood samples.

Identification of the Genome Segments of Bluetongue Virus Serotype 26 (Isolate KUW2010/02) that Restrict Replication in a Culicoides sonorensis Cell Line (KC Cells)

Bluetongue virus (BTV) can infect most ruminant species and is usually transmitted by adult, vector-competent biting midges (Culicoides spp.). Infection with BTV can cause severe clinical signs and can be fatal, particularly in naïve sheep and some deer species. Although 24 distinct BTV serotypes were recognized for several decades, additional 'types' have recently been identified, including BTV-25 (from Switzerland), BTV-26 (from Kuwait) and BTV-27 from France (Corsica). Although BTV-25 has failed to grow in either insect or mammalian cell cultures, BTV-26 (isolate KUW2010/02), which can be transmitted horizontally between goats in the absence of vector insects, does not replicate in a Culicoides sonorensis cell line (KC cells) but can be propagated in mammalian cells (BSR cells). The BTV genome consists of ten segments of linear dsRNA. Mono-reassortant viruses were generated by reverse-genetics, each one containing a single BTV-26 genome segment in a BTV-1 genetic-background. However, attempts to recover a mono-reassortant containing genome-segment 2 (Seg-2) of BTV-26 (encoding VP2), were unsuccessful but a triple-reassortant was successfully generated containing Seg-2, Seg-6 and Seg-7 (encoding VP5 and VP7 respectively) of BTV-26. Reassortants were recovered and most replicated well in mammalian cells (BSR cells). However, mono-reassortants containing Seg-1 or Seg-3 of BTV-26 (encoding VP1, or VP3 respectively) and the triple reassortant failed to replicate, while a mono-reassortant containing Seg-7 of BTV-26 only replicated slowly in KC cells.

Evidence for transmission of bluetongue virus serotype 26 through direct contact

The aim of this study was to assess the mechanisms of transmission of bluetongue virus serotype 26 (BTV-26) in goats. A previous study, which investigated the pathogenicity and infection kinetics of BTV-26 in goats, unexpectedly revealed that one control goat may have been infected through a direct contact transmission route. To investigate the transmission mechanisms of BTV-26 in more detail an experimental infection study was carried out in which three goats were infected with BTV-26, three goats were kept uninfected, but were housed in direct contact with the infected goats, and an additional four goats were kept in indirect contact separated from infected goats by metal gates. This barrier allowed the goats to have occasional face-to-face contact in the same airspace, but feeding, watering, sampling and environmental cleaning was carried out separately. The three experimentally infected goats did not show clinical signs of BTV, however high levels of viral RNA were detected and virus was isolated from their blood. At 21 dpi viral RNA was detected in, and virus was isolated from the blood of the three direct contact goats, which also seroconverted. The four indirect barrier contact goats remained uninfected throughout the duration of the experiment. In order to assess replication in a laboratory model species of Culicoides biting midge, more than 300 Culicoides sonorensis were fed a BTV-26 spiked blood meal and incubated for 7 days. The dissemination of BTV-26 in individual C. sonorensis was inferred from the quantity of virus RNA and indicated that none of the insects processed at day 7 possessed transmissible infections. This study shows that BTV-26 is easily transmitted through direct contact transmission between goats, and the strain does not seem to replicate in C. sonorensis midges using standard incubation conditions.

Longitudinal study of the detection of Bluetongue virus in bull semen and comparison of real-time polymerase chain reaction assays

Infection with Bluetongue virus (BTV) is a significant impediment to the global movement of bovine semen. Repeat testing of blood from donor animals is specified in the World Organization for Animal Health (OIE) Manual for the export of semen from regions where BTV may be present. Screening of blood or semen samples has usually been carried out by virus isolation (VI) either by inoculation of chicken embryos followed by passage onto insect and mammalian cell cultures or in vivo inoculation of sheep followed by serology to detect seroconversion. Direct testing of semen for BTV would enable earlier release of semen samples and avoid repeat testing of the donor, as well as provide an option for releasing batches of semen that were collected without certification of the donor. Quantitative (real-time) reverse transcription polymerase chain reaction (qRT-PCR) assays overcome most of the limitations of other methods and have the potential to provide higher sensitivity. The present study compared 5 qRT-PCR assays, including 2 commercially available kits, for the detection of BTV in semen serially collected from 8 bulls over a period of 90 days after experimental infection. The results of the study show that at least one of the qRT-PCR assays is extremely reproducible and has both very high sensitivity and specificity to reliably detect all available serotypes. The preferred qRT-PCR gave consistently superior results to VI, sheep inoculation, and conventional RT-PCR. Therefore, the assay can be recommended for the screening of bovine semen for freedom from BTV.

A review of experimental infections with bluetongue virus in the mammalian host

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This review focuses on experimental infections with bluetongue virus in mammalian hosts.

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The objectives and justification of experimental infections with bluetongue virus are discussed.

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Experimental infections to study the pathogenicity, virulence, pathogenesis, and transplacental infections of bluetongue are reviewed.

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At the molecular and cellular levels, risks associated with reassortment/recombination of bluetongue viruses are discussed.

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The review is concluded with animal welfare aspects of experimental infections.

Experimental infection studies with bluetongue virus (BTV) in the mammalian host have a history that stretches back to the late 18th century. Studies in a wide range of ruminant and camelid species as well as mice have been instrumental in understanding BTV transmission, bluetongue (BT) pathogenicity/pathogenesis, viral virulence, the induced immune response, as well as reproductive failures associated with BTV infection. These studies have in many cases been complemented by in vitro studies with BTV in different cell types in tissue culture. Together these studies have formed the basis for the understanding of BTV-host interaction and have contributed to the design of successful control strategies, including the development of effective vaccines. This review describes some of the fundamental and contemporary infection studies that have been conducted with BTV in the mammalian host and provides an overview of the principal animal welfare issues that should be considered when designing experimental infection studies with BTV in in vivo infection models. Examples are provided from the authors’ own laboratory where the three Rs (replacement, reduction and refinement) have been implemented in the design of experimental infection studies with BTV in mice and goats. The use of the ARRIVE guidelines for the reporting of data from animal infection studies is emphasized.

Transplacental transmission of field and rescued strains of BTV-2 and BTV-8 in experimentally infected sheep

Transplacental transmission of bluetongue virus has been shown previously for the North European strain of serotype 8 (BTV-8) and for tissue culture or chicken egg-adapted vaccine strains but not for field strains of other serotypes. In this study, pregnant ewes (6 per group) were inoculated with either field or rescued strains of BTV-2 and BTV-8 in order to determine the ability of these viruses to cross the placental barrier. The field BTV-2 and BTV-8 strains was passaged once in Culicoides KC cells and once in mammalian cells. All virus inoculated sheep became infected and seroconverted against the different BTV strains used in this study. BTV RNA was detectable in the blood of all but two ewes for over 28 days but infectious virus could only be detected in the blood for a much shorter period. Interestingly, transplacental transmission of BTV-2 (both field and rescued strains) was demonstrated at high efficiency (6 out of 13 lambs born to BTV-2 infected ewes) while only 1 lamb of 12 born to BTV-8 infected ewes showed evidence of in utero infection. In addition, evidence for horizontal transmission of BTV-2 between ewes was observed. As expected, the parental BTV-2 and BTV-8 viruses and the viruses rescued by reverse genetics showed very similar properties to each other. This study showed, for the first time, that transplacental transmission of BTV-2, which had been minimally passaged in cell culture, can occur; hence such transmission might be more frequent than previously thought.