Reassortment between two serologically unrelated bluetongue virus strains is flexible and can involve any genome segment

Correlates of disease severity in bluetongue as a model of acute arbovirus infection

Most viral diseases display a variable clinical outcome due to differences in virus strain virulence and/or individual host susceptibility to infection. Understanding the biological mechanisms differentiating a viral infection displaying severe clinical manifestations from its milder forms can provide the intellectual framework toward therapies and early prognostic markers. This is especially true in arbovirus infections, where most clinical cases are present as mild febrile illness. Here, we used a naturally occurring vector-borne viral disease of ruminants, bluetongue, as an experimental system to uncover the fundamental mechanisms of virus-host interactions resulting in distinct clinical outcomes. As with most viral diseases, clinical symptoms in bluetongue can vary dramatically. We reproduced experimentally distinct clinical forms of bluetongue infection in sheep using three bluetongue virus (BTV) strains (BTV-1IT2006, BTV-1IT2013 and BTV-8FRA2017). Infected animals displayed clinical signs varying from clinically unapparent, to mild and severe disease. We collected and integrated clinical, haematological, virological, and histopathological data resulting in the analyses of 332 individual parameters from each infected and uninfected control animal. We subsequently used machine learning to select the key viral and host processes associated with disease pathogenesis. We identified and experimentally validated five different fundamental processes affecting the severity of bluetongue: (i) virus load and replication in target organs, (ii) modulation of the host type-I IFN response, (iii) pro-inflammatory responses, (iv) vascular damage, and (v) immunosuppression. Overall, we showed that an agnostic machine learning approach can be used to prioritise the different pathogenetic mechanisms affecting the disease outcome of an arbovirus infection.

Evaluating Temperature Effects on Bluetongue Virus Serotype 10 and 17 Coinfection in Culicoides sonorensis

Bluetongue virus (BTV) is a segmented, double-stranded RNA virus transmitted by Culicoides midges that infects ruminants. As global temperatures increase and geographical ranges of midges expand, there is increased potential for BTV outbreaks from incursions of novel serotypes into endemic regions. However, an understanding of the effect of temperature on reassortment is lacking. The objectives of this study were to compare how temperature affected Culicoides survival, virogenesis, and reassortment in Culicoides sonorensis coinfected with two BTV serotypes. Midges were fed blood meals containing BTV-10, BTV-17, or BTV serotype 10 and 17 and maintained at 20 °C, 25 °C, or 30 °C. Midge survival was assessed, and pools of midges were collected every other day to evaluate virogenesis of BTV via qRT-PCR. Additional pools of coinfected midges were collected for BTV plaque isolation. The genotypes of plaques were determined using next-generation sequencing. Warmer temperatures impacted traits related to vector competence in offsetting ways: BTV replicated faster in midges at warmer temperatures, but midges did not survive as long. Overall, plaques with BTV-17 genotype dominated, but BTV-10 was detected in some plaques, suggesting parental strain fitness may play a role in reassortment outcomes. Temperature adds an important dimension to host-pathogen interactions with implications for transmission and evolution.

Assessing Reassortment between Bluetongue Virus Serotypes 10 and 17 at Different Coinfection Ratios in Culicoides sonorenesis

Bluetongue virus (BTV) is a segmented, double-stranded RNA orbivirus listed by the World Organization for Animal Health and transmitted by Culicoides biting midges. Segmented viruses can reassort, which facilitates rapid and important genotypic changes. Our study evaluated reassortment in Culicoides sonorensis midges coinfected with different ratios of BTV-10 and BTV-17. Midges were fed blood containing BTV-10, BTV-17, or a combination of both serotypes at 90:10, 75:25, 50:50, 25:75, or 10:90 ratios. Midges were collected every other day and tested for infection using pan BTV and cox1 (housekeeping gene) qRT-PCR. A curve was fit to the ∆Ct values (pan BTV Ct-cox1 Ct) for each experimental group. On day 10, the midges were processed for BTV plaque isolation. Genotypes of the plaques were determined by next-generation sequencing. Pairwise comparison of ∆Ct curves demonstrated no differences in viral RNA levels between coinfected treatment groups. Plaque genotyping indicated that most plaques fully aligned with one of the parental strains; however, reassortants were detected, and in the 75:25 pool, most plaques were reassortant. Reassortant prevalence may be maximized upon the occurrence of reassortant genotypes that can outcompete the parental genotypes. BTV reassortment and resulting biological consequences are important elements to understanding orbivirus emergence and evolution.

Recovery of multireassortant bluetongue virus serotype 6 sequences from a mule deer (Odocoileus hemionus) and Dorset sheep (Ovis aries) in Colorado

We report the discovery of two bluetongue virus serotype 6 (BTV-6) reassortants recovered from a domestic sheep and a free-ranging mule deer in northern Colorado. At the time of this publication, whole-genome sequencing of BTV-6 isolates in the Western U.S. have not been undertaken. These findings reflect the incursive movement of geographically distinct BTV serotypes into important agricultural areas of the U.S. and demonstrate reassortment with regionally circulating serotypes.

The First Report on the Complete Sequence Characterization of Bluetongue Virus Serotype 3 in the Republic of Korea

The bluetongue virus (BTV) is a significant animal pathogen with economic implications in the ruminant industry. Despite global reports on BTV detection and epidemiologic investigations, limited studies have focused on the virus in the ROK. In this study, BTV epidemiological research was conducted on blood samples from cattle and goat farms across nine regions during 2013-2014. The results showed that 3.33% of bovine blood samples (194/5824) and 0.19% of goat blood samples (2/1075) tested positive for BTV antibodies using ELISA. In Jeju-do, BTV RNA amplification occurred in 51 of 422 samples (12.1%) using real-time reverse transcription (RT-qPCR). The isolation of one sample revealed it as serotype 3, as indicated by the sequence of segments 2 (Seg-2) and 6 (Seg-6), associated with the eastern BTV topotype. However, based on Seg-1, -3, -4, -5, -7, -8, -9, and -10 analyses, the BTV-3/JJBB35 strain is more closely related to distinct BTV strains. These findings imply BTV circulation and that the Korean-isolated BTV might originate from Asian BTV strains due to multiple reassortment events. This study provides foundational data for ongoing BTV monitoring and disease-control policies in the ROK.

Comprehensive immune profiling reveals that Orbivirus infection activates immune checkpoints during acute T cell immunosuppression

Bluetongue virus (BTV) is an arbovirus transmitted by the bite of infected Culicoides midges that affects domestic and wild ruminants producing great economic losses. The infection induces an IFN response, followed by an adaptive immune response that is essential in disease clearance. BTV can nonetheless impair IFN and humoral responses. The main goal of this study was to gain a more detailed understanding of BTV pathogenesis and its effects on immune cell populations. To this end, we combined flow cytometry and transcriptomic analyses of several immune cells at different times post-infection (pi). Four sheep were infected with BTV serotype 8 and blood samples collected at days 0, 3, 7 and 15pi to perform transcriptomic analysis of B-cell marker+, CD4+, CD8+, and CD14+ sorted peripheral mononuclear cells. The maximum number of differentially expressed genes occurred at day 7pi, which coincided with the peak of infection. KEGG pathway enrichment analysis indicated that genes belonging to virus sensing and immune response initiation pathways were enriched at day 3 and 7 pi in all 4 cell population analyzed. Transcriptomic analysis also showed that at day 7pi T cell exhaustion pathway was enriched in CD4+ cells, while CD8+ cells downregulated immune response initiation pathways. T cell functional studies demonstrated that BTV produced an acute inhibition of CD4+ and CD8+ T cell activation at the peak of replication. This coincided with PD-L1 upregulation on the surface of CD4+ and CD8+ T cells as well as monocytes. Taken together, these data indicate that BTV could exploit the PD1/PD-L1 immune checkpoint to impair T cell responses. These findings identify several mechanisms in the interaction between host and BTV, which could help develop better tools to combat the disease.

Widespread Reassortment Contributes to Antigenic Shift in Bluetongue Viruses from South Africa

Bluetongue (BT), a viral disease of ruminants, is endemic throughout South Africa, where outbreaks of different serotypes occur. The predominant serotypes can differ annually due to herd immunity provided by annual vaccinations using a live attenuated vaccine (LAV). This has led to both wild-type and vaccine strains co-circulating in the field, potentially leading to novel viral strains due to reassortment and recombination. Little is known about the molecular evolution of the virus in the field in South Africa. The purpose of this study was to investigate the genetic diversity of field strains of BTV in South Africa and to provide an initial assessment of the evolutionary processes shaping BTV genetic diversity in the field. Complete genomes of 35 field viruses belonging to 11 serotypes, collected from different regions of the country between 2011 and 2017, were sequenced. The sequences were phylogenetically analysed in relation to all the BTV sequences available from GenBank, including the LAVs and reference strains, resulting in the analyses and reassortment detection of 305 BTVs. Phylogenomic analysis indicated a geographical selection of the genome segments, irrespective of the serotype. Based on the initial assessment of the current genomic clades that circulate in South Africa, the selection for specific clades is prevalent in directing genome segment reassortment, which seems to exclude the vaccine strains and in multiple cases involves Segment-2 resulting in antigenic shift.

Would Climate Change Influence the Potential Distribution and Ecological Niche of Bluetongue Virus and Its Main Vector in Peru?

Bluetongue virus (BTV) is an arbovirus that is transmitted between domestic and wild ruminants by Culicoides spp. Its worldwide distribution depends on competent vectors and suitable environmental ecosystems that are becoming affected by climate change. Therefore, we evaluated whether climate change would influence the potential distribution and ecological niche of BTV and Culicoides insignis in Peru. Here, we analyzed BTV (n = 145) and C. insignis (n = 22) occurrence records under two shared socioeconomic pathway scenarios (SSP126 and SSP585) with five primary general circulation models (GCMs) using the kuenm R package v.1.1.9. Then, we obtained binary presence–absence maps and represented the risk of transmission of BTV and niche overlapping. The niche model approach showed that north and east Peru presented suitability in the current climate scenario and they would have a decreased risk of BTV, whilst its vector would be stable and expand with high agreement for the five GCMs. In addition, its niche overlap showed that the two niches almost overlap at present and would completely overlap with one another in future climate scenarios. These findings might be used to determine the areas of highest priority for entomological and virological investigations and surveillance in order to control and prevent bluetongue infections in Peru.

Field-Reassortment of Bluetongue Virus Illustrates Plasticity of Virus Associated Phenotypic Traits in the Arthropod Vector and Mammalian Host In Vivo

Segmented RNA viruses are a taxonomically diverse group that can infect plant, wildlife, livestock and human hosts. A shared feature of these viruses is the ability to exchange genome segments during coinfection of a host by a process termed "reassortment." Reassortment enables rapid evolutionary change, but where transmission involves a biological arthropod vector, this change is constrained by the selection pressures imposed by the requirement for replication in two evolutionarily distant hosts. In this study, we use an in vivo, host-arbovirus-vector model to investigate the impact of reassortment on two phenotypic traits, virus infection rate in the vector and virulence in the host. Bluetongue virus (BTV) (Reoviridae) is the causative agent of bluetongue (BT), an economically important disease of domestic and wild ruminants and deer. The genome of BTV comprises 10 linear segments of dsRNA, and the virus is transmitted between ruminants by Culicoides biting midges (Diptera: Ceratopogonidae). Five strains of BTV representing three serotypes (BTV-1, BTV-4, and BTV-8) were isolated from naturally infected ruminants in Europe and ancestral/reassortant lineage status assigned through full genome sequencing. Each strain was then assessed in parallel for the ability to replicate in vector Culicoides and to cause BT in sheep. Our results demonstrate that two reassortment strains, which themselves became established in the field, had obtained high replication ability in C. sonorensis from one of the ancestral virus strains, which allowed inferences of the genome segments conferring this phenotypic trait. IMPORTANCE Reassortment between virus strains can lead to major shifts in the transmission parameters and virulence of segmented RNA viruses, with consequences for spread, persistence, and impact. The ability of these pathogens to adapt rapidly to their environment through this mechanism presents a major challenge in defining the conditions under which emergence can occur. Utilizing a representative mammalian host-insect vector infection and transmission model, we provide direct evidence of this phenomenon in closely related ancestral and reassortant strains of BTV. Our results demonstrate that efficient infection of Culicoides observed for one of three ancestral BTV strains was also evident in two reassortant strains that had subsequently emerged in the same ecosystem.

Bluetongue Research at a Crossroads: Modern Genomics Tools Can Pave the Way to New Insights

Bluetongue virus (BTV) is an arthropod-borne, segmented double-stranded RNA virus that can cause severe disease in both wild and domestic ruminants. BTV evolves via several key mechanisms, including the accumulation of mutations over time and the reassortment of genome segments.Additionally, BTV must maintain fitness in two disparate hosts, the insect vector and the ruminant. The specific features of viral adaptation in each host that permit host-switching are poorly characterized. Limited field studies and experimental work have alluded to the presence of these phenomena at work, but our understanding of the factors that drive or constrain BTV's genetic diversification remains incomplete. Current research leveraging novel approaches and whole genome sequencing applications promises to improve our understanding of BTV's evolution, ultimately contributing to the development of better predictive models and management strategies to reduce future impacts of bluetongue epizootics.

Recent Development of Ruminant Vaccine Against Viral Diseases

Pathogens of viral origin produce a large variety of infectious diseases in livestock. It is essential to establish the best practices in animal care and an efficient way to stop and prevent infectious diseases that impact animal husbandry. So far, the greatest way to combat the disease is to adopt a vaccine policy. In the fight against infectious diseases, vaccines are very popular. Vaccination's fundamental concept is to utilize particular antigens, either endogenous or exogenous to induce immunity against the antigens or cells. In light of how past emerging and reemerging infectious diseases and pandemics were handled, examining the vaccination methods and technological platforms utilized for the animals may provide some useful insights. New vaccine manufacturing methods have evolved because of developments in technology and medicine and our broad knowledge of immunology, molecular biology, microbiology, and biochemistry, among other basic science disciplines. Genetic engineering, proteomics, and other advanced technologies have aided in implementing novel vaccine theories, resulting in the discovery of new ruminant vaccines and the improvement of existing ones. Subunit vaccines, recombinant vaccines, DNA vaccines, and vectored vaccines are increasingly gaining scientific and public attention as the next generation of vaccines and are being seen as viable replacements to conventional vaccines. The current review looks at the effects and implications of recent ruminant vaccine advances in terms of evolving microbiology, immunology, and molecular biology.

Identification of a BTV-Strain-Specific Single Gene That Increases Culicoides Vector Infection Rate

Since the 2000s, the distribution of bluetongue virus (BTV) has changed, leading to numerous epidemics and economic losses in Europe. Previously, we found a BTV-4 field strain with a higher infection rate of a Culicoides vector than a BTV-1 field strain has. We reverse-engineered parental BTV-1 and BTV-4 strains and created BTV-1/BTV-4 reassortants to elucidate the influence of individual BTV segments on BTV replication in both C. sonorensis midges and in KC cells. Substitution of segment 2 (Seg-2) with Seg-2 from the rBTV-4 significantly increased vector infection rate in reassortant BTV-14S2 (30.4%) in comparison to reverse-engineered rBTV-1 (1.0%). Replacement of Seg-2, Seg-6 and Seg-7 with those from rBTV-1 in reassortant BTV-41S2S6S7 (2.9%) decreased vector infection rate in comparison to rBTV-4 (30.2%). However, triple-reassorted BTV-14S2S6S7 only replicated to comparatively low levels (3.0%), despite containing Seg-2, Seg-6 and Seg-7 from rBTV-4, indicating that vector infection rate is influenced by interactions of multiple segments and/or host-mediated amino acid substitutions within segments. Overall, these results demonstrated that we could utilize reverse-engineered viruses to identify the genetic basis influencing BTV replication within Culicoides vectors. However, BTV replication dynamics in KC cells were not suitable for predicting the replication ability of these virus strains in Culicoides midges.

Development and Validation of an ELISA for the Detection of Bluetongue Virus Serotype 4-Specific Antibodies

In this article, we describe the development and evaluation of a double antigen sandwich enzyme-linked immunosorbent assay (ELISA) able to detect serotype 4-specific antibodies from BTV-4 infected or vaccinated animals using a recombinant BTV-4 VP2 protein. The coding sequence of VP2 was inserted into a pVote plasmid by recombination in the Gateway^® cloning system. Vaccinia virus (VacV) was used as a vector for the expression of the recombinant VP2. After production in BSR cells, recombinant VP2 was purified by immunoprecipitation using a FLAG tag and then used both as the coated ELISA antigen and as the HRP-tagged conjugate. The performance of the ELISA was evaluated with 1186 samples collected from BTV negative, infected or vaccinated animals. The specificity and sensitivity of the BTV-4 ELISA were above the expected standards for the detection of anti-BTV-4 VP2 antibodies in animals reared in Europe or in the Mediterranean basin. Cross-reactions were observed with reference sera for serotypes 10 and 20, and to a lesser extent with serotypes 12, 17 and 24, due to their genetic proximity to serotype 4. Nevertheless, these serotypes have never been detected in Europe and the Mediterranean area. This ELISA, which requires only the production of a recombinant protein, can be used to detect BTV serotype 4-specific antibodies and is therefore an attractive alternative diagnostic method to serum neutralization.

An updated review on bluetongue virus: epidemiology, pathobiology, and advances in diagnosis and control with special reference to India

Bluetongue (BT) is an economically important, non-contagious viral disease of domestic and wild ruminants. BT is caused by BT virus (BTV) and it belongs to the genus Orbivirus and family Reoviridae. BTV is transmitted by Culicoides midges and causes clinical disease in sheep, white-tailed deer, pronghorn antelope, bighorn sheep, and subclinical manifestation in cattle, goats and camelids. BT is a World Organization for Animal Health (OIE) listed multispecies disease and causes great socio-economic losses. To date, 28 serotypes of BTV have been reported worldwide and 23 serotypes have been reported from India. Transplacental transmission (TPT) and fetal abnormalities in ruminants had been reported with cell culture adopted live-attenuated vaccine strains of BTV. However, emergence of BTV-8 in Europe during 2006, confirmed TPT of wild-type/field strains of BTV. Diagnosis of BT is more important for control of disease and to ensure BTV-free trade of animals and their products. Reverse transcription polymerase chain reaction, agar gel immunodiffusion assay and competitive enzyme-linked immunosorbent assay are found to be sensitive and OIE recommended tests for diagnosis of BTV for international trade. Control measures include mass vaccination (most effective method), serological and entomological surveillance, forming restriction zones and sentinel programs. Major hindrances with control of BT in India are the presence of multiple BTV serotypes, high density of ruminant and vector populations. A pentavalent inactivated, adjuvanted vaccine is administered currently in India to control BT. Recombinant vaccines with DIVA strategies are urgently needed to combat this disease. This review is the first to summarise the seroprevalence of BTV in India for 40 years, economic impact and pathobiology.

The Interplay between Bluetongue Virus Infections and Adaptive Immunity

Viral infections have long provided a platform to understand the workings of immunity. For instance, great strides towards defining basic immunology concepts, such as MHC restriction of antigen presentation or T-cell memory development and maintenance, have been achieved thanks to the study of lymphocytic choriomeningitis virus (LCMV) infections. These studies have also shaped our understanding of antiviral immunity, and in particular T-cell responses. In the present review, we discuss how bluetongue virus (BTV), an economically important arbovirus from the Reoviridae family that affects ruminants, affects adaptive immunity in the natural hosts. During the initial stages of infection, BTV triggers leucopenia in the hosts. The host then mounts an adaptive immune response that controls the disease. In this work, we discuss how BTV triggers CD8+ T-cell expansion and neutralizing antibody responses, yet in some individuals viremia remains detectable after these adaptive immune mechanisms are active. We present some unpublished data showing that BTV infection also affects other T cell populations such as CD4+ T-cells or γδ T-cells, as well as B-cell numbers in the periphery. This review also discusses how BTV evades these adaptive immune mechanisms so that it can be transmitted back to the arthropod host. Understanding the interaction of BTV with immunity could ultimately define the correlates of protection with immune mechanisms that would improve our knowledge of ruminant immunology.

Exposure of Culicoides sonorensis to Enzootic Strains of Bluetongue Virus Demonstrates Temperature- and Virus-Specific Effects on Virogenesis

Bluetongue virus (BTV) is a segmented RNA virus transmitted by Culicoides midges. Climatic factors, animal movement, vector species, and viral mutation and reassortment may all play a role in the occurrence of BTV outbreaks among susceptible ruminants. We used two enzootic strains of BTV (BTV-2 and BTV-10) to explore the potential for Culicoides sonorensis, a key North American vector, to be infected with these viruses, and identify the impact of temperature variations on virogenesis during infection. While BTV-10 replicated readily in C. sonorensis following an infectious blood meal, BTV-2 was less likely to result in productive infection at biologically relevant exposure levels. Moreover, when C. sonorensis were co-exposed to both viruses, we did not detect reassortment between the two viruses, despite previous in vitro findings indicating that BTV-2 and BTV-10 are able to reassort successfully. These results highlight that numerous factors, including vector species and exposure dose, may impact the in vivo replication of varying BTV strains, and underscore the complexities of BTV ecology in North America.

In Vitro Reassortment between Endemic Bluetongue Viruses Features Global Shifts in Segment Frequencies and Preferred Segment Combinations

Bluetongue virus (BTV) is an arthropod-borne pathogen that is associated with sometimes severe disease in both domestic and wild ruminants. Predominantly transmitted by Culicoides spp. biting midges, BTV is composed of a segmented, double-stranded RNA genome. Vector expansion and viral genetic changes, such as reassortment between BTV strains, have been implicated as potential drivers of ongoing BTV expansion into previously BTV-free regions. We used an in vitro system to investigate the extent and flexibility of reassortment that can occur between two BTV strains that are considered enzootic to the USA, BTV-2 and BTV-10. Whole genome sequencing (WGS) was coupled with plaque isolation and a novel, amplicon-based sequencing approach to quantitate the viral genetic diversity generated across multiple generations of in vitro propagation. We found that BTV-2 and BTV-10 were able to reassort across multiple segments, but that a preferred BTV-2 viral backbone emerged in later passages and that certain segments were more likely to be found in reassortant progeny. Our findings indicate that there may be preferred segment combinations that emerge during BTV reassortment. Moreover, our work demonstrates the usefulness of WGS and amplicon-based sequencing approaches to improve understanding of the dynamics of reassortment among segmented viruses such as BTV.

VP2 Gene-Based Molecular Evolutionary Patterns of Major Circulating Bluetongue Virus Serotypes Isolated during 2014-2018 from Telangana and Andhra Pradesh States of India

INTRODUCTION

Bluetongue disease is an economically important viral disease of livestock caused by bluetongue virus (BTV) having multiple serotypes. It belongs to the genus Orbivirus of family Reoviridae and subfamily Sedoreovirinae. The genome of BTV is 10 segmented dsRNA that codes for 7 structural and 4 nonstructural proteins, of which VP2 was reported to be serotype-specific and a major antigenic determinant.

OBJECTIVE

It is important to know the circulating serotypes in a particular geographical location for effective control of the disease. The present study unravels the molecular evolution of the circulating BTV serotypes during 2014-2018 in Telangana and Andhra Pradesh states of India.

METHODS

Multiple sequence alignment with available BTV serotypes in GenBank and phylogenetic analysis were performed for the partial VP2 sequences of major circulating BTV serotypes during the study period.

RESULTS

The multiple sequence alignment of circulating serotypes with respective reference isolates revealed variations in antigenic VP2. The phylogenetic analysis revealed that the major circulating serotypes were grouped into eastern topotypes (BTV-1, BTV-2, BTV-4, and BTV-16) and Western topotypes (BTV-5, BTV-12, and BTV-24).

CONCLUSION

Our study strengthens the need for development of an effective vaccine, which can induce the immune response for a range of serotypes within and in between topotypes.

The Genetic Diversification of a Single Bluetongue Virus Strain Using an In Vitro Model of Alternating-Host Transmission

Bluetongue virus (BTV) is an arbovirus that has been associated with dramatic epizootics in both wild and domestic ruminants in recent decades. As a segmented, double-stranded RNA virus, BTV can evolve via several mechanisms due to its genomic structure. However, the effect of BTV’s alternating-host transmission cycle on the virus’s genetic diversification remains poorly understood. Whole genome sequencing approaches offer a platform for investigating the effect of host-alternation across all ten segments of BTV’s genome. To understand the role of alternating hosts in BTV’s genetic diversification, a field isolate was passaged under three different conditions: (i) serial passages in Culicoides sonorensis cells, (ii) serial passages in bovine pulmonary artery endothelial cells, or (iii) alternating passages between insect and bovine cells. Aliquots of virus were sequenced, and single nucleotide variants were identified. Measures of viral population genetics were used to quantify the genetic diversification that occurred. Two consensus variants in segments 5 and 10 occurred in virus from all three conditions. While variants arose across all passages, measures of genetic diversity remained largely similar across cell culture conditions. Despite passage in a relaxed in vitro system, we found that this BTV isolate exhibited genetic stability across passages and conditions. Our findings underscore the valuable role that whole genome sequencing may play in improving understanding of viral evolution and highlight the genetic stability of BTV.

Refined experimental design may increase the value of murine models for estimation of bluetongue virus virulence

Bluetongue is a serious non-contagious vector-borne viral disease in ruminants, causing poor animal welfare and economic consequences globally. Concern has been raised about the development of novel bluetongue virus (BTV) strains and their possibly altered virulence through the process of viral reassortment. Virulence is traditionally estimated in lethal dose 50 (LD₅₀) studies in murine models, but agreement with both in vitro and virulence in ruminants is questionable, and a refined experimental design is needed. Specific reassortants between wild-type and vaccine strains of BTV-1, -6 and -8 have previously been developed by reverse genetics. The aim of the present study was to rank the in vivo virulence of these parental and reassortant BTV strains by calculating LD₅₀ in a murine model by using an experimental design that is new to virology: a between-patient optimised three-level response surface pathway design. The inoculation procedure was intracranial. Fifteen suckling mice were used to establish LD₅₀ for each strain. Three parental and five reassortant virus strains were included. The LD₅₀s varied from of 0.1 (95% confidence interval (CI) 0-0.20) to 3.3 (95% CI 2.96-3.72) tissue culture infectious dose 50/ml. The results support the hypothesis that reassortment in BTV may lead to increased virulence in mice with potential negative consequences for the natural ruminant host. The ranking showed low agreement with in vitro properties and virulence in ruminants according to existing literature. Refined design such as response surface pathway design was found suitable for use in virology, and it introduces significant ethical and scientific improvements.

Diversity of Transmission Outcomes Following Co-Infection of Sheep with Strains of Bluetongue Virus Serotype 1 and 8

Bluetongue virus (BTV) causes an economically important disease, bluetongue (BT), in susceptible ruminants and is transmitted primarily by species of Culicoides biting midges (Diptera: Ceratopogonidae). Since 2006, northern Europe has experienced multiple incursions of BTV through a variety of routes of entry, including major outbreaks of strains of BTV serotype 8 (BTV-8) and BTV serotype 1 (BTV-1), which overlapped in distribution within southern Europe. In this paper, we examined the variation in response to coinfection with strains of BTV-1 and BTV-8 using an in vivo transmission model involving Culicoides sonorensis, low passage virus strains, and sheep sourced in the United Kingdom. In the study, four sheep were simultaneously infected using BTV-8 and BTV-1 intrathoracically inoculated C. sonorensis and co-infections of all sheep with both strains were established. However, there were significant variations in both the initiation and peak levels of virus RNA detected throughout the experiment, as well as in the infection rates in the C. sonorensis that were blood-fed on experimentally infected sheep at peak viremia. This is discussed in relation to the potential for reassortment between these strains in the field and the policy implications for detection of BTV strains.

BlueTYPE - A low density TaqMan-RT-qPCR array for the identification of all 24 classical Bluetongue virus serotypes

Bluetongue virus is a double-stranded RNA virus with 10 genome segments. VP2 is the primary target for neutralising antibodies and defines the serotype. Today, more than 27 serotypes are known, 24 are defined as "classical", and new serotypes are under investigation. Beside group-specific BTV-genome detection, additional serotype characterisation is important for disease control and epidemiological investigations. Therefore, a low-density RT-qPCR array representing a panel of group- and serotype-specific assays, was combined with an internal control system. For BTV serotype detection, both published and the newly developed in-house PCR systems were combined. The different primer-probe-mixes were placed in advance into a 96-well plate stored at -20 °C until use. At the time of analysis, the only template RNA was added to the prepared primer-probe-mixes and heat denatured at 95 °C for 3 min. After cooling, the master mix was added to each well and the PCR could run for around 90 min. The presented low-density TaqMan-RT-qPCR array enables fast and precise characterisation of the BTV serotype in clinical cases. Furthermore, mixed infections can be easily identified. In addition, the newly developed low-density RT-qPCR-array can easily be adapted to novel BTV strain variants or extended for relevant differential diagnosis.

Development of a Digital RT-PCR Method for Absolute Quantification of Bluetongue Virus in Field Samples

Bluetongue (BT) is a major Office International des Epizooties (OIE)-listed disease of wild and domestic ruminants caused by several serotypes of Bluetongue virus (BTV), a virus with a segmented dsRNA genome belonging to the family Reoviridae, genus Orbivirus. BTV is transmitted through the bites of Culicoides midges. The aim of this study was to develop a new method for quantification of BTV Seg-10 by droplet digital RT-PCR (RTdd-PCR), using nucleic acids purified from complex matrices such as blood, tissues, and midges, that notoriously contain strong PCR inhibitors. First, RTdd-PCR was optimized by using RNAs purified from serially 10-fold dilutions of a BTV-1 isolate (10^5.43TCID₅₀/ml up to 10^−0.57 TCID₅₀/ml) and from the same dilutions spiked into fresh ovine EDTA-blood and spleen homogenate. The method showed a good degree of linearity (R² ≥ 0.995). The limit of detection (LoD) and the limit of quantification (LoQ) established were 10^−0.67TCID₅₀/ml (0.72 copies/μl) and 10^0.03TCID₅₀/ml (3.05 copies/μl) of BTV-1, respectively. Second, the newly developed test was compared, using the same set of biological samples, to the quantitative RT-PCR (RT-qPCR) detecting Seg-10 assay widely used for the molecular diagnosis of BTV from field samples. Results showed a difference mean of 0.30 log between the two assays with these samples (p < 0.05). Anyway, the analysis of correlation demonstrated that both assays provided similar measurements with a very close agreement between the systems.

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.

Bluetongue Serotype 3 in Israel 2013-2018: Clinical Manifestations of the Disease and Molecular Characterization of Israeli Strains

In this paper, the results of the diagnostic activities on Bluetongue virus serotype 3 (BTV-3) conducted at Kimron Veterinary Institute (Beit Dagan, Israel) between 2013 and 2018 are reported. Bluetongue virus is the causative agent of bluetongue (BT), a disease of ruminants, mostly transmitted by competent Culicoides species. In Israel, BTV-3 circulation was first detected in 2013 from a sheep showing classical BT clinical signs. It was also evidenced in 2016, and, since then, it has been regularly detected in Israeli livestock. Between 2013 and 2017, BTV-3 outbreaks were limited in sheep flocks located in the southern area only. In 2018, BTV-3 was instead found in the Israeli coastal area being one of the dominant BTV serotypes isolated from symptomatic sheep, cattle and goats. In Israeli sheep, BTV-3 was able to cause BT classical clinical manifestations and fatalities, while in cattle and goats infection ranged from asymptomatic forms to death cases, depending on either general welfare of the herds or on the occurrence of viral and bacterial co-infections. Three different BTV-3 strains were identified in Israel between 2013 and 2018: ISR-2019/13 isolated in 2013, ISR-2153/16 and ISR-2262/2/16 isolated in 2016. Sequencing and phylogenetic analysis of these strains showed more than 99% identity by segment (Seg) 2, 5, 6, 7, and 8 sequences. In contrast, a wide range of diversity among these strains was exhibited in other viral gene segments, implying the occurrence of genome reassortment between these local circulating strains and those originating from Africa. The genome sequences of the BTV-3 isolated in 2017 and 2018 were most closely related to those of the ISR-2153/16 strain suggesting their common ancestor. Comparison of BTV-3 Israeli strains with those recently detected in the Mediterranean region uncovered high percentage identity (98.19–98.28%) only between Seg-2 of all Israeli strains and the BTV-3 Zarzis/TUN2016 strain. A 98.93% identity was also observed between Seg-4 sequences of ISR-2019/13 and the BTV-3 Zarzis/TUN2016 strain. This study demonstrated that BTV-3 has been circulating in the Mediterranean region at least since 2013, but, unlike the other Mediterranean strains, Israeli BTV-3 were able to cause clinical signs also in cattle.

Letea Virus: Comparative Genomics and Phylogenetic Analysis of a Novel Reassortant Orbivirus Discovered in Grass Snakes (Natrix natrix)

The discovery and characterization of novel arthropod-borne viruses provide valuable information on their genetic diversity, ecology, evolution and potential to threaten animal or public health. Arbovirus surveillance is not conducted regularly in Romania, being particularly very scarce in the remote and diverse areas like the Danube Delta. Here we describe the detection and genetic characterization of a novel orbivirus (Reoviridae: Orbivirus) designated as Letea virus, which was found in grass snakes (Natrix natrix) during a metagenomic and metatranscriptomic survey conducted between 2014 and 2017. This virus is the first orbivirus discovered in reptiles. Phylogenetic analyses placed Letea virus as a highly divergent species in the Culicoides-/sand fly-borne orbivirus clade. Gene reassortment and intragenic recombination were detected in the majority of the nine Letea virus strains obtained, implying that these mechanisms play important roles in the evolution and diversification of the virus. However, the screening of arthropods, including Culicoides biting midges collected within the same surveillance program, tested negative for Letea virus infection and could not confirm the arthropod vector of the virus. The study provided complete genome sequences for nine Letea virus strains and new information about orbivirus diversity, host range, ecology and evolution. The phylogenetic associations warrant further screening of arthropods, as well as sustained surveillance efforts for elucidation of Letea virus natural cycle and possible implications for animal and human health.

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.

Plant-produced Bluetongue chimaeric VLP vaccine candidates elicit serotype-specific immunity in sheep

Bluetongue (BT) is a hemorrhagic non-contagious, biting midge-transmitted disease of wild and domestic ruminants that is caused by bluetongue virus (BTV). Annual vaccination plays a pivotal role in BT disease control in endemic regions. Due to safety concerns of the current BTV multivalent live attenuated vaccine (LAV), a safe efficacious new generation subunit vaccine such as a plant-produced BT virus-like particle (VLP) vaccine is imperative. Previously, homogenous BTV serotype 8 (BTV-8) VLPs were successfully produced in Nicotiana benthamiana plants and provided protective immunity in sheep. In this study, combinations of BTV capsid proteins from more than one serotype were expressed and assembled to form chimaeric BTV-3 and BTV-4 VLPs in N. benthamiana plants. The assembled homogenous BTV-8, as well as chimaeric BTV-3 and chimaeric BTV-4 VLP serotypes, were confirmed by SDS-PAGE, Transmission Electron microscopy (TEM) and protein confirmation using liquid chromatography-mass spectrometry (LC-MS/MS) based peptide sequencing. As VP2 is the major determinant eliciting protective immunity, the percentage coverage and number of unique VP2 peptides detected in assembled chimaeric BT VLPs were used as a guide to assemble the most appropriate chimaeric combinations. Both plant-produced chimaeric BTV-3 and BTV-4 VLPs were able to induce long-lasting serotype-specific neutralizing antibodies equivalent to the monovalent LAV controls. Antibody levels remained high to the end of the trial. Combinations of homogenous and chimaeric BT VLPs have great potential as a safe, effective multivalent vaccine with the ability to distinguish between vaccinated and infected individuals (DIVA) due to the absence of non-structural proteins.

Identification and complete-genome phylogenetic analysis of an epizootic hemorrhagic disease virus serotype 7 strain isolated in China

An epizootic hemorrhagic disease virus (EHDV) strain designated YN09-04 was isolated from sentinel cattle in China. The length of its complete genome was 19,344 bp in total, consisting of 10 segments ranging in size from 810 bp (S10) to 3942 bp (S1). Based on phylogenetic analysis of the S2 sequence, YN09-04 clusters with EHDV serotype 7 (EHDV-7) strains form a distinct, well-supported subgroup, indicating that YN09-04 belongs to EHDV-7. However, the origin of the YN09-04 genome is very complex. The S2 and S6 of YN09-04 cluster with those of Japanese EHDV-7 strains, whereas the S1, S3, S4, S5 and S7 of YN09-04 share high nucleotide sequence identity and a close relationship with those of Japanese Ibaraki viruses, and the S8, S9 and S10 nucleotide sequences of YN09-04 are more similar to those of some Australian EHDV strains than to those of other isolates. These results suggest that the genome of YN09-04 likely originated from a reassortment event between EHDV strains that were similar to the current Japanese and Australian strains and that YN09-04 and some EHDVs from Japan and Australia share the same ancestors. This is the first report of the isolation, identification and complete-genome phylogenetic analysis of an EHDV-7 strain from China.

Inter-serotype reassortment among epizootic haemorrhagic disease viruses in the United States

First described in 1955 in New Jersey, epizootic haemorrhagic disease (EHD) causes a severe clinical disease in wild and domestic ruminants worldwide. Epizootic haemorrhagic disease outbreaks occur in deer populations each year from summer to late autumn. The etiological agent is EHD virus (EHDV) which is a double-stranded segmented icosahedral RNA virus. EHD virus utilizes point mutations and reassortment strategies to maintain viral fitness during infection. In 2018, EHDV serotype 2 was predominantly detected in deer in Illinois. Whole genome sequencing was conducted for two 2018 EHDV2 isolates (IL41747 and IL42218) and the sequence analyses indicated that IL42218 was a reassortant between different serotypes whereas IL41747 was a genetically stable strain. Our data suggest that multiple strains contribute to outbreaks each year.

Contrasting selective patterns across the segmented genome of bluetongue virus in a global reassortment hotspot

For segmented viruses, rapid genomic and phenotypic changes can occur through the process of reassortment, whereby co-infecting strains exchange entire segments creating novel progeny virus genotypes. However, for many viruses with segmented genomes, this process and its effect on transmission dynamics remain poorly understood. Here, we assessed the consequences of reassortment for selection on viral diversity through time using bluetongue virus (BTV), a segmented arbovirus that is the causative agent of a major disease of ruminants. We analysed ninety-two BTV genomes isolated across four decades from India, where BTV diversity, and thus opportunities for reassortment, are among the highest in the world. Our results point to frequent reassortment and segment turnover, some of which appear to be driven by selective sweeps and serial hitchhiking. Particularly, we found evidence for a recent selective sweep affecting segment 5 and its encoded NS1 protein that has allowed a single variant to essentially invade the full range of BTV genomic backgrounds and serotypes currently circulating in India. In contrast, diversifying selection was found to play an important role in maintaining genetic diversity in genes encoding outer surface proteins involved in virus interactions (VP2 and VP5, encoded by segments 2 and 6, respectively). Our results support the role of reassortment in driving rapid phenotypic change in segmented viruses and generate testable hypotheses for in vitro experiments aiming at understanding the specific mechanisms underlying differences in fitness and selection across viral genomes.

Bluetongue Virus in France: An Illustration of the European and Mediterranean Context since the 2000s

Bluetongue (BT) is a non-contagious animal disease transmitted by midges of the Culicoides genus. The etiological agent is the BT virus (BTV) that induces a variety of clinical signs in wild or domestic ruminants. BT is included in the notifiable diseases list of the World Organization for Animal Health (OIE) due to its health impact on domestic ruminants. A total of 27 BTV serotypes have been described and additional serotypes have recently been identified. Since the 2000s, the distribution of BTV has changed in Europe and in the Mediterranean Basin, with continuous BTV incursions involving various BTV serotypes and strains. These BTV strains, depending on their origin, have emerged and spread through various routes in the Mediterranean Basin and/or in Europe. Consequently, control measures have been put in place in France to eradicate the virus or circumscribe its spread. These measures mainly consist of assessing virus movements and the vaccination of domestic ruminants. Many vaccination campaigns were first carried out in Europe using attenuated vaccines and, in a second period, using exclusively inactivated vaccines. This review focuses on the history of the various BTV strain incursions in France since the 2000s, describing strain characteristics, their origins, and the different routes of spread in Europe and/or in the Mediterranean Basin. The control measures implemented to address this disease are also discussed. Finally, we explain the circumstances leading to the change in the BTV status of France from BTV-free in 2000 to an enzootic status since 2018.

Emergence of a Novel Reassortant Strain of Bluetongue Serotype 6 in Israel, 2017: Clinical Manifestations of the Disease and Molecular Characterization

Reassortment contributes to the evolution of RNA viruses with segmented genomes, including Bluetongue virus (BTV). Recently, co-circulation of natural and vaccine BTV variants in Europe, and their ensuing reassortment, were proposed to promote appearance of novel European BTV strains, with potential implications for pathogenicity, spread and vaccination policies. Similarly, the geographical features of the Mediterranean basin, which spans over portions of three continents, may facilitate the appearance of clinically relevant reassortants via co-circulation of BTV strains of African, Asian and European origins. In August–October 2017, BTV serotype 6 (BTV-6) was identified in young animals exhibiting classical clinical signs of Bluetongue (BT) at Israeli sheep and cattle farms. Sequencing and pairwise analysis of this Israeli BTV-6 isolate revealed the closest sequence homology of its serotype-defining Segment 2 was with that of South African reference BTV-6 strain 5011 (93.88% identity). In contrast, the other viral segments showed highest homology (97.0%–99.47% identity) with BTV-3, -4 and -9 of Mediterranean and African origins. Specifically, four viral segments were nearly identical (99.13%–99.47%), with Tunisian and Italian BTV-3 strains (TUN2016 and SAD2018, correspondingly). Together, our data suggest that Mediterranean co-circulation and reassortment of BTV-3 and BTV-6 drove the emergence of a novel and virulent BTV-6 strain

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.

Discovery and Characterization of Bukakata orbivirus (Reoviridae:Orbivirus), a Novel Virus from a Ugandan Bat

While serological and virological evidence documents the exposure of bats to medically-important arboviruses, their role as reservoirs or amplifying hosts is less well-characterized. We describe a novel orbivirus (Reoviridae:Orbivirus) isolated from an Egyptian fruit bat (Rousettus aegyptiacus leachii) trapped in 2013 in Uganda and named Bukakata orbivirus. This is the fifth orbivirus isolated from a bat, however genetic information had previously only been available for one bat-associated orbivirus. We performed whole-genome sequencing on Bukakata orbivirus and three other bat-associated orbiviruses (Fomede, Ife, and Japanaut) to assess their phylogenetic relationship within the genus Orbivirus and develop hypotheses regarding potential arthropod vectors. Replication kinetics were assessed for Bukakata orbivirus in three different vertebrate cell lines. Lastly, qRT-PCR and nested PCR were used to determine the prevalence of Bukakata orbivirus RNA in archived samples from three populations of Egyptian fruit bats and one population of cave-associated soft ticks in Uganda. Complete coding sequences were obtained for all ten segments of Fomede, Ife, and Japanaut orbiviruses and for nine of the ten segments for Bukakata orbivirus. Phylogenetic analysis placed Bukakata and Fomede in the tick-borne orbivirus clade and Ife and Japanaut within the Culicoides/phlebotomine sandfly orbivirus clade. Further, Bukakata and Fomede appear to be serotypes of the Chobar Gorge virus species. Bukakata orbivirus replicated to high titers (10⁶⁻10⁷ PFU/mL) in Vero, BHK-21 [C-13], and R06E (Egyptian fruit bat) cells. Preliminary screening of archived bat and tick samples do not support Bukakata orbivirus presence in these collections, however additional testing is warranted given the phylogenetic associations observed. This study provided complete coding sequence for several bat-associated orbiviruses and in vitro characterization of a bat-associated orbivirus. Our results indicate that bats may play an important role in the epidemiology of viruses in the genus Orbivirus and further investigation is warranted into vector-host associations and ongoing surveillance efforts.

Infection kinetics and antibody responses in Deccani sheep during experimental infection and superinfection with bluetongue virus serotypes 4 and 16

Aim:

The current study was designed to understand the infection kinetics and antibody responses of major circulating serotypes of bluetongue virus (BTV) in India, i.e., BTV-4 and BTV-16 through experimental infection and superinfection of Deccani sheep, a popular breed of sheep found in the southern states of India.

Materials and Methods:

Experimental infection with 10⁶ TCID_50/ml BTV-4 was followed by superinfection with BTV-16 and vice versa. Along with observing for clinical signs and immunological responses in the experimentally infected sheep, the effect of infection of one specific serotype on the outcome of superinfection with a different serotype was also studied.

Results:

Certain interesting findings have been made in the course of experimental infection, such as prominent signs of infection in BTV-4 infection, mild or no clinical signs in BTV-16-infected and superinfected animals, and non-seroconversion of one of the BTV-16-superinfected animals. In addition, BTV was isolated from infected sheep in all the experimental conditions except BTV-16 superinfection. Furthermore, it was observed that immune response in the form of type-specific antibodies was slower with BTV-16 superinfection.

Conclusion:

Superinfection of a sheep with more than one serotype of BTV is a common phenomenon in BT endemic countries like India. Such situation was replicated in an experimental infection in the current study, and the findings to our knowledge are first of a kind and are likely to aid in unfolding the newer aspects of BTV pathogenesis and virulence.

Testicular Degeneration and Infertility following Arbovirus Infection

Arboviruses can cause a variety of clinical signs, including febrile illness, arthritis, encephalitis, and hemorrhagic fever. The recent Zika epidemic highlighted the possibility that arboviruses may also negatively affect the male reproductive tract. In this study, we focused on bluetongue virus (BTV), the causative agent of bluetongue and one of the major arboviruses of ruminants. We show that rams that recovered from bluetongue displayed signs of testicular degeneration and azoospermia up to 100 days after the initial infection. Importantly, testicular degeneration was induced in rams experimentally infected with either a high (BTV-1_IT2006)- or a low (BTV-1_IT2013)-virulence strain of BTV. Rams infected with the low-virulence BTV strain displayed testicular lesions in the absence of other major clinical signs. Testicular lesions in BTV-infected rams were due to viral replication in the endothelial cells of the peritubular areas of the testes, resulting in stimulation of a type I interferon response, reduction of testosterone biosynthesis by Leydig cells and destruction of Sertoli cells and the blood-testis barrier in more severe cases. Hence, BTV induces testicular degeneration and disruption of spermatogenesis by replicating solely in the endothelial cells of the peritubular areas unlike other gonadotropic viruses. This study shows that a naturally occurring arboviral disease can cause testicular degeneration and affect male fertility at least temporarily.IMPORTANCE During the recent Zika epidemic, it has become apparent that arboviruses could potentially cause reproductive health problems in male patients. Little is known regarding the effects that arboviruses have on the male reproductive tract. Here, we studied bluetongue virus (BTV), an arbovirus of ruminants, and its effects on the testes of rams. We show that BTV was able to induce testicular degeneration in naturally and experimentally infected rams. Testicular degeneration was caused by BTV replication in the endothelial cells of the peritubular area surrounding the seminiferous tubules (the functional unit of the testes) and was associated with a localized type I interferon response, destruction of the cells supporting the developing germinal cells (Sertoli cells), and reduction of testosterone synthesis. As a result of BTV infection, rams became azoospermic. This study highlights that problems in the male reproductive tract caused by arboviruses could be more common than previously thought.

Vector competence of pre-alpine Culicoides (Diptera: Ceratopogonidae) for bluetongue virus serotypes 1, 4 and 8

Background

Bluetongue disease, caused by bluetongue virus serotype 8 (BTV-8), appeared for the first time in the northern part of Europe in 2006, and subsequently rapidly spread causing severe economic losses to the farming industry. The implicated vectors of BTV in Europe are Culicoides species within the subgenus Avaritia (C. chiopterus, C. dewulfi, C. obsoletus and C. scoticus). Epidemiological data from Switzerland have shown that BTV, whose spread was eliminated at an early stage by vaccination campaigns, had not been circulating among livestock at higher altitudes where other species dominate the Culicoides fauna. In this study, we investigated the extent that Culicoides spp. prevailing at higher altitudes (mainly C. grisescens) can act as vectors for BTV.

Methods

Culicoides were collected at farms in the pre-alpine region (two sites at 1550 m above sea level, masl, referred to as pre-alpine I; one site at 2030 masl, pre-alpine II) and, for comparative purposes, from the Swiss Plateau (one site, 650 masl). They were fed on bovine blood/BTV suspensions (BTV-1, 4 or 8) and incubated for eight days under a fluctuating temperature regime (13–25 °C, mean 19 °C), reflecting a mid-summer warm spell in the pre-alpine region. Susceptibility to BTV transmission was assessed from head homogenates by RT-qPCR and virus isolation.

Results

Overall, 9196 female Culicoides were exposed to the three BTV strains through an artificial membrane, with feeding rates of 14–27%. Survival rates of blood-engorged Culicoides females at eight days post-infection depended on both virus serotype and altitude of origin. Virus dissemination (C_q ≤ the cut-off value as determined by serial virus dilutions) was confirmed only for BTV-1 in C. scoticus (dissemination efficiency 22.5%; 9/40) and C. obsoletus (5.6%; 1/18) from the Swiss Plateau area. There was no strong evidence of susceptibility to infection for Culicoides from the pre-alpine area when fed with all BTV strains (BTV-1, 4 and 8).

Conclusions

This study confirms the susceptibility of C. scoticus and C. obsoletus to BTV-1 infection, including under cooler temperatures. Culicoides grisescens, which is highly abundant at higher altitudes, cannot be considered a potential vector under these temperature conditions.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3050-y) contains supplementary material, which is available to authorized users.

Comparative Neuropathology of Major Indian Bluetongue Virus Serotypes in a Neonatal BALB/c Mouse Model

Bluetongue virus (BTV) is neurotropic in nature, especially in ruminant fetuses and in-utero infection results in abortion and congenital brain malformations. The aim of the present study was to compare the neuropathogenicity of major Indian BTV serotypes 1, 2, 10, 16 and 23 by gross and histopathological lesions and virus distribution in experimentally infected neonatal BALB/c mice. Each BTV serotype (20 μl of inoculum containing 1 × 10⁵ tissue culture infectious dose [TCID]₅₀/ml of virus) was inoculated intracerebrally into 3-day-old mice, while a control group was inoculated with mock-infected cell culture medium. Infection with BTV serotypes 1, 2 and 23 led to 65-70% mortality at 7-9 days post infection (dpi) and caused severe necrotizing encephalitis with neurodegenerative changes in neurons, swelling and proliferation of vascular endothelial cells in the cerebral cortex, cerebellum, midbrain and brainstem. In contrast, infection with BTV serotypes 10 and 16 led to 25-30% mortality at 9-11 dpi and caused mild neuropathological lesions. BTV antigen was detected by immunohistochemistry, direct fluorescence antibody technique and confocal microscopy in the cytoplasm of neuronal cells of the hippocampus, grey matter of the cerebral cortex and vascular endothelial cells in the midbrain and brainstem of BTV-1, -2, -10, -16 and -23 infected groups from 3 to 20 dpi. BTV nucleic acid was detected in the infected brain tissues from as early as 24 h up to 20 dpi by VP7 gene segment-based one-step reverse transcriptase polymerase chain reaction. This study of the relative neurovirulence of BTV serotypes is likely to help design suitable vaccination and control strategies for the disease.

Standardization and application of real-time polymerase chain reaction for rapid detection of bluetongue virus

Aim

The present study was designed to standardize real-time polymerase chain reaction (PCR) for detecting the bluetongue virus from blood samples of sheep collected during outbreaks of bluetongue disease in the year 2014 in Andhra Pradesh and Telangana states of India.

Materials and Methods

A 10-fold serial dilution of Plasmid PUC59 with bluetongue virus (BTV) NS3 insert was used to plot the standard curve. BHK-21 and KC cells were used for in vitro propagation of virus BTV-9 at a TCID50/ml of 10⁵ ml and RNA was isolated by the Trizol method. Both reverse transcription-PCR and real-time PCR using TaqMan probe were carried out with RNA extracted from virus-spiked culture medium and blood to compare the sensitivity by means of finding out the limit of detection (LoD). The results were verified by inoculating the detected and undetected dilutions onto cell cultures with further cytological (cytopathic effect) and molecular confirmation (by BTV-NS1 group-specific PCR). The standardized technique was then applied to field samples (blood) for detecting BTV.

Results

The slope of the standard curve obtained was −3.23, and the efficiency was 103%. The LoD with RT-PCR was 8.269E×10³ number of copies of plasmid, whereas it was 13 with real-time PCR for plasmid dilutions. Similarly, LoD was determined for virus-spiked culture medium, and blood with both the types of PCR and the values were 10³ TCID 50/ml and 10⁴ TCID 50/ml with RT-PCR and 10° TCID 50/ml and 10² TCID 50/ml with real-time PCR, respectively. The standardized technique was applied to blood samples collected from BTV suspected animals; 10 among 20 samples were found positive with Cq values ranging from 27 to 39. The Cq value exhibiting samples were further processed in cell cultures and were confirmed to be BT positive. Likewise, Cq undetected samples on processing in cell cultures turned out to be BTV negative.

Conclusion

Real-time PCR was found to be a very sensitive as well as reliable method to detect BTV present in different types of samples, including blood samples collected from BTV-infected sheep, compared to RT-PCR. The LoD of BTV is likely influenced by sample type, possibly by the interference by the other components present in the sample.

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.

Diagnostic Reliability of Different RT-PCR Protocols for the Detection of Bluetongue Virus Serotype 14 (BTV-14)

Introduction

The reverse transcription polymerase chain reaction (RT-PCR) is one of the most extensively used methods for identification of animals infected with bluetongue virus (BTV). There are several RT-PCR protocols published and several real-time RT-PCR (rtRT-PCR) commercial kits available on the market. Because Poland faced BTV-14 infection in 2012, different protocols were implemented in the country to confirm the RT-PCR results positive for this virus. The article presents a comparative study of several RT-PCR protocols and discusses their diagnostic reliability and applicability.

Material and Methods

Six rtRT-PCR/RT-PCR protocols were compared for the laboratory diagnostic of fourteen BTV-14 isolates circulating in Poland in 2012-2014.

Results

All 14 isolates were positive in the protocols of Shaw et al. (18), a commercial LSI NS3 kit, and Eschbaumer et al. (5). Four out of fourteen BTV-14 isolates gave positive results in Hoffmann's 2 and 6 protocols and none of the 14 isolates yielded positive results in Maan et al. (8) method. Phylogenetic study of a short fragment of 450 nt of BTV segment 2 (258-696 positions) revealed 100% identity within Polish variants and with Russian and Spanish isolates.

Conclusion

The paper points to the possible false negative results in the diagnosis of BTV infections depending on the protocol used.

Genomic analysis of bluetongue virus episystems in Australia and Indonesia

The distribution of bluetongue viruses (BTV) in Australia is represented by two distinct and interconnected epidemiological systems (episystems)—one distributed primarily in the north and one in the east. The northern episystem is characterised by substantially greater antigenic diversity than the eastern episystem; yet the forces that act to limit the diversity present in the east remain unclear. Previous work has indicated that the northern episystem is linked to that of island South East Asia and Melanesia, and that BTV present in Indonesia, Papua New Guinea and East Timor, may act as source populations for new serotypes and genotypes of BTV to enter Australia’s north. In this study, the genomes of 49 bluetongue viruses from the eastern episystem and 13 from Indonesia were sequenced and analysed along with 27 previously published genome sequences from the northern Australian episystem. The results of this analysis confirm that the Australian BTV population has its origins in the South East Asian/Melanesian episystem, and that incursions into northern Australia occur with some regularity. In addition, the presence of limited genetic diversity in the eastern episystem relative to that found in the north supports the presence of substantial, but not complete, barriers to gene flow between the northern and eastern Australian episystems. Genetic bottlenecks between each successive episystem are evident, and appear to be responsible for the reduction in BTV genetic diversity observed in the north to south–east direction.

Recent US bluetongue virus serotype 3 isolates found outside of Florida indicate evidence of reassortment with co-circulating endemic serotypes

Since 1999, 11 serotypes of bluetongue virus (BTV) similar to Central American or Caribbean strains have been isolated in the southeastern United States, predominantly in Florida. The majority of the incursive serotypes have remained restricted to the southeastern US. In recent years, BTV serotype 3 (BTV-3) has been isolated in areas increasingly distant from Florida. The current study uses whole genome sequencing of recent and historical BTV-3 isolates from the US, Central America and the Caribbean with additional sequences from GenBank to conduct phylogenetic analyses. The individual segments of the BTV genome were analysed to determine if recent BTV-3 isolates are reassortants containing genomic segments from endemic US serotypes or if they retain a majority of Central American/Caribbean genotypes. The analyses indicate that BTV-3 isolates Mississippi 2006, Arkansas 2008 and Mississippi 2009 are closely related reassortants that contain five to six genomic segments that are of US origin and two to three segments of Central American/Caribbean origin. In contrast, the BTV-3 South Dakota 2012 isolate contains seven genomic segments that are more similar to isolates from Central American and the Caribbean. These different evolutionary histories of the BTV-3 isolates suggest that there are at least two different lineages of BTV-3 that are currently circulating in the US.

Isolation and evolutionary analysis of Australasian topotype of bluetongue virus serotype 4 from India

Bluetongue (BT) is a Culicoides-borne disease caused by several serotypes of bluetongue virus (BTV). Similar to other insect-borne viral diseases, distribution of BT is limited to distribution of Culicoides species competent to transmit BTV. In the tropics, vector activity is almost year long, and hence, the disease is endemic, with the circulation of several serotypes of BTV, whereas in temperate areas, seasonal incursions of a limited number of serotypes of BTV from neighbouring tropical areas are observed. Although BTV is endemic in all the three major tropical regions (parts of Africa, America and Asia) of the world, the distribution of serotypes is not alike. Apart from serological diversity, geography-based diversity of BTV genome has been observed, and this is the basis for proposal of topotypes. However, evolution of these topotypes is not well understood. In this study, we report the isolation and characterization of several BTV-4 isolates from India. These isolates are distinct from BTV-4 isolates from other geographical regions. Analysis of available BTV seg-2 sequences indicated that the Australasian BTV-4 diverged from African viruses around 3,500 years ago, whereas the American viruses diverged relatively recently (1,684 CE). Unlike Australasia and America, BTV-4 strains of the Mediterranean area evolved through several independent incursions. We speculate that independent evolution of BTV in different geographical areas over long periods of time might have led to the diversity observed in the current virus population.

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.

Development of a Double-Antigen Microsphere Immunoassay for Simultaneous Group and Serotype Detection of Bluetongue Virus Antibodies

Bluetongue viruses (BTV) are arboviruses responsible for infections in ruminants. The confirmation of BTV infections is based on rapid serological tests such as enzyme-linked immunosorbent assays (ELISAs) using the BTV viral protein 7 (VP7) as antigen. The determination of the BTV serotype by serological analyses could be only performed by neutralization tests (VNT) which are time-consuming and require BSL3 facilities. VP2 protein is considered the major serotype-defining protein of BTV. To improve the serological characterization of BTV infections, the recombinant VP7 and BTV serotype 8 (BTV-8) VP2 were synthesized using insect cells expression system. The purified antigens were covalently bound to fluorescent beads and then assayed with 822 characterized ruminant sera from BTV vaccinations or infections in a duplex microsphere immunoassay (MIA). The revelation step of this serological duplex assay was performed with biotinylated antigens instead of antispecies conjugates to use it on different ruminant species. The results demonstrated that MIA detected the anti-VP7 antibodies with a high specificity as well as a competitive ELISA approved for BTV diagnosis, with a better efficiency for the early detection of the anti-VP7 antibodies. The VP2 MIA results showed that this technology is also an alternative to VNT for BTV diagnosis. Comparisons between the VP2 MIA and VNT results showed that VNT detects the anti-VP2 antibodies in an early stage and that the VP2 MIA is as specific as VNT. This novel immunoassay provides a platform for developing multiplex assays, in which the presence of antibodies against multiple BTV serotypes can be detected simultaneously.