A Review of Knowledge Gaps and Tools for Orbivirus Research

Engineering recombinant replication-competent bluetongue viruses expressing reporter genes for in vitro and non-invasive in vivo studies

Bluetongue virus (BTV) is the causative agent of the important livestock disease bluetongue (BT), which is transmitted via Culicoides bites. BT causes severe economic losses associated with its considerable impact on health and trade of animals. By reverse genetics, we have designed and rescued reporter-expressing recombinant (r)BTV expressing NanoLuc luciferase (NLuc) or Venus fluorescent protein. To generate these viruses, we custom synthesized a modified viral segment 5 encoding NS1 protein with the reporter genes located downstream and linked by the Porcine teschovirus-1 (PTV-1) 2A autoproteolytic cleavage site. Therefore, fluorescent signal or luciferase activity is only detected after virus replication and expression of non-structural proteins. Fluorescence or luminescence signals were detected in cells infected with rBTV/Venus or rBTV/NLuc, respectively. Moreover, the marking of NS2 protein confirmed that reporter genes were only expressed in BTV-infected cells. Growth kinetics of rBTV/NLuc and rBTV/Venus in Vero cells showed replication rates similar to those of wild-type and rBTV. Infectivity studies of these recombinant viruses in IFNAR(-/-) mice showed a higher lethal dose for rBTV/NLuc and rBTV/Venus than for rBTV indicating that viruses expressing the reporter genes are attenuated in vivo. Interestingly, luciferase activity was detected in the plasma of viraemic mice infected with rBTV/NLuc. Furthermore, luciferase activity quantitatively correlated with RNAemia levels of infected mice throughout the infection. In addition, we have investigated the in vivo replication and dissemination of BTV in IFNAR (-/-) mice using BTV/NLuc and non-invasive in vivo imaging systems.IMPORTANCEThe use of replication-competent viruses that encode a traceable fluorescent or luciferase reporter protein has significantly contributed to the in vitro and in vivo study of viral infections and the development of novel therapeutic approaches. In this work, we have generated rBTV that express fluorescent or luminescence proteins to track BTV infection both in vitro and in vivo. Despite the availability of vaccines, BTV and other related orbivirus are still associated with a significant impact on animal health and have important economic consequences worldwide. Our studies may contribute to the advance in orbivirus research and pave the way for the rapid development of new treatments, including vaccines.

In Situ Hybridization (RNAscope) Detection of Bluetongue Virus Serotypes 10 and 17 in Experimentally Co-Infected Culicoides sonorensis

Bluetongue virus (BTV) is a segmented, double-stranded RNA virus transmitted by Culicoides biting midges. Infection of domestic and wild ruminants with BTV can result in a devastating disease and significant economic losses. As a virus with a segmented genome, reassortment among the BTV serotypes that have co-infected a host may increase genetic diversity, which can alter BTV transmission dynamics and generate epizootic events. The objective of this study was to determine the extent of dissemination and characterize the tropism of BTV serotypes 10 and 17 in co-infected Culicoides sonorensis. Midges were exposed to both BTV serotypes via blood meal and processed for histologic slides 10 days after infection. An in situ hybridization approach was employed using the RNAscope platform to detect the nucleic acid segment 2 of both serotypes. Observations of the mosaic patterns in which serotypes did not often overlap suggest that co-infection at the cellular level may not be abundant with these two serotypes in C. sonorensis. This could be a consequence of superinfection exclusion. Understanding BTV co-infection and its biological consequences will add an important dimension to the modeling of viral evolution and emergence.

Characterization of a Novel Orbivirus from Cattle Reveals Active Circulation of a Previously Unknown and Pathogenic Orbivirus in Ruminants in Kenya

Arboviruses are among emerging pathogens of public and veterinary health significance. However, in most of sub-Saharan Africa, their role in the aetiologies of diseases in farm animals is poorly described due to paucity of active surveillance and appropriate diagnosis. Here, we report the discovery of a previously unknown orbivirus in cattle collected in the Kenyan Rift Valley in 2020 and 2021. We isolated the virus in cell culture from the serum of a clinically sick cow aged 2 to 3 years, presenting signs of lethargy. High-throughput sequencing revealed an orbivirus genome architecture with 10 double-stranded RNA segments and a total size of 18,731 bp. The VP1 (Pol) and VP3 (T2) nucleotide sequences of the detected virus, tentatively named Kaptombes virus (KPTV), shared maximum similarities of 77.5% and 80.7% to the mosquito-borne Sathuvachari virus (SVIV) found in some Asian countries, respectively. Screening of 2,039 sera from cattle, goats, and sheep by specific RT-PCR identified KPTV in three additional samples originating from different herds collected in 2020 and 2021. Neutralizing antibodies against KPTV were found in 6% of sera from ruminants (12/200) collected in the region. In vivo experiments with new-born and adult mice induced body tremors, hind limb paralysis, weakness, lethargy, and mortality. Taken together, the data suggest the detection of a potentially disease-causing orbivirus in cattle in Kenya. Its impact on livestock, as well as its potential economic damage, needs to be addressed in future studies using targeted surveillance and diagnostics. IMPORTANCE The genus Orbivirus contains several viruses that cause large outbreaks in wild and domestic animals. However, there is little knowledge on the contribution of orbiviruses to diseases in livestock in Africa. Here, we report the identification of a novel presumably disease-causing orbivirus in cattle, Kenya. The virus, designated Kaptombes virus (KPTV), was initially isolated from a clinically sick cow aged 2 to 3 years, presenting signs of lethargy. The virus was subsequently detected in three additional cows sampled in neighboring locations in the subsequent year. Neutralizing antibodies against KPTV were found in 10% of cattle sera. Infection of new-born and adult mice with KPTV caused severe symptoms and lead to death. Together, these findings indicate the presence of a previously unknown orbivirus in ruminants in Kenya. These data are of relevance as cattle represents an important livestock species in farming industry and often is the main source of livelihoods in rural areas of Africa.

Comparison of Endemic and Epidemic Vesicular Stomatitis Virus Lineages in Culicoides sonorensis Midges

Vesicular stomatitis virus (VSV) primarily infects livestock and is transmitted by direct contact and vectored by Culicoides midges (Diptera: Ceratopogonidae). Endemic to Central and South America, specific VSV lineages spread northward out of endemic regions of Mexico and into the U.S. sporadically every five to ten years. In 2012, a monophyletic epidemic lineage 1.1 successfully spread northward into the U.S. In contrast, the closest endemic ancestor, lineage 1.2, remained circulating exclusively in endemic regions in Mexico. It is not clear what roles virus-animal interactions and/or virus-vector interactions play in the ability of specific viral lineages to escape endemic regions in Mexico and successfully cause outbreaks in the U.S., nor the genetic basis for such incursions. Whole-genome sequencing of epidemic VSV 1.1 and endemic VSV 1.2 revealed significant differences in just seven amino acids. Previous studies in swine showed that VSV 1.1 was more virulent than VSV 1.2. Here, we compared the efficiency of these two viral lineages to infect the vector Culicoides sonorensis (Wirth and Jones) and disseminate to salivary glands for subsequent transmission. Our results showed that midges orally infected with the epidemic VSV 1.1 lineage had significantly higher infection dissemination rates compared to those infected with the endemic VSV 1.2 lineage. Thus, in addition to affecting virus-animal interactions, as seen with higher virulence in pigs, small genetic changes may also affect virus-vector interactions, contributing to the ability of specific viral lineages to escape endemic regions via vector-borne transmission.

Perspectives on the Changing Landscape of Epizootic Hemorrhagic Disease Virus Control

Epizootic hemorrhagic disease (EHD) is an insect-transmitted viral disease of wild and domestic ruminants. It was first described following a 1955 epizootic in North American white-tailed deer (Odocoileus virginianus), a species which is highly susceptible to the causative agent of EHD, epizootic hemorrhagic disease virus (EHDV). EHDV has been detected globally across tropical and temperate regions, largely corresponding to the presence of Culicoides spp. biting midges which transmit the virus between ruminant hosts. It regularly causes high morbidity and mortality in wild and captive deer populations in endemic areas during epizootics. Although cattle historically have been less susceptible to EHDV, reports of clinical disease in cattle have increased in the past two decades. There is a pressing need to identify new methods to prevent and mitigate outbreaks and reduce the considerable impacts of EHDV on livestock and wildlife. This review discusses recent research advancements towards the control of EHDV, including the development of new investigative tools and progress in basic and applied research focused on virus detection, disease mitigation, and vector control. The potential impacts and implications of these advancements on EHD management are also discussed.

Characterization of a novel reassortment Tibet orbivirus isolated from Culicoides spp. in Yunnan, PR China

Orbiviruses are arboviruses with 10 double-stranded linear RNA segments, and some have been identified as pathogens of dramatic epizootics in both wild and domestic ruminants. Tibet orbivirus (TIBOV) is a new orbivirus isolated from hematophagous insects in recent decades, and, currently, most of the strains have been isolated from insects in PR China, except for two from Japan. In this study, we isolated a novel reassortment TIBOV strain, YN15-283-01, from Culicoides spp. To identify and understand more characteristics of YN15-283-01, electrophoresis profiles of the viral genome, electron microscopic observations, plaque assays, growth curves in various cell lines, and bioinformatic analysis were conducted. The results indicated that YN15-283-01 replicated efficiently in mosquito cells, rodent cells and several primate cells. Furthermore, the maximum likelihood phylogenetic trees and simplot analysis of the 10 segments indicated that YN15-283-01 is a natural reassortment isolate that had emerged mainly from XZ0906 and SX-2017a.

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.

Modeling Abundance of Culicoides stellifer, a Candidate Orbivirus Vector, Indicates Nonrandom Hemorrhagic Disease Risk for White-Tailed Deer (Odocoileus virginianus)

(1) Background: Hemorrhagic diseases in white-tailed deer (Odocoileus virginianus) are caused by orbiviruses and have significant economic impact on the deer ranching industry in the United States. Culicoides stellifer is a suspected vector of epizootic hemorrhagic disease virus (EHDV), with recent field evidence from Florida, but its natural history is poorly understood. Studying the distribution and abundance of C. stellifer across the landscape can inform our knowledge of how virus transmission can occur locally. We may then target vector management strategies in areas where viral transmission can occur. (2) Methods: Here, we used an occupancy modeling approach to estimate abundance of adult C. stellifer females at various physiological states to determine habitat preferences. We then mapped midge abundance during the orbiviral disease transmission period (May–October) in Florida. (3) Results: We found that overall, midge abundance was positively associated with sites in closer proximity to large-animal feeders. Additionally, midges generally preferred mixed bottomland hardwood and agricultural/sand/water habitats. Female C. stellifer with different physiological states preferred different habitats. (4) Conclusions: The differences in habitat preferences between midges across states indicate that disease risk for deer is heterogeneous across this landscape. This can inform how effective vector management strategies should be implemented.

Study of molecular diagnosis and viremia of bluetongue virus in sheep and cattle

Bluetongue virus (BTV) is an RNA virus that infects cattle and sheep. The objective of this study was to compare two real-time PCRs for the detection of BTV and to monitor Orbivirus viremia in sheep and cattle for 6 months. The PCR results showed the occurrence of infected animals throughout the experiment without records of clinical signs. The number of positive animals reduced during the experiment, but some animals were positive for BTV RNA during the entire experiment. The performance of the two RT-qPCRs for BTV detection techniques used in this work revealed a kappa index of 0.71 for cattle and 0.75 for sheep.

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

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

Resource Selection by Wild and Ranched White-Tailed Deer (Odocoileus virginianus) during the Epizootic Hemorrhagic Disease Virus (EHDV) Transmission Season in Florida

Simple Summary

Epizootic hemorrhagic disease virus is transmitted by Culicoides midges and causes serious disease in wild and privately ranched white-tailed deer (Odocoileus virginianus) in the United States. The U.S. deer ranching industry is fast growing and generates an estimated ~USD 8 billion annually. In Florida, there are over 400 registered deer farms, and virus rates are high among these populations. While vaccines for the virus are becoming available, many farms have large hunting preserves, where safely capturing deer is difficult. At the same time, these farms are situated in proximity to wild deer populations, and both populations are at risk. We studied habitat selection in ranched deer within a ~180 ha high-fenced preserve. We GPS-collared deer in the hunting preserve and nearby state-managed lands to compare habitat selection. During 2016, we collected GPS data from 15 ranched and eight wild deer and built resource selection function models. These models suggest ranched deer select habitats more likely to support several midge species that transmit the virus compared to wild deer. These differences in habitat use may partially explain previously confirmed higher rates of disease exposure in the ranched deer. Our results may inform ranch land management strategies that reduce midge–deer contact.

Abstract

Epizootic hemorrhagic disease virus (EHDV) causes serious disease in wild and privately ranched white-tailed deer (Odocoileusvirginianus) in the United States. In Florida, there is high EHDV prevalence, yet no treatments. There are few management strategies for the disease due to limited knowledge of virus–vector–host interactions. We conducted a telemetry study on white-tailed deer to examine resource use by wild and ranched animals in the Florida panhandle during the 2016 transmission risk period. We built generalized linear mixed models (GLMMs) to estimate resource selection and map habitat preferences for wild and ranched deer in the study area to reveal how second-order selection may relate to higher disease prevalence in ranched deer. Wild deer preferred areas closer to tertiary roads and supplementary food sources but farther from permanent water. Ranched deer selected bottomland mixed forest and areas closer to tertiary roads, supplementary food sources, and permanent water. Ranched deer behaviors may increase the likelihood of EHDV vector encounters, as these deer selected preferred habitats of several putative vector species, which may increase vector blood meal success and viral transmission risk. Disparate resource selection behaviors may be a factor in observed differential EHDV exposure risk between ranched and wild white-tailed deer in Florida.

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.

Tracking Community Timing: Pattern and Determinants of Seasonality in Culicoides (Diptera: Ceratopogonidae) in Northern Florida

Community dynamics are embedded in hierarchical spatial–temporal scales that connect environmental drivers with species assembly processes. Culicoides species are hematophagous arthropod vectors of orbiviruses that impact wild and domestic ruminants. A better sense of Culicoides dynamics over time is important because sympatric species can lengthen the seasonality of virus transmission. We tested a putative departure from the four seasons calendar in the phenology of Culicoides and the vector subassemblage in the Florida panhandle. Two years of weekly abundance data, temporal scales, persistence and environmental thresholds were analyzed using a tripartite Culicoides β-diversity based modeling approach. Culicoides phenology followed a two-season regime and was explained by stream flow and temperature, but not rainfall. Species richness fit a nested pattern where the species recruitment was maximized during spring months. Midges were active year-round, and two suspected vectors species, Culicoides venustus and Culicoides stellifer, were able to sustain and connect the seasonal modules. Persistence suggests that Orbivirus maintenance does not rely on overwintering and that viruses are maintained year-round, with the seasonal dynamics resembling subtropical Culicoides communities with temporal-overlapping between multivoltine species. Viewing Culicoides-borne orbiviruses as a time-sensitive community-based issue, our results help to recommend when management operations should be delivered.

Evaluation of Bluetongue Virus (BTV) Antibodies for the Immunohistochemical Detection of BTV and Other Orbiviruses

The detection of bluetongue virus (BTV) antigens in formalin-fixed tissues has been challenging; therefore, only a limited number of studies on suitable immunohistochemical approaches have been reported. This study details the successful application of antibodies for the immunohistochemical detection of BTV in BSR variant baby hamster kidney cells (BHK-BSR) and infected sheep lungs that were formalin-fixed and paraffin-embedded (FFPE). BTV reactive antibodies raised against non-structural (NS) proteins 1, 2, and 3/3a and viral structural protein 7 (VP7) were first evaluated on FFPE BTV-infected cell pellets for their ability to detect BTV serotype 1 (BTV-1). Antibodies that were successful in immunolabelling BTV-1 infected cell pellets were further tested, using similar methods, to determine their broader immunoreactivity against a diverse range of BTV and other orbiviruses. Antibodies specific for NS1, NS2, and NS3/3a were able to detect all BTV isolates tested, and the VP7 antibody cross-reacted with all BTV isolates, except BTV-15. The NS1 antibodies were BTV serogroup-specific, while the NS2, NS3/3a, and VP7 antibodies demonstrated immunologic cross-reactivity to related orbiviruses. These antibodies also detected viral antigens in BTV-3 infected sheep lung. This study demonstrates the utility of FFPE-infected cell pellets for the development and validation of BTV immunohistochemistry.

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.

Living la Vida T-LoCoH: site fidelity of Florida ranched and wild white-tailed deer (Odocoileus virginianus) during the epizootic hemorrhagic disease virus (EHDV) transmission period

BACKGROUND

Epizootic hemorrhagic disease virus (EHDV) is a pathogen vectored by Culicoides midges that causes significant economic loss in the cervid farming industry and affects wild deer as well. Despite this, its ecology is poorly understood. Studying movement and space use by ruminant hosts during the transmission season may elucidate EHDV ecology by identifying behaviors that can increase exposure risk. Here we compared home ranges (HRs) and site fidelity metrics within HRs using the T-LoCoH R package and GPS data from collared deer.

METHODS

Here, we tested whether white-tailed deer (Odocoileus virginianus) roaming within a high-fenced, private deer farm (ranched) and native deer from nearby state-managed properties (wild) exhibited differences in home range (HR) size and usage during the 2016 and 2017 EHDV seasons. We captured male and female individuals in both years and derived seasonal HRs for both sexes and both groups for each year. HRs were calculated using a time-scale distance approach in T-LoCoH. We then derived revisitation and duration of visit metrics and compared between years, sexes, and ranched and wild deer.

RESULTS

We found that ranched deer of both sexes tended to have smaller activity spaces (95% HR) and revisited sites within their HR more often but stayed for shorter periods than wild deer. However, core area (25% HR) sizes did not significantly differ between these groups.

CONCLUSIONS

The contrast in our findings between wild and ranched deer suggest that home range usage, rather than size, in addition to differences in population density, likely drive differences in disease exposure during the transmission period.

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.

Three New Orbivirus Species Isolated from Farmed White-Tailed Deer (Odocoileus virginianus) in the United States

We report the detection and gene coding sequences of three novel Orbivirus species found in six dead farmed white-tailed deer in the United States. Phylogenetic analyses indicate that the new orbiviruses are genetically closely related to the Guangxi, Mobuck, Peruvian horse sickness, and Yunnan orbiviruses, which are thought to be solely borne by mosquitos. However, four of the six viruses analyzed in this work were found as co-infecting agents along with a known cervid pathogen, epizootic hemorrhagic disease virus-2 (EHDV-2), raising questions as to whether the new viruses are primary pathogens or secondary pathogens that exacerbate EHDV-2 infections. Moreover, EHDV-2 is known to be a Culicoides-borne virus, raising additional questions as to whether Culicoides species can also serve as vectors for the novel orbiviruses, if mosquitoes can vector EHDV-2, or whether the deer were infected through separate bites by the insects. Our findings expand knowledge of the possible viral pathogens of deer in the United States. Moreover, due to the close genetic relatedness of the three new orbiviruses to viruses that are primary pathogens of cattle and horses, our findings also underscore a crucial need for additional research on the potential role of the three new orbiviruses as pathogens of other animals.

Effects of Arbovirus Multi-Host Life Cycles on Dinucleotide and Codon Usage Patterns

Arthropod-borne viruses (arboviruses) of vertebrates including dengue, zika, chikungunya, Rift Valley fever, and blue tongue viruses cause extensive morbidity and mortality in humans, agricultural animals, and wildlife across the globe. As obligate intercellular pathogens, arboviruses must be well adapted to the cellular and molecular environment of both their arthropod (invertebrate) and vertebrate hosts, which are vastly different due to hundreds of millions of years of separate evolution. Here we discuss the comparative pressures on arbovirus RNA genomes as a result of a dual host life cycle, focusing on pressures that do not alter amino acids. We summarize what is currently known about arboviral genetic composition, such as dinucleotide and codon usage, and how cyclical infection of vertebrate and invertebrate hosts results in different genetic profiles compared with single-host viruses. To serve as a comparison, we compile what is known about arthropod tRNA, dinucleotide, and codon usages and compare this with vertebrates. Additionally, we discuss the potential roles of genetic robustness in arboviral evolution and how it may vary from other viruses. Overall, both arthropod and vertebrate hosts influence the resulting genetic composition of arboviruses, but a great deal remains to be investigated.

Vesicular Stomatitis Virus Transmission: A Comparison of Incriminated Vectors

Vesicular stomatitis (VS) is a viral disease of veterinary importance, enzootic in tropical and subtropical regions of the Americas. In the U.S., VS produces devastating economic losses, particularly in the southwestern states where the outbreaks display an occurrence pattern of 10-year intervals. To date, the mechanisms of the geographic spread and maintenance cycles during epizootics remain unclear. This is due, in part, to the fact that VS epidemiology has a complex of variables to consider, including a broad range of vertebrate hosts, multiple routes of transmission, and an extensive diversity of suspected vector species acting as both mechanical and biological vectors. Infection and viral progression within vector species are highly influenced by virus serotype, as well as environmental factors, including temperature and seasonality; however, the mechanisms of viral transmission, including non-conventional pathways, are yet to be fully studied. Here, we review VS epidemiology and transmission mechanisms, with comparisons of transmission evidence for the four most incriminated hematophagous dipteran taxa: Aedes mosquitoes, Lutzomyia sand flies, Simulium black flies, and Culicoides biting midges.

Genomes of viral isolates derived from different mosquitos species

Eleven viral isolates derived mostly in albopictus C6/36 cells from mosquito pools collected in Southeast Asia and the Americas between 1966 and 2014 contained particles with electron microscopy morphology typical of reoviruses. Metagenomics analysis yielded the near complete genomes of three novel reoviruses, Big Cypress orbivirus, Ninarumi virus, and High Island virus and a new tetravirus, Sarawak virus. Strains of previously characterized Sathuvarachi, Yunnan, Banna and Parry's Lagoon viruses (Reoviridae), Bontang virus (Mesoniviridae), and Culex theileri flavivirus (Flaviviridae) were also characterized. The availability of these mosquito virus genomes will facilitate their detection by metagenomics or PCR to better determine their geographic range, extent of host tropism, and possible association with arthropod or vertebrate disease.

Culicoides-virus interactions: infection barriers and possible factors underlying vector competence

In the United States, Culicoides midges vector arboviruses of economic importance such as Bluetongue Virus and Epizootic Hemorrhagic Disease Virus. A limited number of studies have demonstrated the complexities of midge-virus interactions, including dynamic changes in virus titer and prevalence over the infection time course. These dynamics are, in part, dictated by mesenteron infection and escape barriers. This review summarizes the overarching trends in viral titer and prevalence throughout the course of infection. Essential barriers to infection and dissemination in the midge are highlighted, along with heritable and extrinsic factors that likely contribute to these barriers. Next generation molecular tools and techniques, now available for Culicoides midges, give researchers the opportunity to test how these factors contribute to vector competence.

Functional Validation of Apoptosis Genes IAP1 and DRONC in Midgut Tissue of the Biting Midge Culicoides sonorensis (Diptera: Ceratopogonidae) by RNAi

Culicoides biting midges transmit multiple ruminant viruses, including bluetongue virus and epizootic hemorrhagic disease virus, causing significant economic burden worldwide. To further enhance current control techniques, understanding vector-virus interactions within the midge is critical. We developed previously a double-stranded RNA (dsRNA) delivery method to induce RNA interference (RNAi) for targeted gene knockdown in adult Culicoides sonorensis Wirth & Jones. Here, we confirm the C. sonorensis inhibitor of apoptosis 1 (CsIAP1) as an anti-apoptotic functional ortholog of IAP1 in Drosophila, identify the ortholog of the Drosophila initiator caspase DRONC (CsDRONC), and demonstrate that injection of dsRNA into the hemocoel can be used for targeted knockdown in the midgut in C. sonorensis. We observed CsIAP1 transcript reduction in whole midges, with highest transcript reduction in midgut tissues. IAP1knockdown (kd) resulted in pro-apoptotic caspase activation in midgut tissues. In IAP1kd midges, midgut tissue integrity and size were severely compromised. This phenotype, as well as reduced longevity, was partially reverted by co-RNAi suppression of CsDRONC and CsIAP1. Therefore, RNAi can be directed to the midgut of C. sonorensis, the initial site of virus infection, using dsRNA injection into the hemocoel. In addition, we provide evidence that the core apoptosis pathway is conserved in C. sonorensis and can be experimentally activated in the midgut to reduce longevity in C. sonorensis. This study thus paves the way for future reverse genetic analyses of midgut-virus interactions in C. sonorensis, including the putative antiviral properties of RNAi and apoptosis pathways.

Molecular and Serological Survey of Selected Viruses in Free-Ranging Wild Ruminants in Iran

A molecular and serological survey of selected viruses in free-ranging wild ruminants was conducted in 13 different districts in Iran. Samples were collected from 64 small wild ruminants belonging to four different species including 25 Mouflon (Ovis orientalis), 22 wild goat (Capra aegagrus), nine Indian gazelle (Gazella bennettii) and eight Goitered gazelle (Gazella subgutturosa) during the national survey for wildlife diseases in Iran. Serum samples were evaluated using serologic antibody tests for Peste de petits ruminants virus (PPRV), Pestiviruses [Border Disease virus (BVD) and Bovine Viral Diarrhoea virus (BVDV)], Bluetongue virus (BTV), Bovine herpesvirus type 1 (BHV-1), and Parainfluenza type 3 (PI3). Sera were also ELISA tested for Pestivirus antigen. Tissue samples including spleen, liver, lung, tonsils, mesenteric and mediastinal lymph nodes and white blood cells (WBCs) were tested using polymerase chain reaction (PCR) for PPRV, Foot and Mouth Disease virus (FMDV), Pestivirus, BTV, Ovine herpesvirus type 2 (OvHV-2) and BHV-1. Serologic tests were positive for antibodies against PPRV (17%), Pestiviruses (2%) and BTV (2%). No antibodies were detected for BHV-1 or PI3, and no Pestivirus antigen was detected. PCR results were positive for PPRV (7.8%), FMDV (11%), BTV (3%), OvHV-2 (31%) and BHV-1 (1.5%). None of the samples were positive for Pestiviruses.

Pathogenic potential and growth kinetics of Muko virus in mice and human-derived cells

Background

Ticks have been long known as vectors of various pathogens, some of which can cause high fatality rates among infected individuals. Our enhanced tick surveillance around Nagasaki, Japan, led to the isolation and identification of a new strain of a recently identified Orbivirus, Muko virus (MUV). The orbiviruses have a wide host range, including humans, and is related to a spectrum of clinical outcomes. However, the zoonotic potential of some members of the genus, although reported, were not clearly elucidated. Hence, it is imperative to characterize newly isolated orbiviruses and investigate its ability to endanger public health.

Methods

In this study, we explored the in vivo pathogenicity of a newly isolated MUV strain (MUV-Hay) using a mouse model and demonstrated its growth kinetics in human-derived cells.

Results

Our results showed the ability of MUV-Hay to propagate in human neuronal and renal cells with some cytopathic effect. Furthermore, intracerebral inoculation of our new isolate caused high mortality in adult A129 mice.

Conclusion

Our study provided a first step to experimentally test the hypothesis, that MUV can replicate and produce cytopathic effect in human cells and demonstrate virulence in adult mice.