The orbivirus genus. Diversity, structure, replication and phylogenetic relationships

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.

Equine Encephalosis Virus

Simple Summary

Equine encephalosis (EE) is a febrile disease of horses caused by EE virus (EEV) and transmitted by Culicoides midges. This virus was first isolated from a horse in South Africa in 1967 and until 2008 was believed to be restricted to southern Africa. In 2008–2009, isolation of EEV in an outbreak reported from Israel demonstrated the emergence of this pathogen into new niches. Indeed, further testing revealed that EEV had already spread outside of South Africa since 2001. Although EEV normally does not cause severe clinical disease, it should be considered important since it may indicate the possible spread of other related, much more pathogenic viruses, such as African horse sickness virus (AHSV). The spread of EEV from South Africa to central Africa, the Middle East, and India is an example of the possible emergence of new pathogens in new niches and should be a reminder not to limit the differential diagnoses list when facing a possible outbreak or a cluster of undiagnosed clinical cases. This review summarizes current knowledge regarding EEV structure, pathogenesis, clinical significance, and epidemiology.

Abstract

Equine encephalosis (EE) is an arthropod-borne, noncontagious, febrile disease of horses. It is caused by EE virus (EEV), an Orbivirus of the Reoviridae family transmitted by Culicoides. Within the EEV serogroup, seven serotypes (EEV-1–7) have been identified to date. This virus was first isolated from a horse in South Africa in 1967 and until 2008 was believed to be restricted to southern Africa. In 2008–2009, isolation of EEV in an outbreak reported from Israel demonstrated the emergence of this pathogen into new niches. Indeed, testing in retrospect sera samples revealed that EEV had already been circulating outside of South Africa since 2001. Although EEV normally does not cause severe clinical disease, it should be considered important since it may indicate the possible spread of other related, much more pathogenic viruses, such as African horse sickness virus (AHSV). The spread of EEV from South Africa to central Africa, the Middle East and India is an example of the possible emergence of new pathogens in new niches, as was seen in the case of West Nile virus, and should be a reminder not to limit the differential list when facing a possible outbreak or a cluster of clinical cases. This review summarizes current knowledge regarding EEV structure, pathogenesis, clinical significance, and epidemiology.

Development of a rapid lateral flow immunochromatography assay for the detection of group-specific antibodies against VP7 protein of bluetongue virus in multiple species

Bluetongue virus (BTV), the causative agent of bluetongue disease infects many domestic and wild ruminants. In the present study, colloidal gold nanoparticle-based lateral flow immunochromatography assay (LFIA) was developed to detect the group-specific antibodies to BTV in serum samples of sheep, goats, cattle, and camel. The recombinant VP7 protein of BTV conjugated to colloidal gold nanoparticles (GNPs) was used as a detector reagent. Recombinant streptococcal protein G and monoclonal antibody to BTV group-specific antigen were immobilized as the test and the control line, respectively on a nitrocellulose membrane. The protein G could capture the specific antibodies to BTV present in the serum of multiple ruminant species susceptible to BTV in a common test format and could eliminate the requirement of multiple anti-species antibodies. Upon addition of serum sample, GNP-rVP7 protein-serum complex migrated laterally onto the strip via capillary action and results were analyzed based on appearance of red colour band at test and control line. Serum samples (n = 481) of sheep, goats, cattle, and camel segregated as positive and negative by the commercial competitive-ELISA (c-ELISA) kit were tested in the fabricated LFIA strips to analyze the performance of the assay. In comparison with c-ELISA, the relative diagnostic sensitivity (DSn) of 95.2% with 91.6-97.6 (95%)) confidence interval and relative diagnostic specificity (DSp) of 99.6% 97.8-100.0 (95%) confidence interval were obtained for the optimized LFIA. The agreement between the LFIA and the c-ELISA was excellent as indicated by the kappa coefficient value of 0.949 (SE = 0.0142) with 0.9219 to 0.9779 (95%) confidence interval. The recombinant protein G based LFIA is a sensitive, specific, rapid, one-step test that can be used in the field or poorly equipped laboratories for serological diagnosis and serosurveillance of bluetongue in multiple susceptible species.

Partial glycosylation of the Ibaraki virus NS3 protein is sufficient to support virus propagation

Ibaraki virus (IBAV) causes Ibaraki disease. We have previously shown that IBAV NS3 protein is highly glycosylated and that tunicamycin, an inhibitor of N-linked glycosylation, suppressed NS3 glycosylation and viral propagation. Since tunicamycin is known to cause endoplasmic reticulum (ER) stress, we explored the effects of ER stress and NS3 glycosylation on IBAV infection using tunicamycin and thapsigargin. These reagents both induced ER stress and NS3 glycosylation inhibition in a concentration-dependent manner, and as in our previous report, high concentrations of tunicamycin and thapsigargin suppressed IBAV propagation. However, lower concentrations of these reagents produced limited differences in IBAV propagation, despite their ability to suppress NS3 glycosylation and induce ER stress. These findings suggest that a considerable degree of NS3 glycosylation inhibition and ER stress induction does not suppress IBAV propagation. Conversely, lower concentrations of thapsigargin enhanced IBAV propagation, suggesting that moderate ER stress could benefit IBAV.

Serological Cross-Reactions between Expressed VP2 Proteins from Different Bluetongue Virus Serotypes

Bluetongue (BT) is a severe and economically important disease of ruminants that is widely distributed around the world, caused by the bluetongue virus (BTV). More than 28 different BTV serotypes have been identified in serum neutralisation tests (SNT), which, along with geographic variants (topotypes) within each serotype, reflect differences in BTV outer-capsid protein VP2. VP2 is the primary target for neutralising antibodies, although the basis for cross-reactions and serological variations between and within BTV serotypes is poorly understood. Recombinant BTV VP2 proteins (rVP2) were expressed in Nicotiana benthamiana, based on sequence data for isolates of thirteen BTV serotypes (primarily from Europe), including three 'novel' serotypes (BTV-25, -26 and -27) and alternative topotypes of four serotypes. Cross-reactions within and between these viruses were explored using rabbit anti-rVP2 sera and post BTV-infection sheep reference-antisera, in I-ELISA (with rVP2 target antigens) and SNT (with reference strains of BTV-1 to -24, -26 and -27). Strong reactions were generally detected with homologous rVP2 proteins or virus strains/serotypes. The sheep antisera were largely serotype-specific in SNT, but more cross-reactive by ELISA. Rabbit antisera were more cross-reactive in SNT, and showed widespread, high titre cross-reactions against homologous and heterologous rVP2 proteins in ELISA. Results were analysed and visualised by antigenic cartography, showing closer relationships in some, but not all cases, between VP2 topotypes within the same serotype, and between serotypes belonging to the same 'VP2 nucleotype'.

Ibaraki virus enters host cells by macropinocytosis

Ibaraki virus (IBAV) is the pathogen associated with Ibaraki disease. In a previous study, we suggested that IBAV enters hamster lung (HmLu-1) cells via endocytosis and subsequently escapes into the cytoplasm upon endosomal acidification. However, it is unclear which of the endocytic pathways IBAV utilizes. In this study, we aimed to further elucidate the pathway of IBAV entry into host cells. We found that IBAV replication was not suppressed by inhibitors of clathrin-mediated or caveolin-mediated endocytosis but was markedly suppressed by 5-(N-ethyl-N-isopropyl) amiloride (EIPA) and cytochalasin D, both of which inhibit macropinocytosis. Monensin, which inhibits endosomal acidification, also suppressed IBAV replication. To assess the inhibitory effects of these reagents on endocytosis, dextran and transferrin were used as indicators of macropinocytosis and clathrin-mediated endocytic activity, respectively. Our data confirmed that EIPA and monensin inhibited dextran uptake, and cytochalasin D inhibited the uptake of both. Additionally, we confirmed that endosomal/lysosomal acidification was inhibited by monensin. These results suggest that the macropinocytosis pathway is the major route of IBAV entry and confirm that IBAV infection of HmLu-1 cells is dependent on endosomal acidification.

Characterization of Novel Reoviruses Wad Medani Virus (Orbivirus) and Kundal Virus (Coltivirus) Collected from Hyalomma anatolicum Ticks in India during Surveillance for Crimean Congo Hemorrhagic Fever

In 2011, ticks were collected from livestock following an outbreak of Crimean Congo hemorrhagic fever (CCHF) in Gujarat state, India. CCHF-negative Hyalomma anatolicum tick pools were passaged for virus isolation, and two virus isolates were obtained, designated Karyana virus (KARYV) and Kundal virus (KUNDV), respectively. Traditional reverse transcription-PCR (RT-PCR) identification of known viruses was unsuccessful, but a next-generation sequencing (NGS) approach identified KARYV and KUNDV as viruses in the Reoviridae family, Orbivirus and Coltivirus genera, respectively. Viral genomes were de novo assembled, yielding 10 complete segments of KARYV and 12 nearly complete segments of KUNDV. The VP1 gene of KARYV shared a most recent common ancestor with Wad Medani virus (WMV), strain Ar495, and based on nucleotide identity we demonstrate that it is a novel WMV strain. The VP1 segment of KUNDV shares a common ancestor with Colorado tick fever virus, Eyach virus, Tai Forest reovirus, and Tarumizu tick virus from the Coltivirus genus. Based on VP1, VP6, VP7, and VP12 nucleotide and amino acid identities, KUNDV is proposed to be a new species of Coltivirus Electron microscopy supported the classification of KARYV and KUNDV as reoviruses and identified replication morphology consistent with other orbi- and coltiviruses. The identification of novel tick-borne viruses carried by the CCHF vector is an important step in the characterization of their potential role in human and animal pathogenesis.IMPORTANCE Ticks and mosquitoes, as well Culicoides, can transmit viruses in the Reoviridae family. With the help of next-generation sequencing (NGS), previously unreported reoviruses such as equine encephalosis virus, Wad Medani virus (WMV), Kammavanpettai virus (KVPTV), and, with this report, KARYV and KUNDV have been discovered and characterized in India. The isolation of KUNDV and KARYV from Hyalomma anatolicum, which is a known vector for zoonotic pathogens, such as Crimean Congo hemorrhagic fever virus, Babesia, Theileria, and Anaplasma species, identifies arboviruses with the potential to transmit to humans. Characterization of KUNDV and KARYV isolated from Hyalomma ticks is critical for the development of specific serological and molecular assays that can be used to determine the association of these viruses with disease in humans and livestock.

Apoptosis induced by Ibaraki virus does not affect virus replication and cell death in hamster lung HmLu-1 cells

Ibaraki virus (IBAV) is an arbovirus that is transmitted by biting midges and causes Ibaraki disease in cattle. IBAV induces apoptosis in several mammalian cell lines, and apoptosis in turn facilitates IBAV replication. In addition, virus-induced apoptosis may contribute to mammalian-specific pathogenicity considering that some arboviruses induce apoptosis in mammalian cells but not in insect cells. In this study, we found that when hamster lung cells (HmLu-1) are used as a virus host, IBAV causes severe cytopathic effects with little induction of apoptosis. Furthermore, pharmacological inhibition of apoptosis did not affect IBAV-induced cytotoxicity. These results indicate the existence of an apoptosis-independent pathway in which IBAV replicates and exerts cytotoxicity in mammalian cells.

Amino acid starvation accelerates replication of Ibaraki virus

Ibaraki virus (IBAV) is a strain of epizootic hemorrhagic disease virus 2 that belongs to the genus Orbivirus of the family Reoviridae. IBAV replication is suppressed by the inhibition of autophagy, and since mechanistic target of rapamycin complex 1 (mTORC1) is a key regulator of autophagy, we examined if mTORC1 inhibition by amino acid starvation or mTOR inhibitors (Torin 1 and rapamycin) affects IBAV replication. We found that IBAV replication is significantly enhanced after amino acid starvation of host cells, but not after treatment with mTOR inhibitors, during early stages of viral infection (0-1 hpi). Notably, inhibition of mTORC1 by amino acid starvation was reversible and thus restricted to 0-1 hpi, whereas mTOR inhibitors sustainably suppressed mTORC1 even after the 1-h treatment, suggesting that mTORC1 suppression itself does not affect IBAV replication. To investigate the mechanism of enhanced IBAV replication by amino acid starvation, we examined the endocytic pathway, since IBAV utilizes acidification of endosomes as a trigger for viral replication. Accordingly, we found that amino acid starvation, but not mTOR inhibitors, strongly induced acidification of endosomes/lysosomes and that inhibition of endosomal acidification by bafilomycin A1 effectively blocked enhancement of IBAV replication. Altogether, the inactivation of mTORC1 by amino acid starvation during early stages of infection enhances acidification of endosomes, which in turn enhances IBAV replication.

Analysis of Conserved, Computationally Predicted Epitope Regions for VP5 and VP7 Across three Orbiviruses

Orbiviruses are double-stranded RNA viruses that have profound economic and veterinary significance, 3 of the most important being African horse sickness virus (AHSV), bluetongue virus (BTV), and epizootic hemorrhagic disease virus (EHDV). Currently, vaccination and vector control are used as preventative measures; however, there are several problems with the current vaccines. Comparing viral amino acid sequences, we obtained an AHSV-BTV-EHDV consensus sequence for VP5 (viral protein 5) and for VP7 (viral protein 7) and generated homology models for these proteins. The structures and sequences were analyzed for amino acid sequence conservation, entropy, surface accessibility, and epitope propensity, to computationally determine whether consensus sequences still possess potential epitope regions. In total, 5 potential linear epitope regions on VP5 and 11 on VP7, as well as potential discontinuous B-cell epitopes, were identified and mapped onto the homology models created. Regions identified for VP5 and VP7 could be important in vaccine design against orbiviruses.

Preparation and Characterization of a Monoclonal Antibody Against the Core Protein VP7 of the 25th Serotype of Bluetongue Virus

Bluetongue virus (BTV) is a member of the genus Orbivirus, within the family Reoviridae. The VP7 protein of BTV is used for developing group-specific serological assays. To prepare monoclonal antibody (MAb) against VP7 of the 25th serotype BTV, the RNA S7 encoding VP7 was cloned into prokaryotic expression vectors pET-28a (+) and pGEX-6P-1 to generate recombinant plasmids. The recombinant protein VP7 was expressed in Escherichia coli BL21 (DE3), respectively. The results of SDS-PAGE revealed that the VP7 was expressed and the molecular mass of recombinant fusion protein pET-28a (+)/VP7 and pGEX-6P-1/VP7 was approximately 44 kDa and 64 kDa, respectively. The Western blot analysis indicated that the recombinant VP7 possessed good immunoreactivity. After purification, pET-28a (+)/VP7 was used to immunize BALB/c mice, while pGEX-6P-1/VP7 was used to screen for well-to-well MAb-secreting hybridomas. The hybridoma cell line 3H7 against recombinant VP7 that secreted MAbs was obtained. The isotype of 3H7 was identified as IgG1. The purification of recombinant VP7 protein and the monoclonal antibody will have potential applications on competitive ELISA format for BT-specific serum detection method.

The requirement of environmental acidification for Ibaraki virus infection to host cells

The effect of environmental acidification on Ibaraki virus (IBAV) infection was tested using endosomal inhibitory chemicals and low pH treatment. Treatment of target cells with endosomal inhibitors significantly decreased the progeny virus production. IBAV outer capsid proteins, VP5 and VP2, were removed from virion when purified IBAV was exposed to low pH environment. Further experiment showed that the exposure to low pH buffer facilitated IBAV infection when the cellular endosomal pathway was impaired by bafilomycin A1. Results obtained in this study suggest that acidic environment is essential to initiate IBAV infection.

The effect of glycosylation on cytotoxicity of Ibaraki virus nonstructural protein NS3

The cytotoxicity of Ibaraki virus nonstructural protein NS3 was confirmed, and the contribution of glycosylation to this activity was examined by using glycosylation mutants of NS3 generated by site-directed mutagenesis. The expression of NS3 resulted in leakage of lactate dehydrogenase to the culture supernatant, suggesting the cytotoxicity of this protein. The lack of glycosylation impaired the transport of NS3 to the plasma membrane and resulted in reduced cytotoxicity. Combined with the previous observation that NS3 glycosylation was specifically observed in mammalian cells (Urata et al., Virus Research 2014), it was suggested that the alteration of NS3 cytotoxicity through modulating glycosylation is one of the strategies to achieve host specific pathogenisity of Ibaraki virus between mammals and vector arthropods.

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

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

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

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

Molecular epidemiology of bluetongue virus serotype 1 isolated in 2006 from Algeria

This study reports on an outbreak of disease that occurred in central Algeria during July 2006. Sheep in the affected area presented clinical signs typical of bluetongue (BT) disease. A total of 5245 sheep in the affected region were considered to be susceptible, with 263 cases and thirty-six deaths. Bluetongue virus (BTV) serotype 1 was isolated and identified as the causative agent. Segments 2, 7 and 10 of this virus were sequenced and compared with other isolates from Morocco, Italy, Portugal and France showing that they all belong to a 'western' BTV group/topotype and collectively represent a western Mediterranean lineage of BTV-1.

Re-emergence of bluetongue, African horse sickness, and other orbivirus diseases

Arthropod-transmitted viruses (Arboviruses) are important causes of disease in humans and animals, and it is proposed that climate change will increase the distribution and severity of arboviral diseases. Orbiviruses are the cause of important and apparently emerging arboviral diseases of livestock, including bluetongue virus (BTV), African horse sickness virus (AHSV), equine encephalosis virus (EEV), and epizootic hemorrhagic disease virus (EHDV) that are all transmitted by haematophagous Culicoides insects. Recent changes in the global distribution and nature of BTV infection have been especially dramatic, with spread of multiple serotypes of the virus throughout extensive portions of Europe and invasion of the south-eastern USA with previously exotic virus serotypes. Although climate change has been incriminated in the emergence of BTV infection of ungulates, the precise role of anthropogenic factors and the like is less certain. Similarly, although there have been somewhat less dramatic recent alterations in the distribution of EHDV, AHSV, and EEV, it is not yet clear what the future holds in terms of these diseases, nor of other potentially important but poorly characterized Orbiviruses such as Peruvian horse sickness virus.

Adaptive strategies of African horse sickness virus to facilitate vector transmission

African horse sickness virus (AHSV) is an orbivirus that is usually transmitted between its equid hosts by adult Culicoides midges. In this article, we review the ways in which AHSV may have adapted to this mode of transmission. The AHSV particle can be modified by the pH or proteolytic enzymes of its immediate environment, altering its ability to infect different cell types. The degree of pathogenesis in the host and vector may also represent adaptations maximising the likelihood of successful vectorial transmission. However, speculation upon several adaptations for vectorial transmission is based upon research on related viruses such as bluetongue virus (BTV), and further direct studies of AHSV are required in order to improve our understanding of this important virus.

Genetic and epidemiological characterization of Middle Point orbivirus, a novel virus isolated from sentinel cattle in northern Australia

Middle Point orbivirus (MPOV) was isolated in 1998 from a healthy cow pastured at Beatrice Hill farm, Middle Point (formerly Coastal Plains Research Station), 50 km east of Darwin in Australia's Northern Territory. The isolate could not be identified by using conventional serological tests, and electron microscopy indicated that it belongs to the family Reoviridae, genus Orbivirus. Genetic sequencing of segments 2 and 3 revealed that this virus is related to Yunnan orbivirus, an orbivirus known only from China and not previously associated with a vertebrate host. A real-time RT-PCR test was developed to study the epidemiology of this virus in the field. Over 150 previously unidentified viruses isolated from cattle between 1994 and 2006 were positively identified as isolates of MPOV. Serology was used to demonstrate the development of antibody responses to MPOV in cattle from multiple locations across the Northern Territory.

Regional seroprevalence of bluetongue virus in cattle in Illinois and western Indiana

OBJECTIVE

To estimate seroprevalence of bluetongue virus (BTV) and the geographic distribution of seropositive cattle herds in Illinois and western Indiana.

SAMPLE POPULATION

10,585 serum samples obtained from cattle in 60 herds during 3 transmission seasons (2000 through 2002).

PROCEDURES

In a longitudinal study, serum samples were tested for BTV antibodies by use of a competitive ELISA. Four geographic zones were created by use of mean minimum January temperature. A multivariable mixed-effects logistic regression model with a random effect for herd was used to estimate seropositive risk for zone, age of cattle, herd type, and transmission season.

RESULTS

Overall, BTV antibodies were detected in 156 (1.5%) samples. Estimated seroprevalence in 2000, 2001, and 2002 was 1.49%, 0.97%, and 2.18%, respectively. Risk of being seropositive for BTV was associated with geographic zone and age. Seroprevalence increased progressively from northern to southern zones, with no evidence of BTV infection in the northernmost zone. In the southernmost zone, annual seroprevalence ranged from 8.65% to 11.00%. Adult cattle were 2.35 times as likely as juvenile cattle to be seropositive.

CONCLUSIONS AND CLINICAL RELEVANCE

Overall seroprevalence was lower than has been reported for Illinois cattle. Bluetongue virus antibodies were distributed heterogeneously in this region. Only in the southernmost zone was seroprevalence consistently > 2%. Regionalization of BTV risk based on state borders does not account for such variability. Serologic data could be combined with landscape, climate, and vector data to develop predictive models of BTV risk within transitional regions of the United States.

Recombinant capripoxviruses expressing proteins of bluetongue virus: evaluation of immune responses and protection in small ruminants

The development of recombinant capripoxviruses for protective immunization of ruminants against bluetongue virus (BTV) infection is described. Sheep (n=11) and goats (n=4) were immunized with BTV recombinant capripoxviruses (BTV-Cpox) individually expressing four different genes encoding two capsid proteins (VP2 and VP7) and two non-structural proteins (NS1, NS3) of BTV serotype 2 (BTV-2). Seroconversion was observed against NS3, VP7 and VP2 in both species and a lymphoproliferation specific to BTV antigens was also demonstrated in goats. Finally, partial protection of sheep challenged 3 weeks after BTV-Cpox administration with a virulent strain of BTV-2, was observed.

VP2-segment sequence analysis of some isolates of bluetongue virus recovered in the Mediterranean basin during the 1998-2003 outbreak

The complete nucleotide sequences of the VP2 segments of bluetongue virus (BTV) isolates recovered from Italy, Greece and Israel, from 1998 to 2003, were determined. Phylogenetic analysis of these sequences, those from related viruses and the South African vaccine strains, were used to determine the probable geographic origin of BTV incursions into Italy. Results indicated that viruses from each of the four serotypes isolated in Italy (2, 4, 9 and 16) possibly had a different origin. Analysis of the bluetongue virus serotype 2 (BTV-2) isolates gave evidence that this serotype probably moved from Tunisia. BTV-4 results showed probable incursion from the southwest and not from Greece or Israel. BTV-9 isolates clearly have an eastern origin (most probably Greece), whereas BTV-16 isolates are indistinguishable from the BTV-16 live attenuated vaccine strain. The phylogenetic findings were supported by polyacrylamide gel electrophoresis (PAGE) analysis of the complete amplified genome of each isolate except for BTV-16 Italian field isolate, which showed a slightly different PAGE profile. A combination of the complete VP2 sequencing and PAGE analysis of complete genomes, allowed not only phylogenetic analysis, but also vaccine detection and assessment of reassortment events.

Studies on the Safety and Immunogenicity of the South African Bluetongue Virus Serotype 2 Monovalent Vaccine: Specific Detection of the Vaccine Strain Genome by RT-PCR

In order to study the safety and the immunogenicity of the South African vaccine against the serotype 2 bluetongue virus, two groups of seven sheep were vaccinated with the vaccine used in the French island of Corsica. Vaccinated and non-vaccinated sheep were observed clinically and their rectal temperatures were recorded daily. The serological response in vaccinated animals confirmed the immunogenicity of the vaccine. Post-vaccinal viraemia was investigated and the vaccine genome was detected by reverse transcription polymerase chain reaction (RT-PCR). No viraemia was observed at post-vaccination days 4, 7 and 11 but the vaccine strain of virus was detected by RT-PCR throughout the experiment. The thermostability of the vaccine was also evaluated. The vaccine titre strongly decreased at temperatures higher than 35 degrees C.

Replication of bluetongue virus and epizootic hemorrhagic disease virus in pulmonary artery endothelial cells obtained from cattle, sheep, and deer

OBJECTIVE

To compare replication of bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV) in pulmonary artery endothelial cells (ECs) obtained from juvenile cattle, sheep, white-tailed deer (WTD; Odocoileus virginianus), and black-tailed deer (BTD; O hemionus columbianus).

SAMPLE POPULATION

Cultures of pulmonary artery ECs obtained from 3 cattle, 3 sheep, 3 WTD, and 1 BTD.

PROCEDURE

Purified cultures of pulmonary artery ECs were established. Replication, incidence of infection, and cytopathic effects of prototype strains of BTV serotype 17 (BTV-17) and 2 serotypes of EHDV (EHDV-1), and (EHDV-2) were compared in replicate cultures of ECs from each of the 4 ruminant species by use of virus titration and flow cytometric analysis.

RESULTS

All 3 viruses replicated in ECs from the 4 ruminant species; however, BTV-17 replicated more rapidly than did either serotype of EHDV. Each virus replicated to a high titer in all ECs, although titers of EHDV-1 were significantly lower in sheep ECs than in ECs of other species. Furthermore, all viruses caused extensive cytopathic effects and a high incidence of cellular infection; however, incidence of cellular infection and cytopathic effects were significantly lower in EHDV-1-infected sheep ECs and EHDV-2-infected BTD ECs.

CONCLUSIONS AND CLINICAL RELEVANCE

There were only minor differences in replication, incidence of infection, and cytopathic effects for BTV-17, EHDV-1, or EHDV-2 in ECs of cattle, sheep, BTD, and WTD. It is not likely that differences in expression of disease in BTV- and EHDV-infected ruminants are attributable only to species-specific differences in the susceptibility of ECs to infection with the 2 orbiviruses.

Molecular differentiation between NS1 gene of a field strain Bluetongue virus serotype 2 (BTV-2) and NS1 gene of an attenuated BTV-2 vaccine

At the end of September 2000, clinical symptoms of Bluetongue appeared in sheep flocks of the Balearic Islands (Spain). The presence of the BTV serotype 2 in tissue and blood samples of affected animals was confirmed by laboratory techniques. A systematic vaccination were carried out in affected areas using a live monovalent serotype 2 vaccine available from Onderstepoort laboratory (South Africa). In order to perform epidemiological studies, a new method to differentiate between the NS1 genes of BTV-2 affecting the Balearic islands and that of the Onderstepoort commercial live virus vaccine (monovalent, serotype 2) has been developed. This procedure is based on the use of an RT-PCR, followed by restriction endonuclease analysis. Epidemiological data of a study carried out in the period January-October 2001 using this procedure are included.

Identification of seven serotypes of bluetongue virus from the People's Republic of China

Seven serotypes (1, 2, 3, 4, 12, 15 and 16) of bluetongue virus were isolated from the blood of sheep and cattle in the People's Republic of China between 1986 and 1996. Six of these viruses were isolated in Yunnan province. The sheep from which serotypes 1 and 16 were isolated showed obvious signs of bluetongue disease, whereas the cattle from which serotypes 2, 3, 4, 12 and 15 were isolated were clinically normal. Phylogenetic analyses of these viruses indicate that they are more closely related to one another, and to an Australian strain of serotype 1, than they are to prototype strains of bluetongue virus serotypes 2, 10, 11, 13 and 17 from the USA.

Epidemic of blindness in kangaroos--evidence of a viral aetiology

OBJECTIVE

To determine the cause of an epidemic of blindness in kangaroos.

DESIGN AND PROCEDURES

Laboratory examinations were made of eyes and brains of a large number of kangaroos using serological, virological, histopathological, electron microscopical, immunohistochemical methods, and PCR with cDNA sequencing. In addition, potential insect viral vectors identified during the disease outbreak were examined for specific viral genomic sequences.

SAMPLE POPULATION

For histopathological analysis, 55 apparently blind and 18 apparently normal wild kangaroos and wallabies were obtained from New South Wales, Victoria, South Australia, and Western Australia. A total of 437 wild kangaroos and wallabies (including 23 animals with apparent blindness) were examined serologically.

RESULTS

Orbiviruses of the Wallal and Warrego serogroups were isolated from kangaroos affected with blindness in a major epidemic in south-eastern Australia in 1994 and 1995 and extending to Western Australia in 1995/96. Histopathological examinations showed severe degeneration and inflammation in the eyes, and mild inflammation in the brains. In affected retinas, Wallal virus antigen was detected by immunohistochemical analysis and orbiviruses were seen in electron microscopy. There was serological variation in the newly isolated Wallal virus from archival Wallal virus that had been isolated in northern Australia. There were also variations of up to 20% in genotype sequence from the reference archival virus. Polymerase chain reactions showed that Wallal virus was present during the epidemic in three species of midges, Culicoides austropalpalis, C dycei and C marksi. Wallal virus nucleic acid was also detected by PCR in a paraffin-embedded retina taken from a blind kangaroo in 1975.

CONCLUSION

Wallal virus and perhaps also Warrego virus are the cause of the outbreak of blindness in kangaroos. Other viruses may also be involved, but the evidence in this paper indicates a variant of Wallal virus, an orbivirus transmitted by midges, has the strongest aetiological association, and immunohistochemical analysis implicates it as the most damaging factor in the affected eyes.

EHDV-1, a new Australian serotype of epizootic haemorrhagic disease virus isolated from sentinel cattle in the Northern Territory

In 1992, a virus (DPP2209) isolated from sentinel cattle located at Coastal Plains Research Station, latitude 12 degrees 39'S, longitude 131 degrees 20'E, approximately 60 km east of Darwin, Northern Territory. This virus was identified as a serotype of epizootic haemorrhagic disease (EHD) of deer virus previously undescribed in Australia. An additional 17 isolation of this virus were made from eight animals during the period February to May. Electron microscopic studies showed the presence of orbivirus-like structures. Serogrouping ELISA, indirect immunofluorescence assay and the serogrouping plaque reduction neutralisation test indicated the virus was a member of the epizootic haemorrhagic disease serogroup. Serotype specific plaque reduction neutralisation tests, indicated the virus was a member of the epizootic haemorrhagic disease serogroup not previously isolated in Australia. Analysis of the VP3 gene confirmed this observation. Cross neutralisation testing of the isolate with known epizootic haemorrhagic disease serotype viruses including endemic Australian and exotic strains identified isolate DPP2209 as epizootic haemorrhagic disease virus serotype 1.

The complete nucleotide sequence of rabbit haemorrhagic disease virus (Czech strain V351): use of the polymerase chain reaction to detect replication in Australian vertebrates and analysis of viral population sequence variation

The complete nucleotide sequence of the Czech strain of rabbit haemorrhagic disease virus (RHDV) was determined to be 7437 nucleotides in length with a 5-terminal non-coding region of 9 nucleotides and a 3'-terminal non-coding region of 59 nucleotides. Two open reading frames (ORFs) were found within this sequence coding for polypeptides of 2344 (nucleotides 10-7044) and 117 amino acids (nucleotides 7025-7378). The sequence of this isolate was approximately 1% different from that reported by Meyers et al., having 78 nucleotide changes which resulted in 30 amino acid differences, the majority of these clustering in the N-terminus of the large ORF and the middle of the viral coat protein. Only a single conservative amino acid change was seen in the smaller 3'-terminal ORF. Since the virus cannot at present be propagated in tissue culture, but isolated only after replication in rabbits, the reported sequence must be considered as a consensus sequence from the viral population. To gain some understanding of the possible sequence diversity within this virus population, 97 clones were sequenced from a polymerase chain reaction (PCR) fragment to determine the sequence diversity of the virus population. Four major classes of variant were described with mutations generally in the third base position of codons. A nested reverse transcriptase (RT) PCR (using sequence derived for the coat protein of RHDV) was used to determine the presence or absence of RHDV inoculated into non-host animal species. No replication of the virus was detected in 28 different vertebrate species other than rabbits. PCR tests on both mosquitoes and fleas feeding on RHDV infected rabbits were positive. The RT-PCR test was more sensitive when compared with an antigen capture ELISA to detect the presence of genomic RNA/or virus in infected rabbits.

Characterisation of Wongorr virus, an Australian orbivirus

Sequence analyses of VP3 gene segments of Wongorr virus isolates from the Northern Territory of Australia were compared with the cognate gene segments from Picola and Paroo River viruses. Previous serological investigations had demonstrated some relationships between these viruses, however VP3 gene sequence and phylogenetic analyses placed these viruses within the same serogroup which was distinct from other described orbivirus serogroups. A polymerase chain reaction (PCR) was developed for the detection of this serogroup and used to identify and determine partial sequence data for other isolates of the virus. Wongorr virus and the other tick and mosquito-borne orbiviruses (Kemerovo and Corriparta), were more closely related than the Culicoides transmitted orbiviruses, such as bluetongue (BTV) and African horse sickness virus (AHSV) which were shown to be on a separate branch of the orbivirus phylogenetic tree.

Phylogenetic comparison of the S3 gene of United States prototype strains of bluetongue virus with that of field isolates from California

To better define the molecular epidemiology of bluetongue virus (BTV) infection, the genetic characteristics and phylogenetic relationships of the S3 genes of the five U.S. prototype strains of BTV, the commercially available serotype 10 modified live virus vaccine, and 18 field isolates of BTV serotypes 10, 11, 13, and 17 obtained in California during 1980, 1981, 1989, and 1990 were determined. With the exception of the S3 gene of the U.S. prototype strain of BTV serotype 2 (BTV 2), these viruses had an overall sequence homology of between 95 and 100%. Phylogenetic analyses segregated the prototype U.S. BTV 2 strain to a unique branch (100% bootstrap value), whereas the rest of the viruses clustered in two main monophyletic groups that were not correlated with their serotype, year of isolation, or geographical origin. The lack of consistent association between S3 gene sequence and virus serotype likely is a consequence of reassortment of BTV gene segments during natural mixed infections of vertebrate and invertebrate hosts. The prototype strain of BTV 13, which is considered an introduction to the U.S. like BTV 2, presents an S3 gene which is highly homologous to those of some isolates of BTV 10 and especially to that of the vaccine strain. This finding strongly suggests that the U.S. prototype strain of BTV 13 is a natural reassortant. The different topologies of the phylogenetic trees of the L2 and S3 genes of the various viruses indicate that these two genome segments evolve independently. We conclude that the S3 gene segment of populations of BTV in California is formed by different consensus sequences which cocirculate and which cannot be grouped by serotype.

The epidemiology of bluetongue

The perception that bluetongue virus (BTV), once introduced to a country, would decimate its sheep industry, grew from the acceptance in the late 1950s that it was an emerging virus with Africa as its source. Epidemiological studies in the 1960s and early 1970s confirmed that the geographic distribution of BTV infections included regions of the world, outside the traditionally defined areas where BT was observed. This was interpreted at the time as representing serious and rapid spread of the virus. This review provides evidence to rebut this earlier view. What has emerged through the 1980s is: (a) the recognition that BTV is a common infection of ruminant livestock throughout the tropics and sub-tropics apparently within several separate ecosystems; (b) in most areas of the world, infection is sub-clinical; (c) incursions of virus (with accompanying disease) into temperate climates do occur at certain key locations, but "die out" usually within the same year; (d) recognition of the vector competence of Culicoides spp in the different ecosystems of the world is critical for understanding the epidemiology of disease; (e) persistent infection in ruminants is no longer considered important in the long term perpetuation of the virus.