Experimental infection of white-tailed deer (Odocoileus virginianus) with Northern European bluetongue virus serotype 8

Bluetongue (BT) is an insect-transmitted, economically important disease of domestic and wild ruminants. Although only five of the 26 reported bluetongue virus (BTV) serotypes are considered endemic to the USA, 10 exotic serotypes have been isolated primarily in the southeastern region of the country since 1999. For an exotic BTV serotype to become endemic there must be susceptible animal species and competent vectors. In the USA, sheep and white-tailed deer (WTD) are the primary sentinel livestock and wildlife species, respectively. In 2006, BTV-8 was introduced into Northern Europe and subsequently overwintered, causing unprecedented livestock disease and mortality during the 2006-2007 vector seasons. To assess the risk of the European strain of BTV-8 to North American WTD, and understand the role they could play after a similar introduction, eight bluetongue-seronegative WTD were inoculated with BTV-8. Body temperatures and clinical signs were recorded daily. Blood samples were analyzed for BTV RNA with quantitative real time reverse transcriptase polymerase chain reaction (qRT-PCR), serum analyzed for BTV antibodies by cELISA, and tissues taken for histopathology and qRT-PCR. All eight deer became infected and developed moderate to severe clinical disease from days 8 to 15. Peak viremia was from day 7 to 10 with detectable titers through the end of the study (28 days) in most deer. Serum antibody was detected by day 6, peaked by day 10 and continued through day 28. We conclude that North American WTD are highly susceptible to BTV-8 and would act as clinical disease sentinels and amplifying hosts during an outbreak.

A versatile SERS-based immunoassay for immunoglobulin detection using antigen-coated gold nanoparticles and malachite green-conjugated protein A/G

A surface enhanced Raman scattering (SERS) immunoassay for antibody detection in serum is described in the present work. The developed assay is conducted in solution and utilizes Au nanoparticles coated with the envelope (E) protein of West Nile Virus (WNV) as the SERS-active substrate and malachite green (MG)-conjugated protein A/G (MG-pA/G) as a bi-functional Raman tag/antibody binding reporter. Upon incubation of these reagents with serum collected from rabbits inoculated with E antigen, laser interrogation of the sandwiched immunocomplex revealed a SERS signaling response diagnostic for MG. The intensification of signature spectral peaks is shown to be proportionate to the concentration of added serum and the limit of antibody detection is 2 ng/ml of serum. To assess assay performance relative to more a traditional immunoassay, indirect enzyme-linked immunosorbent assays conducted using the same concentrations of reagents were found to be >400-fold less sensitive. Quartz crystal microbalance with dissipation (QCM-D) monitoring of immunocomplex film deposition on solid Au surfaces also confirmed the formation of antigen-antibody-protein A/G trilayers and provided quantitative measurements of film thickness which likely position MG within the sensing distance of laser-elicited, enhanced electromagnetic fields. The sensitivity and inherent versatility of the assay, which is provided by the binding of pA/G to a broad spectrum of immunoglobulins in different mammalian species, suggest that it could be developed as an alternative immunoassay format to the ELISA.

A multiplex real-time reverse transcription polymerase chain reaction assay for detection and differentiation of Bluetongue virus and Epizootic hemorrhagic disease virus serogroups

Bluetongue virus (BTV) causes disease in domestic and wild ruminants and results in significant economic loss. The closely related Epizootic hemorrhagic disease virus (EHDV) has been associated with bluetongue-like disease in cattle. Although U.S. EHDV strains have not been experimentally proven to cause disease in cattle, there is serologic evidence of infection in cattle. Therefore, rapid diagnosis and differentiation of BTV and EHDV is required. The genetic sequence information and bioinformatic analysis necessary to design a real-time reverse transcription polymerase chain reaction (RT-PCR) assay for the early detection of indigenous and exotic BTV and EHDV is described. This sequence data foundation focused on 2 conserved target genes: one that is highly expressed in infected mammalian cells, and the other is highly expressed in infected insect cells. The analysis of all BTV and EHDV prototype strains indicated that a complex primer design was necessary for both a virus group-comprehensive and virus group-specific gene amplification diagnostic test. This information has been used as the basis for the development of a rapid multiplex BTV-EHDV real-time RT-PCR that detects all known serotypes of both viruses and distinguishes between BTV and EHDV serogroups. The sensitivity of this rapid, single-tube, real-time RT-PCR assay is sufficient for diagnostic application, without the contamination problems associated with standard gel-based RT-PCR, especially nested RT-PCR tests.

Measurement of bluetongue virus binding to a mammalian cell surface receptor by an in situ immune fluorescent staining technique

A quantifiable in situ immune fluorescent assay (IFA) was developed to measure bluetongue virus (BTV) binding to mammalian cells. The utility of the assay was demonstrated with both Chinese hamster ovary (CHO) and bovine pulmonary artery endothelial (CPAE) cells. Since heparin sulfate (HS) has been shown to function as a receptor for a number of viruses, its role as a receptor for BTV was evaluated with the in situ IFA. Binding of BTV to both CHO and CPAE cells was inhibited in a dose dependent manner by HS. In addition, HS deficient CHO cells showed greatly diminished binding of BTV when compared to the parental cell line. The IFA protocol will find application, as a non-isotopic, quantifiable technique, to study virus-cell receptor interactions. Information gained from such studies will expand our understanding of the early steps in virus replication.

Bluetongue virus serotype 17 sequence variation associated with neutralization

Bluetongue virus (BTV) is an insect-transmitted orbivirus of importance to the cattle and sheep industry. The VP2 protein, encoded by L2, contains neutralizing epitopes. Previously, a panel of neutralizing monoclonal antibodies (MAbs) to the BTV serotype 17 (BTV-17) prototype strain was generated and it was determined that the neutralization domain consists of three overlapping epitopes. Over 30 amino acid changes were found between a neutralized BTV-17 prototype strain and a non-neutralized BTV-17 198 strain. In this study, the L2 genes from eight additional strains, representing both the neutralized and non-neutralized groups of BTV-17, were sequenced to determine the degree of conservation of the previously characterized differences. Comparison of the deduced amino acid sequences showed that 91% (30/33) of the previously noted changes were conserved within each group. The sequence of the M5 gene that encodes VP5 was also examined, since this surface protein has also been shown to affect neutralization. No consistent changes were noted between the neutralized and non-neutralized groups of BTV-17 by analysis of the VP5 protein. Finally, the L2 sequences of five MAb neutralization escape mutants were determined to identify specific amino acids involved in neutralization and perhaps virulence. All five mutants contained 1-3 amino acid changes that were in close proximity to a previously described variable region. These amino acid changes likely define critical sites in the overlapping neutralization domains previously described. This is the first description of two BT virus populations that have distinct neutralization characteristics co-circulating in a defined geographical region.

Detection of All Eight Serotypes of Epizootic Hemorrhagic Disease Virus by Real-Time Reverse Transcription Polymerase Chain Reaction

Epizootic hemorrhagic disease virus (EHDV) has been associated with bluetongue-like disease in cattle. Although U.S. EHDV strains have not been experimentally proven to cause disease in cattle, there is serologic evidence of infection. Differentiation of Bluetongue virus (BTV) and EHDV is necessary because diagnosis of infection caused by these viruses is often confused. The previously developed nested reverse transcription polymerase chain reaction (nRT-PCR) test for indigenous EHDV disease is sensitive and specific, but it is prone to contamination problems. Additionally, the EHDV nRT-PCR only detects 7 of the 8 serotypes. To develop an improved diagnostic test, sequence analysis was performed on 2 conserved target genes; one is highly expressed in infected mammalian cells, whereas the other is highly expressed in infected insect cells. This information was used to develop a rapid EHDV real-time PCR that detects all 8 EHDV serotypes. The EHDV assay did not cross-react with BTV strains and performed similarly to the nRT-PCR tests with archived clinical samples. In addition, it is superior to the nRT-PCR, not only because it is a closed system with fewer cross-contamination problems, but also because it detects all 8 serotypes and is less labor and time intensive.

Detection and titration of bluetongue virus in Culicoides insect cell culture by an antigen-capture enzyme-linked immunosorbent assay

Bluetongue virus (BTV) infects sheep, cattle and other ruminants and is transmitted by Culicoides spp. of biting midges. Virus is typically isolated and characterized by infection of susceptible vertebrate cells that undergo detectable and measurable cytopathic effects. Cell lines derived from C. sonorensis may be useful for virus isolation and studies to better understand BTV replication in the insect vector. However, their use is hampered because BTV infection does not produce significant cytopathic effects in these insect cell cultures. Detection of virus replication in these cells typically requires co-cultivation with susceptible vertebrate cell culture. This report describes the use of an antigen-capture enzyme-linked immunosorbent assay (Ag-Cap ELISA) for direct detection and titration of BTV in cultures of a Culicoides cell line. This assay should facilitate use of this cell line for virus isolation, titration and studies of BTV replication.

Persistence of bluetongue virus serotype 2 (BTV-2) in the southeast United States

The prototype United States (US) strains of bluetongue virus serotype 2 [BTV-2 (OnaA) and BTV-2 (OnaB)] made in Florida in 1982 were compared to a recent BTV-2 (FL99) isolate made in Florida in 1999 to determine if the original strain(s) had persisted or if a new strain of BTV-2 had been re-introduced into the southeast US. Viral RNA and protein electropherotypes, and sequence analysis of five RNA genome segments for these early and later BTV-2 isolates were compared. These comparisons indicated that BTV-2 (OnaB) has persisted in the southeast US since its first isolation in 1982. Sequence analysis of concurrent isolates of BTV-13 (FL99) and BTV-17 (FL99) from the same location in Florida in 1999 provides evidence of genetic reassortment between BTV-2 and other co-circulating serotypes of BTV.

Lack of detectable bluetongue virus in skin of seropositive cattle: implications for vertebrate overwintering of bluetongue virus

The overwintering mechanism of bluetongue virus (BTV) has eluded researchers for many years. It was recently proposed that ovine gamma delta T-cells may become persistently infected with BTV, and serve as a reservoir for infection of naive vectors in the next transmission season. Since cattle are more numerous than sheep in the western United States (where BTV is endemic), this hypothesis was tested in bovines. In the winter of 2002-2003, 54 cattle from an endemic site in northern Colorado were age-selected to ensure that possible BTV exposure must have occurred in the summer of 2002. These cattle were tested for the presence of anti-BTV antibody by ELISA; 53 were seropositive, and one was seronegative. Naive Culicoides sonorensis colony insects were fed on skin sites of four seropositive and one seronegative cattle at day 1 (135 days after the first frost), then sequentially on separate sites for three days. Virus isolation and/or reverse transcriptase-nested polymerase chain reaction from engorged insects and 6 mm skin biopsy samples were performed for detection of viable BTV or BTV nucleic acid; all were negative. These data suggest that cattle are not a reservoir host for BTV overwintering in the western United States. The role of sheep in the trans-seasonality of BTV still remains to be determined.

Field-deployable real-time polymerase chain reaction detection of bluetongue and epizootic haemorrhagic disease viral ribonucleic acid

Nucleic acid sequence information from molecular evolution studies of bluetongue virus (BTV) and related epizootic haemorrhagic disease virus (EHDV) strains has resulted in a large database of genomic information. Published sequence data and sequence data from our laboratory were used to design real-time field-deployable reverse transcriptase-polymerase chain reaction assays for the detection of BTV or EHDV viral RNA. The assays used standard RNA extraction and TaqMan chemistries and the entire process was completed in <or=3 h. The reaction conditions have been adapted to run on a field-deployable ruggedised advanced pathogen identification device (RAPID) instrument from Idaho Technologies, Inc. This instrument consists of a 50-lb (22.68 kg) backpack containing everything needed to run the assays. The current assays are specific for United States serotypes of BTV and EHDV; however, new designs based on new sequencing information are being evaluated to improve specificity and sensitivity for additional serotypes. This new technology greatly enhances the speed of virus detection and the ability to monitor disease outbreaks.

Antigen capture competitive enzyme-linked immunosorbent assays using baculovirus-expressed antigens for diagnosis of bluetongue virus and epizootic hemorrhagic disease virus

Bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV) are orbiviruses that infect both livestock and wild ruminants. Antigenic cross-reactivity between BTV and EHDV often results in serologic misdiagnosis. Competitive enzyme-linked immunosorbent assays (c-ELISAs) show increased sensitivity and specificity for the identification of these viral diseases; however, the preparation of cell culture-derived viral antigen for these tests is laborious and variable from batch to batch, and the resulting antigen may be infectious. To overcome these problems, the genes coding for a structural protein, VP7, of BTV and EHDV were cloned into baculovirus and the recombinant proteins were expressed in Sf9 cultured insect cells. Recombinant viral proteins released into the baculovirus-infected Sf9 cell culture supernatant were used in antigen capture c-ELISAs (Ag Cap c-ELISA) tests that specifically detected antibody in the serum of cattle experimentally infected with BTV and EHDV. The diagnostic utility of the Ag Cap c-ELISA was demonstrated by comparison with a commercial c-ELISA. The Ag Cap c-ELISA offers the advantages of using an easily produced, easily standardized, noninfectious antigen that does not require further purification or concentration.

The S7 gene and VP7 protein are highly conserved among temporally and geographically distinct American isolates of epizootic hemorrhagic disease virus

Complete sequences of genome segment 7 (S7) from six isolates of epizootic hemorrhagic disease virus serotype 1 (EHDV-1) and 37 isolates of serotype 2 (EHDV-2) were determined. These isolates were made between 1978 and 2001 from the southeast, mid-Atlantic, Midwest and intermountain United States. Analysis of the S7 sequence similarities showed 98.1% identity among the EHDV-1 isolates and 91.0% identity among the EHDV-2 isolates. Comparison of the deduced amino acid similarities showed an even greater degree of similarity among the isolates (100% among the EHDV-1 isolates and 98.9% identity among the EHDV-2 isolates). There was only 75.8% identity between the EHDV-1 and EHDV-2 isolates at the nucleic acid level; however, there was 93.7% identity between the two groups at the amino acid level. The ratio of non-synonymous to synonymous nucleotide indicates a strong selection for silent substitutions. There was no evidence for reassortment between EHDV-1 and EHDV-2 isolates. The high degree of conservation of S7 gene codons and the VP7 protein, suggests that little variation is allowed in preserving the function of this protein. The high degree of conservation also validates the use of diagnostic tests for EHDV based on S7 and VP7.

Characterization of cell lines developed from field populations of Culicoides sonorensis (Diptera: Ceratopogonidae)

Two cell lines, ABADRL-Cs-W3 (W3) and ABADRL-Cs-W8A (W8), were developed from a field population of Culicoides sonorensis Wirth & Jones. The cell lines were characterized by isozyme phenotyping and the ability to support the replication of bluetongue virus (BLU) and epizootic hemorrhagic disease virus (EHDV) (Orbivirus, Reoviridae). Comparison of isozymes found in the cell lines with those found in adult C. sonorensis colony insects confirmed that the cell lines were of C. sonorensis origin. There was, however, sufficient isozyme variation present in the cell lines to construct a unique isozyme profile for each cell line. Although both cell lines supported BLU and EHDV replication to the same level, one-step growth curves for BLU indicated that virus replication was faster and attained a peak titer earlier in the W3 cell line than in the W8 cell line. Viral proteins and RNA were detected earlier in the W3 cell line as well. The accelerated virus growth kinetics observed in the W3 cell line and the adherent nature of the cells makes it more suitable for certain Orbivirus studies.

Verification of bluetongue virus S9 segment nucleotide sequences

During the course of our bluetongue virus (BTV) nucleic acid sequence investigations, conflicts among United States (US) prototype BTV S9 genome segment sequences deposited in GenBank were noted. In order to rectify these inter-laboratory discrepancies, the S9 segments of Arthropod-borne Animal Diseases Research Laboratory (ABADRL)-stored US prototype BTV 2, BTV 10, BTV 11, BTV 13, and BTV 17 isolates were resequenced. Our S9 sequences, determined by direct sequencing of full-length reverse transcriptase-polymerase chain reaction (RT-PCR) generated amplicons, shared 99% or greater nucleotide identity with one or more respective S9 sequences previously reported. Possible sources of remaining unsupported US prototype BTV S9 sequences were evaluated by amplifying and sequencing the S9 segments of BTV 2 Ona A strain, South African (SA) prototype BTV 1, BTV 2, and BTV 4 strains, and the North American (NA) prototype epizootic hemorrhagic disease virus (EHDV) serotype 2 (Alberta) strain. Comparative analysis using these S9 sequences, as well as sequences of US BTV 2 field isolates, identified potential contributors to inter-laboratory sequence disagreements.

Seasonal transmission of bluetongue virus by Culicoides sonorensis (Diptera: Ceratopogonidae) at a southern California dairy and evaluation of vectorial capacity as a predictor of bluetongue virus transmission

Vectorial capacity of Culicoides sonorensis Wirth & Jones for the transmission of bluetongue (BLU) virus was examined at a southern California dairy from January 1995 to December 1997. Insects were collected one to two times per week in five CDC-type suction traps (without light) baited with CO2 at a constant release rate of 1,000 ml/min. BLU virus was detected in midges collected from May through December with an estimated overall infection rate of 0.08%. The BLU virus infection rate of field-captured midges was not correlated with sentinel calf seroconversions to BLU virus. Sentinel calf seroconversions were highly seasonal, occurring from August through November with most calves seroconverting during September and October. Vector competence of field-collected nulliparous flies fed a locally acquired serotype of BLU virus in the laboratory was stable among years (17-23%). Vectorial capacity was strongly correlated with BLU virus transmission (measured by sentinel calf seroconversions) during 1995 and 1996, but not during 1997. Host biting rate estimated for traps nearest to the sentinel calves was the index best correlated with BLU virus transmission for all study years and was most highly correlated with sentinel seroconversions 4 wk later. The utility of vectorial capacity and its component variables is discussed for this system.

Phylogenetic relationships of bluetongue viruses based on gene S7

Previous phylogenetic analyses based on bluetongue virus (BTV) gene segment L3, which encodes the inner core protein, VP3, indicated a geographical distribution of different genotypes. The inner core protein, VP7, of BTV has been identified as a viral attachment protein for insect cell infection. Because the inner core proteins are involved with infectivity of insect cells, we hypothesized that certain VP7 protein sequences are preferred by the insect vector species present in specific geographic locations. We compared the gene segment S7, which encodes VP7, from 39 strains of BTV isolated from Central America, the Caribbean Basin, the United States, South Africa and Australia. For comparison, the S7 sequences from strains of the related orbiviruses, epizootic hemorrhagic disease virus (EHDV) and African horse sickness virus (AHSV) were included. The S7 gene was highly conserved among BTV strains and fairly conserved among the other orbiviruses examined. VP7 sequence alignment suggests that the BTV receptor-binding site in the insect is also conserved. Phylogenetic analyses revealed that the BTV S7 nucleotide sequences do not unequivocally display geographic distribution. The BTV strains can be separated into five clades based on the deduced VP7 amino acid sequence alignment and phylogeny but evidence for preferential selection by available gnat species for a particular VP7 clade is inconclusive. Differences between clades indicate allowable variation of the VP7 binding protein.

Development of an enzyme-linked immunosorbent assay for the detection of antibody to epizootic hemorrhagic disease of deer virus

An enzyme-linked immunosorbent assay has been developed to detect antibodies to epizootic hemorrhagic disease of deer virus (EHDV). The assay incorporates a monoclonal antibody to EHDV serotype 2 (EHDV-2) that demonstrates specificity for the viral structural protein, VP7. The assay was evaluated with sequential sera collected from cattle experimentally infected with EHDV serotype 1 (EHDV-1) and EHDV-2, as well as the four serotypes of bluetongue virus (BTV), BTV-10, BTV-11, BTV-13, and BTV-17, that currently circulate in the US. A competitive and a blocking format as well as the use of antigen produced from both EHDV-1- and EHDV-2-infected cells were evaluated. The assay was able to detect specific antibody as early as 7 days after infection and could differentiate animals experimentally infected with EHDV from those experimentally infected with BTV. The diagnostic potential of this assay was demonstrated with field-collected serum samples from cattle, deer, and buffalo.

Epizootic hemorrhagic disease: analysis of tissues by amplification and in situ hybridization reveals widespread orbivirus infection at low copy numbers

A recent outbreak of hemorrhagic fever in wild ruminants in the northwest United States was characterized by rapid onset of fever, followed shortly thereafter by hemorrhage and death. As a result, a confirmed 1,000 white-tailed deer and pronghorn antelope died over the course of 3 months. Lesions were multisystemic and included severe edema, congestion, acute vascular necrosis, and hemorrhage. Animals that died with clinical signs and/or lesions consistent with hemorrhagic fever had antibody to epizootic hemorrhagic disease virus serotype 2 (EHDV-2) by radioimmune precipitation but the antibody was limited exclusively to class immunoglobulin M. These findings, indicative of acute infection, were corroborated by the observation that numerous deer were found dead; however, clinically affected deer were rarely seen during the outbreak. Furthermore, only in animals with hemorrhagic lesions was EHDV-2 isolated and/or erythrocyte-associated EHDV-2 RNA detected by serotype-specific reverse transcription (RT)-PCR. By using a novel RT in situ PCR assay, viral nucleic acid was localized to the cytoplasm of large numbers of tissue leukocytes and vascular endothelium in tissues with hemorrhage and to vessels, demonstrating acute intimal and medial necrosis. Because PCR amplification prior to in situ hybridization was essential for detecting EHDV, the virus copy number within individual cells was low, <20 virus copies. These findings suggest that massive covert infection characterized by rapid dissemination of virus facilitates the severe and lethal nature of this disease.

Bluetongue virus detection: a safer reverse-transcriptase polymerase chain reaction for prediction of viremia in sheep

A reversible target capture viral RNA extraction procedure was combined with a reverse-transcriptase nested polymerase chain reaction (PCR) to develop a capture PCR assay providing a rapid and safe prediction method for circulating bluetongue virus in infected ruminants. This new assay was compared with virus isolation and a recently developed antigen-capture enzyme-linked immunosorbent assay (ELISA) for the detection of bluetongue virus. Eight Warhill crossbred sheep were inoculated subcutaneously with bluetongue virus serotype 10, and blood samples were taken sequentially over a period of 28 days. The capture PCR detected the peak of viremia, as determined by virus isolation and antigen-capture ELISA, from day 5 to day 14 after challenge. The results indicate that the rapid-capture bluetongue virus PCR provides a rapid indicator of samples in which virus can be isolated. In addition, this capture bluetongue virus PCR procedure does not require a lengthy phenol extraction or the use of the highly toxic methyl mercury hydroxide denaturant.

Applications of dot-blot, ELISA, and immunoelectron microscopy to field detection of bluetongue virus in Culicoides variipennis sonorensis: an ecological perspective

An avidin-biotin complex (ABC) dot-blot, an antigen capture enzyme-linked immunosorbent assay (ELISA), and immunoelectron microscopy (IEM) were used to detect bluetongue (BLU) virus and viral antigen in field-collected C. varriipennis sonorensis Wirth & Jones from an enzootic BLU area in northeastern Colorado. This is the 1st attempt to apply these immunodiagnostic methods to an epidemiologically relevant, large-scale ecological system. One of the 1,800 midges (0.0005%) was positive by the dot-blot procedure, 2 (0.0011%) were positive by the ELISA, and BLU virus was identified in 8 midges (0.0044%) by IEM. These data are interpreted in context of the "whole system" of the disease to provide a framework for determining the knowledge gaps in our understanding and directing future studies in these areas. Our basic model of BLU ecology suggests that the infection rates found by the diagnostic methods are within expected ranges, thus strongly supporting the proposed ecological model and the work used to parameterize the model. This integration of immunodiagnostic methods and ecology makes it evident that further investigations of daily mortality during the extrinsic incubation period are vital to a better understanding of BLU virus occurrence in Culicoides vector and vertebrate host populations.

Bluetongue virus in laboratory-reared Culicoides variipennis sonorensis: applications of dot-blot, ELISA, and immunoelectron microscopy

An avidin-biotin complex (ABC) dot-blot, an antigen capture enzyme-linked immunosorbent assay (ELISA), and immunoelectron microscopy (IEM) were used to detect bluetongue (BLU) virus or viral antigen or both in adult Culicoides variipennis sonorensis Wirth & Jones. The dot-blot and ELISA procedures detected viral antigen in 10-22% (depending on serotype) of the biting midges infected with BLU-2, BLU-10, BLU-13, and BLU-17 and approximately 68% of the midges infected with BLU-11. IEM analyses revealed BLU virus in salivary glands, fat body, and thoracic muscle tissue from infected insects. There appeared to be selective growth of the virus in salivary gland tissue.

Molecular characterization of the segment 2 gene of epizootic hemorrhagic disease virus serotype 2: gene sequence and genetic diversity

The complete nucleotide sequence of the gene encoding the major outer capsid protein VP2 from the Alberta isolate of epizootic hemorrhagic disease virus serotype 2 (EHDV-2) was determined. Complementary DNA (cDNA) corresponding to segment 2 was 3002 nucleotides in length with a single open reading frame that encoded a VP2 of 982 amino acids. Although the VP2 from EHDV-2 was only 34% homologous to the cognate protein from EHDV-1, their predicted hydropathic profiles were similar, suggesting that conservation of structure is important biologically to these capsid proteins. Sequence analysis of six North American EHDV-2 field isolates showed a high degree of comparative genetic identity (> 97%). Phylogenetic profiles constructed suggest that regionalization of the viruses within the North American continent has contributed to the genetic diversity.

Geographical genetic variation in the gene encoding VP3 from the Alberta isolate of epizootic hemorrhagic disease virus

The complete nucleic acid and deduced amino acid sequences of gene segment 3 and the encoded VP3 from the North American, Alberta isolate of epizootic hemorrhagic disease virus serotype 2 (EHDV-2) are reported. Complementary DNA corresponding to segment 3 was 2768 nucleotides in length with an open reading frame of 2697 base pairs which encoded a VP3 polypeptide of 899 amino acid residues. Sequence comparison with genome segment 3 and VP3 from the Australian strain of EHDV-2 indicated genotypic and phenotypic homologies of 79% and 94%, respectively. Two North American field isolates of EHDV-2, as well as EHDV-1 (New Jersey isolate), had virtually identical homology to the Alberta isolate. Sequence analysis delineated North American EHDV strains as members of a genetically homologous and geographically distinct group of orbiviruses (topotype). The data support the hypothesis that geographic isolation between North American and Australian orbiviruses has permitted the viral topotypes to maintain their genetic distinctness.

Fine mapping of a surface-accessible, immunodominant site on the bluetongue virus major core protein VP7

The 349-amino-acid major core protein VP7 of bluetongue virus (BTV) is both the most abundant viral structural protein and the major immunogenic serogroup-reactive viral antigen. Previous studies indicated that a conformation-dependent antigenic site, defined by the VP7-specific monoclonal antibody 20E9/B7/G2(20E9), was accessible from the virus surface and that the binding of the monoclonal antibody to this epitope could be blocked specifically by antisera raised against different serotypes of bluetongue virus, suggesting it is a serogroup-specific immunodominant epitope. Using a combination of three different mapping strategies, we have located the 20E9 binding site at the N-terminus of the molecule, between amino acids 30 and 48. The fine mapping of the 20E9 immunodominant epitope will facilitate structure-function analyses of the major core protein and provide new opportunities to improve existing BTV serodiagnosis methods based on this immunogenic site.

Complex interactions between vectors and pathogens: Culicoides variipennis sonorensis (Diptera: Ceratopogonidae) infection rates with bluetongue viruses

Two laboratory colonies of Culicoides variipennis sonorensis Wirth & Jones were allowed to take blood meals containing the five U.S. serotypes (2, 10, 11, 13, and 17) of bluetongue (BLU) virus. After 14 d of extrinsic incubation, the flies were assayed for the presence of virus using an antigen capture enzyme-linked immunosorbent assay (ELISA). There was a significant effect of the serotype on infection of C. v. sonorensis with BLU virus. There was no significant difference in infection of the two colonies when averaged across the five BLU virus treatments. However, there was a statistically significant interaction between the colonies and the virus serotypes, which was demonstrated by a higher rate of infection of the AA colony with BLU virus serotype 13 and a higher rate of infection of the AK colony with BLU virus serotype 11.

Identification of an amino acid on VP2 that affects neutralization of bluetongue virus serotype 10

Genome segment 2, coding for the VP2 protein, of a neutralization resistant variant was compared to segment 2 of the bluetongue virus (BTV) serotype 10 parent from which the variant was derived. Full-length double-stranded cDNA of BTV segment 2 RNA, which was prepared by reverse transcription, was used as template to prepare overlapping subgenomic cDNA products by PCR. Purified PCR cDNA fragments were sequenced by the dideoxy chain termination reaction. Each base was determined an average of 3.7 times. Comparison of the sequence of segment 2 of the neutralization resistant variant with segment 2 of the parental virus showed two base changes, one of which resulted in a changed amino acid. This change was in a different region of VP2 than those previously reported in other neutralization resistant variants of BTV. In addition to this change, both the parental virus and the variant virus differed in two amino acids from the previously published sequence of VP2 of BTV serotype 10.

The smallest gene of the orbivirus, epizootic hemorrhagic disease, is expressed in virus-infected cells as two proteins and the expression differs from that of the cognate gene of bluetongue virus

The smallest gene (S10) of the virus of epizootic hemorrhagic disease of deer (EHD, serotype 2) is expressed as two proteins in virus-infected cells. By contrast, the non-structural proteins (NS3 and NS3A) encoded in the smallest gene of bluetongue (BT) viruses are difficult to detect in virus-infected cells. The nucleotide sequence of S10 of EHDV-2 contains two in-frame initiation codons which allow for translation of proteins of mol. wt. 25503 and 23921 analogous to NS3 and NS3A of BT viruses. The S10 genes of BT viruses are highly conserved (82%-99%); the nucleotide sequence similarity of S10 of EHDV-2 and BT viruses is about 64%. Some structural features of NS3 and NS3A are conserved in the two viruses, despite the divergence in the amino acid sequences of the proteins. The hydrophobic domains of the proteins and the putative transmembrane sequences are conserved, as are potential glycosylation sites in the proteins. A cluster of proline residues, which is conserved at residues 36-50 in all of the published sequences of NS3 of BT viruses, is conserved exactly in the alignment of the sequence of NS3 of EHDV-2 with that of the BT viruses. An explanation for the differences in expression of NS3/NS3A in EHD and BT viruses was not evident in comparing the nucleotide sequences of S10 of the viruses.

Detection of bluetongue virus from blood of infected sheep by use of an antigen-capture enzyme-linked immunosorbent assay after amplification of the virus in cell culture

An antigen-capture ELISA was used to detect bluetongue virus (BTV) from blood of infected sheep. A rabbit-origin capture antibody and a mouse-origin detection antibody combined with biotin-avidin amplification were used for the assay. The antigen-capture ELISA could not detect virus directly from the blood of infected sheep because of low virus titer. To enhance detection, virus from infected blood was amplified in cell culture. Virus could then be detected from cell culture supernatant fluids, using the ELISA. This amplification step increased the sensitivity of the assay comparable to that of assays performed in cell culture measuring cytopathic effects. The ELISA procedure was specific for BTV and did not mistakenly identify the antigenically related epizootic hemorrhagic disease virus. The antigen-capture ELISA permitted indirect quantitation and identification of BTV from the blood of infected sheep.

Epitopic mapping of linear and conformation-dependent antigenic determinants on GP5 of five U.S. bluetongue viruses

Two distinct antigenic determinants of the major outer capsid protein, GP5, of five U.S. bluetongue viruses have been identified and mapped using monoclonal and oligoclonal antibodies. One antigenic site, identified by oligoclonal antibody AK-15, was found to be common and conserved in all five U.S. BTV serotypes. This linear epitope was located between amino acid residues 175 and 189 (ALQREAAERSEDEIK). The second determinant identified by monoclonal antibody 34.7 was present in BTV-2, -10, -11, and -17 but absent in BTV-13. The binding of this monoclonal antibody to GP5 could be blocked specifically by one of three short synthetic peptides located among amino acid residues 33-42 (KAAERFAESE), 159-168 (EKILKEEDSK), and 206-215 (EIERDGMQEE), indicating that this antigenic determinant is conformation-dependent. Oligoclonal antibody (AK-15) reacted with denatured GP5 immobilized on nitrocellulose membrane after Western transfer as well as with native GP5 present on the surface of purified BTV virions. Monoclonal antibody (34.7) reacted only with denatured GP5 but not native GP5 using an ELISA assay. However, these two antigenic epitopes alone did not elicit detectable neutralizing antibodies as determined by plaque reduction assay.

Monoclonal antibodies to bluetongue virus define two neutralizing epitopes and a hemagglutinating epitope

Monoclonal antibodies were used to characterize neutralizing epitopes on VP2 of bluetongue virus serotype 10 (BTV-10). Six neutralizing monoclonal antibodies that immune precipitated VP2 demonstrated two distinct patterns of reactivity in the competitive enzyme-linked immune absorbent assay (ELISA). These results suggest that there are at least two distinct domains of neutralization on VP2 of BTV. Monoclonal antibodies defining the two domains were serotype-restricted in plaque neutralization, immune precipitation or ELISA. One of the two neutralizing domains also demonstrated significant hemagglutinating activity. Both cattle and sheep infected with BTV-10 produce antibodies to the two neutralizing epitopes.

Enzyme-linked immunosorbent assay for efficient detection of antibody to bluetongue virus in pronghorn (Antilocapra americana)

An indirect enzyme-linked immunosorbent assay (ELISA), using cell-associated viral antigen, was developed for detection of antibody to bluetongue virus (BTV) in field-collected pronghorn (Antilocapra americana) sera. To test the applicability of the ELISA to seroepizootiologic studies, pronghorn serum samples from three Wyoming counties (USA) were tested. Bluetongue virus ELISA results were compared to those of the bluetongue immunodiffusion assay. Discrepant serum samples were retested for reaction to either BTV or epizootic hemorrhagic disease virus. The pronghorn BTV ELISA gave rapid, quantitative, objective results and should facilitate testing large numbers of sera for BT diagnostic and seroepizootiologic studies.

T lymphocyte subset alterations following bluetongue virus infection in sheep and cattle

To determine potential mechanisms of differential disease expression in ruminants infected with bluetongue virus (BTV), clinically normal, BTV-seronegative, yearling sheep and cattle were infected subcutaneously with a standardized insect-source inoculum of BTV serotype 17 (BTV-17) (three infected and one contact control each) or animal adapted BTV serotype 10 (BTV-10) (three sheep only). BTV was isolated from peripheral blood cell components of infected sheep and cattle and all infected animals showed evidence of seroconversion by 14 days post infection (PI). Sheep infected with both serotypes of BTV developed pyrexia, oral lesions, and leukopenia which were most severe on days 7-8 PI. Analysis of peripheral blood mononuclear leukocytes with specific monoclonal antibodies and flow cytometry revealed panlymphocytopenia on day 7 PI. This response was further characterized by an increase in the CD4/CD8 ratio (greater than 3) resultant from a greater decrease in absolute numbers of circulating SBU-T8(CD8+) ("cytotoxic/suppressor") lymphocytes compared to SBU-T4 (CD4)+ ("helper") lymphocytes. SBU-T19+ lymphocytes were also decreased below baseline values on days 5-14 post infection. On day 14 PI there were increased CD8+ lymphocytes and decreased CD4/CD8 ratios (approximately 0.6) in these sheep. Clinical and hematologic changes in cattle infected with BTV-17 were minimal and consisted of mild pyrexia (rectal temperature 103 degrees F) on day 9 PI in two of three infected animals and mild leukopenia on several days PI in one animal. This leukopenia was the result of a pan T lymphocytopenia with CD4/CD8 ratios in the expected range (1-2). Similar to infected sheep, infected cattle did have a shift (decrease, approximately 0.8) in the peripheral CD4/CD8 ratio associated with an increase in circulating BoT8 (CD8)+ lymphocytes on day 14 post infection. Lymphocytes in the peripheral blood of all sheep and cattle infected with BTV-17 proliferated in vitro in response to purified BTV-17. These results confirm and extend those of previous studies that indicate species differences in the hematologic response to an equivalent BTV infection in domestic ruminants.

Absence of transovarial transmission of bluetongue virus in Culicoides variipennis: immunogold labelling of bluetongue virus antigen in developing oocytes from Culicoides variipennis (Coquillett)

1. Culicoides variipennis midges were fed on a blood meal containing bluetongue virus (BTV) serotype 11 (BTV-11) and on four subsequent non-infective blood meals at 4-day intervals. 2. Eggs were collected before each blood-feeding and reared to adults. 3. Progeny from each egg batch were incubated for 14 days (20 degrees C, 40-60% RH) before plaque assay. 4. Oocytes from several parent flies were sectioned for immunoelectron microscopy. 5. Thirty-two percent of the parent females tested by plaque assay were positive for BTV. 6. All 993 progeny flies were negative for BTV. 7. BTV antigen was dense in proteid yolk bodies and in the vitelline membrane of the developing oocytes.

Enhanced infectivity of bluetongue virus in cell culture by centrifugation

The effects of centrifugation of the infection of cell culture with bluetongue virus (BTV) were investigated. Baby hamster kidney cells were infected with BTV with or without centrifugation. Viral antigen was detected by immunofluorescence at 24 h in both centrifuged and noncentrifuged cultures. However, after 24 h of infection, the production of PFU in centrifuged cell cultures was 10- to 20-fold greater than that seen in cultures not centrifuged. In addition, centrifugation enhanced the direct detection of PFU from blood samples collected from a sheep experimentally infected with BTV.

In vitro neutralization of antigenic variants of bluetongue virus is related to in vivo protection

Neutralization resistant variants of bluetongue virus serotype 10 were selected with a neutralizing monoclonal antibody. Three variants were selected for further characterization. One of these variants was completely resistant to neutralization, while the other two variants showed intermediate resistance to neutralization as compared to the parent virus. The completely resistant variant failed to bind the selecting monoclonal antibody as determined by immune precipitation and enzyme linked immunosorbent assay; whereas, the other two variants bound antibody to a similar extent as the parent virus as determined by these tests. The ability of the variants to bind monoclonal antibody correlated with passive protection in the newborn mouse model. These results indicate that the ability of the virus to bind antibody is directly related to in vivo protection and that in vitro neutralization and in vivo protection are also related.

Isolation and characterization of epizootic hemorrhagic disease virus from sheep and cattle in Colorado

Epizootic hemorrhagic disease virus was isolated from cattle and sheep in northeastern Colorado during July and August 1984. The isolates were identified as serotype 2 by plaque-inhibition serotyping, genome electropherotyping, and protein analysis.

Protein coding assignment for the genome of epizootic haemorrhagic disease virus

Viral genomic RNA was purified from BHK-21 cells infected with epizootic haemorrhagic disease virus and the 10 dsRNA genome segments were isolated by polyacrylamide gel electrophoresis. These genome segments were translated in vitro using the rabbit reticulocyte lysate system and the synthesized proteins were detected by immune precipitation and gel electrophoresis. This allowed the assignment of protein coding to the genome segments and the identification of two additional virus-specified proteins not readily detectable in lysates of virus-infected cells.

Correlation of serotype specificity and protein structure of the five U.S. serotypes of bluetongue virus

The relationship between serotype specificity and protein structure was studied by polyacrylamide gel electrophoresis, peptide mapping and radioimmune precipitation (RIP) of structural and non-structural proteins of the five U.S. serotypes of bluetongue virus (BTV). The surface proteins, VP2 and VP5, showed the most variation in size among the serotypes. Peptide mapping of the proteins showed that VP2 is unique for each of the U.S. serotypes. The nucleocapsid and non-structural proteins showed a high degree of conservation, whereas the other surface protein, VP5, showed intermediate conservation among the serotypes. Monospecific neutralizing antiserum produced in rabbits against each serotype was used in cross-RIP against cytoplasmic extracts prepared from cells infected with each BTV serotype. There were extensive cross-reactions among those proteins which showed a high degree of structural conservation, whereas VP2 was immunoprecipitated best in the homologous RIP system. Thus, a correlation between serotype specificity and protein structure was shown among the five U.S. serotypes of BTV.

Binding of calmodulin to the microfilament network correlates with induction of a macrophage tumoricidal response

Induction of mouse peritoneal macrophage cytotoxicity against SV3T3, a line of virally transformed mouse cells correlated with the distribution of cytoplasmic calmodulin in the macrophages. The organization of the cytoskeleton was examined by fluorescent microscopy and by transmission electron microscopy, using immunogold tagging after Triton-X-100 (TX-100) extraction of the macrophages. Macrophages that had been activated to a tumoricidal state in vivo by vaccinia virus or in vitro by lymphokine stimulation displayed cytoskeletal networks that were more extended and weblike than did resident macrophages. The organization of microfilaments and microtubules in the cytoskeleton was displayed by using either anti-actin or anti-tubulin. Immunogold labeling of tumoricidal macrophage cytoskeletons with anti-calmodulin revealed strong binding to the microfilament network and no binding to microtubules. Anti-calmodulin reacted weakly with the cytoskeletal network of resident macrophages, and this was not demonstrably greater than the reaction with normal sheep serum. However, resident macrophages displayed a high density of calmodulin (CAM) associated with unidentifiable structures in the perinuclear region when reacted with anti-calmodulin. These characteristic distributions of CAM in resident and activated macrophages was confirmed by immunofluorescence. The total and cytoskeletal-associated amounts of calmodulin per unit of protein were determined by radioimmune assay and 125I labeling followed by SDS-PAGE. No statistically significant differences were detected between resident and activated macrophages in either the total cell or cytoskeleton fractions. In summary, our results suggest that induction of tumoricidal activity of mouse peritoneal macrophages correlates with the translocation of calmodulin to the microfilament network of the cytoskeleton.

Binding of calmodulin to the microfilament network correlates with induction of a macrophage tumoricidal response

Induction of mouse peritoneal macrophage cytotoxicity against SV3T3, a line of virally transformed mouse cells correlated with the distribution of cytoplasmic calmodulin in the macrophages. The organization of the cytoskeleton was examined by fluorescent microscopy and by transmission electron microscopy, using immunogold tagging after Triton-X-100 (TX-100) extraction of the macrophages. Macrophages that had been activated to a tumoricidal state in vivo by vaccinia virus or in vitro by lymphokine stimulation displayed cytoskeletal networks that were more extended and weblike than did resident macrophages. The organization of microfilaments and microtubules in the cytoskeleton was displayed by using either anti-actin or anti-tubulin. Immunogold labeling of tumoricidal macrophage cytoskeletons with anti-calmodulin revealed strong binding to the microfilament network and no binding to microtubules. Anti-calmodulin reacted weakly with the cytoskeletal network of resident macrophages, and this was not demonstrably greater than the reaction with normal sheep serum. However, resident macrophages displayed a high density of calmodulin (CAM) associated with unidentifiable structures in the perinuclear region when reacted with anti-calmodulin. These characteristic distributions of CAM in resident and activated macrophages was confirmed by immunofluorescence. The total and cytoskeletal-associated amounts of calmodulin per unit of protein were determined by radioimmune assay and 125I labeling followed by SDS-PAGE. No statistically significant differences were detected between resident and activated macrophages in either the total cell or cytoskeleton fractions. In summary, our results suggest that induction of tumoricidal activity of mouse peritoneal macrophages correlates with the translocation of calmodulin to the microfilament network of the cytoskeleton.

The metabolic defect of methionine dependence occurs frequently in human tumor cell lines

Methionine dependence is the inability of cells to grow when methionine (Met) is replaced by its immediate precursor homocysteine (Hcy) in the culture medium (Met-Hcy+ medium). All normal unestablished cell strains tested to date have been shown to be methionine-independent and thus grow almost as well in Met-Hcy+ medium as they do in Met+-Hcy-medium. Results presented here indicate that out of 23 cell lines derived from diverse types of human tumors, 11 do not grow at all in Met-Hcy+ medium and are absolutely methionine-dependent and 3 grow only slightly in this medium. Many of the tumor cell lines tested have little else in common other than the fact that they are methionine-dependent. The high frequency of occurrence of methionine dependence in diverse types of human tumor cells indicates that methionine dependence may be an important aspect of oncogenic transformation and therapeutically exploitable.

S-adenosylmethionine synthetase in cultured normal and oncogenically-transformed human and rat cells

We have investigated the enzymatic formation of S-adenosylmethionine in extracts of a variety of normal and oncogenically-transformed human and rat cell lines which differ in their ability to grow in medium in which methionine is replaced by its immediate precursor homocysteine. We have localized the bulk of the S-adenosylmethionine synthetase activity to the post-mitochondrial supernatant. We show that in all cell lines a single kinetic species exists in a dialyzed extract with a Km for methionine of about 3-12 microM. In selected lines we have demonstrated a requirement for Mg2+ in addition to that needed to form the Mg X ATP complex for enzyme activity and have shown that the enzyme can be regulated by product feedback inhibition. Because we detect no differences in the enzymatic ability of these cell extracts to utilize methionine for S-adenosylmethionine formation in vitro, we suggest that the failure of oncogenically-transformed cell lines to grow in homocysteine medium may result from the decreased methionine pools in these cells or from the loss of ability of these cells to properly metabolize homocysteine, adenosine, or their cellular product S-adenosylhomocysteine.

Reduced free-methionine in methionine-dependent SV40-transformed human fibroblasts synthesizing apparently normal amounts of methionine

Many different types of cancer cells have been shown to be methionine-dependent. These cells, unlike normal cells, grow poorly or not at all when methionine is replaced by its immediate precursor homocysteine in the growth medium (Met- Hcy+ medium). We have previously shown that apparently normal total amounts of methionine are synthesized by methionine-dependent SV40-transformed human fibroblasts. However, methionine-dependent cells in Met- Hcy+ medium accumulate reduced amounts of S-adenosylmethionine (AdoMet) and elevated amounts of S-adenosylhomocysteine (AdoHcy) that together probably limit growth. In this report, we demonstrate that the amount of free methionine is low in methionine-dependent SV40-transformed human fibroblasts in Met- Hcy+ medium compared to normal human diploid fibroblasts. In contrast, in Met+ Hcy- medium, the amount of free methionine is comparable in both cell types. The deficient pool of free methionine in methionine-dependent cells in Met- Hcy+ medium allows only low amounts of AdoMet to be formed. However, large amounts of the biosynthesized methionine are channeled into protein synthesis. Possible mechanisms are discussed to explain this cancer-associated metabolic defect.

A biochemical comparison of the in vitro replication of a virulent and an avirulent strain of Venezuelan encephalitis virus

The virulent Venezuelan equine encephalitis (VEE) virus strain, Trinidad donkey (TRD) and its vaccine derivative strain TC-83, demonstrated biological and biochemical differences in their replication. These two viruses had similarly shaped growth curves; however, TRD virus-infected cells produced significantly more infectious virus than did the TC-83 virus-infected cells during the very early period of the replication cycle. TRD virus inhibited host cell protein synthesis in Vero cells earlier than did TC-83 virus as measured by the incorporation of [35S]methionine into cellular proteins. Virus-specified proteins were detected 1 to 2 h earlier in TRD virus-infected cells than in the TC-83 virus-infected cells; however, pulse-chase studies failed to show differences in the processing of the viral structural proteins in cells infected by either of the viruses. TRD virus-infected cells produced more virus RNA than did the TC-83 virus-infected cells, and analysis of the intracellular viral RNA species showed an increased synthesis of 26S RNA in the TRD virus-infected cells. The difference in amounts of 26S virus RNA produced was most pronounced early during the infection and may explain why TRD virus infection resulted in an earlier production of viral proteins and inhibition of cellular protein synthesis than was observed in the cells infected with the avirulent vaccine strain of VEE virus.

Glycosylation patterns of the envelope glycoproteins of an equine-virulent venezuelan encephalitis virus and its vaccine derivative

The equine-virulent Venezuelan encephalitis virus, Trinidad donkey (TRD), was compared to its vaccine derivative, TC-83 virus, by examining the glycosylation of the two structural envelope glycoproteins (E1 and E2). The number of size classes of glycopeptides on the glycoproteins was determined by P-6 column chromatography following Pronase digestion. The E1 glycoprotein had three glycopeptide size species and the E2 glycoprotein contained four size species ranging in mol. wt. from 1900 to 2700. Both viruses contained similar glycopeptide size species, although the relative amounts on the E2 glycoproteins appeared to be somewhat different. All of the glycopeptide species appeared to be complex, since all were labelled with glucosamine, mannose, galactose and fucose. No mannose-rich species could be detected. The different glycopeptide species appeared to be sialylation isomers of a smaller core glycopeptide with an apparent mol. wt. of 1800 which was the sole product following desialylation of the larger glycopeptides. The number of oligosaccharide attachment sites present on both E1 and E2 of each virus was determined using reverse-phase high pressure liquid chromatography. This analysis indicated that the E1 glycoprotein of both viruses had six or seven similar sugar-labelled peptide fragments following trypsin digestion. However, the E2 glycoprotein of TRD virus contained three oligosaccharide attachment sites, whereas TC-83 E2 glycoprotein had only two.