Completion of the La Crosse virus genome sequence and genetic comparisons of the L proteins of the Bunyaviridae

Soybean vein necrosis virus: an emerging virus in North America

Few diseases have emerged in such a short period of time as soybean vein necrosis. The disease is present in all major producing areas in North America, affecting one of the major row field instead of row crops for the United States. Because of the significance of soybean in the agricultural economy and the widespread presence of the disease, the causal agent, soybean vein necrosis virus has been studied by several research groups. Research in the past 10 years has focused on virus epidemiology, management, and effects on yield and seed quality. This communication provides a review of the current knowledge on the virus and the disease.

Comparative sequence analyses of La Crosse virus strain isolated from patient with fatal encephalitis, Tennessee, USA

We characterized a La Crosse virus (LACV) isolate from the brain of a child who died of encephalitis-associated complications in eastern Tennessee, USA, during summer 2012. We compared the isolate with LACV sequences from mosquitoes collected near the child's home just after his postmortem diagnosis. In addition, we conducted phylogenetic analyses of these and other sequences derived from LACV strains representing varied temporal, geographic, and ecologic origins. Consistent with historical findings, results of these analyses indicate that a limited range of LACV lineage I genotypes is associated with severe clinical outcomes.

The molecular biology of nairoviruses, an emerging group of tick-borne arboviruses

The nairoviruses are a rapidly emerging group of tick-borne bunyaviruses that includes pathogens of humans (Crimean-Congo hemorrhagic fever virus [CCHFV]) and livestock (Nairobi sheep disease virus [NSDV], also known as Ganjam virus), as well as a large number of viruses for which the normal vertebrate host has not been established. Studies on this group of viruses have been fairly limited, not least because CCHFV is a BSL4 human pathogen, restricting the number of labs able to study the live virus, while NSDV, although highly pathogenic in naive animals, is not seen as a threat in developed countries, making it a low priority. Nevertheless, recent years have seen significant progress in our understanding of the biology of these viruses, particularly that of CCHFV, and this article seeks to draw together our existing knowledge to generate an overall picture of their molecular biology, underlining areas of particular ignorance for future studies.

The variability of the large genomic segment of Ťahyňa orthobunyavirus and an all-atom exploration of its anti-viral drug resistance

Ťahyňa virus (TAHV), a member of the Bunyaviridae family (California complex), is an important but neglected human mosquito-borne pathogen. The virus genome is composed of three segments, i.e., small (S), medium (M), and large (L). Previous studies on genetic variability of viruses within the California complex were focused on S and M segments, but the L segment remains relatively unstudied. To assess the genetic variation and the relation to virus phenotype we analyzed the L segment sequences of biologically diverse TAHV strains isolated in the Czech Republic and Slovakia. Phylogenetic analysis covering all available sequences of the L segment of TAHV clearly revealed two distinguished lineages, tentatively named as "European" and "Asian". The L segment strains within the European lineage are highly conserved (identity 99.3%), whilst Asian strains are more genetically diverse (identity 97%). Based on sequence comparison with other bunyaviruses, several non-synonymous nucleotide substitutions unique for TAHV in the L segment were identified. We also identified specific residue substitutions in the endonuclease domain of TAHV compared with the La Crosse virus. Since the endonuclease domain of the La Crosse virus has been resolved, we employed an all energy landscape algorithm to analyze the ligand migration of a viral polymerase inhibitor. This allowed us to demonstrate, at the atomic level, that this viral polymerase inhibitor randomly explored the specific residue substitutions in the endonuclease domain of the TAHV L segment.

A recombinant chimeric La Crosse virus expressing the surface glycoproteins of Jamestown Canyon virus is immunogenic and protective against challenge with either parental virus in mice or monkeys

La Crosse virus (LACV) and Jamestown Canyon virus (JCV), family Bunyaviridae, are mosquito-borne viruses that are endemic in North America and recognized as etiologic agents of encephalitis in humans. Both viruses belong to the California encephalitis virus serogroup, which causes 70 to 100 cases of encephalitis a year. As a first step in creating live attenuated viral vaccine candidates for this serogroup, we have generated a recombinant LACV expressing the attachment/fusion glycoproteins of JCV. The JCV/LACV chimeric virus contains full-length S and L segments derived from LACV. For the M segment, the open reading frame (ORF) of LACV is replaced with that derived from JCV and is flanked by the untranslated regions of LACV. The resulting chimeric virus retained the same robust growth kinetics in tissue culture as observed for either parent virus, and the virus remains highly infectious and immunogenic in mice. Although both LACV and JCV are highly neurovirulent in 21 day-old mice, with 50% lethal dose (LD₅₀) values of 0.1 and 0.5 log₁₀ PFU, respectively, chimeric JCV/LACV is highly attenuated and does not cause disease even after intracerebral inoculation of 10³ PFU. Parenteral vaccination of mice with 10¹ or 10³ PFU of JCV/LACV protected against lethal challenge with LACV, JCV, and Tahyna virus (TAHV). The chimeric virus was infectious and immunogenic in rhesus monkeys and induced neutralizing antibodies to JCV, LACV, and TAHV. When vaccinated monkeys were challenged with JCV, they were protected against the development of viremia. Generation of highly attenuated yet immunogenic chimeric bunyaviruses could be an efficient general method for development of vaccines effective against these pathogenic viruses.

Molecular characterization of a new Tospovirus infecting soybean

A new, widespread disease was recently observed in soybean in the United States. The disease, named Soybean vein necrosis, is manifested by intraveinal chlorosis and necrosis, and has been found in almost all of the 50 fields visited over a period of 3 years in the midwest and midsouth part of the United States. A virus was isolated from symptomatic material, and detection protocols were developed. More than 150 symptomatic specimens collected from seven US States were tested, and all were found positive for the virus unlike 75 asymptomatic samples, revealing the absolute association between virus and disease. Protein pairwise comparisons coupled with phylogenetic analyses indicate that the virus is a new member of the genus Tospovirus.

Tahyna virus genetics, infectivity, and immunogenicity in mice and monkeys

BACKGROUND

Tahyna virus (TAHV) is a human pathogen of the California encephalitis virus (CEV) serogroup (Bunyaviridae) endemic to Europe, Asia, and Africa. TAHV maintains an enzootic life cycle with several species of mosquito vectors and hares, rabbits, hedgehogs, and rodents serving as small mammal amplifying hosts. Human TAHV infection occurs in summer and early fall with symptoms of fever, headache, malaise, conjunctivitis, pharyngitis, and nausea. TAHV disease can progress to CNS involvement, although unlike related La Crosse virus (LACV), fatalities have not been reported. Human infections are frequent with neutralizing antibodies present in 60-80% of the elderly population in endemic areas.

RESULTS

In order to determine the genomic sequence of wild-type TAHV, we chose three TAHV isolates collected over a 26-year period from mosquitoes. Here we present the first complete sequence of the TAHV S, M, and L segments. The three TAHV isolates maintained a highly conserved genome with both nucleotide and amino acid sequence identity greater than 99%. In order to determine the extent of genetic relatedness to other members of the CEV serogroup, we compared protein sequences of TAHV with LACV, Snowshoe Hare virus (SSHV), Jamestown Canyon virus (JCV), and Inkoo virus (INKV). By amino acid comparison, TAHV was most similar to SSHV followed by LACV, JCV, and INKV. The sequence of the GN protein is most conserved followed by L, N, GC, NSS, and NSM. In a weanling Swiss Webster mouse model, all three TAHV isolates were uniformly neurovirulent, but only one virus was neuroinvasive. In rhesus monkeys, the virus was highly immunogenic even in the absence of viremia. Cross neutralization studies utilizing monkey immune serum demonstrated that TAHV is antigenically distinct from North American viruses LACV and JCV.

CONCLUSIONS

Here we report the first complete sequence of TAHV and present genetic analysis of new-world viruses, LACV, SSHV, and JCV with old-world viruses, TAHV and INKV. Using immune serum generated in monkeys against TAHV, LACV, and JCV, we have demonstrated cross-neutralization within the CEV serogroup. Such cross reactivity may complicate virus identification, especially following JCV infection which elicited antibodies that cross neutralized both LACV and TAHV. These data also suggest that a single vaccine could generate a cross-neutralizing antibody response which may provide protection against CEV serogroup viruses from a wide geographic range.

Tensaw virus genome sequence and its relation to other Bunyaviridae

Tensaw virus (TSV) belongs to the genus Orthobunyavirus within the Bunyaviridae family. Although TSV does not cause hemorrhagic fever as some other members of its family, serological studies have shown that serum from Florida residents react against TSV indicating viral infection in humans. In this study, the three RNA genome segments of a TSV isolated from Anopheles crucians mosquitoes collected in North Central Florida in 2006 and a TSV isolate obtained from the CDC, Fort Collins, were sequenced and compared to other Bunyaviridae. The placement of the TSVs within the Bunyamwera serogroup was confirmed by phylogenetic analysis of the inferred amino acid (aa) sequence of proteins coded by each of the RNA segments separately as well as by the combined tree of the same three inferred proteins. The N terminal glycoprotein (Gn) encoded by the M segment contained the 18 conserved Cysteines present in Bunyamwera and California serogroups, the two glycosylation sites, and residues considered potential proteolytic cleavage sites conserved in other Bunyaviridae. The TSV L protein displayed all the strictly conserved amino acids in the four conserved regions known to be catalytically active for the RNA dependent RNA polymerase transcriptase and replicase activities. The amino acid conservation between the two TSV viral isolates was 100, 99.4, and 99.6% for the S, M, and L segments, respectively.

Generation and analysis of recombinant Bunyamwera orthobunyaviruses expressing V5 epitope-tagged L proteins

The L protein of Bunyamwera virus (BUNV; family Bunyaviridae) is an RNA-dependent RNA polymerase, 2238 aa in length, that catalyses transcription and replication of the negative-sense, tripartite RNA genome. To learn more about the molecular interactions of the L protein and to monitor its intracellular distribution we inserted a 14 aa V5 epitope derived from parainfluenza virus type 5, against which high-affinity antibodies are available, into different regions of the protein. Insertion of the epitope at positions 1935 or 2046 resulted in recombinant L proteins that retained functionality in a minireplicon assay. Two viable recombinant viruses, rBUNL4V5 and rBUNL5V5, expressing the tagged L protein were rescued by reverse genetics, and characterized with respect to their plaque size, growth kinetics and protein synthesis profile. The recombinant viruses behaved similarly to wild-type (wt) BUNV in BHK-21 cells, but formed smaller plaques and grew to lower titres in Vero E6 cells compared with wt BUNV. Immunofluorescent staining of infected cells showed the L protein to have a punctate to reticular distribution in the cytoplasm, and cell fractionation studies indicated that the L protein was present in both soluble and microsomal fractions. Co-immunoprecipitation and confocal microscopic assays confirmed an interaction between BUNV L and N proteins. The recombinant viruses expressing tagged L protein will be highly valuable reagents for the detailed dissection of the role of the BUNV L protein in virus replication.

Sequence and phylogenetic analysis of the large (L) segment of the Tahyna virus genome

The Tahyna virus (TAHV) is an important human pathogen in the Bunyaviridae family. To date, only the S and M segments of this virus have been sequenced, but the sequence of the L segment hasn't been established yet. In this study, we sequenced 963 nucleotides of the L segment of TAHV, comprising pre-motif A and motif A in region 3 of the RNA polymerase gene.

Caraparu virus (group C Orthobunyavirus): sequencing and phylogenetic analysis based on the conserved region 3 of the RNA polymerase gene

Here, for the first time, we report the nucleotide sequence of Caraparu virus (CARV) L segment and the analysis of the RNA polymerase region 3 encoded by this segment. The 1,404 bp nucleotide sequence shares the highest identity with Bunyamwera, La Crosse, Oropouche, and Akabane virus sequences. The amino acid sequence was deduced and aligned with sequences from members of the Bunyaviridae family and used for phylogenetic analysis. The CARV clustered in the Orthobunyavirus genus. The premotif A and motifs A-E are present in the region 3 of the Bunyaviridae family, were also conserved in CARV L protein, as well as other conserved regions among Orthobunyavirus genus.

Genome sequence analysis of La Crosse virus and in vitro and in vivo phenotypes

Background

La Crosse virus (LACV), family Bunyaviridae, is a mosquito-borne virus recognized as a major cause of pediatric encephalitis in North America with 70–130 symptomatic cases each year. The virus was first identified as a human pathogen in 1960 after its isolation from a 4 year-old girl who suffered encephalitis and died in La Crosse, Wisconsin. The majority of LACV infections are mild and never reported, however, serologic studies estimate infection rates of 10–30/100,000 in endemic areas.

Results

In the present study, sequence analysis of the complete LACV genomes of low-passage LACV/human/1960, LACV/mosquito/1978, and LACV/human/1978 strains and of biologically cloned derivatives of each strain, indicates that circulating LACVs are genetically stable over time and geographic distance with 99.6–100%, 98.9–100%, 97.8–99.6%, and 99.2–99.7% amino acid identity for N, NsS, M polyprotein, and L proteins respectively. We identified 5 amino acid differences in the RNA polymerase and 4 nucleotide differences in the non-coding region of the L segment specific to the human virus isolates, which may result in altered disease outcomes.

Conclusion

All three wild type viruses had similar in vitro growth kinetics and phenotypes in mosquito C6/36 and Vero cells, and similar levels of neurovirulence and neuroinvasiveness in Swiss Webster mice. The biologically cloned derivative of LACV/human/1960 was significantly less neuroinvasive than its uncloned parent and differed in sequence at one amino acid position in the G_N glycoprotein, identifying this residue as an attenuating mutation.

Mutagenesis of the La Crosse Virus glycoprotein supports a role for Gc (1066-1087) as the fusion peptide

The La Crosse Virus (LACV) M segment encodes two glycoproteins (Gn and Gc), and plays a critical role in the neuropathogenesis of LACV infection as the primary determinant of neuroinvasion. A recent study from our group demonstrated that the region comprising the membrane proximal two-thirds of Gc, amino acids 860-1442, is critical in mediating LACV fusion and entry. Furthermore, computational analysis identified structural similarities between a portion of this region, amino acids 970-1350, and the E1 fusion protein of two alphaviruses: Sindbis virus and Semliki Forrest virus (SFV). Within the region 970-1350, a 22-amino-acid hydrophobic segment (1066-1087) is predicted to correlate structurally with the fusion peptides of class II fusion proteins. We performed site-directed mutagenesis of key amino acids in this 22-amino acid segment and determined the functional consequences of these mutations on fusion and entry. Several mutations within this hydrophobic domain affected glycoprotein expression to some extent, but all mutations either shifted the pH threshold of fusion below that of the wild-type protein, reduced fusion efficiency, or abrogated cell-to-cell fusion and pseudotype entry altogether. These results, coupled with the aforementioned computational modeling, suggest that the LACV Gc functions as a class II fusion protein and support a role for the region Gc 1066-1087 as a fusion peptide.

Homotypic interaction of Bunyamwera virus nucleocapsid protein

The bunyavirus nucleocapsid protein, N, plays a central role in viral replication in encapsidating the three genomic RNA segments to form functional templates for transcription and replication by the viral RNA-dependent RNA polymerase. Here we report functional mapping of interacting domains of the Bunyamwera orthobunyavirus N protein by yeast and mammalian two-hybrid systems, immunoprecipitation experiments, and chemical cross-linking studies. N forms a range of multimers from dimers to high-molecular-weight structures, independently of the presence of RNA. Deletion of the N- or C-terminal domains resulted in loss of activity in a minireplicon assay and a decreased capacity for N to form higher multimers. Our data suggest a head-to-head and tail-to-tail multimerization model for the orthobunyavirus N protein.

California serogroup Gc (G1) glycoprotein is the principal determinant of pH-dependent cell fusion and entry

Members of the California serogroup of orthobunyaviruses, particularly La Crosse (LAC) and Tahyna (TAH) viruses, are significant human pathogens in areas where their mosquito vectors are endemic. Previous studies using wild-type LAC and TAH181/57, a highly neurovirulent strain with low neuroinvasiveness (Janssen, R., Gonzalez-Scarano, F., Nathanson, N., 1984. Mechanisms of bunyavirus virulence. Comparative pathogenesis of a virulent strain of La Crosse and an avirulent strain of Tahyna virus. Lab. Invest. 50 (4), 447-455), have demonstrated that the neuroinvasive phenotype maps to the M segment, the segment that encodes the two viral glycoproteins Gn (G2) and Gc (G1), as well as a non-structural protein NSm. To further define the role of Gn and Gc in fusion and entry, we prepared a panel of recombinant M segment constructs using LAC, TAH181/57, and V22F, a monoclonal-resistant variant of LAC with deficient fusion function. These M segment constructs were then tested in two surrogate assays for virus entry: a cell-to-cell fusion assay based on T7-luciferase expression, and a pseudotype transduction assay based on the incorporation of the bunyavirus glycoproteins on an MLV backbone. Both assays demonstrated that Gc is the principal determinant of virus fusion and cell entry, and furthermore that the region delineated by amino acids 860-1442, corresponding to the membrane proximal two-thirds of Gc, is key to these processes. These results, coupled with structural modeling suggesting homologies between the carboxy region of Gc and Sindbis virus E1, suggest that the LAC Gc functions as a type II fusion protein.

Sequence analysis of L RNA of Lassa virus

The L RNA of three Lassa virus strains originating from Nigeria, Ghana/Ivory Coast, and Sierra Leone was sequenced and the data subjected to structure predictions and phylogenetic analyses. The L gene products had 2218-2221 residues, diverged by 18% at the amino acid level, and contained several conserved regions. Only one region of 504 residues (positions 1043-1546) could be assigned a function, namely that of an RNA polymerase. Secondary structure predictions suggest that this domain is very similar to RNA-dependent RNA polymerases of known structure encoded by plus-strand RNA viruses, permitting a model to be built. Outside the polymerase region, there is little structural data, except for regions of strong alpha-helical content and probably a coiled-coil domain at the N terminus. No evidence for reassortment or recombination during Lassa virus evolution was found. The secondary structure-assisted alignment of the RNA polymerase region permitted a reliable reconstruction of the phylogeny of all negative-strand RNA viruses, indicating that Arenaviridae are most closely related to Nairoviruses. In conclusion, the data provide a basis for structural and functional characterization of the Lassa virus L protein and reveal new insights into the phylogeny of negative-strand RNA viruses.

Functional L polymerase of La Crosse virus allows in vivo reconstitution of recombinant nucleocapsids

La Crosse virus (LACV), a member of the family Bunyaviridae, is the primary cause of paediatric encephalitis in the United States. In this study, a functional RNA polymerase (L) gene of LACV was cloned and a reverse genetics system established. A reporter minireplicon mimicking the viral genome was constructed by flanking the Renilla luciferase gene with the 3' and 5' noncoding regions of the genomic M segment. These noncoding regions serve as promoters for the viral polymerase. Both L and nucleocapsid (N) genes were expressed by means of T7 RNA polymerase, which was provided by the recombinant T7-expressing modified vaccinia virus Ankara. Renilla reporter activity in transfected cells reflected reconstitution of recombinant nucleocapsids by functional L and N gene products. Time-course experiments revealed a rapid increase in minireplicon activity from 10 to 18 h after the onset of L and N expression. Minireplicon activity was found to be dependent on the correct ratio of L to N plasmids, with too much of either construct resulting in downregulation. Furthermore, a specific inhibitory effect of LACV NSs protein on minireplicon activity was found. In passaging experiments using parental helper virions, it was demonstrated that the recombinant nucleocapsids are a useful model for transcription, replication and packaging of LACV.

A structural and primary sequence comparison of the viral RNA-dependent RNA polymerases

A systematic bioinformatic approach to identifying the evolutionarily conserved regions of proteins has verified the universality of a newly described conserved motif in RNA-dependent RNA polymerases (motif F). In combination with structural comparisons, this approach has defined two regions that may be involved in unwinding double-stranded RNA (dsRNA) for transcription. One of these is the N-terminal portion of motif F and the second is a large insertion in motif F present in the RNA-dependent RNA polymerases of some dsRNA viruses.

Jatobal virus is a reassortant containing the small RNA of Oropouche virus

Jatobal (JAT) virus was isolated in 1985 from a carnivore (Nasua nasua) in Tucuruí, Pará state, Brazil and was classified as a distinct member of the Simbu serogroup of the Bunyavirus genus, family Bunyaviridae on the basis of neutralization tests. On the basis of nucleotide sequencing, we have found that the small (S) RNA of JAT virus is very similar (>95% identity) to that of Oropouche (ORO) virus, in particular, the Peruvian genotype of ORO virus. In comparison, limited nucleotide sequencing of the G2 protein gene, encoded by the middle (M) RNA, of JAT and ORO viruses, revealed relatively little identity (<66%) between these two viruses. Neutralization tests confirmed the lack of cross-reactivity between the viruses. These results suggest that JAT virus is a reassortant containing the S RNA of ORO virus. JAT virus was attenuated in hamsters compared to ORO virus suggesting that the S RNA of ORO virus is not directly involved in hamster virulence.

Completion of the Genome Sequence of Watermelon silver mottle virus and Utilization of Degenerate Primers for Detecting Tospoviruses in Five Serogroups

ABSTRACT The nucleotide sequence of the L RNA of Watermelon silver mottle virus (WSMoV) was determined. Combined with the previous work on M and S RNAs, the whole genomic sequence of this member of the genus Tospovirus was completed. The L RNA is 8,917 nucleotides in length, with one large open reading frame encoding a translation product of 2,878 amino acids (331.8 kDa) on the viral complementary strand. The L protein shares amino acid identities of only 44.3 and 46.5% with Tomato spotted wilt virus (TSWV) and Impatiens necrotic spot virus, respectively; but an amino acid identity of 91.3% with Peanut bud necrosis virus. Among the sequenced tospoviruses, L protein was the most conserved gene product, whereas the nonstructural S protein was generally the most variable. Comparison of the deduced L protein of WSMoV with those of other members of the family Bunyaviridae revealed that its amino acid sequence includes the reported conserved motifs of RNA-dependent RNA polymerases. To develop a method for detecting tospo-viruses by reverse transcription-polymerase chain reaction (RT-PCR), two pairs of degenerate primers were designed from conserved regions of the L genes and used to amplify the corresponding regions of the L genes from total RNAs extracted from plant tissues infected with five serologically distinct tospoviruses. The DNA fragments obtained were identified as those of tospoviruses by restriction enzyme digestion and DNA sequencing. For field samples, watermelon and wax gourd infected with WSMoV, and lisianthus infected with TSWV were also successfully detected by these two pairs of degenerate primers, with a sensitivity similar to N-gene-specific primers. The results indicated that the RT-PCR with the degenerate primers is a fast and reliable method for detecting tospoviruses in different serogroups.

Nucleotide sequence and deduced amino acid sequence of the medium RNA segment of Oropouche, a Simbu serogroup virus: comparison with the middle RNA of Bunyamwera and California serogroup viruses

The Bunyavirus genus of the family Bunyaviridae contains 18 serogroups. To date nucleotide sequence data has been obtained for three serogroups, Bunyamwera, California and Simbu, based on analysis of the small (S) RNA segment. In comparison, there is only nucleotide sequence data for the large and medium (M) RNA segments for members of the Bunyamwera and California serogroups. In this paper we report the nucleotide sequence of the M RNA of Oropouche (ORO) virus, a member of the Simbu serogroup. The M RNA was 4396 nucleotides in length with G1, G2 and NSm proteins similar in size to those reported for members of the Bunyamwera and California serogroups. However, there was limited nucleotide (50-52%) and amino acid (30-32%) homology between ORO virus M RNA and those of published members of the other two serogroups. The Bunyamwera and California serogroups are more closely related to each other than the Simbu serogroup virus Oropouche. These data were consistent with that previously reported for the S RNA (Saeed et al., 2000. J. Gen. Virol. 81, 743-748). It has been noted previously that three of four potential N-linked glycosylation sites of the Bunayamwera and California serogroups are conserved in G1 and G2 proteins. In contrast, ORO virus was found to have only three potential N-linked glycosylation sites of which only one, in G1, was conserved with members of the other two serogroups. Comparison of M RNA sequences of different strains of ORO virus revealed genetic variation consistent with that reported previously for the S RNA.

The Lassa fever virus L gene: nucleotide sequence, comparison, and precipitation of a predicted 250 kDa protein with monospecific antiserum

The large (L) RNA segment of Lassa fever virus (LAS) encodes a putative RNA-dependent RNA polymerase (RdRp or L protein). Similar to other arenaviruses, the LAS L protein is encoded on the genome-complementary strand and is predicted to be 2218 amino acids in length (253 kDa). It has an unusually large non-coding region adjacent to its translation start site. The LAS L protein contains six motifs of conserved amino acids that have been found among arenavirus L proteins and core RdRp of other segmented negative-stranded (SNS) viruses (Arena-, Bunya- and Orthomyxoviridae). Phylogenetic analyses of the RdRp of 20 SNS viruses reveals that arenavirus L proteins represent a distinct cluster divided into LAS-lymphocytic choriomeningitis and Tacaribe-Pichinde virus lineages. Monospecific serum against a synthetic peptide corresponding to the most conserved central domain precipitates a 250 kDa product from LAS and lymphocytic choriomeningitis virus-infected cells.

Detecting bunyaviruses of the Bunyamwera and California serogroups by a PCR technique

Many bunyaviruses of the Bunyamwera and California serogroups are medically important human pathogens. The development of an effective technique to detect the viruses by using molecular biologic tools, such as PCR, improves not only clinical diagnosis but also virologic surveillance of mosquito vectors in the field. In this study, we evaluated eight pairs of primers for reactivity with 44 viruses of the genus Bunyavirus, using a reverse transcriptase PCR technique. With a pair of serogroup-specific primers we designed, all viruses of the serogroups tested could be detected. Further, virus-specific primer pairs were identified for California encephalitis virus, Jamestown Canyon virus, La Crosse virus, and snowshoe hare virus for use in North America. Using this technique, we could detect one La Crosse virus-infected mosquito in a pool of 100 mosquitoes with undetectable plaque titers.

Complete genetic characterization and analysis of isolation of Sin Nombre virus

This study reports completion of the genetic characterization of the entire genome of Sin Nombre (SN) virus (NMH10) detected in autopsy tissues from a patient who died of hantavirus pulmonary syndrome (HPS). The large (L) genome segment was found to be 6,562 nucleotides in length and encoded a putative L polymerase that was 2,153 amino acids in length. No evidence of segment reassortment with other well-characterized hantaviruses was obtained. The sequence of the entire S, M, and L genome segments of SN virus (strain NMR11) isolated from a mouse (trapped in the residence of the patient infected with SN virus [NMH10]) by passage two times in Peromyscus maniculatus and then by five passages in E6 Vero cells was determined and compared with that of the virus detected in autopsy tissues. Only 16 nucleotide differences were detected between the virus genomes, and none of these resulted in virus protein amino acid substitutions. Determination of the exact 5'- and 3'-terminal sequences of all genome segments of SN virus and representatives of other serologic groups in the Hantavirus genus, family Bunyaviridae, showed the existence of conserved nucleotide domains that may be involved in important regulatory mechanisms, such as RNA encapsidation, polymerase binding, and control of transcription and replication.

Protection from La Crosse virus encephalitis with recombinant glycoproteins: role of neutralizing anti-G1 antibodies

La Crosse virus, a member of the California serogroup of bunyaviruses, is an important cause of pediatric encephalitis in the midwestern United States. Like all bunyaviruses, La Crosse virus contains two glycoproteins, G1 and G2, the larger of which, G1, is the target of neutralizing antibodies. To develop an understanding of the role of each of the glycoproteins in the generation of a protective immune response, we immunized 1-week-old mice with three different preparations: a vaccinia virus recombinant (VV.ORF) that expresses both G1 and G2, a vaccinia virus recombinant (VV.G1) that expresses G1 only, and a truncated soluble G1 (sG1) protein prepared in a baculovirus system. Whereas VV.ORF generated a protective response that was mostly directed against G1, VV.G1 was only partially effective at inducing a neutralizing response and at protecting mice from a potentially lethal challenge with La Crosse virus. Nevertheless, a single immunization with the sG1 preparation resulted in a robust immune response and protection against La Crosse virus. These results indicate that (i) the G1 protein by itself can induce an immune response sufficient for protection from a lethal challenge with La Crosse virus, (ii) a neutralizing humoral response correlates with protection, and (iii) the context in which G1 is presented affects its immunogenicity. The key step in the defense against central nervous system infection appeared to be interruption of a transient viremia that occurred just after La Crosse virus inoculation.