Nucleotide and deduced amino acid sequences of the M and S genome segments of two Puumala virus isolates from Russia

In silico design and evaluation of a multiepitope vaccine targeting the nucleoprotein of Puumala orthohantavirus

The Puumala orthohantavirus is present in the body of the bank vole (Myodes glareolus). Humans infected with this virus may develop hemorrhagic fever accompanying renal syndrome. In addition, the infection may further lead to the failure of an immune system completely. The present study aimed to propose a possible vaccine by employing bioinformatics techniques to identify B and T-cell antigens. The best multi-epitope of potential immunogenicity was generated by combining epitopes. Additionally, the linkers EAAAK, AAY, and GPGPG were utilized in order to link the epitopes successfully. Further, C-ImmSim was used to perform in silico immunological simulations upon the vaccine. For the purpose of conducting expression tests in Escherichia coli, the chimeric protein construct was cloned using Snapgene into the pET-9c vector. The designed vaccine showed adequate results, evidenced by the global population coverage and favorable immune response. The developed vaccine was found to be highly effective and to have excellent population coverage in a number of computer-based assessments. This work is fully dependent on the development of nucleoprotein-based vaccines, which would constitute a significant step forward if our findings were used in developing a global vaccination to combat the Puumala virus.

A novel Sin Nombre virus DNA vaccine and its inclusion in a candidate pan-hantavirus vaccine against hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS)

Sin Nombre virus (SNV; family Bunyaviridae, genus Hantavirus) causes a hemorrhagic fever known as hantavirus pulmonary syndrome (HPS) in North America. There have been approximately 200 fatal cases of HPS in the United States since 1993, predominantly in healthy working-age males (case fatality rate 35%). There are no FDA-approved vaccines or drugs to prevent or treat HPS. Previously, we reported that hantavirus vaccines based on the full-length M gene segment of Andes virus (ANDV) for HPS in South America, and Hantaan virus (HTNV) and Puumala virus (PUUV) for hemorrhagic fever with renal syndrome (HFRS) in Eurasia, all elicited high-titer neutralizing antibodies in animal models. HFRS is more prevalent than HPS (>20,000 cases per year) but less pathogenic (case fatality rate 1-15%). Here, we report the construction and testing of a SNV full-length M gene-based DNA vaccine to prevent HPS. Rabbits vaccinated with the SNV DNA vaccine by muscle electroporation (mEP) developed high titers of neutralizing antibodies. Furthermore, hamsters vaccinated three times with the SNV DNA vaccine using a gene gun were completely protected against SNV infection. This is the first vaccine of any kind that specifically elicits high-titer neutralizing antibodies against SNV. To test the possibility of producing a pan-hantavirus vaccine, rabbits were vaccinated by mEP with an HPS mix (ANDV and SNV plasmids), or HFRS mix (HTNV and PUUV plasmids), or HPS/HFRS mix (all four plasmids). The HPS mix and HFRS mix elicited neutralizing antibodies predominantly against ANDV/SNV and HTNV/PUUV, respectively. Furthermore, the HPS/HFRS mix elicited neutralizing antibodies against all four viruses. These findings demonstrate a pan-hantavirus vaccine using a mixed-plasmid DNA vaccine approach is feasible and warrants further development.

Construction and nonclinical testing of a Puumala virus synthetic M gene-based DNA vaccine

Puumala virus (PUUV) is a causative agent of hemorrhagic fever with renal syndrome (HFRS). Although PUUV-associated HFRS does not result in high case-fatality rates, the social and economic impact is considerable. There is no licensed vaccine or specific therapeutic to prevent or treat HFRS. Here we report the synthesis of a codon-optimized, full-length M segment open reading frame and its cloning into a DNA vaccine vector to produce the plasmid pWRG/PUU-M(s2). pWRG/PUU-M(s2) delivered by gene gun produced high-titer neutralizing antibodies in hamsters and nonhuman primates. Vaccination with pWRG/PUU-M(s2) protected hamsters against infection with PUUV but not against infection by related HFRS-associated hantaviruses. Unexpectedly, vaccination protected hamsters in a lethal disease model of Andes virus (ANDV) in the absence of ANDV cross-neutralizing antibodies. This is the first evidence that an experimental DNA vaccine for HFRS can provide protection in a hantavirus lethal disease model.

Muju virus, a novel hantavirus harboured by the arvicolid rodent Myodes regulus in Korea

Acute-phase sera from >5 % of cases of haemorrhagic fever with renal syndrome occurring annually in Korea have been found to exhibit a fourfold or higher antibody titre to Puumala virus (PUUV) than to Hantaan virus (HTNV) by double-sandwich IgM ELISA, suggesting the existence of a PUUV-related hantavirus. Based on the phylogenetic relationships among arvicolid rodents, the royal vole (Myodes regulus) was targeted as a likely reservoir host of hantavirus. Using RT-PCR, a genetically distinct hantavirus, designated Muju virus (MUJV), was detected in lung tissue of royal voles, captured in widely separated geographical regions in Korea during 1996-2007. Pairwise analysis of the full-length S (1857 nt) and M (3634 nt) segments of MUJV indicated approximately 77 % sequence similarity with PUUV. At the amino acid level, MUJV differed from PUUV by 5.5-6.9 % (nucleocapsid) and 10.0-11.6 % (Gn and Gc envelope glycoproteins). Interstrain variation of MUJV sequences from royal voles captured in different regions suggested geographic-specific clustering. Neutralizing antibody titres against PUUV were two- to sixfold higher than to HTNV in sera of MUJV-infected Myodes regulus. Although virus isolation attempts were unsuccessful, the collective data indicate that MUJV is a distinct hantavirus species.

Detection of phylogenetically distinct Puumala-like viruses from red-grey vole Clethrionomys rufocanus in China

In order to investigate whether Puumala virus (PUUV) or PUUV-like virus is present in China, Clethrionomys rufocanus and C. rutilus were captured in the Jilin province during the spring and autumn of 2002-2003 for detection of PUUV viral RNA by RT-PCR and confirmation of PUUV-positive antigens by an immunofluorescence assay. PUUV-positive RNA was identified in six out of 121 C. rufocanus but not in any of the 41 C. rutilus. Complete S and partial M sequences (nt 1,316-1,598 and 2,687-3,089) were amplified by RT-PCR directly from some of the antigen positive lung tissues and subjected to nucleic acid sequencing. It was found that the Chinese PUUV-like viruses were related most closely with the PUUV strains with 77.7-81.7% identity at the nucleotide level and 91.7-97% identity at the amino acid level for S segment, and with 77-78.8% identity at the nucleotide level and 91.5-92.6% identity at the amino acid level for the partial M segment (nt 1,316-1,598). Genetic analysis indicated that the Chinese PUUV-like viruses shared the highest level of identity with the viruses which circulate in C. rufocanus in the Far East region of Russia with 85.1-87.4% identity at the nucleotide level and 95.9% identity at the amino acid level for the partial M segment (nt 2,687-3,089), respectively. Phylogenetic analysis revealed that the Chinese PUUV-like viruses are distinct from those identified from Japan, South Korea, Europe or Russia. These results indicate that PUUV-like virus is present in China in addition to Hantaan, Seoul and Dabieshan viruses.

Identification of Dobrava, Hantaan, Seoul, and Puumala viruses by one-step real-time RT-PCR

We developed four assays for specifically identifying Dobrava (DOB), Hantaan (HTN), Puumala (PUU), and Seoul (SEO) viruses. The assays are based on the real-time one-step reverse transcriptase polymerase chain reaction (RT-PCR) with the small segment used as the target sequence. The detection limits of DOB, HTN, PUU, and SEO assays were 25, 25, 25, and 12.5 plaque-forming units, respectively. The assays were evaluated in blinded experiments, each with 100 samples that contained Andes, Black Creek Canal, Crimean-Congo hemorrhagic fever, Rift Valley fever and Sin Nombre viruses in addition to DOB, HTN, PUU and SEO viruses. The sensitivity levels of the DOB, HTN, PUU, and SEO assays were 98%, 96%, 92% and 94%, respectively. The specificity of DOB, HTN and SEO assays was 100% and the specificity of the PUU assay was 98%. Because of the high levels of sensitivity, specificity, and reproducibility, we believe that these assays can be useful for diagnosing and differentiating these four Old-World hantaviruses.

Mapping of B-cell epitopes in the nucleocapsid protein of Puumala hantavirus

Hantavirus nucleocapsid protein (N) has been proven to induce highly protective immune responses in animal models. The knowledge on the mechanisms behind N-induced protection is still limited, although recent data suggest that both cellular and humoral immune responses are of importance. For a detailed B-cell epitope mapping of Puumala hantavirus (PUUV) N, we used recombinant N derivatives of the Russian strain CG18-20 and the Swedish strain Vranica/Hällnäs, as well as overlapping synthetic peptides corresponding to the Finnish prototype strain Sotkamo. The majority of a panel of monoclonal antibodies (mAbs) reacted with proteins derived from all included PUUV strains demonstrating the antigenic similarity of these proteins. In line with previous results, the epitopes of most mAbs were mapped within the 80 N-terminal amino acids of N. The present study further revealed that the epitopes of four mAbs raised against native viral N were located within amino acids 14-45, whereas one mAb raised against recombinant N was mapped to amino acids 14-39. Differences between the reactivity of the PUUV strains Vranica/Hällnäs and CG18-20 N suggested the importance of amino acid position 35 for the integrity of the epitopes. In line with the patterns obtained by the truncated recombinant proteins, mapping by overlapping peptides (PEPSCAN) confirmed a complex recognition pattern for most analyzed mAbs. Together, the results revealed the existence of several, partially overlapping, and discontinuous B-cell epitopes. In addition, based on differences within the same competition group, novel epitopes were defined.

Long-lived memory T lymphocyte responses after hantavirus infection

Puumala virus (PUUV) is a hantavirus that causes hemorrhagic fever with renal syndrome (HFRS), which is an important public health problem in large parts of Europe. We examined the memory cytolytic T lymphocyte (CTL) responses in 13 Finnish individuals who had HFRS between 1984 and 1995. In seven of these donors, we detected virus-specific CTL responses against the PUUV nucleocapsid (N) protein after in vitro stimulation with PUUV. Six novel CD8(+) CTL epitopes were defined on the N protein and were found to be restricted by various HLA alleles including A2, A28, B7, and B8. This is the first demonstration of PUUV-specific CTL responses in humans, and the first identification of CTL epitopes on PUUV. In addition, this study provides one of the few characterizations of a human antiviral memory T cell response, without the complicating issues of virus persistence or reinfection. Interferon (IFN)-gamma ELISPOT analysis showed that memory CTL specific for these epitopes were present at high frequency in PUUV-immune individuals many years after acute infection in the absence of detectable viral RNA. The frequencies of PUUV-specific CTL were comparable to or exceeded those found in other viral systems including influenza, EBV and HIV, in which CTL responses may be boosted by periodic reinfection or virus persistence.

Generation of recombinant vaccinia viruses expressing Puumala virus proteins and use in isolating cytotoxic T cells specific for Puumala virus

Puumala (PUU) virus causes a form of hemorrhagic fever with renal syndrome (HFRS), called nephropathia epidemica (NE), in Europe. HFRS is characterized by an increased capillary permeability, which we hypothesize is caused by hyperactivation of the host immune system, especially cellular immune responses. To identify cytotoxic T lymphocytes (CTLs) specific for the PUU virus from NE patients, we have made recombinant vaccinia viruses expressing PUU virus proteins, the nucleocapsid (N) and two surface glycoproteins, G1 and G2. Recombinant vaccinia viruses carrying the N or the first half of the G2 cDNA under the control of a strong synthetic promoter were made. To express G1 and the second half of the G2 proteins, however, we needed to use a T7 expression system, where the T7 RNA polymerase is produced from another recombinant vaccinia virus co-infecting the same cells. These recombinant vaccinia viruses were used to detect and clone PUU virus-specific CTLs from the peripheral blood mononuclear cells of NE patients. An HLA-A24-restricted CTL line recognizing the G2 protein was isolated and its 9-mer epitope was determined.

Molecular evolution of Puumala hantavirus

Puumala virus (PUUV) is a negative-stranded RNA virus in the genus Hantavirus, family Bunyaviridae. In this study, detailed phylogenetic analysis was performed on 42 complete S segment sequences of PUUV originated from several European countries, Russia, and Japan, the largest set available thus far for hantaviruses. The results show that PUUV sequences form seven distinct and well-supported genetic lineages; within these lineages, geographical clustering of genetic variants is observed. The overall phylogeny of PUUV is star-like, suggesting an early split of genetic lineages. The individual PUUV lineages appear to be independent, with the only exception to this being the Finnish and the Russian lineages that are closely connected to each other. Two strains of PUUV-like virus from Japan form the most ancestral lineage diverging from PUUV. Recombination points within the S segment were searched for and evidence for intralineage recombination events was seen in the Finnish, Russian, Danish, and Belgian lineages of PUUV. Molecular clock analysis showed that PUUV is a stable virus, evolving slowly at a rate of 0.7 x 10(-7) to 2.2 x 10(-6) nt substitutions per site per year.

Evolutionary diversification of protein-coding genes of hantaviruses

Phylogenetic analyses of the S:, M, and L: genes of the hantaviruses (Bunyaviridae: Hantavirus) revealed three well-differentiated clades corresponding to viruses parasitic on three subfamilies (Murinae, Arvicolinae, and Sigmodontinae) of the rodent family Muridae. In rooted trees of M: and L: genes, the viruses with hosts belonging to Murinae formed an outgroup to those with hosts in Arvicolinae and Sigmodontinae. This phylogeny corresponded with a phylogeny of the murid subfamilies based on mitochondrial cytochrome b sequences, supporting the hypothesis that hantaviruses have coevolved with their mammalian hosts at least since the common ancestor of these three subfamilies, which probably occurred about 50 MYA. The nucleocapsid protein (encoded by the S: gene) differentiated among the viruses parasitic on the three subfamilies in such a way that a high frequency of amino acid residue charge changes occurred in a hypervariable (HV) portion of the molecule, and nonsynonymous nucleotide differences causing amino acid charge changes in the HV region occurred significantly more frequently than expected under random substitution. Along with evidence that at least in some hantaviruses the HV region is a target for host antibodies and the known importance of charged residues in determining antibody epitopes, these results suggest that changes in the HV region may represent adaptation to host-specific characteristics of the immune response.

Genetic diversity of hantaviruses associated with hemorrhagic fever with renal syndrome in the far east of Russia

To identify the hantaviruses causing hemorrhagic fever with renal syndrome (HFRS) in the Far East of Russia, blood samples collected from HFRS patients in 1994-1998, were examined by reverse transcription-polymerase chain reaction. In addition, 36 sera were tested by an immunofluorescence assay for antibodies against Hantaan, Seoul, Puumala, and Khabarovsk viruses, and 54 samples were tested by plaque reduction neutralization test. With both serological assays, the highest antibody titers were to Hantaan and/or Seoul viruses. Of 110 blood samples 36 were found RT-PCR positive. Phylogenetic analysis the sequences of a 256-nucleotide (nt) fragment of the hantavirus M genome segment revealed at least 3 genetically distinct hantavirus lineages. Nucleotide sequence comparison showed that two of the lineages, designated as FE and Amur (AMR), differed from one another by 15.9-21.2% and from Hantaan virus by 9.8-17.5%. The third lineage, VDV, differed from Seoul virus by 2.6-5.1%. All S segment sequences were from FE lineage, and differed from Hantaan virus by 10.7-12.6%. Thirty of the 36 (83%) analyzed sequences were found to be the FE genotype, which is very similar to that of Hantaan virus, strain 76-118. Of the remaining hantaviruses, 11% were the AMR genotype, and 6% the VDV genotype, which are genetically novel genotypes of Hantaan or Seoul viruses, respectively.

A new Clethrionomys-derived hantavirus from Germany: evidence for distinct genetic sublineages of Puumala viruses in Western Europe

Puumala (PUU) viruses are the predominant etiologic agents of hantavirus infections in Europe. The most important reservoir is the bank vole, Clethrionomys glareolus (Cg), belonging to the subfamily Arvicolinae of the Muridae family. Here we report on the molecular characterization of the first rodent-derived sequence (PUU/Cg-Erft) from Germany. Comparison of the S and M segment coding regions revealed 92.5 and 92.8% identity, respectively, with PUU/H-9013, a human isolate from France. However, only 83.1% identity was found with the S segment of a previously reported PUU sequence from a German HFRS case (PUU/H-Berkel) indicating the co-existence of two distinct sublineages in Germany. Phylogenetic and alignment analyses of S and M segment coding regions enabled us to assign PUU viruses/sequences to at least six distinct genetic sublineages. Membership was defined by nucleotide sequence differences of < 8%, whereas a diversity of > 14% clearly outgrouped a virus/sequence. Based on S segment sequences the sublineage represented by Clethrionomys rufocanus-derived viruses from Japan diverged at a well supported node from the clade harbouring all Clethrionomys glareolus-derived European PUU viruses. A correlation between genetic relationship and geographic origin of PUU viruses was observed which may support a co-evolution of PUU viruses with distinct subspecies of their reservoir host.

Cell culture adaptation of Puumala hantavirus changes the infectivity for its natural reservoir, Clethrionomys glareolus, and leads to accumulation of mutants with altered genomic RNA S segment

This paper reports the establishment of a model for hantavirus host adaptation. Wild-type (wt) (bank vole-passaged) and Vero E6 cell-cultured variants of Puumala virus strain Kazan were analyzed for their virologic and genetic properties. The wt variant was well adapted for reproduction in bank voles but not in cell culture, while the Vero E6 strains replicated to much higher efficiency in cell culture but did not reproducibly infect bank voles. Comparison of the consensus sequences of the respective viral genomes revealed no differences in the coding region of the S gene. However, the noncoding regions of the S gene were found to be different at positions 26 and 1577. In one additional and independent adaptation experiment, all analyzed cDNA clones from the Vero E6-adapted variant were found to carry substitutions at position 1580 of the S segment, just 3 nucleotides downstream of the mutation observed in the first adaptation. No differences were found in the consensus sequences of the entire M segments from the wt and the Vero E6-adapted variants. The results indicated different impacts of the S and the M genomic segments for the adaptation process and selective advantages for the variants that carried altered noncoding sequences of the S segment. We conclude that the isolation in cell culture resulted in a phenotypically and genotypically altered hantavirus.

Hantavirus pulmonary syndrome: CD8+ and CD4+ cytotoxic T lymphocytes to epitopes on Sin Nombre virus nucleocapsid protein isolated during acute illness

In 1993 a number of cases of unexplained adult respiratory syndrome occurred in the southwestern United States. The illness was characterized by a prodrome of fever, myalgia, and other symptoms followed by the rapid onset of a capillary leak syndrome with hemoconcentration, thrombocytopenia, and pulmonary edema. Viral RNA sequences in the lungs identified a new member of the hantavirus genus, Sin Nombre virus (SNV), unique to North America. Pulmonary endothelial cells were heavily infected but were not necrotic. We speculated that this capillary leak syndrome was initiated by immune responses to the SNV-infected pulmonary endothelial cells. We isolated a CD8+ cytotoxic T lymphocyte (CTL) clone directly from the blood of a patient with the acute hantavirus pulmonary syndrome (HPS) which recognizes a SNV specific epitope on the virus nucleocapsid protein (aa 234-242) that is restricted by HLA C7 and produces IFN gamma but not IL-4. We identified a second CD8+ CTL epitope located within another site aa 131-139 on the nucleocapsid protein, which is HLA B35 restricted, and a CD4+ CTL epitope located on a third site on nucleocapsid protein aa 372-380 using lymphocytes obtained during HPS from another patient that were stimulated in vitro. Hantavirus specific CD8+ and CD4+ CTL may contribute to the immunopathology and capillary leak syndrome observed in the HPS.

The first human isolate of Puumala virus in Scandinavia as cultured from phytohemagglutinin stimulated leucocytes

A virus isolate was recovered from blood leucocytes of a patient with nephropathia epidemica (NE). Leucocytes were isolated from EDTA-blood by dextran sedimentation and cultured on monolayers of Vero E6 cells in the presence of phytohemagglutinin (PHA) in roller tubes during the first 72 hours of incubation followed by rolling culture for three weeks in total. Thereafter the first subculture was done in a plastic flask and afterward at at least 6 week intervals. Antigen was first detected after 6 months and 2 weeks of culture. When tested by monoclonal antibodies and patient sera the isolate had the characteristics of a PUU virus. PCR amplification using PUU-specific primers and subsequent partial sequencing of the S and M segments revealed that the Umeå/305/human/95 virus differs from the Finnish PUU Sotkamo rodent prototype virus and is similar but not identical to rodent strains of PUU virus acquired from the same region as the patient isolate. It is we concluded that the first human isolate of the etiologic agent of NE in Scandinavia was recovered from blood leucocytes stimulated with PHA by long-term culture in Vero E6 cells. The isolate belongs to the PUU serotype of hantaviruses as shown by its serologic profile and partial sequencing data.

Baculovirus expression of a human G2-specific, neutralizing IgG monoclonal antibody to Puumala virus

We amplified by polymerase chain reaction the heavy- and light-chain antibody genes of a human hybridoma secreting a neutralizing, IgG monoclonal antibody to the G2 protein of Puumala virus. The heavy- and light-chain genes were cloned and sequenced and the deduced amino acids were aligned with those of other human antibodies to identify the constant and variable regions. The genes were cloned into the baculovirus plasmid transfer vector pACUW51 such that the heavy-chain and light-chain genes were under control of the baculovirus polyhedrin or p10 promoters, respectively. The transfer vector plasmid was cotransfected into cultured Spodoptera frugiperda (Sf9) cells with linearized DNA of the baculovirus Autographa californica nuclear polyhedrosis virus, and recombinant baculoviruses were selected by plaque formation on monolayers of Sf9 cells. Expression and secretion of an IgG monoclonal antibody was confirmed by assay of recombinant-infected Sf9 cell supernatants for the presence of the heavy and light chains. Specificity of the expressed human antibody was determined by immune-precipitation of radiolabeled Puumala virus proteins and by ELISA with Puumala virus-infected cell lysates. Similar quantities of the expressed IgG and the authentic monoclonal antibody neutralized Puumala virus in plaque-reduction neutralization assays. Neither the authentic nor the recombinant antibody could passively protect hamsters from challenge with Puumala virus; however, our results demonstrate the potential of this methodology for production of biologically active neutralizing antibodies.

Puumala hantavirus genome in patients with nephropathia epidemica: correlation of PCR positivity with HLA haplotype and link to viral sequences in local rodents

Reverse transcription-PCR was used to analyze specimens from 20 Finnish nephropathia epidemica (NE) patients hospitalized during the period from October 1994 to January 1995. Blood and/or urine sediment specimens from seven patients were found to be positive for the genome sequences of Puumala hantavirus (PUU). PCR positivity of the specimens from the patients correlated well with the HLA-DRB1*0301 and HLA B8 alleles, which previously were shown to associate with severe courses of NE. Genetic analysis of the partial M-and/or S-segment sequences obtained from three severely ill NE patients revealed three PUU strains related to but distinct from previously reported strains from Finland. The M-segment sequence of PUU from bank voles trapped near the probable site of infection for one of the patients showed 98.2% identity to that of the PUU strain obtained from the patient, suggesting a link between wild-type PUU from the natural focus and the NE case. The S-segment sequences from the patient and the bank voles, however, showed substantially lower identity (95.8%). As this difference in diversity for M and S genes (1.8 and 4.2%) is atypical for PUU genetic drift, one possibility is that the strain acquired at the putative place of infection is a reassortant one.

Nucleotide and deduced amino acid sequences of the M and S genome segments of a Swedish Puumala virus isolate

The Swedish Puumala (PUU) virus strain Vindeln 83-L20, isolated from a bank vole trapped in 1983 near Vindeln, Västerbotten county, Sweden, was characterized by nucleotide sequence analysis. The coding region of the M segment was determined by PCR followed by direct sequencing and the entire S segment was characterized by cloning and nucleotide sequence analysis. The genomic organization was found to be very similar to that of other PUU virus strains regarding open reading frames, polypeptide sizes and potential glycosylation sites. According to phylogenetic analysis 83-L20 was found to represent a new lineage within the Puumala virus serotype in the Hantavirus genus. The M segment sequence of 83-L20 was found to be more closely related to the Finnish PUU virus strains than to strains from Central Europe or from Russia. The evolutionary origin of the S segment was not as clearly resolved since the branching points of all PUU virus strains in the phylogenetic tree were nearly the same.

Molecular linkage of hantavirus pulmonary syndrome to the white-footed mouse, Peromyscus leucopus: genetic characterization of the M genome of New York virus

The complete M segment sequences of hantaviruses amplified from tissues of a patient with hantavirus pulmonary syndrome in the northeastern United States and from white-footed mice, Peromyscus leucopus, from New York were 99% identical and differed from those of Four Corners virus by 23%. The serum of this patient failed to recognize a conserved, immunodominant epitope of the Four Corners virus G1 glycoprotein. Collectively, these findings indicate that P. leucopus harbors a genetically and antigenically distinct hantavirus that causes hantavirus pulmonary syndrome.

Coding strategy of the S and M genomic segments of a hantavirus representing a new subtype of the Puumala serotype

The hantavirus strain Vranica was previously reported to have been isolated from a bank vole in Bosnia-Hercegovina and associated with the occurrence of hemorrhagic fever with renal syndrome (HRFS) in humans. The complete cDNA nucleotide sequences of the small (S) and medium (M) genomic RNA segments of this virus were determined. Major open reading frames were found in the S and M segment between nucleotide positions 43 and 1341 coding for a polypeptide of 433 amino acid residues and between nucleotide positions 41 and 3,484 coding for 1,148 amino acid residues, respectively. The analysis and the alignment of the nucleotide and the derived amino acid sequences with known sequences of other hantavirus strains demonstrate that Vranica resembles Swedish strains and represents a new virus subtype of the Puumala serotype distinct from the subtypes represented by virus strains CG18-20 and Sotkamo.

Genetic characterization of a human isolate of Puumala hantavirus from France

PUU90-13 is a strain of Puumala (PUU) virus (family Bunyaviridae: genus Hantavirus) isolated from a human in northeastern France (Rollin et al., 1995). This report describes the full-length sequences of the small (S) and medium (M) genomic RNAs of PUU90-13. The terminal sequences of both the S and M genomic RNAs were found to be conserved and imperfectly complementary. The S RNA of PUU90-13 is 1847 nt in length and contains the nucleocapsid (N) protein gene and a potential overlapping open reading frame (ORF-2) previously described in other hantaviruses. Statistical analysis of the third base substitution frequency in the N ORFs of PUU90-13 and other PUU viruses suggests that the ORF-2 is functional. The M RNA is 3681 nt in length and encodes the glycoprotein precursor. Both genomic segments share the highest degree of nucleotide and amino acid sequence identity with PUUBerkel, a PUU virus from Germany. Phylogenetic analyses of sequences from both segments indicate that PUU90-13 occupies a distinct Western European PUU virus lineage that it shares with PUUBerkel. Both PUU90-13 and PUUBerkel lack a potential N-linked glycosylation site found on the G2 glycoprotein of other PUU viruses.

A vaccinia virus-vectored Hantaan virus vaccine protects hamsters from challenge with Hantaan and Seoul viruses but not Puumala virus

To investigate the ability of a vaccinia virus-vectored vaccine expressing the M and the S segments of Hantaan (HTN) virus (C. S. Schmaljohn, S. E. Hasty, and J. M. Dalrymple, Vaccine 10:10-13, 1992) to elicit a protective immune response against other hantaviruses, we vaccinated hamsters with the recombinant vaccine and challenged them with HTN, Seoul (SEO), or Puumala (PUU) virus. Neutralizing antibodies to HTN virus were found in all vaccinated hamsters both before and after challenge. Neutralizing antibody titers to SEO virus were present at low levels or were undetectable after two immunizations with the vaccine but were positive in all vaccinated hamsters after challenge with SEO virus and were also positive in control animals that were not challenged. Neutralizing antibodies to PUU virus were observed only in hamsters previously challenged with PUU virus. To assay for virus in the blood and tissues of the hamsters, we developed a nested reverse transcriptase (RT)-PCR with cross-reactive outer primers and serotype-specific inner primers. The RT-PCR specifically detected as little as 1 PFU of virus in serum containing high-titer neutralizing antibodies and was more sensitive than immunofluorescent antibody staining for detecting virus in lung and kidney specimens of infected hamsters. By using the RT-PCR, we found that vaccinated hamsters, challenged with HTN or SEO virus, neither were viremic nor had evidence of virus in their lungs or kidneys. In contrast, vaccinated hamsters challenged with PUU virus were viremic and had PUU virus-specific nucleic acid in their organs.

Genetic variation of wild Puumala viruses within the serotype, local rodent populations and individual animal

Reverse transcriptase polymerase chain reaction cloning and sequencing were used to determine the range of S gene/N protein variability in wild Puumala virus (PUU) strains and to study phylogenetic relationships between two groups of strains which originated from Finland and from European Russia. Analyses of the nucleotide and predicted amino acid sequences showed: (1) all PUU strains shared a common ancient ancestor; and (2) the more recent ancestors were different for the Finnish branch and the Russian branch of PUU strains. A cluster of amino acid substitutions in the N protein of Finnish strains was found; this cluster was located within a highly variable region of the molecule carrying B-cell epitopes (Vapalahti et al., J. Med. Virol., 1995, in press). Different levels of S gene/N protein diversity of PUU were revealed supporting the view of geographical clustering of genetic variants. Puumala virus from individual voles was found to be a complex mixture of closely related variants-quasispecies. The ratio of non-silent to silent nucleotide mutations registered in the S genes/N proteins of PUU quasispecies was 4- to 16-fold higher than that in Puumala virus strains, resulting in a more wide range of quasispecies N protein sequence diversity.

Phylogenetically distinct hantavirus implicated in a case of hantavirus pulmonary syndrome in the northeastern United States

Hantavirus pulmonary syndrome (HPS) is an acute respiratory illness with high mortality. It is caused by a newly described New World hantavirus known as Four Corners virus (FCV). Nearly all cases of HPS have occurred in the western United States. The etiologic agents in those cases have been closely related to each other, based upon comparisons of their genetic sequences. We have molecularly cloned the S genomic segment of a hantavirus (Rl-1) implicated in a case on HPS in the northeastern United States. Nucleotide sequence analysis shows that the Rl-1 virus has many similarities to FCV, but is clearly distinct from the western forms of that virus. These data suggest that HPS can be caused by multiple agents that together form a distinctive evolutionary clade.

A newly recognized virus associated with a fatal case of hantavirus pulmonary syndrome in Louisiana

Genetic analysis of virus detected in autopsy tissues of a fatal hantavirus pulmonary syndrome-like case in Louisiana revealed the presence of a previously unrecognized hantavirus. Nucleotide sequence analysis of PCR fragments of the complete S and M segments of the virus amplified from RNA extracted from the tissues showed the virus to be novel, differing from the closest related hantavirus, Sin Nombre virus, by approximately 30%. Both genome segments were unique, and there was no evidence of genetic reassortment with previously characterized hantaviruses. The primary rodent reservoir of Sin Nombre virus, the deer mouse Peromyscus maniculatus, is absent from Louisiana. Thus, the virus detected in Louisiana, referred to here as Bayou virus, must possess a different rodent reservoir.

Antibody responses to Four Corners hantavirus infections in the deer mouse (Peromyscus maniculatus): identification of an immunodominant region of the viral nucleocapsid protein

Antibody responses to Four Corners hantavirus (FCV) infections in the deer mouse (Peromyscus maniculatus) were characterized by using FCV nucleocapsid protein (N), glycoprotein 1 (G1), and glycoprotein 2 (G2) recombinant polypeptides in Western immunoblot assays. Strong immunoglobulin G reactivities to FCV N were observed among FCV-infected wild P. maniculatus mice (n = 34) and in laboratory-infected P. maniculatus mice (n = 11). No immunoglobulin G antibody reactivities to FCV G1 or G2 linear determinants were detected. The strongest N responses were mapped to an amino-proximal segment between amino acids 17 and 59 (QLVTARQKLKDAERAVELDPDDVNKSTLQSRRAAVSALETKLG). FCV N antibodies cross-reacted with recombinant N proteins encoded by Puumala, Seoul, and Hantaan viruses.

Detection and subsequent sequencing of Puumala virus from human specimens by PCR

A sensitive method based on PCR was developed for the detection of Puumala virus (PUU) in human samples. The assay was found to be specific for PUU-like strains and distinguished between these and hantaviruses of other serotypes. The detection limit was found to be 10(-5) focus-forming units. Clinical samples were collected from patients with nephropathia epidemica in Sweden and western Russia. Five whole blood samples collected from patients in Russia with the acute phase of disease were found to be positive by the PCR. All samples were negative for PUU antigen when examined by enzyme-linked immunosorbent assay. Virus isolation on Vero E6 cells from several of the acute-phase samples, including the 5 PCR-positive samples, was not successful. The amplified samples were subjected to direct nucleic acid sequencing for confirmation of identity. The sequences differed from each other and were closely related to the Russian bank vole isolate CG-1820, thereby indicating the origin of nephropathia epidemica. The PCR was used for amplification and subsequent nucleotide sequencing of eight PUU-like isolates with different geographic origins. The Swedish strains were more closely related to the Finnish PUU prototype strain, Sotkamo, than to the Russian isolates. Interestingly, a Belgian isolate, CG-13891, differed markedly from all other PUU strains.

Genetic identification of a novel hantavirus of the harvest mouse Reithrodontomys megalotis

We have cloned the S genomic segment of a novel hantavirus of the harvest mouse Reithrodontomys megalotis. The virus is phylogenetically distinct from other hantaviruses. The new hantavirus was identified in harvest mice separated by approximately 1,000 km. A wood rat (Neotoma mexicana) was found to be infected with the harvest mouse hantavirus.

Antigenic and molecular characterization of hantavirus isolates from China

Hemorrhagic fever with renal syndrome (HFRS) is caused by certain viruses in the genus Hantavirus, family Bunyaviridae, and is a major public health problem in China. By using molecular and serological tests, we characterized 15 hantaviruses isolated either from patients with HFRS or from rodents captured in endemic areas of China. By cross plaque-reduction neutralization tests performed with rabbit immune sera, we identified two serologically distinct groups of viruses, comprised of those related to Hantaan virus, and those related to Seoul virus. To study the genetic relationships among these viruses, we amplified a 330 base pair region of the medium (M) genome segment of each isolate by reverse transcription and polymerase chain reaction (PCR) and compared the nucleotide sequences to those of other, well-characterized hantaviruses. In addition, we PCR-amplified and analyzed the entire coding region of the small (S) genome segment of each isolate by restriction enzyme digestion with a battery of enzymes. The results of our genetic analyses of both the M and S segments of these isolates confirmed our serological data, indicating that Hantaan and Seoul viruses co-circulate in endemic disease regions of China. We constructed a phylogenetic tree based on multiple alignment of the partial M segment sequences. The resulting dendrogram distinguished three genetic subtypes of Hantaan viruses and one type of Seoul virus.