Immunoblot analysis of the serological response in Hantavirus infections

The Role of Nucleoprotein in Immunity to Human Negative-Stranded RNA Viruses—Not Just Another Brick in the Viral Nucleocapsid

Negative-stranded RNA viruses (NSVs) are important human pathogens, including emerging and reemerging viruses that cause respiratory, hemorrhagic and other severe illnesses. Vaccine design traditionally relies on the viral surface glycoproteins. However, surface glycoproteins rarely elicit effective long-term immunity due to high variability. Therefore, an alternative approach is to include conserved structural proteins such as nucleoprotein (NP). NP is engaged in myriad processes in the viral life cycle: coating and protection of viral RNA, regulation of transcription/replication processes and induction of immunosuppression of the host. A broad heterosubtypic T-cellular protection was ascribed very early to this protein. In contrast, the understanding of the humoral immunity to NP is very limited in spite of the high titer of non-neutralizing NP-specific antibodies raised upon natural infection or immunization. In this review, the data with important implications for the understanding of the role of NP in the immune response to human NSVs are revisited. Major implications of the elicited T-cell immune responses to NP are evaluated, and the possible multiple mechanisms of the neglected humoral response to NP are discussed. The intention of this review is to remind that NP is a very promising target for the development of future vaccines.

Levels of HTNV-specific CD8+ T lymphocytes in PBMC from the patients with hemorrhagic fever with renal syndrome

The pathogenesis of hemorrhagic fever with renal syndrome (HFRS) has not been fully clarified. Cell-mediated immunity appears to play a crucial role in the immune pathogenesis of HFRS. To explore the relationship between Hantaan (HTNV)-specific CD8(+) T lymphocytes and the immune pathogenesis of HFRS, the levels of interferon γ (IFN-γ) secreted by HTNV-specific CD8(+) T lymphocytes were detected by flow cytometry in peripheral blood mononuclear cells. Levels of HTNV-specific CD8(+) T lymphocytes in patients with HFRS were associated with different phases of HFRS. In fever phase, it was significantly elevated. The levels of HTNV-specific CD8(+) T lymphocytes in PBMC of patients with HFRS were negatively correlated with the levels of blood urea nitrogen and creatinine in plasma. The results show that the HTNV-specific CD8(+) T lymphocyte levels correlate with disease phases. Therefore, dynamic observation of these levels in patients with HFRS can help to judge the status of HFRS disease and to clarify the immune pathogenesis of HFRS.

Human pathogenic hantaviruses and prevention of infection

Hantaviruses are emerging viruses which are hosted by small mammals. When transmitted to humans, they can cause two clinical syndromes, hemorrhagic fever with renal syndrome or hantavirus cardiopulmonary syndrome. The review compiles the current list of hantaviruses which are thought to be pathogenic in humans on the basis of molecular or at least serological evidence. Whereas induction of a neutralizing humoral immune response is considered to be protective against infection, the dual role of cellular immunity (protection versus immunopathogenicity) is discussed. For active immunisation, inactivated virus vaccines are licensed in certain Asian countries. Moreover, several classical and molecular vaccine approaches are in pre-clinical stages of development. The development of hantavirus vaccines is hampered by the lack of adequate animal models of hantavirus-associated disease. In addition to active immunization strategies, the review summarizes other ways of infection prevention, as passive immunization, chemoprophylaxis, and exposition prophylaxis.

Characterization of cross-reactive and serotype-specific epitopes on the nucleocapsid proteins of hantaviruses

The hantavirus nucleocapsid (N) protein fulfills several key roles in virus replication and assembly and is the major antigen in humoral immune responses in humans and mice. Here we report on epitopes involved in serotype-specific and cross-reactive recognition of the N proteins of hantaviruses using monoclonal antibodies (mAbs) against the N proteins of Andes virus (ANDV) and Sin Nombre virus (SNV). The mAbs define at least twelve different epitopic patterns which span eight sequences, including amino acids 17-59, 66-78, 79-91, 157-169, 222-234, 244-263, 274-286 and 326-338 on the SNV and ANDV N proteins. Studies on the cross-reactivity of these mAbs with different hantavirus N proteins indicated that epitopes located within amino acids 244-286 are related to serotype specificity. We analyzed further the location of epitopes with available three-dimensional structure information including the N-terminal coiled-coil and derived exposed and hidden residues of these epitopes. The generated recombinant N proteins and the characterized mAbs are functional tools being now available for hantavirus diagnostics and replication studies.

A soluble and heat-resistant form of hantavirus nucleocapsid protein for the serodiagnosis of HFRS

Hemorrhagic fever with renal syndrome (HFRS) is a rodent-borne viral zoonosis characterized by fever, hemorrhagic manifestations, and renal disorder. The causative agent of HFRS has been identified as a hantavirus. Hantavirus nucleocapsid proteins have recently been shown to be immunodominant antigens in HFRS, inducing an early and long-lasting immune response, and their amino termini are sensitive tools for the detection of specific antibodies in HFRS patient sera. Previous work has demonstrated that the introduction of the acidic tail of alpha-synuclein (ATS) into heat-labile proteins protects them from heat-induced aggregation. In this study, the ATS peptide was introduced into the N-terminal antigenic portion of the nucleocapsid proteins (amino acid residues 1-70) of the Hantaan virus (HTNV-delta N) and Seoul virus (SEOV-delta N). The recombinant ATS-HTNV-delta N and ATS-SEOV-delta N fusion proteins were heat-resistant, and the proteins purified by heat treatment were immunoreactive to sera from patients with HFRS. Compared with sera from patients with leptospirosis and scrub typhus, sera from patients with HFRS showed much higher reactivity in ATS-HTNV-delta N- or ATS-SEOV-delta N-based IgG ELISAs. Immunoblotting analysis revealed that only sera from patients with HFRS specifically recognized the ATS-HTNV-delta N and ATS-SEOV-delta N, indicating that the ATS-HTNV-delta N and ATS-SEOV-delta N were highly purified species without any other immunoreactive proteins as contaminants. These data demonstrate that the ATS-HTNV-delta N and ATS-SEOV-delta N fusion proteins offer a safe and inexpensive source of pure and specific antigen for large-scale diagnosis and seroepidemiological studies of HFRS, and that ATS-fusion technology can also be utilized to solubilize other antigens that could be used for large-scale diagnosis and seroepidemiological studies of other diseases.

The expression and genetic immunization of chimeric fragment of Hantaan virus M and S segments

Hemorrhagic fever with renal syndrome (HFRS), which is characterized by severe symptoms and high mortality, is caused by hantavirus. There are still no effective prophylactic vaccines directed to HFRS until now. In this research, we fused expressed G2 fragment of M segment and 0.7kb fragment of S segment. We expect it could be a candidate vaccine. Chimeric gene G2S0.7 was first expressed in prokaryotic expression system pGEX-4T. After inducing expressed fusion proteins, GST-G2S0.7 was induced and its molecular weight was about 100kDa. Meanwhile, the fusion protein kept the activity of its parental proteins. Further, BALB/c mice were vaccinated by the chimeric gene. ELISA, cell microculture neutralization test in vitro were used to detect the humoral immune response in immunized BALB/c mice. Lymphocyte proliferation assay was used to detect the cellular immune response. The results showed that the chimeric gene could simultaneously evoke specific antibody against nucleocapsid protein (NP) and glycoprotein (GP). And the immunized mice of every group elicited neutralizing antibodies with different titers. But the titers were low. Lymphocyte proliferation assay results showed that the stimulation indexes of splenocytes of chimeric gene to NP and GP were significantly higher than that of control. It suggested that the chimeric gene of Hantaan virus containing G2 fragment of M segment and 0.7kb fragment of S segment could directly elicit specific anti-Hantaan virus humoral and cellular immune response in BALB/c mice.

Bovine aortic endothelial cells are susceptible to hantavirus infection; a new aspect in hantavirus ecology

Hantaviruses are enveloped RNA viruses that belong to the family Bunyaviridae. They are the causative agents of hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Hantaviruses show a worldwide distribution with specific rodent species as natural hosts. It is known that rodents can transmit the virus via feces, urine, saliva, or bites to humans. Additionally, antibodies against different hantaviruses were also found in domestic animals, For example, Danes et al. documented hantavirus-specific IgG titers in 2% of examined cattle [Ceskoslov. Epidemiol. Mikrobiol. Imunol. 41 (1992) 15]. In order to clarify the possibility of a nonrodent and nonhuman hantavirus infection, the susceptibility of bovine aortic endothelial cells (BAEC) to Hantavirus serotype Puumala infection was investigated. The hantaviral nucleocapsid protein was detected in 95% of infected BAEC at the fourth cell culture passage 12 weeks after initial infection by immunofluorescence assay (IFA). The presence of Puumala virus (PUU) nucleocapsid protein and the viral glycoproteins G1 and G2 in infected cells were additionally confirmed by Western blot analysis. The viral RNA genome was identified in infected BAEC cultures and in cell-free culture medium at the fourth passage by reverse transcription polymerase chain reaction (RT-PCR), verified by cDNA nucleotide sequence analysis, showing a 98-100% homology to the input virus. The infected BAEC cultures were shown to express alpha(V)beta(3)-integrin surface receptors that are known to mediate virus entry in human cells and revealed no major cytopathic effects (CPEs) as assayed by immunofluorescence staining of the cytoskeletal components actin and microtubules. In the present study, we documented for the first time that a nonrodent and nonhuman aortic endothelial cell culture of bovine origin (BAEC) can be efficiently infected with a hantavirus. This finding is of particular importance because it adds new aspects to questions dealing with host species barrier, viral reservoir, virus transmission, and ecology of hantaviruses.

Bovine aortic endothelial cells are susceptible to Hantaan virus infection

Hantavirus serotype Hantaan (HTN) is one of the causative agents of hemorrhagic fever with renal syndrome (HFRS, lethality up to 10%). The natural host of HTN is Apodemus agrarius. Recent studies have shown that domestic animals like cattle are sporadically seropositive for hantaviruses. In the present study, the susceptibility of bovine aortic endothelial cells (BAEC) expressing alpha(V)beta(3)-integrin to a HTN infection was investigated. Viral nucleocapsid protein and genomic RNA segments were detected in infected BAEC by indirect immunofluorescence assay, Western blot analysis, and reverse transcription-polymerase chain reaction (RT-PCR), respectively. The results of this study strongly support our previous observation on Puumala virus (PUU) that has been propagated efficiently in BAEC. These findings open a new window to contemplate the ecology of hantavirus infection and transmission route from animal to man.

Hantavirus infections and their prevention

Hantaviruses are rodent-borne bunyaviruses which cause haemorrhagic fever with renal syndrome and Hantavirus pulmonary syndrome in humans. This review covers the host interactions of the viruses, including the rodent reservoirs, the clinical outcome of human infections as well as the pathogenesis and laboratory diagnosis of infections. The current stage in prophylaxis and therapy of hantaviral diseases is described and different approaches in vaccine development are discussed.

Expression of immunogenic Puumala virus nucleocapsid protein in transgenic tobacco and potato plants

Transgenic plants, expressing recombinant proteins, are suitable alternatives for the production of relevant immunogens. In the present study, the expression of Puumala virus nucleocapsid protein in tobacco and potato plants (Nicotiana tabacum and Solanum tuberosum) and its immunogenicity was investigated. After infection of leaf discs of SR1 tobacco and tuber discs of potato cv. "Desiree" with the Agrobacterium strain LBA4404 (pAL4404, pBinAR-PUU-S) containing the 1302 bp cDNA sequence of S-RNA segment of a Puumala virus, transgenic tobacco and potato plants expressed the Puumala virus nucleocapsid protein under control of the cauliflower 35S promoter. The recombinant proteins were found to be identical to the authentic Puumala virus nucleocapsid protein as analyzed by immunoblotting. Expression of the nucleocapsid protein was investigated over four plant generations (P to F4) and found to be stable (1 ng/3 microg dried leaf tissue). Transgenic tobacco plants were smaller compared to controls. The transformed potato plants were morphologically similar to control plants and produced tubers as the control potatoes. The S-antigen was expressed at a level of 1 ng protein/5 microg and 1 ng protein/4 microg dried leaf and root tissues, respectively, and remained stable in the first generation of vegetatively propagated potato plants. The immunogenicity of the Puumala virus nucleocapsid protein expressed in Nicotiana tabacum and Solanum tuberosum was investigated in New Zealand white rabbits. They were immunized with leaf extracts from transgenic tobacco and potato plants, and the serum recognized Puumala virus nucleocapsid protein. Transgenic plants expressing hantaviral proteins can thus be used for the development of cost-effective diagnostic systems and for alternative vaccination strategies.

Detection of Toscana virus-specific immunoglobulins G and M by an enzyme-linked immunosorbent assay based on recombinant viral nucleoprotein

An enzyme-linked immunosorbent assay (ELISA) based on the recombinant Toscana virus nucleoprotein (rN) has been developed. Its sensitivity and specificity for the detection of virus-specific immunoglobulins G and M in human sera were similar to those of the ELISA that is based on an antigen extracted from infected mouse brain and that is routinely used for serodiagnosis.

Polymerase chain reaction detection of Puumala virus RNA in formaldehyde-fixed biopsy material

BACKGROUND

Infections with hantaviruses, mainly Clethrionomys-derived Puumala viruses, are known causes of acute renal failure [hemorrhagic fever with renal syndrome (HFRS)] in western Europe. Laboratory diagnosis is primarily based on serology. At the time of clinical symptoms, viral RNA can hardly be detected in the blood or urine, indicating that polymerase chain reaction (PCR) is of little diagnostic value for these infections. Biopsy material is usually formaldehyde-fixed and, thus, regarded as poor quality for PCR applications. The aim of this study was to establish a technique to retrieve such material for laboratory diagnostic.

METHODS

Formaldehyde-fixed, paraffin-embedded kidney biopsies of 14 patients with renal failure either clinically suspected for HFRS (7 cases) or caused by unknown (2 cases) or known other causes (drugs, sarcoidosis; 5 cases) were histologically investigated. An established S segment-specific PCR assay was applied to RNA isolated from the biopsies, and amplification products were verified by direct sequence determination.

RESULTS

Investigations revealed a typical histopathological appearance for hantavirus infections in all seven suspected HFRS cases and one case of unknown cause. With five of the suspected HFRS cases, hantavirus-specific RNA was detected. Sequence comparison revealed a close relationship to corresponding nucleoproteins of known Puumala viruses.

CONCLUSION

The established technique provides a simple and powerful tool that expands the diagnostic possibilities, especially for otherwise unidentified or retrospective cases. It further allows insight into the molecular epidemiology of HFRS-causing agents.

Humoral response in Toscana virus acute neurologic disease investigated by viral-protein-specific immunoassays

The Toscana virus (family Bunyaviridae, genus Phlebovirus) is the only sandfly-transmitted virus that demonstrates neurotropic activity. Clinical cases ranging from aseptic meningitis to meningoencephalitis caused by Toscana virus are yearly observed in central Italy during the summer, and several cases have been reported among tourists returning from zones of endemicity (Italy, Portugal, Spain, and Cyprus). In Toscana virus patients, immunoglobulin M (IgM) antibodies, usually present at the onset of symptoms, can reveal elevated titers by enzyme-linked immunosorbent assay and can persist for at least 1 year. IgG antibodies can be absent at the onset of symptoms: titers rise in convalescent sera and persist for many years. At least five proteins have been identified in Toscana virus-infected cells: nucleoprotein N, glycoproteins G1 and G2, a large protein (L) assumed to be a component of the polymerase, and two nonstructural proteins, NSm and NSs. We report results of a study on the antibody response to individual viral proteins in patients with Toscana virus-associated acute neurologic disease. Immunoblotting and semiquantitative radioimmunoprecipitation assay (RIPA) allow identification of nucleoprotein N as the major antigen responsible for both IgM and IgG responses. Antibodies to proteins other than nucleoprotein N are detected only by RIPA. Antibodies to glycoproteins are detected in about one-third of patients, and whereas their presence always predicts neutralization, some serum samples with neutralizing activity have undetectable levels of antibodies to G1-G2. Antibodies to nonstructural proteins NSm and NSs are also identified. The results obtained raise some questions about antigenic variability and relevant neutralization epitopes of Toscana virus.

Stable expression of nucleocapsid proteins of Puumala and Hantaan virus in mammalian cells

The development of an in vitro-system for the stable expression and the analysis of native hantavirus proteins using hantaviral cDNA is of particular interest. As a first step the expression of the hantavirus nucleocapsid (N) proteins in mammalian cells was studied in more detail. The cDNA of the S-RNA segment of Puumala virus strain CG-1820 and Hantaan virus strain 76-118 was used for the construction of eucaryotic expression vectors that allow the generation and selection of mammalian cells harboring and expressing the N protein genes of hantaviruses. A variety of conventional and novel expression vectors as well as different mammalian cell lines were screened. The expression of the N protein of Puumala virus using the pGRE5-1 vector in which the transcription is under control of inducible glucocorticoid responsive elements (GRE) revealed that the Puumala virus N protein can be expressed in Vero E6 cells efficiently without any detectable cell toxicity. From the variety of expression vectors tested, it was found that pCR3.1 is the vector of choice for stable expression of hantavirus N proteins. The successful establishment of different mammalian cell lines expressing considerable amounts of Puumala and Hantaan virus N protein indicates that the stable and efficient expression of this particular viral protein in the cell lines of three evolutionary distinct species (human, monkey, and mouse) is possible. The system described here represents the experimental basis for further studies of hantavirus infection, replication, and pathogenesis using a reverse genetics approach.

Single amino acid substitutions in Puumala virus envelope glycoproteins G1 and G2 eliminate important neutralization epitopes

Two monoclonal antibody escape virus mutants (MARs), rescued from a human MAb to glycoprotein 2 (G2) and a bank vole monoclonal antibody (MAb) directed to glycoprotein 1 (G1) of Puumala virus, strain Sotkamo, were produced by using a combination of neutralization tests and antigen detection. The MARs and the original virus were analyzed by nucleotide sequencing and the responsible mutations were defined and characterized. The G1 mutation was found to constitute an A to T nucleotide substitution, giving raise to an aspartic acid to valine mutation at residue 272, potentially increasing the hydrophobicity of this region. The G2 mutation was found to constitute a C to T substitution, altering the residue 944 from serine into the more hydrophobic phenylalanine and resulting in secondary structure alterations. The mutation was found to be in close vicinity to a glycosylation site. Synthetic peptides covering the regions of the native virus, defined by the MARs, were produced and evaluated for reactivity with the corresponding MAb. The peptides were not recognized by the MAbs, and did not inhibit the binding of the MAbs in competition assays. Sera from mice immunized with the peptides were not able to recognize the native protein. This indicates that the epitopes are non-linear and/or glycosylated in the native state, or alternatively, that the G1 and G2 MAbs binds to regions away from the mutations.

Rapid and specific detection of Sin Nombre virus antibodies in patients with hantavirus pulmonary syndrome by a strip immunoblot assay suitable for field diagnosis

To develop a rapid antibody test for Sin Nombre hantavirus (SNV) infection for diagnosis of hantavirus pulmonary syndrome (HPS) in field settings where advanced instrumentation is not available, a strip immunoblot assay bearing four immobilized antigens for SNV and a recombinant nucleocapsid protein antigen of Seoul hantavirus (SEOV) was prepared. The SNV antigens included a full-length recombinant-expressed nucleocapsid (N) protein (rN), a recombinant-expressed G1 protein (residues 35 to 117), and synthetic peptides derived from N (residues 17 to 59) and G1 (residues 55 to 88). On the basis of the observed reactivities of hantavirus-infected patient and control sera, we determined that a positive assay requires reactivity with SNV or SEOV rN antigen and at least one other antigen. Isolated reactivity to either viral rN antigen is indeterminate, and any pattern of reactivity that does not include reactivity to an rN antigen is considered indeterminate but is unlikely to represent hantavirus infection. Fifty-eight of 59 samples from patients with acute SNV-associated HPS were positive according to these criteria, and one was initially indeterminate. Four of four samples from patients with HPS due to other hantaviruses were positive, as were most samples from patients with SEOV and Puumala virus infections. Of 192 control serum samples, 2 (1%) were positive and 2 were indeterminate. Acute SNV infection was distinguishable from remote SNV infection or infection with hantaviruses other than SNV by the presence of G1 peptide antigen reactivities in the former. The strip immunoblot assay shows promise for the detection of SNV antibodies early in the course of HPS.

A major antigenic domain of hantaviruses is located on the aminoproximal site of the viral nucleocapsid protein

Hantavirus nucleocapsid protein has recently been shown to be an immunodominant antigen in hemorrhagic with renal syndrome (HFRS) inducing an early and long-lasting immune response. Recombinant proteins representing various regions of the nucleocapsid proteins as well as segments of the G1 and the G2 glycoproteins of hantavirus strains CG18-20 (Puumala serotype) and Hantaan 76-118 have been expressed in E. coli. The antigenicity of these proteins was tested in enzyme immunoassays and immunoblots. These studies revealed that human IgG immune response is primarily directed against epitopes located within the amino acid residues 1 to 119 of the amino terminus of viral nucleocapsid proteins. This fragment was recognized by all HFRS patient sera tested (n = 128). The corresponding enzyme immunoassays proved to be more sensitive than the indirect immunofluorescence assays. Furthermore, the majority of bank vole monoclonal antibodies raised against Puumala virus reacted specifically with this site. A recombinant G1 protein (aa 59 to 401) derived from the CG 18-20 strain was recognized by 19 out of 20 sera from HFRS patients.

Immunoblot detection of antibodies to Toscana virus

Sera from patients with sandfly fever caused by Toscana virus (TOSV) infection were tested by immunoblot for specific antibody response to TOSV derived from infected Vero-E6 cells. The 28 kDa TOSV nucleoprotein (N) was identified as the major immunodominant protein recognized by immunoblot. In sera of patients with acute TOSV infection, specific antibodies of the IgM, IgA, and IgG class were detected. Using sandfly fever virus, serotypes Sicilian (SFSV) and Naples (SFNV), as antigens for immunoblot, TOSV antibody-positive sera cross-reacted with the corresponding N proteins. These sera reacted for IgM and IgG by SFSV immunoblot, and for IgM by SFNV immunoblot. The diagnosis of sandfly fever may be confirmed by TOSV immunoblot.

The clinical usefulness of a Puumalavirus recombinant nucleocapsid protein based enzyme-linked immunosorbent assay in the diagnosis of nephropathia epidemica as compared with an immunofluorescence assay

BACKGROUND

Nephropathia epidemica (NE), a hemorrhagic fever with renal syndrome (HFRS) predominantly encountered in northern Europe, is a febrile disease, commonly associated with acute renal impairment. A rapid and reliable serological diagnosis is required to differentiate NE from other acute febrile illnesses in endemic areas.

OBJECTIVE

To evaluate a Puumala (PUU) virus recombinant nucleocapsid protein (rN) based enzyme-linked immunosorbent assay (ELISA) for the serological diagnosis of NE as compared with an immunofluorescence assay (IFA) in a clinically relevant patient sample.

STUDY DESIGN

During a four-month period, 618 serum samples from 512 patients with an illness suggestive of NE, sent to the Department of Clinical Virology for serological analysis, were included in the study. All sera were tested by PUU rN ELISA for presence of specific IgG, IgM and IgA antibodies and by IFA using PUU virus infected cells as antigen for presence of IgG and IgM antibodies. Patients with discordant results by IFA and rN ELISA were further serologically and/or clinically evaluated to assess the probability of NE.

RESULTS

Compared to IFA, the specificities of the IgM and IgG rN ELISA were 100% and the corresponding sensitivities were 94.0%. The positive and negative predictive values of the PUU IgM rN ELISA in diagnosing NE infection was 100 and 98.6%, respectively. The positive predictive values for present NE infection of IgG rN ELISA and IFA were 68.3 and 71.4%, respectively. The positive predictive value of IgA rN ELISA was 95.8% and the negative 92.7%.

CONCLUSIONS

The demonstration of specific IgM by rN ELISA is a highly specific and reliable method for the serological confirmation of NE. Detection of IgG antibodies by rN ELISA or IFA has a low predictive value to diagnose NE in an endemic area. The diagnostic value of IgA determination is in between IgM and IgG determinations.

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 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.

Human B-cell epitopes of Puumala virus nucleocapsid protein, the major antigen in early serological response

Puumala virus (PUU) is a member of the Hantavi rus genus in the family Bunyaviridae and the etiologic agent of nephropathia epidemica (NE), a form of haemorrhagic fever with renal syndrome (HFRS). In this study we compared the immunofluorescence patterns of NE sera and antibodies raised against recombinant PUU proteins and confirm that the nucleocapsid protein is the major target in the early IgG response of NE patients and provides the molecular basis for simple and rapid differentiation between acute illness and old immunity by granular vs. diffuse fluorescence staining in the indirect immunofluorescence test. The differential kinetics of B-cell responses to PUU nucleocapsid vs. envelope proteins was emphasized further by the endpoint titres of IgG antibodies to N, G1 and G2 proteins in NE patients. The granular fluorescence correlated with low IgG avidity in 99.8%, and diffuse fluorescence with high avidity in 100% of 617 NE sera studied. Epitope scanning with overlapping 14-mer peptides covering the whole nucleocapsid protein by a shift of 3 amino acids revealed six major antigenic epitopes recognized by sera from acute-phase NE patients. The epitopes clustered mainly in the hydrophilic regions, and two of them in a highly variable region which could probably serve as an antigen to distinguish serologically between infections of closely related hantaviruses, some apparently apathogenic, some causing lethal infections. The anti-peptide epitope pattern varied between different individuals and a collection of several pin-bound peptides was needed to be recognised by most NE sera studied.

Development of monoclonal antibodies against Hantaan virus nucleocapsid protein

Forty-five hybridoma cell lines producing monoclonal antibodies against Hantaan virus, the etiologic agent of hemorrhagic fever with renal syndrome, were generated by fusion of P3-X63-Ag8.V653 myeloma cells with spleen cells of mice immunized with inactivated Hantaan virus vaccine. Among these, 38 antibodies were identified as binding to the 48-kDa nucleocapsid protein by immunoblot assay or radioimmunoprecipitation. Twenty-six of them were of the immunoglobulin G1 (IgG1), nine were of the IgG2a, and three were of the IgA isotype. According to cross-reactivities with other serotypes of the genus Hantavirus, the antibodies were classified into three groups: 6 antibodies specific to the Hantaan serotype (group I), 20 antibodies cross-reacting with Hantaan and Seoul serotypes (SR-11, Tchoupitoulas, and R22) (group II), and 12 antibodies cross-reacting with Hantaan, Seoul, and Prospect Hill serotypes (group III). None of the antibodies cross-reacted with the Puumala serotype. With a panel of antibodies of different cross-reactivities, serotypes of Hantavirus could be differentiated. Thirty-eight monoclonal antibodies against Hantaan virus nucleocapsid protein which have different cross-reactivities between serotypes were developed. These results confirmed the presence of multiple serotype-specific epitopes on the nucleocapsid protein of Hantaan virus, which can be utilized in differentiation of serotypes.

Seroprevalence of hantavirus antibodies in Germany as determined by a new recombinant enzyme immunoassay

In order to elucidate the epidemiological importance of hemorrhagic fever with renal syndrome in Germany, the prevalence of antibodies against hantaviruses was determined in 13,358 sera from residents of various geographic regions, 1,284 sera from occupational risk groups and 287 sera from chronic hemodialysis patients. Serological investigations were performed using a highly specific transferable solid phase enzyme immunoassay based on the recombinant nucleocapsid proteins of a Hantaan and a Puumala serotype strain. The overall antibody prevalence was found to be 1.68%. In the serum panels from western and southern Germany, it was determined to be 1.83% on average in contrast to only 0.8% in the panel from eastern Germany. An endemic focus revealing an antibody prevalence of 3.12% was detected in a low-mountain area called Suebian Alb, which is located in the federal state of Baden-Württemberg. Occupational risk groups and a group of chronic hemodialysis patients showed a significantly elevated antibody prevalence ranging from 3.3% to 10%. The Puumala serotype was found to be the prevailing virus, but the percentage of sera predominantly recognizing the Hantaan nucleocapsid protein increased towards the south and the east and was significantly elevated in dialysis patients.

Comparison of the kinetics of Puumala virus specific IgM and IgG antibody responses in nephropathia epidemica as measured by a recombinant antigen-based enzyme-linked immunosorbent assay and an immunofluorescence test

Immunoglobulin M and G (IgM and IgG) responses were followed up to 6 months in patients with nephropathia epidemica (NE) by an enzyme-linked immunosorbent assay (ELISA) using a recombinant Puumala virus (PUU) nucleocapsid protein as antigen and an immunofluorescence test (IF) using PUU infected, acetone-treated cells as antigen. The recombinant protein was produced by cloning and expressing the nucleocapsid encoding gene of PUU as a polyhistidine fusion protein in Escherichia coli. The product was purified over a metal chelating ion affinity column. On admission, all 17 patients had an IgM response by both methods. The IgM titers decreased significantly by both methods 3 months after onset (ELISA P < 0.05 and IF P < 0.05). Four of six still had detectable IgM, however at low levels, after 6 months. Presence of specific IgG differed significantly on admission between the two methods: by ELISA 8 of 17 had detectable specific IgG, whereas by IF 15 of 17 had specific IgG (P < 0.02). There were 10 significant titer rises between acute and convalescent serum samples in the same patients by both methods. It is concluded that the IgG antibody response differs in the early phase of NE as measured by a method using a recombinant PUU nucleocapsid protein and a method using PUU infected acetone-treated cells as antigens. Furthermore, the results suggest that it is of importance to rely on specific IgM for serodiagnosis of NE during the acute phase.

Mapping of B-cell determinants in the nucleocapsid protein of Puumala virus: definition of epitopes specific for acute immunoglobulin G recognition in humans

The complete amino acid sequence of the Puumala (PUU) virus nucleocapsid protein (N), deduced from the genome of the prototype strain Sotkamo, was synthesized as decapeptides with 5-amino-acid overlaps. By use of the PEPSCAN method, 86 peptides were examined for reactivity with sera from serologically confirmed nephropathia epidemica (NE) patients and 11 PUU virus N-specific bank vole monoclonal antibodies. The human sera showed reactivity with several different regions, while only one of the monoclonal antibodies reacted with one single peptide. Sequences were selected by this PEPSCAN analysis of human antibody reactivities, and five 15-amino-acid peptides were synthesized and evaluated as antigens by an enzyme-linked immunosorbent assay (ELISA). Peptide-reactive antibodies of the immunoglobulin M (IgM) class were measured in serum samples drawn from patients with acute NE. In comparison with the results of a mu-capture IgM ELISA using native PUU virus antigen, only a few serum samples were found positive (sensitivity, 2 to 10%). Interestingly, when antibodies of the IgG class were measured, the sensitivities of the five peptide ELISAs were found to be 79, 46, 2, 100, and 40%, respectively, as compared with the sensitivity of an IgG ELISA based on native viral antigen. The IgG reactivities of sequentially drawn sera from NE patients with the two peptides giving the highest assay sensitivities were analyzed and compared with their reactivities with native viral antigen. All patients had detectable anti-peptide IgG in the acute-phase sample, which, however, had totally declined in samples drawn after 2 years. The opposite pattern was seen with native viral antigen, in which case all patients showed the highest levels of specific IgG after 2 years. The results suggest the presence of epitopes specific for the acute IgG response.

Rapid differentiation between Hantaan and Seoul viruses by polymerase chain reaction and restriction enzyme analysis

The majority of causative strains of hemorrhagic fever with renal syndrome (HFRS) are known as Hantaan and Seoul viruses in Korea. The clinical manifestations may be indistinguishable between both viruses, although the clinical course of Hantaan virus infection is more severe than that of the Seoul virus. Therefore, the differentiation of Hantaan or Seoul virus may be important for predicting the prognosis. The primers were selected from the published sequences of the S segments of Hantaan virus strain 76-118 and Seoul virus strain SR-11, which made it possible to obtain the same size of 403 bp amplified product by reverse transcriptase polymerase chain reaction (RT-PCR) and nested PCR from both viral strains. The differentiation of the amplified products was carried out by restriction enzyme digestion. With HindIII, the 403 bp amplified product from Hantaan virus strain 76-118 was cleaved into two segments of 175 bp and 228 bp. By contrast, the 403 bp product from Seoul virus strain SR-11 was not cut by HindIII. With HinfI, the 403 bp amplified product from Hantaan virus strain 76-118 was divided into two bands of 280 bp and 60 bp on the electrophoresis. In the case of the digestion of 403 bp PCR product from Seoul virus strain SR-11 with HinfI, more than four bands (155 bp, 115 bp, 60 bp, and 32/29 bp) were observed on the 2% agarose gel electrophoresis. This rapid technique may be useful for the differential diagnosis of Asian HFRS in Korea.

Serological evidence of Hantavirus disease in Northern Ireland

Since, to our knowledge, no clinically documented cases of haemorrhagic fever with renal syndrome (HFRS) have been reported in Northern Ireland, a sero-epidemiological study was carried out to assess the degree of Hantavirus immunity in a group of 627 Northern Irish patients presenting with symptoms suggestive of HFRS and 100 healthy controls. IFA screening for IgG Hantavirus specific antibodies was carried out with a panel of up to 9 different Hantaviral antigens. IgM screening was performed using a commercially available mu-capture ELISA based upon two recombinant Hantaviral nucleocapsid antigens. A seropositivity of 2.1% (15/727) was recorded, with an almost exclusive reaction against a rat-derived R22VP30 strain of the Seoul serotype. Sole reliance upon non-rat-derived classic screening antigens Hantaan (HTN 76-118) and Puumala (CG 18-20) would have resulted in the detection of only 2/15 (13.3%) of cases in IgG IFA, and 8/14 (57.1%) of the cases in IgG ELISA. The findings indicate that for the first time in Europe, and more specifically in N. Ireland, non-laboratory outbreaks of HFRS may be caused by wild rats acting as a reservoir for a Seoul-like Hantavirus. Conventional Hantavirus serology using Hantaan and Puumala as screening antigens does not appear sufficient for the detection of such cases of HFRS. Hence, we propose the addition of a rat derived Hantaviral antigen to the antigen screening panel as a means of improving the specificity of the detection methods.

Class and subclass distribution of Hantavirus-specific serum antibodies at different times after the onset of nephropathia epidemica

Sera from Dutch and Belgium individuals who suffered from nephropathia epidemica (NE), a mild form of haemorrhagic fever with renal syndrome (HFRS), were tested for the distribution of classes and subclasses of Hantavirus (HV)-specific antibodies at different times after the onset of the disease, with class- and subclass-specific Ig capture enzyme-linked immunosorbent assays (ELISAs). In the acute, early convalescent, and convalescent phases, predominantly specific IgA, IgM, and IgG3 antibodies were detected. Specific IgG2 antibodies were only detected at low levels in the early convalescent and convalescent phases. In the late convalescent phase specific IgG1 and IgG3 antibodies were found, whereas in the late postconvalescent phase only specific IgG1 antibodies proved to be present. Specific IgG4 antibodies were not detected in any of the respective phases. These data show that the simultaneous determination of classes and subclasses of HV specific serum antibodies allows the estimation of the time elapsed after the onset of NE.

Baculovirus expression of the nucleocapsid protein of a Puumala serotype Hantavirus

Recombinant baculoviruses were generated harboring the entire coding region of the S segment cDNA of Hantavirus strain CG 18-20 that belongs to the Puumala serotype. The recombinant nucleocapsid protein was expressed in Sf9 cells and shown to be antigenically identical with the authentic viral nucleocapsid protein by means of immunoblot analysis. Acute-phase and convalescent sera from European HFRS patients recognized the recombinant nucleocapsid protein in Western blots and the recombinant Baculovirus in indirect immunofluorescence assays. Insect cells infected with the recombinant Baculoviruses proved to be a suitable noninfectious substitute for Hantavirus-infected Vero E6 cells as an antigen source for immunodiagnostic assays allowing the detection of antibodies in HFRS patients.

Utilization of autopsy RNA for the synthesis of the nucleocapsid antigen of a newly recognized virus associated with hantavirus pulmonary syndrome

A newly recognized hantavirus was recently found to be associated with an outbreak of acute respiratory illness in the southwestern United States. The disease, which has become known as hantavirus pulmonary syndrome, has an unusually high mortality (64%). Virus isolation attempts have been unsuccessful thus far, resulting in a lack of homologous antigen for use in diagnostic assays. For this reason, a molecular approach was initiated to produce recombinant homologous antigen. The virus nucleocapsid (N) protein was selected, since N has been shown to be a sensitive antigenic target in other hantavirus systems. The N protein open reading frame of the virus S genome segment was synthesized from frozen autopsy tissue by polymerase chain reaction amplification, followed by cloning and expression in Hela cells (vaccinia-T7 RNA polymerase system) and Escherichia coli. N protein-expressing Hela cells served as excellent antigens for an improved indirect immunofluorescence assay. Use of the E. coli-expressed N protein in an enzyme-linked immunosorbent assay improved the sensitivity and specificity when compared with heterologous antigens used previously. Preliminary analysis also indicates that the higher sensitivity could result in earlier detection of infected persons. These data demonstrate that even in the absence of a virus isolate, the necessary homologous antigen can be produced and can serve to improve the detection and diagnostic capabilities needed to combat this newly recognized fatal respiratory illness in the United States.

A novel mu-capture enzyme-linked immunosorbent assay based on recombinant proteins for sensitive and specific diagnosis of hemorrhagic fever with renal syndrome

Hantavirus nucleocapsid protein has recently been identified as a major antigen inducing an early and long-lasting humoral immune response in patients with hemorrhagic fever with renal syndrome. A mu-capture enzyme-linked immunosorbent assay utilizing recombinant nucleocapsid proteins of Hantavirus strains Hantaan 76-118 (Hantaan serotype) and CG 18-20 (Puumala serotype) as diagnostic antigens and specific monoclonal antibodies as the detection system has been developed. Histidine-tailed recombinant proteins were expressed in Escherichia coli and purified in a single step by affinity chromatography on a nickel-chelate resin. The assay was evaluated with a panel of sera from patients with hemorrhagic fever with renal syndrome originating from various geographic regions. The overall sensitivity of the mu-capture enzyme-linked immunosorbent assay (both recombinant antigens) was 100%, and its specificity was also found to be 100%. Immunoglobulin M antibodies were detected as early as on day 3, and maximum titers were obtained between days 8 and 25 after onset of the disease. The assay was regularly found to be positive within 3 to 4 months but in some cases up to 2 years after the acute phase of the disease.

The humoral response to Puumala virus infection (nephropathia epidemica) investigated by viral protein specific immunoassays

Enzyme-linked immunosorbent assays for determination of antibodies directed to the nucleocapsid protein (N) or to either of the two envelope glycoproteins (G1 and G2) of Puumala virus were designed and evaluated. The assays were proven to be entirely restricted for each viral structural protein by biotin-labelled monoclonal antibodies. Sera from sequentially bled nephropathia epidemica patients (acute, convalescent, and 2-year sera) and sera from 10-20 year convalescents were examined for antibody specificity. All but one (n = 19) acute phase sera were shown to contain IgM antibodies directed to all three viral proteins. In the convalescent specimens the proportions of IgM to the different viral components were similar, but lower, when compared to the acute samples. Low levels of IgM against N and G2 were found in two out of ten 2-year sera. No virus-specific IgM were detected in sera drawn 10-20 years after infection. IgG antibodies to all three viral proteins were detected in all except one acute phase serum. The IgG response initially increased more rapidly to N, as compared to the anti-glycoprotein responses. The levels of glycoprotein-specific IgG were considerably increased 2 years after the disease, when compared to the levels detected in the convalescent specimens. The levels and specificities of IgG in very late convalescent sera (drawn 10-20 years after disease) resembled those detected 2 years after infection.

Use of recombinant nucleocapsid proteins of the Hantaan and nephropathia epidemica serotypes of Hantaviruses as immunodiagnostic antigens

Hantavirus nucleocapsid protein has previously been identified as the major antigen recognized by the humoral immune response in hemorrhagic fever with renal syndrome (HFRS). It was therefore considered to be a suitable antigen for the development of rapid and reliable immunodiagnostic assays. Genes encoding the nucleocapsid proteins of two Hantavirus strains, one of the Puumala serotype [nephropathia epidemica virus (NEV)] and the other of the Hantaan serotype were expressed in E. coli, and the expression products were used as diagnostic antigens in solid-phase enzyme immunoassays. The assays were used to detect IgG- and IgM-antibodies in sera of HFRS patients originating from different geographic regions (China, Germany, Greece, Yugoslavia, Scandinavia). ELISA was highly sensitive and proved to be superior to the indirect immunofluorescence assay. Both antigens were necessary to diagnose all HFRS cases originating from the different countries. Most of the sera revealed a predominant reactivity with either 1 of the 2 antigens, allowing the characterization of the etiologic virus as Hantaan-like or NEV-like. The results of the analysis of sera obtained from China and Greece suggested that the Hantaviruses prevalent in these countries are closely related to the Hantaan serotype. In contrast, an NEV-like reactivity was observed in Central and Northern European patients. In the sera of Yugoslav patients both reactivity patterns were found, suggesting that both virus types occur in the Balkan region.

Puumala virus antibody and immunoglobulin G avidity assays based on a recombinant nucleocapsid antigen

Puumala virus is the causative agent of nephropathia epidemica (NE), a hantavirus infection which occurs widely in northern and central Europe and is generally diagnosed by the indirect immunofluorescence (IF) method. We have now expressed the Puumala virus Sotkamo strain nucleocapsid (N) protein-coding S genome segment as a beta-galactosidase fusion protein in Escherichia coli by using the pEX2 expression vector. The recombinant protein was purified by cutting the protein band from an agarose gel, melting the agarose, and removing the protein by freezing, incubation on ice, and centrifugation. The recovery was about 1 to 5 mg/200 ml of bacterial suspension, sufficient for coating 100 to 500 enzyme immunoassay microtiter plates. In a study of 312 IF-positive and 233 IF-negative serum samples from NE patients, the recombinant-N-protein enzyme immunoassay detected immunoglobulin G antibodies to Puumala virus with 97.8% sensitivity and 98.5% specificity compared with the IF test results. In addition, an immunoglobulin G avidity enzyme immunoassay was developed and used successfully to diagnose acute NE from a single serum sample. The results demonstrate that the bioengineered antigen is suitable for use in routine diagnostic assays for Puumala virus immunity and recent infection.

Serum antibodies to structural proteins of hantavirus arise at different times after infection

An enzyme-linked immunosorbent assay (ELISA) was developed for the quantification of serum antibodies against group-specific epitopes of the glycoproteins (G1, G2) and nucleoprotein (NP) of the genus Hantavirus. This assay was used to study the kinetics of the development of serum antibodies after natural infection with Puumala-like virus in humans. To this end a panel of 34 serum samples collected from individuals at different times after natural infection was tested by the ELISA. The samples were also tested for specific IgM and IgG levels against Puumala-like virus, which provided confirmatory data about the presumed timing of infection. It was shown that serum antibodies against the G1 epitope were present in the acute and early convalescent period just before antibodies to the NP epitope could be demonstrated. In contrast, antibodies to two G2 epitopes were present not earlier than in the convalescent and late convalescent period. Since all these categories of antibodies seem to persist for long periods, antibodies against the G1 epitope and the NP epitope may be of specific diagnostic value. Furthermore, levels of G1-specific antibodies and antibodies to either NP or G2 may allow estimation of the time elapsed following initial infection.

Primary structure of the large (L) RNA segment of nephropathia epidemica virus strain Hällnäs B1 coding for the viral RNA polymerase

The L RNA segment of the nephropathia epidemica virus (NEV) strain Hällnäs B1 was characterized by molecular cloning of the corresponding cDNA and subsequent determination of the DNA nucleotide sequence. The L RNA segment is 6550 nucleotides long with complementarity of 20 bases at the 3' and 5' termini. The viral messenger sense RNA contains one major open reading frame (ORF) with a coding capacity of 2156 amino acid residues encoding a protein with a calculated molecular weight of 246 kDa and an IEP of pH 7.4. Comparison of the deduced amino acid sequences from NEV hantavirus and Bunyamwera virus (BWV) L segment messenger sense RNAs, revealed a high degree of diversity (overall amino acid identity, 17%). However, three clusters of 30-40% amino acid identity were detected. One of these domains, containing an Asp-Asp motif found in many RNA polymerases, also shares amino acid sequence homology with the PB1 polymerase component of influenza type A. These results indicate that the L RNA segment of the NEV codes for the viral RNA-dependent RNA polymerase. The data presented here complete our previous studies on the characterization of the NEV genome by cDNA sequencing of the viral M and S RNA segments.

Identification and characterization of a Hantavirus strain of unknown origin by nucleotide sequence analysis of the cDNA derived from the viral S RNA segment

The genetic characterization of a serologically Hantaan-like virus but of unknown origin (termed DX) was carried out by molecular cloning and nucleotide sequencing of the corresponding cDNA of the viral S RNA segment. The S RNA was found to be 1765 nucleotides long with 3' and 5' termini being complementary for 24 bases. The virus messenger-sense RNA contains one major open reading frame (ORF) encoding 428 amino acids or a 50 kD polypeptide. A comparison of the DX S RNA segment to those of Sapporo rat, Hantaan, Puumala/Hällnäs B1, and Prospect Hill viruses reveals 95.4, 71.3, 55.3, and 60.9% homology at the nucleotide sequence level, and 94.7, 80.1, 58.4, and 59.8% at the deduced amino acid sequence level. Thus Hantavirus strain DX is very closely related to Sapporo rat virus. We also analyzed the S RNA segments of these Hantaviruses for the presence of a second ORF encoding a potential nonstructural NSs protein. All potential second ORFs detected in the different S RNA segments differ substantially in length and position among the viruses, despite the high conservation of the nucleotide sequences and the overall structure of the nucleocapsid proteins. This suggests that the nucleocapsid protein is the only polypeptide encoded by Hantavirus S RNA segments, setting them apart from the other members of the Bunyaviridae family.

Antigenicity of hantavirus nucleocapsid proteins expressed in E. coli

DNA clones representing the small genomic segment of Nephropathia epidemica virus strain Hällnäs B1 (NEV) and Hantaan virus strain 76-118 (HTV) encoding their nucleocapsid proteins were inserted into the E. coli vector pIN-III-ompA for secretion of proteins into the periplasmic space. The complete HTV and NEV nucleocapsid proteins and two truncated versions of the NEV nucleocapsid proteins were expressed as fusion proteins. Unexpectedly, all products accumulated as insoluble aggregates. Most of the ompA signal peptide remained uncleaved. However, nucleocapsid fusion proteins could be purified from the insoluble fraction by extraction with 8 M urea followed by separation on SDS-PAGE and electroelution. Rabbits were immunized with the eluted proteins and the resulting antibodies reacted specifically with authentic viral nucleocapsid proteins of HTV and NEV. The recombinant nucleocapsid proteins were found to react specifically with various hantavirus-immune sera, but not with human control sera, indicating their suitability as potential diagnostic antigens. This is the first report on the expression of a protein of a NEV serotype strain of hantaviruses by use of recombinant DNA techniques.

Identification of Hantavirus serotypes by testing of post-infection sera in immunofluorescence and enzyme-linked immunosorbent assays

Serum samples were collected from 27 individuals who had been infected with a member of the genus Hantavirus in the Netherlands or Belgium during the last 15 years. These samples were tested in an immunofluorescence assay (IFA) and two enzyme-linked immunosorbent assay (ELISA) systems, using different virus strains that represented each of the four recently proposed serotypes of this genus. The serum samples from 11 individuals who had been infected through contacts with laboratory rats showed the highest reactivities with Hantaan virus (serotype I) and SR-11 (serotype II) in the IFA and ELISA systems. The samples of 16 individuals who had probably been infected through contacts with wild rodents showed the highest reactivities with Hällnäs virus (serotype III) in the IFA. All except two of these also showed the highest reactivity with Hällnäs virus in the two different ELISA systems.

Rapid detection of genomic variations in different strains of hantaviruses by polymerase chain reaction techniques and nucleotide sequence analysis

The polymerase chain reaction (PCR) with subsequent nucleotide sequence analysis was employed to rapidly detect genomic variations among different Hantavirus strains. Using synthetic oligonucleotide primers derived from the M and S segment RNAs of nephropathia epidemica virus strain Hällnäs B1 (NEV) we succeeded in amplifying the corresponding sequences of Hantaan and Puumala viruses. The nucleotide sequences of the cDNAs derived from the Puumala M and S RNA segments were analyzed. It was found that the particular nucleotide sequences of Puumala M and S segments were 81% and 82% homologous to the corresponding genomic segments of NEV, respectively. The amino acid homology was 94% for both segments. In contrast, the degree of homology to the corresponding Hantaan M and S genomic RNA segments was 63% at the nucleotide level for both segments and 53 and 55% at the deduced amino acid level, respectively. This demonstrates that Puumala virus is very similar to NEV and significantly different from Hantaan virus at both the nucleotide and protein level.

Molecular characterization of the RNA S segment of nephropathia epidemica virus strain Hällnäs B1

The S segment RNA of nephropathia epidemica virus (NEV) strain Hällnäs B1 was isolated by molecular cloning of the corresponding cDNA. The RNA is 1785 nucleotides long with the 3' and 5' termini being complementary for 23 bases. The viral messenger-sense RNA contains one major open reading frame (ORF) with a coding capacity of 433 amino acids encoding a 49-kDa polypeptide. Compared to the Hantaan S segment cDNA sequence there is a nucleotide homology of 60 and 61% at the amino acid level. Many of the amino acid differences are conservative exchanges. The C-termini of the NEV and Hantaan nucleocapsid proteins are nearly identical and the hydrophilicity profiles are very similar. In contrast, the following differences are significant: The calculated isoelectric points of the NEV and Hantaan nucleocapsid proteins are 5.6 and 6.7, respectively. The most prominent antigenic determinants predicted by the hydrophilicity profiles are located close to the C-terminus of NEV and close to the N-terminus of Hantaan virus nucleocapsid polypeptides.

Determination of the coding capacity of the M genome segment of nephropathia epidemica virus strain Hällnäs B1 by molecular cloning and nucleotide sequence analysis

The M genome RNA segment of nephropathia epidemica virus (NEV) strain Hällnäs B1 was characterized by molecular cloning and DNA nucleotide sequencing of the corresponding cDNA clones. The size of the M RNA segment is 3682 nucleotides. The 3' and 5' terminal sequences are complementary for 21 bases and their predicted secondary structure is very stable. The viral complementary messenger RNA possesses a single long open reading frame with a coding capacity of 1148 amino acids (polypeptide of 126 kDa). A comparison of the NEV M segment to that of Hantaan virus strain 76-118 reveals 61% sequence homology at the nucleotide level and 53% at the deduced amino acid level. Four out of five potential asparagine-linked glycosylation sites of the encoded glycoproteins have been conserved between NEV and Hantaan M. The isoelectric points (IEP) are nearly identical. Furthermore it was found that 90% of all cysteine residues have been conserved. Putative NEV G1 and G2 are preceded by a short hydrophobic sequence as shown for G1 and G2 of Hantaan virus. Hydrophilicity profiles of the two segments are of striking similarity. These data indicate that NEV- and Hantaan virus M-encoded polypeptides seem to be very similar in structure and function despite the relatively low amino acid sequence homology.