Antigenic and genetic properties of viruses linked to hemorrhagic fever with renal syndrome

A major antigenic domain for the human humoral response to Puumala virus nucleocapsid protein is located at the amino-terminus

Nephropathia epidemica (NE), the major form of hemorrhagic fever with renal syndrome in Europe, is caused by the hantavirus serotype Puumala (PUU). The PUU virus nucleocapsid protein (N) has been shown to be highly immunogenic both in laboratory animals and in man. We aimed to locate domains important in humoral immune reactivity and to use this information to develop a specific and sensitive enzyme-linked immunosorbent assay (ELISA) for serological diagnosis of NE. Escherichia coli poly-histidine fusion protein expression vectors containing over-lapping gene segments encoding the PUU virus N (PUU rN) were constructed. The resulting gene products were examined by immunoblots and ELISA with polyclonal and monoclonal antibodies. The dominating antigenic region of PUU rN was located between amino acids (aa) 7 and 94. A recombinant fusion protein containing aa 7-137 of PUU virus N (PUU rN delta 5) was used for the detection of specific IgG and IgM responses in NE. ELISA based on PUU rN delta 5 was found to have equal sensitivity and specificity as compared to the full length recombinant PUU rN by ELISA, for both acute serological diagnosis of NE and for seroepidemiological screening purposes. Furthermore, this protein is easier to handle than full length PUU rN due to its higher solubility in aqueous solutions.

Vector-borne viral diseases in Sweden--a short review

Ockelbo disease, caused by a Sindbis-related virus transmitted to man by mosquitoes, was first described in the central part of Sweden in the 1960s as clusters of patients with fever, arthralgia and rash. An average annual rate of 30 cases was recorded in the 1980s but no cases have been diagnosed during the last few years. Nephropathia epidemica (NE) characterized by fever, abdominal pain and renal dysfunction has been known to cause considerable morbidity in Sweden during the last 60 years but the etiologic agent (Puumala virus) was not isolated until 1983. This virus's main reservoir is the bank vole (Clethrionomys glareolus). NE is endemic in the northern two thirds of Sweden where more than a hundred cases are diagnosed each year. Tick-borne encephalitis transmitted by Ixodes ricinus ticks is restricted to the archipelago and Lake M-alaren on the east coast close to Stockholm. Between 30 and 110 cases are diagnosed every year. Inkoo virus, a California encephalitis group virus, has been isolated from mosquitoes in Sweden. The antibody prevalence to Inkoo virus is very high in a normal population, but no disease has as yet been associated with this virus in Sweden. Among the vector-borne virus diseases imported to Sweden, dengue is the most important, with approximately 50 cases recorded every year.

Sequence analysis of the complete S genomic segment of a newly identified hantavirus isolated from the white-footed mouse (Peromyscus leucopus): phylogenetic relationship with other sigmodontine rodent-borne hantaviruses

Four Corners (FC) or Sin Nombre virus, a hantavirus harbored by the deer mouse (Peromyscus maniculatus), is the principal etiologic agent of hantavirus pulmonary syndrome (HPS). Recently, a hantavirus, designated New York (NY) virus, isolated from a white-footed mouse (Peromyscus leucopus) captured on Shelter Island, New York, was molecularly linked to a fatal case of HPS occurring in the northeastern United States. To clarify the genetic and phylogenetic relationship between NY and FC viruses and other sigmodontine rodent-borne hantaviruses, we amplified and sequenced the entire S genomic segment of NY virus. The S segment of NY virus was 2078 nucleotides long, with an open reading frame of 1284 nucleotides in the virus complementary strand, capable of encoding a protein of 428 amino acids, and with a 752-nucleotide long 3'-noncoding region, comprised of numerous imperfect repeats. Pairwise analysis indicated that NY virus was more similar to FC virus than to other sigmodontine rodent-borne hantaviruses, differing from strains of FC virus by 16.6-17.8% and 7.0-8.2% at the nucleotide and amino acid levels, respectively. As determined by the maximum parsimony and neighbor-joining methods, NY virus formed a separate lineage from FC virus and was phylogenetically distinct from hantaviruses harbored by other sigmodontine rodents. Whether or not NY and FC viruses represent distinct viral species is unclear. Further analyses of hantaviruses harbored by white-footed mice are needed to clarify the genetic diversity and evolution of Peromyscus-borne hantaviruses.

Antigenic properties and diagnostic potential of puumala virus nucleocapsid protein expressed in insect cells

Puumala virus (PUU) is a member of the genus Hantavirus in the family Bunyaviridae and the causative agent of nephropathia epidemica, a European form of hemorrhagic fever with renal syndrome. Sera of nephropathia epidemica patients react specifically with PUU nucleocapsid (N) protein. In order to safely provide large quantities of antigen for diagnostic purposes, PUU Sotkamo strain N protein was expressed by using the baculovirus system in Sf9 insect cells to up to 30 to 50% of the total cellular protein. The recombinant N protein (bac-PUU-N) was solubilized with 6 M urea, dialyzed, and purified by anion-exchange liquid chromatography. In an immunoglobulin M mu-capture assay purified and unpurified bac-PUU-N antigen showed identical results compared with the results of a similar assay based on native PUU antigen grown in Vero E6 cells. An immunoglobulin G monoclonal antibody-capture assay based on unpurified bac-PUU-N also showed results identical to those of an assay with native PUU-N antigen. Moreover, a panel of monoclonal antibodies reactive with eight different epitopes showed identical reactivity patterns with both natural and bac-PUU-N antigen, while two epitopes in PUU-N expressed as a fusion protein in Escherichia coli were not recognized. Puumala hantavirus N protein expressed by the baculovirus system offers a safe and inexpensive source of specific antigen for large-scale diagnostic and seroepidemiological purposes.

Intraocular pressure changes in nephropathia epidemica. A prospective study of 37 patients with acute systemic Puumala virus infection

BACKGROUND

Nephropathia epidemica is a zoonose in the group of hemorrhagic fevers with renal syndrome and is caused by Puumala virus in Hantavirus genus. The purpose of this study is to find out how the intraocular pressure (IOP) is affected by the acute phase of this disease and how it relates to the previous case reports on angleclosure glaucoma attacks.

PATIENTS AND METHODS

The prospective study documents IOP and anterior chamber depth measurements in 37 patients during the winter epidemic of nephropathia epidemica from 1992 to 1993. Ocular examinations were performed during the acute systemic infection and after clinical recovery.

RESULTS

The IOP was lower and the anterior chamber shallower in the acute phase than after the clinical recovery of nephropathic epidemica. The mean differences in IOP were 1.8 mmHg in the right eye and 1.9 mmHg in the left (P < 0.001) and the mean differences in the anterior chamber depth were 0.22 mm in the right eye and 0.20 mm in the left (P < 0.001). No acute angle-closure attacks with highly elevated IOP were encountered in this study. The mean IOP did not rise higher than 14.3 mmHg in both eyes after the clinical recovery of systemic infection.

CONCLUSION

In contradistinction to earlier assumptions, Puumala virus infection decreases the IOP. Shallowing of anterior chamber and narrowing of the anterior chamber angle in the acute phase of nephropathia epidemica did not lead to angle-closure attacks in this series.

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.

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 new hantavirus detected in Microtus arvalis from Slovakia

A new hantavirus, called Malacky, has been identified in lung tissue specimens of a vole, Microtus arvalis, by the reverse transcriptase polymerase chain reaction (RT-PCR). The voles were trapped in a geographical area in Slovakia where hemorrhagic fever with renal syndrome (HFRS) is endemic in the human population. Sequence analysis of a major part of the S segment showed this virus to represent a new subtype within Tula, a new hantavirus genetic group defined very recently.

Nucleocapsid- and virus-like particles assemble in cells infected with recombinant baculoviruses or vaccinia viruses expressing the M and the S segments of Hantaan virus

The formation of Hantaan (HTN) virus nucleocapsid-like structures (NLS) or virus-like particles (VLP) from expressed gene products was investigated in two eukaryotic systems. Baculovirus expression of the HTN virus small segment (S), which encodes the viral nucleocapsid protein, resulted in assembly of NLS inside infected insect cells. The NLS and authentic ribonucleocapsids, prepared by detergent disruption of HTN virions, had similar sedimentation characteristics and morphologies, and were recognized by HTN virus N-specific antibodies. Co-expression of S and the medium segment (M), which encodes the two viral envelope glycoproteins (G1 and G2), did not efficiently generate VLP in the baculovirus-insect cell system, but VLP were observed in lysates and supernatants of cells infected with a recombinant vaccinia virus co-expressing HTN virus M and S. The VLP sedimented in sucrose to densities consistent with HTN virions, and some of them bore a striking resemblance to Hantaan virions when examined by immunoelectron microscopy.

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.

Effect of MDP-Lys(L18), a derivative of MDP, on enhancing host resistance against Hantaan virus infection in newborn mice

We examined the effect of MDP-Lys(L18), a lipophilic derivative of muramyl dipeptide, on the enhancement of host resistance against virus infection in newborn mice. Newborn mice were inoculated with 4 LD50/mouse of Hantaan virus strain 76-118 (HTN) one day after birth. Mice given 100 micrograms/mouse of MDP-Lys(L18) before infection exhibited significantly higher survival rates than those of non-treated mice. The effect of MDP-Lys(L18) was also restorative when given to the mice 4 or 7 days after infection. The titers of virus isolated from the lungs and spleens 12 days after infection, were about 30-times lower in MDP-Lys(L18)-treated (lung: 1.0 x 10(3) FFU; spleen: 6.8 x 10(1) FFU/mouse), than those of non-treated mice (lung: 3.4 x 10(4) FFU; spleen: 1.9 x 10(3) FFU/mouse). Furthermore, the virus was undetectable in the brains of MDP-Lys(L18)-treated mice, whereas viruses were isolated from 3 of 6 non-treated mice. MDP-Lys(L18) augmented the number of peripheral leukocytes and splenocytes, as well as mitogenic responses of the cells from bone marrow and spleen of newborn mice. These results suggest that MDP-Lys(L18) enhanced the resistance of newborn mice against HTN virus in a systemic infection model, and that this mechanism is involved in the enhancement of hematopoiesis and responsiveness of immune-related cells to mitogens.

Antigenic relationships of hantavirus strains analysed by monoclonal antibodies

The antigenic relationships among 71 hantavirus strains, isolated from rodent species or humans in several geographic regions, were examined by immunofluorescence assay (IFA) using human patient sera and a panel of 22 monoclonal antibodies prepared against Hantaan, Seoul, and Puumala viruses. The study included virus strains, mainly from the former USSR, for which little or no serological data were available. Fifty-nine of the 71 isolates could be placed into five antigenic groups of hantaviruses, Hantaan (HTN), Puumala (PUU), Seoul (SEO), Prospect Hill (PH), Dobrava/Belgrade (DOB). Twelve isolates were found antigenically closely related to, but distinct from, HTN (2 strains), PUU (4 strains) and PH (6 strains), respectively. The antigenic characteristics of these 12 isolates suggested two supplementary antigenic subgroups of HTN, one of PUU, and two of PH. The two antigenic subgroups of HTN included strains isolated in the Far-East of Russia. The PUU subgroup included strains isolated in European Russia as well as strains isolated in Far-Eastern Russia. The PH group comprised two subgroups, both represented by strains isolated from M. fortis in Far-Eastern Russia. The results showed that the PUU and PH antigenic groups are more complex than previously known and that PH-like virus strains isolated in Russia are antigenically more closely related to PUU virus when compared to prototype PH virus isolated in the USA.

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.

Sensitive detection of hantaviruses by biotin-streptavidin enhanced immunoassays based on bank vole monoclonal antibodies

Antigen capture enzyme-linked immunosorbent assays (ELISAs) based on detection of the viral nucleocapsid protein (N) were designed for rapid diagnosis of hantavirus infections. Several combinations of bank vole (Clethrionomys glareolus) monoclonal antibodies with various N-epitope specificities were used for the development of two double-antibody sandwich forms of ELISA; PUU virus AG-ELISA for an exclusive detection of Puumala-related viruses, and Hantavirus AG-ELISA for a more extensive detection of all serotypes of hemorrhagic fever with renal syndrome (HFRS) viruses. The biotin-streptavidin system, in combination with horseradish peroxidase, rendered the assays' sensitivities similar to or even higher than immunoblotting. Calculated detection limits for the PUU virus and the Hantavirus AG-ELISAs were 405 and 50 focus forming units or 80 and 10 infected Vero E6 cells, respectively. The assays were evaluated and found to be suitable for convenient and routine detection of hantaviruses in cell cultures and in infected animal tissue.

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.

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.

Effect of interferon-alpha and cell differentiation on Puumala virus infection in human monocyte/macrophages

Pathogenesis of hantavirus infections is poorly understood. Puumala virus (PUU) is the etiologic agent of nephropathia epidemica, a form of hemorrhagic fever with renal syndrome common in Europe. We have studied PUU infection in primary human monocyte/macrophages and specifically the role of interferon alpha (IFN-alpha) and cell differentiation in it. PUU infection proceeded at a low level in monocyte/macrophages, and nucleocapsid (N) protein accumulation started 2 days postinfection. IFN-induced antiviral MxA protein was detected 3 days postinfection, suggesting IFN-alpha production in culture. IFN-alpha titers remained low, proposing that PUU is a poor IFN inducer. However, the PUU-induced IFN had an inhibitory effect on virus production as was shown by the effect of anti-IFN-alpha. Pretreatment of cells with IFN-alpha caused a dose-dependent inhibition of PUU N accumulation and reduced the yield of infectious virus. Monocytic U-937 cells overexpressing MxA protein were susceptible to PUU, suggesting that, unlike in some other negative strand RNA virus infections, MxA does not mediate resistance to PUU infection. Differentiation of monocyte/macrophages in culture and treatment of THP-1 promonocytic cells with phorbol 12-myristate 13-acetate made the cells more susceptible to PUU. The increased susceptibility of mature macrophages to PUU suggests that after differentiation to tissue macrophages they might function in the spread of the virus during PUU infection.

Hantaviruses: clinical, microbiologic, and epidemiologic aspects

Hantaviruses comprise a genus of the family Bunyaviridae. Bunyaviruses are enveloped viruses with a negative-sense, tripartite RNA genome. Hantaviruses are etiologic agents for two acute and severe illnesses of man, hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Each hantavirus is primarily associated with a single rodent host species or genus, and is transmitted to man through accidental inhalation or ingestion of virus-contaminated rodent excreta. The distribution of hantaviruses is worldwide. HFRS is caused by infection with Hantaan, Seoul, Dobrava/Belgrade, and Puumala hantaviruses, all of which are enzootic in murid rodents of Old World origin. HPS is caused by any of several hantavirus species associated with indigenous New World rodents of the subfamily Sigmodontinae, family Muridae. HFRS and HPS have numerous common epidemiologic, clinical, and laboratory characteristics. Common features include fever, myalgia, thrombocytopenia, neutrophilia, and a profound capillary leak syndrome associated with hypotension, decreased cardiac output, and shock. Worldwide, HPS is much less common than HFRS but is associated with a higher mortality rate. Recovery from hantavirus disease is generally complete, although chronic renal insufficiency may be a rare sequel of HFRS.

Protection against hantavirus infection by dam's immunity transferred vertically to neonates

Antibodies to hantavirus, Seoul type B-1 strain, vertically transferred to rat neonates prevented lethal as well as persistent infection. When relatively high titer viruses were inoculated into neonates, the mother's antibodies protected all the neonates from lethal virus infection. However, the antibodies could not protect all of the neonates from persistent infection but only half of them underwent persistent infection. The other half was completely cured but also became persistently infected when rechallenged with the active viruses after reaching maturity.

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.

Myopic shift and its mechanism in nephropathia epidemica or Puumala virus infection

Nephropathia epidemica (NE) is a zoonose caused by Puumala virus. NE belongs to the group of haemorrhagic fevers with renal syndrome. Transient myopia has been described in the acute phase of the disease. This prospective study presents the changes of refraction and the results of ophthalmic A scan measurements of patients who were managed at Savonlinna Central Hospital for NE during an epidemic in the winter of 1992-3. This involved 37 patients and 74 eyes. The incidence of transient myopia was 8.1% and that of myopic shift 40.5%. A scan ultrasound measurements were performed in patients in the acute phase and after total recovery of their general illness. Statistical analysis revealed that there were significant differences in anterior chamber depth and lens thickness between the acute and control phases of the disease and between the patients who had myopic shift compared with those who did not have a significant myopic change in refraction. Based on these results it seems that the reason for transient myopic shift of NE is mainly a combination of two factors: forward movement of the anterior diaphragm and thickening of the crystalline lens. The term myopic shift should be used rather than transient myopia because it better describes the overall refractive change in NE.

Tula virus: a newly detected hantavirus carried by European common voles

A novel hantavirus has been discovered in European common voles, Microtus arvalis and Microtus rossiaemeridionalis. According to sequencing data for the genomic RNA S segment and nucleocapsid protein and data obtained by immunoblotting with a panel of monoclonal antibodies, the virus, designated Tula virus, is a distinct novel member of the genus Hantavirus. Phylogenetic analyses of Tula virus indicate that it is most closely related to Prospect Hill, Puumala, and Muerto Canyon viruses. The results support the view that the evolution of hantaviruses follows that of their primary carriers. Comparison of strains circulating within a local rodent population revealed a genetic drift via accumulation of base substitutions and deletions or insertions. The Tula virus population from individual animals is represented by quasispecies, indicating the potential for rapid evolution of the agent.

Strand-specific detection of Hantaan virus RNA sequences by in vitro DNA amplification

Hantaan virus often causes a fatal human disease, hemorrhagic fever with renal syndrome (HFRS). An assay for strand-specific detection and quantitation of Hantaan virus RNA was developed based on the polymerase chain reaction (PCR). A protocol for the efficient detection of both genomic RNA and its transcript is presented, in which a reverse transcriptase reaction (RTR) followed by PCR with two common primers was used to distinguish between positive- and negative-stranded RNA. Using this method, the growth characteristics of Hantaan virus, strain 76-118, were studied in Vero E6 cells. Positive-stranded RNA was detected on the next day after infection, and the amount increased remarkably beginning from 3 days after infection. The negative-stranded RNA (genomic), was detected at 2 days after infection which predominated over the transcript RNA. Three days after infection, the amount of viral RNA attained 80% of the maximum amount which was detected by 6 days after infection, while, 4 days after infection the amount of the positive-stranded RNA became over 80% of the maximum amount of 6 days after infection and reached the amount of viral RNA. Both RNAs reached plateaus at 6 days after infection and after that the amounts of synthesized viral RNA and its transcripts were constant.

Haemorrhagic fever with renal syndrome in Korean children. Korean Society of Pediatric Nephrology

Haemorrhagic fever with renal syndrome (HFRS) is an acute disease caused by Hantavirus and clinically characterised by abrupt onset of fever, various haemorrhagic manifestations and transient renal and hepatic dysfunction. We retrospectively reviewed 63 cases of HFRS in children from 13 different hospitals in Korea who presented over a 15-year period. The age of the patients ranged from 7 to 15 years, with a male to female ratio of 8 to 1. Fifty-four (86%) patients were 10 years or older. On admission, 24 (38%) were in the febrile phase and 35 (56%) were in the oliguric phase. Fever (100%) abdominal pain (91%), headache (76%) and vomiting (73%) were the most common symptoms. Backache, subconjunctival haemorrhage and hypertension were also noted in about one-third of patients. Hypotension was documented in only 7 (11%) patients. Leucocytosis (> 10,000/mm3) and thrombocytopenia (< 150,000/mm3) were noted in more than two-thirds of patients. Elevated blood urea nitrogen and serum creatinine was observed in 94% by the 7th (median) day of illness. Elevated aspartate aminotransferase and/or alanine aminotransferase were found in more than two-thirds of patients. Renal biopsy was performed in 12 patients and revealed various stages of acute tubular necrosis with occasional interstitial cell infiltration and oedema. Only 2 showed evidence of interstitial haemorrhage. Eleven patients required 1-3 days of dialysis and the remaining patients required only conservative management. Three (5%) patients died of shock, respiratory failure and pulmonary haemorrhage. All other patients recovered without sequelae. Although childhood cases were much less common than adults, clinical and laboratory findings were in general similar between children and adults.

Hemorrhagic fever with renal syndrome: a study of sequelae following nephropathia epidemica

Sequelae following Nephropathia epidemica (NE) were investigated in 792 individuals living in an endemic area of Sweden. Volunteers were tested for presence of Puumala (PUU) virus specific IgG antibodies in serum, as well as several parameters linked with renal dysfunction and cardiovascular disease (systolic and diastolic blood pressure, ECG, BMI, total cholesterol and serum creatinine). No differences were seen in any of the variables tested between PUU virus antibody positive (n = 110) and negative individuals (n = 682). In addition, the blood pressure was measured in 62 serologically confirmed patients diagnosed with clinical NE 2-6 years previously. One patient with moderate hypertension was found.

Characterization of human antibody responses to four corners hantavirus infections among patients with hantavirus pulmonary syndrome

Hantavirus pulmonary syndrome (HPS) is a human disease caused by a newly identified hantavirus, which we will refer to as Four Corners virus (FCV). FCV is related most closely to Puumala virus (PUU) and to Prospect Hill virus (PHV). Twenty-five acute HPS serum samples were tested for immunoglobulin G (IgG) and IgM antibody reactivities to FCV-encoded recombinant proteins in Western blot (immunoblot) assays. All HPS serum samples contained both IgG and IgM antibodies to the FCV nucleocapsid (N) protein. FCV N antibodies cross-reacted with PUU N and PHV N proteins. A dominant FCV N epitope was mapped to the segment between amino acids 17 and 59 (QLVTARQKLKDAERAVELDPDDVNKSTLQSRRAAVSALETKLG). All HPS serum samples contained IgG antibodies to the FCV glycoprotein-1 (G1) protein, and 21 of 25 serum samples contained FCV G1 IgM antibodies. The FCV G1 antibodies did not cross-react with PUU G1 and PHV G1 proteins. The FCV G1 type-specific antibody reactivity mapped to a segment between amino acids 59 and 89 (LKIESSCNFDLHVPATTTQKYNQVDWTKKSS). One hundred twenty-eight control serum samples were tested for IgG reactivities to the FCV N and G1 proteins. Nine (7.0%) contained FCV N reactivities, 3 (2.3%) contained FCV G1 reactivities, and one (0.8%) contained both FCV N and FCV G1 reactivities. The epitopes recognized by antibodies present in control serum samples were different from the epitopes recognized by HPS antibodies, suggesting that the control antibody reactivities were unrelated to FCV infections. These reagents constitute a type-specific assay for FCV antibodies.

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.

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.

High frequency of antibodies to Hantaan virus and hepatitis C virus in chronic haemodialysis patients. Coincidence or cross-reaction?

OBJECTIVES

To address the question of whether there is any coincidence or cross-reaction between hepatitis C virus (HCV) and Hantaan virus (both RNA arboviruses), as well as to assess the frequency of antibodies to the above viruses amongst chronic haemodialysis patients in our region.

DESIGN

Collection of serum samples from consecutive unselected chronic haemodialysis patients.

SETTING

A tertiary referral center (University Hospital).

SUBJECTS

One hundred and fourteen chronic haemodialysis patients were investigated for the presence of antibodies to HCV (anti-HCV) and Hantaan virus disease (anti-HVD). Eleven unselected non-haemodialysis patients with well-defined haemorrhagic fever with renal syndrome (HFRS) were also investigated for the anti-HCV antibodies comprising the disease control group.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

The utility of an anti-HVD positive test in chronic haemodialysis patients.

RESULTS

Seventeen patients (14.9% 95% confidence interval [CI] 8.4-21.4%) were anti-HCV positive, whereas 15 (13.2%, 95% CI 6.9-19.3%) were anti-HVD positive. An anti-HCV positive test was confirmed by recombinant immunoblot assay (RIBA II) in 88.2%. The presence of anti-HCV antibodies was not associated with transfusions but with the longer duration of haemodialysis (62.8 +/- 29.8 vs. 31.2 +/- 29.3 months, P < 0.001). Anti-HVD antibodies were not associated with transfusions or with the duration of haemodialysis. Three patients were positive for both anti-HCV and anti-HVD antibodies. None of the 11 patients with well-defined HFRS had anti-HCV antibodies.

CONCLUSIONS

Chronic haemodialysis patients are a high risk group for HCV infection in association with the duration of haemodialysis and, at least for our geographical area, these patients have to be examined for anti-HVD antibodies especially when a definite causative agent for chronic renal failure is not found. The HVD and HCV infection are not exceptional amongst haemodialysis patients in our region, whereas the possibility of a cross-reaction between these two RNA arboviruses is rather excluded as there was no evidence of HCV infection amongst the patients with well-defined HFRS.

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

Hemorrhagic fever with renal syndrome (HFRS) is caused by viruses in the Hantavirus genus, family Bunyaviridae. Three serologically distinct hantaviruses, Hantaan, Seoul and Puumala viruses, are known to cause HFRS. We report here, for the first time, gene sequences of two human Puumala virus isolates, P360 and K27, obtained in an HFRS endemic region of the former Soviet Union. We compared the nucleotide sequences and the derived amino acid sequences of their gene products to a Puumala virus isolate from rodents.

Anti-idiotypic antibodies against Puumala virus glycoprotein-specific monoclonal antibodies inhibit virus infection in cell cultures

Rabbit anti-idiotypic antibodies (anti-ids) were generated against three bank vole and one human monoclonal antibody (MAb) specific for the two envelope glycoproteins of Puumala virus (G1 and G2). The anti-ids were purified by sequential immunoaffinity chromatography. Each anti-id inhibited the antigen binding of its respective MAb in a competitive ELISA. This inhibition, and the absence of cross-reactivity among the anti-ids for heterologous MAbs, showed that they all were specific for unique determinants on the antigen binding site of the homologous MAb. The anti-ids reacted with non-infected Vero E6 cells when examined by immunofluorescence and ELISA, indicating the presence of antibodies that mimic epitopes on the virus. Preincubation of Vero E6 cells with two of the anti-ids produced against neutralizing MAbs inhibited Puumala virus infection, suggesting that these two anti-ids blocked a cellular component involved in virus infection.

Comparison of virulence between Seoul virus strain SR-11 and Hantaan virus strain 76-118 of hantaviruses in newborn mice

Virulence of hantavirus strain of SR-11 Seoul virus and Hantaan 76-118 (HTN) of Hantaan virus were compared. Infections of both strains were lethal in newborn mice. However, inoculum required to cause lethal infection was about 4,000 times higher for strain HTN (1.65 x 10(3) PFU/mouse/LD50) than for strain SR-11 (0.36 PFU). Thus, both strains were considered pathogenic to newborn mice but they possessed different levels of virulence. The assay system used for these strains in newborn mice proved to be useful in the study of hantavirus virulence. Growth curves of the two strains in CV-7 cell cultures were compared. Strain SR-11 was shown to have higher activity of virus replication and virus release into the culture fluids than strain HTN. The possibility of a relationship between replication activity and high levels of virulence in mice was suggested.

Epizootiological study of hantavirus infection among Rattus norvegicus in Tokyo Bay area, Japan

The prevalence of antibodies against hantavirus in 413 rats (Rattus norvegicus) captured in eight regions of the Tokyo Bay area from 1983 to 1992 were examined by the indirect fluorescent antibody test. Antibody-positive rats were found in Tokyo Port in 1983 (34.8%), 1984 (25.9%), 1985 (22.0%) and 1986 (15.6%), in Kasai Seaside Park in 1989 (3.2%) and 1990 (4.2%) and in Chiba Port in 1990 (6.7%). In Tokyo Port, antibody-positive rats were found in any season in 1984 and 1985, and seroprevalences among two age groups, i. e., less than six months and six or more months of age were 18.1% and 28.4%, respectively. Three virus strains were isolated from rats captured on reclaimed land No. 13 in Tokyo Port in 1985 and named TQR-23, TQR-48 and TQR-50. These strains were antigenically identical with other rat strains, e. g., strain SR-11 and TR-352 but were discriminated from 76-118 strain by the neutralization test. Until 1990, persistence of hantavirus among rats inhabiting the Tokyo Bay area was demonstrated and hantavirus may be continuously prevalent in rats in this area.

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.

Immunoglobulin G subclass responses against the structural components of Puumala virus

Sera from sequentially bled nephropathia epidemica patients (acute-phase, convalescent-phase, and 2-year sera) and sera from 10 to 20 years postinfection were examined by immunoglobulin G (IgG) subclass-specific ELISAs for reactivities against each of the Puumala virus structural proteins (N, G1, and G2). IgG1 was found to be the dominating antiviral subclass, and most of the patients had IgG1 directed to all three structural proteins at all times with a continuous increase over time. IgG2 to the three viral proteins was detected in very low amounts in only a few of the samples. All of the serially bled patients developed IgG3 against each of the proteins, but the responses against the different viral components varied; anti-N- and anti-G1-specific IgG3 showed a peak in the convalescent-phase samples, while the anti-G2 IgG3 response was highest in the acute-phase sera. Eight of ten serially bled patients developed specific IgG4. The IgG4 responses showed similar patterns against all three viral proteins with very low optical density values in the acute- and convalescent-phase samples, followed by higher optical densities in the sera drawn 2 years after infection. Seven of nine 10-year sera contained virus-specific IgG4. These results support the theory concerning the persistence of Puumala virus or viral antigens several years after infection.

Dobrava virus as a new Hantavirus: evidenced by comparative sequence analysis

Dobrava virus, recently isolated from a yellow-neck mouse (Apodemus flavicollis), captured in a northern Slovenian village where severe cases of hemorrhagic fever with renal syndrome were recognized, was shown by serology and restriction enzyme digestion of PCR-amplified gene segments to be related to previously recognized hantaviruses. To investigate further the relationship of this new isolate to other hantaviruses, a portion of the medium (M) genome segment of Dobrava virus was amplified by PCR and the nucleotide sequence determined. Comparing the nucleotide sequence with the same gene region of other hantaviruses revealed an overall homology of 41.7%. A phylogenetic tree based on pairwise sequence similarity clearly showed that Dobrava virus is genetically distinct, and probably represents a new virus in the genus Hantavirus of the family Bunyaviridae.

Puumala virus infection without signs of renal involvement

Five cases of Puumala virus infection without renal involvement are described. The main signs were fever, headache, chills and thirst. Pulmonary involvement was also common. Neither increased levels of serum creatinine nor abnormal urinalyses were detected. We suggest that Hantavirus infection is included in the differential diagnosis of any febrile condition when exposure to aerosols from infectious secretions or secretions from rodents is suspected.

Chronic renal dysfunction in hemorrhagic fever with renal syndrome patients

During the last 9 years, 32 cases of hemorrhagic fever with renal syndrome (HFRS) have been diagnosed in our institution. Seven patients died. Twenty-three patients were discharged healthy while in another 2 some degree of renal dysfunction, which remained stable 12-15 months later, was evident. In 12 out of the 23 healthy individuals thorough examination of renal function was performed 1-5 years after their discharge. Three out of the 12 had renal tubular acidosis (RTA) type I (distal), complete or incomplete, and 2 (1 of whom also had incomplete RTA) had reduced urine concentrating ability. The development of chronic renal dysfunction was independent of the clinical severity of the acute illness.

Antibodies to Puumala virus in humans determined by neutralization test

An assay for detection of neutralizing antibodies to Puumala virus using 96-well microtiter plates (NT-ELISA) was developed and evaluated. The test proved to have similar sensitivity and specificity as an IgG ELISA and indirect immunofluorescence test, when screening 187 sera (with an antibody prevalence rate of 19%) from normal populations in an endemic area of Nephropathia epidemica (NE) in Sweden. NE-patients monitored for 2 years had neutralizing antibodies in early sera collected 1-4 days after the onset of disease with a continuous increase in neutralizing antibodies with time. Furthermore, high titers of neutralizing antibodies were detected 10-20 years post-infection. This neutralization assay was also evaluated as a screening method in the production of monoclonal antibodies. The format of the NT-ELISA makes it feasible to screen a large number of specimens with results similar to the standard plaque or focus-reduction neutralization tests.

Selective amplification of cDNA sequence from total RNA by cassette-ligation mediated polymerase chain reaction (PCR): application to sequencing 6.5 kb genome segment of hantavirus strain B-1

A method, referred to as cassette-ligation mediated polymerase chain reaction (PCR), has been developed to permit selective and specific amplification of cDNA sequence from total cellular RNA. This technique comprises (i) digestion of cDNA with multiple restriction enzymes, (ii) ligation of cleavage products to double-stranded DNA cassettes possessing a corresponding restriction site and (iii) amplification of cassette-ligated restriction fragments containing a short, known sequence (but not all the other ligation products) by PCR using the specific and cassette primers; the specific primer is designed to prime synthesis from the known sequence of the cDNA whereas the cassette primer anneals to one strand of the cassette. Sequencing from the cassette primer provides information to design a new primer for the next walking step. The amplified cDNA fragments are often larger than the maximum DNA fragments (500-600 bp) that can be sequenced without the need of synthesizing internal sequencing primer. Each of such large cDNA fragments is dissected into smaller DNA fragments by repeating cassette-ligation mediated PCR exploiting different restriction sites and different sets of cassette primers. This dissection process reduces the number of specific primers to a minimum, thereby increasing the speed of sequencing and minimizing the overall cost. We have successfully applied this cDNA walking and sequencing by the cassette-ligation mediated PCR to the sequencing of an entire 6.5 kb genome segment of hantavirus strain B-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-endothelial cell antibodies in nephropathia epidemica and other viral diseases

Increased capillary permeability is a central feature of the severe forms of haemorrhagic fever with renal syndrome (HFRS) and occurs also, though less frequently, in nephropathia epidemica (NE), one of the milder forms of this syndrome, caused by Puumala virus. We therefore searched for antiendothelial cell antibodies (AECA) in patients with NE and in those with other presumed or serologically proven acute viral illnesses. By enzyme immunoassay, using human umbilical vein endothelial cells (HUVEC) as the substrate, IgG class AECA were detected significantly more frequently in patients with NE and with influenza A than in Red Cross blood donors. A lesser degree of reactivity could be shown with a human alveolar cell carcinoma line and with human and mouse embryonic fibroblasts. Pretreatment of HUVEC with interferon-gamma (IFN-gamma), but not with IL-1 or tumour necrosis factor-alpha (TNF-alpha), increased their ability to bind IgG of sera from patients with NE and acute febrile illnesses. We conclude that, although AECA can be demonstrated in NE, they occur also in other acute viral illnesses and, unless cytopathic by a mechanism not shared by the AECA of these other illnesses, are unlikely to be casually related to the capillary leak in HFRS.