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

Rift Valley fever virus(Bunyaviridae: Phlebovirus): an update on pathogenesis, molecular epidemiology, vectors, diagnostics and prevention

Rift Valley fever(RVF) virus is an arbovirus in the Bunyaviridae family that, from phylogenetic analysis, appears to have first emerged in the mid-19th century and was only identified at the beginning of the 1930's in the Rift Valley region of Kenya. Despite being an arbovirus with a relatively simple but temporally and geographically stable genome, this zoonotic virus has already demonstrated a real capacity for emerging in new territories, as exemplified by the outbreaks in Egypt (1977), Western Africa (1988) and the Arabian Peninsula (2000), or for re-emerging after long periods of silence as observed very recently in Kenya and South Africa. The presence of competent vectors in countries previously free of RVF, the high viral titres in viraemic animals and the global changes in climate, travel and trade all contribute to make this virus a threat that must not be neglected as the consequences of RVF are dramatic, both for human and animal health. In this review, we present the latest advances in RVF virus research. In spite of this renewed interest, aspects of the epidemiology of RVF virus are still not fully understood and safe, effective vaccines are still not freely available for protecting humans and livestock against the dramatic consequences of this virus.

Central nervous system-related symptoms and findings are common in acute Puumala hantavirus infection

BACKGROUND

Puumala hantavirus (PUUV) causes a hemorrhagic fever with renal syndrome (HFRS) also called nephropathia epidemica (NE). Recent case reports and retrospective studies suggest that NE may damage the pituitary gland. Based on these observations, our goal was to explore the nature of this complication prospectively.

METHODS

A total of 58 hospitalized patients with acute NE volunteered to participate. Central nervous system (CNS) symptoms were recorded, cerebrospinal fluid (CSF) samples were collected, human leukocyte antigen (HLA) haplotype was analyzed, brain magnetic resonance imaging (MRI) was acquired, and electroencephalography (EEG) was recorded. Patients with abnormal pituitary MRI finding were examined by an endocrinologist.

RESULTS

Most patients experienced CNS symptoms, and half of the CSF samples were positive for PUUV IgM, elevated protein level, or leukocyte count. CSF of patients negative for DR15(2)-DQ6 haplotype was less frequently affected. MRI revealed pituitary hemorrhage in two patients; these two patients suffered sudden loss of vision associated with headache, and they both developed hypopituitarism. Only one patient required long-term hormonal replacement therapy.

CONCLUSION

CNS-related symptoms and inflammation in the CSF are common in acute NE. Genetic properties of the host may predispose to CNS involvement. It does seem that pituitary injury and subsequent hormonal insufficiency may complicate the recovery.

Hantavirus infections in fluctuating host populations: the role of maternal antibodies

Infected females may transfer maternal antibodies (MatAbs) to their offspring, which may then be transiently protected against infections the mother has encountered. However, the role of maternal protection in infectious disease dynamics in wildlife has largely been neglected. Here, we investigate the effects of Puumala hantavirus (PUUV)-specific MatAbs on PUUV dynamics, using 7 years' data from a cyclic bank vole population in Finland. For the first time to our knowledge, we partition seropositivity data from a natural population into separate dynamic patterns for MatAbs and infection. The likelihood of young of the year carrying PUUV-specific MatAbs during the breeding season correlated positively with infection prevalence in the overwintered parent population in the preceding spring. The probability of PUUV infection varied between seasons (highest in spring, lowest in late summer) and depended on population structure, but was also, in late autumn, notably, negatively related to summer MatAb prevalence, as well as to infection prevalence earlier in the breeding season. Hence, our results suggest that high infection prevalence in the early breeding season leads to a high proportion of transiently immune young individuals, which causes delays in transmission. This suggests, in turn, that MatAb protection has the potential to affect infection dynamics in natural populations.

A global perspective on hantavirus ecology, epidemiology, and disease

Hantaviruses are enzootic viruses that maintain persistent infections in their rodent hosts without apparent disease symptoms. The spillover of these viruses to humans can lead to one of two serious illnesses, hantavirus pulmonary syndrome and hemorrhagic fever with renal syndrome. In recent years, there has been an improved understanding of the epidemiology, pathogenesis, and natural history of these viruses following an increase in the number of outbreaks in the Americas. In this review, current concepts regarding the ecology of and disease associated with these serious human pathogens are presented. Priorities for future research suggest an integration of the ecology and evolution of these and other host-virus ecosystems through modeling and hypothesis-driven research with the risk of emergence, host switching/spillover, and disease transmission to humans.

Cytoplasmic tails of hantavirus glycoproteins interact with the nucleocapsid protein

Here we characterize the interaction between the glycoproteins (Gn and Gc) and the ribonucleoprotein (RNP) of Puumala virus (PUUV; genus Hantavirus, family Bunyaviridae). The interaction was initially established with native proteins by co-immunoprecipitating PUUV nucleocapsid (N) protein with the glycoprotein complex. Mapping of the interaction sites revealed that the N protein has multiple binding sites in the cytoplasmic tail (CT) of Gn and is also able to bind to the predicted CT of Gc. The importance of Gn- and Gc-CTs to the recognition of RNP was further verified in pull-down assays using soluble peptides with binding capacity to both recombinant N protein and the RNPs of PUUV and Tula virus. Additionally, the N protein of PUUV was demonstrated to interact with peptides of Gn and Gc from a variety of hantavirus species, suggesting a conserved RNP-recognition mechanism within the genus. Based on these and our previous results, we suggest that the complete hetero-oligomeric (Gn-Gc)(4) spike complex of hantaviruses mediates the packaging of RNP into virions.

Interactions and oligomerization of hantavirus glycoproteins

In this report the basis for the structural architecture of the envelope of hantaviruses, family Bunyaviridae, is systematically studied by the interactions of two glycoproteins N and C (Gn and Gc, respectively) and their respective disulfide bridge-mediated homo- and heteromeric oligomerizations. In virion extracts Gn and Gc associated in both homo- and hetero-oligomers which were, at least partially, thiol bridge mediated. Due to strong homo-oligomerization, the hetero-oligomers of Gn and Gc are likely to be mediated by homo-oligomeric subunits. A reversible pH-induced disappearance of a neutralizing epitope in Gc and dissociation of the Gn-Gc complex at pH values below 6.2 provide proteochemical evidence for the fusogenicity of Gc. Incomplete inactivation of virions at acidic pH indicates that additional factors are required for hantavirus fusion, as in the case of pestiviruses of the Flaviviridae. Based on similarities to class II fusion proteins, a structure model was created of hantavirus Gc using the Semliki Forest virus E1 protein as a template. In total, 10 binding regions for Gn were found by peptide scanning, of which five represent homotypic (Gn(I) to Gn(V)) and five represent heterotypic (Gc(I) to Gc(V)) interaction sites that we assign as intra- and interspike connections, respectively. In conclusion, the glycoprotein associations were compiled to a model wherein the surface of hantaviruses is formed of homotetrameric Gn complexes interconnected with Gc homodimers. This organization would create the grid-like surface pattern described earlier for hantaviruses in negatively stained electron microscopy specimens.

Tula hantavirus NSs protein accumulates in the perinuclear area in infected and transfected cells

The small RNA segment of some hantaviruses (family Bunyaviridae) encodes two proteins: the nucleocapsid protein and, in an overlapping reading frame, a non-structural (NSs) protein. The hantavirus NSs protein, like those of orthobunya- and phleboviruses, counteracts host innate immunity. Here, for the first time, the NSs protein of a hantavirus (Tula virus) has been observed in infected cells and shown to localize in the perinuclear area. Transiently expressed NSs protein showed similar localization, although the kinetics was slightly different, suggesting that to reach its proper location in the infected cell, the NSs protein does not have to cooperate with other viral proteins.

Case-control study on Puumala virus infection: smoking is a risk factor

Puumala hantavirus (PUUV) is apparently transmitted to humans by inhalation of aerosolized secretions of carrier rodents (bank voles). The means of transmission and the associated risk factors are poorly defined. An epidemiological study during the peak of an epidemic season in Finland was conducted based on 282 acute clinical PUUV infections and 204 controls without PUUV infection or immunity. The main risk factors adjusted by age, sex and living environment were cigarette smoking [odds ratio (OR) 3.6, 95% confidence interval (CI) 2.1-5.9, P<0.0001] and buildings with holes allowing rodents to enter (OR 3.3, 95% CI 2.0-5.6); these results were similar in two subsets. Further, use of rodent traps (OR3.5, 95% CI 2.2-5.7) and handling firewood (OR 2.7, 95% CI 1.6-4.4) were associated with a risk. The risk attributed to smoking also remained high using simulated population controls with average smoking habits. The results suggest that hantavirus transmission occurs by inhalation mainly indoors and is dependent on the condition of the respiratory tract.

Analysis of the immune response to Hantaan virus nucleocapsid protein C-terminal-specific CD8(+) T cells in patients with hemorrhagic fever with renal syndrome

Hantaan virus (HTNV), the prototype member of the Hantavirus genus in the family Bunyaviridae, causes hemorrhagic fever with renal syndrome (HFRS), which is characterized by capillary leakage, hemorrhage, and renal injury, and is an important public health problem in China. Some kinds of immune cells, particularly CD8(+) T cells, are involved in the pathogenesis of Hantavirus infection. The nucleocapsid protein (NP) of the Hantavirus is the most conserved structural protein and the most abundant viral protein produced during infection. It is one of the important target antigens that induce the CD8(+) T-cell response. In this study, we examined the CD8(+) T-cell response to HTNV NP C-terminal polypeptides. We synthesized 23 overlapping C-terminal polypeptides and detected the antigen-specific CD8(+) T cell response in 15 patients with HFRS. The results demonstrated that there were NP-specific T-cell responses in bulk cultures of peripheral blood mononuclear cells (PBMCs) from 9 of 15 patients. The peptide 51 (aa 301-315: SPSSIWVFAGAPDRC), peptide 60 (aa 355-369: LRKKSSFYQSYLRRT), and peptide 70 (aa 415-429: DVKVKEISNQEPLKL) induced strong CD8(+) T-cell responses. Among them, peptide 70 induced CTL responses in donors 7, 9, and 11, and the strongest responses were seen in donor 11. Depletion of CD8(+) T cells from PBMCs completely abrogated the peptide-specific T-cell response, while depletion of CD4(+) T cells did not diminish the number of IFN-gamma spot-forming cells. These data suggest that infection with HTNV results in CTL responses to immunodominant regions on the NP.

Laboratory diagnosis of human hantavirus infection: novel insights and future potential

Infections by Hantavirus (Bunyaviridae) can cause severe human diseases, such as hemorrhagic fever with renal syndrome in Eurasia and cardiopulmonary syndrome in the Americas. These diseases are emergent and became a serious public health problem worldwide. Thus, rapid, sensitive and reliable methods for diagnosis of hantavirus infection are necessary in order to manage patients and control this rodent-borne virosis. Serological methods, such as neutralization tests, immunoblots and enzyme immunoassays using hantavirus-recombinant proteins as antigens, are discussed in this article, as well as new methods such as an immunochromatographic test. Hantavirus genome detection by different kinds of reverse transcription-PCR, including the real-time variant, is also discussed.

Hantaviruses: an emerging public health threat in India? A review

The emerging viral diseases haemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS) are a cause of global concern as they are increasingly reported from newer regions of the world. The hantavirus species causing HFRS include Hantaan virus,Seoul virus, Puumala virus, and Dobrava-Belgrade virus while Sin Nombre virus was responsible for the 1993 outbreak of HCPS in the Four Corners Region of the US. Humans are accidental hosts and get infected by aerosols generated from contaminated urine,feces and saliva of infected rodents. Rodents are the natural hosts of these viruses and develop persistent infection. Human to human infections are rare and the evolution of the virus depends largely on that of the rodent host. The first hantavirus isolate to be cultured, Thottapalayam virus,is the only indigenous isolate from India,isolated from an insectivore in 1964 in Vellore, South India. Research on hantaviruses in India has been slow but steady since 2005. Serological investigation of patients with pyrexic illness revealed presence of anti-hantavirus IgM antibodies in 14.7% of them. The seropositivity of hantavirus infections in the general population is about 4% and people who live and work in close proximity with rodents have a greater risk of acquiring hantavirus infections. Molecular and serological evidence of hantavirus infections in rodents and man has also been documented in this country. The present review on hantaviruses is to increase awareness of these emerging pathogens and the threats they pose to the public health system.

Laboratory safe detection of nucleocapsid protein of Rift Valley fever virus in human and animal specimens by a sandwich ELISA

A safe laboratory procedure, based on a sandwich ELISA (sAg-ELISA), was developed and evaluated for the detection of nucleocapsid protein (NP) of Rift Valley fever virus (RVFV) in specimens inactivated at 56 degrees C for 1h in the presence of 0.5% Tween-20 (v/v) before testing. Polyclonal capture and detection immune sera were generated respectively in sheep and rabbits immunized with recombinant NP antigen. The assay was highly repeatable and specific; it detected strains of RVFV from the entire distributional range of the disease, isolated over a period of 53 years; no cross-reactivity with genetically related African phleboviruses or other members of the family Bunyaviridae was observed. In specimens spiked with RVFV, including human and animal sera, homogenates of liver and spleen tissues of domestic ruminants, and Anopheles mosquito homogenates, the sAg-ELISA detection limit ranged from log(10)10(2.2) to 10(3.2) TCID(50)/reaction volume. The ELISA detected NP antigen in spiked bovine and sheep liver homogenates up to at least 8 days of incubation at 37 degrees C whereas infectious virus could not be detected at 48h incubation in these adverse conditions. Compared to virus isolation from sera from RVF patients and sheep infected experimentally, the ELISA had 67.7% and 70% sensitivity, and 97.97% and 100% specificity, respectively. The assay was 100% accurate when testing tissues of various organs from mice infected experimentally and buffalo foetuses infected naturally. The assay was able to detect NP antigen in infective culture supernatants 16-24h before cytopathic effects were observed microscopically and as early as 8h after inoculation with 10(5.8) TCID(50)/ml of RVFV. This ability renders the assay for rapid identification of the virus when its primary isolation is attempted in vitro. As a highly specific, safe and simple assay format, the sAg-ELISA represents a valuable diagnostic tool for use in less equipped laboratories in Africa, and for routine differential diagnosis of viral hemorrhagic fevers.

Hantaviruses and TNF-alpha act synergistically to induce ERK1/2 inactivation in Vero E6 cells

Background

We have previously reported that the apathogenic Tula hantavirus induces apoptosis in Vero E6 epithelial cells. To assess the molecular mechanisms behind the induced apoptosis we studied the effects of hantavirus infection on cellular signaling pathways which promote cell survival. We previously also observed that the Tula virus-induced cell death process is augmented by external TNF-α. Since TNF-α is involved in the pathogenesis of hantavirus-caused hemorrhagic fever with renal syndrome (HFRS) we investigated its effects on HFRS-causing hantavirus-infected cells.

Results

We studied both apathogenic (Tula and Topografov) and pathogenic (Puumala and Seoul) hantaviruses for their ability to regulate cellular signaling pathways and observed a direct virus-mediated down-regulation of external signal-regulated kinases 1 and 2 (ERK1/2) survival pathway activity, which was dramatically enhanced by TNF-α. The fold of ERK1/2 inhibition correlated with viral replication efficiencies, which varied drastically between the hantaviruses studied.

Conclusion

We demonstrate that in the presence of a cytokine TNF-α, which is increased in HFRS patients, hantaviruses are capable of inactivating proteins that promote cell survival (ERK1/2). These results imply that hantavirus-infected epithelial cell barrier functions might be compromised in diseased individuals and could at least partially explain the mechanisms of renal dysfunction and the resulting proteinuria seen in HFRS patients.

How to diagnose hantavirus infections and detect them in rodents and insectivores

Hantaviruses are carried by rodents and insectivores in which they cause persistent and generally asymptomatic infections. Several hantaviruses can infect humans and many of them cause either haemorrhagic fever with renal syndrome (HFRS) in Eurasia or hantavirus cardiopulmonary syndrome (HCPS) in the Americas. In humans hantavirus infections are diagnosed using IgM-capture tests but also by RT-PCR detection of viral RNA. For detection of hantavirus infections in rodents and insectivores, serology followed by immunoblotting of, for example, lung tissue, and RT-PCR detection of viral RNA may be used, and if of interest followed by sequencing and virus isolation. For sero/genotyping of hantavirus infections in humans and carrier animals neutralisation tests/RNA sequencing are required. Hantaviruses are prime examples of emerging and re-emerging infections and it seems likely that many new hantaviruses will be detected in the near future.

Pathology of Puumala hantavirus infection in macaques

Hantaviruses are globally important human pathogens that cause hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. Capillary leakage is central to hantaviral diseases, but how it develops, has remained unknown. It has been hypothesized that the pathogenesis of hantavirus infection would be a complex interplay between direct viral effects and immunopathological mechanisms. Both of these were studied in the so far best model of mild hemorrhagic fever with renal syndrome, i.e. cynomolgus macaques infected with wild-type Puumala hantavirus. Viral RNA detected by in situ hybridization and nucleocapsid protein detected by immunohistochemical staining were observed in kidney, spleen and liver tissues. Inflammatory cell infiltrations and tubular damage were found in the kidneys, and these infiltrations contained mainly CD8-type T-cells. Importantly, these results are consistent with those obtained from patients with hantaviral disease, thus showing that the macaque model of hantavirus infection mimics human infection also on the tissue level. Furthermore, both the markers of viral replication and the T-cells appeared to co-localize in the kidneys to the sites of tissue damage, suggesting that these two together might be responsible for the pathogenesis of hantavirus infection.

Cross-reactive and serospecific epitopes of nucleocapsid proteins of three hantaviruses: prospects for new diagnostic tools

The diagnosis of infectious diseases is sometimes difficult because of extensive immunological cross-reactivity between related viral antigens. On the path of constructing sero-specific antigens, we have identified residues involved in sero-specific and cross-reactive recognition of the nucleocapsid proteins (NPs) of Puumala virus (PUUV), Seoul virus (SEOV), and Sin Nombre virus (SNV) using serum samples from 17 Nephropathia epidemica patients. The mapping was performed by enzyme-linked immunosorbent assay (ELISA) and Western blot analysis on a panel of N protein derivatives and alanine-substitution mutants in the three different hantavirus backgrounds. Four regions with different serological profiles were identified encompassing the amino acids (aa) 14-17, 22-24, 26, and 35-38. One of the regions showed strong cross-reactivity and was important for the recognition of SEOV and SNV antigens, but not the PUUV antigen (aa 35-38). Two regions displayed perceivable SEOV characteristics (aa 14-17 and aa 22-24 and 26) and the combined result of the alanine replacements resulted in a synergetic effect against the PUUV antigen (aa 14-17, 22-24, 26).

Truncated recombinant puumala virus nucleocapsid proteins protect mice against challenge in vivo

In Europe, Puumala virus and Dobrava virus are the major hantaviruses that cause hemorrhagic fever with renal syndrome in humans. As hantaviruses can cause diseases with high morbidity and mortality rates, and as to date there is no specific treatment, efforts are concentrated on the development of vaccines. In this study we characterized the immunogenicity of recombinant nucleocapsid proteins of Puumala virus (PUUV) linked to a carrier protein corresponding to the outer membrane protein A from Klebsiella pneumoniae (rP40). The rP40 molecule is a novel carrier protein that facilitates exogenous antigen uptake by dendritic cells. We cloned and expressed the recombinant PUUV proteins in the E. coli mutant ICONE 200 using the tryptophan promoter-controlled pTEXmp18 expression vector. All recombinant PUUV proteins were found to be highly immunogenic in NMRI mice after three immunizations of 10 microg each of the protein. Only the truncated construct, P40-Puu118, gave high antibody titers after two vaccinations of 0.2 microg each. Likewise in the challenge experiments in NMRI mice, only the truncated construct P40-Puu118 resulted in 100% protection after three immunizations of 10 microg each. The results suggest that P40-Puu118 in particular is a good candidate for a recombinant vaccine against Puumala virus. All recombinant proteins linked to rP40 induced high antibody responses, indicating that rP40 is a carrier protein with potential for use in other vaccines.

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.

Recombinant nucleocapsid-based ELISA for detection of IgG antibody to Rift Valley fever virus in African buffalo

Wild ruminants are thought to serve as natural hosts for Rift Valley fever virus (RVFV) but the role of these animals as reservoirs for RVFV during inter-epidemic periods and as amplifiers during epidemics is not well understood. An indirect enzyme-linked immunoassay (I-ELISA) based on the recombinant nucleocapsid protein (rNp) of RVFV was validated for the detection of specific IgG antibodies in African buffalo. Data sets derived from testing buffalo sera from Kenya (n=405) and South Africa (n=618) were dichotomised according to the results of a virus neutralisation test. The assay characteristic performance was analysed using threshold values optimised by the two-graph receiver operating characteristics (TG-ROC) analysis, and by mean plus two, as well as by mean plus three standard deviations derived from I-ELISA PP values in uninfected animals. Among 1023 buffalo sera tested, 77 (7.5%) had detectable virus neutralising antibodies. The assay had high intra- and inter-plate repeatability in routine runs. At a cut-off optimised by the TG-ROC at 95% accuracy level, the diagnostic sensitivity of the I-ELISA was 98.7% and diagnostic specificity 99.36% while estimates for the Youden's index (J) and efficiency (Ef) were 0.98 and 99.31%. When cut-off values determined by traditional statistical approaches were used, the diagnostic sensitivity was 100% but estimates of J, Ef and other combined measures of diagnostic accuracy were lower compared to those based on cut-off value derived from the TG-ROC. Results of the study indicate that the I-ELISA based on the rNp would be useful for seroepidemiological studies of RVFV infections in African buffalo.

Tula and Puumala hantavirus NSs ORFs are functional and the products inhibit activation of the interferon-beta promoter

The S RNA genome segment of hantaviruses carried by Arvicolinae and Sigmodontinae rodents encodes the nucleocapsid (N) protein and has an overlapping (+1) open reading frame (ORF) for a putative nonstructural protein (NSs). The aim of this study was to determine whether the ORF is functional. A protein corresponding to the predicted size of Tula virus (TULV) NSs was detected using coupled in vitro transcription and translation from a cloned S segment cDNA, and a protein corresponding to the predicted size of Puumala virus (PUUV) NSs was detected in infected cells by Western blotting with an anti-peptide serum. The activities of the interferon beta (IFN-beta) promoter, and nuclear factor kappa B (NF-kappaB)- and interferon regulatory factor-3 (IRF-3) responsive promoters, were inhibited in COS-7 cells transiently expressing TULV or PUUV NSs. Also IFN-beta mRNA levels in IFN-competent MRC5 cells either infected with TULV or transiently expressing NSs were decreased. These data demonstrate that Tula and Puumala hantaviruses have a functional NSs ORF. The findings may explain why the NSs ORF has been preserved in the genome of most hantaviruses during their long evolution and why hantavirus-infected cells secrete relatively low levels of IFNs.

Prevalence and protein specificity of human antibodies to Inkoo virus infection

Inkoo virus (INKV), a member of the California serogroup orthobunyaviruses, is circulating widely in northern Europe. Although the virus was discovered over 40 years ago, the disease associations and immune responses in human infection are poorly characterized. We first developed an immunofluorescence assay (IFA) for the detection of INKV antibodies in humans, and then we studied a panel of 1,292 sera in patients with a febrile illness in Finland. We found four acute (immunoglobulin M [IgM] positive) INKV infections and an IgG seroprevalence of 51.3%. The data indicate that the infection has become more common than it was in the 1960s, especially in southern Finland. Two distinct IgG IFA fluorescence patterns were observed: a granular pattern in sera from patients with acute INKV infection and a diffuse pattern in those with long-standing immunity. Further analysis with a panel of INKV-positive sera (n = 18; verified by neutralization assay) of protein-specific responses, using immunoprecipitation and IFA based on baculovirus-expressed INK N, Gn, and Gc proteins, demonstrated a strong IgG response predominantly towards N protein in the acute phase. In contrast, in patients with long-standing immunity, the Gc response was more prominent and the N response was weaker. In conclusion, a diagnostic IgG IFA pattern distinguishing between acute infection and long-standing immunity was observed. N protein seems to be the optimal antigen for the serodiagnosis of acute infection, and the Gc protein could be appropriate for the serosurveillance of INKV.

Endemic hantavirus infection impairs the winter survival of its rodent host

The influence of pathogens on host fitness is one of the key questions in infection ecology. Hantaviruses have coevolved with their hosts and are generally thought to have little or no effect on host survival or reproduction. We examined the effect of Puumala virus (PUUV) infection on the winter survival of bank voles (Myodes glareolus), the host of this virus. The data were collected by monitoring 22 islands over three consecutive winters (a total of 55 island populations) in an endemic area of central Finland. We show that PUUV infected bank voles had a significantly lower overwinter survival probability than antibody negative bank voles. Antibody negative female bank voles from low-density populations living on large islands had the highest survival. The results were similar at the population level as the spring population size and density were negatively correlated with PUUV prevalence in the autumn. Our results provide the first evidence for a significant effect of PUUV on host survival suggesting that hantaviruses, and endemic pathogens in general, deserve even more attention in studies of host population dynamics.

Validation of an indirect ELISA based on a recombinant nucleocapsid protein of Rift Valley fever virus for the detection of IgG antibody in humans

An indirect enzyme-linked immunoassay (I-ELISA) based on the recombinant nucleocapsid protein (rNp) of Rift Valley fever virus was validated for the detection of specific IgG antibody in human sera. Validation data sets derived from testing sera collected in Africa (n=2967) were categorized according to the results of a virus neutralisation test. The assay had high intra- and inter-plate repeatability in routine runs. No detectable cross-reactions between IgG antibodies generated from mice experimentally infected with viruses representing genus Phlebovirus, Nairovirus, Orthobunyavirus and Bhanja virus of the family Bunyaviridae were observed. At a cut-off optimised by the two-graph receiver operating characteristics analysis at 95% accuracy level, the diagnostic sensitivity of the I-ELISA was 99.72% and diagnostic specificity 99.62% while estimates for the Youden's index (J) and efficiency (Ef) were 0.993 and 99.62%. When cut-off values determined by mean plus two and by mean plus three standard deviations derived from I-ELISA readings in an uninfected reference population were used, the diagnostic sensitivity was 100% but estimates of Y, Ef and other combined measures of diagnostic accuracy were lower. The I-ELISA based on rNp is highly sensitive, specific and robust and can be applied for diagnosis of infection of Rift Valley fever and disease-surveillance studies in humans.

Cloning and expression of Rift Valley fever virus nucleocapsid (N) protein and evaluation of a N-protein based indirect ELISA for the detection of specific IgG and IgM antibodies in domestic ruminants

Serodiagnosis of Rift Valley fever (RVF) currently relies on the use of live or inactivated whole virus as antigens. The recombinant nucleocapsid (N) protein of RVF virus was tested for diagnostic applicability in an indirect enzyme-linked immunosorbent assay (I-ELISA), using sera from experimentally infected sheep (n=128), vaccinated sheep (n=240), and field-collected sera from sheep (n=251), goats (n=362) and cattle (n=100). The N-protein based I-ELISA performed at least as good as VN and HI tests. In goat the diagnostic sensitivity (D-Sn) and specificity (D-Sp) of the I-ELISA was 100% when using the anti-species IgG conjugate. Using protein G as a detection system, the D-Sn and D-Sp in goats were 99.4% and 99.5%, in sheep field sera both 100%, in cattle 100% and 98.3%, respectively. The I-ELISA based on recombinant N-protein has the potential to complement the traditional assays for serodiagnosis of RVF. Advantages of the N-protein are its safety, stability and cost-effectiveness in use and production.

Maternal antibodies postpone hantavirus infection and enhance individual breeding success

The transfer of maternal antibodies from mother to progeny is a well-known phenomenon in avian and mammalian species. Optimally, they protect the newborn against the pathogens in the environment. The effect of maternal antibodies on microparasite transmission dynamics may have important consequences for both the fitness of the host and the epizootic processes of the pathogens. However, there is a scarcity of studies examining these effects in free-living wild species. We studied the influence of maternal antibodies against the zoonotic Puumala hantavirus (PUUV) on the fitness of bank voles (Clethrionomys glareolus) and on PUUV transmission by exposing young maternal antibody-positive (MatAb+) and negative (MatAb-) bank voles (n=160) to PUUV in experimental populations. PUUV-specific maternal antibodies delayed the timing of infection. Females were more susceptible to PUUV infection than males. Interestingly, both the females and the males with maternal antibodies matured earlier than the other individuals in the population. Our results highlight the significance of maternal antibodies in the transmission of a pathogen and in the breeding success of the carriers.

Preparation and evaluation of a recombinant Rift Valley fever virus N protein for the detection of IgG and IgM antibodies in humans and animals by indirect ELISA

This paper describes the cloning, sequencing and bacterial expression of the N protein of the Rift Valley fever virus (RVFV) ZIM688/78 isolate and its evaluation in indirect ELISAs (I-ELISA) for the detection of IgM and IgG antibodies in human and sheep sera. Sera used for the evaluation were from 106 laboratory workers immunised with an inactivated RVF vaccine, 16 RVF patients, 168 serial bleeds from 8 sheep experimentally infected with wild type RVFV and 210 serial bleeds from 10 sheep vaccinated with the live attenuated Smithburn RVFV strain. All human and animal sera that tested positive in the virus neutralisation test were also positive in the IgG I-ELISA. There was a high correlation (R2=0.8571) between virus neutralising titres and IgG I-ELISA readings in human vaccinees. In experimentally infected sheep IgG antibodies were detected from day 4 to 5 post-infection onwards and IgM antibodies from day 3 to 4. The IgG I-ELISA was more sensitive than virus neutralisation and haemagglutination-inhibition tests in detecting the early immune response in experimentally infected sheep. The I-ELISAs demonstrated that the IgG and IgM response to the Smithburn vaccine strain was slower and the levels of antibodies induced markedly lower than to wild type RVFV infection.

Regions of importance for interaction of puumala virus nucleocapsid subunits

Puumala virus (PUUV) is a hantavirus that causes a mild form of hemorrhagic fever with renal syndrome in northern and central Europe, and in large parts of Russia. The nucleocapsid (N) protein encoded by hantaviruses plays an important role in the life-cycle of these viruses, and one important function for the N-protein is to oligomerize, surround and protect the viral RNAs. We have identified amino- and carboxy-terminal regions involved in PUUV N-N interactions, which comprise amino acids 100-120 and 330-405. Our findings strengthen the hypothesis that the amino-terminus of the N-protein of hantaviruses holds a more regulatory function regarding N-N interactions, while conserved residues in the carboxy-terminal region, F335 together with F336 and W392, in concert with Y388 and/or F400 seems to play a more critical role in the PUUV N-N formation. This study provides evidence that the amino-terminal regions involved in the N-N interaction of Puumala virus are similar to those reported for Seoul virus (SEOV) and to some extent Hantaan virus (HTNV), even though the identity between PUUV N and SEOV/HTNV N is markedly lower than between PUUV N and Tula virus (TULV) N or Sin Nombre virus (SNV) N.

Cross-reactive immune responses in mice after genetic vaccination with cDNA encoding hantavirus nucleocapsid proteins

Hantaviruses cause hemorrhagic fever with renal syndrome (HFRS) in about 150,000 individuals in Eurasia, and several hundred cases of hantavirus pulmonary syndrome (HPS) on the American continent annually. There is consequently a need for rapid diagnostics and effective prevention of hantaviral infections. In this study we have performed DNA-vaccination of mice with full-length genes encoding the immunogenic nucleocapsid protein (NP) of Puumala (PUUV), Seoul (SEOV) and Sin Nombre virus (SNV). The antibody reactivity towards the NPs, and deleted or truncated variants thereof, were studied to localise and investigate the major polyclonal B-cell epitopes. Our findings clearly show that the antibody reactivity in each immunised mouse is unique, not only in a quantitative respect (titers) but also in cross-reactivity and most likely also in the epitope specificity. Our experimental data in combination with B-cell prediction software indicate that strong homologous virus species specific and cross-reactive epitopes are located around amino acid residue 40 in the nucleocapsid proteins.

Prolonged survival of Puumala hantavirus outside the host: evidence for indirect transmission via the environment

The capability of rodent-borne viruses to survive outside the host is critical for the transmission dynamics within rodent populations and to humans. The transmission of Puumala virus (PUUV) in colonized bank voles (Clethrionomys glareolus) was investigated and additional longevity studies in cell culture with PUUV and Tula (TULV) hantaviruses were performed. Wild-type PUUV excreted by experimentally infected donor bank voles was shown to be transmitted indirectly between rodents through contaminated beddings, and maintained its infectivity to recipient voles at room temperature for 12-15 days. In cell culture supernatants, PUUV and TULV remained infectious for 5-11 days at room temperature and up to 18 days at 4 degrees C, but were inactivated after 24 h at 37 degrees C. Interestingly, a fraction of dried virus was still infectious after 1 h at 56 degrees C. These results demonstrated that hantavirus transmission does not require direct contact between rodents, or between rodents and humans, and that the indirect transmission of PUUV through contaminated environment takes place among the rodents for a prolonged period of time. The results also have implications for safety recommendations for work with hantaviruses and for preventive measures.

Characterization of the RNA chaperone activity of hantavirus nucleocapsid protein

Hantaviruses are tripartite negative-sense RNA viruses and members of the Bunyaviridae family. The nucleocapsid (N) protein, encoded by the smallest of the three genome segments (S), has nonspecific RNA chaperone activity. This activity results in transient dissociation of misfolded RNA structures, may be required for facilitating correct higher-order RNA structure, and may function in viral genome replication. We carried out a series of experiments to further characterize the ability of N to dissociate RNA duplexes. As might be expected, N dissociated RNA duplexes but not DNA duplexes or RNA-DNA heteroduplexes. The RNA-destabilizing activity of N is ATP independent, has a pH optimum of 7.5, and has an Mg(2+) concentration optimum of 1 to 2 mM. N protein is unable to unwind the RNA duplexes that are completely double stranded. However, in the presence of an adjoining single-stranded region, helix unwinding takes place in the 3'-to-5' direction through an unknown mechanism. The N protein trimer specifically recognizes and unwinds the terminal panhandle structure in the viral RNA and remains associated with unwound 5' terminus. We suggest that hantaviral nucleocapsid protein has an active role in hantaviral replication by working cooperatively with viral RNA polymerase. After specific recognition of the panhandle structure by N protein, the unwound 5' terminus likely remains transiently bound to N protein, creating an opportunity for the viral polymerase to initiate transcription at the accessible 3' terminus.

Corticosteroids combined with continuous veno-venous hemodiafiltration for treatment of hantavirus pulmonary syndrome caused by Puumala virus infection

Reported here are two cases of hantavirus pulmonary syndrome caused by Puumala virus infection, which rapidly resolved after initiation of corticosteroid treatment combined with continuous veno-venous hemodiafiltration. These cases emphasize the role of the inflammatory response in the pathogenesis of hantavirus pulmonary syndrome.

Puumala virus in Croatia in the 2002 HFRS outbreak

HFRS is an endemic disease throughout Croatia. The incidence of HFRS varies in a cyclic fashion, with peaks occurring every couple of years, coinciding with peaks in vole populations. PUUV was shown to be dominant pathogen during the last HFRS outbreak in Croatia in 2002. We focused our research on two newly discovered localities (Okucani and Nova Gradiska) with a high number of reported HFRS cases and a significant increase in rodent population. PUUV infection was verified in 84.2% of patients at this region during the 2002 outbreak. Genetic analysis of wild-type (wt) PUUV strains was performed. Fifty seven bank voles Clethrionomys glareolus originating from PUUV-associated HFRS areas were screened for the presence of PUUV N antigen and 15 (26%) were found positive. Total RNA isolated from rodent lung tissues was reverse transcribed followed by PCR amplification with primers specific for PUUV medium (M) or small (S) genome segments. Partial PUUV M segment sequences (approximately 450 bp long) were recovered from five bank voles and partial S segment sequences (app. 250 nt long)-from two bank voles. Genetic analysis of Croatian wt-PUUV strains revealed their close relatedness suggesting that the two localities belong to the same natural focus of infection. On phylogenetic trees Croatian PUUV strains clustered together with the strains from Slovenia and Austria forming distinct Alpe-Adrian genetic lineage.

Hantavirus nucleocapsid protein: a multifunctional molecule with both housekeeping and ambassadorial duties

In recent years important progress has been made studying the nucleocapsid (N) protein of hantaviruses. The N protein presents a good example of a multifunctional viral macromolecule. It is a major structural component of a virion that encapsidates viral RNA (vRNA). It also interacts with the virus polymerase (L protein) and one of the glycoproteins. On top of these "house keeping" duties, the N protein performs interactive "ambassadorial" functions interfering with important regulatory pathways in the infected cells.

Tula hantavirus triggers pro-apoptotic signals of ER stress in Vero E6 cells

Tula virus is a member of the Hantavirus genus of the family Bunyaviridae. Viruses of this family have an unusual pattern of intracellular maturation at the ER–Golgi compartment. We recently found that Tula virus, similar to several other hantaviruses, is able to induce apoptosis in cultured cells [Li, X.D., Kukkonen, S., Vapalahti, O., Plyusnin, A., Lankinen, H., Vaheri, A., 2004. Tula hantavirus infection of Vero E6 cells induces apoptosis involving caspase 8 activation. J. Gen. Virol. 85, 3261–3268.]. However, the cellular mechanisms remain to be clarified. In this study, we demonstrate that the progressive replication of Tula virus in Vero E6 cells initiates several death programs that are intimately associated with ER stress: (1) early activation of ER-resident caspase-12; (2) phosphorylation of Jun NH₂-terminal kinase (JNK) and its downstream target transcriptional factor, c-jun; (3) induction of the pro-apoptotic transcriptional factor, growth arrest- and DNA damage-inducible gene 153, or C/EBP homologous protein (Gadd153/chop); and (4) changes in the ER-membrane protein BAP31 implying cross-talk with the mitochondrial apoptosis pathway. Furthermore, we confirmed that a sustained ER stress was induced marked by an increased expression of an ER chaperone Grp78/BiP. Taken together, we have identified involvement of ER stress-mediated death program in Tula virus-infected Vero E6 cells which provides a new approach to understand the mechanisms in hantavirus-induced apoptosis.

Oligomerization of Hantavirus N protein: C-terminal alpha-helices interact to form a shared hydrophobic space

The structure of the nucleocapsid protein of bunyaviruses has not been defined. Earlier we have shown that Tula hantavirus N protein oligomerization is dependent on the C-terminal domains. Of them, the helix-loop-helix motif was found to be an essential structure. Computer modeling predicted that oligomerization occurs via helix protrusions, and the shared hydrophobic space formed by amino acids residues 380-IILLF-384 in the first helix and 413-LI-414 in the second helix is responsible for stabilizing the interaction. The model was validated by two approaches. First, analysis of the oligomerization capacity of the N protein mutants performed with the mammalian two-hybrid system showed that both preservation of the helix structure and formation of the shared hydrophobic space are crucial for the interaction. Second, oligomerization was shown to be a prerequisite for the granular pattern of transiently expressed N protein in transfected cells. N protein trimerization was supported by three-dimensional reconstruction of the N protein by electron microscopy after negative staining. Finally, we discuss how N protein trimerization could occur.

Tula hantavirus infection of Vero E6 cells induces apoptosis involving caspase 8 activation

Hantaviruses are known to cause two severe human diseases: haemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. The mechanisms of pathogenesis of these two diseases are progressively becoming understood. Recently, two hantaviruses, Hantaan and Prospect Hill were reported to cause programmed cell death of Vero E6 cells. This study shows that Tula hantavirus (TULV) infection efficiently triggers an apoptotic programme in infected Vero E6 cells, and that the replication of TULV is required for the activation of caspase 3 and the cleavage of poly (ADP-ribose) polymerase, two molecular hallmarks of apoptosis. The enforced treatment of infected Vero E6 cells with tumour necrosis factor alpha (TNF-alpha), but not interferon alpha (IFN-alpha), advanced the time course of apoptosis. Furthermore, caspase 8 was activated on day 4 post-infection, the same day when caspase 3 was activated. TNF receptor 1 was induced during a late stage of TULV infection. These data suggest that, unlike during influenza A virus infection, TNF-alpha, but not type I IFN-alpha/beta, may contribute significantly to apoptosis in a synergistic manner with TULV propagation. Interestingly, pretreatment with a broad-spectrum caspase inhibitor, z-VAD-fmk, efficiently inhibited apoptosis of TULV-infected Vero E6 cells. Taken together, these results suggest that TULV replication initiates a typical apoptotic programme involving caspase 8 activation.

Hantaviruses: Immunology, Treatment, and Prevention

Hantaviruses are rodent-borne bunyaviruses that are associated with two main clinical diseases in humans: hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. It has been suggested that host-related immune mechanisms rather than direct viral cytopathology may be responsible for the principal abnormality (vascular dysfunction) in these syndromes. This review summarizes the current knowledge on hantaviral host immune responses, immune abnormalities, laboratory diagnosis, and antiviral therapy as well as the current approaches in vaccine development.

Detection of Puumala Hantavirus Antibody with ELISA Using a Recombinant Truncated Nucleocapsid Protein Expressed inEscherichia coli

A truncated recombinant nucleocapsid protein (rNp118) consisting of the first 118 amino-terminal amino acids (AA) of the Puumala hantavirus (PUUV) nucleocapsid protein expressed in Escherichia coli, was evaluated for its antigenicity and reliability as serodiagnostic antigen in an enzyme-linked immunosorbent assay (ELISA) for detection of PUUV antibodies in human sera. The PUUV nucleocapsid protein has been shown to contain several B-cell epitopes, mapped within the first 118 amino-terminal AA. This finding makes the rNp118 an interesting recombinant protein to use as serodiagnostic antigen. The sensitivity of this new PUUV-rNp118 ELISA, was compared with those of a commercially available PUUV ELISA assay and an home-made ELISA based on a recombinant whole nucleocapsid protein of PUUV. Eighty-six human serum samples clinically suspected for PUUV-induced nephropathia epidemica, and previously screened with the reference assays, were tested. The sensitivity of the new assay was compared with that of the reference assays and an excellent correlation between the assays was found. Sera found to be negative by other methods were also negative in our assay. The ELISA based on rNp118 represents an alternative and valid test for detection of antibodies to PUUV in human sera.

Immune responses to Puumala virus infection and the pathogenesis of nephropathia epidemica

Puumala virus, causative agent of a mild form of hemorrhagic fever with renal syndrome, also known as nephropathia epidemica, induces long-lasting humoral and cellular immunity in patients. The virus itself is not cytopathic, and the immune responses to the virus may be involved in teh pathogenesis of the disease.

Hantavirus infections in Europe

Hantaviruses are enveloped RNA viruses each carried by a specific rodent species. Three hantaviruses, Puumala, Dobrava, and Saaremaa viruses, are known to cause haemorrhagic fever with renal syndrome. In Europe. Puumala causes a generally mild disease, nephropathia epidemica, which presents most commonly with fever, headache, gastrointestinal symptoms, impaired renal function, and blurred vision, whereas Dobrava infections often also have haemorrhagic complications. There are few available data about the clinical picture of confirmed Saaremaa infections, but epidemiological evidence suggests that it is less pathogenic than Dobrava, and that Saaremaa infections are more similar to nephropathia epidemica caused by Puumala. Along with its rodent host, the bank vole (Clethrionomys glareolus), Puumala is reported throughout most of Europe (excluding the Mediterranean region), whereas Dobrava, carried by the yellow-necked mouse (Apodemus flavicollis), and Saaremaa, carried by the striped field mouse (Apodemus agrarius), are reported mainly in eastern and central Europe. The diagnosis of acute hantavirus infection is based on the detection of virus-specific IgM. Whereas Puumala is distinct, Dobrava and Saaremaa are genetically and antigenically very closely related and were previously thought to be variants of the same virus. Typing of a specific hantavirus infection requires neutralisation antibody assays or reverse transcriptase PCR and sequencing.

Hantavirus infections in Spain: analysis of sera from the general population and from patients with pneumonia, renal disease and hepatitis

BACKGROUND

Hantaviruses are rodent borne viruses in the family Bunyaviridae that cause significant morbidity in large areas of Europe. There are only a few reports available on hantavirus infections from Spain. Although the results of these earlier studies indicated the presence of hantavirus infections, no confirmative or serotype-specific analyses have been performed.

OBJECTIVES

To investigate whether hantaviruses cause human infection/disease in Spain.

STUDY DESIGN

Ten thousand, four hundred and eighteen serum samples from the general population and 599 sera from 492 patients with potential hantavirus infections (renal disease, pneumonia or hepatitis) were initially screened by immunofluorescence assay (IFA) using Hantaan, Seoul and Puumala hantavirus antigens. Altogether 193 suspicious samples (165 from healthy people and 28 from patients) were selected for confirmation by quality-assured assays.

RESULTS AND CONCLUSIONS

Of the 165 pre-screened serum samples from healthy individuals, only five could be confirmed by IFA for hantavirus-reactive antibodies (using Dobrava, Saaremaa, Hantaan or Puumala virus antigens). In addition, one serum was found weakly positive for hantavirus-reactive IgG by ELISA using recombinant Saaremaa virus (SAAV) nucleocapsid (N) antigen, and subsequently confirmed by immunoblotting. Thus, the results indicated a low (0.06%) total antibody prevalence to hantaviruses in Spain. Of 28 pre-screened serum samples from hospitalized patients, eight reacted as positive or showed border-line reactivities for hantavirus-specific IgM by ELISA using recombinant Saaremaa and Puumala virus N antigens. The IFA/ELISA reactive/border-line samples were subsequently analyzed by a focus reduction neutralization test, which revealed low titers (1:80) against SAAV in two samples from a patient with hepatic disease. The nature of the hantavirus(es) potentially involved remain, however, unknown, since none of the positive samples showed neutralizing titers of the expected range to any of the known European hantaviruses.

Expression of the nucleoprotein of the Puumala virus from the recombinant Semliki Forest virus replicon: characterization and use as a potential diagnostic tool

Puumala virus (Bunyaviridae family, Hantavirus genus) causes a mild form of hemorrhagic fever with renal syndrome (HFRS) called nephropathia epidemica in northern and central Europe. Serological tests are used for diagnosis, but antigen production is difficult because the virus grows poorly in tissue culture. We expressed the N protein (nucleoprotein) of Puumala virus via the Semliki Forest virus (SFV) replicon in mammalian cells and compared its antigenic properties with those of the native antigen derived from Puumala virus-infected cells. Detection of immunoglobulin G or immunoglobulin M by enzyme-linked immunosorbent assay (ELISA), micro -capture ELISA, and indirect immunofluorescence assay was (at least) as effective with the recombinant antigen as with the native antigen when HFRS patient sera or organ washes from wild rodents were tested. No nonspecific reaction was observed. Thus, the SFV-expressed N protein of Puumala virus appears as a valid antigen, specific and sensitive for serological investigations.

Distribution of Puumala hantavirus in Denmark: analysis of bank voles (Clethrionomys glareolus) from Fyn and Jutland

The majority of hantaviral infections in Denmark since 1957 have occurred on the island of Fyn. We have recently shown the presence of Puumala hantavirus (PUUV) in bank voles (Clethrionomys glareolus) on Fyn. To learn more about the distribution and prevalence of PUUV in Denmark, 310 small mammals, belonging to six rodent and two insectivore species, were trapped in four localities on Fyn and three localities on the Jutland Peninsula (mainland Denmark), where only a few cases of nephropathia epidemica (NE) have been confirmed so far. Serum samples (heart extracts) from all animals were initially analyzed for the presence of hantavirus-specific antibodies (Ab) by enzyme immunoassay, and lung tissue samples of bank voles for the presence of the viral nucleocapsid protein antigen by immunoblotting. Altogether 11 Ab-positive rodents were found, all of them bank voles from Fyn. PUUV genome sequences (nucleotides 2,168-2,569 from the medium genomic segment) were recovered by reverse transcription-polymerase chain reaction from seven bank voles. They showed an overall diversity up to 5% and formed a well-supported genetic lineage on the phylogenetic tree with a clustering of two strains from southeastern Fyn together and a separation from the one strain from western Fyn. Our data confirmed the circulation of PUUV in both the southeastern and western parts of the island, known to have the highest numbers of human NE cases.

Non-covalent interaction between nucleocapsid protein of Tula hantavirus and small ubiquitin-related modifier-1, SUMO-1

To find cellular binding counterparts for the nucleocapsid protein (N) of Tula hantavirus (TULV), two cDNA libraries were screened using yeast two-hybrid systems based on LexA and Gal4 transcription factors. Five cDNA clones encoding SUMO-1 (Small Ubiquitin-related MOdifier, also known as sentrin) were selected in the LexA system. Confocal microscopy revealed that, in infected cells, TULV N protein and SUMO-1 colocalize at the perinuclear area providing further evidence for interaction between the two proteins. Neither endogenous nor transiently expressed SUMO-1 was found to be covalently linked to the N protein. Additional evidence that the interaction is non-covalent was obtained in immunoprecipitation experiments: N protein-specific antibodies precipitated SUMO-1 from TULV-infected Vero E6 cell lysate. By using a pepscan assay, two basic amino acid stretches in the N-terminal part of SUMO-1 were shown to be involved in the interaction.

Hantavirus immunology

Two clinical syndromes are associated with hantavirus infection in humans: hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Autopsy findings typically reveal a common feature of increased permeability in microvascular beds, suggesting vascular endothelium is a prime target for virus infection. Endothelial cells are susceptible to hantavirus infection; however, virus does not cause cytopathic effects, to explain increased endothelium permeability. Therefore, immune mechanisms were suggested to play a crucial role in hantavirus pathogenesis. In this review, we summarize data on hantavirus-induced immune disturbances and discuss their implication in capillary leakage caused by hantavirus infection.

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

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

Serological study of hantavirus in man in the Autonomous Community of Madrid, Spain

Data relating to hantavirus infection in Spain are scarce and limited to rural areas. The aim of this work was to study the seroprevalence of hantavirus infection in the Autonomous Community of Madrid (ACM), a region containing both rural and urban populations in different ecological settings. Sera from 3852 individuals (1849 male, 2003 female) were screened by indirect inmunofluorescence, with Vero E6 cells infected with Puumala, Hantaan and Seoul viruses as antigens. Screen-positive results were confirmed by Western blot with recombinant Seoul virus nucleocapsid protein as antigen. Antibodies against hantavirus were detected in 12 sera (0.31%). No statistical differences were found according to sex and age. The highest prevalence was found in the southeastern area, significantly higher than the central and north-western areas. The most frequent serological pattern was reactivity against all three viruses used (33.3% of all positive sera). Therefore, this study confirms the presence of hantavirus infection in the ACM, including for the first time an urban area of Spain, but with the highest prevalence in a rural area. Serological evidence suggests that there is more than one circulating serotype.

Long-lived memory T lymphocyte responses after hantavirus infection

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

Hypophyseal hemorrhage and panhypopituitarism during Puumala Virus Infection: Magnetic Resonance Imaging and detection of viral antigen in the hypophysis

We describe 3 cases of nephropathia epidemica (NE) that confirm that Puumala virus infection may cause hypophyseal injury. Autopsy revealed a hemorrhagic hypophysis positive for Puumala virus antigen in both neuroendocrine stromal and vascular endothelial cells in 1 patient, and 2 patients developed hypophyseal hemorrhage (diagnosed with magnetic resonance imaging) during or shortly after acute NE, both of whom developed panhypopituitarism.