Evaluation of serological methods for diagnosis of Puumala hantavirus infection (nephropathia epidemica)

Use of a Novel Detection Tool to Survey Orthohantaviruses in Wild-Caught Rodent Populations

Orthohantaviruses are negative-stranded RNA viruses with trisegmented genomes that can cause severe disease in humans and are carried by several host reservoirs throughout the world. Old World orthohantaviruses are primarily located throughout Europe and Asia, causing hemorrhagic fever with renal syndrome, and New World orthohantaviruses are found in North, Central, and South America, causing hantavirus cardiopulmonary syndrome (HCPS). In the United States, Sin Nombre orthohantavirus (SNV) is the primary cause of HCPS with a fatality rate of ~36%. The primary SNV host reservoir is thought to be the North American deer mouse, Peromyscus maniculatus. However, it has been shown that other species of Peromyscus can carry different orthohantaviruses. Few studies have systemically surveyed which orthohantaviruses may exist in wild-caught rodents or monitored spillover events into additional rodent reservoirs. A method for the rapid detection of orthohantaviruses is needed to screen large collections of rodent samples. Here, we report a pan-orthohantavirus, two-step reverse-transcription quantitative real-time PCR (RT-qPCR) tool designed to detect both Old and New World pathogenic orthohantavirus sequences of the S segment of the genome and validated them using plasmids and authentic viruses. We then performed a screening of wild-caught rodents and identified orthohantaviruses in lung tissue, and we confirmed the findings by Sanger sequencing. Furthermore, we identified new rodent reservoirs that have not been previously reported as orthohantavirus carriers. This novel tool can be used for the efficient and rapid detection of various orthohantaviruses, while uncovering potential new orthohantaviruses and host reservoirs that may otherwise go undetected.

Immune response during hantavirus diseases: implications for immunotherapies and vaccine design

Orthohantaviruses, previously named hantaviruses, cause two emerging zoonotic diseases: haemorrhagic fever with renal syndrome (HFRS) in Eurasia and hantavirus cardiopulmonary syndrome (HCPS) in the Americas. Overall, over 200 000 cases are registered every year worldwide, with a fatality rate ranging between 0·1% and 15% for HFRS and between 20% and 40% for HCPS. No specific treatment or vaccines have been approved by the U.S. Food and Drug Administration (FDA) to treat or prevent hantavirus-caused syndromes. Currently, little is known about the mechanisms at the basis of hantavirus-induced disease. However, it has been hypothesized that an excessive inflammatory response plays an essential role in the course of the disease. Furthermore, the contributions of the cellular immune response to either viral clearance or pathology have not been fully elucidated. This article discusses recent findings relative to the immune responses elicited to hantaviruses in subjects suffering HFRS or HCPS, highlighting the similarities and differences between these two clinical diseases. Also, we summarize the most recent data about the cellular immune response that could be important for designing new vaccines to prevent this global public health problem.

Heterologous boosting of nonrelated toxoid immunity during acute Puumala hantavirus infection

Persistence of immune memory in humans is a crucial yet poorly understood aspect of immunology. Here we have studied the effect of Puumala hantavirus infection on unrelated, pre-existing immune memory by studying T cell- and antibody responses against toxoid vaccine antigens of diphtheria, tetanus and pertussis in a cohort of 45 patients. We found that tetanus- and pertussis -specific IgG concentrations elevate during acute Puumala virus infection. Increase in vaccine IgG was associated with proliferation of heterologous T cells. Interestingly, increases in tetanus-specific IgG persisted a year after the infection while pertussis-specific IgG declined rapidly; a difference in IgG kinetics resembling the difference seen after vaccination against tetanus and pertussis. These results suggest that persistence of immune memory is facilitated by heterologous boosting of old memory during memory formation against newly encountered antigens. They also show that different toxoid antigens may be treated differently. Our study gives new insight into how immune memory formation may alter pre-existing immune memory, and also shows that heterologous immunity may have an impact on vaccination outcomes.

Serogrouping and seroepidemiology of North European hantaviruses using a novel broadly targeted synthetic nucleoprotein antigen array

Introduction: Hantaviruses are globally distributed zoonotic pathogens. Great diversity and high antigenic cross-reactivity makes diagnosis by traditional methods cumbersome.

Materials and methods: ‘Megapeptides’, 119–120-mers from the amino terminus of the nucleoprotein of 16 hantaviruses, representing the four major branches of the hantavirus phylogenetic tree, were utilized in a novel IgG-based hantavirus suspension multiplex immunoassay (HSMIA) for detection of past hantavirus infections in 155 North European human samples. We compared HSMIA with established EIAs and focus reduction neutralization test (FRNT).

Results and discussion: The Puumala hantavirus (PUUV) component in the HSMIA gave concordant results with a PUUV IgG EIA in 142 sera from Northern Sweden (of which 31 were EIA positive, 7 borderline and 104 EIA negative, sensitivity 30/31 = 97%, specificity 104/ 104 = 100%, 134/135 = 99% concordance), with another immunoassay in 40 PUUV IgG positive sera from Finland (36/40 = 90% sensitivity), and was concordant in 8 of 11 cases with PUUV and DOBV neutralization titers, respectively. Two major IgG reactivity patterns were found: (i) a PUUV-specific pattern covering phylogroup IV and its serogroups B and C; and (ii) a Dobrava virus (DOBV)-specific pattern, covering the serogroup A portion of phylogroup III. In addition, we found several minor patterns with reactivity to only one or two megapeptides indicating additional hantaviruses infecting humans in the Swedish and Finnish populations.

Conclusion: The broadly reactive and rational HSMIA yielded results highly correlated with the established PUUV EIAs and the NT results. It is a sensitive and specific assay, which will be suited for efficient serosurveillance of hantaviruses in humans. Its use in animals should be further investigated.

Expansion of spatial and host range ofPuumalavirus in Sweden: an increasing threat for humans?

Hantaviruses are globally distributed and cause severe human disease.Puumalahantavirus (PUUV) is the most common species in Northern Europe, and the only hantavirus confirmed to circulate in Sweden, restricted to the northern regions of the country. In this study, we aimed to further add to the natural ecology of PUUV in Sweden by investigating prevalence, and spatial and host species infection patterns. Specifically, we wanted to ascertain whether PUUV was present in the natural reservoir, the bank vole (Myodes glareolus) further south than Dalälven river, in south-central Sweden, and whether PUUV can be detected in other rodent species in addition to the natural reservoir. In total, 559 animals were collected at Grimsö (59°43′N; 15°28′E), Sala (59°55′N; 16°36′E) and Bogesund (59°24′N; 18°14′E) in south-central Sweden between May 2013 and November 2014. PUUV ELISA-reactive antibodies were found both in 2013 (22/295) and in 2014 (18/264), and nine samples were confirmed as PUUV-specific by focus reduction neutralization test. Most of the PUUV-specific samples were from the natural host, the bank vole, but also from other rodent hosts, indicating viral spill-over. Finally, we showed that PUUV is present in more highly populated central Sweden.

Kidney disease in Puumala hantavirus infection

Acute kidney injury (AKI) remains a predominant clinical expression of nephropathia epidemica (NE). Its pathogenesis is not yet fully understood. Here, we describe the tissue injury comprehensively and present new data aimed to characterize the injury and explain its pathophysiology. When compared to tubulointerstitial nephritis of a wide variety of other aetiologies, a high degree of proteinuria is a distinguished trait of NE, a finding that is also helpful in the clinical suspicion of the disease. Recently, novel biomarkers for the prediction of severe AKI, including neutrophil gelatinase-associated lipocalin (NGAL), have been identified and ultrastructural tissue changes have been more accurately described. A role for soluble urokinase-type plasminogen activator (suPAR) in the pathogenesis of NE has been suggested, and data on gene polymorphisms, in relation to the severity of AKI have been presented. Smoking is a risk factor for NE and smoking is also associated with aggravated AKI in NE. Although no specific treatment is in sight, recent case reports concerning therapy directed against vascular permeability and vasodilation are of interest. In fact, future work trying to explain the pathophysiology of AKI might need concentrated efforts towards the mechanisms of increased vascular permeability and vasodilatation, which irrespective of organ manifestation, are two major determinants of NE.

Prediction of B Cell Epitopes Among Hantavirus Strains Causing Hemorragic Fever With Renal Syndrome

Hantavirus infections are now recognized to be a global problem. The hantaviruses include several genotypic variants of the virus with different distributions in varying geographical regions. The virus genotypes seem to segregate in association with certain manifestations specific for each syndrome. They primarily include HFRS, HCPS, febrile illness with or without mild involvement of renal diseases. In the course of our study on hantavirus etiology of febrile illnesses, we recovered a hantavirus strain identified by nPCR. This has been sequenced to be Hantaan-like virus (partial S segment). The current manuscript is focused on understanding the N protein coded by S segment in terms of variation of amino acid sequences of the virus genotypes associated with HFRS. The diagnosis of this infection is achieved by PCR testing of serum/plasma or demonstration of IgM/IgG in serum. The limitations of PCR are temporal often not positive after 7 days of onset of infection. IgM detection is possible around this period and up to 21 days. IgG detection is less definitive in acute infections. Here, we report characterization of the sequence diversity of HFRS strains, 3D structure of Hantaan N protein, and B-cell epitopes on this molecule. We predicted a 20 amino acid sequence length peptide by using BepiPred online server in IEDB analysis resource program. We suggest this peptide may be used for development of geographic region-specific immunoassays like EIAs for antibody detection, monoclonal antibody development, and immunoblots (line immunoassay). J. Cell. Biochem. 118: 1182-1188, 2017. © 2016 Wiley Periodicals, Inc.

Human Puumala hantavirus infection in northern Sweden; increased seroprevalence and association to risk and health factors

Background

The rodent borne Puumala hantavirus (PUUV) causes haemorrhagic fever with renal syndrome in central and northern Europe. The number of cases has increased and northern Sweden has experienced large outbreaks in 1998 and 2006–2007 which raised questions regarding the level of immunity in the human population.

Methods

A randomly selected population aged between 25 and 74 years from northern Sweden were invited during 2009 to participate in a WHO project for monitoring of trends and determinants in cardiovascular disease. Health and risk factors were evaluated and sera from 1,600 participants were available for analysis for specific PUUV IgG antibodies using a recombinant PUUV nucleocapsid protein ELISA.

Results

The overall seroprevalence in the investigated population was 13.4 %, which is a 50 % increase compared to a similar study only two decades previously. The prevalence of PUUV IgG increased with age, and among 65–75 years it was 22 %. More men (15.3 %) than women (11.4 %) were seropositive (p < 0.05). The identified risk factors were smoking (OR = 1.67), living in rural areas (OR = 1.92), and owning farmland or forest (OR = 2.44). No associations were found between previous PUUV exposure and chronic lung disease, diabetes, hypertension, renal dysfunction, stroke or myocardial infarction.

Conclusions

PUUV is a common infection in northern Sweden and there is a high life time risk to acquire PUUV infection in endemic areas. Certain risk factors as living in rural areas and smoking were identified. Groups with increased risk should be targeted for future vaccination when available, and should also be informed about appropriate protection from rodent secreta.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-1879-2) contains supplementary material, which is available to authorized users.

Risk factors and potential preventive measures for nephropatia epidemica in Sweden 2011-2012: a case-control study

INTRODUCTION

Nephropatia epidemica (NE), a relatively mild form of hemorrhagic fever with renal syndrome caused by the Puumala virus (PUUV), is endemic in northern Sweden. We aim to study the risk factors associated with NE in this region.

METHODS

We conducted a matched case-control study between June 2011 and July 2012. We compared confirmed NE cases with randomly selected controls, matched by age, sex, and place of infection or residence. We analyzed the association between NE and several occupational, environmental, and behavioral exposures using conditional logistic regression.

RESULTS

We included in the final analysis 114 cases and 300 controls, forming 246 case-control pairs. Living in a house with an open space beneath, making house repairs, living less than 50 m from the forest, seeing rodents, and smoking were significantly associated with NE.

CONCLUSION

Our results could orient public health policies targeting these risk factors and subsequently reduce the NE burden in the region.

Competitive Homogeneous Immunoassay for Rapid Serodiagnosis of Hantavirus Disease

In this study, we describe a competitive homogeneous immunoassay that makes use of Förster resonance energy transfer (FRET) in rapid detection of pathogen-specific antibodies. The assay principle is based on competition between a monoclonal antibody (MAb) and serum antibodies to a given antigen. In the assay, named competitive FRET immunoassay (CFRET-IA), the FRET signal is induced if MAb carrying a donor label binds to an acceptor-labeled antigen. Specific antibodies in serum compete for antigen binding, resulting in reduced FRET signal. The proof-of-principle for the assay was obtained using donor-labeled Puumala virus nucleocapsid protein (PUUV-N) and acceptor-labeled anti-PUUV-N MAb. The assay was evaluated by analyzing 329 clinical samples comprising 101 from individuals with acute PUUV infection, 42 from individuals with past infection, and 186 from individuals with PUUV-seronegative sera, and the results were compared to those of reference tests. The rapid serodiagnostic test we introduced herein performed with 100% sensitivity and 99% specificity for diagnosing acute hantavirus disease.

The use of chimeric virus-like particles harbouring a segment of hantavirus Gc glycoprotein to generate a broadly-reactive hantavirus-specific monoclonal antibody

Monoclonal antibodies (MAbs) against viral glycoproteins have important diagnostic and therapeutic applications. In most cases, the MAbs specific to viral glycoproteins are raised against intact virus particles. The biosynthesis of viral glycoproteins in heterologous expression systems such as bacteria, yeast, insect or mammalian cells is often problematic due to their low expression level, improper folding and limited stability. To generate MAbs against hantavirus glycoprotein Gc, we have used initially a recombinant yeast-expressed full-length Puumala virus (PUUV) Gc protein. However, this approach was unsuccessful. As an alternative recombinant antigen, chimeric virus-like particles (VLPs) harboring a segment of PUUV Gc glycoprotein were generated in yeast Saccharomyces cerevisiae. A 99 amino acid (aa)-long segment of Gc protein was inserted into the major capsid protein VP1 of hamster polyomavirus at previously defined positions: either site #1 (aa 80-89) or site #4 (aa 280-289). The chimeric proteins were found to self-assemble to VLPs as evidenced by electron microscopy. Chimeric VLPs induced an efficient insert-specific antibody response in immunized mice. Monoclonal antibody (clone #10B8) of IgG isotype specific to hantavirus Gc glycoprotein was generated. It recognized recombinant full-length PUUV Gc glycoprotein both in ELISA and Western blot assay and reacted specifically with hantavirus-infected cells in immunofluorescence assay. Epitope mapping studies revealed the N-terminally located epitope highly conserved among different hantavirus strains. In conclusion, our approach to use chimeric VLPs was proven useful for the generation of virus-reactive MAb against hantavirus Gc glycoprotein. The generated broadly-reactive MAb #10B8 might be useful for various diagnostic applications.

Seroprevalence of hantavirus infections in Switzerland in 2009: difficulties in determining prevalence in a country with low endemicity

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The pathogenesis of nephropathia epidemica: new knowledge and unanswered questions

Puumala virus (PUUV) causes an acute hemorrhagic fever with renal syndrome (HFRS), a zoonosis also called nephropathia epidemica (NE). The reservoir host of PUUV is the bank vole (Myodes glareolus). Herein we review the main clinical manifestations of NE, acute kidney injury, increased vascular permeability, coagulation abnormalities as well as pulmonary, cardiac, central nervous system and ocular manifestations of the disease. Several biomarkers of disease severity have recently been discovered: interleukin-6, pentraxin-3, C-reactive protein, indoleamine 2,3-dioxygenase, cell-free DNA, soluble urokinase-type plasminogen activator, GATA-3 and Mac-2 binding protein. The role of cytokines, vascular endothelial growth hormone, complement, bradykinin, cellular immune response and other mechanisms in the pathogenesis of NE as well as host genetic factors will be discussed. Finally therapeutic aspects and directions for further research will be handled.

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

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

Second external quality assurance study for the serological diagnosis of hantaviruses in Europe

Hantaviruses are endemic throughout the world and hosted by rodents and insectivores. Two human zoonoses, hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS), are caused by hantaviruses and case fatality rates have reached 12% for HFRS and 50% for HPS in some outbreaks. Symptomatic hantavirus infections in Europe are summarised as HFRS mainly due to Puumala, Dobrava-Belgrade and Saaremaa virus. While HFRS has an overall low incidence in Europe, the number of cases varies from 100 per year in all Eastern and Southern Europe up to 1,000 per year only in Finland. To assess the quality of hantavirus diagnostics, the European Network for the Diagnostics of “Imported” Viral Diseases (ENIVD) organised a first external quality assurance (EQA) in 2002. The purpose of this second EQA study is to collect updated information on the efficiency and accurateness of hantavirus serological methods applied by expert laboratories. A serum panel of 14 samples was sent to 28 participants in Europe of which 27 sent results. Performance in hantavirus diagnosis varied not only on the method used but also on the laboratories and the subclass of antibodies tested. Commercial and in-house assays performed almost equally. Enzyme immunoassays were mainly used but did not show the best performances while immunoblot assays were the less employed and showed overall better performances. IgM antibodies were not detected in 61% of the positive IgM samples and IgM detection was not performed by 7% of the laboratories indicating a risk of overlooking acute infections in patients. Uneven performances using the same method is indicating that there is still a need for improving testing conditions and standardizing protocols.

Hantaviruses are endemic throughout the world and naturally hosted by rodents. The vast majority of human hantavirus infections are asymptomatic. In Europe, symptomatic hantavirus infections are summarised as hemorrhagic fever with renal syndrome (HFRS) mainly due to Puumala, Dobrava-Belgrade and Saaremaa virus. HFRS can cause fever, headache, and flank and abdominal pain. Moreover, renal dysfunction can lead to acute renal failure. Despite numerous research efforts, there is still no safe and effective vaccine or specific antiviral treatment against hantavirus infections. In this context, an accurate diagnosis as well as a reliable surveillance of hantavirus infections is essential. The diagnostics of hantavirus infections are based on serology using in-house or commercial assays. To assess the quality of hantavirus diagnostics, the European Network for the Diagnostics of “Imported” Viral Diseases organised a first external quality assurance (EQA) in 2002. In this publication we describe a second EQA study launched in 2011 with the objective to collect updated information on the efficiency and accurateness of hantavirus serological methods applied by expert laboratories. The study shows uneven performances indicating that there is still a need for improving testing conditions and standardizing protocols.

Phylogenetic analysis of Puumala virus subtype Bavaria, characterization and diagnostic use of its recombinant nucleocapsid protein

Puumala virus (PUUV) is the predominant hantavirus species in Germany causing large numbers of mild to moderate cases of haemorrhagic fever with renal syndrome (HFRS). During an outbreak in South-East Germany in 2004 a novel PUUV subtype designated Bavaria was identified as the causative agent of HFRS in humans [1]. Here we present a molecular characterization of this PUUV strain by investigating novel partial and almost entire nucleocapsid (N) protein-encoding small (S-) segment sequences and partial medium (M-) segment sequences from bank voles (Myodes glareolus) trapped in Lower Bavaria during 2004 and 2005. Phylogenetic analyses confirmed their classification as subtype Bavaria, which is further subdivided into four geographical clusters. The entire N protein, harbouring an amino-terminal hexahistidine tag, of the Bavarian strain was produced in yeast Saccharomyces cerevisiae and showed a slightly different reactivity with N-specific monoclonal antibodies, compared to the yeast-expressed N protein of the PUUV strain Vranica/Hällnäs. Endpoint titration of human sera from different parts of Germany and from Finland revealed only very slight differences in the diagnostic value of the different recombinant proteins. Based on the novel N antigen indirect and monoclonal antibody capture IgG-ELISAs were established. By using serum panels from Germany and Finland their validation demonstrated a high sensitivity and specificity. In summary, our investigations demonstrated the Bavarian PUUV strain to be genetically divergent from other PUUV strains and the potential of its N protein for diagnostic applications.

Expression of recombinant Araraquara Hantavirus nucleoprotein in insect cells and its use as an antigen for immunodetection compared to the same antigen expressed in Escherichia coli

Background

Antigens for Hantavirus serological tests have been produced using DNA recombinant technology for more than twenty years. Several different strategies have been used for that purpose. All of them avoid the risks and difficulties involved in multiplying Hantavirus in the laboratory. In Brazil, the Araraquara virus is one of the main causes of Hantavirus Cardio-Pulmonary Syndrome (HCPS).

Methods

In this investigation, we report the expression of the N protein of the Araraquara Hantavirus in a Baculovirus Expression System, the use of this protein in IgM and IgG ELISA and comparison with the same antigen generated in E. coli.

Results

The protein obtained, and purified in a nickel column, was effectively recognized by antibodies from confirmed HCPS patients. Comparison of the baculovirus generated antigen with the N protein produced in E. coli showed that both were equally effective in terms of sensitivity and specificity.

Conclusions

Our results therefore indicate that either of these proteins can be used in serological tests in Brazil.

Characterization of monoclonal antibodies against hantavirus nucleocapsid protein and their use for immunohistochemistry on rodent and human samples

Monoclonal antibodies are important tools for various applications in hantavirus diagnostics. Recently, we generated Puumala virus (PUUV)-reactive monoclonal antibodies (mAbs) by immunisation of mice with chimeric polyomavirus-derived virus-like particles (VLPs) harbouring the 120-amino-acid-long amino-terminal region of the PUUV nucleocapsid (N) protein. Here, we describe the generation of two mAbs by co-immunisation of mice with hexahistidine-tagged full-length N proteins of Sin Nombre virus (SNV) and Andes virus (ANDV), their characterization by different immunoassays and comparison with the previously generated mAbs raised against a segment of PUUV N protein inserted into VLPs. All of the mAbs reacted strongly in ELISA and western blot tests with the antigens used for immunization and cross-reacted to varying extents with N proteins of other hantaviruses. All mAbs raised against a segment of the PUUV N protein presented on chimeric VLPs and both mAbs raised against the full-length AND/SNV N protein reacted with Vero cells infected with different hantaviruses. The reactivity of mAbs with native viral nucleocapsids was also confirmed by their reactivity in immunohistochemistry assays with kidney tissue specimens from experimentally SNV-infected rodents and human heart tissue specimens from hantavirus cardiopulmonary syndrome patients. Therefore, the described mAbs represent useful tools for the immunodetection of hantavirus infection.

Hormonal deficiencies during and after Puumala hantavirus infection

Previous reports have described panhypopituitarism associated with severe cases of hemorrhagic fever with renal syndrome (HFRS), but the prevalence of hormonal deficiencies after nephropathia epidemica (NE), a milder form of HFRS, has not been studied. This study was conducted in order to determine the prevalence of hormonal defects in patients with acute NE and during long-term follow-up. Fifty-four patients with serologically confirmed acute NE were examined by serum hormonal measurements during the acute NE, after 3 months, and after 1 to 10 (median 5) years. Thirty out of 54 (56%) patients had abnormalities of the gonadal and/or thyroid axis during the acute NE. After a median follow-up of 5 years, 9 (17%) patients were diagnosed with a chronic, overt hormonal deficit: hypopituitarism was found in five patients and primary hypothyroidism in five patients. In addition, chronic subclinical testicular failure was found in five men. High creatinine levels and inflammatory markers during NE were associated with the acute central hormone deficiencies, but not with the chronic deficiencies. Hormonal defects are common during acute NE and, surprisingly, many patients develop chronic hormonal deficiencies after NE. The occurrence of long-term hormonal defects cannot be predicted by the severity of acute NE.

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.

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.

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.

Development and evaluation of serological assays for detection of Hantaanvirus-specific antibodies in human sera using yeast-expressed nucleocapsid protein

Indirect and capture enzyme-linked immunosorbent assays (ELISAs) for detection of Hantaan virus (HTNV)-specific immunoglobulins G (IgG) and M (IgM) in human serum samples were developed on the basis of recombinant yeast-expressed nucleocapsid (N) protein of HTNV. The sensitivities and specificities of the indirect and capture ELISAs were evaluated by comparing the reactivity of sera from patients with hemorrhagic fever with renal syndrome (HFRS) from China with that of a commercial IgG/IgM kit. The sensitivity of the indirect IgG and IgM ELISA tests was both 100% and the specificity of the indirect IgM and IgG ELISA test was 98% and 99%, respectively. The sensitivity and specificity of the capture IgM ELISA was 100% and 97%, respectively. The novel assays were found to detect HTNV-specific antibodies in acute phase sera from suspected HFRS patients in China. The results indicate that these novel ELISAs are suitable for the diagnosis of HTNV and for sero-epidemiological studies.

Characterization of hemorrhagic fever with renal syndrome caused by hantaviruses, Estonia

Thirty cases of hemorrhagic fever with renal syndrome (HFRS) due to Puumala virus (PUUV), Saaremaa virus (SAAV), and Dobrava virus infection were confirmed in Estonia. Except for the levels of serum creatinine, no remarkable differences were found in the clinical course of HFRS caused by PUUV and SAAV.

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

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

Utilization of hantavirus antibody results generated over a five-year period to develop an improved serologic algorithm for detecting acute Sin Nombre hantavirus infection

In the United States most cases of hantavirus pulmonary syndrome (HPS) are caused by the Sin Nombre virus (SNV) and are typically identified by serology. The goal of this study was to assess the performance of our hantavirus serologic testing algorithm by reviewing results generated over five years. Sera were screened for pan-hantavirus immunoglobulin (Ig)G and IgM by enzyme-linked immunosorbent assay (ELISA). Screen IgG+ sera were then tested by immunoblot for SNV glycoprotein-specific IgG, and screen IgM+ sera were tested for SNV-specific IgM using an ELISA that measured differential reactivity to SNV and Seoul nucleocapsid proteins. Although only 13% of sera were positive in one or both screening assays, 85% of screen+sera lacked SNV antibodies. Nearly all (97%) screen IgM-IgG+ samples lacked SNV IgG, and 90% of screen IgM+IgG- samples lacked SNV IgM. However, SNV IgM testing of screen IgM+IgG- samples appears to be necessary, since this test identified nine of 37 patients with acute HPS (based on clinical feedback). A screen IgM+IgG+ result was a good predictor of SNV antibody detection and acute HPS. These findings were used to design a modified algorithm that identified all 37 patients with acute HPS, but reduced the number of specimens that required SNV antibody testing by 42%.

Development of novel immunoglobulin G (IgG), IgA, and IgM enzyme immunoassays based on recombinant Puumala and Dobrava hantavirus nucleocapsid proteins

Human infections with Asian and European hantaviruses can result in hemorrhagic fever with renal syndromes of differing severities characterized by renal dysfunction and sometimes by pulmonary symptoms. For the serological detection of human infections by hantaviruses relevant for Europe, we developed monoclonal antibody capture immunoglobulin G (IgG) and IgA enzyme-linked immunosorbent assays (ELISAs) based on yeast-expressed nucleocapsid proteins of Puumala and Dobrava hantaviruses. Moreover, for diagnosis of acute infections, mu-capture IgM ELISAs were established with nucleocapsid proteins expressed in Drosophila melanogaster Schneider S2 cells. The cutoff values of the ELISAs were determined by investigation of up to 500 human anti-hantavirus-negative serum samples. The specificities of the Puumala and Dobrava virus-specific IgM, IgA, and IgG ELISAs were found to be 100%. The sensitivities of these ELISAs were determined to be 100% with panels of characterized anti-Puumala or anti-Dobrava virus-positive human serum samples. In most cases, Puumala and Dobrava virus infections could be differentiated by ELISA reactivity alone, i.e., endpoint titration with homologous and heterologous antigens.

Serological assays for the detection of human andes hantavirus infections based on its yeast-expressed nucleocapsid protein

BACKGROUND

The objective of the study was to develop and evaluate IgM and IgG ELISAs and an IgG Western blot test for the serological detection of human infections with Andes virus (ANDV), the major cause of hantavirus cardiopulmonary syndrome (HCPS) in South America.

METHODS

The entire nucleocapsid (N) protein-encoding sequence of ANDV (strain AH-1) was cloned and expressed in the yeast Saccharomyces cerevisiae. The polyhistidine-tagged recombinant N (rN) protein of ANDV was purified by nickel-chelation chromatography and characterized by its reactivity with different N-specific monoclonal antibodies. To detect an antibody response directed against ANDV in humans, indirect IgM and IgG ELISAs and an IgG Western blot test based on ANDV rN antigen were developed. The evaluation of the tests was performed using a negative serum panel and 63 blinded sera from Argentina and Chile, containing acute-phase and convalescent sera from HCPS patients.

RESULTS

The specificities and sensitivities for the IgM and IgG ELISAs were demonstrated to be very high. The IgG ELISA data were confirmed by the IgG Western blot assay based on the same rN antigen. Almost all anti-ANDV-positive sera reacted to higher endpoint titers with N protein of ANDV than with those of Sin Nombre, Laguna Negra or Puumala virus. The cross-reactivity of anti-ANDV-N IgG-positive sera to rN proteins of other hantaviruses was found to be increased with time after the onset of HCPS.

CONCLUSION

The high sensitivity of the novel assays should facilitate early diagnosis of ANDV infections and might contribute to a successful treatment of HCPS patients.

Viral zoonoses in Europe

A number of new virus infections have emerged or re-emerged during the past 15 years. Some viruses are spreading to new areas along with climate and environmental changes. The majority of these infections are transmitted from animals to humans, and thus called zoonoses. Zoonotic viruses are, as compared to human-only viruses, much more difficult to eradicate. Infections by several of these viruses may lead to high mortality and also attract attention because they are potential bio-weapons. This review will focus on zoonotic virus infections occurring in Europe.

Nucleocapsid protein of cell culture-adapted Seoul virus strain 80-39: analysis of its encoding sequence, expression in yeast and immuno-reactivity

Seoul virus (SEOV) is a hantavirus causing a mild to moderate form of hemorrhagic fever with renal syndrome that is distributed mainly in Asia. The nucleocapsid (N) protein-encoding sequence of SEOV (strain 80-39) was RT-PCR-amplified and cloned into a yeast expression vector containing a galactose-inducible promoter. A survey of the pattern of synonymous codon preferences for a total of 22 N protein-encoding hantavirus genes including 13 of SEOV strains revealed that there is minor variation in codon usage by the same gene in different viral genomes. Introduction of the expression plasmid into yeast Saccharomyces cerevisiae resulted in the high-level expression of a hexahistidine-tagged N protein derivative. The nickel-chelation chromatography purified, yeast-expressed SEOV N protein reacted in the immunoblot with a SEOV-specific monoclonal antibody and certain HTNV- and PUUV-cross-reactive monoclonal antibodies. The immunization of a rabbit with the recombinant N protein resulted in the induction of a high-titered antibody response. In ELISA studies, the N protein was able to detect antibodies in sera of experimentally infected laboratory rats and in human anti-hantavirus-positive sera or serum pools of patients from different geographical origin. The yeast-expressed SEOV N protein represents a promising antigen for development of diagnostic tools in serology, sero prevalence studies and vaccine development.

Development and evaluation of serological assays for detection of human hantavirus infections caused by Sin Nombre virus

BACKGROUND

The hantavirus cardiopulmonary syndrome (HCPS) was first recognized in 1993 after a cluster of acute respiratory distress syndrome deaths in the southwestern of the United States. The major causative agent of HCPS in North America is the Sin Nombre virus (SNV) carried by the deer mouse Peromyscus maniculatus. The first HCPS case imported to Europe was reported in 2002.

OBJECTIVES

The objective of the study was to develop and evaluate ELISA and Western blot tests for the serological detection of human infections caused by SNV including those imported to Europe.

STUDY DESIGN

A polyhistidine (His)-tagged recombinant nucleocapsid (rN) protein of SNV was expressed in Saccharomyces cerevisiae and purified by nickel chelation chromatography. On the basis of the purified SNV rN protein mu-capture and indirect IgM and IgG ELISAs and an IgG Western blot were developed. The evaluation of the tests was performed using a negative serum panel and a blinded serum panel from the US containing acute-phase sera from HCPS patients.

RESULTS

Based upon the results obtained using a panel of negative control sera the specificity for SNV mu-capture and indirect IgM and IgG ELISAs were found to be 100%. All 33 sera from SNV-infected HCPS patients included in the blinded panel were detected by the SNV mu-capture and indirect IgM ELISAs. Twenty-nine out of the 33 SNV-IgM positive sera reacted also in the SNV-IgG ELISA. An SNV-IgG Western blot confirmed the data of the SNV-IgG ELISA. Although the majority of anti-SNV positive sera cross-reacted with rN proteins of Puumala virus and Dobrava virus, the lacking reactivity of a few sera with these heterologous rN antigens in the corresponding IgM and IgG ELISAs demonstrates the value of virus-specific test formats for acute-phase sera.

CONCLUSIONS

The novel SNV ELISA and Western blot tests represent a useful tool for the serological detection of SNV infections.

Human and rodent humoral immune responses to Andes virus structural proteins

In the present work we identified B-cell epitopes recognized by sera of humans and rodents naturally infected with Andes virus, a hantavirus present in Chile and Argentina. Analysis of patient and rodent sera with overlapping peptides revealed 21 human and rodent epitopes on the three structural proteins. Whereas in the nucleoprotein the region comprising aa 248-260 was shown to be the key determinant of human sera, the major antigenic site of rodent antibody reactivity is located at aa 326-338. In G1, the main epitope recognized by human sera was mapped to aa 14-26, while rodent antibodies bound predominantly to aa 599-611. In contrast, humans and mice had strong responses to three regions in G2 (aa 691-703, aa 918-930, aa 955-967), of which the last two are associated with neutralization of Hantaan virus. This insight affords important information for the development of immunotherapies for the acute phase of hantavirus cardiopulmonary syndrome.

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.

High yields of stable and highly pure nucleocapsid proteins of different hantaviruses can be generated in the yeast Saccharomyces cerevisiae

Recently, the high-level expression of authentic and hexahistidine (His)-tagged Puumala (strain Vranica/Hällnäs) hantavirus nucleocapsid protein derivatives in the yeast Saccharomyces cerevisiae has been reported [Dargeviciute et al., Vaccine, 20 (2002) 3523-3531]. Here we describe the expression of His-tagged nucleocapsid proteins of other Puumala virus strains (Sotkamo, Kazan) as well as Dobrava (strains Slovenia and Slovakia) and Hantaan (strain Fojnica) hantaviruses using the same system. All nucleocapsid proteins were expressed in the yeast S. cerevisiae at high levels. The nucleocapsid proteins can be easily purified by nickel chelate chromatography; the yield for all nucleocapsid proteins ranged from 0.5 to 1.5 mg per g wet weight of yeast cells. In general, long-term storage of all nucleocapsid proteins without degradation can be obtained by storage in PBS at -20 degrees C or lyophilization. The nucleocapsid protein of Puumala virus (strain Vranica/Hällnäs) was demonstrated to contain only traces of less than 10 pg nucleic acid contamination per 100 microg of protein. The yeast-expressed nucleocapsid proteins of Hantaan, Puumala and Dobrava viruses described here represent useful tools for serological hantavirus diagnostics and for vaccine development.

Quality control measures for the serological diagnosis of hantavirus infections

BACKGROUND

With society's rapidly increasing mobility, patients infected with severe viral infections can become seriously ill at any place in Europe and elsewhere. Improving the diagnostics of these infections is the most important step in detecting the pathogens and dealing with them, and for this purpose, quality control measures are essential tools.

OBJECTIVES

To assess the diagnostic reality for rare hantavirus infections in Europe by (1) running a pre-evaluation panel (four samples, sent out in 1999) to optimise sample preparation and shipping procedure and afterwards (2) starting an External Quality Assurance (EQA) program (20 samples, sent out in 2001).

STUDY DESIGN

All samples sent out had to be tested for the presence of specific IgG and IgM antibodies against hantavirus. For the pre-evaluation panel, four samples were distributed (two samples IgG+/IgM-, one sample IgG-borderline/IgM-, one sample IgG-/IgM-), for the EQA 20 samples (six samples IgG+/IgM+, eight samples IgG+/IgM-, one sample IgG-borderline/IgM-, five samples IgG-/IgM-). Thirteen laboratories took part in the pre-evaluation panel, 18 laboratories participated in the first EQA run.

RESULTS

For the pre-evaluation panel, the participants reported correct results for 64% of the IgG-positive samples (85% excluding borderline-positive sample), and 92% for the IgG-negative sample. IgM testing was correctly negative in all laboratories. For the EQA, the participants reported correct results for 76% of the IgG-positive samples, and 97% correct results for the IgG-negative samples. For the IgM-positive samples, 53% correct results were reported, and 98% correct results for the IgM-negative samples.

CONCLUSIONS

The results presented here prove the importance of quality measures also for viruses only rarely suspected, like hantavirus, and they clearly demonstrate the need for improvement of the existing test systems.

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.

Diagnostic rapid tests for acute hantavirus infections: specific tests for Hantaan, Dobrava and Puumala viruses versus a hantavirus combination test

Hantaviruses infecting humans in Eurasia include Hantaan, Seoul, Puumala and the closely related Dobrava and Saaremaa viruses. These viruses are causative agents of hemorrhagic fever with renal syndrome (HFRS), which is recognized as a severe health care problem in several countries. Diagnostics of hantavirus infections relies on serology, performed principally with enzyme immunoassay (EIA) or immunofluorescence assay (IFA). We developed four 5-min immunochromatographic IgM-antibody tests for diagnostics of acute Puumala, Dobrava and Hantaan virus infections and a similar combination test to detect all Eurasian pathogenic hantavirus infections. We evaluated the assays using 100 fingertip blood samples collected randomly from Finnish volunteers, 28 confirmed hantavirus IgM-negative sera, and 77 sera from patients with acute infections of various hantaviruses. The specificities and sensitivities of the Puumala-, Dobrava- and Hantaan virus -specific tests varied from 96 to 100%, whereas, the combination test showed 96% specificity and 80 to 93% sensitivity. Cross-reactions were observed commonly between the Dobrava and the Hantaan virus tests, but only rarely between the Puumala and the Hantaan virus, or the Puumala and the Dobrava virus, tests. Altogether, the rapid tests showed less cross-reactivity than the respective EIA tests. According to the results, the performance of these tests meets well the requirements for diagnostic use. Nevertheless, the specific one-antigen tests were markedly more sensitive than the combination test. However, if optimized, a combination test would be suitable for regions where several hantaviruses circulate.

Enzyme-linked immunosorbent assay using recombinant antigens expressed in mammalian cells for serodiagnosis of tick-borne encephalitis

A recombinant plasmid that expresses the tick-borne encephalitis (TBE) virus premembrane (prM) and envelope (E) proteins in mammalian cells was constructed. Recombinant proteins retained antigenic and conformational structures similar to those of native virus proteins, and transfected cells released virus-like particles (VLPs), which were 1.13-1.14 g/ml in density and 20-30 nm in diameter, into the culture medium. Recombinant E proteins were used for the development of an enzyme-linked immunosorbent assay (ELISA) to detect TBE virus-specific IgM and IgG antibodies in serum. The results of this ELISA correlated well with the results of commercial ELISA, when tested with 95 serum samples from clinically TBE-suspected patients. In addition, ELISA using recombinant antigens showed no cross-reactivity against serum from Japanese encephalitis (JE) patients, despite the cross-reactivity shown by commercial ELISA systems. These observations indicated that this newly developed ELISA system could distinguish tick-borne encephalitis from Japanese encephalitis infection, and that it constitutes a useful and safe alternative to conventional ELISA systems.

The multimerization of hantavirus nucleocapsid protein depends on type-specific epitopes

Multimerization of the Hantaan virus nucleocapsid protein (NP) in Hantaan virus-infected Vero E6 cells was observed in a competitive enzyme-linked immunosorbent assay (ELISA). Recombinant and truncated NPs of Hantaan, Seoul, and Dobrava viruses lacking the N-terminal 49 amino acids were also detected as multimers. Although truncated NPs of Hantaan virus lacking the N-terminal 154 amino acids existed as a monomer, those of Seoul and Dobrava formed multimers. The multimerized truncated NP antigens of Seoul and Dobrava viruses could detect serotype-specific antibodies, whereas the monomeric truncated NP antigen of Hantaan virus lacking the N-terminal 154 amino acids could not, suggesting that a hantavirus serotype-specific epitope on the NP results in multimerization. The NP-NP interaction was also detected by using a yeast two-hybrid assay. Two regions, amino acids 100 to 125 (region 1) and amino acids 404 to 429 (region 2), were essential for the NP-NP interaction in yeast. The NP of Seoul virus in which the tryptophan at amino acid number 119 was replaced by alanine (W119A mutation) did not multimerize in the yeast two-hybrid assay, indicating that tryptophan 119 in region 1 is important for the NP-NP interaction in yeast. However, W119A mutants expressed in mammalian cells were detected as the multimer by using competitive ELISA. Similarly, the truncated NP of Seoul virus expressing amino acids 155 to 429 showed a homologous interaction in a competitive ELISA but not in the yeast two-hybrid assay, indicating that the C-terminal region is important for the multimerization detected by competitive ELISA. Combined, the results indicate that several steps and regions are involved in multimerization of hantavirus NP.

Hantaviruses in Estonia

Human serum samples collected from healthy individuals in 14 counties were screened by ELISA in order to investigate the presence of hantavirus infections in Estonia. Out of 1,234 serum samples, 124 were found positive for hantavirus-specific IgG and were subsequently serotyped by a focus reduction neutralization test. A total of 112 samples neutralized at least one of the examined hantaviruses-Puumala (PUUV), Saaremaa (SAAV), Dobrava (DOBV), Hantaan, and Seoul viruses-and thereby, the focus reduction neutralization test confirmed the overall hantavirus seroprevalence rate in Estonia to be 9.1%. Most of the sera showed a specific reaction (at least 4-fold higher endpoint titer) of neutralizing antibodies to PUUV (5.1%), while 3.4% showed a SAAV- or SAAV/DOBV-specific reaction. The fact that seven sera (0.6%) could not be serotyped may indicate the presence of an unknown hantavirus serotype. Hantavirus infections were confirmed in 13 of 14 investigated counties, with highly varying seroprevalence rates (1.0-28.4%). The sex ratio was 1.8:1.0 (M:F), and the antibody prevalence peaked in the age group 45-54 years. A total of 513 rodents of seven species trapped in seven counties were examined for the presence of hantavirus antigen, in order to study the distribution of hantavirus natural carriers. Two species, Clethrionomys glareolus and Apodemus agrarius, were found positive for hantaviral antigen in 13.7% and 4.5% of the investigated rodents, respectively. Analyses of viral sequences recovered from infected C. glareolus tissue samples showed that the infecting virus belonged to the PUUV genotype, confirming that PUUV circulates in mainland Estonia. The Estonian PUUV strains were placed in the closest proximity to Russian PUUV strains in phylogenetic trees, suggesting a common evolutionary history. Together with earlier data on SAAV in A. agrarius, the results revealed that two hantaviruses, PUUV and SAAV, are common in Estonia and that the incidence of human infection is high in both cases.

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.

Comparison of a new immunochromatographic rapid test with a commercial EIA for the detection of Puumala virus specific IgM antibodies

BACKGROUND

Hantaviruses are associated with two human diseases: haemorrhagic fever with renal syndrome (HFRS) and Hantavirus pulmonary syndrome (HPS). Puumala virus (PUUV), which is one of the Hantaviruses, is a causative agent of nephropathia epidemica (NE), a mild form of HFRS.

OBJECTIVE

a new 5 min rapid test, POC PUUMALA (Erilab Ltd, Finland), for detecting IgM antibodies to PUUV was evaluated and compared with the commercially available Hantavirus (Puumala) IgM ELISA test (Progen, Germany). Discrepant test results between the two tests were confirmed by a mu-capture reference EIA.

STUDY DESIGN

Two hundred and thirty five serum samples, which had earlier been analyzed with the Progen IgM ELISA, were assayed with the POC PUUMALA rapid test. Five persons, without knowing the Progen IgM ELISA test results, interpreted independently the rapid test results. In addition, a panel of 48 serum samples was analyzed in parallel with the rapid test and the Progen IgM ELISA by one technician in daily routine diagnostics in a clinical microbiology laboratory.

RESULTS

the agreement between the results of the five interpreters was 95%, and the congruence of the results between individual readers and commercial ELISA test varied from 93 to 96%. Diagnostic efficacy of the rapid test varied between 98 and 99% compared with 96% of the Progen IgM ELISA. The POC PUUMALA rapid test showed higher or similar sensitivity compared with the Progen IgM ELISA, whereas both the tests had similar levels of specificity.

CONCLUSIONS

the analytical performance of the POC PUUMALA rapid test was found to be as good or even slightly better than the analytical performance of the Progen IgM ELISA. In addition, the rapid and straightforward procedure makes the POC PUUMALA a feasible tool for the diagnosis of the acute PUUV infection.

Hantavirus infections and their prevention

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

New immunochromatographic rapid test for diagnosis of acute Puumala virus infection

A new immunochromatographic rapid test, POC PUUMALA (Erilab Ltd., Kuopio, Finland), for detection of acute-phase Puumala virus (PUUV) infection was developed based on a highly purified baculovirus-expressed PUUV nucleocapsid protein antigen and lateral immunodiffusion techniques. After addition of sample (5 microl of serum, plasma, or fingertip blood) and buffer, PUUV-specific immunoglobulin M (IgM) antibodies, if present, together with the gold-conjugated anti-human IgM, formed a specific colored line in 5 min. The sensitivity and specificity of the test were evaluated with 200 serum samples and 30 fingertip blood samples. The reference method for the serum samples was a micro-capture enzyme immunoassay (EIA) for IgM and an immunofluorescence assay (IFA) for IgG antibodies. The analytical sensitivity and specificity of the rapid test were 100 and 99%, respectively, for unfrozen serum samples (n = 103; 12 PUUV IgM-positive samples). When freeze-thawed serum samples were used, the sensitivity and specificity were each 97.1% (n = 70; 35 PUUV IgM-positive samples). The specificity of the test was 96.2% for 27 serum samples with nonspecific IgM antibodies or rheumatoid factor (RF). The fingertip blood samples (n = 30) were negative, but they gave clear positive results when spiked with IgM-positive sera (n = 20). The results were in good agreement with the standard diagnostic methods. The rapid performance, the lack of need for refined laboratory equipment, and the high specificity with fresh serum and fingertip blood samples indicate that the developed POC PUUMALA rapid test is a useful tool for fast diagnosis of acute PUUV infection.