An Insight into Nanomedicinal Approaches to Combat Viral Zoonoses

BACKGROUND

Emerging viral zoonotic diseases are one of the major obstacles to secure the "One Health" concept under the current scenario. Current prophylactic, diagnostic and therapeutic approaches often associated with certain limitations and thus proved to be insufficient for customizing rapid and efficient combating strategy against the highly transmissible pathogenic infectious agents leading to the disastrous socio-economic outcome. Moreover, most of the viral zoonoses originate from the wildlife and poor knowledge about the global virome database renders it difficult to predict future outbreaks. Thus, alternative management strategy in terms of improved prophylactic vaccines and their delivery systems; rapid and efficient diagnostics and effective targeted therapeutics are the need of the hour.

METHODS

Structured literature search has been performed with specific keywords in bibliographic databases for the accumulation of information regarding current nanomedicine interventions along with standard books for basic virology inputs.

RESULTS

Multi-arrayed applications of nanomedicine have proved to be an effective alternative in all the aspects regarding the prevention, diagnosis, and control of zoonotic viral diseases. The current review is focused to outline the applications of nanomaterials as anti-viral vaccines or vaccine/drug delivery systems, diagnostics and directly acting therapeutic agents in combating the important zoonotic viral diseases in the recent scenario along with their potential benefits, challenges and prospects to design successful control strategies.

CONCLUSION

This review provides significant introspection towards the multi-arrayed applications of nanomedicine to combat several important zoonotic viral diseases.

Hantavirus and tuberculosis co-infection in an Indian child

Hantaviruses are a group of antigenically distinct viruses carried out in rodents and insectivores. Humans are accidental hosts and get infected by aerosols generated from contaminated urine, faeces and saliva of infected rodents. Hantaviruses are identified as aetiological agents of two human diseases, haemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. Hantavirus causing pulmonary renal disease has rarely been reported in children in India. Hantavirus infection is uncommon under the age of 12 years. We report a 9-year-old girl from Mumbai, India with fever, bilateral pleural effusion, thrombocytopaenia, haemoconcentration and oliguria due to hantavirus infection. She also had associated tuberculosis.

Hantavirus infection: a case report from India

The clinical presentation of hantavirus infections in India is unclear. We report here a case of hantavirus infection in a 46 year old quarry worker presenting with fever, abdominal pain, jaundice, thrombocytopenia and renal dysfunction. Seroconversion and rising anti-hantavirus IgG titers were taken as evidence of hantavirus infection. Clinicians should consider hantavirus infections in the differential diagnosis of acute febrile illness along with scrub typhus, leptospirosis and dengue.

Phylogenetic characterization of hantaviruses from wild rodents and hantavirus pulmonary syndrome cases in the state of Parana (southern Brazil)

Over 1,100 cases of hantavirus pulmonary syndrome (HPS) have occurred in Brazil since 1993, but little is known about Brazilian hantaviruses, and many of their rodent hosts remain unknown. The Araucaria hantavirus (ARAUV) was described recently from HPS patients from Paraná, in southern Brazil, but its host could not be identified. In this study, rodents were captured from regions with high HPS prevalence to address this issue. ARAUV RNA was detected in three distantly related rodent species: Oligoryzomys nigripes, Oxymycterus judex and Akodon montensis. Furthermore, a specimen of A. montensis was infected with a Jaborá-like virus, implying that A. montensis can be infected by at least two different hantaviruses. The presence of the same hantavirus strain in three different rodent species and the co-circulation of two different strains in the same rodent species highlight the potential for genomic reassortment, which could have an impact on hantavirus transmission dynamics in nature and on human epidemiology.

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.

Truncated Recombinant Dobrava Hantavirus Nucleocapsid Proteins Induce Strong, Long-Lasting Immune Responses in Mice

We describe the cloning and expression of Dobrava hantavirus (DOBV) nucleocapsid proteins and a truncated form consisting of the first 118 N-terminal amino acids, and the capacity of these E. coli ICONE 200-expressed recombinant proteins (rNp) to induce a protective immune response against DOBV in mice. As an alternative carrier protein, the outer membrane protein A derived from Klebsiella pneumoniae (rP40) has been coupled to different rNp constructs. All recombinant proteins were found to be highly immunogenic after three immunizations of rNp. The immunizations resulted in the induction of a strong Np-specific IgG response with a predominance of IgG1 over IgG2b and IgG2a, suggesting a mixed Th1/Th2 cell involvement. A specific IgG3 response could not be detected. Mice immunized with recombinant DOBV rNp without rP40 showed lower nucleocapsid-specific antibody responses in comparison with the rP40-conjugated constructs, but all mice were found to be protected against DOBV challenge. Our results indicate that the rNp constructs coupled to rP40, represent promising vaccine candidates.

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.

The in vitro and in vivo protective activity of monoclonal antibodies directed against Hantaan virus: potential application for immunotherapy and passive immunization

Hantaan virus (HTNV), a member of the genus Hantavirus, family Bunyaviridae, is an etiologic agent causing a serious human disease, hemorrhagic fever with renal syndrome (HFRS), with a mortality as high as 15% and is also a potential bioterrorism agent. It is urgently needed to develop anti-HTNV-neutralizing monoclonal antibodies (MAbs) for treatment and prevention of HTNV infection. In the present study, 18 murine MAbs directed against HTNV strain Chen were generated and characterized. Among these MAbs, 13 were directed against viral nucleocapsid protein (NP), four recognized the viral envelope glycoprotein G2 and one reacted with both NP and G2. Only those MAbs that recognize the epitopes on G2 were positive in hemagglutination inhibition (HI) test and had in vitro virus-neutralizing activity and in vivo protective activity against HTNV infection of susceptible mice. Since all the mice were protected by administration of the virus-neutralizing MAbs one day before and two days after HTNV challenge, these neutralizing MAbs are potentially useful for pre- and post-exposure prophylaxis and for immunotherapy of HTNV infection. Phase II clinical trials of these neutralizing MAbs for emergent treatment of patients with HTNV infection in early stages of HRFS are carried out in endemic areas in China.

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.

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.

Highly sensitive Taqman PCR detection of Puumala hantavirus

An increasing number of clinical cases of Hantavirus infections have been reported from various regions in Asia, Europe and North America. Hantaviruses (family Bunyaviridae, genus Hantavirus) are enveloped and possess a single-stranded trisegmented RNA genome of negative polarity. Rodents or insectivores are natural hosts of hantaviruses and transmit the virus to humans chiefly by aerosolisation. These viruses are the causative agents of haemorrhagic fever with renal and pulmonary syndromes. In the northeast of France, Puumala hantavirus causes, every year, more than 150 mild forms of haemorrhagic fever with a renal syndrome known as nephropathia epidemica. Serological tests may lack sensitivity for diagnosing early stages of infection and virus isolation is limited because it grows poorly in cell culture. Since reverse transcription (RT)-PCR amplification is an efficient method for detecting viral genomes in patient specimens, we developed an assay using a Taqman probe and compared it with the classical RT-PCR amplification. To achieve this goal, a Puumala strain was grown in Vero E6 cells and RNA extracted from the culture supernatant. We found that the semi-nested RT-PCR detected a minimal amount of 300 TCID(50) mL(-1), while the Taqman PCR allowed detection of less than 10 TCID(50) mL(-1 )and provided a quantitative analysis.

T-helper and humoral responses to Puumala hantavirus nucleocapsid protein: identification of T-helper epitopes in a mouse model

Puumala hantavirus (PUUV) is a rodent-borne agent causing nephropathia epidemica in humans, a milder form of haemorrhagic fever with renal syndrome occurring in Fennoscandia, central Europe and western Russia. In this study we characterized the immunogenicity of an E. coli-expressed nucleocapsid (N) protein of PUUV (strain Kazan-E6) in inbred mice (BALB/c, CBA and C57/BL6). The recombinant N (rN) protein raised PUUV-specific antibodies in all three tested murine haplotypes, and all IgG subclasses were detected. Epitope mapping using peptides spanning the N protein revealed that the B-cell recognition sites were mainly located at the amino-terminal part of the protein. Proliferative T-helper (Th) lymphocyte responses were detected in all haplotypes after a single immunization with rN. Several Th-recognition sites, spanning amino acids 6-27, 96-117, 211-232 and 256-277, were identified using overlapping peptides. Peptides representing the identified sites could also prime Th-lymphocytes to proliferate in response to recall with rN protein, thereby confirming the authenticity of the identified sites. The rN-primed Th-lymphocytes produced predominantly interleukin (IL)-2 and gamma interferon, together with lower levels of IL-4 and IL-6, indicating a mixed Th1/Th2 response.

Immunoglobulin A responses to Puumala hantavirus

Puumala hantavirus (PUUV) causes nephropathia epidemica (NE), a form of haemorrhagic fever with renal syndrome that occurs in northern and central Europe. The immunoglobulin A (IgA) response in NE patients was studied. The levels of total serum IgA in acute-phase samples from NE patients were found to be significantly elevated when compared with the levels in healthy controls. ELISAs for detection of the IgA1 and IgA2 responses against each PUUV structural protein (N, G1 and G2) were developed and evaluated. Sequential sera from NE patients (acute, convalescent, 2-year) and 10-20 year NE-convalescent sera were examined. Most patients developed detectable levels of IgA1 against N and G2, while the G1 responses were low or undetectable. Seven of nine 10-20 year sera contained virus-specific IgA1, which may indicate the prolonged presence of viral antigens after the initial infection. PEPSCAN analysis revealed several IgA-reactive antigenic regions in the N protein. Serum IgA and IgG was purified by affinity chromatography and examined by a virus-neutralization assay. Three of five sera from acute-phase NE patients contained neutralizing IgA1. The diagnostic potential of the PUUV-specific IgA1 response was evaluated. The N and G2 assays showed specificities of 100% with sensitivities of 91 and 84%, respectively, compared with an IgM mu-capture ELISA. Several NE patients, clinically diagnosed for acute PUUV infection, with borderline or undetectable levels of PUUV-specific IgM, were found to be highly positive for the presence of PUUV N-specific serum IgA1, proving the diagnostic value of IgA analysis as a complement to detection of IgM.

A neutralizing recombinant human antibody Fab fragment against Puumala hantavirus

A combinatorial human antibody Fab pComb3H library, generated from splenic lymphocytes of a Puumala hantavirus (PUUV) immune individual, was selected against PUUV using the phage display technique. Panning was carried out with antigens immobilized by MAbs directed to the two PUUV envelope glycoproteins G1 and G2. Thirteen Fabs, with reactivity directed to PUUV and specifically the G2 protein, as assessed by immunofluorescence and ELISA respectively, were isolated in crude preparations. By a focus reduction neutralization test (FRNT), four of the 13 crude Fab preparations exhibited type-specific neutralization of PUUV (strain Sotkamo) with 44-54% reduction in the number of foci. After affinity purification, the four Fab clones exhibited 50% focus reduction of PUUV at concentrations below 2 microg/ml. Sequencing of the heavy and light chain complementarity determining regions (CDR) 1-3 showed that the four selected clones were identical within the antibody binding regions. In inhibition tests with the PUUV G2-specific MAbs, 4G2 and 1C9, a new epitope important for neutralization, designated as G2-a3, was defined. This epitope, overlapping partially the neutralizing epitope recognized by the human MAb 1C9, seems to be unique for the PUUV serotype since none of the Fab clones neutralized any of the other hantaviruses tested.

New chimaeric hepatitis B virus core particles carrying hantavirus (serotype Puumala) epitopes: immunogenicity and protection against virus challenge

Virus-like particles generated by the heterologous expression of virus structural proteins are able to potentiate the immunogenicity of foreign epitopes presented on their surface. In recent years epitopes of various origin have been inserted into the core antigen of hepatitis B virus (HBV) allowing the formation of chimaeric HBV core particles. Chimaeric core particles carrying the 45 N-terminal amino acids of the Puumala hantavirus nucleocapsid protein induced protective immunity in bank voles, the natural host of this hantavirus. Particles applied in the absence of adjuvant are still immunogenic and partially protective in bank voles. Although a C-terminally truncated core antigen of HBV (HBcAg delta) tolerates the insertion of extended foreign sequences, for the construction of multivalent vaccines the limited insertion capacity is still a critical factor. Recently, we have described a new system for generating HBV 'mosaic particles' in an Escherichia coli suppressor strain based on a readthrough mechanism on a stop linker located in front of the insert. Those mosaic particles are built up by both HBcAg delta and the HBcAg delta/Puumala nucleocapsid readthrough protein. The particles formed presented the 114 amino acid (aa) long hantavirus sequence, at least in part, on their surface and induced antibodies against the hantavirus sequence in bank voles. Variants of the stop linker still allowed the formation of mosaic particles demonstrating that stop codon suppression alone is sufficient for the packaging of longer foreign sequences in mosaic particles. Another approach to increase the insertion capacity is based on the simultaneous insertion of different Puumala nucleocapsid protein sequences (aa 1-45 and aa 75-119) into two different positions (aa 78 and behind aa 144) of a single HBcAg molecule. The data presented are of high relevance for the generation of multivalent vaccines requiring a high insertion capacity for foreign sequences.

Dobrava virus infection: serological diagnosis and cross-reactions to other hantaviruses

Recent data have shown that Dobrava (DOB) hantavirus is the cause of severe haemorrhagic fever with renal syndrome (HFRS) in central and eastern Europe. To determine whether serological assays need to be based on the homologous viral antigen rather than on closely related hantavirus antigens, acute and convalescent sera from patients with HFRS collected in former Yugoslavia were examined for IgM and IgG to three hantavirus antigens; DOB, Hantaan (HTN) and Puumala (PUU). Focus reduction neutralization test was included for comparison and confirmation of the enzyme-linked immunosorbent assay (ELISA) results. Although the results showed that the cross-reactivity was high between these three antigens during the acute phase of the disease, one of 155 patients serum samples reacted only in the DOB antigen-based IgM assay. The evaluation of IgG reactivities revealed that a DOB antigen-based IgG ELISA has to be used in sero-epidemiological studies; 7.1% (11/155) of the acute phase/early convalescent sera and 12.5% (2/16) of the late convalescent sera, respectively, reacted only with the homologous DOB antigen.

Isolation and characterization of a hantavirus from Lemmus sibiricus: evidence for host switch during hantavirus evolution

A novel hantavirus, first detected in Siberian lemmings (Lemmus sibiricus) collected near the Topografov River in the Taymyr Peninsula, Siberia (A. Plyusnin et al., Lancet 347:1835-1836, 1996), was isolated in Vero E6 cells and in laboratory-bred Norwegian lemmings (Lemmus lemmus). The virus, named Topografov virus (TOP), was most closely related to Khabarovsk virus (KBR) and Puumala viruses (PUU). In a cross focus reduction neutralization test, anti-TOP Lemmus antisera showed titers at least fourfold higher with TOP than with other hantaviruses; however, a rabbit anti-KBR antiserum neutralized TOP and KBR at the same titer. The TOP M segment showed 77% nucleotide and 88% amino acid identity with KBR and 76% nucleotide and 82% amino acid identity with PUU. However, the homology between TOP and the KBR S segment was disproportionately higher: 88% at the nucleotide level and 96% at the amino acid level. The 3' noncoding regions of KBR and the TOP S and M segments were alignable except for 113- and 58-nucleotide deletions in KBR. The phylogenetic relationships of TOP, KBR, and PUU and their respective rodent carriers suggest that an exceptional host switch took place during the evolution of these viruses; while TOP and KBR are monophyletic, the respective rodent host species are only distantly related.

Development of humoral cross-reactivity to the nucleocapsid protein of heterologous hantaviruses in nephropathia epidemica

A hantavirus infection is followed by a prominent antibody response to the viral nucleocapsid protein. Antibodies from patients infected with one hantavirus cross-react to varying degrees with the nucleocapsid protein of other viruses of the genus. We studied the cross-reactivity in serially obtained blood samples from 17 patients with nephropathia epidemica, a European form of hemorrhagic fever with renal syndrome caused by Puumala virus. Recombinant truncated nucleocapsid protein (aa 1-117) of Puumala virus and four other hantaviruses, Hantaan, Seoul, Dobrava and Sin Nombre viruses, were used as antigens in an indirect ELISA. In most patients, an IgG response to the Puumala virus derived recombinant protein was detected within 2-8 days of onset of disease, remained high for 2-5 months, and declined gradually within 2-3 years. All patients had IgG antibodies cross-reacting with the nucleocapsid protein of Sin Nombre virus. The ratio of the ELISA values obtained with Sin Nombre vs. Puumala virus protein as antigen increased with time after onset of disease. To a lesser extent, cross-reacting IgG antibodies also occurred to Hantaan, Seoul, and Dobrava virus antigens. In the acute phase of the disease, two patients showed IgG antibodies to one or more of these viruses whereas 2-5 months later, 11 of 16 patients had IgG antibodies to all three viruses. IgM and IgA responses to the nucleocapsid protein of Puumala virus were transitory and cross-reactivities were weak. In conclusion, after onset of nephropathia epidemica the IgG response to the Puumala virus nucleocapsid protein was associated with a gradually increasing cross-reactivity to the nucleocapsid protein of heterologous hantavirus. Our findings have implications for the interpretation of serological data, both in the diagnostics of nephropathia epidemica and in seroprevalence studies.

Evaluation of Puumala virus IgG and IgM enzyme immunoassays based on recombinant baculovirus-expressed nucleocapsid protein for early nephropathia epidemica diagnosis

BACKGROUND

Puumala virus (PUU), a member of Hantavirus genus, is the causative agent of nephropathia epidemica (NE), a milder form of hemorrhagic fever with renal syndrome (HFRS). Rapid diagnosis is essential for clinical management of NE.

OBJECTIVES

To evaluate the usefulness of recombinant protein-based IgM (direct- and mu-capture) and IgG (direct-and antigen (Ag)-capture) enzyme immunoassays (EIA) in early diagnosis of NE in comparison to IgG immunofluorescence assay (IF), and to find out the time limit for PUU-specific antibody seroconversion.

STUDY DESIGN

The specific IgM and IgG antibody responses in serum were analyzed in 109 patients (235 serial sera) and 114 patients (233 serial sera), respectively. The serum panel used was selected from a larger material according to the availability of information concerning the date after onset of symptoms, the panel also containing NE patients who had been IgG-IF negative in their first (early) samples to find out the possible differences between sensitivities of the EIAs and IF.

RESULTS

All NE patients tested became IgM-positive at the latest on the 6th (mu-capture EIA) or 7th (direct-IgM EIA) day after onset of symptoms. Out of a panel of very early NE-patient sera (n = 38) that could not be detected by IgG-IF, 66% were already positive with both direct-IgM EIA and mu-capture EIA. When comparing IgG EIAs and IgG-IF, 98% of IF-positive sera from NE patients were also positive with direct-IgG EIA, and 99% with Ag-capture IgG EIA. Out of a panel of very early NE-patient sera (n = 37) that could not be detected by IgG-IF, 57% were positive with direct-IgG EIA, and 27% with Ag-capture IgG EIA.

CONCLUSIONS

The baculovirus-expressed PUU-N-based IgG and IgM EIAs were found most suitable for NE diagnosis, giving the opportunity in some cases for earlier diagnosis as compared with PUU-IgG IF.

Chimaeric HBV core particles carrying a defined segment of Puumala hantavirus nucleocapsid protein evoke protective immunity in an animal model

Hantaviruses are rodent-born agents which are pathogenic in humans causing haemorrhagic fever with renal syndrome or hantavirus pulmonary syndrome. To induce a protective immunity against a European hantavirus (Puumala) we constructed chimaeric hepatitis B virus (HBV) core particles carrying defined fragments of the Puumala virus nucleocapsid protein. After immunisation of bank voles, the natural host of Puumala virus, with core particles possessing an insertion of the N-terminal part of Puumala virus nucleocapsid protein, four of five animals were protected against subsequent virus challenge. The results show that the major protective region of the nucleocapsid protein is located between amino acids 1 and 45 and that chimaeric HBV core-like particles are useful carriers of foreign protective epitopes.

Prevalence of serum antibodies to hantaviruses in northern Sweden as measured by recombinant nucleocapsid proteins

An enzyme-linked immunosorbent assay (ELISA) based on recombinant nucleocapsid protein (rN delta) (aa 1-117) of Hantaan, Seoul, Dobrava, Sin Nombre and Puumala hantaviruses was used to determine the prevalence of antibodies among randomized and stratified individuals from northern Sweden. In total, 137/1533 individuals (8.9%) had specific serum IgG antibodies to Puumala virus, the only hantavirus known to occur in the region. The prevalence of antibodies to Puumala virus (8.9%) was determined to be higher than previously reported (5.4%) in the same serum material, by use of immunofluorescence assay. As expected, sera reactive to Puumala virus rN delta did frequently cross-react with Sin Nombre virus protein. Unexpectedly, 21/1533 (1.4%) individuals recognized the Sin Nombre virus rN delta exclusively. Another 8 subjects showed reactivity in the ELISA to Hantaan, Seoul, or Dobrava virus-derived rN delta but not Puumala virus or Sin Nombre virus rN delta. The present demonstration in some individuals of antibodies specifically recognizing the Sin Nombre, Dobrava, Hantaan and Seoul virus protein justifies an awareness of the possibility that hantaviruses antigenically different from Puumala virus might occur in the region.

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

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

Characterization of Tula virus antigenic determinants defined by monoclonal antibodies raised against baculovirus-expressed nucleocapsid protein

Tula virus was recently discovered by RT-PCR in lung samples from European common voles (Microtus arvalis and M. rossiaemeridionalis). Since virus isolation attempts had been unsuccessful, no antigen was available for analysis or for use in immunoassays. To circumvent this, complete Tula virus nucleocapsid protein (bac-TUL-N) was expressed in recombinant baculovirus. Rodent antibody end-point titers to bac-TUL-N and to truncated N fragments indicated that the NH2-terminal region is the major antigenic target and revealed a high cross-reactivity to Puumala virus N. Immunizations with crude bac-TUL-N preparations evoked high antibody responses to native hantavirus N in Balb/c mice and six monoclonal antibodies (Mabs) were generated. Epitope mapping of the Mabs, based on a competitive assay, reactivities to truncated recombinant N fragments, and reactivity patterns to different hantavirus strains, identified five recognition sites on Tula virus N. One epitope, which was identified as specific for Tula virus, was located in a region of N which is highly variable among the hantaviruses (aa 226-293), and four epitopes were mapped to the NH2-terminal region of the protein (aa 1-61). One epitope was expressed only in Tula and Prospect Hill viruses, one epitope in Tula, Prospect Hill, Khabarovsk, and Sin Nombre viruses, while two epitopes were conserved in all examined hantaviruses carried by rodents within the subfamily Arvicolinae of the Muridae family.

Biotin-labeled antigen: a novel approach for detection of Puumala virus-specific IgM

A novel enzyme-linked immunosorbent assay, BLA IgM-ELISA, based on baculovirus-expressed Puumala (PUU) virus nucleocapsid protein, was developed for rapid diagnosis of nephropathia epidemica. The recombinant antigen (bac-PUU-N) was purified to homogeneity by HPLC and conjugated to biotin. The biotin-streptavidin system, in combination with the mu-capture technique, rendered the BLA IgM-ELISA a sensitivity similar to or higher than that of PUU virus IgM mu-capture ELISA based on native antigen. The assay was shown to be highly specific when evaluated using a panel of 160 patient and control sera.

Genetic variation in Tula hantaviruses: sequence analysis of the S and M segments of strains from Central Europe

Hantavirus carried by the European common vole Microtus arvalis from Moravia (Czech Republic) was analyzed by RT-PCR-sequencing and by reactivity with a panel of monoclonal antibodies (MAbs). Sequencing of the full-length S segment and the proximal part of the M segment showed that the virus belonged to genotype Tula (TUL) we discovered earlier in Microtus arvalis from Central Russia. This finding supported the concept of host dependence of hantaviruses. Phylogenetic analyses suggested a similar evolutionary history for S and M genes of TUL strains; thus far there is no evidence for reassortment in TUL. Geographic clustering of TUL genetic variants was observed and different levels of the genetic variability were revealed resembling those estimated for another hantavirus, Puumala (PUU). Comparison of the deduced N protein sequence from Russia and from Moravia showed that genetic drift in TUL occurred not only by accumulation of point mutations but also by the deletion of a nucleotide triplet. It encoded Ser252 which was located within a highly variable hydrophilic part of the N protein carrying B-cell epitopes and presumably forming a loop. Analysis of naturally expressed TUL N-antigen derived from lung tissue of infected voles with MAbs indicated antigenic heterogeneity among TUL strains.

Antigenic relationships of hantavirus strains analysed by monoclonal antibodies

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