Stability of a formalin-inactivated Rift Valley fever vaccine: evaluation of a vaccination campaign for cattle in Mozambique

In Africa and the Arabian Peninsula, outbreaks of Rift Valley fever (RVF) are characterized by abortions in gestating animals and high mortality rates among domestic ruminants. An immunization program using a formalin-inactivated vaccine was initiated in Mozambique in 2002 to control RVF in cattle. In this intervention, the vaccine must be transported for more than a week within the country before it can be administered to the animals, and it is practically impossible to maintain low storage temperatures during that time. Here, we evaluated the influence of transportation conditions on the efficacy of the vaccine. Sixty-three previously unvaccinated and RVF virus seronegative cattle were divided into four groups, which were given vaccine that had been stored for 1 week at 4°C (n=9, group A), at 25°C (n=8, group B), or alternating between 4 and 25°C (n=8, group C), or under the temperature conditions ordinarily occurring during transportation within Mozambique (n=38, group D). The antibody responses induced were monitored for 6-9 months and in some animals up to 21 months. Two immunizations (3 weeks apart) with the formalin-inactivated vaccine induced a long-lasting neutralizing antibody response that was still detectable up to 21 months later. The antibody titers in the animals did not differ significantly between the temperature-assigned vaccine groups A, B, and C, whereas they were significantly higher in group D. These results show that the formalin-inactivated RVF virus vaccine is stable, and, importantly, it is not adversely affected by the variation in temperature that ordinarily occurs during transport within Mozambique.

Tick-borne encephalitis increasing in Sweden, 2011

Until August, 161 cases of tick-borne encephalitis (TBE) were recorded in Sweden for 2011, leading to an incidence of 1.7 per 100,000 population. Fifty to 59 year-olds (24%) were most affected, 55% of the cases were males. An increase in TBE in Sweden has occurred in the last decade and might be explained by enlarged tick populations, more contact between TBE virus infected ticks and man, and also by growing awareness of the disease. Climatic conditions may have contributed to the increase.

Identification of Anaplasma phagocytophilum in tick populations in Estonia, the European part of Russia and Belarus

Anaplasma phagocytophilum is associated with diseases of goats, sheep, cattle, dogs and horses. In the beginning of the 1990s it was identified as a human pathogen, causing human granulocytic anaplasmosis (HGA) in the USA, Europe and the far east of Russia. A. phagocytophilum is maintained in nature in an enzootic cycle including ticks as the main vector and a wide range of mammalian species as reservoirs. Ixodes ricinus and I. persulcatus ticks were collected in Estonia, Belarus and the European part of Russia and screened for the presence of A. phagocytophilum by real-time PCR. Positive samples were found only among I. ricinus, in 13.4% in the European part of Russia, 4.2% in Belarus, 1.7% in mainland Estonia and 2.6% on Saaremaa Island. Positive samples were sequenced for partial 16S rRNA, groESL and ankA genes and phylogenetic analyses were performed. The results showed that A. phagocytophilum circulating in Eastern Europe belongs to different groESL lineages and 16S rRNA gene variants and also consists of variable numbers of repetitive elements within the ankA gene.

Viscoelastic Properties of Healthy Human Artery Measured in Saline Solution by AFM-Based Indentation Technique

Using an Atomic Force Microscope with an attachment for indentation, we have measured local, in vitro mechanical properties of healthy femoral artery tissue held in saline solution. The elastic modulus (34.3 kPa) and viscoelastic response (τɛ = 16.9 s and τσ = 29.3 s) of the unstretched, intimal vessel wall have been determined using Sneddon theory and a three element model (standard linear solid) for viscoelastic materials. The procedures necessary to employ the indenting attachment to detect elastic moduli in the kPa range in liquid are described.

Self-priming of reverse transcriptase impairs strand-specific detection of dengue virus RNA

Dengue virus infection is the most frequent arthropod-borne infection affecting humans in the world. Our understanding of the pathophysiological events leading to mild or severe outcomes of the disease remains limited by the fact that viral target cells in the human body are poorly characterized. One of the most sensitive strategies for detecting cells supporting active replication of this positive-strand RNA virus is the search for the replicative intermediate, an antigenome of negative polarity, by RT-PCR. However, a phenomenon described as 'false priming' of the reverse transcriptase (RT) prevents strand-specific detection. The results of the current study showed that this event corresponds to cDNA synthesis that is independent of any primer addition. This property was general to all RNAs tested and was not associated with small free nucleic acids, such as tRNAs and microRNAs. Rather, it corresponded to initiation of cDNA synthesis from the 3' end of the RNA template, and a model is proposed in which the template RNA snaps back upon itself and creates a transient RNA primer suitable for the RT. Such a property would explain why many assays proposed for detection of a replicative intermediate are not specific, and may help in the development of a molecular biology protocol that could allow replication studies of RNA viruses of human interest, such as dengue virus, hepatitis C virus and enteroviruses.

The European network of Biosafety-Level-4 laboratories: enhancing European preparedness for new health threats

Emerging and re-emerging infections and possible bioterrorism acts will continue to challenge both the medical community and civilian populations worldwide, urging health authorities to respond rapidly and effectively. Established in 2005, the European Community (EC)-funded European Network of Biosafety-Level-4 laboratories (Euronet-P4), which brings together the laboratories in Porton Down, London, Hamburg, Marburg, Solna, Lyon and Rome, seeks to increase international collaboration in the areas of high containment laboratory biosafety and viral diagnostic capability, to strengthen Europe's capacity to respond to an infectious disease emergency, and to offer assistance to countries not equipped with such costly facilities. Network partners have agreed on a common strategy to fill the gaps identified in the field of risk group-4 agents’ laboratory diagnosis, namely the lack of standardization and of reference samples. The network has received a further 3-year funding, to offer assistance to external laboratories, and to start the planning of field activities.

Serological and genetic evidence for the presence of Seoul hantavirus in Rattus norvegicus in Flanders, Belgium

Seoul hantavirus (SEOV), carried by Rattus rattus (black rat) and R. norvegicus (Norway, brown rat), was reported to circulate as well as cause HFRS cases in Asia. As Rattus sp. are present worldwide, SEOV has the potential to cause human disease worldwide. In Europe however, only SEOV prevalence in rats from France was reported and no confirmed cases of SEOV infection were published. We here report genetic and serological evidence for the presence of SEOV virus in brown rat populations in Belgium. We also serologically screened an at-risk group that was in contact with R. norvegicus on a daily basis and found no evidence for SEOV infection.

Gene segment reassortment between American and Asian lineages of avian influenza virus from waterfowl in the Beringia area

Since prehistoric times, the Bering Strait area (Beringia) has served as an avenue of dispersal between the Old and the New Worlds. On a field expedition to this area, we collected fecal samples from dabbling ducks, geese, shorebirds, and gulls on the Chukchi Peninsula, Siberia, and Pt. Barrow, Alaska, and characterized the subtypes of avian influenza virus present in them. Four of 202 samples (2%) from Alaska were positive for influenza A virus RNA in two independent polymerase chain reaction (PCR)-based screening assays, while all shorebird samples from the Chukchi Peninsula were negative. Subtypes H3N8 and H6N1 were recorded once, while subtype H8N4 was found in two samples. Full-length sequences were obtained from the three unique isolates, and phylogenetic analysis with representative sequences for the Eurasian and North American lineages of influenza A virus showed that one HA gene clustered with the Eurasian rather than the North American lineage. However, the closest relative to this sequence was a North American isolate from Delaware described in 2002, indicating that a H6 spillover from Asia has established itself in North America.

Ex vivo stability of the rodent-borne Hantaan virus in comparison to that of arthropod-borne members of the Bunyaviridae family

The possible effect of virus adaptation to different transmission routes on virus stability in the environment is not well known. In this study we have compared the stabilities of three viruses within the Bunyaviridae family: the rodent-borne Hantavirus Hantaan virus (HTNV), the sand fly-borne Phlebovirus sandfly fever Sicilian virus (SFSV), and the tick-borne Nairovirus Crimean-Congo hemorrhagic fever virus (CCHFV). These viruses differ in their transmission routes: SFSV and CCHFV are vector borne, whereas HTNV is spread directly between its hosts, and to humans, via the environment. We studied whether these viruses differed regarding stability when kept outside of the host. Viral survival was analyzed at different time points upon exposure to different temperatures (4 degrees C, 20 degrees C, and 37 degrees C) and drying at 20 degrees C. We observed clearly different stabilities under wet conditions, particularly at 4 degrees C, where infectious SFSV, HTNV, and CCHFV were detectable after 528, 96, and 15 days, respectively. All three viruses were equally sensitive to drying, as shown by drying on aluminum discs. Furthermore, HTNV and SFSV partially survived for 2 min in 30% ethanol, whereas CCHFV did not. Electron microscopy images of HTNV, SSFSV, and CCHFV stored at 37 degrees C until infectivity was lost still showed the occurrence of virions, but with abnormal shapes and densities compared to those of the nonincubated samples. In conclusion, our study points out important differences in ex vivo stability among viruses within the Bunyaviridae family.

Exogenous nitric oxide inhibits Crimean Congo hemorrhagic fever virus

Crimean Congo hemorrhagic fever virus (CCHFV) is a geographically widespread pathogen that causes severe hemorrhagic fever with high mortality. Even though one of the main objectives focuses on the progress of antiviral agents, the research on CCHFV is strongly hampered due to its BSL-4 classification. Nitric oxide (NO), a mediator with broad biological effects, has been shown to possess inhibitory properties against various pathogens. The molecule constitutes a component of the innate immunity and serves to assist in the early immunological events where it contributes to clearance of microorganisms. In this study, we investigated the inhibitory properties of exogenous NO on CCHFV. We found that NO had a significant antiviral activity against CCHFV replication. By using the NO-donor S-nitroso-N-acetylpenicillamine (SNAP) we were able to show up to 99% reduction in virion progeny yield. In contrast, 3-morpholinosydnonimine hydrochloride (SIN-1), a peroxynitrite donor, had no significant antiviral activity against CCHFV. Furthermore the expression of viral proteins; the nucleocapsid protein and the glycoprotein, were clearly reduced with increasing concentrations of SNAP. We have also shown that the amount of total vRNA in SNAP-treated cells was reduced by about 50% compared to the controls.

Tick-borne virus diseases of human interest in Europe

Several human diseases in Europe are caused by viruses transmitted by tick bite. These viruses belong to the genus Flavivirus, and include tick-borne encephalitis virus, Omsk haemorrhagic fever virus, louping ill virus, Powassan virus, Nairovirus (Crimean-Congo haemorrhagic fever virus) and Coltivirus (Eyach virus). All of these viruses cause more or less severe neurological diseases, and some are also responsible for haemorrhagic fever. The epidemiology, clinical picture and methods for diagnosis are detailed in this review. Most of these viral pathogens are classified as Biosafety Level 3 or 4 agents, and therefore some of them have been classified in Categories A-C of potential bioterrorism agents by the Centers for Disease Control and Prevention. Their ability to cause severe disease in man means that these viruses, as well as any clinical samples suspected of containing them, must be handled with specific and stringent precautions.

Delayed viremia and antibody responses in Puumala hantavirus challenged passively immunized cynomolgus macaques

No specific therapy is currently available against hemorrhagic fever with renal syndrome (HFRS) or hantavirus pulmonary syndrome. In order to study if passive immunization could inhibit hantavirus infection and/or symptoms, we inoculated two cynomolgus macaques with neutralizing monoclonal antibodies and subsequently challenged them with wild-type Puumala virus (PUUV), recently shown to induce typical signs of milder HFRS in cynomolgus macaques. Although viral load and antibody titers did not differ substantially as compared to the two control monkeys, a delayed onset of viremia and seroconversion was observed in the immunized monkeys. Interestingly, one of the immunized monkeys showed no symptoms, nor elevated of levels of IL-6, IL-10, and TNF-alpha, while the other developed severe symptoms and elevated levels of those cytokines, believed to be involved in PUUV-pathogenesis.

Rapid field test for detection of hantavirus antibodies in rodents

Puumala virus (PUUV) is the causative agent of nephropathia epidemica, a mild form of haemorrhagic fever with renal syndrome. PUUV is transmitted to humans via aerosolized excreta of the infected bank vole (Clethrionomys glareolus). Current methods for screening of the PUUV prevalence among bank vole populations are laborious, combining sampling in the field and subsequent analyses in the laboratory. In order to facilitate animal testing, a new serological immunochromatographic rapid test was developed. The test uses PUUV nucleocapsid protein as antigen, and it detects anti-PUUV IgG antibodies in rodents. With fresh and undiluted bank-vole blood samples (n = 105) the efficacy of the test was 100%, and with frozen and diluted samples (n = 78) the efficacy was 91%. The test was also shown to detect related hantavirus infections in Norway lemmings and sibling voles (n = 31) with 99% efficacy. The test provides an applicable tool for studying PUUV and related hantavirus infections in arvicoline rodents.

Rodent host specificity of European hantaviruses: evidence of Puumala virus interspecific spillover

In order to investigate rodent host specificity of European hantaviruses, experimental infection of colonized and wild-trapped rodents was performed. In addition to the natural rodent reservoir, Clethrionomys glareolus, Puumala hantavirus (PUUV) could infect colonized Microtus agrestis and Lemmus sibiricus, but not Syrian hamsters or Balb/C mice. Neither C. glareolus, nor M. agrestis, could be readily infected by Tula hantavirus (TULV). Wild-trapped Apodemus flavicollis and A. agrarius, the natural reservoirs of Dobrava (DOBV) and Saaremaa (SAAV) hantaviruses, respectively, could both be infected by SAAV. NMRI mice could also be infected by SAAV, but with lower efficiency as compared to Apodemus mice. Balb/C and NMRI laboratory mice, but not C. glareolus, could be infected by DOBV. To our knowledge, this is the first time DOBV and SAAV have been shown to infect adult laboratory mice. Moreover, potential hantavirus spillover infections were investigated in wild-trapped rodents. In addition to the natural host C. glareolus, we also found M. arvalis and A. sylvaticus with a history of PUUV infection. We did not find any C. glareolus or A. sylvaticus infected with TULV, a hantavirus which is known to circulate in the same geographical regions of Belgium.

Distribution of hantavirus foci in Belgium

During 1999 and 2000, we performed rodent captures on 15 sites all over Belgium to evaluate the presence of hantaviruses in local rodent populations. Viral antibody and RNA detection was performed by ELISA/focus reduction neutralisation test and RT-PCR, respectively. We found hantavirus-positive rodents on 13 out of 15 trapping sites and 3 rodent species were found positive for hantavirus infection. Apart from Puumala virus that was carried by Clethrionomys glareolus, 2 additional rodent species, Microtus arvalis and Apodemus sylvaticus, were found antibody- and/or RNA-positive.

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.

Hantavirus infections in Latvia

In order to investigate the presence of hantavirus infections in Latvia, 333 randomly selected human serum samples were screened using an enzyme-linked immunoassay. Fifteen samples were positive for hantavirus-specific IgG and were subsequently serotyped using a focus reduction neutralization test. Fourteen of these samples neutralized at least one of the hantaviruses included in the test, indicating a 4.2% overall seroprevalence in Latvia. Among 14 focus reduction neutralization test-positive sera, specific reactivity (at least 4-fold higher endpoint titer) of neutralizing antibodies was as follows: six sera were specific for Saaremaa hantavirus, three showed equal titers to Saaremaa and Dobrava hantaviruses, and five showed the highest endpoint titers to Puumala hantavirus. Hantavirus infections were confirmed in individuals residing in 11 of 26 investigated counties. The sex ratio was 1:2.5 (M:F), and the antibody prevalence increased with age. This is the first report on the presence of hantavirus infections in Latvia, and the results indicate that two hantaviruses pathogenic to man, Saaremaa virus and Puumala virus, are widely distributed in this country.

Tula hantavirus in Belgium

European common voles (Microtus arvalis), captured in Belgium in 1999, were proven by molecular as well as by serological techniques to be infected with Tula hantavirus (TULV). This is the first evidence for the presence of TULV in this country. No indication of spill-over infections of Puumala virus, known to be highly endemic among bank voles (Clethrionomys glareolus) within the same geographical regions as the trapped TULV-infected common voles, was observed. Together with previous reports on the circulation of TULV in eastern/central Europe, this finding suggests a more wide-spread circulation of this hantavirus serotype throughout the continent.

Tula virus infection associated with fever and exanthema after a wild rodent bite

Reported here is the first case of human acute infection with Tula virus, which occurred in a 12-year-old boy in Switzerland. This hantavirus had been considered apathogenic to humans, and in Switzerland only TULV-genome sequences have been demonstrated in wild rodents to date. In this case, paronychia, fever and exanthema occurred after the patient was bitten by a wild rodent, indicating an unusual route of hantavirus transmission. Thus, Tula virus infection should be taken into account in patients with appropriate clinical symptoms and contact with rodents.

Serological divergence of Dobrava and Saaremaa hantaviruses: evidence for two distinct serotypes

In order to investigate the serological relationship of Dobrava hantavirus (DOBV, originating from Slovenia) and the Dobrava-like Saaremaa virus (SAAV, recently discovered in Estonia) we analysed 37 human serum samples, 24 from Estonia and 13 from the Balkans, by focus reduction neutralization test (FRNT). Most of the Estonian sera (19), including all sera from Saaremaa island (12), reacted with higher FRNT end-point titres to the local SAAV; the majority of them (15 and 11, respectively), with at least fourfold or higher titres to SAAV than to DOBV. In contrast, out of the 13 sera collected in Slovenia, Bosnia-Herzegovina and Greece, only one reacted more strongly with SAAV (with a twofold higher titre), while 10 of these sera reacted more strongly with the local DOBV (9/10 with fourfold or higher titres). These results indicate that DOBV and SAAV define unique hantavirus serotypes.

Wild-type Puumala hantavirus infection induces cytokines, C-reactive protein, creatinine, and nitric oxide in cynomolgus macaques

Hantaviruses cause two severe human diseases: hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Approximately 200,000 cases are reported annually, and there is to date no specific treatment available. A major obstacle in studying the medical aspects of HFRS and HPS has been the lack of an adequate animal model. Here we show that infection of cynomolgus macaques by wild-type Puumala hantavirus resulted in typical signs of HFRS including lethargy, anorexia, proteinuria, and/or hematuria, in addition to cytokine (interleukin 6 [IL-6], IL-10, and tumor necrosis factor alpha), C-reactive protein, creatinine, and nitric oxide responses. Viral RNA was detected in plasma from days 3 to 7 postinoculation until days 24 to 28 postinoculation, infectious virus was recovered, and the virus-specific immune responses (immunoglobulin M [IgM], IgG, and neutralizing antibodies) mimicked those seen in humans. The results indicated that the monkey model will provide a valuable tool for studies of pathogenesis, candidate vaccines, and antivirals for hantavirus disease.

Tick-borne encephalitis virus in Lithuania

Tick-borne encephalitis (TBE) is a severe problem in Lithuania, indicated by the 171 to 645 serologically confirmed cases that occurred each year between 1993 and 1999. In the present report, the first isolation and partial genetic analysis of a Lithuanian TBE virus (TBEV) strain isolated from a patient's serum sample is described. The patient was bitten by a tick while visiting the Lazdijai district (Veisiejai forest) in the southernmost part of Lithuania, a geographical area where Ixodes ricinus but not Ixodes persulcatus ticks are known to be present. The E protein-encoding viral gene sequence (nt 74-1273) recovered from the TBEV isolate showed the closest similarity to previously characterized European strains of the Western TBEV subtype, including the prototype TBEV strain Neudoerfl and those from neighbouring Latvia. Accordingly, the Lithuanian isolate was placed within the Western genetic lineage of TBEV in phylogenetic trees.

DNA vaccination of mice with a plasmid encoding Puumala hantavirus nucleocapsid protein mimics the B-cell response induced by virus infection

Inoculation of naked DNA has been applied for the development of prophylactic and therapeutic vaccines against different viral infections. To study the humoral immune response induced by DNA vaccination we cloned the entire nucleocapsid protein-encoding sequence of the Puumala hantavirus strain Vranica/Hällnäs into the CMV promoter-driven expression unit of the plasmid pcDNA3, generating pcDNA3-VR1. A single dose injection of 50 microg of plasmid DNA into each M. tibialis anterior of BALB/c mice induced a high-titered antibody response against the nucleocapsid protein as documented 6 and 11 weeks after immunisation. PEPSCAN analysis of a serum pool of the pcDNA3-VR1-vaccinated animals revealed antibodies reacting with epitopes covering the whole nucleocapsid protein. The epitope-specificity of the immune response induced by DNA vaccination seems to reflect the antibody response in experimentally virus-infected bank voles (the natural host of the Puumala virus) and humans. The data suggest that DNA vaccination could be used for the identification of highly immunogenic epitopes in viral proteins.

A chemiluminescence detection method of hantaviral antigens in neutralisation assays and inhibitor studies

A protocol for chemiluminescence detection of hantaviral antigens in infected cell foci is described. This focus detection is based on the conversion of a substrate into a luminescent product by peroxidase-antibody conjugates; the emitted light of infected cell foci can easily be recorded by autoradiography or video imaging providing a hard copy for documentation. The main advantage of this method as compared to conventional immunochemical staining is a higher detection sensitivity due to the inherent magnification effect of luminescence causing an obvious boost in focal image and intensity. This enables reduction of (i) incubation time of virus-infected cells and (ii) amount of needed antibody for antigen detection in foci. This method is applied to a chemiluminescence focus reduction assay for the serotyping of hantavirus-specific neutralising antibodies in infected persons and for the determination of activity of antiviral agents against hantavirus.

Dobrava hantavirus causes hemorrhagic fever with renal syndrome in central Europe and is carried by two different Apodemus mice species

In central Europe, hemorrhagic fevers with renal syndrome (HFRS) in humans are caused by the hantavirus species Puumala (transmitted by voles) and a second, Hantaan-related species (transmitted by mice). The second virus could be identified as Dobrava virus. To date, 19 clinical cases of Dobrava infection have been found in Germany and Slovakia. All patients exhibited a mild/moderate clinical course and no case fatality occurred. Screening for infected rodents revealed that the striped field mouse (Apodemus agrarius) represents the main reservoir for Dobrava virus in central Europe. Nucleotide sequence comparisons and phylogenetic analysis based on complete and partial genomic S segment nucleotide sequences placed the Slovakian A. agrarius-derived hantavirus strains within the Dobrava species, forming a cluster on the Dobrava phylogenetic tree. In east Slovakia, a single Dobrava virus-infected yellow-necked mouse (Apodemus flavicollis) was trapped in a locality that predominantly showed Dobrava-infected A. agrarius. Comparison of the S segment sequence (nucleotides 381-935) revealed that the Dobrava strain from A. flavicollis shows only 84.3% nucleotide homology to A. agrarius-derived strains from this location but 96.3% homology to A. flavicollis-derived Dobrava strains from the Balkans (southeast Europe). Phylogenetic analysis of the partial S segment placed the A. flavicollis-derived Dobrava strain from Slovakia on a distinct Dobrava lineage (DOB-Af) together with the south-east European A. flavicollis-derived strains. The results indicate that Dobrava strains from A. agrarius (DOB-Aa) vs. A. flavicollis (DOB-Af) could develop different degrees of virulence in humans.

Puumala (PUU) hantavirus strain differences and insertion positions in the hepatitis B virus core antigen influence B-cell immunogenicity and protective potential of core-derived particles

Hepatitis B virus (HBV) core-derived chimeric particles carrying a Puumala (PUU) hantavirus (strain Vranica/Hällnäs) nucleocapsid (N) protein sequence (aa 1-45), alternatively inserted at three distinct positions (N-, C-terminus, or the internal region), and mosaic particles consisting of HBV core as well as core/PUU (Vranica/Hällnäs) N (aa 1-45) readthrough protein were generated. Chimeric particles carrying the insert at the N-terminus or the internal region of core induced some protective immune response in bank voles (Clethrionomys glareolus) against a subsequent PUU virus (strain Kazan) challenge; 40-50% of the animals showed markers of protection. In contrast, internal insertion of PUU strain CG18-20 N (aa 1-45) into the HBV core caused a highly protective immune response in the bank vole model. Immunizations with particles carrying aa 75-119 of PUU (CG18-20) N at the C-terminus of core verified the presence of a second, minor protective region in the N protein. A strong PUU N-specific antibody response was detected not only in bank voles immunized with chimeric particles containing internal and N-terminal fusions of PUU N protein but also in animals immunized with the corresponding mosaic particles. Except for the exclusive occurrence of antibodies directed against aa 231-240 of N in non-protected animals post virus challenge, there was no additional obvious difference in the epitope-specificity of N-specific antibodies from immunized animals prior and post virus challenge.

Diagnostic potential of puumala virus nucleocapsid protein expressed in Drosophila melanogaster cells

Puumala virus (PUU) nucleocapsid protein (N) was expressed in insect cells by using the Drosophila Expression System (DES; Invitrogen BV, Groningen, The Netherlands). Stable transfectants were established by hygromycin B selection and showed continuous expression of the recombinant protein (DES-PUU-N) for at least 5 months. The antigenic property of DES-PUU-N was shown to be identical to that of native PUU N when examined with a panel of hantavirus-specific monoclonal antibodies. Enzyme-linked immunosorbent assays (ELISAs) for detection of human immunoglobulin M (IgM) and IgG antibodies were established by using DES-PUU-N as antigen and were compared to assays based on native N. The ELISAs were evaluated for patient diagnosis and seroepidemiological purposes with panels of sera collected from patients with hemorrhagic fever with renal syndrome (HFRS) and from healthy blood donors. Equally high sensitivities and specificities for detection of PUU-specific IgM in acute-phase HFRS patient sera were obtained by the ELISA based on DES-PUU-N and the assay based on the native antigen. For detection of PUU-specific IgG, the ELISA based on monoclonal antibody-captured DES-PUU-N antigen showed optimal sensitivity and specificity.

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.

Antigenic properties and diagnostic potential of recombinant dobrava virus nucleocapsid protein

Dobrava hantavirus (DOBV) causes severe hemorrhagic fever with renal syndrome in the Balkan region and has been detected recently also in Russia, Estonia, and Germany. DOBV nucleocapsid protein (N) was produced in insect cells, using the baculovirus expression system (bac-DOBV-N), and in E. coli as a truncated (aa 1-165) glutathione-S transferase fusion protein (DOBV-dN-GST). The antigenic properties of bac-DOBV-N were found identical to native DOBV-N when examined by a panel of hantavirus-specific monoclonal antibodies. Enzyme immunoassays for detection of IgM and IgG antibodies were set up using DOBV recombinant N proteins and compared with those based on recombinant Hantaan and Puumala virus N, using panels of sera collected from DOBV, Hantaan and Puumala virus-infected patients. Full-length N protein (bac-DOBV-N) was found to be a more sensitive antigen than DOBV-dN-GST. The sensitivity values for sera from DOBV-infected patients were 100% for bac-DOBV-N and 86% for DOBV-dN-GST by IgM assays, and 98% for bac-DOBV-N and 88% for DOBV-dN-GST by IgG assays. The specificity values were 100% for bac-DOBV-N and 99% for DOBV-dN-GST by IgM assays, and 100% for both antigens by IgG assays.

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.

Spatial and temporal dynamics of Puumala hantavirus infection in red bank vole (Clethrionomys glareolus) populations in Belgium

Dynamics of hantavirus infection and population densities in rodents were investigated from 1996 to 1999 in southern Belgium. Evidence of Puumala infection was restricted to Clethrionomys glareolus. Although the serotype was not determined, antibodies against hantavirus were also found in eight Apodemus sylvaticus. In fall 1996, the seroprevalence in C. glareolus was high (20.1%, 37 of 184) and the infection was widely distributed in the area studied whereas a focal occurrence of positive rodents and lower seroprevalence rates were recorded in spring 1997 (14.3%, six of 42), fall 1997 (6. 6%, 11 of 166), spring 1998 (6.4%, three of 47) and fall 1998 (6.7%, 11 of 165). A pullulation of rodents was observed in spring 1999 and was associated with a markedly higher seroprevalence in C. glareolus (47.7%, 189 of 396). In all seasons, infection rates in adults were higher than in juveniles and subadults. No significant difference of prevalence was recorded between males and females. In two trapping sites, the temporary disappearance of positive animals after a crash in rodent populations suggests that a threshold in density is necessary for the maintenance of the enzootic cycle.

Characterization of tick-borne encephalitis virus from Latvia

Viruses of the tick-borne encephalitis (TBE) antigenic complex, within the family Flaviviridae, cause a variety of diseases including uncomplicated febrile illness, encephalitis, meningo-encephalitis, hemorrhagic fever and chronic disease in humans, domesticated animals or wildlife species. TBE is a serious problem in Latvia with up to a 1,000 patients confirmed serologically annually 1994-1995. No previous data had been reported on the causative agent of TBE in Latvia. In the present study, a virus was isolated from serum of a patient with clinical symptoms of an acute TBE infection. Nucleotide sequence information obtained by direct reverse transcription-polymerase chain reaction (RT-PCR) and the serological characteristics of the isolated virus strain, designated TBE-Latvia-1-96, indicated a closer relationship to the Vasilchenko strain, isolated in Novosibirsk (Siberia, Russia), as compared to the western European or far eastern subtypes of TBE viruses. In a mouse neurovirulence assay, a significant difference in survival rates (days) was shown between Latvia-1-96 and the western European TBE virus subtype.

Serologic evidence of Puumala virus infection in wild moose in northern Sweden

Puumala (PUU) virus is the causative agent of nephropathia epidemica, the Scandinavian form of hemorrhagic fever with renal syndrome. The infection is acquired by airborne transmission of PUU virus from its rodent reservoir, the bank vole. Besides serologic data indicating that the virus may spread also to heterologous rodents, there is little information on the susceptibility of wild living animals to PUU virus. We studied the occurrence of antibodies to PUU virus in serum samples from 427 wild-living moose, of which 260 originated from the PUU virus-endemic northern and central parts of Sweden and 167 originated from the southern, nonendemic part of Sweden. Samples from 5 animals showed reactivity in an ELISA for recombinant PUU virus nucleocapsid protein, an immunofluorescent assay, and a neutralization test. These 5 animals all originated from the PUU virus-endemic northern part of Sweden. In conclusion, 5 of 260 moose from the endemic region showed convincing serologic evidence of past PUU virus infection. The seroprevalence was low, suggesting that the moose is subjected to endstage infection rather than being part of an enzootic transmission cycle.

Phage-displayed peptides mimicking the discontinuous neutralization sites of puumala Hantavirus envelope glycoproteins

We selected peptide ligands mimicking the surface structure of discontinuous binding sites of Puumala hantavirus-neutralizing monoclonal antibodies from a random 18-amino acid peptide library containing a disulfide bridge in a fixed position and displayed on a filamentous phage. The varying of selection conditions, either by shortening of the association time or by competitive elution with antigen, was crucial for the selection of peptide inserts that could be aligned with the primary sequences of the envelope glycoproteins G1 and G2. Correspondingly, when the envelope glycoprotein sequences were synthesized as overlapping peptides as spots on membrane, the same site in primary structure was found as with phage display, which corroborates the use of the two methods in mapping of conformational epitopes. Also, epitopes reactive with early-phase sera from Puumala virus infection were defined with the pepspot assay in the amino-terminal region of G1. Similarities of the selected phage clones to a monoclonal antibody-escape mutant site and to a linear early-phase epitope were found.

Short report: simultaneous occurrence of Dobrava, Puumala, and Tula Hantaviruses in Slovakia

The prevalence of antibody to hantaviruses in Slovakia (serum panel n = 2,133) was lower in the western part (0.54%) and higher in the eastern part (1.91%) of the country and was found to be significantly enhanced in a group of forest workers from eastern Slovakia (5.88%). One-third of the IgM-negative convalescent phase sera from patients with hemorrhagic fever with renal syndrome exhibited antibodies reacting predominantly with Puumala virus antigen, while two-thirds had antibodies directed mainly against Hantaan virus antigen. Fine analysis of two Hantaan virus-reactive sera by a focus reduction neutralization test showed that Dobrava hantavirus was the source of these human infections. Initial results of rodent screening indicated the circulation of Dobrava virus in populations of striped field mice (Apodemus agrarius) in eastern Slovakia.

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.

[Increased travelling--increased risk of imported viruses. A review of the diagnostic capacity of the Swedish Institute for Infectious Disease Control]

The increase in global travel, especially by air, has facilitated the spread of infectious agents from one part of the world to another. Returning travellers are often vectors for viral disease import to Sweden. While dengue fever has been quite frequently diagnosed during the past five years, especially in travellers returning from Thailand, only isolated cases of sandfly fever, Japanese encephalitis and Ross River fever have been seen. Dobrava virus was recently shown to have caused a severe form of haemorrhagic fever with renal syndrome in several European countries, and thus constitutes a risk for travellers to areas where it is endemic.

A major outbreak of hantavirus infection in Belgium in 1995 and 1996

Haemorrhagic fever with renal syndrome (HFRS) is a human disease characterized by flu-like symptoms, renal dysfunction, and in severe cases, haemorrhagic manifestations. The causative agents of HFRS are Hantaan (HTN), Seoul (SEO), Puumala (PUU) and Dobrava (DOB) hantaviruses. Hantavirus infections are of increasing importance in Europe. Outbreaks occur in Belgium with a 3- to 4-year interval with an increasing number of cases. We describe the largest outbreak so far in Belgium with 217 serologically and clinically confirmed cases in the period between October 1995 and December 1996. We demonstrated that the use of viral antigen derived from a local PUU-strain was able to detect significantly more sera positive for IgM in an immunofluorescence assay. Furthermore, although in some cases SEO, HTN and DOB antibody-reactivities were detected by ELISA, only PUU infections could be confirmed by neutralization test. The presence of an unknown hantavirus serotype circulating in Belgium should be considered.