Isolation and characterization of Tula virus, a distinct serotype in the genus Hantavirus, family Bunyaviridae

Phylogeographic analysis of Tula hantavirus highlights a single introduction to central Europe

Orthohantaviruses are zoonotic pathogens of humans, unique among the bunyaviruses in not being transmitted by an arthropod vector. Tula orthohantavirus (TULV) is an old-world hantavirus, of yet unclear human pathogenicity, with few reported cases of clinically relevant human infection. So far, phylogeographic studies exploring the global pathways of hantaviral migration are scarce and generally do not focus on a specific hantavirus species. The aim of the present study was to reconstruct the dispersal history of TULV lineages across Eurasia based on S segment sequences sampled from different geographic areas. Maximum-likelihood and Bayesian inference methods were used to perform the phylogenetic analysis and phylogeographic reconstructions. Sampling time and trapping localities were obtained for a total of 735 TULV S segment sequences available in public databases at the time of the study. The estimated substitution rate of the analyzed partial S segment alignment was 2.26 × 10-3 substitutions/site/year (95 per cent highest posterior density interval: 1.79 × 10-3 to 2.75 × 10-3). Continuous phylogeography of TULV S segment sequences placed the potential root and origin of TULV spread in the Black Sea region. In our study, we detect a single-lineage introduction of TULV to Europe, followed by local viral circulation further on.

Orthohantaviruses in Reservoir and Atypical Hosts in the Czech Republic: Spillover Infection and Indication of Virus-Specific Tissue Tropism

Orthohantaviruses (genus Orthohantavirus) are a diverse group of viruses that are closely associated with their natural hosts (rodents, shrews, and moles). Several orthohantaviruses cause severe disease in humans. Central and western Europe are areas with emerging orthohantavirus occurrences. In our study, several orthohantaviruses, including the pathogenic Kurkino virus (KURV), were detected in their natural hosts trapped at several study sites in the Czech Republic. KURV was detected mainly in its typical host, the striped field mouse (Apodemus agrarius). Nevertheless, spillover infections were also detected in wood mice (Apodemus sylvaticus) and common voles (Microtus arvalis). Similarly, Tula virus (TULV) was found primarily in common voles, and events of spillover to rodents of other host species, including Apodemus spp., were recorded. In addition, unlike most previous studies, different tissues were sampled and compared to assess their suitability for orthohantavirus screening and possible tissue tropism. Our data suggest possible virus-specific tissue tropism in rodent hosts. TULV was most commonly detected in the lung tissue, whereas KURV was more common in the liver, spleen, and brain. Moreover, Seewis and Asikkala viruses were detected in randomly found common shrews (Sorex araneus). In conclusion, we have demonstrated the presence of human-pathogenic KURV and the potentially pathogenic TULV in their typical hosts as well as their spillover to atypical host species belonging to another family. Furthermore, we suggest the possibility of virus-specific tissue tropism of orthohantaviruses in their natural hosts. IMPORTANCE Orthohantaviruses (genus Orthohantavirus, family Hantaviridae) are a diverse group of globally distributed viruses that are closely associated with their natural hosts. Some orthohantaviruses are capable of infecting humans and causing severe disease. Orthohantaviruses are considered emerging pathogens due to their ever-increasing diversity and increasing numbers of disease cases. We report the detection of four different orthohantaviruses in rodents and shrews in the Czech Republic. Most viruses were found in their typical hosts, Kurkino virus (KURV) in striped field mice (Apodemus agrarius), Tula virus (TULV) in common voles (Microtus arvalis), and Seewis virus in common shrews (Sorex araneus). Nevertheless, spillover infections of atypical host species were also recorded for KURV, TULV, and another shrew-borne orthohantavirus, Asikkala virus. In addition, indications of virus-specific patterns of tissue tropism were observed. Our results highlight the circulation of several orthohantaviruses, including KURV, which is pathogenic to humans, among rodents and shrews in the Czech Republic.

Tula Virus as Causative Agent of Hantavirus Disease in Immunocompetent Person, Germany

We report molecular evidence of Tula virus infection in an immunocompetent patient from Germany who had typical signs of hantavirus disease. Accumulating evidence indicates that Tula virus infection, although often considered nonpathogenic, represents a threat to human health.

Spatial and Temporal Dynamics and Molecular Evolution of Tula orthohantavirus in German Vole Populations

Tula orthohantavirus (TULV) is a rodent-borne hantavirus with broad geographical distribution in Europe. Its major reservoir is the common vole (Microtus arvalis), but TULV has also been detected in closely related vole species. Given the large distributional range and high amplitude population dynamics of common voles, this host-pathogen complex presents an ideal system to study the complex mechanisms of pathogen transmission in a wild rodent reservoir. We investigated the dynamics of TULV prevalence and the subsequent potential effects on the molecular evolution of TULV in common voles of the Central evolutionary lineage. Rodents were trapped for three years in four regions of Germany and samples were analyzed for the presence of TULV-reactive antibodies and TULV RNA with subsequent sequence determination. The results show that individual (sex) and population-level factors (abundance) of hosts were significant predictors of local TULV dynamics. At the large geographic scale, different phylogenetic TULV clades and an overall isolation-by-distance pattern in virus sequences were detected, while at the small scale (<4 km) this depended on the study area. In combination with an overall delayed density dependence, our results highlight that frequent, localized bottleneck events for the common vole and TULV do occur and can be offset by local recolonization dynamics.

Development of a Comparative European Orthohantavirus Microneutralization Assay With Multi- Species Validation and Evaluation in a Human Diagnostic Cohort

Orthohantaviruses (family Hantaviridae, order Bunyavirales) can cause two serious syndromes in humans: hemorrhagic fever with renal syndrome (HFRS), associated with the Old World orthohantaviruses, and hantavirus cardiopulmonary syndrome (HCPS), associated with orthohantaviruses in the Americas. In Europe, four different orthohantaviruses (DOBV, PUUV, SEOV, and TULV) are associated with human disease. As disease severity and zoonotic source differ between orthohantavirus species, conclusive determination of the infecting species by either RT-PCR or comparative virus neutralization test (VNT) is of importance. Currently, the focus reduction neutralization test (FRNT) is considered the ‘Gold Standard’ for orthohantavirus VNTs, however this test is laborious and time-consuming. Consequently, more high-throughput alternatives are needed. In this study, we developed a comparative orthohantavirus microneutralization test (MNT) including all four human pathogenic orthohantavirus species circulating in Europe. The assay was validated using RT-PCR-confirmed rodent (n=17) and human sera (n=17), DOBV-suspected human sera (n=3) and cohorts of orthohantavirus-negative rodent (n=3) and human sera (n=85). 16/17 RT-PCR-confirmed rodent sera and 18/20 of the RT-PCR-confirmed and DOBV-suspected human sera were serotyped successfully, while for the remaining rodent (n=1) and human sera (n=2) no neutralizing titers could be detected. All negative control sera tested negative in the MNT. The assay was subsequently evaluated using a clinical cohort of 50 orthohantavirus patients. Orthohantavirus infection was confirmed in all 50 patients, and 47/50 (94%) sera were serotyped successfully, confirming PUUV as the major cause of orthohantavirus infections in Netherlands. Notably, two previously unrecognized SEOV cases from 2013 were diagnosed using the MNT, underlining the added value of the MNT in a diagnostic setting. In conclusion, we demonstrate the successful development and clinical implementation of a comparative European orthohantavirus MNT to determine the infecting virus species in European HFRS patients. Identification of the causative species is needed for an adequate Public Health response and can support individual patient care. For many labs, the implementation of orthohantavirus neutralization tests has not been a straightforward procedure. This issue will be addressed by the rollout of the comparative MNT to multiple European laboratories to support patient diagnostics, surveillance and Public Health responses.

Puumala and Tula Virus Differ in Replication Kinetics and Innate Immune Stimulation in Human Endothelial Cells and Macrophages

Old world hantaviruses cause hemorrhagic fever with renal syndrome (HFRS) upon zoonotic transmission to humans. In Europe, the Puumala virus (PUUV) is the main causative agent of HFRS. Tula virus (TULV) is also widely distributed in Europe, but there is little knowledge about the pathogenicity of TULV for humans, as reported cases are rare. We studied the replication of TULV in different cell types in comparison to the pathogenic PUUV and analyzed differences in stimulation of innate immunity. While both viruses replicated to a similar extent in interferon (IFN)-deficient Vero E6 cells, TULV replication in human lung epithelial (A549) cells was slower and less efficient when compared to PUUV. In contrast to PUUV, no replication of TULV could be detected in human microvascular endothelial cells and in macrophages. While a strong innate immune response towards PUUV infection was evident at 48 h post infection, TULV infection triggered only a weak IFN response late after infection of A549 cells. Using appropriate in vitro cell culture models for the orthohantavirus infection, we could demonstrate major differences in host cell tropism, replication kinetics, and innate immune induction between pathogenic PUUV and the presumably non- or low-pathogenic TULV that are not observed in Vero E6 cells and may contribute to differences in virulence.

Common vole (Microtus arvalis) and bank vole (Myodes glareolus) derived permanent cell lines differ in their susceptibility and replication kinetics of animal and zoonotic viruses

Pathogenesis and reservoir host adaptation of animal and zoonotic viruses are poorly understood due to missing adequate cell culture and animal models. The bank vole (Myodes glareolus) and common vole (Microtus arvalis) serve as hosts for a variety of zoonotic pathogens. For a better understanding of virus association to a putative animal host, we generated two novel cell lines from bank voles of different evolutionary lineages and two common vole cell lines and assayed their susceptibility, replication and cytopathogenic effect (CPE) formation for rodent-borne, suspected to be rodent-associated or viruses with no obvious rodent association. Already established bank vole cell line BVK168, used as control, was susceptible to almost all viruses tested and efficiently produced infectious virus for almost all of them. The Puumala orthohantavirus strain Vranica/Hällnäs showed efficient replication in a new bank vole kidney cell line, but not in the other four bank and common vole cell lines. Tula orthohantavirus replicated in the kidney cell line of common voles, but was hampered in its replication in the other cell lines. Several zoonotic viruses, such as Cowpox virus, Vaccinia virus, Rift Valley fever virus, and Encephalomyocarditis virus 1 replicated in all cell lines with CPE formation. West Nile virus, Usutu virus, Sindbis virus and Tick-borne encephalitis virus replicated only in a part of the cell lines, perhaps indicating cell line specific factors involved in replication. Rodent specific viruses differed in their replication potential: Murine gammaherpesvirus-68 replicated in the four tested vole cell lines, whereas murine norovirus failed to infect almost all cell lines. Schmallenberg virus and Foot-and-mouth disease virus replicated in some of the cell lines, although these viruses have never been associated to rodents. In conclusion, these newly developed cell lines may represent useful tools to study virus-cell interactions and to identify and characterize host cell factors involved in replication of rodent associated viruses.

Revisiting the genetic diversity of emerging hantaviruses circulating in Europe using a pan-viral resequencing microarray

Hantaviruses are zoonotic agents transmitted from small mammals, mainly rodents, to humans, where they provoke diseases such as Hemorrhagic fever with Renal Syndrome (HFRS) and its mild form, Nephropathia Epidemica (NE), or Hantavirus Cardio-Pulmonary Syndrome (HCPS). Hantaviruses are spread worldwide and monitoring animal reservoirs is of primary importance to control the zoonotic risk. Here, we describe the development of a pan-viral resequencing microarray (PathogenID v3.0) able to explore the genetic diversity of rodent-borne hantaviruses endemic in Europe. Among about 800 sequences tiled on the microarray, 52 correspond to a tight molecular sieve of hantavirus probes covering a large genetic landscape. RNAs from infected animal tissues or from laboratory strains have been reverse transcribed, amplified, then hybridized to the microarray. A classical BLASTN analysis applied to the sequence delivered through the microarray allows to identify the hantavirus species up to the exact geographical variant present in the tested samples. Geographical variants of the most common European hantaviruses from France, Germany, Slovenia and Finland, such as Puumala virus, Dobrava virus and Tula virus, were genetically discriminated. Furthermore, we precisely characterized geographical variants still unknown when the chip was conceived, such as Seoul virus isolates, recently emerged in France and the United Kingdom.

Tula orthohantavirus nucleocapsid protein is cleaved in infected cells and may sequester activated caspase-3 during persistent infection to suppress apoptosis

The family Hantaviridae mostly comprises rodent-borne segmented negative-sense RNA viruses, many of which are capable of causing devastating disease in humans. In contrast, hantavirus infection of rodent hosts results in a persistent and inapparent infection through their ability to evade immune detection and inhibit apoptosis. In this study, we used Tula hantavirus (TULV) to investigate the interplay between viral and host apoptotic responses during early, peak and persistent phases of virus infection in cell culture. Examination of early-phase TULV infection revealed that infected cells were refractory to apoptosis, as evidenced by the complete lack of cleaved caspase-3 (casp-3C) staining, whereas in non-infected bystander cells casp-3C was highly abundant. Interestingly, at later time points, casp-3C was abundant in infected cells, but the cells remained viable and able to continue shedding infectious virus, and together these observations were suggestive of a TULV-associated apoptotic block. To investigate this block, we viewed TULV-infected cells using laser scanning confocal and wide-field deconvolution microscopy, which revealed that TULV nucleocapsid protein (NP) colocalized with, and sequestered, casp-3C within cytoplasmic ultrastructures. Consistent with casp-3C colocalization, we showed for the first time that TULV NP was cleaved in cells and that TULV NP and casp-3C could be co-immunoprecipitated, suggesting that this interaction was stable and thus unlikely to be solely confined to NP binding as a substrate to the casp-3C active site. To account for these findings, we propose a novel mechanism by which TULV NP inhibits apoptosis by spatially sequestering casp-3C from its downstream apoptotic targets within the cytosol.

Orthohantaviruses belonging to three phylogroups all inhibit apoptosis in infected target cells

Orthohantaviruses, previously known as hantaviruses, are zoonotic viruses that can cause hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS) in humans. The HPS-causing Andes virus (ANDV) and the HFRS-causing Hantaan virus (HTNV) have anti-apoptotic effects. To investigate if this represents a general feature of orthohantaviruses, we analysed the capacity of six different orthohantaviruses – belonging to three distinct phylogroups and representing both pathogenic and non-pathogenic viruses – to inhibit apoptosis in infected cells. Primary human endothelial cells were infected with ANDV, HTNV, the HFRS-causing Puumala virus (PUUV) and Seoul virus, as well as the putative non-pathogenic Prospect Hill virus and Tula virus. Infected cells were then exposed to the apoptosis-inducing chemical staurosporine or to activated human NK cells exhibiting a high cytotoxic potential. Strikingly, all orthohantaviruses inhibited apoptosis in both settings. Moreover, we show that the nucleocapsid (N) protein from all examined orthohantaviruses are potential targets for caspase-3 and granzyme B. Recombinant N protein from ANDV, PUUV and the HFRS-causing Dobrava virus strongly inhibited granzyme B activity and also, to certain extent, caspase-3 activity. Taken together, this study demonstrates that six different orthohantaviruses inhibit apoptosis, suggesting this to be a general feature of orthohantaviruses likely serving as a mechanism of viral immune evasion.

A novel genetic lineage of Tula orthohantavirus in Altai voles (Microtus obscurus) from Turkey

Orthohantaviruses (family Hantaviridae order Bunyavirales) are emerging pathogens with a significant impact on human health. They are transmitted via aerosolized excreta of rodents which also act as reservoir hosts, constituting a unique route for dispersion. Dobrava-Belgrade and Puumala orthohantaviruses have been previously reported from Anatolia, in rodents, case reports and occasional outbreaks. We have collected rodents at several locations during a surveillance study in eastern Anatolia. The specimens were morphologically-identified and various tissues were screened via a generic orthohantavirus reverse transcription polymerase chain reaction assay. DNA barcoding via mitochondrial cytochrome b sequencing was performed in rodents with detectable orthohantavirus sequences. High throughput sequencing was performed for viral genome characterization. Fifty rodents were collected and identified morphologically as Microtus spp. (96%) and Apodemus spp. (4%). Orthohantavirus sequences were detected in lung and spleen or liver tissues of 4 voles (8%), barcoded as Microtus obscurus. The virus sequences were identified as Tula orthohantavirus (TULV) and near-complete genomic segments of the prototype viral genome, tentatively named as the Tula orthohantavirus-Turkey (TULV-T), could be characterized. Putative open reading frames for viral nucleocapsid and a nonstructural protein on the S segment, glycoproteins G1 and G2 on the M segment and viral replicase on the L segment were identified on the TULV-T. Several minor sequence variants were further characterized. No evidence of recombination could be detected and pairwise comparisons displayed over 95% amino acid sequence identities to various Eurasian TULV strains. Phylogenetic analyses revealed distinct clustering of all genome segments from previously-characterized TULV strains via various approaches and models. Here, TULV-T constituted a novel lineage, forming an intermediate among Asian and European TULV lineages. This report describes the initial documentation of TULV circulation and its potential reservoir in Anatolia. The extent of virus dispersion, alternate hosts or outcomes of human exposure require elucidation.

Globally emerging hantaviruses: An overview

Hantaviruses are known to cause haemorrhagic fever with renal syndrome in Eurasia and hantavirus cardiopulmonary syndrome in the Americas. They are globally emerging pathogens as newer serotypes are routinely being reported. This review discusses hantavirus biology, clinical features and pathogenesis of hantavirus disease, its diagnostics, distribution and mammalian hosts. Hantavirus research in India is also summarised.

Estimation of main diversification time-points of hantaviruses using phylogenetic analyses of complete genomes

Because of the great variability of their reservoir hosts, hantaviruses are excellent models to evaluate the dynamics of virus-host co-evolution. Intriguing questions remain about the timescale of the diversification events that influenced this evolution. In this paper we attempted to estimate the first ever timing of hantavirus diversification based on thirty five available complete genomes representing five major groups of hantaviruses and the assumption of co-speciation of hantaviruses with their respective mammal hosts. Phylogenetic analyses were used to estimate the main diversification points during hantavirus evolution in mammals while host diversification was mostly estimated from independent calibrators taken from fossil records. Our results support an earlier developed hypothesis of co-speciation of known hantaviruses with their respective mammal hosts and hence a common ancestor for all hantaviruses carried by placental mammals.

High Prevalence of Tula Hantavirus in Common Voles in The Netherlands

Tula virus (TULV) is a zoonotic hantavirus. Knowledge about TULV in the Netherlands is very scarce. Therefore in 2014, 49 common voles (Microtus arvalis) from a region in the south of the Netherlands, and in 2015, 241 common voles from regions in the north of the Netherlands were tested with the TULV quantitative RT-PCR. In the southern region, prevalence of TULV was 41% (20/49). In the northern regions, prevalence ranged from 12% (4/34) to 45% (17/38). Phylogenetic analysis of the obtained sequences showed that the regions fall within different clusters. Voles from the south were also tested on-site for the presence of hantavirus antibodies, but serology results were poorly associated with qRT-PCR results. These findings suggest that TULV may be more widespread than previously thought. No human TULV cases have been reported thus far in the Netherlands, but differentiation between infection by TULV or the closely related Puumala virus is not made in humans in the Netherlands, thus cases may be misdiagnosed.

Infection of human airway epithelial cells by different subtypes of Dobrava-Belgrade virus reveals gene expression patterns corresponding to their virulence potential

Dobrava-Belgrade virus (DOBV) is a pathogen causing hemorrhagic fever with renal syndrome in Europe. Virulence and case fatality rate are associated with virus genotype; however the reasons for these differences are not well understood. In this work we present virus-specific effects on the gene expression profiles of human lung epithelial cells (A549) infected with different genotypes of DOBV (Dobrava, Kurkino, and Sochi), as well as the low-virulent Tula virus (TULV). The data was collected by whole-genome gene expression microarrays and confirmed by quantitative real-time PCR. Despite their close genetic relationship, the expression profiles induced by infection with different hantaviruses are significantly varying. Major differences were observed in regulation of immune response genes, which were especially induced by highly virulent DOBV genotypes Dobrava and Sochi in contrast to less virulent DOBV-Kurkino and TULV. This work gives first insights into the differences of virus - host interactions of DOBV on genotype level.

High genetic structuring of Tula hantavirus

Tula virus (TULV) is a vole-associated hantavirus with low or no pathogenicity to humans. In the present study, 686 common voles (Microtus arvalis), 249 field voles (Microtus agrestis) and 30 water voles (Arvicola spec.) were collected at 79 sites in Germany, Luxembourg and France and screened by RT-PCR and TULV-IgG ELISA. TULV-specific RNA and/or antibodies were detected at 43 of the sites, demonstrating a geographically widespread distribution of the virus in the studied area. The TULV prevalence in common voles (16.7 %) was higher than that in field voles (9.2 %) and water voles (10.0 %). Time series data at ten trapping sites showed evidence of a lasting presence of TULV RNA within common vole populations for up to 34 months, although usually at low prevalence. Phylogenetic analysis demonstrated a strong genetic structuring of TULV sequences according to geography and independent of the rodent species, confirming the common vole as the preferential host, with spillover infections to co-occurring field and water voles. TULV phylogenetic clades showed a general association with evolutionary lineages in the common vole as assessed by mitochondrial DNA sequences on a large geographical scale, but with local-scale discrepancies in the contact areas.

Epidemiological dynamics of nephropathia epidemica in the Republic of Tatarstan, Russia, during the period of 1997-2013

This report summarizes epidemiological data on nephropathia epidemica (NE) in the Republic of Tatarstan, Russia. NE cases identified in the period 1997-2013 were investigated in parallel with the hantavirus antigen prevalence in small rodents in the study area. A total of 13 930 NE cases were documented in all but one district of Tatarstan, with most cases located in the central and southeastern districts. The NE annual incidence rate exhibited a cyclical pattern, with the highest numbers of cases being registered once in every 3-5 years. The numbers of NE cases rose gradually from July to November, with the highest morbidity in adult males. The highest annual disease incidence rate, 64·4 cases/100 000 population, was observed in 1997, with a total of 2431 NE cases registered. NE cases were mostly associated with visiting forests and agricultural activities. The analysis revealed that the bank vole Myodes glareolus not only comprises the majority of the small rodent communities in the region, but also consistently displays the highest hantavirus prevalence compared to other small rodent species.

Hantavirus infections

Over the past few decades understanding and recognition of hantavirus infection has greatly improved worldwide, but both the amplitude and the magnitude of hantavirus outbreaks have been increasing. Several novel hantaviruses with unknown pathogenic potential have been identified in a variety of insectivore hosts. With the new hosts, new geographical distributions of hantaviruses have also been discovered and several new species were found in Africa. Hantavirus infection in humans can result in two clinical syndromes: haemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS) caused by Old World and New World hantaviruses, respectively. The clinical presentation of HFRS varies from subclinical, mild, and moderate to severe, depending in part on the causative agent of the disease. In general, HFRS caused by Hantaan virus, Amur virus and Dobrava virus are more severe with mortality rates from 5 to 15%, whereas Seoul virus causes moderate and Puumala virus and Saaremaa virus cause mild forms of disease with mortality rates <1%. The central phenomena behind the pathogenesis of both HFRS and HCPS are increased vascular permeability and acute thrombocytopenia. The pathogenesis is likely to be a complex multifactorial process that includes contributions from immune responses, platelet dysfunction and the deregulation of endothelial cell barrier functions. Also a genetic predisposition, related to HLA type, seems to be important for the severity of the disease. As there is no effective treatment or vaccine approved for use in the USA and Europe, public awareness and precautionary measures are the only ways to minimize the risk of hantavirus disease.

Andes virus nucleocapsid protein interrupts protein kinase R dimerization to counteract host interference in viral protein synthesis

Pathogenic hantaviruses delay the type I interferon response during early stages of viral infection. However, the robust interferon response and induction of interferon-stimulated genes observed during later stages of hantavirus infection fail to combat the virus replication in infected cells. Protein kinase R (PKR), a classical interferon-stimulated gene product, phosphorylates the eukaryotic translation initiation factor eIF2α and causes translational shutdown to create roadblocks for the synthesis of viral proteins. The PKR-induced translational shutdown helps host cells to establish an antiviral state to interrupt virus replication. However, hantavirus-infected cells do not undergo translational shutdown and fail to establish an antiviral state during the course of viral infection. In this study, we showed for the first time that Andes virus infection induced PKR overexpression. However, the overexpressed PKR was not active due to a significant inhibition of autophosphorylation. Further studies revealed that Andes virus nucleocapsid protein inhibited PKR dimerization, a critical step required for PKR autophosphorylation to attain activity. The studies reported here establish a hantavirus nucleocapsid protein as a new PKR inhibitor. These studies provide mechanistic insights into hantavirus resistance to the host interferon response and solve the puzzle of the lack of translational shutdown observed in hantavirus-infected cells. The sensitivity of hantavirus replication to PKR has likely imposed a selective evolutionary pressure on hantaviruses to evade the PKR antiviral response for survival. We envision that evasion of the PKR antiviral response by NP has likely helped hantaviruses to exist during evolution and to survive in infected hosts with a multifaceted antiviral defense.

IMPORTANCE

Protein kinase R (PKR), a versatile antiviral host factor, shuts down the translation machinery upon activation in virus-infected cells to create hurdles for the manufacture of viral proteins. The studies reported here reveal that the hantavirus nucleocapsid protein counteracts the PKR antiviral response by inhibiting PKR dimerization, which is required for its activation. We report the discovery of a new PKR inhibitor whose expression in hantavirus-infected cells prevents the PKR-induced host translational shutdown to ensure the continuous synthesis of viral proteins required for efficient virus replication.

Tula hantavirus infection in immunocompromised host, Czech Republic

We report molecular evidence of Tula hantavirus as an etiologic agent of pulmonary-renal syndrome in an immunocompromised patient. Acute hantavirus infection was confirmed by using serologic and molecular methods. Sequencing revealed Tula virus genome RNA in the patient’s blood. This case shows that Tula virus can cause serious disease in humans.

Involvement of the Akt/NF-κB pathways in the HTNV-mediated increase of IL-6, CCL5, ICAM-1, and VCAM-1 in HUVECs

Background

Hantaan virus (HTNV) infection causes a severe form of HFRS(hemorrhagic fever with renal syndrome)in Asia. Although HTNV has been isolated for nearly forty years, the pathogenesis of HFRS is still unknown, and little is known regarding the signaling pathway that is activated by the virus.

Methodology/Principal Findings

Cardamonin was selected as a NF-κB inhibitor, and indirect immunofluorescence assays were used to detect the effect of cardamonin on HTNV-infected HUVECs. The effect of cardamonin on the HTNV-induced phosphorylation of Akt and DNA-binding activity of NF-κB were determined using Western blot analysis and electrophoretic mobility shift assays (EMSAs), respectively. Then, flow cytometric and quantitative real-time PCR analyses were performed to quantify the expression levels of the adhesion molecules ICAM-1 and VCAM-1, and the concentrations of IL-6, IL-8, and CCL5 in HUVEC supernatants were examined using ELISA. The results showed that cardamonin did not effect the proliferation of HUVECs or the replication of HTNV in HUVECs. Instead, cardamonin inhibited the phosphorylation of Akt and nuclear transduction of NF-κB and further reduced the expression of the adhesion molecules ICAM-1 and VCAM-1 in HTNV-infected HUVECs. Cardamonin also inhibited the secretion of IL-6 and CCL5, but not IL-8.

Conclusion/Significance

HTNV replication may not be dependent upon the ability of the virus to activate NF-κB in HUVECs. The Akt/NF-κB pathways may be involved in the pathogenesis of HFRS; therefore, cardamonin may serve as a potential beneficial agent for HFRS therapy.

Role of vascular and lymphatic endothelial cells in hantavirus pulmonary syndrome suggests targeted therapeutic approaches

BACKGROUND

Hantaviruses in the Americas cause a highly lethal acute pulmonary edema termed hantavirus pulmonary syndrome (HPS). Hantaviruses nonlytically infect microvascular and lymphatic endothelial cells and cause dramatic changes in barrier functions without disrupting the endothelium. Hantaviruses cause changes in the function of infected endothelial cells that normally regulate fluid barrier functions. The endothelium of arteries, veins, and lymphatic vessels are unique and central to the function of vast pulmonary capillary beds that regulate pulmonary fluid accumulation.

RESULTS

We have found that HPS-causing hantaviruses alter vascular barrier functions of microvascular and lymphatic endothelial cells by altering receptor and signaling pathway responses that serve to permit fluid tissue influx and clear tissue edema. Infection of the endothelium provides several mechanisms for hantaviruses to cause acute pulmonary edema, as well as potential therapeutic targets for reducing the severity of HPS disease.

CONCLUSIONS

Here we discuss interactions of HPS-causing hantaviruses with the endothelium, roles for unique lymphatic endothelial responses in HPS, and therapeutic targeting of the endothelium as a means of reducing the severity of HPS disease.

Hantavirus regulation of type I interferon responses

Hantaviruses primarily infect human endothelial cells (ECs) and cause two highly lethal human diseases. Early addition of Type I interferon (IFN) to ECs blocks hantavirus replication and thus for hantaviruses to be pathogenic they need to prevent early interferon induction. PHV replication is blocked in human ECs, but not inhibited in IFN deficient VeroE6 cells and consistent with this, infecting ECs with PHV results in the early induction of IFNβ and an array of interferon stimulated genes (ISGs). In contrast, ANDV, HTNV, NY-1V and TULV hantaviruses, inhibit early ISG induction and successfully replicate within human ECs. Hantavirus inhibition of IFN responses has been attributed to several viral proteins including regulation by the Gn proteins cytoplasmic tail (Gn-T). The Gn-T interferes with the formation of STING-TBK1-TRAF3 complexes required for IRF3 activation and IFN induction, while the PHV Gn-T fails to alter this complex or regulate IFN induction. These findings indicate that interfering with early IFN induction is necessary for hantaviruses to replicate in human ECs, and suggest that additional determinants are required for hantaviruses to be pathogenic. The mechanism by which Gn-Ts disrupt IFN signaling is likely to reveal potential therapeutic interventions and suggest protein targets for attenuating hantaviruses.

Hantavirus infections in Europe and their impact on public health

Hantaviruses (genus Hantavirus, family Bunyaviridae) are enveloped tri-segmented negative-stranded RNA viruses each carried by a specific rodent or insectivore host species. Several different hantaviruses known to infect humans circulate in Europe. The most common is Puumala (PUUV) carried by the bank vole; another two important, genetically closely related ones are Dobrava-Belgrade (DOBV) and Saaremaa viruses (SAAV) carried by Apodemus mice (species names follow the International Committee on Taxonomy of Viruses nomenclature). Of the two hantaviral diseases, hemorrhagic fever with renal syndrome (HFRS) and hantaviral cardiopulmonary syndrome, the European viruses cause only HFRS: DOBV with often severe symptoms and a high case fatality rate, and PUUV and SAAV more often mild disease. More than 10,000 HFRS cases are diagnosed annually in Europe and in increasing numbers. Whether this is because of increasing recognition by the medical community or due to environmental factors such as climate change, or both, is not known. Nevertheless, in large areas of Europe, the population has a considerable seroprevalence but only relatively few HFRS cases are reported. Moreover, no epidemiological data are available from many countries. We know now that cardiac, pulmonary, ocular and hormonal disorders are, besides renal changes, common during the acute stage of PUUV and DOBV infection. About 5% of hospitalized PUUV and 16%-48% of DOBV patients require dialysis and some prolonged intensive-care treatment. Although PUUV-HFRS has a low case fatality rate, complications and long-term hormonal, renal, and cardiovascular consequences commonly occur. No vaccine or specific therapy is in general use in Europe. We conclude that hantaviruses have a significant impact on public health in Europe.

The Role of the Endothelium in HPS Pathogenesis and Potential Therapeutic Approaches

American hantaviruses cause a highly lethal acute pulmonary edema termed hantavirus pulmonary syndrome (HPS). Hantaviruses nonlytically infect endothelial cells and cause dramatic changes in barrier functions of the endothelium without disrupting the endothelium. Instead hantaviruses cause changes in the function of infected endothelial cells that normally regulate fluid barrier functions of capillaries. The endothelium of arteries, veins, and lymphatic vessels is unique and central to the function of vast pulmonary capillary beds, which regulate pulmonary fluid accumulation. The endothelium maintains vascular barrier functions through a complex series of redundant receptors and signaling pathways that serve to both permit fluid and immune cell efflux into tissues and restrict tissue edema. Infection of the endothelium provides several mechanisms for hantaviruses to alter capillary permeability but also defines potential therapeutic targets for regulating acute pulmonary edema and HPS disease. Here we discuss interactions of HPS causing hantaviruses with the endothelium, potential endothelial cell-directed permeability mechanisms, and therapeutic targeting of the endothelium as a means of reducing the severity of HPS disease.

Tula virus infections in the Eurasian water vole in Central Europe

Recent reports of novel hantaviruses in shrews and moles and the detection of rodent-borne hantaviruses in different rodent species raise important questions about their host range and specificity, evolution, and host adaptation. Tula virus (TULV), a European hantavirus, is believed to be slightly or non-pathogenic in humans and was initially detected in the common vole Microtus arvalis, the East European vole M. levis (formerly rossiaemeridionalis), and subsequently in other Microtus species. Here we report the first multiple RT-PCR detection and sequence analyses of TULV in the Eurasian water vole Arvicola amphibius from different regions in Germany and Switzerland. Additional novel TULV S-, M-, and L-segment sequences were obtained from M. arvalis and M. agrestis trapped in Germany at sites close to trapping sites of TULV-RT-PCR-positive water voles. Serological investigations using a recombinant TULV nucleocapsid protein revealed the presence of TULV-reactive antibodies in RT-PCR-positive and a few RT-PCR-negative water voles. Phylogenetic analyses revealed a geographical clustering of the novel S-, M-, and L-segment sequences from A. amphibius with those of M. arvalis- and M. agrestis-derived TULV lineages, and may suggest multiple TULV spillover or a potential host switch to A. amphibius. Future longitudinal studies of sympatric Microtus and Arvicola populations and experimental infection studies have to prove the potential of A. amphibius as an additional TULV reservoir host.

The cytoplasmic tail of hantavirus Gn glycoprotein interacts with RNA

We recently characterized the interaction between the intraviral domains of envelope glycoproteins (Gn and Gc) and ribonucleoprotein (RNP) of Puumala and Tula hantaviruses (genus Hantavirus, family Bunyaviridae). Herein we report a direct interaction between spike-forming glycoprotein and nucleic acid. We show that the envelope glycoprotein Gn of hantaviruses binds genomic RNA through its cytoplasmic tail (CT). The nucleic acid binding of Gn-CT is unspecific, as demonstrated by interactions with unrelated RNA and with single-stranded DNA. Peptide scan and protein deletions of Gn-CT mapped the nucleic acid binding to regions that overlap with the previously characterized N protein binding sites and demonstrated the carboxyl-terminal part of Gn-CT to be the most potent nucleic acid-binding site. We conclude that recognition of the RNP complex by the Gn-CT could be mediated by interactions with both genomic RNA and the N protein. This would provide the required selectivity for the genome packaging of hantaviruses.

Comparison of innate immune responses to pathogenic and putative non-pathogenic hantaviruses in vitro

Hantaviruses are human pathogens that cause hemorrhagic fever with renal syndrome or hantavirus cardiopulmonary syndrome. The mechanisms accounting for the differences in virulence between pathogenic and non-pathogenic hantaviruses are not well known. We have examined the pathogenesis of different hantavirus groups by comparing the innate immune responses induced in the host cell following infection by pathogenic (Sin Nombre, Hantaan, and Seoul virus) and putative non-pathogenic (Prospect Hill, Tula, and Thottapalayam virus) hantaviruses. Pathogenic hantaviruses were found to replicate more efficiently in interferon-competent A549 cells than putative non-pathogenic hantaviruses. The former also suppressed the expression of the interferon-β and myxovirus resistance protein genes, while the transcription level of both genes increased rapidly within 24 h post-infection in the latter. In addition, the induction level of interferon correlated with the activation level of interferon regulatory factor-3. Taken together, these results suggest that the observed differences are correlated with viral pathogenesis and further indicate that pathogenic and putative non-pathogenic hantaviruses differ in terms of early interferon induction via activation of the interferon regulatory factor-3 in infected host cells.

Inactivation of hantaviruses by N-ethylmaleimide preserves virion integrity

Thiol groups of cysteine residues are crucial for the infectivity of various enveloped viruses, but their role in the infectivity of viruses of the family Bunyaviridae has thus far not been studied. This report shows that thiol groups are essential to the infectivity of hantaviruses. Alkylation of the thiol functional groups using the membrane-permeable compound N-ethylmaleimide (NEM) and membrane-impermeable compound 5,5′-dithio-bis-(2-nitrobenzoic acid) (DTNB) showed NEM to be a highly effective inactivator of Puumala and Tula hantaviruses. The NEM-inactivated hantavirus maintained the buoyant density of the wild-type virus. Furthermore, the antigenicity of glycoproteins and the cell attachment capacity of virions were retained at NEM concentrations that totally abolished virus infectivity. These results signified preservation of virion integrity following inactivation with NEM, making chemically inactivated virions valuable research antigens. It was demonstrated with biotin-conjugated maleimide, a mechanistic analogue of NEM, that all the structural proteins of hantavirus were sensitive towards thiol alkylation. In contrast to hantaviruses, NEM did not abolish Uukuniemi phlebovirus infectivity to the same extent. This indicates differences in the use of free thiols in virus entry among members of the family Bunyaviridae.

The C-terminal 42 residues of the Tula virus Gn protein regulate interferon induction

Hantaviruses primarily infect the endothelial cell lining of capillaries and cause two vascular permeability-based diseases. The ability of pathogenic hantaviruses to regulate the early induction of interferon determines whether hantaviruses replicate in endothelial cells. Tula virus (TULV) and Prospect Hill virus (PHV) are hantaviruses which infect human endothelial cells but fail to cause human disease. PHV is unable to inhibit early interferon (IFN) responses and fails to replicate within human endothelial cells. However, TULV replicates successfully in human endothelial cells, suggesting that TULV is capable of regulating cellular IFN responses. We observed a >300-fold reduction in the IFN-stimulated genes (ISGs) MxA and ISG56 following TULV versus PHV infection of endothelial cells 1 day postinfection. Similar to results with pathogenic hantaviruses, expressing the TULV Gn protein cytoplasmic tail (Gn-T) blocked RIG-I- and TBK1-directed transcription from IFN-stimulated response elements (ISREs) and IFN-β promoters (>90%) but not transcription directed by constitutively active IFN regulatory factor-3 (IRF3). In contrast, expressing the PHV Gn-T had no effect on TBK1-induced transcriptional responses. Analysis of Gn-T truncations demonstrated that the C-terminal 42 residues of the Gn-T (Gn-T-C42) from TULV, but not PHV, inhibited IFN induction >70%. These findings demonstrate that the TULV Gn-T inhibits IFN- and ISRE-directed responses upstream of IRF3 at the level of the TBK1 complex and further define a 42-residue domain of the TULV Gn-T that inhibits IFN induction. In contrast to pathogenic hantavirus Gn-Ts, the TULV Gn-T lacks a C-terminal degron domain and failed to bind tumor necrosis factor (TNF) receptor-associated factor 3 (TRAF3), a TBK1 complex component required for IRF3 activation. These findings indicate that the nonpathogenic TULV Gn-T regulates IFN induction but accomplishes this via unique interactions with cellular TBK1 complexes. These findings fundamentally distinguish nonpathogenic hantaviruses, PHV and TULV, and demonstrate that IFN regulation alone is insufficient for hantaviruses to cause disease. Yet regulating the early IFN response is necessary for hantaviruses to replicate within human endothelial cells and to be pathogenic. Thus, in addition to IFN regulation, hantaviruses contain discrete virulence determinants which permit them to be human pathogens.

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.

Tula virus in populations of small terrestrial mammals in a rural landscape

Over 5 years (2000-2004), populations of small mammals from a rural landscape in southern Moravia (Czech Republic) were investigated for the presence of Tula virus (TULV) antigen using the ELISA set Hantagnost. In total, 1566 individuals from 10 species were examined. The prevalence in the common vole (Microtus arvalis Pallas 1778), the main reservoir of TULV, was 10% (n = 871). The prevalence of TULV antigen increases with its population numbers. The highest number of TULV antigen-positive common voles was found in set-aside plots and winter crops, such as rape and winter wheat. All these habitats are important for common vole overwintering. Older and heavier individuals were more often hantavirus antigen positive. From the other small mammal species, 186 pygmy field mice (Apodemus uralensis Pallas, 1811) were examined, of which 3 were positive, which represents the first hantavirus antigen positive record for this species, and of 195 wood mice (Apodemus sylvaticus Linnaeus, 1758) only 1 was positive. The remaining five rodent species (Apodemus flavicollis Melchior, 1834, Mus musculus Linnaeus, 1758, Micromys minutus Pallas, 1771, Myodes glareolus Schreber, 1780, Microtus subterraneus de Sélys-Longchamps, 1836) and two Soricomorpha (Sorex araneus Linnaeus, 1758, Sorex minutus Linnaeus, 1766) were hantavirus antigen negative.

A global perspective on hantavirus ecology, epidemiology, and disease

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

Electron cryotomography of Tula hantavirus suggests a unique assembly paradigm for enveloped viruses

Hantaviruses (family Bunyaviridae) are rodent-borne emerging viruses that cause a serious, worldwide threat to human health. Hantavirus diseases include hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome. Virions are enveloped and contain a tripartite single-stranded negative-sense RNA genome. Two types of glycoproteins, G(N) and G(C), are embedded in the viral membrane and form protrusions, or "spikes." The membrane encloses a ribonucleoprotein core, which consists of the RNA segments, the nucleocapsid protein, and the RNA-dependent RNA polymerase. Detailed information on hantavirus virion structure and glycoprotein spike composition is scarce. Here, we have studied the structures of Tula hantavirus virions using electron cryomicroscopy and tomography. Three-dimensional density maps show how the hantavirus surface glycoproteins, membrane, and ribonucleoprotein are organized. The structure of the G(N)-G(C) spike complex was solved to 3.6-nm resolution by averaging tomographic subvolumes. Each spike complex is a square-shaped assembly with 4-fold symmetry. Spike complexes formed ordered patches on the viral membrane by means of specific lateral interactions. These interactions may be sufficient for creating membrane curvature during virus budding. In conclusion, the structure and assembly principles of Tula hantavirus exemplify a unique assembly paradigm for enveloped viruses.

Extensive host sharing of central European Tula virus

To examine the host association of Tula virus (TULV), a hantavirus present in large parts of Europe, we investigated a total of 791 rodents representing 469 Microtus arvalis and 322 Microtus agrestis animals from northeast, northwest, and southeast Germany, including geographical regions with sympatric occurrence of both vole species, for the presence of TULV infections. Based on serological investigation, reverse transcriptase PCR, and subsequent sequence analysis of partial small (S) and medium (M) segments, we herein show that TULV is carried not only by its commonly known host M. arvalis but also frequently by M. agrestis in different regions of Germany for a prolonged time period. At one trapping site, TULV was exclusively detected in M. agrestis, suggesting an isolated transmission cycle in this rodent reservoir separate from spillover infections of TULV-carrying M. arvalis. Phylogenetic analysis of the S and M segment sequences demonstrated geographical clustering of the TULV sequences irrespective of the host, M. arvalis or M. agrestis. The novel TULV lineages from northeast, northwest, and southeast Germany described here are clearly separated from each other and from other German, European, or Asian lineages, suggesting their stable geographical localization and fast sequence evolution. In conclusion, these results demonstrate that TULV represents a promiscuous hantavirus with a large panel of susceptible hosts. In addition, this may suggest an alternative evolution mode, other than a strict coevolution, for this virus in its Microtus hosts, which should be proven in further large-scale investigations on sympatric Microtus hosts.

Degradation and aggresome formation of the Gn tail of the apathogenic Tula hantavirus

The cytoplasmic tails of envelope glycoprotein Gn of pathogenic hantaviruses but not of the apathogenic Prospect Hill virus (PHV) were recently reported to be proteasomally degraded in simian COS7 cells. Here, we show that the cytoplasmic tails of the glycoproteins of the apathogenic hantaviruses Tula virus (TULV) and PHV are also degraded through the ubiquitin-proteasome pathway, both in human HEK-293 and in simian Vero E6 cells. TULV Gn tails formed aggresomes in cells with proteasomal inhibitors. We conclude that degradation upon aggregation of Gn tails, which may represent a general cellular response to misfolded protein used by hantaviruses to control maturation of virions, is unrelated to pathogenicity.

First molecular evidence of Tula hantavirus in Microtus voles in Slovenia

Different Microtus species, present in a worldwide range habitat populating North America, Europe, Asia, and few other species have been recognized previously as a hantavirus reservoir. Tula hantavirus was first reported in Microtus arvalis and Microtus rossiaemeridionalis from Central Russia and later discovered in several European countries. Using molecular techniques we have demonstrated the presence of Tula hantavirus in three different Microtus species in Slovenia. Phylogenetic analyses of partial S segment placed Slovenian strains in the same genetic lineage as Austrian and Croatian strains.

Serological evidence of viruses naturally associated with the montane water vole (Arvicola scherman) in eastern France

We surveyed 12 populations of the montane water vole (Arvicola scherman), previously known as the fossorial form of the water vole A. terrestris, in eastern France for antibodies (immunoglobulin G) to Puumala virus (PUUV), lymphocytic choriomeningitis virus (LCMV), and cowpox virus (CPXV). Antibodies to PUUV were found in 9 (5.5%) of 164 voles from 7 populations, antibodies to LCMV were found in 13 (26.0%) of 50 voles from 2 populations, and antibodies to CPXV were found in 66 (41.8%) of 158 voles from 7 populations. Antibody status to CPXV was statistically associated with the phase of the A. scherman population density cycle and the percentage of grassland areas surrounding the sampling sites.

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

Background

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

Results

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

Conclusion

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

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

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

New Genetic Lineage of Tula Hantavirus in Microtus arvalis obscurus in Eastern Kazakhstan

Genomic sequences of Tula (TULV) hantavirus were recovered from tissue samples of European common voles Microtus arvalis (subspecies obscurus) captured in Kazakhstan, Central Asia. Phylogenetic analysis of the S genomic segment of Kazakh TULV strains showed that they form distinct, well supported genetic lineage and share a more ancient common ancestor with two Russian lineages of TULV. The deduced sequence of the nucleocapsid (N) protein of Kazakh TULV strains carried specific amino acid signature: T274Q276T281. The Microtus arvalis group includes several sibling species and/or subspecies in Eurasia, indicating recent and ongoing evolutionary radiation. Our data on TULV lineages in Central Asia, the region not studied for hantaviruses earlier, highlight the diversity of both Microtus host and the virus and also their co-evolution.

Hantaviruses direct endothelial cell permeability by sensitizing cells to the vascular permeability factor VEGF, while angiopoietin 1 and sphingosine 1-phosphate inhibit hantavirus-directed permeability

Hantaviruses infect human endothelial cells and cause two vascular permeability-based diseases: hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. Hantavirus infection alone does not permeabilize endothelial cell monolayers. However, pathogenic hantaviruses inhibit the function of alphav beta3 integrins on endothelial cells, and hemorrhagic disease and vascular permeability deficits are consequences of dysfunctional beta3 integrins that normally regulate permeabilizing vascular endothelial growth factor (VEGF) responses. Here we show that pathogenic Hantaan, Andes, and New York-1 hantaviruses dramatically enhance the permeability of endothelial cells in response to VEGF, while the nonpathogenic hantaviruses Prospect Hill and Tula have no effect on endothelial cell permeability. Pathogenic hantaviruses directed endothelial cell permeability 2 to 3 days postinfection, coincident with pathogenic hantavirus inhibition of alphav beta3 integrin functions, and hantavirus-directed permeability was inhibited by antibodies to VEGF receptor 2 (VEGFR2). These studies demonstrate that pathogenic hantaviruses, similar to alphav beta3 integrin-deficient cells, specifically enhance VEGF-directed permeabilizing responses. Using the hantavirus permeability assay we further demonstrate that the endothelial-cell-specific growth factor angiopoietin 1 (Ang-1) and the platelet-derived lipid mediator sphingosine 1-phosphate (S1P) inhibit hantavirus directed endothelial cell permeability at physiologic concentrations. These results demonstrate the utility of a hantavirus permeability assay and rationalize the testing of Ang-1, S1P, and antibodies to VEGFR2 as potential hantavirus therapeutics. The central importance of beta3 integrins and VEGF responses in vascular leak and hemorrhagic disease further suggest that altering beta3 or VEGF responses may be a common feature of additional viral hemorrhagic diseases. As a result, our findings provide a potential mechanism for vascular leakage after infection by pathogenic hantaviruses and the means to inhibit hantavirus-directed endothelial cell permeability that may be applicable to additional vascular leak syndromes.

Tula hantavirus isolate with the full-length ORF for nonstructural protein NSs survives for more consequent passages in interferon-competent cells than the isolate having truncated NSs ORF

Background

The competitiveness of two Tula hantavirus (TULV) isolates, TULV/Lodz and TULV/Moravia, was evaluated in interferon (IFN) -competent and IFN-deficient cells. The two isolates differ in the length of the open reading frame (ORF) encoding the nonstructural protein NSs, which has previously been shown to inhibit IFN response in infected cells.

Results

In IFN-deficient Vero E6 cells both TULV isolates survived equally well. In contrast, in IFN-competent MRC5 cells TULV/Lodz isolate, that possesses the NSs ORF for the full-length protein of 90 aa, survived for more consequent passages than TULV/Moravia isolate, which contains the ORF for truncated NSs protein (66–67 aa).

Conclusion

Our data show that expression of a full-length NSs protein is beneficial for the virus survival and competitiveness in IFN-competent cells and not essential in IFN-deficient cells. These results suggest that the N-terminal aa residues are important for the full activity of the NSs protein.

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

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

Chemokine production predominates in human monocytes infected with Tula virus

Many reports suggest the hypothesis of a complex immune response accompanying hantaviral infections. However, little is known about the immunopathogenesis of nonpathogenic hantaviruses, especially Tula virus (TULV). The aim of our study was to determine the cytokine/chemokine profile induced after the infection of human macrophages with TULV and the role of viral replication in this process. Also, we wanted to establish how the study of TULV is relevant to our previous study of pathogenic hantaviruses. We showed that TULV-infected macrophages produced chemokines (interleukin-8, macrophage chemoattractant protein-1, and macrophage inflammatory protein-1beta) important for recruiting inflammatory cells, whereas no significant changes were recorded in the tested cytokine levels. This property was not influenced by ultraviolet inactivation. There were some differences in chemokine production compared with our previous study with pathogenic hantaviruses. A possible explanation could be a different way of entering host cells found in the pathogenic and nonpathogenic hantaviruses and activation of different intracellular signaling pathways.

Degrons at the C terminus of the pathogenic but not the nonpathogenic hantavirus G1 tail direct proteasomal degradation

Pathogenic hantaviruses cause two human diseases: hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS). The hantavirus G1 protein contains a long, 142-amino-acid cytoplasmic tail, which in NY-1 virus (NY-1V) is ubiquitinated and proteasomally degraded (E. Geimonen, I. Fernandez, I. N. Gavrilovskaya, and E. R. Mackow, J. Virol. 77: 10760-10768, 2003). Here we report that the G1 cytoplasmic tails of pathogenic Andes (HPS) and Hantaan (HFRS) viruses are also degraded by the proteasome and that, in contrast, the G1 tail of nonpathogenic Prospect Hill virus (PHV) is stable and not proteasomally degraded. We determined that the signals which direct NY-1V G1 tail degradation are present in a hydrophobic region within the C-terminal 30 residues of the protein. In contrast to that of PHV, the NY-1V hydrophobic domain directs the proteasomal degradation of green fluorescent protein and constitutes an autonomous degradation signal, or "degron," within the NY-1V G1 tail. Replacing 4 noncontiguous residues of the NY-1V G1 tail with residues present in the stable PHV G1 tail resulted in a NY-1V G1 tail that was not degraded by the proteasome. In contrast, changing a different but overlapping set of 4 PHV residues to corresponding NY-1V residues directed proteasomal degradation of the PHV G1 tail. The G1 tails of pathogenic, but not nonpathogenic, hantaviruses contain intervening hydrophilic residues within the C-terminal hydrophobic domain, and amino acid substitutions that alter the stability or degradation of NY-1V or PHV G1 tails result from removing or adding intervening hydrophilic residues. Our results identify residues that selectively direct the proteasomal degradation of pathogenic hantavirus G1 tails. Although a role for the proteasomal degradation of the G1 tail in HPS or HFRS is unclear, these findings link G1 tail degradation to viral pathogenesis and suggest that degrons within hantavirus G1 tails are potential virulence determinants.