Isolation of virus causing hemorrhagic fever with renal syndrome (HFRS) through a cell culture system

A Portable Diagnostic Assay, Genetic Diversity, and Isolation of Seoul Virus from Rattus norvegicus Collected in Gangwon Province, Republic of Korea

Seoul virus (SEOV), an etiological agent for hemorrhagic fever with renal syndrome, poses a significant public health threat worldwide. This study evaluated the feasibility of a mobile Biomeme platform for facilitating rapid decision making of SEOV infection. A total of 27 Rattus norvegicus were collected from Seoul Metropolitan City and Gangwon Province in Republic of Korea (ROK), during 2016–2020. The serological and molecular prevalence of SEOV was 5/27 (18.5%) and 2/27 (7.4%), respectively. SEOV RNA was detected in multiple tissues of rodents using the Biomeme device, with differences in Ct values ranging from 0.6 to 2.1 cycles compared to a laboratory benchtop system. Using amplicon-based next-generation sequencing, whole-genome sequences of SEOV were acquired from lung tissues of Rn18-1 and Rn19-5 collected in Gangwon Province. Phylogenetic analysis showed a phylogeographical diversity of rat-borne orthohantavirus collected in Gangwon Province. We report a novel isolate of SEOV Rn19-5 from Gangwon Province. Our findings demonstrated that the Biomeme system can be applied for the molecular diagnosis of SEOV comparably to the laboratory-based platform. Whole-genome sequencing of SEOV revealed the phylogeographical diversity of orthohantavirus in the ROK. This study provides important insights into the field-deployable diagnostic assays and genetic diversity of orthohantaviruses for the rapid response to hantaviral outbreaks in the ROK.

Selection and Validation of siRNAs Preventing Uptake and Replication of SARS-CoV-2

In 2019, the novel highly infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak rapidly led to a global pandemic with more than 346 million confirmed cases worldwide, resulting in 5.5 million associated deaths (January 2022). Entry of all SARS-CoV-2 variants is mediated by the cellular angisin-converting enzyme 2 (ACE2). The virus abundantly replicates in the epithelia of the upper respiratory tract. Beyond vaccines for immunization, there is an imminent need for novel treatment options in COVID-19 patients. So far, only a few drugs have found their way into the clinics, often with modest success. Specific gene silencing based on small interfering RNA (siRNA) has emerged as a promising strategy for therapeutic intervention, preventing/limiting SARS-CoV-2 entry into host cells or interfering with viral replication. Here, we pursued both strategies. We designed and screened nine siRNAs (siA1-9) targeting the viral entry receptor ACE2. SiA1, (siRNA against exon1 of ACE2 mRNA) was most efficient, with up to 90% knockdown of the ACE2 mRNA and protein for at least six days. In vitro, siA1 application was found to protect Vero E6 and Huh-7 cells from infection with SARS-CoV-2 with an up to ∼92% reduction of the viral burden indicating that the treatment targets both the endosomal and the viral entry at the cytoplasmic membrane. Since the RNA-encoded genome makes SARS-CoV-2 vulnerable to RNA interference (RNAi), we designed and analysed eight siRNAs (siV1-8) directly targeting the Orf1a/b region of the SARS-CoV-2 RNA genome, encoding for non-structural proteins (nsp). As a significant hallmark of this study, we identified siV1 (siRNA against leader protein of SARS-CoV-2), which targets the nsp1-encoding sequence (a.k.a. ‘host shutoff factor’) as particularly efficient. SiV1 inhibited SARS-CoV-2 replication in Vero E6 or Huh-7 cells by more than 99% or 97%, respectively. It neither led to toxic effects nor induced type I or III interferon production. Of note, sequence analyses revealed the target sequence of siV1 to be highly conserved in SARS-CoV-2 variants. Thus, our results identify the direct targeting of the viral RNA genome (ORF1a/b) by siRNAs as highly efficient and introduce siV1 as a particularly promising drug candidate for therapeutic intervention.

Broad and potently neutralizing monoclonal antibodies isolated from human survivors of New World hantavirus infection

New World hantaviruses (NWHs) are endemic in North and South America and cause hantavirus cardiopulmonary syndrome (HCPS), with a case fatality rate of up to 40%. Knowledge of the natural humoral immune response to NWH infection is limited. Here, we describe human monoclonal antibodies (mAbs) isolated from individuals previously infected with Sin Nombre virus (SNV) or Andes virus (ANDV). Most SNV-reactive antibodies show broad recognition and cross-neutralization of both New and Old World hantaviruses, while many ANDV-reactive antibodies show activity for ANDV only. mAbs ANDV-44 and SNV-53 compete for binding to a distinct site on the ANDV surface glycoprotein and show potently neutralizing activity to New and Old World hantaviruses. Four mAbs show therapeutic efficacy at clinically relevant doses in hamsters. These studies reveal a convergent and potently neutralizing human antibody response to NWHs and suggest therapeutic potential for human mAbs against HCPS.

Engdahl et al. show that monoclonal antibodies isolated from human survivors of New World hantavirus infection display broad and potent neutralization across hantavirus species and recognize distinct sites on the glycoprotein spike. Multiple antibodies demonstrate potential therapeutic candidates for New World hantavirus infection. Some antibodies also neutralized Old World hantaviruses.

Immunological Responses to Seoul Orthohantavirus in Experimentally and Naturally Infected Brown Rats (Rattus norvegicus)

To clarify the mechanism of Seoul orthohantavirus (SEOV) persistence, we compared the humoral and cell-mediated immune responses to SEOV in experimentally and naturally infected brown rats. Rats that were experimentally infected by the intraperitoneal route showed transient immunoglobulin M (IgM) production, followed by an increased anti-SEOV immunoglobulin G (IgG) antibody response and maturation of IgG avidity. The level of SEOV-specific cytotoxic T lymphocytes (CTLs) peaked at 6 days after inoculation and the viral genome disappeared from serum. In contrast, naturally infected brown rats simultaneously had a high rate of SEOV-specific IgM and IgG antibodies (28/43). Most of the IgM-positive rats (24/27) had the SEOV genome in their lungs, suggesting that chronic SEOV infection was established in those rats. In female rats with IgG avidity maturation, the viral load in the lungs was decreased. On the other hand, there was no relationship between IgG avidity and viral load in the lungs in male rats. A CTL response was not detected in naturally infected rats. The difference between immune responses in the experimentally and naturally infected rats is associated with the establishment of chronic infection in natural hosts.

Small animal jet injection technique results in enhanced immunogenicity of hantavirus DNA vaccines

DNA vaccine evaluation in small animals is hampered by low immunogenicity when the vaccines are delivered using a needle and syringe. To overcome this technical hurdle we tested the possibility that a device developed for human intradermal medicine delivery might be adapted to successfully deliver a DNA vaccine to small animals. Disposable syringe jet injection (DSJI) does not currently exist for small animals. However, a commercialized, human intradermal device used to to administer medicines to the human dermis in a 0.1 mL volume was evaluated in Syrian hamsters. Here, we found that hantavirus DNA vaccines administered to hamsters using DSJI were substantially more immunogenic than the same vaccines delivered by needle/syringe or particle mediated epidermal delivery (gene gun) vaccination. By adjusting how the device was used we could deliver vaccine to either subcutaneous tissues, or through the skin into the muscle. RNA and/or antigen expression was detected in epidermal, subepidermal and fibroblast cells. We directly compared six optimized and non-optimized hantavirus DNA vaccines in hamsters. Optimization, including codon-usage and mRNA stability, did not necessarily result in increased immunogenicity for all vaccines tested; however, optimization of the Andes virus (ANDV) DNA vaccine protected vaccinated hamsters from lethal disease. This is the first time active vaccination with an ANDV DNA vaccine has shown protective efficacy in the hamster model. The adaptation of a human intradermal jet injection device for use as a method of subcutaneous and intramuscular jet injection of DNA vaccines will advance the development of nucleic acid based medical countermeasures for diseases modeled in hamsters.

Viral Disease

This chapter discusses infections of rats with viruses in the following 14 virus families: Adenoviridae, Arenaviridae, Coronaviridae, Flaviviridae, Hantaviridae, Hepeviridae, Herpesviridae, Paramyxoviridae, Parvoviridae, Picornaviridae, Pneumoviridae, Polyomaviridae, Poxviridae, and Reoviridae . Serological surveys indicate that parvoviruses, coronaviruses, cardioviruses, and pneumoviruses are the most prevalent in laboratory rats. A new polyomavirus and a new cardiovirus that cause disease in laboratory rats are described. Metagenomic analyses of feces or intestinal contents from wild rats have detected viruses from an additional nine virus families that could potentially cause infections in laboratory rats.

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.

Serological Evidence of Thailand Orthohantavirus or Antigenically Related Virus Infection Among Rodents in a Chronic Kidney Disease of Unknown Etiology Endemic Area, Girandurukotte, Sri Lanka

We have reported high seroprevalence to Thailand orthohantavirus (THAIV) or THAIV-related orthohantavirus (TRHV) among patients with chronic kidney disease of unknown etiology in Girandurukotte, Sri Lanka. THAIV or TRHV infection is considered to be transmitted by rodent hosts in this area, but its reservoir rodents have not yet been identified. Hence, 116 rodents were captured, and seroprevalences were examined by indirect immunofluorescent antibody assay (immunofluorescence assay [IFA]) using antigens of THAIV strain Thai749-infected Vero E6 cells and recombinant nucleocapsid protein of THAIV expressed in Vero E6 cell. Molecular biological species identification of rodents was carried out by sequencing rag1, irbp, and mitochondrial cytb genes. The majority (112/116) of the captured rodents were lineage Ib of black rats (Rattus rattus). Among them, 19.6% (22/112) of the rats possessed antibodies against THAIV. Also, a lesser bandicoot rat (Bandicota bengalensis), which belongs to the Sri Lankan endemic genetic lineage, was seropositive (1/1). Two Mus booduga and one Murinae sp. were seronegative. Rodent sera showed less cross-reactivities to antigens of Vero E6 cells infected with Hantaan orthohantavirus (HTNV), Seoul orthohantavirus (SEOV), and Puumala orthohantavirus (PUUV) in IFA. These results suggest that the hantavirus present in rodents in Sri Lanka is related to THAIV or TRHV rather than to SEOV, HTNV, or PUUV. However, it might be serologically distinct from the prototype THAIV strain, Thai749, used in this study. This study revealed that black rats and lesser bandicoot rats belonging to Sri Lankan endemic lineages are possible reservoirs for THAIV or TRHV in Girandurukotte. Further multiple geographical studies are needed to confirm the THAIV or TRHV reservoir status of black and lesser bandicoot rats in Sri Lanka.

Wild Rats, Laboratory Rats, Pet Rats: Global Seoul Hantavirus Disease Revisited

Recent reports from Europe and the USA described Seoul orthohantavirus infection in pet rats and their breeders/owners, suggesting the potential emergence of a “new” public health problem. Wild and laboratory rat-induced Seoul infections have, however, been described since the early eighties, due to the omnipresence of the rodent reservoir, the brown rat Rattus norvegicus. Recent studies showed no fundamental differences between the pathogenicity and phylogeny of pet rat-induced Seoul orthohantaviruses and their formerly described wild or laboratory rat counterparts. The paucity of diagnosed Seoul virus-induced disease in the West is in striking contrast to the thousands of cases recorded since the 1980s in the Far East, particularly in China. This review of four continents (Asia, Europe, America, and Africa) puts this “emerging infection” into a historical perspective, concluding there is an urgent need for greater medical awareness of Seoul virus-induced human pathology in many parts of the world. Given the mostly milder and atypical clinical presentation, sometimes even with preserved normal kidney function, the importance of simple but repeated urine examination is stressed, since initial but transient proteinuria and microhematuria are rarely lacking.

Animal Models for the Study of Rodent-Borne Hemorrhagic Fever Viruses: Arenaviruses and Hantaviruses

Human pathogenic hantaviruses and arenaviruses are maintained in nature by persistent infection of rodent carrier populations. Several members of these virus groups can cause significant disease in humans that is generically termed viral hemorrhagic fever (HF) and is characterized as a febrile illness with an increased propensity to cause acute inflammation. Human interaction with rodent carrier populations leads to infection. Arenaviruses are also viewed as potential biological weapons threat agents. There is an increased interest in studying these viruses in animal models to gain a deeper understating not only of viral pathogenesis, but also for the evaluation of medical countermeasures (MCM) to mitigate disease threats. In this review, we examine current knowledge regarding animal models employed in the study of these viruses. We include analysis of infection models in natural reservoirs and also discuss the impact of strain heterogeneity on the susceptibility of animals to infection. This information should provide a comprehensive reference for those interested in the study of arenaviruses and hantaviruses not only for MCM development but also in the study of viral pathogenesis and the biology of these viruses in their natural reservoirs.

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.

More novel hantaviruses and diversifying reservoir hosts--time for development of reservoir-derived cell culture models?

Due to novel, improved and high-throughput detection methods, there is a plethora of newly identified viruses within the genus Hantavirus. Furthermore, reservoir host species are increasingly recognized besides representatives of the order Rodentia, now including members of the mammalian orders Soricomorpha/Eulipotyphla and Chiroptera. Despite the great interest created by emerging zoonotic viruses, there is still a gross lack of in vitro models, which reflect the exclusive host adaptation of most zoonotic viruses. The usually narrow host range and genetic diversity of hantaviruses make them an exciting candidate for studying virus-host interactions on a cellular level. To do so, well-characterized reservoir cell lines covering a wide range of bat, insectivore and rodent species are essential. Most currently available cell culture models display a heterologous virus-host relationship and are therefore only of limited value. Here, we review the recently established approaches to generate reservoir-derived cell culture models for the in vitro study of virus-host interactions. These successfully used model systems almost exclusively originate from bats and bat-borne viruses other than hantaviruses. Therefore we propose a parallel approach for research on rodent- and insectivore-borne hantaviruses, taking the generation of novel rodent and insectivore cell lines from wildlife species into account. These cell lines would be also valuable for studies on further rodent-borne viruses, such as orthopox- and arenaviruses.

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

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

Seoul virus-infected rat lung endothelial cells and alveolar macrophages differ in their ability to support virus replication and induce regulatory T cell phenotypes

Hantaviruses cause a persistent infection in reservoir hosts that is attributed to the upregulation of regulatory responses and downregulation of proinflammatory responses. To determine whether rat alveolar macrophages (AMs) and lung microvascular endothelial cells (LMVECs) support Seoul virus (SEOV) replication and contribute to the induction of an environment that polarizes CD4(+) T cell differentiation toward a regulatory T (Treg) cell phenotype, cultured primary rat AMs and LMVECs were mock infected or infected with SEOV and analyzed for viral replication, cytokine and chemokine responses, and expression of cell surface markers that are related to T cell activation. Allogeneic CD4(+) T cells were cocultured with SEOV-infected or mock-infected AMs or LMVECs and analyzed for helper T cell (i.e., Treg, Th17, Th1, and Th2) marker expression and Treg cell frequency. SEOV RNA and infectious particles in culture media were detected in both cell types, but at higher levels in LMVECs than in AMs postinfection. Expression of Ifnβ, Ccl5, and Cxcl10 and surface major histocompatibility complex class II (MHC-II) and MHC-I was not altered by SEOV infection in either cell type. SEOV infection significantly increased Tgfβ mRNA in AMs and the amount of programmed cell death 1 ligand 1 (PD-L1) in LMVECs. SEOV-infected LMVECs, but not AMs, induced a significant increase in Foxp3 expression and Treg cell frequency in allogeneic CD4(+) T cells, which was virus replication and cell contact dependent. These data suggest that in addition to supporting viral replication, AMs and LMVECs play distinct roles in hantavirus persistence by creating a regulatory environment through increased Tgfβ, PD-L1, and Treg cell activity.

Isolation of Hokkaido virus, genus Hantavirus, using a newly established cell line derived from the kidney of the grey red-backed vole (Myodes rufocanus bedfordiae)

Hantaviruses belong to the family Bunyaviridae and are maintained in wild rodents. Although Vero E6 cells, which originate from African green monkey kidney, are used widely in hantavirus research, isolation of hantaviruses from this cell line is difficult. To develop an efficient method of propagation and isolation of hantaviruses we established a novel cell line, MRK101, derived from the kidney of the grey red-backed vole (Myodes rufocanus bedfordiae), the natural host of Hokkaido virus (HOKV). The MRK101 cells showed a significantly higher susceptibility to Puumala virus (PUUV) hosted by Myodes glareolus than Vero E6 cells. Viral nucleocapsid protein in PUUV-infected MRK101 cells was detected earlier than in Vero E6 cells, and the viral titre in the culture fluid of MRK101 cells was higher than that of Vero E6 cells during the early phase of infection. In contrast, MRK101 cells showed no susceptibility to Hantaan virus. HOKV, which has not been isolated to date, was isolated successfully using MRK101 cells. Moreover, the newly isolated HOKV was successfully propagated in MRK101, but not Vero E6, cells. Phylogenic analyses of the S (small), M (medium) and L (large) segment sequences revealed that HOKV is related most closely to PUUV, but is distinct from other hantaviruses. These data suggest that the MRK101 cell line is a useful tool for the isolation and propagation of hantaviruses. Moreover, this is (to our knowledge) the first report of hantavirus isolation in a cell line that originated from the natural host.

Isolation and characterization of hantaviruses in Far East Russia and etiology of hemorrhagic fever with renal syndrome in the region

Hemorrhagic fever with renal syndrome (HFRS) is a serious public health issue in Far East Russia. Two different hantaviruses were isolated from rodents captured in the Khabarovsk region: Amur virus (AMRV; Khekhtsir/AP209/2005 strain from Apodemus peninsulae) and Hantaan virus (HTNV; Galkino/AA57/2002 strain from A. agrarius). Genetic analysis of the new isolates revealed that the M and L segments were apparently different between AMRV and HTNV, but S segments of the two viruses were closer. The antigenicities of AMRV, HTNV, and Seoul virus (SEOV) were differentiated by cross-neutralization. Serological differential diagnoses of 67 HFRS patients in the Prymorsky and Khabarovsk regions of Far East Russia were conducted using a neutralization test. The results revealed that the major cause of HFRS varied with location in Far East Russia: SEOV for Vladivostok city in the Prymorsky region, AMRV in rural areas of the Primorsky region, and probably HTNV for the Khabarovsk region.

An efficient in vivo method for the isolation of Puumala virus in Syrian hamsters and the characterization of the isolates from Russia

Puumala virus (PUUV) and other Arvicolinae-borne hantaviruses are difficult to cultivate in cell culture. To isolate these hantaviruses efficiently, hantavirus nucleocapsid protein (NP)-positive but seronegative wild rodents were selected by NP-detection ELISA. Three of 68 Myodes glareolus captured in Samara, Russia, were NP-positive and seronegative. Syrian hamsters were inoculated with lung homogenates from NP-positive rodents for virus propagation. Virus isolation in vitro was carried out by inoculation of lung homogenates of NP-positive hamsters to Vero E6 cell monolayers. Two PUUV strains (Samara49/CG/2005 and Samara94/CG/2005) from M. glareolus were isolated in Vero E6 cells. Nucleotide and amino acid sequence identities of the S segment of these isolates to those of PUUV F-s808 from a fatal HFRS patient in Samara region were 96.7-99.3% and 99.3-100.0%, respectively. Morphologic features of Vero E6 cells infected with PUUV strain Samara49/CG/2005 were quite similar to those of Hantaan virus-infected cells. Isolation of Hokkaido virus from Myodes rufocanus captured in Hokkaido, Japan, was also performed. Hokkaido virus NP and RNA were recovered and maintained in hamsters. These results suggest that inoculation of Syrian hamsters with rodent samples is an efficient method for the isolation and maintenance of PUUV and other Arvicolinae-borne hantaviruses.

New World hantaviruses activate IFNlambda production in type I IFN-deficient vero E6 cells

BACKGROUND

Hantaviruses indigenous to the New World are the etiologic agents of hantavirus cardiopulmonary syndrome (HCPS). These viruses induce a strong interferon-stimulated gene (ISG) response in human endothelial cells. African green monkey-derived Vero E6 cells are used to propagate hantaviruses as well as many other viruses. The utility of the Vero E6 cell line for virus production is thought to owe to their lack of genes encoding type I interferons (IFN), rendering them unable to mount an efficient innate immune response to virus infection. Interferon lambda, a more recently characterized type III IFN, is transcriptionally controlled much like the type I IFNs, and activates the innate immune system in a similar manner.

METHODOLOGY/PRINCIPAL FINDINGS

We show that Vero E6 cells respond to hantavirus infection by secreting abundant IFNlambda. Three New World hantaviruses were similarly able to induce IFNlambda expression in this cell line. The IFNlambda contained within virus preparations generated with Vero E6 cells independently activates ISGs when used to infect several non-endothelial cell lines, whereas innate immune responses by endothelial cells are specifically due to viral infection. We show further that Sin Nombre virus replicates to high titer in human hepatoma cells (Huh7) without inducing ISGs.

CONCLUSIONS/SIGNIFICANCE

Herein we report that Vero E6 cells respond to viral infection with a highly active antiviral response, including secretion of abundant IFNlambda. This cytokine is biologically active, and when contained within viral preparations and presented to human epithelioid cell lines, results in the robust activation of innate immune responses. We also show that both Huh7 and A549 cell lines do not respond to hantavirus infection, confirming that the cytoplasmic RNA helicase pathways possessed by these cells are not involved in hantavirus recognition. We demonstrate that Vero E6 actively respond to virus infection and inhibiting IFNlambda production in these cells might increase their utility for virus propagation.

Molecular epidemiological and serological studies of hantavirus infection in northern Vietnam

The distribution of anti-hantavirus antibodies in humans and rodents in northern Vietnam was examined. In total, 837 serum samples from healthy humans (617) and patients with fever (220), living in six different areas were screened for IgG antibodies against Hantaan or Seoul virus (SEOV) by ELISA, IFA, and Western blot analysis. Antibody-positive sera were identified in 7/617 (1.1%) healthy donors, 5/150 port workers in the port of Hai Phong, and 2/185 residents of Ha Nam Province. In comparison, positive sera were detected in 5/220 (2.3%) fever patients in the provinces of Ha Nam (1/58) and Thanh Hoa (4/146). Antibody-positive Rattus norvegicus were found in the provinces of Ha Nam (7/52) and Thanh Hoa (1/67), in Haibatrung District (7/43) in Hanoi, and in Hai Phong Port (21/62), while antibody-positive R. rattus (2/17) were found in Hai Phong Port. Part of the Gc region from the viral genome was amplified by RT-PCR using lung tissue samples from R. norvegicus in Haibatrung (2/7) and Hai Phong Port (7/9), but not from R. rattus (0/2). Viral sequences were located in the SEOV clade and formed a single lineage with Indonesian SEOV, suggesting that Vietnamese SEOV is part of a distinct lineage among Asian SEOVs.

Hantavirus infection in East Asia

Hantaviruses are enveloped RNA viruses that belong to the Hantavirus genus of the family Bunyaviridae. These viruses persistently infect their rodent reservoirs without causing disease. The virus is transmitted to humans via the inhalation of infectious aerosols generated from contaminated animal secretions or through the contaminated saliva of animal bites. Hantaviruses cause haemorrhagic fever with renal syndrome in Euro-Asia, and hantavirus pulmonary syndrome (HPS) in North and South America. Here, we review the epidemiology and epizootiology of hantavirus infection in Asian countries.

Open reading frame 8a of the human severe acute respiratory syndrome coronavirus not only promotes viral replication but also induces apoptosis

Background. A unique genomic difference between human and civet severe acute respiratory syndrome coronaviruses (SARS-CoVs) is that the former has a deletion of 29 nucleotides from open reading frame (orf) 8d that results in the generation of orf8a and orf8b. The objectives of the present study were to analyze antibody reactivity to ORF8a in patients with SARS and to elucidate the function of ORF8a.

Methods. Western-blot and immunofluorescent antibody assays were used to detect anti-ORF8a antibody. SARS-CoV HKU39849 was used to infect stable clones expressing ORF8a and cells transfected with small interfering RNA (siRNA). The virus loads (VLs) and cytopathic effects (CPEs) were recorded. Confocal microscopy and several mitochondria-related tests were used to study the function of ORF8a.

Results. Two (5.4%) of 37 patients with SARS had anti-ORF8a antibodies. The VLs in the stable clones expressing ORF8a were significantly higher than those in control subjects 5 days after infection. siRNA against orf8a significantly reduced VLs and interrupted the CPE. ORF8a was found to be localized in mitochondria, and overexpression resulted in increases in mitochondrial transmembrane potential, reactive oxygen species production, caspase 3 activity, and cellular apoptosis.

Conclusions. ORF8a not only enhances viral replication but also induces apoptosis through a mitochondria-dependent pathway.

Identifying epitopes responsible for neutralizing antibody and DC-SIGN binding on the spike glycoprotein of the severe acute respiratory syndrome coronavirus

The severe acute respiratory syndrome-associated coronavirus (SARS-CoV) uses dendritic cell-specific ICAM-3 grabbing nonintegrin (DC-SIGN) to facilitate cell entry via cellular receptor-angiotensin-converting enzyme 2. For this project, we used recombinant baculoviruses expressing different lengths of SARS-CoV spike (S) protein in a capture assay to deduce the minimal DC-SIGN binding region. Our results identified the region location between amino acid (aa) residues 324 to 386 of the S protein. We then generated nine monoclonal antibodies (MAbs) against the S protein to map the DC-SIGN-binding domain using capture assays with pseudotyped viruses and observed that MAb SIa5 significantly blocked S protein-DC-SIGN interaction. An enhancement assay using the HKU39849 SARS-CoV strain and human immature dendritic cells confirmed our observation. Data from a pepscan analysis and M13 phage peptide display library system mapped the reactive MAb SIa5 epitope to aa residues 363 to 368 of the S protein. Results from a capture assay testing three pseudotyped viruses with mutated N-linked glycosylation sites of the S protein indicate that only two pseudotyped viruses (N330Q and N357Q, both of which lost glycosylation sites near the SIa5 epitope) had diminished DC-SIGN-binding capacity. We also noted that MAb SIb4 exerted a neutralizing effect against HKU39849; its reactive epitope was mapped to aa residues 435 to 439 of the S protein. We offer the data to facilitate the development of therapeutic agents and preventive vaccines against SARS-CoV infection.

Hantaan/Andes virus DNA vaccine elicits a broadly cross-reactive neutralizing antibody response in nonhuman primates

At least four hantavirus species cause disease with prominent renal involvement-hemorrhagic fever with renal syndrome (HFRS); and several hantavirus strains cause disease with significant pulmonary involvement-hantavirus pulmonary syndrome (HPS). The most prevalent and lethal hantaviruses associated with HFRS and HPS are Hantaan virus (HTNV) and Andes virus (ANDV), respectively. Here, we constructed a DNA vaccine plasmid (pWRG/HA-M) that contains both the HTNV and ANDV M gene segments. Rhesus macaques vaccinated with pWRG/HA-M produced antibodies that bound the M gene products (i.e., G1 and G2 glycoproteins), and neutralized both HTNV and ANDV. Neutralizing antibody titers elicited by the dual-immunogen pWRG/HA-M, or single-immunogen plasmids expressing only the HTNV or ANDV glycoproteins, increased rapidly to high levels after a booster vaccination administered 1-2 years after the initial vaccination series. Memory responses elicited by this long-range boost exhibited an increased breadth of cross-neutralizing activity relative to the primary response. This is the first time that hantavirus M gene-based DNA vaccines have been shown to elicit a potent memory response, and to elicit antibody responses that neutralize viruses that cause both HFRS and HPS.

Identification of Dobrava, Hantaan, Seoul, and Puumala viruses by one-step real-time RT-PCR

We developed four assays for specifically identifying Dobrava (DOB), Hantaan (HTN), Puumala (PUU), and Seoul (SEO) viruses. The assays are based on the real-time one-step reverse transcriptase polymerase chain reaction (RT-PCR) with the small segment used as the target sequence. The detection limits of DOB, HTN, PUU, and SEO assays were 25, 25, 25, and 12.5 plaque-forming units, respectively. The assays were evaluated in blinded experiments, each with 100 samples that contained Andes, Black Creek Canal, Crimean-Congo hemorrhagic fever, Rift Valley fever and Sin Nombre viruses in addition to DOB, HTN, PUU and SEO viruses. The sensitivity levels of the DOB, HTN, PUU, and SEO assays were 98%, 96%, 92% and 94%, respectively. The specificity of DOB, HTN and SEO assays was 100% and the specificity of the PUU assay was 98%. Because of the high levels of sensitivity, specificity, and reproducibility, we believe that these assays can be useful for diagnosing and differentiating these four Old-World hantaviruses.

Genetic and antigenic characterization of the Amur virus associated with hemorrhagic fever with renal syndrome

The genetic and antigenic characteristics of the Amur (AMR) and Far East (FE) virus lineages, which are both within the genus Hantavirus, were studied. Representative viruses, H5 and B78 for AMR and Bao 14 for FE, were used. The entire small (S) and medium (M) segments, except for the 3'- and 5'-ends, were sequenced. The deduced amino acid sequences of AMR had 96.7 and 92.0-92.2% identities with the Hantaan (HTN) virus in the S and M segments, respectively. The amino acid sequences of FE had 99.1 and 97.9% identities in the S and M segments, respectively. The three viral strains and HTN virus had similar binding patterns to a panel of monoclonal antibodies (MAbs), except that one MAb did not bind AMR. However, sera from Apodemus peninsulae, naturally infected with AMR virus, neutralized homologous viruses at 1:160 to 1:320 dilutions and HTN at 1:20 to 1:40 dilutions. The anti-AMR serum neutralized homologous viruses at a 1:80 dilution and HTN at a 1:40 dilution. The anti-HTN serum did not neutralize AMR (<1:40 dilution), although it had a high neutralizing titer (1:320) against the homologous virus. Therefore, we suggest that AMR virus may constitute a distinct serotype within the genus Hantavirus.

Hantaviruses induce cytopathic effects and apoptosis in continuous human embryonic kidney cells

Hantaviruses are maintained in nature in persistently infected rodents and can also persistently infect cultured mammalian cells, causing little or no cytopathology. An unexpected outcome of this study was the observation of cytopathic effects (CPE) in the hantavirus-infected human embryonic kidney cell line HEK293. It was confirmed that hantaviruses induce apoptosis in HEK293 cells, although apoptosis appeared mostly in uninfected, bystander cells and rarely in infected HEK293 cells. Although studies by others suggest that the nucleocapsid protein of Puumala virus interacts with the Fas-mediated apoptosis enhancer Daxx at the gene expression level, it was determined that members of the TNF receptor superfamily did not contribute to the apoptosis observed in infected HEK293 cells. The observation of CPE in HEK293 cells might lead to a better understanding of the mechanisms of persistence and pathogenesis in hantavirus infections.

Evidence of the presence of Seoul virus in Cambodia

A study was conducted in agricultural and urban areas in Cambodia to assess the presence of hantaviruses in rodent populations. In 1998, rodents were trapped in two villages and in Phnom Penh city around market places and a rubbish dump. IgG antibodies to Hantaan virus were detected in 54 (8.2%) rodents among 660 tested: 6.4% (13/203) among roof rats (Rattus rattus), 20.9% (39/187) among Norway rats (R. norvegicus), 16.7% (2/12) among unidentified Rattus species and none in 183 Polynesian rats (R. exulans) or in 75 bandicoot rats (Bandicota sp.). The presence of the viral genome was detected by a reverse transcription-PCR amplifying part of the sequence coding for the nucleoprotein in the S segment, in 87% of the seropositive rodents. Thirty-one representative cDNAs were sequenced. Phylogenetic studies of the sequences indicated a close relationship with Seoul virus. However, the Cambodian Seoul virus sequences clustered within two different phylogenetic lineages, one associated with R. rattus and the other with R. norvegicus.

Establishment of an enzyme-linked immunosorbent assay for detection of hantavirus antibody of rats using a recombinant of nucleocapsid protein expressed in Escherichia coli

A recombinant nucleocapsid protein of Hantaan virus (HTN) 76-118 strain expressed in E. coli was applied as a serodiagnostic antigen in an enzyme-linked immunosorbent assay (rHTN-ELISA) for detection of hantavirus antibody in rat sera. The sensitivity and specificity of the rHTN-ELISA were compared with those of the indirect immunofluoresent assay (IFA) using virus-infected cells. The sensitivity of rHTN-ELISA was similar to that of the IFA both in experimentally SR-11 infected rat and naturally infected rat sera. Sera showing a low antibody titer in IFA and suspected to be negative by other methods were also found to be negative in rHTN-ELISA. These results indicate that rHTN-ELISA is effective as a screening method for serodiagnosis of hantaviruses, because of its high sensitivity, specificity, safety and suitability for processing large number of samples.

A lethal disease model for hantavirus pulmonary syndrome

Hantaviruses are associated with two human diseases, hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Development of vaccines and therapies to prevent and treat HFRS and HPS have been hampered by the absence of a practical animal model. Here we report that Andes virus (ANDV), a South American hantavirus, is highly lethal in adult Syrian hamsters. The characteristics of the disease in hamsters, including the incubation period, symptoms of rapidly progressing respiratory distress, and pathologic findings of pulmonary edema and pleural effusion, closely resemble HPS in humans. This is the first report of a lethal disease model for hantaviruses that causes HPS.

DNA vaccination with the Hantaan virus M gene protects Hamsters against three of four HFRS hantaviruses and elicits a high-titer neutralizing antibody response in Rhesus monkeys

Four hantaviruses-Hantaan virus (HTNV), Seoul virus (SEOV), Dobrava virus (DOBV) and Puumala virus-are known to cause hemorrhagic fever with renal syndrome (HFRS) in Europe and Asia. HTNV causes the most severe form of HFRS (5 to 15% case-fatality rate) and afflicts tens of thousands of people annually. Previously, we demonstrated that DNA vaccination with a plasmid expressing the SEOV M gene elicited neutralizing antibodies and protected hamsters against infection with SEOV and HTNV. Here, we report the construction and evaluation of a DNA vaccine that expresses the HTNV M gene products, G1 and G2. DNA vaccination of hamsters with the HTNV M gene conferred sterile protection against infection with HTNV, SEOV, and DOBV. DNA vaccination of rhesus monkeys with either the SEOV or HTNV M gene elicited high levels of neutralizing antibodies. These are the first immunogenicity data for hantavirus DNA vaccines in nonhuman primates. Because a neutralizing antibody response is considered a surrogate marker for protective immunity in humans, our protection data in hamsters combined with the immunogenicity data in monkeys suggest that hantavirus M gene-based DNA vaccines could protect humans against the most severe forms of HFRS.

Truncated hantavirus nucleocapsid proteins for serotyping Hantaan, Seoul, and Dobrava hantavirus infections

Truncated recombinant nucleocapsid proteins (rNPs) of Hantaan virus (HTNV), Seoul virus (SEOV), and Dobrava virus (DOBV) were expressed by a baculovirus system. The truncated rNPs, which lacked 49 (rNP50) or 154 (rNP155) N-terminal amino acids of the NPs of HTNV, SEOV, and DOBV, were able to differentiate HTNV-, SEOV-, and DOBV-specific immune sera. Recombinant NP50s retained higher reactivities than rNP155s and were proven useful for enzyme-linked immunosorbent assay (ELISA). The ELISAs based on the rNP50s of HTNV, SEOV, and DOBV successfully differentiated three groups of patient sera, previously defined by neutralization tests: 17 with HTNV infection, 12 with SEOV infection, and 20 with DOBV infection. The entire rNP of Puumala virus (PUUV) distinguished PUUV infection from the other types of hantavirus infection. Serotyping with these rNP50s can be recommended as a rapid and efficient system for hantavirus diagnosis.

Genetic diversity of hantaviruses isolated in china and characterization of novel hantaviruses isolated from Niviventer confucianus and Rattus rattus

The antigenic and genetic properties of 46 hantaviruses from China, 13 from patients, 23 from rodents, and 10 from unknown hosts, were compared with those of other hantaviruses. The viruses were classified as either Hantaan (HTN) or Seoul (SEO) viruses. A phylogenetic analysis of the partial M (300 bp) and S (around 485 bp) genomes of HTN viruses identified nine distinct genetic subtypes, one consisting of isolates from Korea. The SEO viruses were divided into five genetic subtypes, although they had less variability than the HTN subtypes. There was a correlation between the subtype and province of origin for four subtypes of HTN viruses, confirming geographical clustering. Hantaan virus NC167 isolated from Niviventer confucianus and SEO virus Gou3 isolated from Rattus rattus were the basal clades in each virus. The phylogenetic trees constructed from the entire S and M segments suggested that NC167 was introduced to N. confucianus in a host-switching event. The reactivity of a panel of 35 monoclonal antibodies was almost exactly the same in NC167 and a representative HTN virus and in Gou3 and a representative SEO virus. However, there was a one-way cross-neutralization between them. These results confirm the varied nature of Murinae-associated hantaviruses in China.

Genetic diversity of hantaviruses associated with hemorrhagic fever with renal syndrome in the far east of Russia

To identify the hantaviruses causing hemorrhagic fever with renal syndrome (HFRS) in the Far East of Russia, blood samples collected from HFRS patients in 1994-1998, were examined by reverse transcription-polymerase chain reaction. In addition, 36 sera were tested by an immunofluorescence assay for antibodies against Hantaan, Seoul, Puumala, and Khabarovsk viruses, and 54 samples were tested by plaque reduction neutralization test. With both serological assays, the highest antibody titers were to Hantaan and/or Seoul viruses. Of 110 blood samples 36 were found RT-PCR positive. Phylogenetic analysis the sequences of a 256-nucleotide (nt) fragment of the hantavirus M genome segment revealed at least 3 genetically distinct hantavirus lineages. Nucleotide sequence comparison showed that two of the lineages, designated as FE and Amur (AMR), differed from one another by 15.9-21.2% and from Hantaan virus by 9.8-17.5%. The third lineage, VDV, differed from Seoul virus by 2.6-5.1%. All S segment sequences were from FE lineage, and differed from Hantaan virus by 10.7-12.6%. Thirty of the 36 (83%) analyzed sequences were found to be the FE genotype, which is very similar to that of Hantaan virus, strain 76-118. Of the remaining hantaviruses, 11% were the AMR genotype, and 6% the VDV genotype, which are genetically novel genotypes of Hantaan or Seoul viruses, respectively.

Comparison of the protective efficacy of naked DNA, DNA-based Sindbis replicon, and packaged Sindbis replicon vectors expressing Hantavirus structural genes in hamsters

Seoul virus (SEOV) is a member of the Hantavirus genus (family Bunyaviridae) and an etiological agent of hemorrhagic fever with renal syndrome. The medium (M) and small (S) gene segments of SEOV encode the viral envelope glycoproteins and nucleocapsid protein, respectively. We compared the immunogenicity and protective efficacy of naked DNA (pWRG7077), DNA-based Sindbis replicon (pSIN2.5), and packaged Sindbis replicon vectors (pSINrep5), containing either the M or S gene segment of SEOV in Syrian hamsters. All of the vectors elicited an anti-SEOV immune response to the expressed SEOV gene products. Vaccinated hamsters were challenged with SEOV and monitored for evidence of infection. Protection from infection was strongly associated with M-gene vaccination. A small number of S-gene-vaccinated animals also were protected. Hamsters vaccinated with the pWRG7077 vector expressing the M gene demonstrated the most consistent protection from SEOV infection and also were protected from heterologous hantavirus (Hantaan virus) infection.

Low pH-induced cytopathic effect--a survey of seven hantavirus strains

Hantaviruses do not produce cytopathic effects (CPE) in cell culture. However, a syncytial CPE can be induced in 7-day cultures of hantavirus growing in Vero E6 cells by reduction of the pH to approximately 6.2 using a HEPES based buffer. The appearance of this acid induced CPE was examined for seven different hantavirus strains. The differences noted were striking and reflected the taxonomic differences between hantaviruses. At 10-100 TCID50% the size of syncytial foci was very large for Seoul type viruses and smallest for Puumala viruses. The size of syncytia for Hantaan (HTN) virus was intermediate between Puumala (PUU) and Seoul (SEO) type viruses.

DNA vaccination with hantavirus M segment elicits neutralizing antibodies and protects against seoul virus infection

Seoul virus (SEOV) is one of four known hantaviruses causing hemorrhagic fever with renal syndrome (HFRS). Candidate naked DNA vaccines for HFRS were constructed by subcloning cDNA representing the medium (M; encoding the G1 and G2 glycoproteins) or small (S; encoding the nucleocapsid protein) genome segment of SEOV into the DNA expression vector pWRG7077. We vaccinated BALB/c mice with three doses of the M or S DNA vaccine at 4-week intervals by either gene gun inoculation of the epidermis or needle inoculation into the gastrocnemius muscle. Both routes of vaccination resulted in antibody responses as measured by ELISA; however, gene gun inoculation elicited a higher frequency of seroconversion and higher levels of antibodies in individual mice. We vaccinated Syrian hamsters with the M or S construct using the gene gun and found hantavirus-specific antibodies in five of five and four of five hamsters, respectively. Animals vaccinated with the M construct developed a neutralizing antibody response that was greatly enhanced in the presence of guinea pig complement. Immunized hamsters were challenged with SEOV and, after 28 days, were monitored for evidence of infection. Hamsters vaccinated with M were protected from infection, but hamsters vaccinated with S were not protected.

Antigenic characterization of Hantaan and Seoul virus nucleocapsid proteins expressed by recombinant baculovirus: application of a truncated protein, lacking an antigenic region common to the two viruses, as a serotyping antigen

Hantaan virus (HTN) and Seoul virus (SEO) are members of the genus Hantavirus in the family Bunyaviridae and are causative agents of hemorrhagic fever with renal syndrome. The complete and truncated nucleocapsid proteins (NP) of HTN and SEO were expressed by a recombinant baculovirus system. Antigenic characterization of the NP using monoclonal antibodies (MAbs) indicated that the binding sites for the serotype-specific MAbs were located between amino acids (aa) 155 and 429. A Western blot assay indicated that the serotype-specific epitopes were conformation dependent. An indirect immunofluorescence antibody (IFA) assay with the truncated NP (aa 155 to 429) was able to distinguish convalescent-phase sera from HTN and SEO patients. However, the antibody titers with the truncated NP were lower than those with the whole NP. The truncated NP of SEO (aa 155 to 429) could be used as an enzyme-linked immunosorbent assay (ELISA) antigen, but the truncated NP from HTN lost its reactivity when used for ELISA. The IFA assay using baculovirus-expressed truncated NP as an antigen is a rapid, simple, and safe test for distinguishing between HTN and SEO infections by serotype.

Modes of Seoul virus infections: persistency in newborn rats and transiency in adult rats

To understand the mode of persistent infection of Seoul virus in rodents, we examined the distribution of the virus genome and antibody production in infected rats. When 1-day-old rats were inoculated with the KI-83-262 strain, the S segment of viral genome was detected in sera, clots, lungs and kidneys from 3 to 184 days post inoculation (d.p.i.) by nested reverse transcriptase PCR. On the other hand, when 7-week-old rats were infected with this virus, viral genome was detected only in the lungs from 3 to 50 d.p.i. The neutralizing antibody titers of rats inoculated at 1-day of age were higher than those of rats inoculated at 7 weeks of age. In both age groups, however, the IgG avidity of antibody increased along with the course of infection. We found that urban rats (Rattus norvegicus) infected early in life harbored the virus for more than 6 months.

Adjuvant activity of muramyl dipeptide derivatives to enhance immunogenicity of a hantavirus-inactivated vaccine

The adjuvant effect of two lipophilic derivatives of muramyl dipeptide (MDP), B30-MDP and MDP-Lys(L18), on the ability of an inactivated vaccine of B-1 virus (B-1 vaccine) to induce immune response against Hantavirus causing hemorrhagic fever with renal syndrome (HFRS) was examined. When mice were immunized subcutaneously (s.c.) twice at 2-week intervals with B-1 vaccine admixed with or without 100 micrograms mouse-1 of B30-MDP (B-1/B30-MDP) or MDP-Lys(L18) [B-1/MDP-Lys(L18)], mice immunized with B-1/B30-MDP as well as B-1/MDP-Lys(L18) showed significantly higher indirect fluorescent antibody (IFA) titers against HFRS virus than mice immunized with B-1 vaccine alone. Both mice treated with B-1/B30-MDP and B-1/MDP-Lys(L18) also exhibited significantly higher neutralizing antibody titers against HFRS virus than mice immunized with B-1 vaccine alone during 3-9 weeks after the primary immunization. The evaluation of antibody-producing cells by enzyme-linked immunospot (ELISPOT) assay on week 4 revealed that both MDP derivatives enhanced the number of HFRS virus-specific IgG1 and IgM antibody-producing cells. Furthermore, mice treated with B-1/B30-MDP as well as B-1/MDP-Lys(L18) showed a higher level of Th-2 type cytokines, IL-4 and IL-6, in sera than mice treated with B-1 alone. In an in-vitro analysis of T lymphocyte proliferation to baculovirus-expressed recombinant nucleocapsid protein (rNP) of Hantaan 76-118 strain, the splenocytes of mice treated with B-1/B30-MDP and B-1/MDP-Lys(L18) on week 4 showed a significantly higher proliferating activity than those treated with B-1 vaccine alone. In addition, when mice were immunized once with B-1 vaccine admixed with or without B30-MDP and MDP-Lys(L18) and followed by intrafootpad (i.f.) injection of B-1 vaccine on day 7, mice immunized with B-1/B30-MDP and B-1/MDP-Lys(L18) induced a higher delayed-type hypersensitivity (DTH) reaction than mice immunized with B-1 vaccine alone. These results suggest that B30-MDP and MDP-Lys(L18) are useful immunoadjuvants to enhance the ability of inactivated B-1 vaccine to induce a humoral and cellular response to HFRS virus.

Hantavirus infection in SCID mice

Severe combined immunodeficiency (SCID) mice were inoculated with Hantaan virus strain 76-118 (HTN) or Seoul virus strain SR-11 (SR) of hantaviruses. Susceptibility of SCID mice was compared with those of immunocompetent adult mice, newborn mice and nude mice. SCID mice inoculated with HTN or SR died 32 to 35 days after infection. Unlike newborn mice which also died of hantavirus infection, SCID mice survived longer than newborn mice and showed typical wasting symptoms rather than nervous symptoms. Immunohistochemical staining and virus isolation indicated that both HTN and SR inoculated SCID and SR inoculated nude mice showed systemic infection, but nude mice inoculated with SR survived for longer than 8 weeks after inoculation. Passive transfer of spleen cells from immunocompetent BALB/c mice conferred protection on SCID mice within 2 weeks of HTN infection. Immune mediated pathologic mechanism was examined by transferring the spleen cells to SCID mice inoculated with HTN virus 3 weeks before the cell transfer. The recipient SCID mice showed an increase of serum BUN level coinciding with the appearance of serum antibody to HTN virus, suggesting the immune mediated pathogenicity.

A colorimetric PCR-enzyme immunoassay to identify hantaviruses

BACKGROUND

Hantaviruses cause two serious human diseases: hantavirus pulmonary syndrome and hemorrhagic fever with renal syndrome. At least nine hantaviruses are known to be pathogenic for humans and numerous others, with unknown disease potential, have been detected in rodents. Assays to quickly identify specific hantaviruses would be useful both for clinical diagnosis and in risk assessment studies.

OBJECTIVES

The goal of our study was to develop and test a specific and sensitive PCR-based assay for identification and differentiation of hantaviruses.

STUDY DESIGN

We developed an assay that combined RNA-PCR amplification and colorimetric enzymatic detection to identify representative European, Asian, and north American hantaviruses. RNAs from 18 hantavirus strains of nine species were amplified in the presence of digoxigenin-dUTP by using a single pair of oligonucleotide primers and polymerase chain reaction (PCR) performed by using rTth DNA polymerase. Digoxigenin-labeled PCR products were hybridized in solution to virus type-specific biotinilated probes, captured onto streptavidin-coated microtiter plates and detected by horseradish peroxidase-labeled anti-digoxigenin antibodies and a chromogenic substrate.

RESULTS AND CONCLUSIONS

The assay correctly identified each homologous virus type tested. The detection limit of the assay was approximately 15 PFU or at least 50 copies of the viral genome. The assay is simple and strain-specific and is adaptable for automation, making it more practical than other available techniques for accurate and reliable diagnosis and typing of hantaviruses.

Characterization of the mode of Hantaan virus infection in adult mice using a nested reverse transcriptase polymerase chain reaction: transient virus replication in adult mice

A polymerase chain reaction (PCR) for the detection of hantavirus genome was established and applied to analyze the mode of infection of Hantaan virus in adult ICR mice. The cDNA for the S genome segment of Hantaan virus was reverse-transcribed from the total RNA of organs of the infected mice. The sequence in the S genome segment of Hantaan virus was successfully amplified by reverse transcriptase (RT)-PCR followed by nested PCR. In 5-week-old ICR mice inoculated intraperitoneally with Hantaan virus, strain 76-118 (1.3 x 10(5) FFU/mouse), the virus was detected in clots and lungs from 3 to 10 days post-inoculation (p.i.) by nested PCR and virus-isolation techniques. No virus was detected in any specimens collected on 1 day and after 28 days p.i., and in spleens and brains through the observation period by both methods. The antibody which was measured by indirect immunofluorescence antibody assay (IFA) appeared at 7 days p.i. and the geometric mean titer was elevated to its maximum level of 1:203 at 10 days p.i., maintaining the same level until 35 days p.i. These results suggest that adult mice are transiently infected with Hantaan virus.

Protection against hantavirus infection by dam's immunity transferred vertically to neonates

Antibodies to hantavirus, Seoul type B-1 strain, vertically transferred to rat neonates prevented lethal as well as persistent infection. When relatively high titer viruses were inoculated into neonates, the mother's antibodies protected all the neonates from lethal virus infection. However, the antibodies could not protect all of the neonates from persistent infection but only half of them underwent persistent infection. The other half was completely cured but also became persistently infected when rechallenged with the active viruses after reaching maturity.

Comparison of nucleotide sequences of M genome segments among Seoul virus strains isolated from eastern Asia

The nucleotide sequences of the M genome segments of three Seoul virus strains (KI strains) which were isolated from urban rats inhabiting the same enzootic focus between 1983 and 1988 were compared. The viral cDNAs were amplified by PCR and were directly sequenced. The nucleotide sequences of KI strains were extremely homologous regardless of isolation year (less than 10 substitutions in 3651 nucleotides, less than 4 substitutions in 1133 amino acids). In addition, the nucleotide sequence of the KI strain isolated in 1983 (KI-83-262) was also quite similar to that of other Seoul viruses, which were isolated from laboratory rats in Japan (strain SR-11, 98.1% and B-1 strain, 96.5%), from an urban rat in Korea (Seoul 80-39, 96.5%) and from an urban rat in China (R22 strain, 93.4%). All possible N-glycosylation sites in the deduced amino acid sequences were conserved among all Seoul viruses examined. The nucleotide and amino acid sequences of Seoul virus strains were highly conserved although they were isolated from various districts of eastern Asia. These results indicate the genetic stability of Seoul virus strains maintained under a natural environment and the homology of Seoul viruses isolated from various districts of eastern Asia. The relationship among Seoul virus strains isolated from eastern Asia was compared by phylogenetic analysis.

Comparison of virulence between Seoul virus strain SR-11 and Hantaan virus strain 76-118 of hantaviruses in newborn mice

Virulence of hantavirus strain of SR-11 Seoul virus and Hantaan 76-118 (HTN) of Hantaan virus were compared. Infections of both strains were lethal in newborn mice. However, inoculum required to cause lethal infection was about 4,000 times higher for strain HTN (1.65 x 10(3) PFU/mouse/LD50) than for strain SR-11 (0.36 PFU). Thus, both strains were considered pathogenic to newborn mice but they possessed different levels of virulence. The assay system used for these strains in newborn mice proved to be useful in the study of hantavirus virulence. Growth curves of the two strains in CV-7 cell cultures were compared. Strain SR-11 was shown to have higher activity of virus replication and virus release into the culture fluids than strain HTN. The possibility of a relationship between replication activity and high levels of virulence in mice was suggested.