First human isolate of Hantavirus (Andes virus) in the Americas

Viral shedding and viraemia of Andes virus during acute hantavirus infection: a prospective study

BACKGROUND

Andes virus (ANDV) is a zoonotic Orthohantavirus leading to hantavirus cardiopulmonary syndrome. Although most transmissions occur through environmental exposure to rodent faeces and urine, rare person-to-person transmission has been documented, mainly for close contacts. This study investigates the presence and infectivity of ANDV in body fluids from confirmed cases and the duration of viraemia.

METHODS

In this prospective study, 131 participants with confirmed ANDV infection were enrolled in Chile in a prospective study between 2008 and 2022. Clinical samples (buffy coat, plasma, gingival crevicular fluid [GCF], saliva, nasopharyngeal swabs [NPS], and urine) were collected weekly for 3 weeks together with clinical and epidemiological data. Samples were categorised as acute or convalescent (up to and after 16 days following onset of symptoms). Infectivity of positive fluids was assessed after the culture of samples on Vero E6 cells and use of flow cytometry assays to determine the production of ANDV nucleoprotein.

FINDINGS

ANDV RNA was detected in 100% of buffy coats during acute phase, declining to 95% by day 17, and to 93% between days 23-29. ANDV RNA in GCF and saliva decreased from 30% and 12%, respectively, during the acute phase, to 12% and 11% during the convalescent phase. Successful infectivity assays of RT-qPCR-positive fluids, including GCF, saliva, NPS, and urine, were observed in 18 (42%) of 43 samples obtained during the acute phase of infection. After re-culture, the capacity to infect Vero E6 cells was maintained in 16 (89%) of 18 samples. Severity was associated with the presence of ANDV RNA in one or more fluids besides blood (odds ratio 2·58 [95% CI 1·42-5·18]).

INTERPRETATION

ANDV infection is a systemic and viraemic infection, that affects various organs. The presence of infectious particles in body fluids contributes to our understanding of potential mechanisms for person-to-person transmission, supporting the development of preventive strategies. Detection of ANDV RNA in additional fluids at hospital admission is a predictor of disease severity.

FUNDING

None.

TRANSLATION

For the Spanish translation of the abstract see Supplementary Materials section.

Presence and Persistence of Andes Virus RNA in Human Semen

When infecting humans, Andes orthohantavirus (ANDV) may cause a severe disease called hantavirus cardiopulmonary syndrome (HCPS). Following non-specific symptoms, the infection may progress to a syndrome of hemorrhagic fever combined with hyper-acute cardiopulmonary failure. The case fatality rate ranges between 25-40%, depending on the outbreak. In this study, we present the follow-up of a male patient who recovered from HCPS six years ago. We demonstrate that the ANDV genome persists within the reproductive tract for at least 71 months. Genome sequence analysis early and late after infection reveals a low number of mutations (two single nucleotide variants and one deletion), suggesting limited replication activity. We can exclude the integration of the viral genome into the host genome, since the treatment of the specimen with RNAse led to a loss of signal. We demonstrate a long-lasting, strong neutralizing antibody response using pseudovirions expressing the ANDV glycoprotein. Taken together, our results show that ANDV has the potential for sexual transmission.

Human-to-Human Transmission of Andes Virus Modeled in Syrian Hamsters

Several occurrences of human-to-human transmission of Andes virus, an etiological agent of hantavirus cardiopulmonary syndrome, are documented. Syrian hamsters consistently model human hantavirus cardiopulmonary syndrome, yet neither transmission nor shedding has been investigated. We demonstrate horizontal virus transmission and show that Andes virus is shed efficiently from both inoculated and contact-infected hamsters.

Comparative Analysis of Molecular Pathogenic Mechanisms and Antiviral Development Targeting Old and New World Hantaviruses

Background

Hantaviruses - dichotomized into New World (i.e. Andes virus, ANDV; Sin Nombre virus, SNV) and Old-World viruses (i.e. Hantaan virus, HTNV) - are zoonotic viruses transmitted from rodents to humans. Currently, no FDA-approved vaccines against hantaviruses exist. Given the recent breakthrough to human-human transmission by the ANDV, an essential step is to establish an effective pandemic preparedness infrastructure to rapidly identify cell tropism, infective potential, and effective therapeutic agents through systematic investigation.

Methods

We established human cell model systems in lung (airway and distal lung epithelial cells), heart (pluripotent stem cell-derived (PSC-) cardiomyocytes), and brain (PSC-astrocytes) cell types and subsequently evaluated ANDV, HTNV and SNV tropisms. Transcriptomic, lipidomic and bioinformatic data analyses were performed to identify the molecular pathogenic mechanisms of viruses in different cell types. This cell-based infection system was utilized to establish a drug testing platform and pharmacogenomic comparisons.

Results

ANDV showed broad tropism for all cell types assessed. HTNV replication was predominantly observed in heart and brain cells. ANDV efficiently replicated in human and mouse 3D distal lung organoids. Transcriptomic analysis showed that ANDV infection resulted in pronounced inflammatory response and downregulation of cholesterol biosynthesis pathway in lung cells. Lipidomic profiling revealed that ANDV-infected cells showed reduced level of cholesterol esters and triglycerides. Further analysis of pathway-based molecular signatures showed that, compared to SNV and HTNV, ANDV infection caused drastic lung cell injury responses. A selective drug screening identified STING agonists, nucleoside analogues and plant-derived compounds that inhibited ANDV viral infection and rescued cellular metabolism. In line with experimental results, transcriptome data shows that the least number of total and unique differentially expressed genes were identified in urolithin B- and favipiravir-treated cells, confirming the higher efficiency of these two drugs in inhibiting ANDV, resulting in host cell ability to balance gene expression to establish proper cell functioning.

Conclusions

Overall, our study describes advanced human PSC-derived model systems and systems-level transcriptomics and lipidomic data to better understand Old and New World hantaviral tropism, as well as drug candidates that can be further assessed for potential rapid deployment in the event of a pandemic.

Andes Virus Genome Mutations That Are Likely Associated with Animal Model Attenuation and Human Person-to-Person Transmission

We performed whole-genome sequencing with bait enrichment techniques to analyze Andes virus (ANDV), a cause of human hantavirus pulmonary syndrome. We used cryopreserved lung tissues from a naturally infected long-tailed colilargo, including early, intermediate, and late cell culture, passages of an ANDV isolate from that animal, and lung tissues from golden hamsters experimentally exposed to that ANDV isolate. The resulting complete genome sequences were subjected to detailed comparative genomic analysis against American orthohantaviruses. We identified four amino acid substitutions related to cell culture adaptation that resulted in attenuation of ANDV in the typically lethal golden hamster animal model of hantavirus pulmonary syndrome. Changes in the ANDV nucleocapsid protein, glycoprotein, and small nonstructural protein open reading frames correlated with mutations typical for ANDV strains associated with increased virulence in the small-animal model. Finally, we identified three amino acid substitutions, two in the small nonstructural protein and one in the glycoprotein, that were only present in the clade of viruses associated with efficient person-to-person transmission. Our results indicate that there are single-nucleotide polymorphisms that could be used to predict strain-specific ANDV virulence and/or transmissibility. IMPORTANCE Several orthohantaviruses cause the zoonotic disease hantavirus pulmonary syndrome (HPS) in the Americas. Among them, HPS caused by Andes virus (ANDV) is of great public health concern because it is associated with the highest case fatality rate (up to 50%). ANDV is also the only orthohantavirus associated with relatively robust evidence of person-to-person transmission. This work reveals nucleotide changes in the ANDV genome that are associated with virulence attenuation in an animal model and increased transmissibility in humans. These findings may pave the way to early severity predictions in future ANDV-caused HPS outbreaks.

Hemorrhagic Fever with Renal Syndrome in Asia: History, Pathogenesis, Diagnosis, Treatment, and Prevention

Hemorrhagic Fever with Renal Syndrome (HFRS) is the most frequently diagnosed zoonosis in Asia. This zoonotic infection is the result of exposure to the virus-contaminated aerosols. Orthohantavirus infection may cause Hemorrhagic Fever with Renal Syndrome (HRFS), a disease that is characterized by acute kidney injury and increased vascular permeability. Several species of orthohantaviruses were identified as causing infection, where Hantaan, Puumala, and Seoul viruses are most common. Orthohantaviruses are endemic to several Asian countries, such as China, South Korea, and Japan. Along with those countries, HFRS tops the list of zoonotic infections in the Far Eastern Federal District of Russia. Recently, orthohantavirus circulation was demonstrated in small mammals in Thailand and India, where orthohantavirus was not believed to be endemic. In this review, we summarized the current data on orthohantaviruses in Asia. We gave the synopsis of the history and diversity of orthohantaviruses in Asia. We also described the clinical presentation and current understanding of the pathogenesis of orthohantavirus infection. Additionally, conventional and novel approaches for preventing and treating orthohantavirus infection are discussed.

Comparison of indirect immunofluorescence and western blot method in the diagnosis of hantavirus infections

BACKGROUND

Serologic cross-reactivity between hantaviruses often complicates the interpretation of the results.

AIM

To analyze the diagnostic value of indirect immunofluorescence assay (IFA) and western blot (WB) in the diagnosis of hantavirus infections.

METHODS

One hundred eighty-eight serum samples from Puumala (PUUV) and Dobrava (DOBV) orthohantavirus infected patients were analyzed. Serology was performed using commercial tests (Euroimmun, Lübeck, Germany).

RESULTS

Using IFA, 49.5% of acute-phase samples showed a monotypic response to PUUV, while 50.5% cross-reacted with other hantaviruses. The overall cross-reactivity was higher for immunoglobulin G (IgG) (50.0%) than for immunoglobulin M (IgM) (25.5%). PUUV IgM/IgG antibodies showed low/moderate reactivity with orthohantaviruses Hantaan (12.3%/31.5%), Seoul (7.5%/17.8%), DOBV (5.4%/ 28.1%), and Saaremaa (4.8%/15.7%). Both DOBV IgM and IgG antibodies were broadly reactive with Hantaan (76.2%/95.2%), Saaremaa (80.9%/83.3%), and Seoul (78.6%/85.7%) and moderate with PUUV (28.5%/38.1%). Using a WB, serotyping was successful in most cross-reactive samples (89.5%).

CONCLUSION

The presented results indicate that WB is more specific than IFA in the diagnosis of hantavirus infections, confirming serotype in most IFA cross-reactive samples.

Differential pathogenesis between Andes virus strains CHI-7913 and Chile-9717869in Syrian Hamsters

Hantavirus cardiopulmonary syndrome (HCPS) is a severe respiratory disease caused by orthohantaviruses in the Americas with a fatality rate as high as 35%. In South America, Andes orthohantavirus (Hantaviridae, Orthohantavirus, ANDV) is a major cause of HCPS, particularly in Chile and Argentina, where thousands of cases have been reported since the virus was discovered. Two strains of ANDV that are classically used for experimental studies of the virus are Chile-9717869, isolated from the natural reservoir, the long-tailed pygmy rice rat, and CHI-7913, an isolate from a lethal human case of HCPS. An important animal model for studying pathogenesis of HCPS is the lethal Syrian golden hamster model of ANDV infection. In this model, ANDV strain Chile-9717869 is uniformly lethal and has been used extensively for pathogenesis, vaccination, and therapeutic studies. Here we show that the CHI-7913 strain, despite having high sequence similarity with Chile-9717869, does not cause lethal disease in Syrian hamsters. CHI-7913, while being able to infect hamsters and replicate to moderate levels, showed a reduced ability to replicate within the tissues compared with Chile-9717869. Hamsters infected with CHI-7913 had reduced expression of cytokines IL-4, IL-6, and IFN-γ compared with Chile-9717869 infected animals, suggesting potentially limited immune-mediated pathology. These results demonstrate that certain ANDV strains may not be lethal in the classical Syrian hamster model of infection, and further exploration into the differences between lethal and non-lethal strains provide important insights into molecular determinants of pathogenic hantavirus infection.Importance:Andes orthohantavirus (ANDV) is a New World hantavirus that is a major cause of hantavirus cardiopulmonary syndrome (HCPS, also referred to as hantavirus pulmonary syndrome) in South America, particularly in Chile and Argentina. ANDV is one of the few hantaviruses for which there is a reliable animal model, the Syrian hamster model, which recapitulates important aspects of human disease. Here we infected hamsters with a human isolate of ANDV, CHI-7913, to assess its pathogenicity compared with the classical lethal Chile-9717869 strain. CHI-7913 had 22 amino acid differences compared with Chile-9717869, did not cause lethal disease in hamsters, and showed reduced ability to replicate in vivo Our data indicate potentially important molecular signatures for pathogenesis of ANDV infection in hamsters and may lead to insights into what drives pathogenesis of certain hantaviruses in humans.

Biodefense Implications of New-World Hantaviruses

Hantaviruses, part of the Bunyaviridae family, are a genus of negative-sense, single-stranded RNA viruses that cause two major diseases: New-World Hantavirus Cardiopulmonary Syndrome and Old-World Hemorrhagic Fever with Renal Syndrome. Hantaviruses generally are found worldwide with each disease corresponding to their respective hemispheres. New-World Hantaviruses spread by specific rodent-host reservoirs and are categorized as emerging viruses that pose a threat to global health and security due to their high mortality rate and ease of transmission. Incidentally, reports of Hantavirus categorization as a bioweapon are often contradicted as both US National Institute of Allergy and Infectious Diseases and the Centers for Disease Control and Prevention refer to them as Category A and C bioagents respectively, each retaining qualitative levels of importance and severity. Concerns of Hantavirus being engineered into a novel bioagent has been thwarted by Hantaviruses being difficult to culture, isolate, and purify limiting its ability to be weaponized. However, the natural properties of Hantaviruses pose a threat that can be exploited by conventional and unconventional forces. This review seeks to clarify the categorization of Hantaviruses as a bioweapon, whilst defining the practicality of employing New-World Hantaviruses and their effect on armies, infrastructure, and civilian targets.

Development of RT-qPCR and semi-nested RT-PCR assays for molecular diagnosis of hantavirus pulmonary syndrome

Hantavirus Pulmonary Syndrome is an, often fatal, emerging zoonotic disease in the Americas caused by hantaviruses (family: Hantaviridae). In Brazil, hantavirus routine diagnosis is based on serology (IgM-ELISA) while RT-PCR is often used to confirm acute infection. A Semi-nested RT-PCR and an internally controlled RT-qPCR assays were developed for detection and quantification of four hantaviruses strains circulating in the Brazilian Amazon: Anajatuba (ANAJV) and Castelo dos Sonhos (CASV) strains of Andes virus (ANDV) species; and Rio Mamoré (RIOMV) and Laguna Negra (LNV) strains of LNV species. A consensus region in the N gene of these hantaviruses was used to design the primer sets and a hydrolysis probe. In vitro transcribed RNA was diluted in standards with known concentration. MS2 bacteriophage RNA was detected together with hantavirus RNA as an exogenous control in a duplex reaction. RT-qPCR efficiency was around 100% and the limit of detection was 0.9 copies/μL of RNA for RT-qPCR and 10 copies/μL of RNA for Semi-nested RT-PCR. There was no amplification of either negative samples or samples positive to other pathogens. To assess the protocol for clinical sensitivity, specificity and general accuracy values, both assays were used to test two groups of samples: one comprising patients with disease (n = 50) and other containing samples from healthy individuals (n = 50), according to IgM-ELISA results. A third group of samples (n = 27) infected with other pathogens were tested for specificity analysis. RT-qPCR was more sensitive than semi-nested RT-PCR, being able to detect three samples undetected by conventional RT-PCR. RT-qPCR clinical sensitivity, specificity and general accuracy values were 92.5%, 100% and 97.63%, respectively. Thus, the assays developed in this study were able to detect the four Brazilian Amazon hantaviruses with good specificity and sensitivity, and may become powerful tools in diagnostic, surveillance and research applications of these and possibly other hantaviruses.

Hantavirus Pulmonary Syndrome (HPS) is a serious and often fatal disease caused by viruses known as hantaviruses. These viruses are harbored by wild rodents and people can become infected through contact with infected-rodents droppings, urine or saliva. After an incubation time of 1–8 weeks, patients usually present flu-like symptoms such as fever, fatigue and muscle aches, although some patients may also present headaches, dizziness, chills, nausea, vomiting, diarrhea, and abdominal pain. It is only 4–10 days after initial symptoms, however, that the severe stage of disease takes place. Symptoms include coughing, shortness of breath and eventually the lungs fill with fluid which can lead to shock and death. As such, HPS should be diagnosed quickly as any delay may have great impact on patient recovery. However, given the unspecific nature of early symptoms, clinical diagnosis of HPS is difficult and laboratory assays are needed to confirm hantavirus infection as soon as possible, helping physicians to choose the most adequate treatment. In this study, we developed new laboratory assays that can help detect the virus in infected patients in early stages of disease. In addition, we showed these assays have a good performance in discriminating HPS from other similar diseases by testing not only several samples collected from both HPS patients and healthy individuals but also samples infected with other pathogens. Our results show that these assays may become important tools for rapid, sensitive and specific diagnosis of HPS.

Fast, Sensitive and Specific Detection of Thailand orthohantavirus and its Variants Using One-Step Real-Time Reverse-Transcription Polymerase Chain Reaction Assay

Genetic variants of Thailand orthohantavirus (THAIV) have been recently reported from rodents in South-East Asia and in islands from the South-West part of the Indian Ocean. In order to detect THAIV and its variants, we developed a sensitive and specific real-time RT-PCR targeting the S segment. Our assay was developed in two different RT-PCR systems that gave similar results in terms of sensitivity. Moreover, our results demonstrated a specificity of 100%.

Molecular organization and dynamics of the fusion protein Gc at the hantavirus surface

The hantavirus envelope glycoproteins Gn and Gc mediate virion assembly and cell entry, with Gc driving fusion of viral and endosomal membranes. Although the X-ray structures and overall arrangement of Gn and Gc on the hantavirus spikes are known, their detailed interactions are not. Here we show that the lateral contacts between spikes are mediated by the same 2-fold contacts observed in Gc crystals at neutral pH, allowing the engineering of disulfide bonds to cross-link spikes. Disrupting the observed dimer interface affects particle assembly and overall spike stability. We further show that the spikes display a temperature-dependent dynamic behavior at neutral pH, alternating between ‘open’ and ‘closed’ forms. We show that the open form exposes the Gc fusion loops but is off-pathway for productive Gc-induced membrane fusion and cell entry. These data also provide crucial new insights for the design of optimized Gn/Gc immunogens to elicit protective immune responses.

Hantaviruses infect rodents and other small mammals, but do not harm them. When transmitted to humans, often through rodent urine, feces or saliva, they can cause serious and even fatal diseases. Currently, there are no known methods that effectively prevent hantavirus infections or treat the diseases that they cause.

During an infection, viruses invade the cells of their host. A hantavirus interacts with target cells through proteins on its surface called Gn and Gc glycoproteins. Previous work has shown that these glycoproteins are organized in bundles of four Gn and four Gc proteins, termed spikes, which project from the membrane that surrounds the virus. The Gc protein changes shape when it is activated and exposes a hidden region that can insert into the membrane of the target cell. The Gc proteins then change shape again to force the cell to fuse with the viral membrane. This process allows the virus to be taken up into the cell, where it can replicate.

While the structures of each viral glycoprotein have been determined in isolation, it was not known how they interact within the Gn/Gc spike. Such information is crucial to understand how the viruses infect cells and which areas are exposed to the immune system of the host – and so could be targeted by antiviral treatments.

Bignon et al. have now identified the molecular contacts that occur between spikes and interconnect them into a grid-like lattice on the surface of the virus. Genetically altering specific sections of the Gc glycoprotein strengthened or weakened these contacts, which correspondingly increased or decreased how stable the spike was. Preventing the contacts from forming resulted in cells releasing fewer virus-like particles.

Bignon et al. also show that at the body temperature of mammals, the shape of the spike fluctuates between an ‘open’ form that exposes the region of Gc that inserts into the cell membrane, and a ‘closed’ form that hides this region. However, when Gc is activated, the open form becomes unable to cause the viral and cell membranes to fuse together.

Together, the results presented by Bignon et al. help us to understand how changes to the hantavirus surface enable the virus to infect cells. This knowledge will help researchers to design vaccines that protect against hantavirus infections.

Unique Interferon Pathway Regulation by the Andes Virus Nucleocapsid Protein Is Conferred by Phosphorylation of Serine 386

Andes virus (ANDV) causes hantavirus pulmonary syndrome (HPS) and is the only hantavirus shown to spread person to person and cause a highly lethal HPS-like disease in Syrian hamsters. The unique ability of ANDV N protein to inhibit beta interferon (IFNβ) induction may contribute to its virulence and spread. Here we analyzed IFNβ regulation by ANDV N protein substituted with divergent residues from the nearly identical Maporal virus (MAPV) N protein. We found that MAPV N fails to inhibit IFNβ signaling and that replacing ANDV residues 252 to 296 with a hypervariable domain (HVD) from MAPV N prevents IFNβ regulation. In addition, changing ANDV residue S386 to the histidine present in MAPV N or the alanine present in other hantaviruses prevented ANDV N from regulating IFNβ induction. In contrast, replacing serine with phosphoserine-mimetic aspartic acid (S386D) in ANDV N robustly inhibited interferon regulatory factor 3 (IRF3) phosphorylation and IFNβ induction. Additionally, the MAPV N protein gained the ability to inhibit IRF3 phosphorylation and IFNβ induction when ANDV HVD and H386D replaced MAPV residues. Mass spectroscopy analysis of N protein from ANDV-infected cells revealed that S386 is phosphorylated, newly classifying ANDV N as a phosphoprotein and phosphorylated S386 as a unique determinant of IFN regulation. In this context, the finding that the ANDV HVD is required for IFN regulation by S386 but dispensable for IFN regulation by D386 suggests a role for HVD in kinase recruitment and S386 phosphorylation. These findings delineate elements within the ANDV N protein that can be targeted to attenuate ANDV and suggest targeting cellular kinases as potential ANDV therapeutics.IMPORTANCE ANDV contains virulence determinants that uniquely permit it to spread person to person and cause highly lethal HPS in immunocompetent hamsters. We discovered that ANDV S386 and an ANDV-specific hypervariable domain permit ANDV N to inhibit IFN induction and that IFN regulation is directed by phosphomimetic S386D substitutions in ANDV N. In addition, MAPV N proteins containing D386 and ANDV HVD gained the ability to inhibit IFN induction. Validating these findings, mass spectroscopy analysis revealed that S386 of ANDV N protein is uniquely phosphorylated during ANDV infection. Collectively, these findings reveal new paradigms for ANDV N protein as a phosphoprotein and IFN pathway regulator and suggest new mechanisms for hantavirus regulation of cellular kinases and signaling pathways. Our findings define novel IFN-regulating virulence determinants of ANDV, identify residues that can be modified to attenuate ANDV for vaccine development, and suggest the potential for kinase inhibitors to therapeutically restrict ANDV replication.

Molecular detection of viruses causing hemorrhagic fevers in rodents in the south-west of Korea

Many pathogens causing hemorrhagic fevers of medical and veterinary importance have been identified and isolated from rodents in the Republic of Korea (ROK). We investigated the occurrence of emerging viruses causing hemorrhagic fevers, such as hemorrhagic fever with renal syndrome (HFRS), severe fever with thrombocytopenia syndrome (SFTS), and flaviviruses, from wild rodents. Striped field mice, Apodemus agrarius (n = 39), were captured during 2014-2015 in the south-west of ROK. Using molecular methods, lung samples were evaluated for SFTS virus, hantavirus, and flavivirus, and seropositivity was evaluated in the blood. A high positive rate of hantavirus (46.2%) was detected in A. agrarius lungs by reverse transcription-nested polymerase chain reaction (RT-N-PCR). The monthly occurrence of hantavirus was 16.7% in October, 86.7% in November, and 25% in August of the following year (p < 0.001). Moreover, 17.9% of blood samples were serologically positive for hantavirus antibodies. The most prevalent strain in A. agrarius was Hantaan virus. All samples were positive for neither SFTS virus nor flavivirus. Hantaan virus was detected in 86.7% of A. agrarius in November (autumn), and thus, virus shedding from A. agrarius can increase the risk of humans contracting HFRS. These findings may help to predict and prevent disease outbreaks in ROK.

Silent Orthohantavirus Circulation Among Humans and Small Mammals from Central Minas Gerais, Brazil

New World orthohantaviruses are emerging RNA viruses that cause hantavirus cardiopulmonary syndrome (HCPS). These viruses are a burden to public health around the world with a lethality rate of around 60%. In South America, rodents of Sigmodontinae subfamily are the main reservoirs of orthohantaviruses. We described a serosurvey for orthohantaviruses circulation in an apparently healthy human population and small mammals from rural areas in Central Minas Gerais State, Brazil. A total of 240 individuals and 50 small mammals (26 rodents belonging to 10 different species and 24 marsupials from 4 different species) were sampled during 2012-2013. The seroprevalence rates of IgG/IgM antibodies in humans were 7.1 and 1.6%, respectively. Only one rodent, an Oligoryzomys nigripes captured in peridomestic area, tested positive for IgG antibodies and viral RNA. Our findings suggest a silent circulation of orthohantaviruses in a region of intensive agriculture production. The detection of seropositive humans in an area with a lack of previous HCPS reports highlights potential oligosymptomatic cases and the need for surveillance strategies that could reduce the risk of future outbreaks.

The Andes Virus Nucleocapsid Protein Directs Basal Endothelial Cell Permeability by Activating RhoA

Andes virus (ANDV) predominantly infects microvascular endothelial cells (MECs) and nonlytically causes an acute pulmonary edema termed hantavirus pulmonary syndrome (HPS). In HPS patients, virtually every pulmonary MEC is infected, MECs are enlarged, and infection results in vascular leakage and highly lethal pulmonary edema. We observed that MECs infected with the ANDV hantavirus or expressing the ANDV nucleocapsid (N) protein showed increased size and permeability by activating the Rheb and RhoA GTPases. Expression of ANDV N in MECs increased cell size by preventing tuberous sclerosis complex (TSC) repression of Rheb-mTOR-pS6K. N selectively bound the TSC2 N terminus (1 to 1403) within a complex containing TSC2/TSC1/TBC1D7, and endogenous TSC2 reciprocally coprecipitated N protein from ANDV-infected MECs. TSCs normally restrict RhoA-induced MEC permeability, and we found that ANDV infection or N protein expression constitutively activated RhoA. This suggests that the ANDV N protein alone is sufficient to activate signaling pathways that control MEC size and permeability. Further, RhoA small interfering RNA, dominant-negative RhoA(N19), and the RhoA/Rho kinase inhibitors fasudil and Y27632 dramatically reduced the permeability of ANDV-infected MECs by 80 to 90%. Fasudil also reduced the bradykinin-directed permeability of ANDV and Hantaan virus-infected MECs to control levels. These findings demonstrate that ANDV activation of RhoA causes MEC permeability and reveal a potential edemagenic mechanism for ANDV to constitutively inhibit the basal barrier integrity of infected MECs. The central importance of RhoA activation in MEC permeability further suggests therapeutically targeting RhoA, TSCs, and Rac1 as potential means of resolving capillary leakage during hantavirus infections.

HPS is hallmarked by acute pulmonary edema, hypoxia, respiratory distress, and the ubiquitous infection of pulmonary MECs that occurs without disrupting the endothelium. Mechanisms of MEC permeability and targets for resolving lethal pulmonary edema during HPS remain enigmatic. Our findings suggest a novel underlying mechanism of MEC dysfunction resulting from ANDV activation of the Rheb and RhoA GTPases that, respectively, control MEC size and permeability. Our studies show that inhibition of RhoA blocks ANDV-directed permeability and implicate RhoA as a potential therapeutic target for restoring capillary barrier function to the ANDV-infected endothelium. Since RhoA activation forms a downstream nexus for factors that cause capillary leakage, blocking RhoA activation is liable to restore basal capillary integrity and prevent edema amplified by tissue hypoxia and respiratory distress. Targeting the endothelium has the potential to resolve disease during symptomatic stages, when replication inhibitors lack efficacy, and to be broadly applicable to other hemorrhagic and edematous viral diseases.

Acidification triggers Andes hantavirus membrane fusion and rearrangement of Gc into a stable post-fusion homotrimer

The hantavirus membrane fusion process is mediated by the Gc envelope glycoprotein from within endosomes. However, little is known about the specific mechanism that triggers Gc fusion activation, and its pre- and post-fusion conformations. We established cell-free in vitro systems to characterize hantavirus fusion activation. Low pH was sufficient to trigger the interaction of virus-like particles with liposomes. This interaction was dependent on a pre-fusion glycoprotein arrangement. Further, low pH induced Gc multimerization changes leading to non-reversible Gc homotrimers. These trimers were resistant to detergent, heat and protease digestion, suggesting characteristics of a stable post-fusion structure. No acid-dependent oligomerization rearrangement was detected for the trypsin-sensitive Gn envelope glycoprotein. Finally, acidification induced fusion of glycoprotein-expressing effector cells with non-susceptible CHO cells. Together, the data provide novel information on the Gc fusion trigger and its non-reversible activation involving lipid interaction, multimerization changes and membrane fusion which ultimately allow hantavirus entry into cells.

Molecular method for the detection of Andes hantavirus infection: validation for clinical diagnostics

Hantavirus cardiopulmonary syndrome is a severe disease caused by exposure to New World hantaviruses. Early diagnosis is difficult due to the lack of specific initial symptoms. Antihantavirus antibodies are usually negative until late in the febrile prodrome or the beginning of cardiopulmonary phase, while Andes hantavirus (ANDV) RNA genome can be detected before symptoms onset. We analyzed the effectiveness of quantitative reverse transcription polymerase chain reaction (RT-qPCR) as a diagnostic tool detecting ANDV-Sout genome in peripheral blood cells from 78 confirmed hantavirus patients and 166 negative controls. Our results indicate that RT-qPCR had a low detection limit (~10 copies), with a specificity of 100% and a sensitivity of 94.9%. This suggests the potential for establishing RT-qPCR as the assay of choice for early diagnosis, promoting early effective care of patients, and improving other important aspects of ANDV infection management, such as compliance of biosafety recommendations for health personnel in order to avoid nosocomial transmission.

Person-to-person household and nosocomial transmission of andes hantavirus, Southern Chile, 2011

Four persons became ill after exposure to a patient infected with the virus; 2 cases involved hospital transmission.

Andes hantavirus (ANDV) causes hantavirus cardiopulmonary syndrome in Chile and is the only hantavirus for which person-to-person transmission has been proven. We describe an outbreak of 5 human cases of ANDV infection in which symptoms developed in 2 household contacts and 2 health care workers after exposure to the index case-patient. Results of an epidemiologic investigation and sequence analysis of the virus isolates support person-to-person transmission of ANDV for the 4 secondary case-patients, including nosocomial transmission for the 2 health care workers. Health care personnel who have direct contact with ANDV case-patients or their body fluids should take precautions to prevent transmission of the virus. In addition, because the incubation period of ANDV after environmental exposure is longer than that for person-to-person exposure, all persons exposed to a confirmed ANDV case-patient or with possible environmental exposure to the virus should be monitored for 42 days for clinical symptoms.

Co-circulation in a single biome of the Juquitiba and Araraquara hantavirus detected in human sera in a sub-tropical region of Brazil

Hantaviruses is an emerging infectious disease. Although HCPS has been reported in several regions of Brazil, more cases of HCPS have recently been reported in Minas Gerais than in any other state. In 2009, we analyzed 27 samples presenting antibodies against hantaviruses. These samples originated from 688 symptomatic patients, as determined based on the Hemorrhagic Fever Protocol. A subsequent SYBR Green-based real-time RT-PCR demonstrated the presence of the virus in 22 of the samples. Among the RT-PCR-positive samples, 17 were analyzed using DNA sequencing; these sequences were compared with others deposited in GenBank and showed similarity with the Araraquara and Juquitiba virus clusters. This work describe the detection of Juquitiba virus, including three fatal cases, in Minas Gerais state, furthermore, showed that it is feasible to characterize the circulating strains using a small fragment of S segment. Finally, the results suggest the co-circulation of Araraquara and Juquitiba virus in a single biome in Minas Gerais state.

Rapid enzyme-linked immunosorbent assay for the detection of hantavirus-specific antibodies in divergent small mammals

We assessed the utility of an enzyme-linked immunosorbent assay (ELISA) for the detection of hantavirus-specific antibodies from sera of Oligoryzomys longicaudatus, the principal reservoir of Andes virus (ANDV), using an antigen previously developed for detection of antibodies to Sin Nombre virus (SNV) in sera from Peromyscus maniculatus. The assay uses a protein A/G horseradish peroxidase conjugate and can be performed in as little as 1.5 hours. Serum samples from Oligoryzomys longicaudatus collected in central-south Chile were used and the assay identified several that were antibody positive. This assay can be used for the rapid detection of antibodies to divergent hantaviruses from geographically and phylogenetically distant rodent species.

Slit2-Robo4 receptor responses inhibit ANDV directed permeability of human lung microvascular endothelial cells

Hantaviruses nonlytically infect human endothelial cells (ECs) and cause edematous and hemorrhagic diseases. Andes virus (ANDV) causes hantavirus pulmonary syndrome (HPS), and Hantaan virus (HTNV) causes hemorrhagic fever with renal syndrome (HFRS). Hantaviruses enhance vascular endothelial growth factor directed EC permeability resulting in the disassembly of inter-endothelial cell adherens junctions (AJs). Recent studies demonstrate that Slit2 binding to Robo1/Robo4 receptors on ECs has opposing effects on AJ disassembly and vascular fluid barrier functions. Here we demonstrate that Slit2 inhibits ANDV and HTNV induced permeability and AJ disassembly of pulmonary microvascular ECs (PMECs) by interactions with Robo4. In contrast, Slit2 had no effect on the permeability of ANDV infected human umbilical vein ECs (HUVECs). Analysis of Robo1/Robo4 expression determined that PMECs express Robo4, but not Robo1, while HUVECs expressed both Robo4 and Robo1 receptors. SiRNA knockdown of Robo4 in PMECs prevented Slit2 inhibition of ANDV induced permeability demonstrating that Robo4 receptors determine PMEC responsiveness to Slit2. Collectively, this data demonstrates a selective role for Slit2/Robo4 responses within PMECs that inhibits ANDV induced permeability and AJ disassembly. These findings suggest Slit2s utility as a potential HPS therapeutic that stabilizes the pulmonary endothelium and antagonizes ANDV induced pulmonary edema.

Hantavirus fever without pulmonary syndrome in Panama

In Panama, hantavirus pulmonary syndrome (HPS) is caused by Choclo virus, a species phylogenetically related to Andes and Maporal viruses. Up to 60% of the population has been positive for specific serum antibody in community-based surveys, but mortality is very uncommon. In four western Panama clinics, we tested individuals presenting with a severe febrile prodrome for acute hantavirus (HV) infection by immunoglobulin M enzyme-linked immunosorbent assay and reverse transcription polymerase chain reaction as well as clinically similar infections, such as dengue and leptospirosis. From 2006 to 2009, at least 21% of 117 patients diagnosed with HV infection had HV Fever (HF) with no evidence of pulmonary edema (no respiratory distress or radiographic lung infiltrates), and 44% of patients had very mild HPS (radiographic pulmonary edema but no respiratory insufficiency). HV infection caused by Choclo virus in Panama presents often as HF, which contrasts with HV in the Americas but is consistent with the high seroprevalence in endemic regions.

A rapid method for infectivity titration of Andes hantavirus using flow cytometry

The focus assay is currently the most commonly used technique for hantavirus titer determination. This method requires an incubation time of between 5 and 11 days to allow the appearance of foci after several rounds of viral infection. The following work presents a rapid Andes virus (ANDV) titration assay, based on viral nucleocapsid protein (N) detection in infected cells by flow cytometry. To this end, an anti-N monoclonal antibody was used that was developed and characterized previously. ANDV N could be detected as early as 6 h post-infection, while viral release was not observed until 24-48 h post-infection. Given that ANDV detection was performed during its first round of infection, a time reduction for titer determination was possible and provided results in only two days. The viral titer was calculated from the percentage of N positive cells and agreed with focus assay titers. Furthermore, the assay was applied to quantify the inhibition of ANDV cell entry by patient sera and by preventing endosome acidification. This novel hantavirus titration assay is a highly quantitative and sensitive tool that facilitates infectivity titration of virus stocks, rapid screening for antiviral drugs, and may be further used to detect and quantify infectious virus in human samples.

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.

The Andes hantavirus NSs protein is expressed from the viral small mRNA by a leaky scanning mechanism

The small mRNA (SmRNA) of all Bunyaviridae encodes the nucleocapsid (N) protein. In 4 out of 5 genera in the Bunyaviridae, the smRNA encodes an additional nonstructural protein denominated NSs. In this study, we show that Andes hantavirus (ANDV) SmRNA encodes an NSs protein. Data show that the NSs protein is expressed in the context of an ANDV infection. Additionally, our results suggest that translation initiation from the NSs initiation codon is mediated by ribosomal subunits that have bypassed the upstream N protein initiation codon through a leaky scanning mechanism.

Human pathogenic hantaviruses and prevention of infection

Hantaviruses are emerging viruses which are hosted by small mammals. When transmitted to humans, they can cause two clinical syndromes, hemorrhagic fever with renal syndrome or hantavirus cardiopulmonary syndrome. The review compiles the current list of hantaviruses which are thought to be pathogenic in humans on the basis of molecular or at least serological evidence. Whereas induction of a neutralizing humoral immune response is considered to be protective against infection, the dual role of cellular immunity (protection versus immunopathogenicity) is discussed. For active immunisation, inactivated virus vaccines are licensed in certain Asian countries. Moreover, several classical and molecular vaccine approaches are in pre-clinical stages of development. The development of hantavirus vaccines is hampered by the lack of adequate animal models of hantavirus-associated disease. In addition to active immunization strategies, the review summarizes other ways of infection prevention, as passive immunization, chemoprophylaxis, and exposition prophylaxis.

Infection of human monocyte-derived dendritic cells by ANDES Hantavirus enhances pro-inflammatory state, the secretion of active MMP-9 and indirectly enhances endothelial permeability

Background

Andes virus (ANDV), a rodent-borne Hantavirus, is the major etiological agent of Hantavirus cardiopulmonary syndrome (HCPS) in South America, which is mainly characterized by a vascular leakage with high rate of fatal outcomes for infected patients. Currently, neither specific therapy nor vaccines are available against this pathogen. ANDV infects both dendritic and epithelial cells, but in despite that the severity of the disease directly correlates with the viral RNA load, considerable evidence suggests that immune mechanisms rather than direct viral cytopathology are responsible for plasma leakage in HCPS. Here, we assessed the possible effect of soluble factors, induced in viral-activated DCs, on endothelial permeability. Activated immune cells, including DC, secrete gelatinolytic matrix metalloproteases (gMMP-2 and -9) that modulate the vascular permeability for their trafficking.

Methods

A clinical ANDES isolate was used to infect DC derived from primary PBMC. Maturation and pro-inflammatory phenotypes of ANDES-infected DC were assessed by studying the expression of receptors, cytokines and active gMMP-9, as well as some of their functional status. The ANDES-infected DC supernatants were assessed for their capacity to enhance a monolayer endothelial permeability using primary human vascular endothelial cells (HUVEC).

Results

Here, we show that in vitro primary DCs infected by a clinical isolate of ANDV shed virus RNA and proteins, suggesting a competent viral replication in these cells. Moreover, this infection induces an enhanced expression of soluble pro-inflammatory factors, including TNF-α and the active gMMP-9, as well as a decreased expression of anti-inflammatory cytokines, such as IL-10 and TGF-β. These viral activated cells are less sensitive to apoptosis. Moreover, supernatants from ANDV-infected DCs were able to indirectly enhance the permeability of a monolayer of primary HUVEC.

Conclusions

Primary human DCs, that are primarily targeted by hantaviruses can productively be infected by ANDV and subsequently induce direct effects favoring a proinflammatory phenotype of infected DCs. Finally, based on our observations, we hypothesize that soluble factors secreted in ANDV-infected DC supernatants, importantly contribute to the endothelial permeability enhancement that characterize the HCPS.

VEGFR2 and Src kinase inhibitors suppress Andes virus-induced endothelial cell permeability

Hantaviruses predominantly infect human endothelial cells and, in the absence of cell lysis, cause two diseases resulting from increased vascular permeability. Andes virus (ANDV) causes a highly lethal acute pulmonary edema termed hantavirus pulmonary syndrome (HPS). ANDV infection enhances the permeability of endothelial cells in response to vascular endothelial growth factor (VEGF) by increasing signaling responses directed by the VEGFR2-Src-VE-cadherin pathway, which directs adherens junction (AJ) disassembly. Here we demonstrate that inhibiting pathway-specific VEGFR2 and Src family kinases (SFKs) blocks ANDV-induced endothelial cell permeability. Small interfering RNA (siRNA) knockdown of Src within ANDV-infected endothelial cells resulted in an ∼70% decrease in endothelial cell permeability compared to that for siRNA controls. This finding suggested that existing FDA-approved small-molecule kinase inhibitors might similarly block ANDV-induced permeability. The VEGFR2 kinase inhibitor pazopanib as well as SFK inhibitors dasatinib, PP1, bosutinib, and Src inhibitor 1 dramatically inhibited ANDV-induced endothelial cell permeability. Consistent with their kinase-inhibitory concentrations, dasatinib, PP1, and pazopanib inhibited ANDV-induced permeability at 1, 10, and 100 nanomolar 50% inhibitory concentrations (IC(50)s), respectively. We further demonstrated that dasatinib and pazopanib blocked VE-cadherin dissociation from the AJs of ANDV-infected endothelial cells by >90%. These findings indicate that VEGFR2 and Src kinases are potential targets for therapeutically reducing ANDV-induced endothelial cell permeability and, as a result, capillary permeability during HPS. Since the functions of VEGFR2 and SFK inhibitors are already well defined and FDA approved for clinical use, these findings rationalize their therapeutic evaluation for efficacy in reducing HPS disease. Endothelial cell barrier functions are disrupted by a number of viruses that cause hemorrhagic, edematous, or neurologic disease, and as a result, our findings suggest that VEGFR2 and SFK inhibitors should be considered for regulating endothelial cell barrier functions altered by additional viral pathogens.

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.

Highly differentiated, resting gn-specific memory CD8+ T cells persist years after infection by andes hantavirus

In man, infection with South American Andes virus (ANDV) causes hantavirus cardiopulmonary syndrome (HCPS). HCPS due to ANDV is endemic in Southern Chile and much of Argentina and increasing numbers of cases are reported all over South America. A case-fatality rate of about 36% together with the absence of successful antiviral therapies urge the development of a vaccine. Although T-cell responses were shown to be critically involved in immunity to hantaviruses in mouse models, no data are available on the magnitude, specificity and longevity of ANDV-specific memory T-cell responses in patients. Using sets of overlapping peptides in IFN-γ ELISPOT assays, we herein show in 78 Chilean convalescent patients that Gn-derived epitopes were immunodominant as compared to those from the N- and Gc-proteins. Furthermore, while the relative contribution of the N-specific response significantly declined over time, Gn-specific responses remained readily detectable ex vivo up to 13 years after the acute infection. Tetramer analysis further showed that up to 16.8% of all circulating CD3⁺CD8⁺ T cells were specific for the single HLA-B*3501-restricted epitope Gn_465–473 years after the acute infection. Remarkably, Gn_465–473–specific cells readily secreted IFN-γ, granzyme B and TNF-α but not IL-2 upon stimulation and showed a ‘revertant’ CD45RA⁺CD27⁻CD28⁻CCR7⁻CD127⁻ effector memory phenotype, thereby resembling a phenotype seen in other latent virus infections. Most intriguingly, titers of neutralizing antibodies increased over time in 10/17 individuals months to years after the acute infection and independently of whether they were residents of endemic areas or not. Thus, our data suggest intrinsic, latent antigenic stimulation of Gn-specific T-cells. However, it remains a major task for future studies to proof this hypothesis by determination of viral antigen in convalescent patients. Furthermore, it remains to be seen whether Gn-specific T cells are critical for viral control and protective immunity. If so, Gn-derived immunodominant epitopes could be of high value for future ANDV vaccines.

In man, hantavirus cardiopulmonary syndrome (HCPS) caused by Andes Virus (ANDV) is endemic in the Southern cone of Chile and Argentina but cases of HCPS are being increasingly reported all over South America since 1995. HCPS is characterized by fulminant pulmonary edema which progresses to shock and death in about 36% of patients with HCPS. Nevertheless, to date, neither antiviral treatments nor vaccines inducing neutralizing antibodies (NAb) have proven effective against HCPS-causing hantaviruses. We set out for the first study on human cellular immunity towards ANDV in 78 convalescent survivors of ANDV infection. We found that Gn-specific responses were predominant as compared to N- and Gc-specific responses, even up to 13 years after the infection. Surprisingly, most of the Gn-specific responses were restricted to two neighboring epitopes within the Gn carboxyterminus. Interestingly, among HLA-B*3501⁺ patients, Gn_465−473-specific CD8⁺ T-cells showed highly differentiated but resting phenotype and functions. It remains to be seen in future studies whether the immunodominace of Gn-specific T-cells is crucial for protective immunity. Most intriguingly, titers of neutralizing antibodies increased in 10/17 individuals months to years after the acute infection and independently of whether they were residents of endemic areas or not. Thus, our data suggest viral persistence or latency in part of ANDV-convalescent patients. However, it remains a major task for future studies to proof the concept of latent/persistent human ANDV infection by the determination of viral antigen in convalescent patients.

Andes virus recognition of human and Syrian hamster beta3 integrins is determined by an L33P substitution in the PSI domain

Andes virus (ANDV) causes a fatal hantavirus pulmonary syndrome (HPS) in humans and Syrian hamsters. Human alpha(v)beta(3) integrins are receptors for several pathogenic hantaviruses, and the function of alpha(v)beta(3) integrins on endothelial cells suggests a role for alpha(v)beta(3) in hantavirus directed vascular permeability. We determined here that ANDV infection of human endothelial cells or Syrian hamster-derived BHK-21 cells was selectively inhibited by the high-affinity alpha(v)beta(3) integrin ligand vitronectin and by antibodies to alpha(v)beta(3) integrins. Further, antibodies to the beta(3) integrin PSI domain, as well as PSI domain polypeptides derived from human and Syrian hamster beta(3) subunits, but not murine or bovine beta(3), inhibited ANDV infection of both BHK-21 and human endothelial cells. These findings suggest that ANDV interacts with beta(3) subunits through PSI domain residues conserved in both Syrian hamster and human beta(3) integrins. Sequencing the Syrian hamster beta(3) integrin PSI domain revealed eight differences between Syrian hamster and human beta(3) integrins. Analysis of residues within the PSI domains of human, Syrian hamster, murine, and bovine beta(3) integrins identified unique proline substitutions at residues 32 and 33 of murine and bovine PSI domains that could determine ANDV recognition. Mutagenizing the human beta(3) PSI domain to contain the L33P substitution present in bovine beta(3) integrin abolished the ability of the PSI domain to inhibit ANDV infectivity. Conversely, mutagenizing either the bovine PSI domain, P33L, or the murine PSI domain, S32P, to the residue present human beta(3) permitted PSI mutants to inhibit ANDV infection. Similarly, CHO cells transfected with the full-length bovine beta(3) integrin containing the P33L mutation permitted infection by ANDV. These findings indicate that human and Syrian hamster alpha(v)beta(3) integrins are key receptors for ANDV and that specific residues within the beta(3) integrin PSI domain are required for ANDV infection. Since L33P is a naturally occurring human beta(3) polymorphism, these findings further suggest the importance of specific beta(3) integrin residues in hantavirus infection. These findings rationalize determining the role of beta(3) integrins in hantavirus pathogenesis in the Syrian hamster model.

Study of Andes virus entry and neutralization using a pseudovirion system

Andes virus (ANDV), a member of the Hantavirus genus in the family Bunyaviridae, causes an acute disease characteristic of New-World hantaviruses called hantavirus pulmonary syndrome (HPS). HPS is a highly pathogenic disease with a case-fatality rate of 40%. ANDV is the only hantavirus reported to spread directly from human-to-human. The aim of the present study was to develop a quantitative and high-throughput pseudovirion assay to study ANDV infection and neutralization in biosafety level 2 facilities (BSL-2). This pseudovirion assay is based on incorporation of ANDV glycoproteins onto replication-defective vesicular stomatitis virus (VSV) cores in which the gene for the surface G protein has been replaced by that encoding Renilla luciferase. Infection by the pseudovirions can be quantified by luciferase activity of infected cell lysates. ANDV pseudovirions were neutralized by ANDV-specific antisera, and there was good concordance between specificity and neutralization titers of ANDV hamster sera as determined by our pseudovirion assay and a commonly used plaque reduction neutralization titer (PRNT) assay. In addition, the pseudovirions were used to evaluate the requirements for ANDV entry, like pH dependency and the role of beta3 integrin, the reported receptor for other pathogenic hantaviruses, on entry.

Andes virus antigens are shed in urine of patients with acute hantavirus cardiopulmonary syndrome

Hantavirus cardiopulmonary syndrome (HCPS) is a highly pathogenic emerging disease (40% case fatality rate) caused by New World hantaviruses. Hantavirus infections are transmitted to humans mainly by inhalation of virus-contaminated aerosol particles of rodent excreta and secretions. At present, there are no antiviral drugs or immunotherapeutic agents available for the treatment of hantaviral infection, and the survival rates for infected patients hinge largely on early virus recognition and hospital admission and aggressive pulmonary and hemodynamic support. In this study, we show that Andes virus (ANDV) interacts with human apolipoprotein H (ApoH) and that ApoH-coated magnetic beads or ApoH-coated enzyme-linked immunosorbent assay plates can be used to capture and concentrate the virus from complex biological mixtures, such as serum and urine, allowing it to be detected by both immunological and molecular approaches. In addition, we report that ANDV-antigens and infectious virus are shed in urine of HCPS patients.

Case report: T-cell responses during clearance of Andes virus from blood cells 2 months after severe hantavirus cardiopulmonary syndrome

Hantavirus Cardiopulmonary Syndrome (HCPS) due to Andes virus (ANDV) is endemic in Chile and Argentina and currently demonstrates a case-fatality rate of 37% in humans. By contrast to the chronically infected rodents, it is believed that ANDV in humans is cleared during the acute phase. Moreover, to date, both magnitude and quality of human T-cell responses during ANDV infection and clearance are unknown. Using IFN-gamma and granzyme B ELISPOT assays as well as flow cytometry, we prospectively studied the ANDV-specific T-cell responses in a 56-year-old convalescing survivor of severe HCPS, whose blood cells remained PCR-positive for ANDV-RNA until day 53 after hospital admission, that is, 67 days after infection and 42 days after discharge. PCR-negativity was closely related to the increase and function of (Gn(46-60))-specific IFN-gamma(+) granzyme B(+) CD8(+) T-cells, but not to neutralizing antibody titers. Concurrently, the phenotype of CD45RA(+)CCR7(-) Gn(46-60)-specific T-cells shifted from a CD28(-)CD27(+) "intermediate" to a CD28(-) CD27(-) "late" effector memory beyond day 53 after hospital admission. This is the first report that shows that ANDV can persist in the human hosts for more than 2 months. Moreover, the kinetics of T-cell responses during ANDV clearance may indicate a major role of T-cells for clearance of ANDV and human immunity to this pathogen.

Effect on Hantavirus Replication of Resins from Heliotropium Species and Other Selected Compounds

The present investigation on Heliotropium species was carried out in an attempt to detect possible replication inhibitors of Hantavirus variety Andes. Using the plaque inhibition assay, we have evaluated a group of compounds and resins isolated from Heliotropium species. The antiviral activity was determined between the concentration range 2.5-40.0 μg/mL. Antiviral activity was detected in all the tested resins, particularly that of H. huascoense, with an EC50 value of 12.5 μg/mL. Of the pure compounds tested, the aromatic geranyl derivative filifolinone was the most active. The EC50 value of this compound, 11.3 μg/mL, was similar to that of the control, ribavirin. However, these substances were not selective, but this screening has served to identify those compounds with most promise.

Characterization of cross-reactive and serotype-specific epitopes on the nucleocapsid proteins of hantaviruses

The hantavirus nucleocapsid (N) protein fulfills several key roles in virus replication and assembly and is the major antigen in humoral immune responses in humans and mice. Here we report on epitopes involved in serotype-specific and cross-reactive recognition of the N proteins of hantaviruses using monoclonal antibodies (mAbs) against the N proteins of Andes virus (ANDV) and Sin Nombre virus (SNV). The mAbs define at least twelve different epitopic patterns which span eight sequences, including amino acids 17-59, 66-78, 79-91, 157-169, 222-234, 244-263, 274-286 and 326-338 on the SNV and ANDV N proteins. Studies on the cross-reactivity of these mAbs with different hantavirus N proteins indicated that epitopes located within amino acids 244-286 are related to serotype specificity. We analyzed further the location of epitopes with available three-dimensional structure information including the N-terminal coiled-coil and derived exposed and hidden residues of these epitopes. The generated recombinant N proteins and the characterized mAbs are functional tools being now available for hantavirus diagnostics and replication studies.

Detection and typing of human pathogenic hantaviruses by real-time reverse transcription-PCR and pyrosequencing

BACKGROUND

Because the clinical course of human infections with hantaviruses can vary from subclinical to fatal, rapid and reliable detection of hantaviruses is essential. To date, the diagnosis of hantavirus infection is based mainly on serologic assays, and the detection of hantaviral RNA by the commonly used reverse transcription (RT)-PCR is difficult because of high sequence diversity of hantaviruses and low viral loads in clinical specimens.

METHODS

We developed 5 real-time RT-PCR assays, 3 of which are specific for the individual European hantaviruses Dobrava, Puumala, or Tula virus. Two additional assays detect the Asian species Hantaan virus together with Seoul virus and the American species Andes virus together with Sin Nombre virus. Pyrosequencing was established to provide characteristic sequence information of the amplified hantavirus for confirmation of the RT-PCR results or for a more detailed virus typing.

RESULTS

The real-time RT-PCR assays were specific for the respective hantavirus species and optimized to run on 2 different platforms, the LightCycler and the ABI 7900/7500. Each assay showed a detection limit of 10 copies of a plasmid containing the RT-PCR target region, and pyrosequencing was possible with 10 to 100 copies per reaction. With this assay, viral genome could be detected in 16 of 552 (2.5%) specimens of suspected hantavirus infections of humans and mice.

CONCLUSIONS

The new assays detect, differentiate, and quantify hantaviruses in clinical specimens from humans and from their natural hosts and may be useful for in vitro studies of hantaviruses.

Puumala hantavirus viremia diagnosed by real-time reverse transcriptase PCR using samples from patients with hemorrhagic fever and renal syndrome

Puumala virus (PUUV) is the endemic hantavirus in northern Sweden and causes nephropathia epidemica (NE), a milder form of hemorrhagic fever with renal syndrome. There is a need for fast and reliable diagnostics to differentiate the disease from other infections. By aligning virus RNA sequences isolated from 11 different bank voles and one human patient, we designed a real-time reverse transcriptase (RT) PCR method for detection of PUUV RNA. The real-time RT-PCR assay showed linearity from 20 to 2 x 10(6) virus copies with a correlation coefficient above 0.98 to 0.99 for all experiments. The detection threshold for PUUV cDNA was two copies per reaction. A two-step qualitative RT-PCR to detect PUUV RNA showed 100% concordance with the real-time RT-PCR assay. PUUV RNA viremia was detected in 33 of 34 PUUV immunoglobulin M (IgM)-positive patients with typical clinical NE disease from the region of endemicity. One PUUV IgM-negative sample had PUUV RNA, and 4 days later, the patient was IgM positive. Of samples with indeterminate IgM, 43% were PUUV RNA positive. The kinetics of antibody titers and PUUV viremia were studied, and five of six NE patients displayed a decrease in PUUV viremia a few days after disease outbreak coupled with an increase in PUUV IgM and IgG. In one patient with continuously high PUUV RNA levels but low IgM and no IgG response, the infection was lethal. These findings demonstrated that real-time RT-PCR is a useful method for diagnosis of PUUV viremia and for detecting PUUV RNA at early time points, before the appearance of IgM antibodies.

Temporal analysis of Andes virus and Sin Nombre virus infections of Syrian hamsters

Andes virus (ANDV) and Sin Nombre virus (SNV) are rodent-borne hantaviruses that cause a highly lethal hemorrhagic fever in humans known as hantavirus pulmonary syndrome (HPS). There are no vaccines or specific drugs to prevent or treat HPS, and the pathogenesis is not understood. Syrian hamsters infected with ANDV, but not SNV, develop a highly lethal disease that closely resembles HPS in humans. Here, we performed a temporal pathogenesis study comparing ANDV and SNV infections in hamsters. SNV was nonpathogenic and viremia was not detected despite the fact that all animals were infected. ANDV was uniformly lethal with a mean time to death of 11 days. The first pathology detected was lymphocyte apoptosis starting on day 4. Animals were viremic and viral antigen was first observed in multiple organs by days 6 and 8, respectively. Levels of infectious virus in the blood increased 4 to 5 logs between days 6 and 8. Pulmonary edema was first detected ultrastructurally on day 6. Ultrastructural analysis of lung tissues revealed the presence of large inclusion bodies and substantial numbers of vacuoles within infected endothelial cells. Paraendothelial gaps were not observed, suggesting that fluid leakage was transcellular and directly attributable to infecting virus. Taken together, these data imply that HPS treatment strategies aimed at preventing virus replication and dissemination will have the greatest probability of success if administered before the viremic phase; however, because vascular leakage is associated with infected endothelial cells, a therapeutic strategy targeting viral replication might be effective even at later times (e.g., after disease onset).

Andes Hantavirus as possible cause of disease in travellers to South America

BACKGROUND

Hantaviruses in Europe and Asia cause haemorrhagic fever with renal syndrome and epidemic nephritis (mortality rate <1-15%). New strains of Hantaviruses cause Hantavirus pulmonary syndrome (HPS) from Canada to South America. Andes virus mortality rate is about 30% in Chile.

METHOD

Clinical charts of 54 patients were reviewed.

RESULTS

Inhalation of aerosolized urine, faeces or saliva of rodents is the principal cause of infection. The incubation period is between 8 and 43 days. The main prodromal symptoms are: myalgias, fever, fatigue, gastrointestinal disorders, dyspnoea, petechiae and coughing. After the 4th day pulmonary oedema, hypotension and renal failure appear. Haemorrhagic disorders may occur. The first laboratory tests presenting alterations are: haemoconcentration, leukocytosis, low platelet count <150 micro/L, and presence of immunoblasts. The treatment is supportive: mechanical ventilation, vasopressor drugs, haemofiltration or haemodialysis, and extracorporeal membrane oxygenation. There is no specific treatment for HPS. Preventive measures must be empathised.

CONCLUSION

The principal risk factors for tourists are: accommodation in abandoned or closed up facilities; failure to use indicated pathways when walking in forests; camping outside recommended areas; drinking water from natural sources and fishing in risk areas. The risk of infection for foreign tourists in Chile is low.

Diagnosis and treatment of new world hantavirus infections

PURPOSE OF REVIEW

The purpose of this review is to summarize the current knowledge regarding the diagnosis and treatment of indigenous new world hantavirus infections.

RECENT FINDINGS

Recent studies have defined the incubation period of new world hantavirus infections, provided additional evidence for person-to-person transmission of Andes virus, described a rapid method for the presumptive diagnosis of infection in the cardiopulmonary phase through a review of the peripheral smear, and suggested that intravenous ribavirin is probably not effective for the treatment of new world hantavirus infections when started in the cardiopulmonary phase.

SUMMARY

Presumptive diagnosis may be made by a review of the peripheral blood smear after the onset of the cardiopulmonary phase. Critical care management includes the avoidance of fluid overload, pressors to maintain cardiac output, and the use of extracorporeal membrane oxygenation in the most severe cases, but treatment with intravenous ribavirin is probably not effective.

Person-to-person transmission of Andes virus

Despite the fact that rodents are considered to be the infectious source of hantavirus for humans, another route of transmission was demonstrated. Andes virus (ANDV) has been responsible for most of the cases recorded in Argentina. Person-to-person transmission of ANDV Sout lineage was described during an outbreak of hantavirus pulmonary syndrome in southwest Argentina. In this study, we analyzed 4 clusters that occurred in 2 disease-endemic areas for different ANDV lineages. We found new evidence of interhuman transmission for ANDV Sout lineage and described the first event in which another lineage, ANDV Cent BsAs, was implicated in this mechanism of transmission. On the basis of epidemiologic and genetic data, we concluded that person-to-person spread of the virus likely took place during the prodromal phase or shortly after it ended, since close and prolonged contact occurred in the events analyzed here, and the incubation period was 15-24 days.

Bidirectional virus secretion and nonciliated cell tropism following Andes virus infection of primary airway epithelial cell cultures

Hantavirus pulmonary syndrome (HPS) is an acute disease resulting from infection with any one of a number of New World hantaviruses. HPS has a mortality rate of 40% and, unlike many other severe respiratory diseases, often occurs in young, healthy adults. Infection is usually initiated after inhalation of rodent excreta containing virus particles, but human-to-human transmission has been documented. Postmortem tissue samples show high levels of viral antigen within the respiratory endothelium, but it is not clear how the virus can traverse the respiratory epithelium in order to initiate infection in the microvasculature. We have utilized Andes virus infection of primary, differentiated airway epithelial cells to investigate the ability of the virus to interact with and cross the respiratory epithelium. Andes virus infects the Clara and goblet cell populations but not the ciliated cells, and this infection pattern corresponds to the expression of beta(3) integrin, the viral receptor. The virus can infect via the apical or basolateral membrane, and progeny virus particles are secreted bidirectionally. There is no obvious cytopathology associated with infection, and beta(3) integrins do not appear to be critical for respiratory epithelial cell monolayer integrity. Our data suggest that hantavirus infection of the respiratory epithelium may play an important role in the early or prodrome phase of disease as well as serving as a source of virus involved in transmission.

Hantaviruses in Central South America: phylogenetic analysis of the S segment from HPS cases in Paraná, Brazil

We sequenced the complete S segments of hantaviruses detected from 12 HPS patients living in southern of Brazil. Samples were obtained from patients diagnosed in different years, in distinct areas, and with a broad spectrum of clinical signs. Despite these differences, all the S proteins of hantavirus from Paraná were identical, except for one amino acid substitution. Phylogenetic analyses of the complete S segment nucleotide and amino acid sequences indicated that hantaviruses from Paraná form a distinct clade from those circulating in South and North America. Other hantaviruses from Brazil were not placed in the same clade. The Oligoryzomys nigripes-associated strains ITA37 and ITA38 from Paraguay were found to belong to the same clade as the hantaviruses from Paraná. Paraguay and Paraná state are located at the same latitude and some ecosystems are similar in both places. The geographic position and common rodent hosts could explain this phylogenetic relationship.

Human and rodent humoral immune responses to Andes virus structural proteins

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

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.