Molecular linkage of hantavirus pulmonary syndrome to the white-footed mouse, Peromyscus leucopus: genetic characterization of the M genome of New York virus

Case of Human Orthohantavirus Infection, Michigan, USA, 2021

Orthohantaviruses cause hantavirus cardiopulmonary syndrome; most cases occur in the southwest region of the United States. We discuss a clinical case of orthohantavirus infection in a 65-year-old woman in Michigan and the phylogeographic link of partial viral fragments from the patient and rodents captured near the presumed site of infection.

Effects of habitat management on rodent diversity, abundance, and virus infection dynamics

As anthropogenic factors continue to degrade natural areas, habitat management is needed to restore and maintain biodiversity. However, the impacts of different habitat management regimes on ecosystems have largely focused on vegetation analyses, with limited evaluation of downstream effects on wildlife. We compared the effects of grassland management regimes (prescribed burning, cutting/haying, or no active management) on rodent communities and the viruses they hosted. Rodents were trapped in 13 existing grassland sites in Northwest Arkansas, USA during 2020 and 2021. Rodent blood samples were screened for antibodies against three common rodent-borne virus groups: orthohantaviruses, arenaviruses, and orthopoxviruses. We captured 616 rodents across 5953 trap nights. Burned and unmanaged sites had similarly high abundance and diversity, but burned sites had a higher proportion of grassland species than unmanaged sites; cut sites had the highest proportion of grassland species but the lowest rodent abundance and diversity. A total of 38 rodents were seropositive for one of the three virus groups (34 orthohantavirus, three arenavirus, and one orthopoxvirus). Thirty-six seropositive individuals were found in burned sites, and two orthohantavirus-seropositive individuals were found in cut sites. Cotton rats and prairie voles, two grassland species, accounted for 97% of the rodents seropositive for orthohantavirus. Our study indicates that prescribed burns lead to a diverse and abundant community of grassland rodent species compared with other management regimes; as keystone taxa, these results also have important implications for many other species in food webs. Higher prevalence of antibodies against rodent-borne viruses in burned prairies shows an unexpected consequence likely resulting from robust host population densities supported by the increased habitat quality of these sites. Ultimately, these results provide empirical evidence that can inform grassland restoration and ongoing management strategies.

Virus isolation data improve host predictions for New World rodent orthohantaviruses

Identifying reservoir host species is crucial for understanding the ecology of multi-host pathogens and predicting risks of pathogen spillover from wildlife to people. Predictive models are increasingly used for identifying ecological traits and prioritizing surveillance of likely zoonotic reservoirs, but these often employ different types of evidence for establishing host associations. Comparisons between models with different infection evidence are necessary to guide inferences about the trait profiles of likely hosts and identify which hosts and geographical regions are likely sources of spillover. Here, we use New World rodent-orthohantavirus associations to explore differences in the performance and predictions of models trained on two types of evidence for infection and onward transmission: RT-PCR and live virus isolation data, representing active infections versus host competence, respectively. Orthohantaviruses are primarily carried by muroid rodents and cause the diseases haemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS) in humans. We show that although boosted regression tree (BRT) models trained on RT-PCR and live virus isolation data both performed well and capture generally similar trait profiles, rodent phylogeny influenced previously collected RT-PCR data, and BRTs using virus isolation data displayed a narrower list of predicted reservoirs than those using RT-PCR data. BRT models trained on RT-PCR data identified 138 undiscovered hosts and virus isolation models identified 92 undiscovered hosts, with 27 undiscovered hosts identified by both models. Distributions of predicted hosts were concentrated in several different regions for each model, with large discrepancies between evidence types. As a form of validation, virus isolation models independently predicted several orthohantavirus-rodent host associations that had been previously identified through empirical research using RT-PCR. Our model predictions provide a priority list of species and locations for future orthohantavirus sampling. More broadly, these results demonstrate the value of multiple data types for predicting zoonotic pathogen hosts. These methods can be applied across a range of systems to improve our understanding of pathogen maintenance and increase efficiency of pathogen surveillance.

Use of a Novel Detection Tool to Survey Orthohantaviruses in Wild-Caught Rodent Populations

Orthohantaviruses are negative-stranded RNA viruses with trisegmented genomes that can cause severe disease in humans and are carried by several host reservoirs throughout the world. Old World orthohantaviruses are primarily located throughout Europe and Asia, causing hemorrhagic fever with renal syndrome, and New World orthohantaviruses are found in North, Central, and South America, causing hantavirus cardiopulmonary syndrome (HCPS). In the United States, Sin Nombre orthohantavirus (SNV) is the primary cause of HCPS with a fatality rate of ~36%. The primary SNV host reservoir is thought to be the North American deer mouse, Peromyscus maniculatus. However, it has been shown that other species of Peromyscus can carry different orthohantaviruses. Few studies have systemically surveyed which orthohantaviruses may exist in wild-caught rodents or monitored spillover events into additional rodent reservoirs. A method for the rapid detection of orthohantaviruses is needed to screen large collections of rodent samples. Here, we report a pan-orthohantavirus, two-step reverse-transcription quantitative real-time PCR (RT-qPCR) tool designed to detect both Old and New World pathogenic orthohantavirus sequences of the S segment of the genome and validated them using plasmids and authentic viruses. We then performed a screening of wild-caught rodents and identified orthohantaviruses in lung tissue, and we confirmed the findings by Sanger sequencing. Furthermore, we identified new rodent reservoirs that have not been previously reported as orthohantavirus carriers. This novel tool can be used for the efficient and rapid detection of various orthohantaviruses, while uncovering potential new orthohantaviruses and host reservoirs that may otherwise go undetected.

Binding of the Andes Virus Nucleocapsid Protein to RhoGDI Induces the Release and Activation of the Permeability Factor RhoA

Andes virus (ANDV) nonlytically infects pulmonary microvascular endothelial cells (PMECs), causing acute pulmonary edema termed hantavirus pulmonary syndrome (HPS). In HPS patients, virtually every PMEC is infected; however, the mechanism by which ANDV induces vascular permeability and edema remains to be resolved. The ANDV nucleocapsid (N) protein activates the GTPase RhoA in primary human PMECs, causing VE-cadherin internalization from adherens junctions and PMEC permeability. We found that ANDV N protein failed to bind RhoA but coprecipitates RhoGDI (Rho GDP dissociation inhibitor), the primary RhoA repressor that normally sequesters RhoA in an inactive state. ANDV N protein selectively binds the RhoGDI C terminus (residues 69 to 204) but fails to form ternary complexes with RhoA or inhibit RhoA binding to the RhoGDI N terminus (residues 1 to 69). However, we found that ANDV N protein uniquely inhibits RhoA binding to an S34D phosphomimetic RhoGDI mutant. Hypoxia and vascular endothelial growth factor (VEGF) increase RhoA-induced PMEC permeability by directing protein kinase Cα (PKCα) phosphorylation of S34 on RhoGDI. Collectively, ANDV N protein alone activates RhoA by sequestering and reducing RhoGDI available to suppress RhoA. In response to hypoxia and VEGF-activated PKCα, ANDV N protein additionally directs the release of RhoA from S34-phosphorylated RhoGDI, synergistically activating RhoA and PMEC permeability. These findings reveal a fundamental edemagenic mechanism that permits ANDV to amplify PMEC permeability in hypoxic HPS patients. Our results rationalize therapeutically targeting PKCα and opposing protein kinase A (PKA) pathways that control RhoGDI phosphorylation as a means of resolving ANDV-induced capillary permeability, edema, and HPS. IMPORTANCE HPS-causing hantaviruses infect pulmonary endothelial cells (ECs), causing vascular leakage, pulmonary edema, and a 35% fatal acute respiratory distress syndrome (ARDS). Hantaviruses do not lyse or disrupt the endothelium but dysregulate normal EC barrier functions and increase hypoxia-directed permeability. Our findings reveal a novel underlying mechanism of EC permeability resulting from ANDV N protein binding to RhoGDI, a regulatory protein that normally maintains edemagenic RhoA in an inactive state and inhibits EC permeability. ANDV N sequesters RhoGDI and enhances the release of RhoA from S34-phosphorylated RhoGDI. These findings indicate that ANDV N induces the release of RhoA from PKC-phosphorylated RhoGDI, synergistically enhancing hypoxia-directed RhoA activation and PMEC permeability. Our data suggest inhibiting PKC and activating PKA phosphorylation of RhoGDI as mechanisms of inhibiting ANDV-directed EC permeability and therapeutically restricting edema in HPS patients. These findings may be broadly applicable to other causes of ARDS.

New Exposure Location for Hantavirus Pulmonary Syndrome Case, California, USA, 2018

We describe a case of hantavirus pulmonary syndrome in a patient exposed to Sin Nombre virus in a coastal county in California, USA, that had no previous record of human cases. Environmental evaluation coupled with genotypic analysis of virus isolates from the case-patient and locally trapped rodents identified the likely exposure location.

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.

Hantaviridae: Current Classification and Future Perspectives

In recent years, negative-sense RNA virus classification and taxon nomenclature have undergone considerable transformation. In 2016, the new order Bunyavirales was established, elevating the previous genus Hantavirus to family rank, thereby creating Hantaviridae. Here we summarize affirmed taxonomic modifications of this family from 2016 to 2019. Changes involve the admission of >30 new hantavirid species and the establishment of subfamilies and novel genera based on DivErsity pArtitioning by hieRarchical Clustering (DEmARC) analysis of genomic sequencing data. We outline an objective framework that can be used in future classification schemes when more hantavirids sequences will be available. Finally, we summarize current taxonomic proposals and problems in hantavirid taxonomy that will have to be addressed shortly.

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.

Complete Genome Sequences of a Hantavirus Isolate from New York

We report here the complete genome sequences for all three segments of the New York hantavirus (New York 1). This is the first reported L segment sequence for hantaviruses maintained in Peromyscus spp. endemic to the eastern United States and Canada.

Global Diversity and Distribution of Hantaviruses and Their Hosts

Rodents represent 42% of the world's mammalian biodiversity encompassing 2,277 species populating every continent (except Antarctica) and are reservoir hosts for a wide diversity of disease agents. Thus, knowing the identity, diversity, host-pathogen relationships, and geographic distribution of rodent-borne zoonotic pathogens, is essential for predicting and mitigating zoonotic disease outbreaks. Hantaviruses are hosted by numerous rodent reservoirs. However, the diversity of rodents harboring hantaviruses is likely unknown because research is biased toward specific reservoir hosts and viruses. An up-to-date, systematic review covering all known rodent hosts is lacking. Herein, we document gaps in our knowledge of the diversity and distribution of rodent species that host hantaviruses. Of the currently recognized 681 cricetid, 730 murid, 61 nesomyid, and 278 sciurid species, we determined that 11.3, 2.1, 1.6, and 1.1%, respectively, have known associations with hantaviruses. The diversity of hantaviruses hosted by rodents and their distribution among host species supports a reassessment of the paradigm that each virus is associated with a single-host species. We examine these host-virus associations on a global taxonomic and geographical scale with emphasis on the rodent host diversity and distribution. Previous reviews have been centered on the viruses and not the mammalian hosts. Thus, we provide a perspective not previously addressed.

Infection resistance and tolerance in Peromyscus spp., natural reservoirs of microbes that are virulent for humans

The widely-distributed North American species Peromyscus leucopus and P. maniculatus of cricetine rodents are, between them, important natural reservoirs for several zoonotic diseases of humans: Lyme disease, human granulocytic anaplasmosis, babesiosis, erhlichiosis, hard tickborne relapsing fever, Powassan virus encephalitis, hantavirus pulmonary syndrome, and plague. While these infections are frequently disabling and sometimes fatal for humans, the peromyscines display little pathology and apparently suffer few consequences, even when prevalence of persistent infection in a population is high. While these Peromyscus spp. are unable to clear some of the infections, they appear to have partial resistance, which limits the burden of the pathogen. In addition, they display traits of infection tolerance, which reduces the damage of the infection. Research on these complementary resistance and tolerance phenomena in Peromyscus has relevance both for disease control measures targeting natural reservoirs and for understanding the mechanisms of the comparatively greater sickness of many humans with these and other infections.

A method to distinguish morphologically similar Peromyscus species using extracellular RNA and high-resolution melt analysis

A method applying high-resolution melt (HRM) analysis to PCR products copied and amplified from extracellular RNA (exRNA) has been developed to distinguish two morphologically similar Peromyscus species: Peromyscus leucopus and Peromyscus maniculatus. P. leucopus is considered the primary reservoir host of Borrelia burgdorferi, the causative agent for Lyme disease in North America. In northern Minnesota the habitat ranges of P. leucopus overlaps with that of P. maniculatus. Serum samples from live mice of both species were collected from cheek bleeds, total extracellular RNA (exRNA) was extracted, copied using reverse transcription and amplified by PCR followed by HRM analysis. A circulating ribosomal RNA (rRNA) was identified which differed at seven nucleotides between the two species and a method of HRM analysis was developed allowing rapid species confirmation. In the future, this HRM based method may be adapted for additional species.

Multiplex Analysis of Serum Cytokines in Humans with Hantavirus Pulmonary Syndrome

Hantavirus pulmonary syndrome (HPS) is an acute zoonotic disease transmitted primarily through inhalation of virus-contaminated aerosols. Hantavirus infection of endothelial cells leads to increased vascular permeability without a visible cytopathic effect. For this reason, it has been suggested that the pathogenesis of HPS is indirect with immune responses, such as cytokine production, playing a dominant role. In order to investigate their potential contribution to HPS pathogenesis, we analyzed the serum of hantavirus-infected subjects and healthy controls for 68 different cytokines, chemokines, angiogenic, and growth factors. Our analysis identified differential expression of cytokines that promote tissue migration of mononuclear cells including T lymphocytes, natural killer cells, and dendritic cells. Additionally, we observed a significant upregulation of cytokines known to regulate leukocyte migration and subsequent repair of lung tissue, as well as cytokines known to increase endothelial monolayer permeability and facilitate leukocyte transendothelial migration. Conversely, we observed a downregulation of cytokines associated with platelet numbers and function, consistent with the thrombocytopenia observed in subjects with HPS. This study corroborates clinical findings and extends our current knowledge regarding immunological and laboratory findings in subjects with HPS.

Peromyscus leucopus mice: a potential animal model for haematological studies

Peromyscus leucopus mice share physical similarities with laboratory mice Mus musculus (MM) but have higher agility and longer lifespan. We compared domesticated P. leucopus linville (PLL) and M. musculus C57BL/6 (MMB6) mice for cellular composition of peripheral blood (PB), bone marrow (BM) and spleen. PLL mice had significantly fewer platelets and significantly more monocytes in the blood, and notably fewer megakaryocytes in the BM. Spleens of PLL mice were significantly smaller, with 50% fewer cells and reduced 'red pulp'. There was no obvious haematological change in PLL mice between 2-8 and 16-26 months of age, except for a significant increase in blood monocytes. Cellular reactive oxygen species (ROS) content showed no change with age but differed significantly between different cell types. Treating two to eight month-old PLL mice with antioxidant N-acetylcysteine in drinking water for three months did not affect cellular ROS content, but increased blood leucocytes especially the concentration of monocytes. The low platelets, low megakaryocytes, high monocytes and low splenic erythropoiesis in PLL mice resemble human measurements better than the values seen in MMB6.

Hantavirus reservoirs: current status with an emphasis on data from Brazil

Since the recognition of hantavirus as the agent responsible for haemorrhagic fever in Eurasia in the 1970s and, 20 years later, the descovery of hantavirus pulmonary syndrome in the Americas, the genus Hantavirus has been continually described throughout the World in a variety of wild animals. The diversity of wild animals infected with hantaviruses has only recently come into focus as a result of expanded wildlife studies. The known reservoirs are more than 80, belonging to 51 species of rodents, 7 bats (order Chiroptera) and 20 shrews and moles (order Soricomorpha). More than 80genetically related viruses have been classified within Hantavirus genus; 25 recognized as human pathogens responsible for a large spectrum of diseases in the Old and New World. In Brazil, where the diversity of mammals and especially rodents is considered one of the largest in the world, 9 hantavirus genotypes have been identified in 12 rodent species belonging to the genus Akodon, Calomys, Holochilus, Oligoryzomys, Oxymycterus, Necromys and Rattus. Considering the increasing number of animals that have been implicated as reservoirs of different hantaviruses, the understanding of this diversity is important for evaluating the risk of distinct hantavirus species as human pathogens.

Epidemiology of Hantavirus infections in humans: a comprehensive, global overview

Hantaviruses comprise an emerging global threat for public health, affecting about 30,000 humans annually. Infection may lead to Hantavirus pulmonary syndrome (HPS) in the Americas and hemorrhagic fever with renal syndrome (HFRS) in the Europe and Asia. Humans are spillover hosts, acquiring infection primarily through the inhalation of aerosolized excreta from infected rodents and insectivores. Risk factors for infection include involvement in outdoor activities, such as rural- and forest-related activities, peridomestic rodent presence, exposure to potentially infected dust and outdoor military training; prolonged, intimate contact with infected individuals promotes transmission of Andes virus, the only Hantavirus known to be transmitted from human-to-human. The total number of Hantavirus case reports is generally on the rise, as is the number of affected countries. Knowledge of the geographical distribution, regional incidence and associated risk factors of the disease are crucial for clinicians to suspect and diagnose infected individuals early on. Climatic, ecological and environmental changes are related to fluctuations in rodent populations, and subsequently to human epidemics. Thus, prevention may be enhanced by host-reservoir control and human exposure prophylaxis interventions, which likely have led to a dramatic reduction of human cases in China over the past decades; vaccination may also play a role in the future.

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.

Geographic distribution of hantaviruses associated with neotomine and sigmodontine rodents, Mexico

El Moro Canyon virus and Limestone Canyon virus are widely distributed and may cause hantavirus pulmonary syndrome.

To increase our knowledge of the geographic distribution of hantaviruses associated with neotomine or sigmodontine rodents in Mexico, we tested 876 cricetid rodents captured in 18 Mexican states (representing at least 44 species in the subfamily Neotominae and 10 species in the subfamily Sigmodontinae) for anti-hantavirus IgG. We found antibodies against hantavirus in 35 (4.0%) rodents. Nucleotide sequence data from 5 antibody-positive rodents indicated that Sin Nombre virus (the major cause of hantavirus pulmonary syndrome [HPS] in the United States) is enzootic in the Mexican states of Nuevo León, San Luis Potosí, Tamaulipas, and Veracruz. However, HPS has not been reported from these states, which suggests that in northeastern Mexico, HPS has been confused with other rapidly progressive, life-threatening respiratory diseases. Analyses of nucleotide sequence data from 19 other antibody-positive rodents indicated that El Moro Canyon virus and Limestone Canyon virus are geographically widely distributed in Mexico.

Hantavirus pulmonary syndrome

Hantavirus pulmonary syndrome (HPS) is a severe disease characterized by a rapid onset of pulmonary edema followed by respiratory failure and cardiogenic shock. The HPS associated viruses are members of the genus Hantavirus, family Bunyaviridae. Hantaviruses have a worldwide distribution and are broadly split into the New World hantaviruses, which includes those causing HPS, and the Old World hantaviruses [including the prototype Hantaan virus (HTNV)], which are associated with a different disease, hemorrhagic fever with renal syndrome (HFRS). Sin Nombre virus (SNV) and Andes virus (ANDV) are the most common causes of HPS in North and South America, respectively. Case fatality of HPS is approximately 40%. Pathogenic New World hantaviruses infect the lung microvascular endothelium without causing any virus induced cytopathic effect. However, virus infection results in microvascular leakage, which is the hallmark of HPS. This article briefly reviews the knowledge on HPS-associated hantaviruses accumulated since their discovery, less than 20 years ago.

Maporal virus as a surrogate for pathogenic New World hantaviruses and its inhibition by favipiravir

BACKGROUND

Pathogenic hantaviruses geographically distributed in the Old World cause haemorrhagic fever with renal syndrome (HFRS), whereas New World hantaviruses are the aetiological agents of hantavirus cardiopulmonary syndrome (HCPS). Ribavirin, a drug associated with toxicities, is presently indicated for treatment of HFRS, whereas treatment of the more frequently lethal HCPS is limited to supportive care. Because of the need for safe and effective antivirals to treat severe hantaviral infections, we evaluated favipiravir (T-705) against Dobrava and Maporal viruses as representative Old World and New World hantaviruses, respectively. Dobrava virus causes HFRS in Europe. Maporal virus (MPRLV), recently isolated from western Venezuela, is phylogenetically similar to Andes virus, the principal cause of HCPS in Argentina.

METHODS

Hantavirus replication in the presence of various inhibitors was measured by focus-forming unit assays and quantitative reverse transcriptase PCR. Phylogenetic relationships were assessed by the neighbour-joining and bootstrap consensus methods.

RESULTS

Here, we show that infection of Vero E6 cells with MPRLV is dependent on β3 integrins, similar to that reported for pathogenic hantaviruses. Furthermore, by analysis of molecular determinants associated with the G1 glycoprotein cytoplasmic tail, we show the close genetic proximity of MPRLV to other HCPS-causing hantaviruses in these regions predictive of pathogenicity. We also demonstrate anti-hantavirus activity by favipiravir with inhibitory concentrations ranging from 65 to 93 μM and selectivity indices>50.

CONCLUSIONS

Our data suggest that MPRLV may serve as a safer alternative to modelling infection caused by the highly lethal Andes virus and that hantaviruses are sensitive to the effects of favipiravir in cell culture.

The delicate pygmy rice rat (Oligoryzomys delicatus) is the principal host of Maporal virus (family Bunyaviridae, genus Hantavirus)

Choclo virus (CHOV) and Maporal virus (MAPV) are enzootic in Panama and western Venezuela, respectively. The results of previous studies suggested that the fulvous pygmy rice rat (Oligoryzomys fulvescens) is the principal host of both viruses. The results of an analysis of nucleotide sequence data in this study indicated that the rodent associated with CHOV is the Costa Rican pygmy rice rat (Oligoryzomys costaricensis) and that the rodent associated with MAPV is the delicate pygmy rice rat (Oligoryzomys delicatus). As such, MAPV is ecologically distinct from CHOV and should be considered a species separate from CHOV.

Pathology of Black Creek Canal virus infection in juvenile hispid cotton rats (Sigmodon hispidus)

The purpose of this study was to assess the effect of inoculum dose on the pathogenesis of Black Creek Canal virus (BCCV) infection in the hispid cotton rat (Sigmodon hispidus), the principal host of BCCV. No sign of illness was observed in any of the 52 juvenile hispid cotton rats inoculated with 3.1, 1.1, -0.9, or -2.9 log(10) median infectious doses(VeroE6) (ID(50-VeroE6)) of BCCV and euthanized on day 9, 18, 27, or 54 postinoculation (PI). Analysis of virus assay and serological data indicated that inoculum dose could significantly affect the pathogenesis of BCCV infection in juvenile hispid cotton rats. For example, the six animals inoculated with 3.1 or 1.1 log(10) ID(50-VeroE6) and euthanized on day 54 PI were virus positive and antibody positive, whereas the six animals inoculated with -0.9 or -2.9 log(10) ID(50-VeroE6) and euthanized on day 54 PI were virus positive but antibody negative. Microscopic examination of tissues from the animals inoculated with 3.1 or 1.1 log(10) ID(50-VeroE6) revealed diffuse, subacute pneumonitis in the lungs of all the animals euthanized on day 18 PI or thereafter, and indicated that the severity of pneumonitis was dependent upon inoculum dose as well as duration of infection (i.e., amount of time elapsed since inoculation).

Ecology of hantaviruses and their hosts in North America

Since the 1993 discovery of a highly pathogenic hantavirus associated with the North American deer mouse (Peromyscus maniculatus), intensive ecological studies have led to many advances in our understanding of the natural history of New World hantaviruses as it relates to human disease. Seventeen named hantaviruses have been identified in North America. Field and laboratory studies of Sin Nombre and other hantaviruses have delineated host associations, geographical distributions, mechanisms of transmission, temporal infection dynamics of these viruses in host populations, and environmental factors that influence these dynamics. Using data from these studies, preliminary predictive models of the risk of hantavirus infection to humans have been developed. Improved models using satellite-derived data are under development. Multidisciplinary collaboration, integration of field and laboratory studies, and establishment and maintenance of long-term monitoring studies will be critical to continued advancement in the understanding of hantavirus-host ecology and disease prevention in humans.

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.

Extensive host sharing of central European Tula virus

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

Hantavirus evolution in relation to its rodent and insectivore hosts: no evidence for codivergence

Hantaviruses are considered one of the best examples of a long-term association between RNA viruses and their hosts. Based on the appearance of strong host specificity, it has been suggested that hantaviruses cospeciated with the rodents and insectivores they infect since these mammals last shared a common ancestor, approximately 100 million years ago. We tested this hypothesis of host-virus codivergence in two ways: 1) we used cophylogenetic reconciliation analysis to assess the fit of the virus tree onto that of the host and 2) we estimated the evolutionary rates and divergence times for the Hantavirus genus using a Bayesian Markov Chain Monte Carlo method and similarly compared these with those of their hosts. Our reconciliation analysis provided no evidence for a history of codivergence between hantaviruses and their hosts. Further, the divergence times for the Hantavirus genus were many orders of magnitude too recent to correspond with the timescale of their hosts' speciation. We therefore propose that apparent similarities between the phylogenies of hantaviruses and their mammalian hosts are the result of a more recent history of preferential host switching and local adaptation. Based on the presence of clade-defining amino acids in all genomic segments, we propose that the patterns of amino acid replacement in these viruses are also compatible with a history of host-specific adaptation.

Choclo virus infection in the Syrian golden hamster

Andes virus and Choclo virus are agents of hantavirus pulmonary syndrome. Andes virus in hamsters almost always causes a disease that is pathologically indistinguishable from fatal hantavirus pulmonary syndrome. The purpose of this study was to assess the pathogenicity of Choclo virus in hamsters. None of 18 hamsters infected with Choclo virus exhibited any symptom of disease. No evidence of inflammation or edema was found in the lungs of the 10 animals killed on days 7, 9, 11, 13, and 16 post-inoculation or in the lungs of the 8 animals killed on day 28 post-inoculation; however, hantavirus antigen was present in large numbers of endothelial cells in the microvasculature of the lungs of the animals killed on days 7, 9, 11, and 13 post-inoculation. These results suggest that infection in the microvasculature of lung tissue alone does not result in the life-threatening pulmonary edema in hamsters infected with Andes virus.

Genetic characterization and phylogeny of a hantavirus from Western Mexico

Hantaviruses can cause two serious illnesses when transmitted from their rodent reservoirs to humans; hantavirus pulmonary syndrome (HPS) in the New World and hemorrhagic fever with renal syndrome in the Old World. Cases of HPS were first recognized in the Americas in small, focal outbreaks in rural populations in the Southwestern USA in 1993. Since that time, outbreaks as well as sporadic cases of HPS have been recognized throughout the Americas. Remarkably, HPS cases have not been reported in Mexico. Mexico is one of the most biodiverse regions in the world and this is reflected in the species diversity of the peromyscine, sigmodontine and oryzomyine rodents; all potential hosts of hantaviruses. Hence, we collected and surveyed several rodent species in Western Mexico and identified three previously unrecognized rodents with antibodies to hantaviral antigens: Oryzomys couesi, Sigmodon mascotensis and Baiomys musculus. The S and M segments cloned from O. couesi and S. mascotensis, referred to herein as Playa de Oro (ORO) virus, showed strongest similarity to Bayou and Catacamas viruses with 92/93% and 92/92% similarity based on S/M amino acid sequences, respectively. This and phylogenetic analysis of the M and S segments suggests that ORO virus is a unique genotype within Hantavirus.

Hantavirus and arenavirus antibodies in persons with occupational rodent exposure

Risk for infection was low among those who handled neotomine or sigmodontine rodents on the job.

Rodents are the principal hosts of Sin Nombre virus, 4 other hantaviruses known to cause hantavirus pulmonary syndrome in North America, and the 3 North American arenaviruses. Serum samples from 757 persons who had worked with rodents in North America and handled neotomine or sigmodontine rodents were tested for antibodies against Sin Nombre virus, Whitewater Arroyo virus, Guanarito virus, and lymphocytic choriomeningitis virus. Antibodies against Sin Nombre virus were found in 4 persons, against Whitewater Arroyo virus or Guanarito virus in 2 persons, and against lymphocytic choriomeningitis virus in none. These results suggest that risk for infection with hantaviruses or arenaviruses usually is low in persons whose occupations entail close physical contact with neotomine or sigmodontine rodents in North America.

Phylogenetic and geographical relationships of hantavirus strains in eastern and western Paraguay

Recently, we reported the discovery of several potential rodent reservoirs of hantaviruses in western (Holochilus chacarius) and eastern Paraguay (Akodon montensis, Oligoryzomys chacoensis, and O. nigripes). Comparisons of the hantavirus S- and M-segments amplified from these four rodents revealed significant differences from each another and from other South American hantaviruses. The ALP strain from the semiarid Chaco ecoregion clustered with Leguna Negra and Rio Mamore (LN/RM), whereas the BMJ-NEB strain from the more humid lower Chaco ecoregion formed a clade with Oran and Bermejo. The other two strains, AAI and IP37/38, were distinct from known hantaviruses. With respect to the S-segment sequence, AAI from eastern Paraguay formed a clade with ALP/LN/RM, but its M-segment clustered with Pergamino and Maciel, suggesting a possible reassortment. AAI was found in areas experiencing rapid land cover fragmentation and change within the Interior Atlantic Forest. IP37/38 did not show any strong association with any of the known hantavirus strains.

Catacamas virus, a hantaviral species naturally associated with Oryzomys couesi (Coues' oryzomys) in Honduras

The primary objective of this study was to extend our knowledge of the geographical distribution, genetic diversity, and natural host associations of the hantaviruses indigenous to North America. Antibody to a hantavirus was found in 5 (20.8%) of 24 Coues' oryzomys (Oryzomys couesi) and none of 41 other rodents captured near the town of Catacamas in eastern Honduras, and a hantavirus was isolated from one of the antibody-positive Coues' oryzomys. Analyses of nucleotide and amino acid sequence data indicated that the viral isolate is a strain of a novel hantaviral species (proposed species name "Catacamas virus") that is phylogenetically most closely related to Bayou virus, a hantaviral species that is principally associated with Oryzomys palustris (marsh oryzomys) in the southeastern United States. Catacamas virus is the first evidence for the occurrence of a hantaviral species in Honduras and the first evidence that a hantaviral species is naturally associated with an Oryzomys species other than O. palustris.

Puumala hantavirus in Slovenia: analyses of S and M segment sequences recovered from patients and rodents

In Slovenia, the co-existence of Dobrava and Puumala (PUUV) hantaviruses in a single endemic region has been demonstrated. This study presents selected Slovenian HFRS cases caused by PUUV combined with genetic analysis of viral genome sequences recovered from clinical specimens and tissue samples of Clethrionomys glareolus (bank voles). Serum samples from nine HFRS patients were included in the study. Rodents study sites were selected with regard to the HFRS cases. Partial S segment sequences were recovered from all nine patients and partial M segment sequences could be recovered from seven. Partial S and M segments sequences were also recovered from five C. glareouls captured at three different study sites. The sequences from Slovenian clinical specimens and rodent tissue samples belonged to the PUUV genotype and formed a distinct genetic lineage of PUUV. Human and rodent PUUV sequences located in the closest proximity to each other on the phylogenetic trees suggest genetic links between the human cases and the hantaviral strains circulating in natural foci of this zoonotic infection. Analysis of the complete S segment sequences recovered for two wild-type PUUV strains confirmed the existence of a distinct genetic lineage and also indicated a possible quasispecies type of Slovenian PUUV.

New Ecological Aspects of Hantavirus Infection: A Change of A Paradigm and a Challenge of Prevention- A Review

In the last decades a significant number of so far unknown or underestimated pathogens have emerged as fundamental health hazards of the human population despite intensive research and exceptional efforts of modern medicine to embank and eradicate infectious diseases. Almost all incidents caused by such emerging pathogens could be ascribed to agents that are zoonotic or expanded their host range and crossed species barriers. Many different factors influence the status of a pathogen to remain unnoticed or evolves into a worldwide threat. The ability of an infectious agent to adapt to changing environmental conditions and variations in human behavior, population development, nutrition, education, social, and health status are relevant factors affecting the correlation between pathogen and host. Hantaviruses belong to the emerging pathogens having gained more and more attention in the last decades. These viruses are members of the family Bunyaviridae and are grouped into a separate genus known as Hantavirus. The serotypes Hantaan (HTN), Seoul (SEO), Puumala (PUU), and Dobrava (DOB) virus predominantly cause hemorrhagic fever with renal syndrome (HFRS), a disease characterized by renal failure, hemorrhages, and shock. In the recent past, many hantavirus isolates have been identified and classified in hitherto unaffected geographic regions in the New World (North, Middle, and South America) with characteristic features affecting the lungs of infected individuals and causing an acute pulmonary syndrome. Hantavirus outbreaks in the United States of America at the beginning of the 10th decade of the last century fundamentally changed our knowledge about the appearance of the hantavirus specific clinical picture, mortality, origin, and transmission route in human beings. The hantavirus pulmonary syndrome (HPS) was first recognized in 1993 in the Four Corners Region of the United States and had a lethality of more than 50%. Although the causative virus was first termed in connection with the geographic name of its outbreak region the analysis of the individual viruses indicate that the causing virus of HPS was a genetically distinct hantavirus and consequently termed as Sin Nombre virus. Hantaviruses are distributed worldwide and are assumed to share a long time period of co-evolution with specific rodent species as their natural reservoir. The degree of relatedness between virus serotypes normally coincides with the relatedness between their respective hosts. There are no known diseases that are associated with hantavirus infections in rodents underlining the amicable relationship between virus and host developed by mutual interaction in hundreds of thousands of years. Although rodents are the major reservoir, antibodies against hantaviruses are also present in domestic and wild animals like cats, dogs, pigs, cattle, and deer. Domestic animals and rodents live jointly in a similar habitat. Therefore the transmission of hantaviruses from rodents to domestic animals seems to be possible, if the target organs, tissues, and cell parenchyma of the co-habitat domestic animals possess adequate virus receptors and are suitable for hantavirus entry and replication. The most likely incidental infection of species other than rodents as for example humans turns hantaviruses from harmless to life-threatening pathogenic agents focusing the attention on this virus group, their ecology and evolution in order to prevent the human population from a serious health risk. Much more studies on the influence of non-natural hosts on the ecology of hantaviruses are needed to understand the directions that the hantavirus evolution could pursue. At least, domestic animals that share their environmental habitat with rodents and humans particularly in areas known as high endemic hantavirus regions have to be copiously screened. Each transfer of hantaviruses from their original natural hosts to other often incidental hosts is accompanied by a change of ecology, a change of environment, a modulation of numerous factors probably influencing the pathogenicity and virulence of the virus. The new environment exerts a modified evolutionary pressure on the virus forcing it to adapt and probably to adopt a form that is much more dangerous for other host species compared to the original one.

Outbreak of hantavirus pulmonary syndrome, Los Santos, Panama, 1999-2000

An outbreak of hantavirus pulmonary syndrome occurred in the province of Los Santos, Panama, in late 1999 and early 2000. Eleven cases were identified; 9 were confirmed by serology. Three cases were fatal; however, no confirmed case-patient died. Case-neighborhood serologic surveys resulted in an overall hantavirus antibody prevalence of 13% among household and neighborhood members from the outbreak foci. Epidemiologic investigations did not suggest person-to-person transmission of hantavirus infection. By use of Sin Nombre virus antigen, hantavirus antibodies were detected in Oligoryzomys fulvescens and Zygodontomys brevicauda cherriei. This outbreak resulted in the first documented cases of human hantavirus infections in Central America.

Maporal virus, a hantavirus associated with the fulvous pygmy rice rat (Oligoryzomys fulvescens) in western Venezuela

Oryzomine rodents in the southeastern United States, Panama, and southern South America are natural hosts of 6 of the 13 viruses known to cause hantavirus pulmonary syndrome. The purpose of this study was to extend our knowledge of the geographical distribution and genetic diversity of the hantaviruses associated with oryzomine rodents in South America. An infectious hantavirus was isolated from two fulvous pygmy rice rats captured in western Venezuela. Analyses of complete nucleocapsid protein and glycoprotein precursor sequences indicated that the isolates are strains of a novel hantavirus (proposed name "Maporal") which is phylogenetically most closely related to the viruses known to cause hantavirus pulmonary syndrome in southern South America.

Bovine aortic endothelial cells are susceptible to hantavirus infection; a new aspect in hantavirus ecology

Hantaviruses are enveloped RNA viruses that belong to the family Bunyaviridae. They are the causative agents of hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Hantaviruses show a worldwide distribution with specific rodent species as natural hosts. It is known that rodents can transmit the virus via feces, urine, saliva, or bites to humans. Additionally, antibodies against different hantaviruses were also found in domestic animals, For example, Danes et al. documented hantavirus-specific IgG titers in 2% of examined cattle [Ceskoslov. Epidemiol. Mikrobiol. Imunol. 41 (1992) 15]. In order to clarify the possibility of a nonrodent and nonhuman hantavirus infection, the susceptibility of bovine aortic endothelial cells (BAEC) to Hantavirus serotype Puumala infection was investigated. The hantaviral nucleocapsid protein was detected in 95% of infected BAEC at the fourth cell culture passage 12 weeks after initial infection by immunofluorescence assay (IFA). The presence of Puumala virus (PUU) nucleocapsid protein and the viral glycoproteins G1 and G2 in infected cells were additionally confirmed by Western blot analysis. The viral RNA genome was identified in infected BAEC cultures and in cell-free culture medium at the fourth passage by reverse transcription polymerase chain reaction (RT-PCR), verified by cDNA nucleotide sequence analysis, showing a 98-100% homology to the input virus. The infected BAEC cultures were shown to express alpha(V)beta(3)-integrin surface receptors that are known to mediate virus entry in human cells and revealed no major cytopathic effects (CPEs) as assayed by immunofluorescence staining of the cytoskeletal components actin and microtubules. In the present study, we documented for the first time that a nonrodent and nonhuman aortic endothelial cell culture of bovine origin (BAEC) can be efficiently infected with a hantavirus. This finding is of particular importance because it adds new aspects to questions dealing with host species barrier, viral reservoir, virus transmission, and ecology of hantaviruses.

Experimental evaluation of rodent exclusion methods to reduce hantavirus transmission to residents in a Native American community in New Mexico

We conducted a pilot study to evaluate the efficacy of rodent proofing continuously occupied homes as a method for lowering the risk for hantavirus pulmonary syndrome (HPS) among residents of a Native American community in northwestern New Mexico. Rodent proofing of dwellings was paired with culturally appropriate health education. Seventy homes were randomly assigned to treatment or control categories. Treatment homes were rodent-proofed by sealing openings around foundations, doors, roofs, and pipes and repairing screens and windows. Repairs to each dwelling were limited to $500 US. After repairs were completed, 15-20 snap traps were placed in each treatment and control home and checked approximately every 2 days for an average of 3-4 weeks. During 23,373 trap nights, one house mouse (Mus musculus) was captured in one treatment home, and 20 mice (16 deer mice, Peromyscus maniculatus, two Pinyon mice, Peromyscus truei, and two unidentified mice) were captured in five control homes (one house had 14 captures, two had two captures, and two had one capture). Trap success was 0.01% in treatment homes and 0.15% in controls. Intensity of infestation (mean number of mice captured per infested home) was 1 in treatment homes and 4 in controls. Observations of evidence of infestation (feces, nesting material, gnaw marks, or reports of infestation by occupant) per 100 days of observation were 1.2 in treatment homes and 3.1 in controls. Statistical power of the experiment was limited because it coincided with a period of low rodent abundance (August-November 2000). Nevertheless, these results suggest that inexpensive rodent proofing of occupied rural homes can decrease the frequency and intensity of rodent intrusion, thereby reducing the risk of HPS among rural residents in the southwestern United States.

Hantavirus immunology

Two clinical syndromes are associated with hantavirus infection in humans: hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Autopsy findings typically reveal a common feature of increased permeability in microvascular beds, suggesting vascular endothelium is a prime target for virus infection. Endothelial cells are susceptible to hantavirus infection; however, virus does not cause cytopathic effects, to explain increased endothelium permeability. Therefore, immune mechanisms were suggested to play a crucial role in hantavirus pathogenesis. In this review, we summarize data on hantavirus-induced immune disturbances and discuss their implication in capillary leakage caused by hantavirus infection.

Analysis of hantavirus genetic diversity in Argentina: S segment-derived phylogeny

Nucleotide sequences were determined for the complete S genome segments of the six distinct hantavirus genotypes from Argentina and for two cell culture-isolated Andes virus strains from Chile. Phylogenetic analysis indicates that, although divergent from each other, all Argentinian hantavirus genotypes group together and form a novel phylogenetic clade with the Andes virus. The previously characterized South American hantaviruses Laguna Negra virus and Rio Mamore virus make up another clade that originates from the same ancestral node as the Argentinian/Chilean viruses. Within the clade of Argentinian/Chilean viruses, three subclades can be defined, although the branching order is somewhat obscure. These are made of (i) "Lechiguanas-like" virus genotypes, (ii) Maciel virus and Pergamino virus genotypes, and (iii) strains of the Andes virus. Two hantavirus genotypes from Brazil, Araraquara and Castello dos Sonhos, were found to group with Maciel virus and Andes virus, respectively. The nucleocapsid protein amino acid sequence variability among the members of the Argentinian/Chilean clade does not exceed 5.8%. It is especially low (3.5%) among oryzomyine species-associated virus genotypes, suggesting recent divergence from the common ancestor. Interestingly, the Maciel and Pergamino viruses fit well with the rest of the clade although their hosts are akodontine rodents. Taken together, these data suggest that under conditions in which potential hosts display a high level of genetic diversity and are sympatric, host switching may play a prominent role in establishing hantavirus genetic diversity. However, cospeciation still remains the dominant factor in the evolution of hantaviruses.

Genetic and serotypic characterization of Sin Nombre-like viruses in Canadian Peromyscus maniculatus mice

In Canada, hantavirus infected deer mice (Peromyscus maniculatus) have been collected from British Columbia to Newfoundland. Partial sequencing of G1 and N protein encoding regions from Canadian Peromyscus maniculatus-borne hantaviruses demonstrated the existence of significant genotypic divergence among strains. Phylogenetic analysis showed that Sin Nombre (SN)-like viruses from eastern and western Canadian deer mice can be divided into at least two broad-based genogroups. Sequencing of mitochondrial DNA from infected deer mice originating from various eastern and western provinces showed that SN-like virus genogroups appeared to be associated with distinct haplotypes of mice. Sera from deer mice infected with eastern and western viral genotypes neutralized the Sin Nombre virus strain, Convict Creek 107, but not the New York 1 hantavirus. Despite the genetic heterogeneity of Canadian SN-like strains these hantaviruses do not appear to define unique hantavirus serotypes.

Cellular receptors and hantavirus pathogenesis

Hantaviruses cause two potentially lethal diseases, HPS and HFRS, and both diseases result in defects in vascular permeability and platelet function. Human beta 3 integrins confer cellular susceptibility to HPS- and HFRS-causing hantaviruses, a fact directly linking platelets, endothelial cells, and hantavirus diseases to the use of [figure: see text] cellular receptors that maintain capillary integrity and regulate platelet function. The role of vitronectin, PAI-1, uPAR, and complement cascades in hantavirus pathogenesis are unstudied but may contribute to specific disease syndromes effected by hantaviruses. The divergence of hantavirus surface glycoproteins and common beta 3-integrin usage provides further insight into the interaction of hantaviruses with cells. G1 and G2 glycoprotein variation is likely to contribute to additional interactions that determine pathogenic responses to individual viruses. beta 3-integrin usage also suggests that common elements exist on G1 or the more highly conserved G2 surface glycoprotein, which mediate viral attachment to integrins. Although there is currently no data defining the virion attachment protein, the development of antibodies that recognize the hantavirus attachment protein and block integrin interactions is of interest since it is likely to provide an additional point for therapeutic intervention and vaccine development. There are a plethora of effects that could be elicited by hantavirus regulation of cellular beta 3 integrins and their ligands that are consistent with hantavirus diseases. Since beta 3 integrins are critical adhesive receptors on platelets and endothelial cells and regulate both vascular permeability and platelet activation and adhesion, the use of these receptors by hantaviruses is likely to be fundamental to hantavirus pathogenesis. The lack of an animal model for hantavirus pathogenesis has prevented a systematic analysis of immune and cellular responses to hantavirus infections, and it impedes our ability to study protective or therapeutic approaches to hantavirus diseases. However, recent findings suggest that human beta 3 integrins within transgenic mice may provide animal models of hantavirus pathogenesis and have the potential to radically alter the ability to investigate hantavirus disease.

Evolutionary diversification of protein-coding genes of hantaviruses

Phylogenetic analyses of the S:, M, and L: genes of the hantaviruses (Bunyaviridae: Hantavirus) revealed three well-differentiated clades corresponding to viruses parasitic on three subfamilies (Murinae, Arvicolinae, and Sigmodontinae) of the rodent family Muridae. In rooted trees of M: and L: genes, the viruses with hosts belonging to Murinae formed an outgroup to those with hosts in Arvicolinae and Sigmodontinae. This phylogeny corresponded with a phylogeny of the murid subfamilies based on mitochondrial cytochrome b sequences, supporting the hypothesis that hantaviruses have coevolved with their mammalian hosts at least since the common ancestor of these three subfamilies, which probably occurred about 50 MYA. The nucleocapsid protein (encoded by the S: gene) differentiated among the viruses parasitic on the three subfamilies in such a way that a high frequency of amino acid residue charge changes occurred in a hypervariable (HV) portion of the molecule, and nonsynonymous nucleotide differences causing amino acid charge changes in the HV region occurred significantly more frequently than expected under random substitution. Along with evidence that at least in some hantaviruses the HV region is a target for host antibodies and the known importance of charged residues in determining antibody epitopes, these results suggest that changes in the HV region may represent adaptation to host-specific characteristics of the immune response.

Emerging infectious diseases in the 21st century

The emergence of novel infectious diseases, and the re-emergence of others, is not new. The global ecosystem is constantly changing, influencing the micro- and macroenvironments in which humans and their microbial companions reside and interact. Sometimes the environmental circumstances favour the pathogen and there is an unexpected increase in disease activity or emergence of a new infection. Alternatively, pathogenicity factors are acquired by the microbe, allowing new diseases to emerge or old diseases to increase in importance. The forces that drive the emergence, submergence and re-emergence of infectious diseases are varied, but the influence that humans have on the global ecosystem is often of central importance. This review considers infections that are of particular emerging importance.

Transmission of Black Creek Canal virus between cotton rats

Black Creek Canal (BCC) virus is a hantavirus associated with hantavirus pulmonary syndrome in southeastern North America. The virus was isolated from the spleen of a cotton rat (Sigmodon hispidus) trapped in southern Florida. Our previous studies have shown that we could consistently infect male cotton rats with BCC virus in the laboratory. These animals became persistently infected and virus could be detected in salivary glands, urine, and feces. In this report we show: (1) female and male cotton rats are equally susceptible to BCC virus infection, (2) susceptibility to infection was not influenced by age, (3) all inoculated rats transmitted the infection to uninoculated cage mates, and (4) offspring of infected rats became infected despite the presence of high maternal antibodies. The course of BCC virus infection, as determined by antibody response and the ability to isolate or detect virus, appeared to be similar regardless of whether the rats obtained their infection by inoculation or contact with inoculated rats. J. Med. Virol. 60:70-76, 2000. Published 2000 Wiley-Liss, Inc.

Hantavirus pulmonary syndrome associated with Monongahela virus, Pennsylvania

The first two recognized cases of rapidly fatal hantavirus pulmonary syndrome in Pennsylvania occurred within an 8-month period in 1997. Illness in the two patients was confirmed by immunohistochemical techniques on autopsy material. Reverse transcription-polymerase chain reaction analysis of tissue from one patient and environmentally associated Peromyscus leucopus (white-footed mouse) identified the Monongahela virus variant. Physicians should be vigilant for such Monongahela virus-associated cases in the eastern United States and Canada, particularly in the Appalachian region.