Genomic and phylogenetic characterization of Merino Walk virus, a novel arenavirus isolated in South Africa

Mammarenaviruses of Rodents, South Africa and Zimbabwe

We conducted a survey for group-specific indirect immunofluorescence antibody to mammarenaviruses by using Lassa fever and Mopeia virus antigens on serum specimens of 5,363 rodents of 33 species collected in South Africa and Zimbabwe during 1964-1994. Rodents were collected for unrelated purposes or for this study and stored at -70°C. We found antibody to be widely distributed in the 2 countries; antibody was detected in serum specimens of 1.2%-31.8% of 14 species of myomorph rodents, whereas 19 mammarenavirus isolates were obtained from serum specimens and viscera of 4 seropositive species. Phylogenetic analysis on the basis of partial nucleoprotein sequences indicates that 14 isolates from Mastomys natalensis, the Natal multimammate mouse, were Mopeia virus, whereas Merino Walk virus was characterized as a novel virus in a separate study. The remaining 4 isolates from 3 rodent species potentially constitute novel viruses pending full characterization.

Multiple Mammarenaviruses Circulating in Angolan Rodents

Rodents are a speciose group of mammals with strong zoonotic potential. Some parts of Africa are still underexplored for the occurrence of rodent-borne pathogens, despite this high potential. Angola is at the convergence of three major biogeographical regions of sub-Saharan Africa, each harbouring a specific rodent community. This rodent-rich area is, therefore, strategic for studying the diversity and evolution of rodent-borne viruses. In this study we examined 290 small mammals, almost all rodents, for the presence of mammarenavirus and hantavirus RNA. While no hantavirus was detected, we found three rodent species positive for distinct mammarenaviruses with a particularly high prevalence in Namaqua rock rats (Micaelamys namaquensis). We characterised four complete virus genomes, which showed typical mammarenavirus organisation. Phylogenetic and genetic distance analyses revealed: (i) the presence of a significantly divergent strain of Luna virus in Angolan representatives of the ubiquitous Natal multimammate mouse (Mastomys natalensis), (ii) a novel Okahandja-related virus associated with the Angolan lineage of Micaelamys namaquensis for which we propose the name Bitu virus (BITV) and (iii) the occurrence of a novel Mobala-like mammarenavirus in the grey-bellied pygmy mouse (Mus triton) for which we propose the name Kwanza virus (KWAV). This high virus diversity in a limited host sample size and in a relatively small geographical area supports the idea that Angola is a hotspot for mammarenavirus diversity.

Taxonomy of the family Arenaviridae and the order Bunyavirales: update 2018

In 2018, the family Arenaviridae was expanded by inclusion of 1 new genus and 5 novel species. At the same time, the recently established order Bunyavirales was expanded by 3 species. This article presents the updated taxonomy of the family Arenaviridae and the order Bunyavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV) and summarizes additional taxonomic proposals that may affect the order in the near future.

Evolutionary analysis of Old World arenaviruses reveals a major adaptive contribution of the viral polymerase

The Old World (OW) arenavirus complex includes several species of rodent-borne viruses, some of which (i.e., Lassa virus, LASV and Lymphocytic choriomeningitis virus, LCMV) cause human diseases. Most LCMV and LASV infections are caused by rodent-to-human transmissions. Thus, viral evolution is largely determined by events that occur in the wildlife reservoirs. We used a set of human- and rodent-derived viral sequences to investigate the evolutionary history underlying OW arenavirus speciation, as well as the more recent selective events that accompanied LASV spread in West Africa. We show that the viral RNA polymerase (L protein) was a major positive selection target in OW arenaviruses and during LASV out-of-Nigeria migration. No evidence of selection was observed for the glycoprotein, whereas positive selection acted on the nucleoprotein (NP) during LCMV speciation. Positively selected sites in L and NP are surrounded by highly conserved residues, and the bulk of the viral genome evolves under purifying selection. Several positively selected sites are likely to modulate viral replication/transcription. In both L and NP, structural features (solvent exposed surface area) are important determinants of site-wise evolutionary rate variation. By incorporating several rodent-derived sequences, we also performed an analysis of OW arenavirus codon adaptation to the human host. Results do not support a previously hypothesized role of codon adaptation in disease severity for non-Nigerian strains. In conclusion, L and NP represent the major selection targets and possible determinants of disease presentation; these results suggest that field surveys and experimental studies should primarily focus on these proteins.

Taxonomic Changes and Additions for Human and Animal Viruses, 2012 to 2015

Taxonomical classification of newly discovered viruses and reclassification of previously discovered viruses provide an important foundation for detailing biological differences of scientific and clinical interest. The development of molecular analytical methods has enabled finer levels and more precise levels of classification. Periodically, there is need to refresh the literature and common understanding of current taxonomic classification, which we attempt to do here in addressing changes in human and animal viruses of medical significance between 2012 and 2015.

Small-Molecule Fusion Inhibitors Bind the pH-Sensing Stable Signal Peptide-GP2 Subunit Interface of the Lassa Virus Envelope Glycoprotein

Arenavirus species are responsible for severe life-threatening hemorrhagic fevers in western Africa and South America. Without effective antiviral therapies or vaccines, these viruses pose serious public health and biodefense concerns. Chemically distinct small-molecule inhibitors of arenavirus entry have recently been identified and shown to act on the arenavirus envelope glycoprotein (GPC) to prevent membrane fusion. In the tripartite GPC complex, pH-dependent membrane fusion is triggered through a poorly understood interaction between the stable signal peptide (SSP) and the transmembrane fusion subunit GP2, and our genetic studies have suggested that these small-molecule inhibitors act at this interface to antagonize fusion activation. Here, we have designed and synthesized photoaffinity derivatives of the 4-acyl-1,6-dialkylpiperazin-2-one class of fusion inhibitors and demonstrate specific labeling of both the SSP and GP2 subunits in a native-like Lassa virus (LASV) GPC trimer expressed in insect cells. Photoaddition is competed by the parental inhibitor and other chemically distinct compounds active against LASV, but not those specific to New World arenaviruses. These studies provide direct physical evidence that these inhibitors bind at the SSP-GP2 interface. We also find that GPC containing the uncleaved GP1-GP2 precursor is not susceptible to photo-cross-linking, suggesting that proteolytic maturation is accompanied by conformational changes at this site. Detailed mapping of residues modified by the photoaffinity adducts may provide insight to guide the further development of these promising lead compounds as potential therapeutic agents to treat Lassa hemorrhagic fever.

IMPORTANCE

Hemorrhagic fever arenaviruses cause lethal infections in humans and, in the absence of licensed vaccines or specific antiviral therapies, are recognized to pose significant threats to public health and biodefense. Lead small-molecule inhibitors that target the arenavirus envelope glycoprotein (GPC) have recently been identified and shown to block GPC-mediated fusion of the viral and cellular endosomal membranes, thereby preventing virus entry into the host cell. Genetic studies suggest that these inhibitors act through a unique pH-sensing intersubunit interface in GPC, but atomic-level structural information is unavailable. In this report, we utilize novel photoreactive fusion inhibitors and photoaffinity labeling to obtain direct physical evidence for inhibitor binding at this critical interface in Lassa virus GPC. Future identification of modified residues at the inhibitor-binding site will help elucidate the molecular basis for fusion activation and its inhibition and guide the development of effective therapies to treat arenaviral hemorrhagic fevers.

Past, present, and future of arenavirus taxonomy

Until recently, members of the monogeneric family Arenaviridae (arenaviruses) have been known to infect only muroid rodents and, in one case, possibly phyllostomid bats. The paradigm of arenaviruses exclusively infecting small mammals shifted dramatically when several groups independently published the detection and isolation of a divergent group of arenaviruses in captive alethinophidian snakes. Preliminary phylogenetic analyses suggest that these reptilian arenaviruses constitute a sister clade to mammalian arenaviruses. Here, the members of the International Committee on Taxonomy of Viruses (ICTV) Arenaviridae Study Group, together with other experts, outline the taxonomic reorganization of the family Arenaviridae to accommodate reptilian arenaviruses and other recently discovered mammalian arenaviruses and to improve compliance with the Rules of the International Code of Virus Classification and Nomenclature (ICVCN). PAirwise Sequence Comparison (PASC) of arenavirus genomes and NP amino acid pairwise distances support the modification of the present classification. As a result, the current genus Arenavirus is replaced by two genera, Mammarenavirus and Reptarenavirus, which are established to accommodate mammalian and reptilian arenaviruses, respectively, in the same family. The current species landscape among mammalian arenaviruses is upheld, with two new species added for Lunk and Merino Walk viruses and minor corrections to the spelling of some names. The published snake arenaviruses are distributed among three new separate reptarenavirus species. Finally, a non-Latinized binomial species name scheme is adopted for all arenavirus species. In addition, the current virus abbreviations have been evaluated, and some changes are introduced to unequivocally identify each virus in electronic databases, manuscripts, and oral proceedings.

The search for animal models for Lassa fever vaccine development

Lassa virus (LASV) is the most prevalent arenavirus in West Africa and is responsible for several hundred thousand infections and thousands of deaths annually. The sizeable disease burden, numerous imported cases of Lassa fever (LF) and the possibility that LASV can be used as an agent of biological warfare make a strong case for vaccine development. Currently there is no licensed LF vaccine and research and devlopment is hampered by the high cost of nonhuman primate animal models and by biocontainment requirements (BSL-4). In addition, a successful LF vaccine has to induce a strong cell-mediated cross-protective immunity against different LASV lineages. All of these challenges will be addressed in this review in the context of available and novel animal models recently described for evaluation of LF vaccine candidates.

Reservoirs and vectors of emerging viruses

Wildlife, especially mammals and birds, are hosts to an enormous number of viruses, most of which we have absolutely no knowledge about even though we know these viruses circulate readily in their specific niches. More often than not, these viruses are silent or asymptomatic in their natural hosts. In some instances, they can infect other species, and in rare cases, this cross-species transmission might lead to human infection. There are also instances where we know the reservoir hosts of zoonotic viruses that can and do infect humans. Studies of these animal hosts, the reservoirs of the viruses, provide us with the knowledge of the types of virus circulating in wildlife species, their incidence, pathogenicity for their host, and in some instances, the potential for transmission to other hosts. This paper describes examples of some of the viruses that have been detected in wildlife, and the reservoir hosts from which they have been detected. It also briefly explores the spread of arthropod-borne viruses and their diseases through the movement and establishment of vectors in new habitats.

Arenavirus budding: a common pathway with mechanistic differences

The Arenaviridae is a diverse and growing family of viruses that includes several agents responsible for important human diseases. Despite the importance of this family for public health, particularly in Africa and South America, much of its biology remains poorly understood. However, in recent years significant progress has been made in this regard, particularly relating to the formation and release of new enveloped virions, which is an essential step in the viral lifecycle. While this process is mediated chiefly by the viral matrix protein Z, recent evidence suggests that for some viruses the nucleoprotein (NP) is also required to enhance the budding process. Here we highlight and compare the distinct budding mechanisms of different arenaviruses, concentrating on the role of the matrix protein Z, its known late domain sequences, and the involvement of cellular endosomal sorting complex required for transport (ESCRT) pathway components. Finally we address the recently described roles for the nucleoprotein NP in budding and ribonucleoprotein complex (RNP) incorporation, as well as discussing possible mechanisms related to its involvement.

Arenavirus variations due to host-specific adaptation

Arenavirus particles are enveloped and contain two single-strand RNA genomic segments with ambisense coding. Genetic plasticity of the arenaviruses comes from transcription errors, segment reassortment, and permissive genomic packaging, and results in their remarkable ability, as a group, to infect a wide variety of hosts. In this review, we discuss some in vitro studies of virus genetic and phenotypic variation after exposure to selective pressures such as high viral dose, mutagens and antivirals. Additionally, we discuss the variation in vivo of selected isolates of Old World arenaviruses, particularly after infection of different animal species. We also discuss the recent emergence of new arenaviruses in the context of our observations of sequence variations that appear to be host-specific.

Vaccine Platforms to Control Arenaviral Hemorrhagic Fevers

Arenaviruses are rodent-borne emerging human pathogens. Diseases caused by these viruses, e.g., Lassa fever (LF) in West Africa and South American hemorrhagic fevers (HFs), are serious public health problems in endemic areas. We have employed replication-competent and replication-deficient strategies to design vaccine candidates potentially targeting different groups "at risk". Our leader LF vaccine candidate, the live reassortant vaccine ML29, is safe and efficacious in all tested animal models including non-human primates. In this study we showed that treatment of fatally infected animals with ML29 two days after Lassa virus (LASV) challenge protected 80% of the treated animals. In endemic areas, where most of the target population is poor and many live far from health care facilities, a single-dose vaccination with ML29 would be ideal solution. Once there is an outbreak, a fast-acting vaccine or post-exposure prophylaxis would be best. The 2(nd) vaccine technology is based on Yellow Fever (YF) 17D vaccine. We designed YF17D-based recombinant viruses expressing LASV glycoproteins (GP) and showed protective efficacy of these recombinants. In the current study we developed a novel technology to clone LASV nucleocapsid within YF17D C gene. Low immunogenicity and stability of foreign inserts must be addressed to design successful LASV/YFV bivalent vaccines to control LF and YF in overlapping endemic areas of West Africa. The 3(rd) platform is based on the new generation of alphavirus replicon virus-like-particle vectors (VLPV). Using this technology we designed VLPV expressing LASV GP with enhanced immunogenicity and bivalent VLPV expressing cross-reactive GP of Junin virus (JUNV) and Machupo virus (MACV), causative agents of Argentinian and Bolivian HF, respectively. A prime-boost regimen required for VLPV immunization might be practical for medical providers, military, lab personnel, and visitors in endemic areas.

Advanced vaccine candidates for Lassa fever

Lassa virus (LASV) is the most prominent human pathogen of the Arenaviridae. The virus is transmitted to humans by a rodent reservoir, Mastomys natalensis, and is capable of causing lethal Lassa Fever (LF). LASV has the highest human impact of any of the viral hemorrhagic fevers (with the exception of Dengue Fever) with an estimated several hundred thousand infections annually, resulting in thousands of deaths in Western Africa. The sizeable disease burden, numerous imported cases of LF in non-endemic countries, and the possibility that LASV can be used as an agent of biological warfare make a strong case for vaccine development. Presently there is no licensed vaccine against LF or approved treatment. Recently, several promising vaccine candidates have been developed which can potentially target different groups at risk. The purpose of this manuscript is to review the LASV pathogenesis and immune mechanisms involved in protection. The current status of pre-clinical development of the advanced vaccine candidates that have been tested in non-human primates will be discussed. Major scientific, manufacturing, and regulatory challenges will also be considered.

Serological assays based on recombinant viral proteins for the diagnosis of arenavirus hemorrhagic fevers

The family Arenaviridae, genus Arenavirus, consists of two phylogenetically independent groups: Old World (OW) and New World (NW) complexes. The Lassa and Lujo viruses in the OW complex and the Guanarito, Junin, Machupo, Sabia, and Chapare viruses in the NW complex cause viral hemorrhagic fever (VHF) in humans, leading to serious public health concerns. These viruses are also considered potential bioterrorism agents. Therefore, it is of great importance to detect these pathogens rapidly and specifically in order to minimize the risk and scale of arenavirus outbreaks. However, these arenaviruses are classified as BSL-4 pathogens, thus making it difficult to develop diagnostic techniques for these virus infections in institutes without BSL-4 facilities. To overcome these difficulties, antibody detection systems in the form of an enzyme-linked immunosorbent assay (ELISA) and an indirect immunofluorescence assay were developed using recombinant nucleoproteins (rNPs) derived from these viruses. Furthermore, several antigen-detection assays were developed. For example, novel monoclonal antibodies (mAbs) to the rNPs of Lassa and Junin viruses were generated. Sandwich antigen-capture (Ag-capture) ELISAs using these mAbs as capture antibodies were developed and confirmed to be sensitive and specific for detecting the respective arenavirus NPs. These rNP-based assays were proposed to be useful not only for an etiological diagnosis of VHFs, but also for seroepidemiological studies on VHFs. We recently developed arenavirus neutralization assays using vesicular stomatitis virus (VSV)-based pseudotypes bearing arenavirus recombinant glycoproteins. The goal of this article is to review the recent advances in developing laboratory diagnostic assays based on recombinant viral proteins for the diagnosis of VHFs and epidemiological studies on the VHFs caused by arenaviruses.

Molecular surveillance and phylogenetic analysis of Old World arenaviruses in Zambia

In order to survey arenaviruses in the Republic of Zambia, we captured 335 rodents from three cities between 2010 and 2011. Eighteen Luna virus (LUNV) and one lymphocytic choriomeningitis virus (LCMV)-related virus RNAs were detected by one-step RT-PCR from Mastomys natalensis and Mus minutoides, respectively. Four LUNV strains and one LCMV-related virus were isolated, and the whole genome nucleotide sequence was determined by pyrosequencing. Phylogenetic analyses revealed that the LUNV clade consists of two branches that are distinguished by geographical location and that the LCMV-related virus belongs to the LCMV clade, but diverges from the typical LCMVs. Comparison of nucleoprotein amino acid sequences indicated that the LCMV-related virus could be designated a novel arenavirus, which was tentatively named as the Lunk virus. Amino acid sequences of the GP, NP, Z and L proteins showed poor similarity among the three Zambian arenavirus strains, i.e. Luna, Lunk and Lujo virus.

Novel arenavirus, Zambia

To investigate arenavirus in Zambia, we characterized virus from the kidneys of 5 arenavirus RNA–positive rodents (Mastomys natalensis) among 263 captured. Full-genome sequences of the viruses suggested that they were new strains similar to Lassa virus–related arenaviruses. Analyzing samples from additional rodents and other species can elucidate epizootiologic aspects of arenaviruses.

Metagenomics and future perspectives in virus discovery

Monitoring the emergence and re-emergence of viral diseases with the goal of containing the spread of viral agents requires both adequate preparedness and quick response. Identifying the causative agent of a new epidemic is one of the most important steps for effective response to disease outbreaks. Traditionally, virus discovery required propagation of the virus in cell culture, a proven technique responsible for the identification of the vast majority of viruses known to date. However, many viruses cannot be easily propagated in cell culture, thus limiting our knowledge of viruses. Viral metagenomic analyses of environmental samples suggest that the field of virology has explored less than 1% of the extant viral diversity. In the last decade, the culture-independent and sequence-independent metagenomic approach has permitted the discovery of many viruses in a wide range of samples. Phylogenetically, some of these viruses are distantly related to previously discovered viruses. In addition, 60-99% of the sequences generated in different viral metagenomic studies are not homologous to known viruses. In this review, we discuss the advances in the area of viral metagenomics during the last decade and their relevance to virus discovery, clinical microbiology and public health. We discuss the potential of metagenomics for characterization of the normal viral population in a healthy community and identification of viruses that could pose a threat to humans through zoonosis. In addition, we propose a new model of the Koch's postulates named the 'Metagenomic Koch's Postulates'. Unlike the original Koch's postulates and the Molecular Koch's postulates as formulated by Falkow, the metagenomic Koch's postulates focus on the identification of metagenomic traits in disease cases. The metagenomic traits that can be traced after healthy individuals have been exposed to the source of the suspected pathogen.

The curious case of arenavirus entry, and its inhibition

Arenaviruses comprise a diverse family of enveloped negative-strand RNA viruses that are endemic to specific rodent hosts worldwide. Several arenaviruses cause severe hemorrhagic fevers in humans, including Junín and Machupo viruses in South America and Lassa fever virus in western Africa. Arenavirus entry into the host cell is mediated by the envelope glycoprotein complex, GPC. The virion is endocytosed on binding to a cell-surface receptor, and membrane fusion is initiated in response to physiological acidification of the endosome. As with other class I virus fusion proteins, GPC-mediated membrane fusion is promoted through a regulated sequence of conformational changes leading to formation of the classical postfusion trimer-of-hairpins structure. GPC is, however, unique among the class I fusion proteins in that the mature complex retains a stable signal peptide (SSP) as a third subunit, in addition to the canonical receptor-binding and fusion proteins. We will review the curious properties of the tripartite GPC complex and describe evidence that SSP interacts with the fusion subunit to modulate pH-induced activation of membrane fusion. This unusual solution to maintaining the metastable prefusion state of GPC on the virion and activating the class I fusion cascade at acidic pH provides novel targets for antiviral intervention.

Biodefense Oriented Genomic-Based Pathogen Classification Systems: Challenges and Opportunities

Countermeasures that will effectively prevent or diminish the impact of a biological attack will depend on the rapid and accurate generation and analysis of genomic information. Because of their increasing level of sensitivity, rapidly decreasing cost, and their ability to effectively interrogate the genomes of previously unknown organisms, Next Generation Sequencing (NGS) technologies are revolutionizing the biological sciences. However, the exponential accumulation microbial data is equally outpacing the computational performance of existing analytical tools in their ability to translate DNA information into reliable detection, prophylactic and therapeutic countermeasures. It is now evident that the bottleneck for next-generation sequence data analysis will not be solved simply by scaling up our computational resources, but rather accomplished by implementing novel biodefense-oriented algorithms that overcome exiting vulnerabilities of speed, sensitivity and accuracy. Considering these circumstances, this document highlights the challenges and opportunities that biodefense stakeholders must consider in order to exploit more efficiently genomic information and translate this data into integrated countermeasures. The document overviews different genome analysis methods and explains concepts of DNA fingerprints, motif fingerprints, genomic barcodes and genomic signatures. A series of recommendations to promote genomics and bioinformatics as an effective form of deterrence and a valuable scientific platform for rapid technological insertion of detection, prophylactic, therapeutic countermeasures are discussed.

Arenavirus budding

Several arenaviruses cause hemorrhagic fever disease in humans and pose a significant public health concern in their endemic regions. On the other hand, the prototypic arenavirus LCMV is a superb workhorse for the investigation of virus-host interactions and associated disease. The arenavirus small RING finger protein called Z has been shown to be the main driving force of virus budding. The budding activity of Z is mediated by late (L) domain motifs, PT/SAP, and PPXY, located at the C-terminus of Z. This paper will present the current knowledge on arenavirus budding including the diversity of L domain motifs used by different arenaviruses. We will also discuss how improved knowledge of arenavirus budding may facilitate the development of novel antiviral strategies to combat human pathogenic arenaviruses.

Lymphocytic choriomeningitis virus (LCMV) infection of macaques: a model for Lassa fever

Arenaviruses such as Lassa fever virus (LASV) and lymphocytic choriomeningitis virus (LCMV) are benign in their natural reservoir hosts, and can occasionally cause severe viral hemorrhagic fever (VHF) in non-human primates and in human beings. LCMV is considerably more benign for human beings than Lassa virus, however certain strains, like the LCMV-WE strain, can cause severe disease when the virus is delivered as a high-dose inoculum. Here we describe a rhesus macaque model for Lassa fever that employs a virulent strain of LCMV. Since LASV must be studied within Biosafety Level-4 (BSL-4) facilities, the LCMV-infected macaque model has the advantage that it can be used at BSL-3. LCMV-induced disease is rarely as severe as other VHF, but it is similar in cases where vascular leakage leads to lethal systemic failure. The LCMV-infected macaque has been valuable for describing the course of disease with differing viral strains, doses and routes of infection. By monitoring system-wide changes in physiology and gene expression in a controlled experimental setting, it is possible to identify events that are pathognomonic for developing VHF and potential treatment targets.

Novel arenavirus sequences in Hylomyscus sp. and Mus (Nannomys) setulosus from Côte d'Ivoire: implications for evolution of arenaviruses in Africa

This study aimed to identify new arenaviruses and gather insights in the evolution of arenaviruses in Africa. During 2003 through 2005, 1,228 small mammals representing 14 different genera were trapped in 9 villages in south, east, and middle west of Côte d'Ivoire. Specimens were screened by pan-Old World arenavirus RT-PCRs targeting S and L RNA segments as well as immunofluorescence assay. Sequences of two novel tentative species of the family Arenaviridae, Menekre and Gbagroube virus, were detected in Hylomyscus sp. and Mus (Nannomys) setulosus, respectively. Arenavirus infection of Mus (Nannomys) setulosus was also demonstrated by serological testing. Lassa virus was not found, although 60% of the captured animals were Mastomys natalensis. Complete S RNA and partial L RNA sequences of the novel viruses were recovered from the rodent specimens and subjected to phylogenetic analysis. Gbagroube virus is a closely related sister taxon of Lassa virus, while Menekre virus clusters with the Ippy/Mobala/Mopeia virus complex. Reconstruction of possible virus–host co-phylogeny scenarios suggests that, within the African continent, signatures of co-evolution might have been obliterated by multiple host-switching events.

Arenaviruses and hantaviruses: from epidemiology and genomics to antivirals

The arenaviruses and hantaviruses are segmented genome RNA viruses that are hosted by rodents. Due to their association with rodents, they are globally widespread and can infect humans via direct or indirect routes of transmission, causing considerable human morbidity and mortality. Nevertheless, despite their obvious and emerging importance as pathogens, there are currently no effective antiviral drugs (except ribavirin which proved effective against Lassa virus) with which to treat humans infected by any of these viruses. The EU-funded VIZIER project (Comparative Structural Genomics of Viral Enzymes Involved in Replication) was instigated with an ultimate view of contributing to the development of antiviral therapies for RNA viruses, including the arenaviruses and bunyaviruses. This review highlights some of the major features of the arenaviruses and hantaviruses that have been investigated during recent years. After describing their classification and epidemiology, we review progress in understanding the genomics as well as the structure and function of replicative enzymes achieved under the VIZIER program and the development of new disease control strategies.

Novel therapeutic targets for arenavirus hemorrhagic fevers

Several members of the family Arenaviridae can cause severe hemorrhagic fevers in humans, representing a serious public health problem in endemic areas of Africa and South America. The Lassa virus is the most prevalent and dangerous arenavirus, causing over 300,000 infections per year and several thousand deaths. Furthermore, pathogenic arenaviruses are considered as category A potential agents for bioterrorism. Based on the danger of arenaviruses for human health, the increased emergence of new viral species in recent years and the lack of effective tools for their control or prevention, the search for novel antiviral compounds effective against these pathogenic agents is a continuous demanding effort. This article focuses on novel strategies to identify inhibitors for arenavirus therapy, analyzing viral and host proteins essential for virus infection as potential targets for antiviral development.

A specific interaction of small molecule entry inhibitors with the envelope glycoprotein complex of the Junín hemorrhagic fever arenavirus

Arenaviruses are responsible for acute hemorrhagic fevers worldwide and are recognized to pose significant threats to public health and biodefense. Small molecule compounds have recently been discovered that inhibit arenavirus entry and protect against lethal infection in animal models. These chemically distinct inhibitors act on the tripartite envelope glycoprotein (GPC) through its unusual stable signal peptide subunit to stabilize the complex against pH-induced activation of membrane fusion in the endosome. Here, we report the production and characterization of the intact transmembrane GPC complex of Junín arenavirus and its interaction with these inhibitors. The solubilized GPC is antigenically indistinguishable from the native protein and forms a homogeneous trimer in solution. When reconstituted into a lipid bilayer, the purified complex interacts specifically with its cell-surface receptor transferrin receptor-1. We show that small molecule entry inhibitors specific to New World or Old World arenaviruses bind to the membrane-associated GPC complex in accordance with their respective species selectivities and with dissociation constants comparable with concentrations that inhibit GPC-mediated membrane fusion. Furthermore, competitive binding studies reveal that these chemically distinct inhibitors share a common binding pocket on GPC. In conjunction with previous genetic studies, these findings identify the pH-sensing interface of GPC as a highly vulnerable target for antiviral intervention. This work expands our mechanistic understanding of arenavirus entry and provides a foundation to guide the development of small molecule compounds for the treatment of arenavirus hemorrhagic fevers.