New World Arenavirus Biology

Lassa fever diagnostics: past, present, and future

Lassa fever is a unique viral hemorrhagic fever that is endemic in parts of West Africa, primarily Sierra Leone, Guinea, Liberia, and Nigeria. The disease is caused by the Lassa virus, an Old World arenavirus that has as primary reservoir host the multimammate rodent Mastomys nataliensis, which lives in association with humans. Recent estimates suggest LF causes two million cases and 5000-10000 deaths annually, mainly in West Africa. Clinical diagnosis and laboratory confirmation have always been major challenges for effective management and control of the disease in afflicted areas of West Africa. Recent advancements in molecular biology, recombinant DNA technology, and genomics sequencing has facilitated major advancement in development of better diagnostic and surveillance tools for Lassa fever virus. These include, the multiplex, magnetic bead-based immunodiagnostics for both Lassa virus antigens and antibodies; molecular probe-based quantitative real-time PCR for genomic signatures; rapid diagnostics tests that detects the most prevalent West African lineages; and the successful utilization of next-generation sequencing technology to diagnose and characterize Lassa virus in West Africa. These advances will continue to improve disease treatment, control, and prevention. In this review we will discuss progression of Lassa virus diagnostics from the past and into the future.

Coronavirus genomic RNA packaging

RNA viruses carry out selective packaging of their genomes in a variety of ways, many involving a genomic packaging signal. The first coronavirus packaging signal was discovered nearly thirty years ago, but how it functions remains incompletely understood. This review addresses the current state of knowledge of coronavirus genome packaging, which has mainly been studied in two prototype species, mouse hepatitis virus and transmissible gastroenteritis virus. Despite the progress that has been made in the mapping and characterization of some packaging signals, there is conflicting evidence as to whether the viral nucleocapsid protein or the membrane protein plays the primary role in packaging signal recognition. The different models for the mechanism of genomic RNA packaging that have been prompted by these competing views are described. Also discussed is the recent exciting discovery that selective coronavirus genome packaging is critical for in vivo evasion of the host innate immune response.

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Selective incorporation of the coronavirus genome into virions is mediated by a cis-acting RNA packaging signal.

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Packaging signals vary across different coronavirus genera and lineages.

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Different lines of evidence attribute packaging signal recognition to either the nucleocapsid or the membrane protein.

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Selective coronavirus genome packaging plays a role in evasion of host innate immunity.

Identification of a clinical compound losmapimod that blocks Lassa virus entry

Lassa virus (LASV) causes Lassa hemorrhagic fever in humans and poses a significant threat to public health in West Africa. Current therapeutic treatments for Lassa fever are limited, making the development of novel countermeasures an urgent priority. In this study, we identified losmapimod, a p38 mitogen-activated protein kinase (MAPK) inhibitor, from 102 screened compounds as an inhibitor of LASV infection. Losmapimod exerted its inhibitory effect against LASV after p38 MAPK down-regulation, and, interestingly, had no effect on other arenaviruses capable of causing viral hemorrhagic fever. Mechanistic studies showed that losmapimod inhibited LASV entry by affecting the stable signal peptide (SSP)-GP2 subunit interface of the LASV glycoprotein, thereby blocking pH-dependent viral fusion. As an aryl heteroaryl bis-carboxyamide derivative, losmapimod represents a novel chemical scaffold with anti-LASV activity, and it provides a new lead structure for the future development of LASV fusion inhibitors.

Identification of Clotrimazole Derivatives as Specific Inhibitors of Arenavirus Fusion

Arenaviruses are a large family of emerging enveloped negative-strand RNA viruses that include several causative agents of viral hemorrhagic fevers. For cell entry, human-pathogenic arenaviruses use different cellular receptors and endocytic pathways that converge at the level of acidified late endosomes, where the viral envelope glycoprotein mediates membrane fusion. Inhibitors of arenavirus entry hold promise for therapeutic antiviral intervention and the identification of "druggable" targets is of high priority. Using a recombinant vesicular stomatitis virus pseudotype platform, we identified the clotrimazole-derivative TRAM-34, a highly selective antagonist of the calcium-activated potassium channel KCa3.1, as a specific entry inhibitor for arenaviruses. TRAM-34 specifically blocked entry of most arenaviruses, including hemorrhagic fever viruses, but not Lassa virus and other enveloped viruses. Anti-arenaviral activity was likewise observed with the parental compound clotrimazole and the derivative senicapoc, whereas structurally unrelated KCa3.1 inhibitors showed no antiviral effect. Deletion of KCa3.1 by CRISPR/Cas9 technology did not affect the antiarenaviral effect of TRAM-34, indicating that the observed antiviral effect of clotrimazoles was independent of the known pharmacological target. The drug affected neither virus-cell attachment, nor endocytosis, suggesting an effect on later entry steps. Employing a quantitative cell-cell fusion assay that bypasses endocytosis, we demonstrate that TRAM-34 specifically inhibits arenavirus-mediated membrane fusion. In sum, we uncover a novel antiarenaviral action of clotrimazoles that currently undergo in vivo evaluation in the context of other human diseases. Their favorable in vivo toxicity profiles and stability opens the possibility to repurpose clotrimazole derivatives for therapeutic intervention against human-pathogenic arenaviruses.IMPORTANCE Emerging human-pathogenic arenaviruses are causative agents of severe hemorrhagic fevers with high mortality and represent serious public health problems. The current lack of a licensed vaccine and the limited treatment options makes the development of novel antiarenaviral therapeutics an urgent need. Using a recombinant pseudotype platform, we uncovered that clotrimazole drugs, in particular TRAM-34, specifically inhibit cell entry of a range of arenaviruses, including important emerging human pathogens, with the exception of Lassa virus. The antiviral effect was independent of the known pharmacological drug target and involved inhibition of the unusual membrane fusion mechanism of arenaviruses. TRAM-34 and its derivatives currently undergo evaluation against a number of human diseases and show favorable toxicity profiles and high stability in vivo Our study provides the basis for further evaluation of clotrimazole derivatives as antiviral drug candidates. Their advanced stage of drug development will facilitate repurposing for therapeutic intervention against human-pathogenic arenaviruses.

Prevalence of Wēnzhōu virus in small mammals in Yunnan Province, China

Background

Mammarenaviruses are associated with human hemorrhagic fever diseases in Africa and America. Recently, a rodent mammarenavirus, Wēnzhōu virus (WENV) and related viruses, have been reported in China, Cambodia, and Thailand. Moreover, in Cambodia, these viruses were suspected to be associated with human disease. In China, Yunnan Province is famous for its abundant animal and plant diversity and is adjacent to several South-eastern Asia countries. Therefore, it is necessary to know whether WENV-related viruses, or other mammarenaviruses, are prevalent in this province.

Methodology/Principal findings

Small mammals were trapped, euthanized, and sampled. Mammarenavirus RNA was detected using a nested reverse transcription polymerase chain reaction (RT-PCR) and quantified by real-time RT-PCR. A total of 1040 small mammals belonging to 13 genera and 26 species were trapped in Yunnan Province. WENV-related mammarenaviruses were detected in 41 rodent liver samples, mainly in brown rats (Rattus norvegicus) and oriental house rats (R. tanezumi).Viral nucleocapsid protein was detected in liver sections by indirect immunofluorescence assay. Full-length-genomes were amplified by RT-PCR and used for phylogenetic analysis with the MEGA package. Recombination analysis was performed using the SimPlot and Recombination Detection Program.

Conclusions/Significance

WENV related viruses circulated in small mammals in Yunnan Province. Whole genome sequence analysis of five selected viral strains showed that these viruses are closely related to WENVs discovered in Asia and form an independent branch in the phylogenetic tree in the WENV clade. Paying attention to investigate the influence of these viruses to public health is essential in the epidemic regions.

Rodents are natural reservoirs of mammarenavirus. Lymphocytic choriomeningitis virus (LCMV), isolated in Asian countries during the 1990s, has a worldwide distribution and was the first mammarenavirus isolated. In 2014, a second mammarenavirus, Wēnzhōu virus (WENV), was identified in rodents in Zhejiang Province of China and later in Guangdong, Shandong, and Hainan Provinces. Most importantly, WENV or related viruses were reported in Thailand and Cambodia. In Cambodia, the isolated virus was associated with human respiratory diseases. In this study, we detected WENV or related viruses in Yunnan Province and found a high prevalence in rats of two species (Rattus norvegicus and R. tanezumi). Phylogenetic analysis of the complete L and S segments of five strains showed that these viruses form an independent phylogenetic branch in WENV clade most closely related to WENVs found in China and Cambodia. Considering the wide spread distribution of rats and altered distribution patterns due to ecological changes, we propose that these viruses may have a wider prevalence and be found in countries from South-eastern Asia to China. Given that WENV may be associated with human diseases, it is necessary to improve surveillances of these viruses in their natural reservoirs and in humans.

TRIM2, a novel member of the antiviral family, limits New World arenavirus entry

Tripartite motif (TRIM) proteins belong to a large family with many roles in host biology, including restricting virus infection. Here, we found that TRIM2, which has been implicated in cases of Charcot-Marie-Tooth disease (CMTD) in humans, acts by blocking hemorrhagic fever New World arenavirus (NWA) entry into cells. We show that Trim2-knockout mice, as well as primary fibroblasts from a CMTD patient with mutations in TRIM2, are more highly infected by the NWAs Junín and Tacaribe virus than wild-type mice or cells are. Using mice with different Trim2 gene deletions and TRIM2 mutant constructs, we demonstrate that its antiviral activity is uniquely independent of the RING domain encoding ubiquitin ligase activity. Finally, we show that one member of the TRIM2 interactome, signal regulatory protein α (SIRPA), a known inhibitor of phagocytosis, also restricts NWA infection and conversely that TRIM2 limits phagocytosis of apoptotic cells. In addition to demonstrating a novel antiviral mechanism for TRIM proteins, these studies suggest that the NWA entry and phagocytosis pathways overlap.

Human Pathogenic Arenaviruses (Arenaviridae)

Several arenaviruses cause hemorrhagic fever (HF) disease in humans and have a vast impact on public health in their endemic regions. In addition, evidence indicates that the worldwide-distributed arenavirus lymphocytic choriomeningitis virus (LCMV) is a neglected human pathogen. Current medical countermeasures to treat human pathogenic arenaviruses are very limited. Progress in arenavirus molecular genetics has made it possible to manipulate the arenavirus genome, which has contributed to significant progress in understanding arenavirus molecular and cell biology, as well as arenavirus-host interactions underlying arenavirus-induced disease in humans. Likewise, these advances in arenavirus biology might facilitate the development of novel vaccines and antiviral drugs to combat human pathogenic arenaviruses.

Tangeretin, an extract from Citrus peels, blocks cellular entry of arenaviruses that cause viral hemorrhagic fever

The family Arenaviridae consists of numerous enveloped RNA viruses with ambisense coding strategies. Eight arenaviruses, including Lassa virus, are known to cause severe and fatal viral hemorrhagic fever (VHF) in humans, yet vaccines and treatments for disease caused by arenaviruses are very limited. In this study, we screened a natural product library consisting of 131 compounds and identified tangeretin, a polymethoxylated flavone widely present in citrus fruit peels, as a Lassa virus entry inhibitor that blocks viral fusion. Further analyses demonstrated the efficacy of tangeretin against seven other VHF-causing arenaviruses, suggesting that this compound, which has a history of medical usage, could be used to develop an effective therapeutic to treat infection and disease caused by Lassa virus and related viruses.

Complex and Dynamic Interactions between Parvovirus Capsids, Transferrin Receptors, and Antibodies Control Cell Infection and Host Range

Antibody and receptor binding are key virus-host interactions that control host range and determine the success of infection. Canine and feline parvovirus capsids bind the transferrin receptor type 1 (TfR) to enter host cells, and specific structural interactions appear necessary to prepare the stable capsids for infection. Here, we define the details of binding, competition, and occupancy of wild-type and mutant parvovirus capsids with purified receptors and antibodies. TfR-capsid binding interactions depended on the TfR species and varied widely, with no direct relationship between binding affinity and infection. Capsids bound feline, raccoon, and black-backed jackal TfRs at high affinity but barely bound canine TfRs, which mediated infection efficiently. TfRs from different species also occupied capsids to different levels, with an estimated 1 to 2 feline TfRs but 12 black-backed jackal TfRs binding each capsid. Multiple alanine substitutions within loop 1 on the capsid surface reduced TfR binding but substitutions within loop 3 did not, suggesting that loop 1 directly engaged the TfR and loop 3 sterically affected that interaction. Binding and competition between different TfRs and/or antibodies showed complex relationships. Both antibodies 14 and E competed capsids off TfRs, but antibody E could also compete capsids off itself and antibody 14, likely by inducing capsid structural changes. In some cases, the initial TfR or antibody binding event affected subsequent TfR binding, suggesting that capsid structure changes occur after TfR or antibody binding and may impact infection. This shows that precise, host-specific TfR-capsid interactions, beyond simple attachment, are important for successful infection.IMPORTANCE Host receptor binding is a key step during viral infection and may control both infection and host range. In addition to binding, some viruses require specific interactions with host receptors in order to infect, and anti-capsid antibodies can potentially disrupt these interactions, leading to neutralization. Here, we examine the interactions between parvovirus capsids, the receptors from different hosts, and anti-capsid antibodies. We show that interactions between parvovirus capsids and host-specific TfRs vary in both affinity and in the numbers of receptors bound, with complex effects on infection. In addition, antibodies binding to two sites on the capsids had different effects on TfR-capsid binding. These experiments confirm that receptor and antibody binding to parvovirus capsids are complex processes, and the infection outcome is not determined simply by the affinity of attachment.

Crossing the Iron Gate: Why and How Transferrin Receptors Mediate Viral Entry

Because both the host and pathogen require iron, the innate immune response carefully orchestrates control over iron metabolism to limit its availability during times of infection. Nutritional iron deficiency can impair host immunity, while iron overload can cause oxidative stress to propagate harmful viral mutations. An emerging enigma is that many viruses use the primary gatekeeper of iron metabolism, the transferrin receptor, as a means to enter cells. Why and how this iron gate is a viral target for infection are the focus of this review.