Current perspectives on the phylogeny of Filoviridae

A Novel and Secure Pseudovirus Reporter System Based Assay for Neutralizing and Enhancing Antibody Assay Against Marburg Virus

Marburg virus (MARV) is one of the principal members of the filovirus family, which can cause fatal hemorrhagic fever in humans. There are currently no prophylactic and therapeutic drugs on the market, and the high pathogenicity and infectivity of MARV make its research highly dependent on biosafety level 4 conditions, severely hindering the development of vaccines and therapies. Therefore, the development of medicines, such as MARV serological diagnosis, vaccines, and therapeutic antibody drugs, urgently needs a safe, convenient, and biosafety level 2 detection method to measure the neutralizing activity of MARV antibodies. To this end, we report a neutralization assay relying on a Rabies virus (RABV) reverse genetic operating system. We constructed infectious clones carrying the eGFP reporter gene and the full length of the original unmodified MARV GP gene. Based on the critical parameters of phylogenetic analysis, recombinant viruses targeting representative strains in the two major MARV lineages were successfully rescued. These pseudoviruses are safe in mice, and their inability to infect cells after being neutralized by antibodies can be visualized under a fluorescence microscope. We tested the system using the neutralizing antibody MR191. MR191 can significantly block the infection of BSR cells with pseudovirus. We compared it with the traditional lentivirus-type pseudovirus system to verify the system’s credibility and obtained the same results as reported in the literature. In general, we have established a safe and visualized method for evaluating the neutralizing activity of MARV antibodies. Compared with traditional methods, it has the advantages of convenient operation, short cycle, and low cost. It is a candidate method that can replace actual viruses for a neutralization assay.

Natural History and Pathogenesis of Wild-Type Marburg Virus Infection in STAT2 Knockout Hamsters

Marburg virus (MARV; family Filoviridae) causes sporadic outbreaks of Marburg hemorrhagic fever in sub-Saharan Africa with case fatality rates reaching 90%. Wild-type filoviruses, including MARV and the closely related Ebola virus, are unable to suppress the type I interferon response in rodents, and therefore require adaptation of the viruses to cause disease in immunocompetent animals. In the current study, we demonstrate that STAT2 knockout Syrian hamsters are susceptible to infection with different wild-type MARV variants. MARV Musoke causes a robust and systemic infection resulting in lethal disease. Histopathological findings share features similar to those observed in human patients and other animal models of filovirus infection. Reverse-transcription polymerase chain reaction analysis of host transcripts shows a dysregulation of the innate immune response. Our results demonstrate that the STAT2 knockout hamster represents a novel small animal model of severe MARV infection and disease without the requirement for virus adaptation.

The methyltransferase domain of the Sudan ebolavirus L protein specifically targets internal adenosines of RNA substrates, in addition to the cap structure

Mononegaviruses, such as Ebola virus, encode an L (large) protein that bears all the catalytic activities for replication/transcription and RNA capping. The C-terminal conserved region VI (CRVI) of L protein contains a K-D-K-E catalytic tetrad typical for 2'O methyltransferases (MTase). In mononegaviruses, cap-MTase activities have been involved in the 2'O methylation and N7 methylation of the RNA cap structure. These activities play a critical role in the viral life cycle as N7 methylation ensures efficient viral mRNA translation and 2'O methylation hampers the detection of viral RNA by the host innate immunity. The functional characterization of the MTase+CTD domain of Sudan ebolavirus (SUDV) revealed cap-independent methyltransferase activities targeting internal adenosine residues. Besides this, the MTase+CTD also methylates, the N7 position of the cap guanosine and the 2'O position of the n1 guanosine provided that the RNA is sufficiently long. Altogether, these results suggest that the filovirus MTases evolved towards a dual activity with distinct substrate specificities. Whereas it has been well established that cap-dependent methylations promote protein translation and help to mimic host RNA, the characterization of an original cap-independent methylation opens new research opportunities to elucidate the role of RNA internal methylations in the viral replication.

A Serological Point-of-Care Test for the Detection of IgG Antibodies against Ebola Virus in Human Survivors

Ebola virus disease causes widespread and highly fatal epidemics in human populations. Today, there is still great need for point-of-care tests for diagnosis, patient management and surveillance, both during and post outbreaks. We present a point-of-care test comprising an immunochromatographic strip and a smartphone reader, which detects and semiquantifies Ebola-specific antibodies in human survivors. We developed a Sudan virus glycoprotein monoplex platform and validated it using sera from 90 human survivors and 31 local noninfected controls. The performance of the glycoprotein monoplex was 100% sensitivity and 98% specificity compared to standard whole antigen enzyme-linked immunosorbent assay (ELISA), and it was validated with freshly collected patient samples in Uganda. Moreover, we constructed a multiplex test for simultaneous detection of antibodies against three recombinant Sudan virus proteins. A pilot study comprising 15 survivors and 5 noninfected controls demonstrated sensitivity and specificity of 100% compared to standard ELISA. Finally, we developed a second multiplex subtype assay for the identification of exposure to three related EVD species: Sudan virus, Bundibugyo virus and Ebola virus (formerly Zaire) using recombinant viral glycoprotein. This multiplex test could distinguish between the host's immunity to specific viral species and identify cross-reactive immunity. These developed serological platforms consisted of capture ligands with high specificity and sensitivity, in-house developed strips and a compatible smartphone application. These platforms enabled rapid and portable testing, data storage and sharing as well as geographical tagging of the tested individuals in Uganda. This platform holds great potential as a field tool for diagnosis, vaccine development, and therapeutic evaluation.

Viral hemorrhagic fever in the tropics: Report from the task force on tropical diseases by the World Federation of Societies of Intensive and Critical Care Medicine

Viral hemorrhagic fevers (VHFs) are a group of illnesses caused by four families of viruses namely Arenaviruses, Filoviruses, Bunyaviruses, and Flaviviruses. Humans are not the natural reservoir for any of these organisms and acquire the disease through vectors from animal reservoirs. In some conditions human to human transmission is possible increasing the risk to healthy individuals in the vicinity, more so to Health Care Workers (HCW). The pathogenesis of VHF, though poorly understood, varies according to the viruses involved. The resultant microvascular damage leads to increased vascular permeability, organ dysfunction and even death. The management is generally supportive but antiviral agents are of benefit in certain circumstances.

Ebola virus disease: Report from the task force on tropical diseases by the World Federation of Societies of Intensive and Critical Care Medicine

Ebola virus is a filovirus that can cause fatal hemorrhagic fever (HF) and five distinct species exist that vary in terms of geographical distribution and virulence. Once the more virulent forms enter the human population, transmission occurs primarily through direct contact with infected body fluids and may result in significant outbreaks. The devastating has been the recent West African outbreak. Clinically, signs and symptoms are similar to those of the other VHFs [4]. The incubation period is 2-21days, followed by fever, headache, myalgia, diarrhoea, vomiting and dehydration; thereafter, there may be recovery or deterioration with collapse, neurological manifestations and bleeding, that can lead to a fatal outcome. Elevated hepatic transaminases is common and severe hepatitis is more common in fatal cases and frequently there is associated fluid depletion. Real time reverse transcription-PCR (RT-PCR) techniques on blood specimens are the gold standard for diagnosis [6]. Management is discussed and is essentially supportive with strict attention to infection control and prevention. None of the pharmacological interventions have shown conclusive benefit and future management of epidemics should centre around prevention and containment, specifically isolation, hygiene, and vaccination.

Rapid detection and quantification of Ebola Zaire virus by one-step real-time quantitative reverse transcription-polymerase chain reaction

Given that Ebola virus causes severe hemorrhagic fever in humans with mortality rates as high as 90%, rapid and accurate detection of this virus is essential both for controlling infection and preventing further transmission. Here, a one-step qRT-PCR assay for rapid and quantitative detection of an Ebola Zaire strain using GP, VP24 or VP40 genes as a target is introduced. Routine assay conditions for hydrolysis probe detection were established from the manufacturer's protocol used in the assays. The analytical specificity and sensitivity of each assay was evaluated using in vitro synthesized viral RNA transcripts. The assays were highly specific for the RNA transcripts, no cross-reactivity being observed among them. The limits of detection of the assays ranged from 10² to 10³ copies per reaction. The assays were also evaluated using viral RNAs extracted from cell culture-propagated viruses (Ebola Zaire, Sudan and Reston strains), confirming that they are gene- and strain-specific. The RT-PCR assays detected viral RNAs in blood samples from virus-infected animal, suggesting that they can be also a useful method for identifying Ebola virus in clinical samples.

Ebolavirus Glycoprotein Fc Fusion Protein Protects Guinea Pigs against Lethal Challenge

Ebola virus (EBOV), a member of the Filoviridae that can cause severe hemorrhagic fever in humans and nonhuman primates, poses a significant threat to the public health. Currently, there are no licensed vaccines or therapeutics to prevent and treat EBOV infection. Several vaccines based on the EBOV glycoprotein (GP) are under development, including vectored, virus-like particles, and protein-based subunit vaccines. We previously demonstrated that a subunit vaccine containing the extracellular domain of the Ebola ebolavirus (EBOV) GP fused to the Fc fragment of human IgG1 (EBOVgp-Fc) protected mice against EBOV lethal challenge. Here, we show that the EBOVgp-Fc vaccine formulated with QS-21, alum, or polyinosinic-polycytidylic acid-poly-L-lysine carboxymethylcellulose (poly-ICLC) adjuvants induced strong humoral immune responses in guinea pigs. The vaccinated animals developed anti-GP total antibody titers of approximately 10⁵−10⁶ and neutralizing antibody titers of approximately 10³ as assessed by a BSL-2 neutralization assay based on vesicular stomatitis virus (VSV) pseudotypes. The poly-ICLC formulated EBOVgp-Fc vaccine protected all the guinea pigs against EBOV lethal challenge performed under BSL-4 conditions whereas the same vaccine formulated with QS-21 or alum only induced partial protection. Vaccination with a mucin-deleted EBOVgp-Fc construct formulated with QS-21 adjuvant did not have a significant effect in anti-GP antibody levels and protection against EBOV lethal challenge compared to the full-length GP construct. The bulk of the humoral response induced by the EBOVgp-Fc vaccine was directed against epitopes outside the EBOV mucin region. Our findings indicate that different adjuvants can eliciting varying levels of protection against lethal EBOV challenge in guinea pigs vaccinated with EBOVgp-Fc, and suggest that levels of total anti-GP antibodies elicit by protein-based GP subunit vaccines do not correlate with protection. Our data further support the development of Fc fusions of GP as a candidate vaccine for human use.

Ecological Contexts of Index Cases and Spillover Events of Different Ebolaviruses

Ebola virus disease afflicts both human and animal populations and is caused by four ebolaviruses. These different ebolaviruses may have distinct reservoir hosts and ecological contexts that determine how, where, and when different ebolavirus spillover events occur. Understanding these virus-specific relationships is important for preventing transmission of ebolaviruses from wildlife to humans. We examine the ecological contexts surrounding 34 human index case infections of ebolaviruses from 1976-2014. Determining possible sources of spillover from wildlife, characterizing the environment of each event, and creating ecological niche models to estimate habitats suitable for spillover, we find that index case infections of two ebolaviruses, Ebola virus and Sudan virus, have occurred under different ecological contexts. The index cases of Ebola virus infection are more associated with tropical evergreen broadleaf forests and consuming bushmeat than the cases of Sudan virus. Given these differences, we emphasize caution when generalizing across different ebolaviruses and that location and virus-specific ecological knowledge will be essential to unravelling how human and animal behavior lead to the emergence of Ebola virus disease.

Large-Scale Screening and Identification of Novel Ebola Virus and Marburg Virus Entry Inhibitors

Filoviruses are highly infectious, and no FDA-approved drug therapy for filovirus infection is available. Most work to find a treatment has involved only a few strains of Ebola virus and testing of relatively small drug libraries or compounds that have shown efficacy against other virus types. Here we report the findings of a high-throughput screening of 319,855 small molecules from the Molecular Libraries Small Molecule Repository library for their activities against Marburg virus and Ebola virus. Nine of the most potent, novel compounds that blocked infection by both viruses were analyzed in detail for their mechanisms of action. The compounds inhibited known key steps in the Ebola virus infection mechanism by blocking either cell surface attachment, macropinocytosis-mediated uptake, or endosomal trafficking. To date, very few specific inhibitors of macropinocytosis have been reported. The 2 novel macropinocytosis inhibitors are more potent inhibitors of Ebola virus infection and less toxic than ethylisopropylamiloride, one commonly accepted macropinocytosis inhibitor. Each compound blocked infection of primary human macrophages, indicating their potential to be developed as new antifiloviral therapies.

Ebola virus disease: societal challenges and new treatments

Ebola virus disease (EVD) is a zoonotic disease that causes severe haemorrhagic fever, with high fatality rates of up to 90% in humans. Today, there is no effective treatment available. Person-to-person transmission occurs through exposure to blood or body fluids, which can threaten other household members and first-line healthcare workers. The first cases of EVD in Guinea were identified on 22 March 2014. It was initially believed that this like previous outbreaks would be self-limiting. However, lack of public health infrastructure, delays in virus detection and late implementation of control interventions contributed to widespread transmission of EVD in a region inexperienced in dealing with the disease. Socio-cultural and economic factors probably also played a key role in the spread of the disease, resulting in the current large-scale outbreak. Some promising candidate treatments for this disease are now being developed.

The crux and crust of ebolavirus: Analysis of genome sequences and glycoprotein gene

The recent 2013-15 epidemic of Ebola virus disease (EVD) has initiated extensive sequencing and analysis of ebolavirus genomes. All ebolavirus genomes available until December 2014 have been collated and analyzed in this study to obtain phylogenetic relationship and uncover the variations amongst them. The terminal 'leader' and 'trailer' nucleotide sequences of the genomes were omitted and analysis of the intermediate region accommodating the sole seven genes (hepta-CDS region) of the virus showed relative stability of the genome, including the ones isolated from the current epidemic. The genome information was scrutinized to detect the variation in the surface glycoprotein gene and annotate its three protein products, resulting from its atypical transcription. This study will make an easy understanding of the genomes for those who desire to exploit the genome sequences for different investigations in EVD.

Ebola virus disease: history, epidemiology and outbreaks

Over the past 40 years, sporadic Ebola virus disease (EVD) outbreaks have occurred mostly in the central African region. In March 2014, an outbreak of EVD was recognized in Guinea which would become the most significant outbreak of haemorrhagic fever in Africa to date. The outbreak started in Guinea and rapidly spread to Liberia and Sierra Leone, claiming thousands of lives. Many questions still remain regarding the ecology of Ebola viruses, but it is believed that contact with infected bushmeat is an important risk factor for initial spill over of the virus into the human population. At present, there is still no registered prophylaxis or curative biologicals against EVD.

Ebola virus disease: a highly fatal infectious disease reemerging in West Africa

Ebolavirus can cause a highly fatal and panic-generating human disease which may jump from bats to other mammals and human. High viral loads in body fluids allow efficient transmission by contact. Lack of effective antivirals, vaccines and public health infrastructures in parts of Africa make it difficult to health workers to contain the outbreak.

Outbreaks of Ebola virus disease in Africa: the beginnings of a tragic saga

The tremendous outbreak of Ebola virus disease occurring in West Africa since the end of 2013 surprises by its remoteness from previous epidemics and dramatic extent. This review aims to describe the 27 manifestations of Ebola virus that arose after its discovery in 1976. It provides an update on research on the ecology of Ebola viruses, modes of contamination and human transmission of the disease that are mainly linked to close contact with an infected animal or a patient suffering from the disease. The recommendations to contain the epidemic and challenges to achieve it are reminded.

Emerging infectious diseases associated with bat viruses

Bats play important roles as pollen disseminators and pest predators. However, recent interest has focused on their role as natural reservoirs of pathogens associated with emerging infectious diseases. Prior to the outbreak of severe acute respiratory syndrome (SARS), about 60 bat virus species had been reported. The number of identified bat viruses has dramatically increased since the initial SARS outbreak, and most are putative novel virus species or genotypes. Serious infectious diseases caused by previously identified bat viruses continue to emerge throughout in Asia, Australia, Africa and America. Intriguingly, bats infected by these different viruses seldom display clinical symptoms of illness. The pathogenesis and potential threat of bat-borne viruses to public health remains largely unknown. This review provides a brief overview of bat viruses associated with emerging human infectious diseases.

Molecular evolution of viruses of the family Filoviridae based on 97 whole-genome sequences

Viruses in the Ebolavirus and Marburgvirus genera (family Filoviridae) have been associated with large outbreaks of hemorrhagic fever in human and nonhuman primates. The first documented cases occurred in primates over 45 years ago, but the amount of virus genetic diversity detected within bat populations, which have recently been identified as potential reservoir hosts, suggests that the filoviruses are much older. Here, detailed Bayesian coalescent phylogenetic analyses are performed on 97 whole-genome sequences, 55 of which are newly reported, to comprehensively examine molecular evolutionary rates and estimate dates of common ancestry for viruses within the family Filoviridae. Molecular evolutionary rates for viruses belonging to different species range from 0.46 × 10(-4) nucleotide substitutions/site/year for Sudan ebolavirus to 8.21 × 10(-4) nucleotide substitutions/site/year for Reston ebolavirus. Most recent common ancestry can be traced back only within the last 50 years for Reston ebolavirus and Zaire ebolavirus species and suggests that viruses within these species may have undergone recent genetic bottlenecks. Viruses within Marburg marburgvirus and Sudan ebolavirus species can be traced back further and share most recent common ancestors approximately 700 and 850 years before the present, respectively. Examination of the whole family suggests that members of the Filoviridae, including the recently described Lloviu virus, shared a most recent common ancestor approximately 10,000 years ago. These data will be valuable for understanding the evolution of filoviruses in the context of natural history as new reservoir hosts are identified and, further, for determining mechanisms of emergence, pathogenicity, and the ongoing threat to public health.

Serological evidence of ebolavirus infection in bats, China

Background

The genus Ebolavirus of the family Filoviridae currently consists of five species. All species, with the exception of Reston ebolavirus, have been found in Africa and caused severe human diseases. Bats have been implicated as reservoirs for ebolavirus. Reston ebolavirus, discovered in the Philippines, is the only ebolavirus species identified in Asia to date. Whether this virus is prevalent in China is unknown.

Findings

In this study, we developed an enzyme linked immunosorbent assay (ELISA) for ebolavirus using the recombinant nucleocapsid protein and performed sero-surveillance for the virus among Chinese bat populations. Our results revealed the presence of antibodies to ebolavirus in 32 of 843 bat sera samples and 10 of 16 were further confirmed by western blot analysis.

Conclusion

To our knowledge, this is the first report of any filovirus infection in China.

The evolution of endogenous viral elements

Endogenous retroviruses are a common component of the eukaryotic genome, and their evolution and potential function have attracted considerable interest. More surprising was the recent discovery that eukaryotic genomes contain sequences from RNA viruses that have no DNA stage in their life cycle. Similarly, several single-stranded DNA viruses have left integrated copies in their host genomes. This review explores some major evolutionary aspects arising from the discovery of these endogenous viral elements (EVEs). In particular, the reasons for the bias toward EVEs derived from negative-sense RNA viruses are considered, as well as what they tell us about the long-term "arms races" between hosts and viruses, characterized by episodes of selection and counter-selection. Most dramatically, the presence of orthologous EVEs in divergent hosts demonstrates that some viral families have ancestries dating back almost 100 million years, and hence are far older than expected from the phylogenetic analysis of their exogenous relatives.

dsRNA binding characterization of full length recombinant wild type and mutants Zaire ebolavirus VP35

The Ebola viruses (EBOVs) VP35 protein is a multifunctional major virulence factor involved in EBOVs replication and evasion of the host immune system. EBOV VP35 is an essential component of the viral RNA polymerase, it is a key participant of the nucleocapsid assembly and it inhibits the innate immune response by antagonizing RIG-I like receptors through its dsRNA binding function and, hence, by suppressing the host type I interferon (IFN) production. Insights into the VP35 dsRNA recognition have been recently revealed by structural and functional analysis performed on its C-terminus protein. We report the biochemical characterization of the Zaire ebolavirus (ZEBOV) full-length recombinant VP35 (rVP35)–dsRNA binding function. We established a novel in vitro magnetic dsRNA binding pull down assay, determined the rVP35 optimal dsRNA binding parameters, measured the rVP35 equilibrium dissociation constant for heterologous in vitro transcribed dsRNA of different length and short synthetic dsRNA of 8 bp, and validated the assay for compound screening by assessing the inhibitory ability of auryntricarboxylic acid (IC₅₀ value of 50 μg/mL). Furthermore, we compared the dsRNA binding properties of full length wt rVP35 with those of R305A, K309A and R312A rVP35 mutants, which were previously reported to be defective in dsRNA binding-mediated IFN inhibition, showing that the latter have measurably increased K_d values for dsRNA binding and modified migration patterns in mobility shift assays with respect to wt rVP35. Overall, these results provide the first characterization of the full-length wt and mutants VP35–dsRNA binding functions.

Evolutionary maintenance of filovirus-like genes in bat genomes

BACKGROUND

Little is known of the biological significance and evolutionary maintenance of integrated non-retroviral RNA virus genes in eukaryotic host genomes. Here, we isolated novel filovirus-like genes from bat genomes and tested for evolutionary maintenance. We also estimated the age of filovirus VP35-like gene integrations and tested the phylogenetic hypotheses that there is a eutherian mammal clade and a marsupial/ebolavirus/Marburgvirus dichotomy for filoviruses.

RESULTS

We detected homologous copies of VP35-like and NP-like gene integrations in both Old World and New World species of Myotis (bats). We also detected previously unknown VP35-like genes in rodents that are positionally homologous. Comprehensive phylogenetic estimates for filovirus NP-like and VP35-like loci support two main clades with a marsupial and a rodent grouping within the ebolavirus/Lloviu virus/Marburgvirus clade. The concordance of VP35-like, NP-like and mitochondrial gene trees with the expected species tree supports the notion that the copies we examined are orthologs that predate the global spread and radiation of the genus Myotis. Parametric simulations were consistent with selective maintenance for the open reading frame (ORF) of VP35-like genes in Myotis. The ORF of the filovirus-like VP35 gene has been maintained in bat genomes for an estimated 13. 4 MY. ORFs were disrupted for the NP-like genes in Myotis. Likelihood ratio tests revealed that a model that accommodates positive selection is a significantly better fit to the data than a model that does not allow for positive selection for VP35-like sequences. Moreover, site-by-site analysis of selection using two methods indicated at least 25 sites in the VP35-like alignment are under positive selection in Myotis.

CONCLUSIONS

Our results indicate that filovirus-like elements have significance beyond genomic imprints of prior infection. That is, there appears to be, or have been, functionally maintained copies of such genes in mammals. "Living fossils" of filoviruses appear to be selectively maintained in a diverse mammalian genus (Myotis).