Characteristics of Filoviridae: Marburg and Ebola viruses

Production and Purification of Filovirus Glycoproteins

Ebola (EBOV) and Marburg (MARV) viruses cause hemorrhagic fever disease in humans and non-human primates (NHPs) with case-fatality rates as high as 90%. The 2013-2016 Ebola virus disease (EVD) outbreak led to over 28,000 cases and 11,000 deaths and took an enormous toll on the economy of West African nations, in the absence of any vaccine or therapeutic options. Like EVD, there have been at least 6 outbreaks of MVD with ~88% case-fatality and the most recent cases emerging in Equatorial Guinea in February 2023. These outbreaks have spurred an unprecedented global effort to develop vaccines and therapeutics for EVD and MVD and led to an approved vaccine (ERVEBO™) and two monoclonal antibody (mAb) therapeutics for EBOV. In contrast to EVD, therapeutic options against Marburg and another Ebola-relative Sudan virus (SUDV) are lacking. The filovirus glycoprotein (GP), which mediates host cell entry and fusion, is the primary target of neutralizing antibodies. In addition to its pre- and post-fusion trimeric states, the protein is highly glycosylated making production of pure and homogeneous trimers on a large scale, a requirement for subunit vaccine development, a challenge. In efforts to address this roadblock, we have developed a unique combination of structure-based design, selection of expression system, and purification methods to produce uniform and stable EBOV and MARV GP trimers at scales appropriate for vaccine production.

Microparticle-Based Detection of Viruses

Surveillance of viral pathogens in both point-of-care and clinical settings is imperative to preventing the widespread propagation of disease-undetected viral outbreaks can pose dire health risks on a large scale. Thus, portable, accessible, and reliable biosensors are necessary for proactive measures. Polymeric microparticles have recently gained popularity for their size, surface area, and versatility, which make them ideal biosensing tools. This review cataloged recent investigations on polymeric microparticle-based detection platforms across eight virus families. These microparticles were used as labels for detection (often with fluorescent microparticles) and for capturing viruses for isolation or purification (often with magnetic microparticles). We also categorized all methods by the characteristics, materials, conjugated receptors, and size of microparticles. Current approaches were compared, addressing strengths and weaknesses in the context of virus detection. In-depth analyses were conducted for each virus family, categorizing whether the polymeric microparticles were used as labels, for capturing, or both. We also summarized the types of receptors conjugated to polymeric microparticles for each virus family.

Filoviruses: Innate Immunity, Inflammatory Cell Death, and Cytokines

Filoviruses are a group of single-stranded negative sense RNA viruses. The most well-known filoviruses that affect humans are ebolaviruses and marburgviruses. During infection, they can cause life-threatening symptoms such as inflammation, tissue damage, and hemorrhagic fever, with case fatality rates as high as 90%. The innate immune system is the first line of defense against pathogenic insults such as filoviruses. Pattern recognition receptors (PRRs), including toll-like receptors, retinoic acid-inducible gene-I-like receptors, C-type lectin receptors, AIM2-like receptors, and NOD-like receptors, detect pathogens and activate downstream signaling to induce the production of proinflammatory cytokines and interferons, alert the surrounding cells to the threat, and clear infected and damaged cells through innate immune cell death. However, filoviruses can modulate the host inflammatory response and innate immune cell death, causing an aberrant immune reaction. Here, we discuss how the innate immune system senses invading filoviruses and how these deadly pathogens interfere with the immune response. Furthermore, we highlight the experimental difficulties of studying filoviruses as well as the current state of filovirus-targeting therapeutics.

Bridging Animal and Human Data in Pursuit of Vaccine Licensure

The FDA Animal Rule was devised to facilitate approval of candidate vaccines and therapeutics using animal survival data when human efficacy studies are not practical or ethical. This regulatory pathway is critical for candidates against pathogens with high case fatality rates that prohibit human challenge trials, as well as candidates with low and sporadic incidences of outbreaks that make human field trials difficult. Important components of a vaccine development plan for Animal Rule licensure are the identification of an immune correlate of protection and immunobridging to humans. The relationship of vaccine-induced immune responses to survival after vaccination and challenge must be established in validated animal models and then used to infer predictive vaccine efficacy in humans via immunobridging. The Sabin Vaccine Institute is pursuing licensure for candidate filovirus vaccines via the Animal Rule and has convened meetings of key opinion leaders and subject matter experts to define fundamental components for vaccine licensure in the absence of human efficacy data. Here, filoviruses are used as examples to review immune correlates of protection and immunobridging. The points presented herein reflect the presentations and discussions during the second meeting held in October 2021 and are intended to address important considerations for developing immunobridging strategies.

Comparative overview of emerging RNA viruses: Epidemiology, pathogenesis, diagnosis and current treatment

From many decades, emerging infections have threatened humanity. The pandemics caused by different CoVs have already claimed and will continue to claim millions of lives. The SARS, Ebola, MERS epidemics and the most recent emergence of COVID-19 pandemic have threatened populations across borders. Since a highly pathogenic CoV has been evolved into the human population in the twenty-first century known as SARS, scientific advancements and innovative methods to tackle these viruses have increased in order to improve response preparedness towards the unpredictable threat posed by these rapidly emerging pathogens. Recently published review articles on SARS-CoV-2 have mainly focused on its pathogenesis, epidemiology and available treatments. However, in this review, we have done a systematic comparison of all three CoVs i.e., SARS, MERS and SARS-CoV-2 along with Ebola and Zika in terms of their epidemiology, virology, clinical features and current treatment strategies. This review focuses on important emerging RNA viruses starting from Zika, Ebola and the CoVs which include SARS, MERS and SARS-CoV-2. Each of these viruses has been elaborated on the basis of their epidemiology, virulence, transmission and treatment. However, special attention has been given to SARS-CoV-2 and the disease caused by it i.e., COVID-19 due to current havoc caused worldwide. At the end, insights into the current understanding of the lessons learned from previous epidemics to combat emerging CoVs have been described. The travel-related viral spread, the unprecedented nosocomial outbreaks and the high case-fatality rates associated with these highly transmissible and pathogenic viruses highlight the need for new prophylactic and therapeutic actions which include but are not limited to clinical indicators, contact tracing, and laboratory investigations as important factors that need to be taken into account in order to arrive at the final conclusion.

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Recently published review articles on SARS-CoV-2 have mainly focused on its pathogenesis, epidemiology and available treatments.

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The pandemics caused by different CoVs have already claimed and will continue to claim millions of lives.

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This review focuses on important emerging RNA viruses starting from Zika, Ebola and the CoVs which include SARS, MERS and SARS-CoV-2.

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Globally, numerous studies and researchers have recently started fighting this virus.

Pathogenicity and virulence of Marburg virus

Marburg virus (MARV) has been a major concern since 1967, with two major outbreaks occurring in 1998 and 2004. Infection from MARV results in severe hemorrhagic fever, causing organ dysfunction and death. Exposure to fruit bats in caves and mines, and human-to-human transmission had major roles in the amplification of MARV outbreaks in African countries. The high fatality rate of up to 90% demands the broad study of MARV diseases (MVD) that correspond with MARV infection. Since large outbreaks are rare for MARV, clinical investigations are often inadequate for providing the substantial data necessary to determine the treatment of MARV disease. Therefore, an overall review may contribute to minimizing the limitations associated with future medical research and improve the clinical management of MVD. In this review, we sought to analyze and amalgamate significant information regarding MARV disease epidemics, pathophysiology, and management approaches to provide a better understanding of this deadly virus and the associated infection.

Plant-Derived Recombinant Vaccines against Zoonotic Viruses

Emerging and re-emerging zoonotic diseases cause serious illness with billions of cases, and millions of deaths. The most effective way to restrict the spread of zoonotic viruses among humans and animals and prevent disease is vaccination. Recombinant proteins produced in plants offer an alternative approach for the development of safe, effective, inexpensive candidate vaccines. Current strategies are focused on the production of highly immunogenic structural proteins, which mimic the organizations of the native virion but lack the viral genetic material. These include chimeric viral peptides, subunit virus proteins, and virus-like particles (VLPs). The latter, with their ability to self-assemble and thus resemble the form of virus particles, are gaining traction among plant-based candidate vaccines against many infectious diseases. In this review, we summarized the main zoonotic diseases and followed the progress in using plant expression systems for the production of recombinant proteins and VLPs used in the development of plant-based vaccines against zoonotic viruses.

Ebola Virus Disease and Current Therapeutic Strategies: A Review

The Ebola virus disease is a severe hemorrhagic fever that affects humans and other primates. Ebola virus, the causative agent of the disease, is transmitted to humans from wild animals and is highly contagious and aggressive with an estimated fatality rate to be around 50%. Since 1976, 11 outbreaks of Ebola virus disease have been reported in total, affecting mostly sub-Saharan Africa, while the most recent ongoing outbreak in the Democratic Republic of the Congo has more than 3000 reported cases and 72 deaths. Although an effective vaccine against Ebola virus disease has become available, no targeted treatment with proven efficacy upon infection is developed. Herein, we review the epidemiology of Ebola virus and the current situation in terms of prevention, diagnosis, and treatment of the disease.

Human Parainfluenza Virus 3 Phosphoprotein Is a Tetramer and Shares Structural and Interaction Features with Ebola Phosphoprotein VP35

The human parainfluenza virus 3 (HPIV3) poses a risk for pneumonia development in young children and immunocompromised patients. To investigate mechanisms of HPIV3 pathogenesis, we characterized the association state and host protein interactions of HPIV3 phosphoprotein (HPIV3 P), an indispensable viral polymerase cofactor. Sequence analysis and homology modeling predict that HPIV3 P possesses a long, disordered N-terminal tail (P_TAIL) a coiled-coil multimerization domain (P_MD), similar to the well-characterized paramyxovirus phosphoproteins from measles and Sendai viruses. Using a recombinantly expressed and purified construct of P_MD and P_TAIL, we show that HPIV3 P in solution is primarily an alpha-helical tetramer that is stable up to 60 °C. Pulldown and isothermal titration calorimetry experiments revealed that HPIV3 P binds the host hub protein LC8, and turbidity experiments demonstrated a new role for LC8 in increasing the solubility of HPIV3 P in the presence of crowding agents such as RNA. For comparison, we show that the multimerization domain of the Zaire Ebola virus phosphoprotein VP35 is also a tetramer and binds LC8 but with significantly higher affinity. Comparative analysis of the domain architecture of various virus phosphoproteins in the order Mononegavirales show multiple predicted and verified LC8 binding motifs, suggesting its prevalence and importance in regulating viral phosphoprotein structures. Our work provides evidence for LC8 binding to phosphoproteins with multiple association states, either tetrameric, as in the HPIV3 and Ebola phosphoproteins shown here, or dimeric as in rabies virus phosphoprotein. Taken together the data suggest that the association states of a virus-specific phosphoprotein and the complex formed by binding of the phosphoprotein to host LC8 are important regulators of viral function.

Bat E-Commerce: Insights Into the Extent and Potential Implications of This Dark Trade

Little is known about the global bat souvenir trade despite previous research efforts into bat harvest for bushmeat. We screened eBay listings of bats in Australia, Canada, Italy, Switzerland, United Kingdom and USA to assess the nature and extent of the online offers. A total of 237 listings were retrieved in between the 11th and 25th of May 2020 with a median price per item of US$38.50 (range: US$8.50–2,500.00). Items on offer were mostly taxidermy (61.2%) or skull (21.1%) specimens. Overall, 32 different species of bat were advertised, most of which (n = 28) are listed as “Least Concern” on the International Union for Conservation of Nature (IUCN) Red List. One species (Nycteris javanica) is classified as “Vulnerable” and one (Eidolon helvum) as “Near Threatened.” Pteropus spp. specimens were the most expensive specimens on offer and the conservations status of these species may range from “Critically Endangered” to “Data Deficient” by IUCN and the entire genus is listed in the Appendix II by the Convention on the International Trade in Endangered Species of Wild Fauna and Flora (CITES). However, the exact species concerned, and their respective conservation status, could not be confirmed based on the listings' photos. The sourcing of bat was restricted to mostly South-East Asian countries (a third of items sourced from Indonesia) and to two African countries. Our survey revealed that the online offer of bat products is diverse, abundant, and facilitated by worldwide sellers although most offered bats species are from South-East Asia. With a few exceptions, the species on offer were of little present conservation concern, however, many unknowns remain on the potential animal welfare, biosecurity, legal implications, and most importantly public health risks associated with this dark trade.

Lipid-specific oligomerization of the Marburg virus matrix protein VP40 is regulated by two distinct interfaces for virion assembly

Marburg virus (MARV) is a lipid-enveloped virus harboring a negative-sense RNA genome, which has caused sporadic outbreaks of viral hemorrhagic fever in sub-Saharan Africa. MARV assembles and buds from the host cell plasma membrane where MARV matrix protein (mVP40) dimers associate with anionic lipids at the plasma membrane inner leaflet and undergo a dynamic and extensive self-oligomerization into the structural matrix layer. The MARV matrix layer confers the virion filamentous shape and stability but how host lipids modulate mVP40 oligomerization is mostly unknown. Using in vitro and cellular techniques, we present a mVP40 assembly model highlighting two distinct oligomerization interfaces: the (N-terminal domain [NTD] and C-terminal domain [CTD]) in mVP40. Cellular studies of NTD and CTD oligomerization interface mutants demonstrate the importance of each interface in matrix assembly. The assembly steps include protein trafficking to the plasma membrane, homo-multimerization that induced protein enrichment, plasma membrane fluidity changes, and elongations at the plasma membrane. An ascorbate peroxidase derivative (APEX)-transmission electron microscopy method was employed to closely assess the ultrastructural localization and formation of viral particles for wildtype mVP40 and NTD and CTD oligomerization interface mutants. Taken together, these studies present a mechanistic model of mVP40 oligomerization and assembly at the plasma membrane during virion assembly that requires interactions with phosphatidylserine for NTD–NTD interactions and phosphatidylinositol-4,5-bisphosphate for proper CTD–CTD interactions. These findings have broader implications in understanding budding of lipid-enveloped viruses from the host cell plasma membrane and potential strategies to target protein–protein or lipid–protein interactions to inhibit virus budding.

Understanding the Activated Form of a Class-I Fusion Protein: Modeling the Interaction of the Ebola Virus Glycoprotein 2 with a Lipid Bilayer

The fusion of the viral and target cell membranes is a key step in the life cycle of all enveloped viruses. Here, a range of structural data is used to generate an evidence-based model of the active conformation of an archetypical type-I fusion protein, the Ebola glycoprotein 2 (GP2). The stability of the trimeric complex is demonstrated using molecular dynamics and validated by simulating the interaction of the complex with a lipid bilayer. In this model, the fusion peptides project away from the central helix bundle parallel to the target membrane. This maximizes contact with the host membrane, enhances lateral stability, and would explain why, when activated, viral fusion proteins are trimeric.

Applying Antibodies Inside Cells: Principles and Recent Advances in Neurobiology, Virology and Oncology

To interfere with cell function, many scientists rely on methods that target DNA or RNA due to the ease with which they can be applied. Proteins are usually the final executors of function but are targeted only indirectly by these methods. Recent advances in targeted degradation of proteins based on proteolysis-targeting chimaeras (PROTACs), ubiquibodies, deGradFP (degrade Green Fluorescent Protein) and other approaches have demonstrated the potential of interfering directly at the protein level for research and therapy. Proteins can be targeted directly and very specifically by antibodies, but using antibodies inside cells has so far been considered to be challenging. However, it is possible to deliver antibodies or other proteins into the cytosol using standard laboratory equipment. Physical methods such as electroporation have been demonstrated to be efficient and validated thoroughly over time. The expression of intracellular antibodies (intrabodies) inside cells is another way to interfere with intracellular targets at the protein level. Methodological strategies to target the inside of cells with antibodies, including delivered antibodies and expressed antibodies, as well as applications in the research areas of neurobiology, viral infections and oncology, are reviewed here. Antibodies have already been used to interfere with a wide range of intracellular targets. Disease-related targets included proteins associated with neurodegenerative diseases such as Parkinson's disease (α-synuclein), Alzheimer's disease (amyloid-β) or Huntington's disease (mutant huntingtin [mHtt]). The applications of intrabodies in the context of viral infections include targeting proteins associated with HIV (e.g. HIV1-TAT, Rev, Vif, gp41, gp120, gp160) and different oncoviruses such as human papillomavirus (HPV), hepatitis B virus (HBV), hepatitis C virus (HCV) and Epstein-Barr virus, and they have been used to interfere with various targets related to different processes in cancer, including oncogenic pathways, proliferation, cell cycle, apoptosis, metastasis, angiogenesis or neo-antigens (e.g. p53, human epidermal growth factor receptor-2 [HER2], signal transducer and activator of transcription 3 [STAT3], RAS-related RHO-GTPase B (RHOB), cortactin, vascular endothelial growth factor receptor 2 [VEGFR2], Ras, Bcr-Abl). Interfering at the protein level allows questions to be addressed that may remain unanswered using alternative methods. This review addresses why direct targeting of proteins allows unique insights, what is currently feasible in vitro, and how this relates to potential therapeutic applications.

Annexin A2 depletion exacerbates the intracerebral microhemorrhage induced by acute rickettsia and Ebola virus infections

Intracerebral microhemorrhages (CMHs) are small foci of hemorrhages in the cerebrum. Acute infections induced by some intracellular pathogens, including rickettsia, can result in CMHs. Annexin a2 (ANXA2) has been documented to play a functional role during intracellular bacterial adhesion. Here we report that ANXA2-knockout (KO) mice are more susceptible to CMHs in response to rickettsia and Ebola virus infections, suggesting an essential role of ANXA2 in protecting vascular integrity during these intracellular pathogen infections. Proteomic analysis via mass spectrometry of whole brain lysates and brain-derived endosomes from ANXA2-KO and wild-type (WT) mice post-infection with R. australis revealed that a variety of significant proteins were differentially expressed, and the follow-up function enrichment analysis had identified several relevant cell-cell junction functions. Immunohistology study confirmed that both infected WT and infected ANXA2-KO mice were subjected to adherens junctional protein (VE-cadherin) damages. However, key blood-brain barrier (BBB) components, tight junctional proteins ZO-1 and occludin, were disorganized in the brains from R. australis-infected ANXA2-KO mice, but not those of infected WT mice. Similar ANXA2-KO dependent CMHs and fragments of ZO-1 and occludin were also observed in Ebola virus-infected ANXA2-KO mice, but not found in infected WT mice. Overall, our study revealed a novel role of ANXA2 in the formation of CMHs during R. australis and Ebola virus infections; and the underlying mechanism is relevant to the role of ANXA2-regulated tight junctions and its role in stabilizing the BBB in these deadly infections.

Inside the Cell: Assembly of Filoviruses

This chapter reviews our current knowledge about the spatiotemporal assembly of filoviral particles. We will follow particles from nucleocapsid entry into the cytoplasm until the nucleocapsids are enveloped at the plasma membrane. We will also highlight the currently open scientific questions surrounding filovirus assembly.

Design of a multiepitopic Zaire ebolavirus protein and its expression in plant cells

The recent Ebola virus disease (EVD) outbreaks make the development of efficacious and low cost vaccines against Ebola virus (EBOV) an urgent goal. Multiepitopic vaccines allow a rational design rendering vaccines able to induce proper immune responses in terms of polarization and potency. In addition, the pathogen variants can be easily covered by including epitopes conserved among relevant isolates. Other important aspects to consider in vaccination are the costs associated to production, distribution, and administration of the vaccine. Plants provide an advantageous platform for this purpose, since they yield biomass at very low costs and some species can be used to formulate purification-free oral vaccines. In the present study, a multiepitopic protein called Zerola, which carries epitopes from the EBOV glycoprotein (GP), was designed based on immunoinformatic approaches and current experimental evidence on B cell protective GP epitopes. Moreover, expression studies performed in nuclear-transformed tobacco lines confirmed the capacity of the plant cell to synthetize the Zerola antigenic protein. The generation of this plant-based candidate vaccine is a step forward in the development of highly efficient and low cost EBOV vaccines.

Glycoprotein GP as a basis for the universal vaccine against Ebola virus disease

Ebola virus disease (EVD) is one of the deadliest viral infections affecting humans and nonhuman primates. Of 6 known representatives of the Ebolavirus genus responsible for the disease, 3 can infect humans, causing acute highly contagious fever characterized by up to 90% fatality. These include Bundibugyo ebolavirus (BDBV), Zaire ebolavirus (ZEBOV) and Sudan ebolavirus (SUDV). The majority of the reported EVD cases are caused by ZEBOV. Vaccine development against the virus started in 1976, immediately after the causative agent of the infection was identified. So far, 4 vaccines have been approved. All of them are based on the protective epitope of the ZEBOV glycoprotein GP. Because SUDV and BDBV can also cause outbreaks and epidemics, it is vital to design a vaccine capable of conferring protection against all known ebolaviruses posing a threat to the human population. This article presents systematized data on the structure, immunogenicity and protective properties of ebolavirus glycoprotein GP, looks closely at the immunodominant epitopes of ZEBOV, SUDV and BDBV glycoprotein GP required to elicit a protective immune response, and offers a rational perspective on the development of a universal vaccine against EVD that relies on the use of vectors expressing two variants of GP represented by ZEBOV and SUDV.

Exchange Protein Directly Activated by cAMP Modulates Ebola Virus Uptake into Vascular Endothelial Cells

Members of the family Filoviridae, including Ebola virus (EBOV) and Marburg virus (MARV), cause severe hemorrhagic fever in humans and nonhuman primates. Given their high lethality, a comprehensive understanding of filoviral pathogenesis is urgently needed. In the present studies, we revealed that the exchange protein directly activated by cAMP 1 (EPAC1) gene deletion protects vasculature in ex vivo explants from EBOV infection. Importantly, pharmacological inhibition of EPAC1 using EPAC-specific inhibitors (ESIs) mimicked the EPAC1 knockout phenotype in the ex vivo model. ESI treatment dramatically decreased EBOV infectivity in both ex vivo vasculature and in vitro vascular endothelial cells (ECs). Furthermore, postexposure protection of ECs against EBOV infection was conferred using ESIs. Protective efficacy of ESIs in ECs was observed also in MARV infection. Additional studies using a vesicular stomatitis virus pseudotype that expresses EBOV glycoprotein (EGP-VSV) confirmed that ESIs reduced infection in ECs. Ultrastructural studies suggested that ESIs blocked EGP-VSV internalization via inhibition of macropinocytosis. The inactivation of EPAC1 affects the early stage of viral entry after viral binding to the cell surface, but before early endosome formation, in a phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)-dependent manner. Our study delineated a new critical role of EPAC1 during EBOV uptake into ECs.

Herd Immunity to Ebolaviruses Is Not a Realistic Target for Current Vaccination Strategies

The recent West African Ebola virus pandemic, which affected >28,000 individuals increased interest in anti-Ebolavirus vaccination programs. Here, we systematically analyzed the requirements for a prophylactic vaccination program based on the basic reproductive number (R₀, i.e., the number of secondary cases that result from an individual infection). Published R₀ values were determined by systematic literature research and ranged from 0.37 to 20. R₀s ≥ 4 realistically reflected the critical early outbreak phases and superspreading events. Based on the R₀, the herd immunity threshold (I_c) was calculated using the equation I_c = 1 - (1/R₀). The critical vaccination coverage (V_c) needed to provide herd immunity was determined by including the vaccine effectiveness (E) using the equation V_c = I_c/E. At an R₀ of 4, the I_c is 75% and at an E of 90%, more than 80% of a population need to be vaccinated to establish herd immunity. Such vaccination rates are currently unrealistic because of resistance against vaccinations, financial/logistical challenges, and a lack of vaccines that provide long-term protection against all human-pathogenic Ebolaviruses. Hence, outbreak management will for the foreseeable future depend on surveillance and case isolation. Clinical vaccine candidates are only available for Ebola viruses. Their use will need to be focused on health-care workers, potentially in combination with ring vaccination approaches.

On revealing the gene targets of Ebola virus microRNAs involved in the human skin microbiome

Ebola virus, a negative-sense single-stranded RNA virus, causes severe viral hemorrhagic fever and has a high mortality rate. Histopathological and immunopathological analyses of Ebola virus have revealed that histopathological changes in skin tissue are associated with various degrees of endothelial cell swelling and necrosis. The interactions of microbes within or on a host are a crucial for the skin immune shield. The discovery of microRNAs (miRNAs) in Ebola virus implies that immune escape, endothelial cell rupture, and tissue dissolution during Ebola virus infection are a result of the effects of Ebola virus miRNAs. Keratinocytes obtained from normal skin can attach and spread through expression of the thrombospondin family of proteins, playing a role in initiation of cell-mediated immune responses in the skin. Several miRNAs have been shown to bind the 3′ untranslated region of thrombospondin mRNA, thereby controlling its stability and translational activity. In this study, we discovered short RNA sequences that may act as miRNAs from Propionibacterium acnes using a practical workflow of bioinformatics methods. Subsequently, we deciphered the common target gene. These RNA sequences tended to bind to the same thrombospondin protein, THSD4, emphasizing the potential importance of the synergistic binding of miRNAs from Ebola virus, Propionibacterium acnes, and humans to the target. These results provide important insights into the molecular mechanisms of thrombospondin proteins and miRNAs in Ebola virus infection.

Proteases and protease inhibitors in infectious diseases

There are numerous proteases of pathogenic organisms that are currently targeted for therapeutic intervention along with many that are seen as potential drug targets. This review discusses the chemical and biological makeup of some key druggable proteases expressed by the five major classes of disease causing agents, namely bacteria, viruses, fungi, eukaryotes, and prions. While a few of these enzymes including HIV protease and HCV NS3-4A protease have been targeted to a clinically useful level, a number are yet to yield any clinical outcomes in terms of antimicrobial therapy. A significant aspect of this review discusses the chemical and pharmacological characteristics of inhibitors of the various proteases discussed. A total of 25 inhibitors have been considered potent and safe enough to be trialed in humans and are at different levels of clinical application. We assess the mechanism of action and clinical performance of the protease inhibitors against infectious agents with their developmental strategies and look to the next frontiers in the use of protease inhibitors as anti-infective agents.

Epidemiology and Management of the 2013-16 West African Ebola Outbreak

The 2013-16 West African Ebola outbreak is the largest, most geographically dispersed, and deadliest on record, with 28,616 suspected cases and 11,310 deaths recorded to date in Guinea, Liberia, and Sierra Leone. We provide a review of the epidemiology and management of the 2013-16 Ebola outbreak in West Africa aimed at stimulating reflection on lessons learned that may improve the response to the next international health crisis caused by a pathogen that emerges in a region of the world with a severely limited health care infrastructure. Surveillance efforts employing rapid and effective point-of-care diagnostics designed for environments that lack advanced laboratory infrastructure will greatly aid in early detection and containment efforts during future outbreaks. Introduction of effective therapeutics and vaccines against Ebola into the public health system and the biodefense armamentarium is of the highest priority if future outbreaks are to be adequately managed and contained in a timely manner.

Bat-man disease transmission: zoonotic pathogens from wildlife reservoirs to human populations

Bats are natural reservoir hosts and sources of infection of several microorganisms, many of which cause severe human diseases. Because of contact between bats and other animals, including humans, the possibility exists for additional interspecies transmissions and resulting disease outbreaks. The purpose of this article is to supply an overview on the main pathogens isolated from bats that have the potential to cause disease in humans.

Survey of laboratory-acquired infections around the world in biosafety level 3 and 4 laboratories

Laboratory-acquired infections due to a variety of bacteria, viruses, parasites, and fungi have been described over the last century, and laboratory workers are at risk of exposure to these infectious agents. However, reporting laboratory-associated infections has been largely voluntary, and there is no way to determine the real number of people involved or to know the precise risks for workers. In this study, an international survey based on volunteering was conducted in biosafety level 3 and 4 laboratories to determine the number of laboratory-acquired infections and the possible underlying causes of these contaminations. The analysis of the survey reveals that laboratory-acquired infections have been infrequent and even rare in recent years, and human errors represent a very high percentage of the cases. Today, most risks from biological hazards can be reduced through the use of appropriate procedures and techniques, containment devices and facilities, and the training of personnel.

Dose Response of MARV/Angola Infection in Cynomolgus Macaques following IM or Aerosol Exposure

Marburg virus infection in humans causes a hemorrhagic disease with a high case fatality rate. Countermeasure development requires the use of well-characterized animal models that mimic human disease. To further characterize the cynomolgus macaque model of MARV/Angola, two independent dose response studies were performed using the intramuscular or aerosol routes of exposure. All animals succumbed at the lowest target dose; therefore, a dose effect could not be determined. For intramuscular-exposed animals, 100 PFU was the first target dose that was not significantly different than higher target doses in terms of time to disposition, clinical pathology, and histopathology. Although a significant difference was not observed between aerosol-exposed animals in the 10 PFU and 100 PFU target dose groups, 100 PFU was determined to be the lowest target dose that could be consistently obtained and accurately titrated in aerosol studies.

Epitope-based peptide vaccine design and target site depiction against Ebola viruses: an immunoinformatics study

Ebola viruses (EBOVs) have been identified as an emerging threat in recent year as it causes severe haemorrhagic fever in human. Epitope‐based vaccine design for EBOVs remains a top priority because a mere progress has been made in this regard. Another reason is the lack of antiviral drug and licensed vaccine although there is a severe outbreak in Central Africa. In this study, we aimed to design an epitope‐based vaccine that can trigger a significant immune response as well as to prognosticate inhibitor that can bind with potential drug target sites using various immunoinformatics and docking simulation tools. The capacity to induce both humoral and cell‐mediated immunity by T cell and B cell was checked for the selected protein. The peptide region spanning 9 amino acids from 42 to 50 and the sequence TLASIGTAF were found as the most potential B and T cell epitopes, respectively. This peptide could interact with 12 HLAs and showed high population coverage up to 80.99%. Using molecular docking, the epitope was further appraised for binding against HLA molecules to verify the binding cleft interaction. In addition with this, the allergenicity of the epitopes was also evaluated. In the post‐therapeutic strategy, docking study of predicted 3D structure identified suitable therapeutic inhibitor against targeted protein. However, this computational epitope‐based peptide vaccine designing and target site prediction against EBOVs open up a new horizon which may be the prospective way in Ebola viruses research; the results require validation by in vitro and in vivo experiments.

Persistence of Ebola Virus in Sterilized Wastewater

In the wake of the ongoing 2014/2015 Ebola virus outbreak, significant questions regarding the appropriate handling of Ebola virus-contaminated liquid waste remain, including the persistence of Ebola virus in wastewater. To address these uncertainties, we evaluated the persistence of Ebola virus spiked in sterilized domestic sewage. The viral titer decreased approximately 99% within the first test day from an initial viral titer of 106 TCID50 mL-1; however, it could not be determined if this initial rapid decrease was due to aggregation or inactivation of the viral particles. The subsequent viral titer decrease was less rapid, and infectious Ebola virus particles persisted for all 8 days of the test. The inactivation constant (k) was determined to be -1.08 (2.1 days for a 90% viral titer decrease). Due to experimental conditions, we believe these results to be an upper bound for Ebola virus persistence in wastewater. Wastewater composition is inherently heterogeneous; subsequently, we caution that interpretation of these results should be made within a holistic assessment, including the effects of wastewater composition, dilution, and potential exposure routes within wastewater infrastructure. While it remains unknown if Ebola virus may be transmitted via wastewater, these data demonstrate a potential exposure route to infectious Ebola virus via wastewater and emphasize the value of a precautionary approach to wastewater handling in an epidemic response.

The Ebola epidemic is ongoing in West Africa and responses from China are positive

The ongoing Ebola outbreak poses an alarming risk to the countries of West Africa and beyond. On August 8, 2014, the World Health Organization (WHO) declared the cross-country Ebola outbreak a Public Emergency of International Concern. China has had no confirmed cases of Ebola. In this paper, virologic characteristics, pathogenesis, clinical manifestations, laboratory examination and prophylactic vaccines and therapeutic drugs of Ebola are summarized. Importantly, active responses and actions from China are introduced. Moreover, the key issues in the future prevention and control of Ebola were also addressed.

Mapping the zoonotic niche of Ebola virus disease in Africa

Ebola virus disease (EVD) is a complex zoonosis that is highly virulent in humans. The largest recorded outbreak of EVD is ongoing in West Africa, outside of its previously reported and predicted niche. We assembled location data on all recorded zoonotic transmission to humans and Ebola virus infection in bats and primates (1976–2014). Using species distribution models, these occurrence data were paired with environmental covariates to predict a zoonotic transmission niche covering 22 countries across Central and West Africa. Vegetation, elevation, temperature, evapotranspiration, and suspected reservoir bat distributions define this relationship. At-risk areas are inhabited by 22 million people; however, the rarity of human outbreaks emphasises the very low probability of transmission to humans. Increasing population sizes and international connectivity by air since the first detection of EVD in 1976 suggest that the dynamics of human-to-human secondary transmission in contemporary outbreaks will be very different to those of the past.

DOI:http://dx.doi.org/10.7554/eLife.04395.001

Since the first outbreaks of Ebola virus disease in 1976, there have been numerous other outbreaks in humans across Africa with fatality rates ranging from 50% to 90%. Humans can become infected with the Ebola virus after direct contact with blood or bodily fluids from an infected person or animal. The virus also infects and kills other primates—such as chimpanzees or gorillas—though Old World fruit bats are suspected to be the most likely carriers of the virus in the wild.

The largest recorded outbreak of Ebola virus disease is ongoing in West Africa: more people have been infected in this current outbreak than in all previous outbreaks combined. The current outbreak is also the first to occur in West Africa—which is outside the previously known range of the Ebola virus.

Pigott et al. have now updated predictions about where in Africa wild animals may harbour the virus and where the transmission of the virus from these animals to humans is possible. As such, the map identifies the regions that are most at risk of a future Ebola outbreak. The data behind these new maps include the locations of all recorded primary cases of Ebola in human populations—the ‘index’ cases—many of which have been linked to animal sources. The data also include the locations of recorded cases of Ebola virus infections in wild bats and primates from the last forty years. The maps, which were modelled using more flexible methods than previous predictions, also include new information—collected using satellites—about environmental factors and new predictions of the range of wild fruit bats.

Pigott et al. report that the transmission of Ebola virus from animals to humans is possible in 22 countries across Central and West Africa—and that 22 million people live in the areas at risk. However, outbreaks in human populations are rare and the likelihood of a human getting the disease from an infected animal still remains very low. The updated map does not include data about how infections spread from one person to another, so the next challenge is to use existing data on human-to-human transmission to better understand the likely size and extent of current and future outbreaks. As more people live in, and travel to and from, the at-risk regions than ever before, Pigott et al. note that new outbreaks of Ebola virus disease are likely to be very different to those of the past.

DOI:http://dx.doi.org/10.7554/eLife.04395.002

A highly immunogenic fragment derived from Zaire Ebola virus glycoprotein elicits effective neutralizing antibody

In order to produce polyvalent vaccines based on single rVSV vector, we investigated the immunogenicity, antibody neutralizing activity, and antigenic determinant domain of Zaire Ebola's fragment MFL (aa 393-556) that contains furin site and internal fusion loop. Both the recombinant protein and the recombinant plasmid of fragment MFL elicited high levels of antibody, similar to those of Zaire Ebola GP (ZGP). The MFL fragment of ZGP also elicited high levels of neutralizing antibody and induced moderate cellular immune response in mice, as revealed by the proliferation and cytokine secretion of splenocytes. Through the analysis of the induction of neutralizing antibody by pVAX1-based recombinant plasmids that expressed truncated fragments of MFL, we found that the domain containing the internal fusion loop and the furin site was the major contributor of fragment MFL's immunogenicity. Furthermore, the rVSV-based bivalent vaccine expressing Sudan Ebola GP (SGP) and MFL fragment elicited efficient cross-immunity against ZGP and SGP with high levels of neutralizing antibody. Our results indicate that fragment MFL is an effective and novel antigen for the production of neutralizing antibody and polyvalent vaccines of Ebola virus.

Bats and their virome: an important source of emerging viruses capable of infecting humans

Bats are being increasingly recognized as an important reservoir of zoonotic viruses of different families, including SARS coronavirus, Nipah virus, Hendra virus and Ebola virus. Several recent studies hypothesized that bats, an ancient group of flying mammals, are the major reservoir of several important RNA virus families from which other mammalian viruses of livestock and humans were derived. Although this hypothesis needs further investigation, the premise that bats carry a large number of viruses is commonly accepted. The question of whether bats have unique biological features making them ideal reservoir hosts has been the subject of several recent reviews. In this review, we will focus on the public health implications of bat derived zoonotic viral disease outbreaks, examine the drivers and risk factors of past disease outbreaks and outline research directions for better control of future disease events.

Prediction and identification of mouse cytotoxic T lymphocyte epitopes in Ebola virus glycoproteins

Background

Ebola viruses (EBOVs) cause severe hemorrhagic fever with a high mortality rate. At present, there are no licensed vaccines or efficient therapies to combat EBOV infection. Previous studies have shown that both humoral and cellular immune responses are crucial for controlling Ebola infection. CD8⁺ T cells play an important role in mediating vaccine-induced protective immunity. The objective of this study was to identify H-2^d-specific T cell epitopes in EBOV glycoproteins (GPs).

Results

Computer-assisted algorithms were used to predict H-2^d-specific T cell epitopes in two species of EBOV (Sudan and Zaire) GP. The predicted peptides were synthesized and identified in BALB/c mice immunized with replication-deficient adenovirus vectors expressing the EBOV GP. Enzyme-linked immunospot assays and intracellular cytokine staining showed that the peptides RPHTPQFLF (Sudan EBOV), GPCAGDFAF and LYDRLASTV (Zaire EBOV) could stimulate splenoctyes in immunized mice to produce large amounts of interferon-gamma.

Conclusion

Three peptides within the GPs of two EBOV strains were identified as T cell epitopes. The identification of these epitopes should facilitate the evaluation of vaccines based on the Ebola virus glycoprotein in a BALB/c mouse model.

Simian hemorrhagic fever virus infection of rhesus macaques as a model of viral hemorrhagic fever: clinical characterization and risk factors for severe disease

Simian Hemorrhagic Fever Virus (SHFV) has caused sporadic outbreaks of hemorrhagic fevers in macaques at primate research facilities. SHFV is a BSL-2 pathogen that has not been linked to human disease; as such, investigation of SHFV pathogenesis in non-human primates (NHPs) could serve as a model for hemorrhagic fever viruses such as Ebola, Marburg, and Lassa viruses. Here we describe the pathogenesis of SHFV in rhesus macaques inoculated with doses ranging from 50 PFU to 500,000 PFU. Disease severity was independent of dose with an overall mortality rate of 64% with signs of hemorrhagic fever and multiple organ system involvement. Analyses comparing survivors and non-survivors were performed to identify factors associated with survival revealing differences in the kinetics of viremia, immunosuppression, and regulation of hemostasis. Notable similarities between the pathogenesis of SHFV in NHPs and hemorrhagic fever viruses in humans suggest that SHFV may serve as a suitable model of BSL-4 pathogens.

Production and characterization of monoclonal antibodies to nucleoprotein of Marburg virus

Monoclonal antibodies (MAbs) against the nucleoprotein of Marburg virus (MARV-NP) with high specificity and activity would be useful for the diagnosis of MARV. In this report, a recombinant MARV-NP was successfully expressed by an Escherichia coli expression system. After immunization and cell fusion, three mouse hybridomas (1H4, 2G1, and 3B5) producing MAbs to MARV-NP were established. The MAbs obtained were fully characterized using indirect ELISA and Western blot analysis. The ELISA results showed that the MAbs' titers were in the range of 1:6.400 x 10(3) - 1:1.280 x 10(4) in culture fluids, and 1:1.024 x 10(6) - 1:8.192 x 106 in ascitic fluids. The isotypes of the three MAbs were tested to be IgG1(kappa) and all the MAbs recognized the same antigenic epitope. Western blot analyses demonstrated that all the MAbs were directed against MARV-NP with the affinity constants (Kaff) of about 1.100 x 10(9) M(-1), 1.235 x 10(9) M(-1), and 1.408 x 10(9) M(-1) for the MAbs 1H4, 2G1, and 3B5, respectively.

Containing a haemorrhagic fever epidemic: the Ebola experience in Uganda (October 2000-January 2001)

INTRODUCTION

The Ebola virus, belonging to the family of filoviruses, was first recognized in 1976 when it caused concurrent outbreaks in Yambuku in the Democratic Republic of Congo (DRC), and in the town of Nzara in Sudan. Both countries share borders with Uganda. A total of 425 cases and 224 deaths attributed to Ebola haemorrhagic fever (EHF) were recorded in Uganda in 2000/01. Although there was delayed detection at the community level, prompt and efficient outbreak investigation led to the confirmation of the causative agent on 14 October 2000 by the National Institute of Virology in South Africa, and the subsequent institution of control interventions.

CONTROL INTERVENTIONS

Public health interventions to contain the epidemic aimed at minimizing transmission in the health care setting and in the community, reducing the case fatality rate due to the epidemic, strengthening co-ordination for the response and building capacity for on-going surveillance and control. Co-ordination of the control interventions was organized through the Interministerial Committee, National Ebola Task Force, District Ebola Task Forces, and the Technical Committees at national and district levels. The World Health Organization (WHO) under the Global Outbreak Alert and Response Network co-ordinated the international response. The post-outbreak control interventions addressed weaknesses prior to outbreak detection and aimed at improving preparations for future outbreak detection and response. Challenges to control efforts included inadequate and poor quality protective materials, deaths of health workers, numerous rumors and the rejection of convalescent cases by members of the community.

CONCLUSIONS

This was recognized as the largest reported outbreak of EHF in the world. Control interventions were very successful in containing the epidemic. The community structures used to contain the epidemic have continued to perform well after containment of the outbreak, and have proved useful in the identification of other outbreaks. This was also the first outbreak response co-ordinated by the WHO under the Global Outbreak Alert and Response Network, a voluntary organization recently created to co-ordinate technical and financial resources to developing countries during outbreaks.

Mapping of two dominant sites of VP35 of Marburg virus

Five types of anti-VP35 monoclonal antibodies (MAbs), four immune sera against Marburg virus (MBGV), and 11 overlapping recombinant VP35 fragments were used to map the epitopes for VP35 of MBGV. The purified full-size recombinant VP35 was highly immunogenic and retained the B-cell epitopes that were identical to those of the viral VP35. Two major sites on VP35 and a set of truncated VP35 fragments were found by use of an enzyme immunoassay and immunoblot. Site I was located in a region between amino acids 1 and 174 of the VP35 sequence, and only polyclonal antibodies (PAbs) against MBGV recognized epitopes at this site. Site II was mapped by use of anti-VP35 MAbs to the region between amino acid residues 167 and 278 of VP35. Amino acids 252-278 of VP35 might be involved in the formation of the epitopes for MAbs. B-cell epitopes were not found on the C-terminus of VP35 by use of PAbs or MAbs.

Diagnostic electron microscopy is still a timely and rewarding method

BACKGROUND

Parallel to its technical development starting in the 1930s, electron microscopy (EM) became an important tool in basic and clinical virology. First utilized in the rapid diagnosis of smallpox, it developed to a diagnostic routine in the early 1960s using the negative staining technique. EM was applied to infected cell-cultures and also to 'dirty' specimens including urine, feces, vesicle fluid, liquor. With the implementation of molecular biological and genetic techniques, the use of diagnostic EM decreased.

OBJECTIVES

(1) To give a perspective on future indications and possible uses by discussing the past and the present of diagnostic EM, (2) To describe the system of External Quality Assessment on EM virus diagnosis (EQA-EMV) established in 1994 by our laboratory and its achievements.

STUDY DESIGN

EQA-EMV is run to evaluate, to confirm and to improve the quality of diagnostic EM. Two different types of specimen are sent out: (1) prepared grids to assess and train the diagnostic skills of the participants, (2) stabilized virus particle suspensions to assess preparation efficiency.

RESULTS

Diagnostic EM differs from other diagnostic tests in its rapidity and its undirected 'open view'. To emphasize these advantages, the indications for diagnostic EM are discussed, fundamental for a continuing future adaptation. Besides appropriate techniques, quality control measures are required to achieve and keep high diagnostic standards. The results from 6 years of EQA-EMV are presented.

CONCLUSIONS

In the history of diagnostic EM in virology, a change in use has been seen. Starting in the 1990s and coincident with the broad introduction of 'modern' diagnostic techniques, the number of EM diagnostic labs has decreased considerably--in spite of the obvious advantages of this technique. To guarantee the continuing performance of diagnostic EM in the future. EQA runs have to be performed as with other techniques in the diagnostic armament. The growing number of participants and participating countries indicates an interest in as well as a need for this program.