Sequence-based human leukocyte antigen-B typing of patients infected with Ebola virus in Uganda in 2000: identification of alleles associated with fatal and nonfatal disease outcomes

Genetic loci regulate Sarbecovirus pathogenesis: A comparison across mice and humans

Coronavirus (CoV) cause considerable morbidity and mortality in humans and other mammals, as evidenced by the emergence of Severe Acute Respiratory CoV (SARS-CoV) in 2003, Middle East Respiratory CoV (MERS-CoV) in 2012, and SARS-CoV-2 in 2019. Although poorly characterized, natural genetic variation in human and other mammals modulate virus pathogenesis, as reflected by the spectrum of clinical outcomes ranging from asymptomatic infections to lethal disease. Using multiple human epidemic and zoonotic Sarbecoviruses, coupled with murine Collaborative Cross genetic reference populations, we identify several dozen quantitative trait loci that regulate SARS-like group-2B CoV pathogenesis and replication. Under a Chr4 QTL, we deleted a candidate interferon stimulated gene, Trim14 which resulted in enhanced SARS-CoV titers and clinical disease, suggesting an antiviral role during infection. Importantly, about 60 % of the murine QTL encode susceptibility genes identified as priority candidates from human genome-wide association studies (GWAS) studies after SARS-CoV-2 infection, suggesting that similar selective forces have targeted analogous genes and pathways to regulate Sarbecovirus disease across diverse mammalian hosts. These studies provide an experimental platform in rodents to investigate the molecular-genetic mechanisms by which potential cross mammalian susceptibility loci and genes regulate type-specific and cross-SARS-like group 2B CoV replication, immunity, and pathogenesis in rodent models. Our study also provides a paradigm for identifying susceptibility loci for other highly heterogeneous and virulent viruses that sporadically emerge from zoonotic reservoirs to plague human and animal populations.

Safety, tolerability, and immunogenicity of the Ebola Sudan chimpanzee adenovirus vector vaccine (cAd3-EBO S) in healthy Ugandan adults: a phase 1, open-label, dose-escalation clinical trial

BACKGROUND

Sudan Ebola virus can cause severe viral disease, with an average case fatality rate of 54%. A recent outbreak of Sudan Ebola virus in Uganda caused 55 deaths among 164 confirmed cases in the second half of 2022. Although vaccines and therapeutics specific for Zaire Ebola virus have been approved for use during outbreak situations, Sudan Ebola virus is an antigenically distinct virus with no approved vaccines available.

METHODS

In this phase 1, open-label, dose-escalation trial we evaluated the safety, tolerability, and immunogenicity of a monovalent chimpanzee adenovirus 3 vaccine against Sudan Ebola virus (cAd3-EBO S) at Makerere University Walter Reed Project in Kampala, Uganda. Study participants were recruited from the Kampala metropolitan area using International Review Board-approved written and electronic media explaining the trial intervention. Healthy adults without previous receipt of Ebola, Marburg, or cAd3 vectored-vaccines were enrolled to receive cAd3-EBO S at either 1 × 1010 or 1 × 1011 particle units (PU) in a single intramuscular vaccination and were followed up for 48 weeks. Primary safety and tolerability endpoints were assessed in all vaccine recipients by reactogenicity for the first 7 days, adverse events for the first 28 days, and serious adverse events throughout the study. Secondary immunogenicity endpoints included evaluation of binding antibody and T-cell responses against the Sudan Ebola virus glycoprotein, and neutralising antibody responses against the cAd3 vector at 4 weeks after vaccination. This study is registered with ClinicalTrials.gov, NCT04041570, and is completed.

FINDINGS

40 healthy adults were enrolled between July 22 and Oct 1, 2019, with 20 receiving 1 × 1010 PU and 20 receiving 1 × 1011 PU of cAd3-EBO S. 38 (95%) participants completed all follow-up visits. The cAd3-EBO S vaccine was well tolerated with no severe adverse events. The most common reactogenicity symptoms were pain or tenderness at the injection site (34 [85%] of 40), fatigue (29 [73%] of 40), and headache (26 [65%] of 40), and were mild to moderate in severity. Positive responses for glycoprotein-specific binding antibodies were induced by 2 weeks in 31 (78%) participants, increased to 34 (85%) participants by 4 weeks, and persisted to 48 weeks in 31 (82%) participants. Most participants developed glycoprotein-specific T-cell responses (20 [59%, 95% CI 41-75] of 34; six participants were removed from the T cell analysis after failing quality control parameters) by 4 weeks after vaccination, and neutralising titres against the cAd3 vector were also increased from baseline (90% inhibitory concentration of 47, 95% CI 30-73) to 4 weeks after vaccination (196, 125-308).

INTERPRETATION

The cAd3-EBO S vaccine was safe at both doses, rapidly inducing immune responses in most participants after a single injection. The rapid onset and durability of the vaccine-induced antibodies make this vaccine a strong candidate for emergency deployment in Sudan Ebola virus outbreaks.

FUNDING

National Institutes of Health via interagency agreement with Walter Reed Army Institute of Research.

EBOLA VIRUS DISEASE DYNAMICS WITH SOME PREVENTIVE MEASURES: A CASE STUDY OF THE 2018–2020 KIVU OUTBREAK

To fight against Ebola virus disease, several measures have been adopted. Among them, isolation, safe burial and vaccination occupy a prominent place. In this paper, we present a model which takes into account these three control strategies as well as the indirect transmission through a polluted environment. The asymptotic behavior of our model is achieved. Namely, we determine a threshold value [Formula: see text] of the control reproduction number [Formula: see text], below which the disease is eliminated in the long run. Whenever the value of [Formula: see text] ranges from [Formula: see text] and 1, we prove the existence of a backward bifurcation phenomenon, which corresponds to the case, where a locally asymptotically stable positive equilibrium co-exists with the disease-free equilibrium, which is also locally asymptotically stable. The existence of this bifurcation complicates the control of Ebola, since the requirement of [Formula: see text] below one, although necessary, is no longer sufficient for the elimination of Ebola, more efforts need to be deployed. When the value of [Formula: see text] is greater than one, we prove the existence of a unique endemic equilibrium, locally asymptotically stable. That is the disease may persist and become endemic. Numerically, we fit our model to the reported data for the 2018–2020 Kivu Ebola outbreak which occurred in Democratic Republic of Congo. Through the sensitivity analysis of the control reproduction number, we prove that the transmission rates of infected alive who are outside hospital are the most influential parameters. Numerically, we explore the usefulness of isolation, safe burial combined with vaccination and investigate the importance to combine the latter control strategies to the educational campaigns or/and case finding.

Peripheral Neuronopathy Associated With Ebola Virus Infection in Rhesus Macaques: A Possible Cause of Neurological Signs and Symptoms in Human Ebola Patients

Neurological signs and symptoms are the most common complications of Ebola virus disease. However, the mechanisms underlying the neurologic manifestations in Ebola patients are not known. In this study, peripheral ganglia were collected from 12 rhesus macaques that succumbed to Ebola virus (EBOV) disease from 5 to 8 days post exposure. Ganglionitis, characterized by neuronal degeneration, necrosis, and mononuclear leukocyte infiltrates, was observed in the dorsal root, autonomic, and enteric ganglia. By immunohistochemistry, RNAscope in situ hybridization, transmission electron microscopy, and confocal microscopy, we confirmed that CD68+ macrophages are the target cells for EBOV in affected ganglia. Further, we demonstrated that EBOV can induce satellite cell and neuronal apoptosis and microglial activation in infected ganglia. Our results demonstrate that EBOV can infect peripheral ganglia and results in ganglionopathy in rhesus macaques, which may contribute to the neurological signs and symptoms observed in acute and convalescent Ebola virus disease in human patients.

Ebola Virus Disease in Humans: Pathophysiology and Immunity

Viruses of the Ebolavirus genus cause sporadic epidemics of severe and systemic febrile disease that are fueled by human-to-human transmission. Despite the notoriety of ebolaviruses, particularly Ebola virus (EBOV), as prominent viral hemorrhagic fever agents, and the international concern regarding Ebola virus disease (EVD) outbreaks, very little is known about the pathophysiology of EVD in humans and, in particular, about the human immune correlates of survival and immune memory. This lack of basic knowledge about physiological characteristics of EVD is probably attributable to the dearth of clinical and laboratory data gathered from past outbreaks. The unprecedented magnitude of the EVD epidemic that occurred in West Africa from 2013 to 2016 has allowed, for the first time, evaluation of clinical, epidemiological, and immunological parameters in a significant number of patients using state-of-the-art laboratory equipment. This review will summarize the data from the literature regarding human pathophysiologic and immunologic responses to filoviral infection.

Assessing the effects of modeling the spectrum of clinical symptoms on the dynamics and control of Ebola

Mathematical modelers have attempted to capture the dynamics of Ebola transmission and to evaluate the effectiveness of control measures, as well as to make predictions about ongoing outbreaks. Many of their models consider only infections with typical symptoms, but Ebola presents clinically in a more complicated way. Even the most common symptom, fever, is not experienced by 13% of patients. This suggests that infected individuals could be asymptomatic or have moderately symptomatic infections as reported during previous Ebola outbreaks. To account crudely for the spectrum of clinical symptoms that characterizes Ebola infection, we developed a model including moderate and severe symptoms. Our model captures the dynamics of the recent outbreak of Ebola in Liberia. Our estimate of the basic reproduction number is 1.83 (CI: 1.72, 1.86), consistent with the WHO response team's estimate using early outbreak case data. We also estimate the effectiveness of interventions using observations before and after their introduction. As the final epidemic size is linked to the timing of interventions in an exponential fashion, a simple empirical formula is provided to guide policy-making. It suggests that early implementation could significantly decrease final size. We also compare our model to one with typical symptoms by excluding moderate ones. The model with only typical symptoms overestimates the basic reproduction number and effectiveness of control measures, and exaggerates changes in peak size attributable to the timing of interventions. In addition, uncertainty about how moderate symptoms affect the basic reproduction number is considered, and PRCC (Partial rank correlation coefficient) is used to analyze the global sensitivity of relevant parameters. Possible control strategies are evaluated through numerical simulations and sensitivity analysis, indicating that simultaneously strengthening contact-tracing and effectiveness of isolation in hospital would be most effective. In this study, we show that asymptomatic Ebola infections may have implications for policy-making.

Human T-cell immunity against the emerging and re-emerging viruses

Over the past decade, we have seen an alarming number of high-profile outbreaks of newly emerging and re-emerging viruses. Recent outbreaks of avian influenza viruses, Middle East respiratory syndrome coronaviruses, Zika virus and Ebola virus present great threats to global health. Considering the pivotal role of host T-cell immunity in the alleviation of symptoms and the clearance of viruses in patients, there are three issues to be primarily concerned about T-cell immunity when a new virus emerges: first, does the population possess pre-existing T-cells against the new virus through previous infections of genetically relevant viruses; second, does a proper immune response arise in the patients to provide protection through an immunopathogenic effect; lastly, how long can the virus-specific immune memory persist. Herein, we summarize the current updates on the characteristics of human T-cell immunological responses against recently emerged or re-emerged viruses, and emphasize the necessity for timely investigation on the T-cell features of these viral diseases, which may provide beneficial recommendations for clinical diagnosis and vaccine development.

Assays to Measure Suppression of Type I Interferon Responses by Filovirus VP35 Proteins

Innate immunity is the first line of defense against virus infections and is marked by production of type I interferons (IFN), a family of cytokines that includes IFN-β and several IFN-αs. For the filoviruses and many other RNA viruses that replicate in the cytoplasm, the RIG-I-like pattern recognition receptors (RLRs) are potential triggers of IFN production. To counteract such innate antiviral responses, many viruses encode proteins that antagonize RLR signaling. Ebola virus (EBOV) and other filoviruses produce VP35 proteins that block IFN induction via RLR signaling. We describe here cell-based reporter gene assays that quantify the IFN-antagonist function of filovirus VP35 proteins by assessing activation of the IFN-β promoter.

Molecular mechanisms of Ebola pathogenesis

Ebola viruses (EBOVs) and Marburg viruses (MARVs) are among the deadliest human viruses, as highlighted by the recent and widespread Ebola virus outbreak in West Africa, which was the largest and longest epidemic of Ebola virus disease (EVD) in history, resulting in significant loss of life and disruptions across multiple continents. Although the number of cases has nearly reached its nadir, a recent cluster of 5 cases in Guinea on March 17, 2016, has extended the enhanced surveillance period to June 15, 2016. New, enhanced 90-d surveillance windows replaced the 42-d surveillance window to ensure the rapid detection of new cases that may arise from a missed transmission chain, reintroduction from an animal reservoir, or more important, reemergence of the virus that has persisted in an EVD survivor. In this review, we summarize our current understanding of EBOV pathogenesis, describe vaccine and therapeutic candidates in clinical trials, and discuss mechanisms of viral persistence and long-term health sequelae for EVD survivors.

[Ebola virus disease: Clinical presentation, prognosis and treatment]

The clinical spectrum of Ebola virus disease (EVD) ranges from very serious forms with organ failure and death within days to paucisymptomatic forms and perhaps even asymptomatic. The authors propose a focus on the clinical manifestations of EVD, on prognosis and on therapeutic aspects (excluding resuscitation). This work extracts from the literature the main data gathered during the 2014-2015 epidemic that raged in Guinea Conakry and Sierra Leone. These two countries, even if they are separated by a border, are one and the same population base. The characteristics of the epidemic in Liberia have not been analyzed. The authors have treated EVD patients in the health workers treatment center of Conakry and enrich this work about their personal experience.

Novel Chemical Ligands to Ebola Virus and Marburg Virus Nucleoproteins Identified by Combining Affinity Mass Spectrometry and Metabolomics Approaches

The nucleoprotein (NP) of Ebola virus (EBOV) and Marburg virus (MARV) is an essential component of the viral ribonucleoprotein complex and significantly impacts replication and transcription of the viral RNA genome. Although NP is regarded as a promising antiviral druggable target, no chemical ligands have been reported to interact with EBOV NP or MARV NP. We identified two compounds from a traditional Chinese medicine Gancao (licorice root) that can bind both NPs by combining affinity mass spectrometry and metabolomics approaches. These two ligands, 18β-glycyrrhetinic acid and licochalcone A, were verified by defined compound mixture screens and further characterized with individual ligand binding assays. Accompanying biophysical analyses demonstrate that binding of 18β-glycyrrhetinic acid to EBOV NP significantly reduces protein thermal stability, induces formation of large NP oligomers, and disrupts the critical association of viral ssRNA with NP complexes whereas the compound showed no such activity on MARV NP. Our study has revealed the substantial potential of new analytical techniques in ligand discovery from natural herb resources. In addition, identification of a chemical ligand that influences the oligomeric state and RNA-binding function of EBOV NP sheds new light on antiviral drug development.

Exploring the mechanism how Marburg virus VP35 recognizes and binds dsRNA by molecular dynamics simulations and free energy calculations

Filoviruses often cause terrible infectious disease which has not been successfully dealt with pharmacologically. All filoviruses encode a unique protein termed VP35 which can mask doubled-stranded RNA to deactivate interferon. The interface of VP35-dsRNA would be a feasible target for structure-based antiviral agent design. To explore the essence of VP35-dsRNA interaction, molecular dynamics simulation combined with MM-GBSA calculations were performed on Marburg virus VP35-dsRNA complex and several mutational complexes. The energetic analysis indicates that nonpolar interactions provide the main driving force for the binding process. Although the intermolecular electrostatic interactions play important roles in VP35-dsRNA interaction, the whole polar interactions are unfavorable for binding which result in a low binding affinity. Compared with wild type VP35, the studied mutants F228A, R271A, and K298A have obviously reduced binding free energies with dsRNA reflecting in the reduction of polar or nonpolar interactions. The results also indicate that the loss of binding affinity for one dsRNA strand would abolish the total binding affinity. Three important residues Arg271, Arg294, and Lys298 which makes the largest contribution for binding in VP35 lose their binding affinity significantly in mutants. The uncovering of VP35-dsRNA recognition mechanism will provide some insights for development of antiviral drug.

Effects of Mother's Illness and Breastfeeding on Risk of Ebola Virus Disease in a Cohort of Very Young Children

Background

Young children who contract Ebola Virus Disease (EVD) have a high case fatality rate, but their sources of infection and the role of breastfeeding are unclear.

Methods/Principal Findings

Household members of EVD survivors from the Kerry Town Ebola Treatment Centre in Sierra Leone were interviewed four to 10 months after discharge to establish exposure levels for all members of the household, whether or not they became ill, and including those who died. We analysed a cohort of children under three years to examine associations between maternal illness, survival and breastfeeding, and the child’s outcome. Of 77 children aged zero to two years in the households we surveyed, 43% contracted EVD. 64 children and mothers could be linked: 25/40 (63%) of those whose mother had EVD developed EVD, compared to 2/24 (8%) whose mother did not have EVD, relative risk adjusted for age, sex and other exposures (aRR) 7·6, 95%CI 2·0–29·1. Among those with mothers with EVD, the risk of EVD in the child was higher if the mother died (aRR 1·5, 0·99–2·4), but there was no increased risk associated with breast-feeding (aRR 0·75, 0·46–1·2). Excluding those breastfed by infected mothers, half (11/22) of the children with direct contact with EVD cases with wet symptoms (diarrhoea, vomiting or haemorrhage) remained well.

Conclusion/Significance

This is the largest study of mother-child pairs with EVD to date, and the first attempt at assessing excess risk from breastfeeding. For young children the key exposure associated with contracting EVD was mother’s illness with EVD, with a higher risk if the mother died. Breast feeding did not confer any additional risk in this study but high risk from proximity to a sick mother supports WHO recommendations for separation. This study also found that many children did not become ill despite high exposures.

Our study is the first to quantify sources of infection and describe risk of transmission of Ebola to young children. We found that the risk of a child under three developing Ebola disease was low unless their mother had EVD, and that the risk was particularly high if their mother died of EVD. But we found no additional risk from breastfeeding. WHO recommends separating asymptomatic breast-fed infants from their mothers if they develop Ebola, and using formula feeding. We support the need for separation because of the high risk related to proximity, but more research is needed to more fully understand this, particularly given the importance of breast-feeding in preventing other childhood illnesses. We also found young children in Ebola-affected households whose mothers were not ill had a surprisingly low risk of developing EVD which was not all explained by low exposure to the virus. Many children stayed well despite having direct contact with EVD patients with diarrhoea, vomiting or bleeding who are considered the most infectious. We hope these findings will provide impetus for more detailed studies into age-related response to the Ebola virus.

New paradigms in sepsis: from prevention to protection of failing microcirculation

Sepsis, also known as septicemia, is one of the 10 leading causes of death worldwide. The rising tide of sepsis due to bacterial, fungal and viral infections cannot be stemmed by current antimicrobial therapies and supportive measures. New paradigms for the mechanism and resolution of sepsis and consequences for sepsis survivors are emerging. Consistent with Benjamin Franklin's dictum 'an ounce of prevention is worth a pound of cure', sepsis can be prevented by vaccinations against pneumococci and meningococci. Recently, the NIH NHLBI Panel redefined sepsis as 'severe endothelial dysfunction syndrome in response to intravascular and extravascular infections causing reversible or irreversible injury to the microcirculation responsible for multiple organ failure'. Microvascular endothelial injury underlies sepsis-associated hypotension, edema, disseminated intravascular coagulation, acute respiratory distress syndrome and acute kidney injury. Microbial genome products trigger 'genome wars' in sepsis that reprogram the human genome and culminate in a 'genomic storm' in blood and vascular cells. Sepsis can be averted experimentally by endothelial cytoprotection through targeting nuclear signaling that mediates inflammation and deranged metabolism. Endothelial 'rheostats' (e.g. inhibitors of NF-κB, A20 protein, CRADD/RAIDD protein and microRNAs) regulate endothelial signaling. Physiologic 'extinguishers' (e.g. suppressor of cytokine signaling 3) can be replenished through intracellular protein therapy. Lipid mediators (e.g. resolvin D1) hasten sepsis resolution. As sepsis cases rose from 387 330 in 1996 to 1.1 million in 2011, and are estimated to reach 2 million by 2020 in the US, mortality due to sepsis approaches that of heart attacks and exceeds deaths from stroke. More preventive vaccines and therapeutic measures are urgently needed.

Filoviruses: One of These Things is (not) Like the Other

The family Filoviridae contains several of the most deadly pathogens known to date and the current Ebola virus disease (EVD) outbreak in Western Africa, due to Ebola virus (EBOV) infection, highlights the need for active and broad research into filovirus pathogenesis. However, in comparison, the seven other known filovirus family members are significantly understudied. Many of these, including Marburgviruses and Ebolaviruses other than EBOV, are also highly virulent and fully capable of causing widespread epidemics. This review places the focus on these non-EBOV filoviruses, including known immunological and pathological data. The available animal models, research tools and currently available therapeutics will also be discussed along with an emphasis in the large number of current gaps in knowledge of these less highlighted filoviruses. It is evident that much research is yet to be done in order to bring the non-EBOV filovirus field to the forefront of current research and, importantly, to the development of more effective vaccines and therapeutics to combat potential future outbreaks.

Human Leukocyte Antigen Diversity: A Southern African Perspective

Despite the increasingly well-documented evidence of high genetic, ethnic, and linguistic diversity amongst African populations, there is limited data on human leukocyte antigen (HLA) diversity in these populations. HLA is part of the host defense mechanism mediated through antigen presentation to effector cells of the immune system. With the high disease burden in southern Africa, HLA diversity data is increasingly important in the design of population-specific vaccines and the improvement of transplantation therapeutic interventions. This review highlights the paucity of HLA diversity data amongst southern African populations and defines a need for information of this kind. This information will support disease association studies, provide guidance in vaccine design, and improve transplantation outcomes.

Addressing Therapeutic Options for Ebola Virus Infection in Current and Future Outbreaks

Ebola virus can cause severe hemorrhagic disease with high fatality rates. Currently, no specific therapeutic agent or vaccine has been approved for treatment and prevention of Ebola virus infection of humans. Although the number of Ebola cases has fallen in the last few weeks, multiple outbreaks of Ebola virus infection and the likelihood of future exposure highlight the need for development and rapid evaluation of pre- and postexposure treatments. Here, we briefly review the existing and future options for anti-Ebola therapy, based on the data coming from rare clinical reports, studies on animals, and results from in vitro models. We also project the mechanistic hypotheses of several potential drugs against Ebola virus, including small-molecule-based drugs, which are under development and being tested in animal models or in vitro using various cell types. Our paper discusses strategies toward identifying and testing anti-Ebola virus properties of known and medically approved drugs, especially those that can limit the pathological inflammatory response in Ebola patients and thereby provide protection from mortality. We underline the importance of developing combinational therapy for better treatment outcomes for Ebola patients.

Biomarker correlates of survival in pediatric patients with Ebola virus disease

Children who had certain endothelial and immune function markers were more likely to survive infection.

Outbreaks of Ebola virus disease (EVD) occur sporadically in Africa and are associated with high case-fatality rates. Historically, children have been less affected than adults. The 2000–2001 Sudan virus–associated EVD outbreak in the Gulu district of Uganda resulted in 55 pediatric and 161 adult laboratory-confirmed cases. We used a series of multiplex assays to measure the concentrations of 55 serum analytes in specimens from patients from that outbreak to identify biomarkers specific to pediatric disease. Pediatric patients who survived had higher levels of the chemokine regulated on activation, normal T-cell expressed and secreted marker and lower levels of plasminogen activator inhibitor 1, soluble intracellular adhesion molecule, and soluble vascular cell adhesion molecule than did pediatric patients who died. Adult patients had similar levels of these analytes regardless of outcome. Our findings suggest that children with EVD may benefit from different treatment regimens than those for adults.

Animal models for ebolavirus countermeasures discovery: what defines a useful model?

INTRODUCTION

Ebolaviruses are highly pathogenic filoviruses, which cause disease in humans and nonhuman primates (NHP) in Africa. The Zaire ebolavirus outbreak in 2014, which continues to greatly affect Western Africa and other countries to which the hemorrhagic fever was exported due to travel of unsymptomatic yet infected individuals, was complicated by the lack of available licensed vaccines or therapeutics to combat infection. After almost a year of research at an increased pace to find and test vaccines and therapeutics, there is now a deeper understanding of the available disease models for ebolavirus infection. Demonstration of vaccine or therapeutic efficacy in NHP models of ebolavirus infection is crucial to the development and eventual licensure of ebolavirus medical countermeasures, so that safe and effective countermeasures can be accelerated into human clinical trials.

AREAS COVERED

The authors describe ebolavirus hemorrhagic fever (EHF) disease in various animal species: mice, guinea pigs, hamsters, pigs and NHP, to include baboons, marmosets, rhesus and cynomolgus macaques, as well as African green monkeys. Because the NHP models are supremely useful for therapeutics and vaccine testing, emphasis is placed on comparison of these models, and their use as gold-standard models of EHF.

EXPERT OPINION

Animal models of EHF varying from rodents to NHP species are currently under evaluation for their reproducibility and utility for modeling infection in humans. Complete development and licensure of therapeutic agents and vaccines will require demonstration that mechanisms conferring protection in NHP models of infection are predictive of protective responses in humans, for a given countermeasure.

An Intrinsically Disordered Peptide from Ebola Virus VP35 Controls Viral RNA Synthesis by Modulating Nucleoprotein-RNA Interactions

During viral RNA synthesis, Ebola virus (EBOV) nucleoprotein (NP) alternates between an RNA-template-bound form and a template-free form to provide the viral polymerase access to the RNA template. In addition, newly synthesized NP must be prevented from indiscriminately binding to noncognate RNAs. Here, we investigate the molecular bases for these critical processes. We identify an intrinsically disordered peptide derived from EBOV VP35 (NPBP, residues 20-48) that binds NP with high affinity and specificity, inhibits NP oligomerization, and releases RNA from NP-RNA complexes in vitro. The structure of the NPBP/ΔNPNTD complex, solved to 3.7 Å resolution, reveals how NPBP peptide occludes a large surface area that is important for NP-NP and NP-RNA interactions and for viral RNA synthesis. Together, our results identify a highly conserved viral interface that is important for EBOV replication and can be targeted for therapeutic development.

Ebola: a holistic approach is required to achieve effective management and control

The current Ebola outbreak in West Africa has already caused substantial mortality and dire human and economic consequences. It continues to represent an alarming public health threat in the region and beyond and jeopardizes the provision of health care and other services in the affected countries. The scale of the epidemic has accelerated research efforts for diagnostics, treatment, and prevention galvanized through increased availability of funding. Our knowledge relating to the virus, disease pathogenesis, risk factors, dynamics of transmission, and epidemic control is increasing, and sociocultural factors have emerged as critical determinants for the success and failure of control efforts. However, there is a long way to go. In this review we summarize the current knowledge, examine the sociocultural context in West Africa, and outline priority areas for future research.

Ebola hemorrhagic Fever: novel biomarker correlates of clinical outcome

BACKGROUND

Ebola hemorrhagic fever (EHF) outbreaks occur sporadically in Africa and result in high rates of death. The 2000-2001 outbreak of Sudan virus-associated EHF in the Gulu district of Uganda led to 425 cases, of which 216 were laboratory confirmed, making it the largest EHF outbreak on record. Serum specimens from this outbreak had been preserved in liquid nitrogen from the time of collection and were available for analysis.

METHODS

Available samples were tested using a series of multiplex assays to measure the concentrations of 55 biomarkers. The data were analyzed to identify statistically significant associations between the tested biomarkers and hemorrhagic manifestations, viremia, and/or death.

RESULTS

Death, hemorrhage, and viremia were independently associated with elevated levels of several chemokines and cytokines. Death and hemorrhage were associated with elevated thrombomodulin and ferritin levels. Hemorrhage was also associated with elevated levels of soluble intracellular adhesion molecule. Viremia was independently associated with elevated levels of tissue factor and tissue plasminogen activator. Finally, samples from nonfatal cases had higher levels of sCD40L.

CONCLUSIONS

These novel associations provide a better understanding of EHF pathophysiology and a starting point for researching new potential targets for therapeutic interventions.

Structural basis for Marburg virus VP35-mediated immune evasion mechanisms

Filoviruses, marburgvirus (MARV) and ebolavirus (EBOV), are causative agents of highly lethal hemorrhagic fever in humans. MARV and EBOV share a common genome organization but show important differences in replication complex formation, cell entry, host tropism, transcriptional regulation, and immune evasion. Multifunctional filoviral viral protein (VP) 35 proteins inhibit innate immune responses. Recent studies suggest double-stranded (ds)RNA sequestration is a potential mechanism that allows EBOV VP35 to antagonize retinoic-acid inducible gene-I (RIG-I) like receptors (RLRs) that are activated by viral pathogen-associated molecular patterns (PAMPs), such as double-strandedness and dsRNA blunt ends. Here, we show that MARV VP35 can inhibit IFN production at multiple steps in the signaling pathways downstream of RLRs. The crystal structure of MARV VP35 IID in complex with 18-bp dsRNA reveals that despite the similar protein fold as EBOV VP35 IID, MARV VP35 IID interacts with the dsRNA backbone and not with blunt ends. Functional studies show that MARV VP35 can inhibit dsRNA-dependent RLR activation and interferon (IFN) regulatory factor 3 (IRF3) phosphorylation by IFN kinases TRAF family member-associated NFkb activator (TANK) binding kinase-1 (TBK-1) and IFN kB kinase e (IKKe) in cell-based studies. We also show that MARV VP35 can only inhibit RIG-I and melanoma differentiation associated gene 5 (MDA5) activation by double strandedness of RNA PAMPs (coating backbone) but is unable to inhibit activation of RLRs by dsRNA blunt ends (end capping). In contrast, EBOV VP35 can inhibit activation by both PAMPs. Insights on differential PAMP recognition and inhibition of IFN induction by a similar filoviral VP35 fold, as shown here, reveal the structural and functional plasticity of a highly conserved virulence factor.

Nonhuman primates as models for the discovery and development of ebolavirus therapeutics

INTRODUCTION

Ebolaviruses are human pathogenic Category A priority pathogens for which no vaccines or therapeutics are currently licensed; however, several therapeutic agents have shown promising efficacy in nonhuman primate models of infection and are potential candidates for use in humans. Demonstration of efficacy in nonhuman primate models of ebolavirus infection will probably be central to the development and eventual licensure of ebolavirus medical countermeasures given the ethical and feasibility constraints of human efficacy assessments.

AREAS COVERED

The authors describe ebolavirus hemorrhagic fever (EHF), with an emphasis on comparing human and nonhuman primate pathophysiology. Published data examining human and animal clinical disease parameters, histopathological findings, and immune responses in fatal and nonfatal cases are synthesized and evaluated. Importantly, the authors also introduce and describe the FDA Animal Efficacy Rule as well as recent advances in antiviral drug development strategies for the treatment of EHF.

EXPERT OPINION

Well-characterized models of ebolavirus infection are currently under development and scrutiny as to their accuracy and utility for modeling fatal infection in humans. The advanced development and eventual licensure of therapeutic agents will require demonstration that mechanisms conferring protection in nonhuman primate models of infection are predictive of protective responses in humans.

Mouse models for filovirus infections

The filoviruses marburg- and ebolaviruses can cause severe hemorrhagic fever (HF) in humans and nonhuman primates. Because many cases have occurred in geographical areas lacking a medical research infrastructure, most studies of the pathogenesis of filoviral HF, and all efforts to develop drugs and vaccines, have been carried out in biocontainment laboratories in non-endemic countries, using nonhuman primates (NHPs), guinea pigs and mice as animal models. NHPs appear to closely mirror filoviral HF in humans (based on limited clinical data), but only small numbers may be used in carefully regulated experiments; much research is therefore done in rodents. Because of their availability in large numbers and the existence of a wealth of reagents for biochemical and immunological testing, mice have become the preferred small animal model for filovirus research. Since the first experiments following the initial 1967 marburgvirus outbreak, wild-type or mouse-adapted viruses have been tested in immunocompetent or immunodeficient mice. In this paper, we review how these types of studies have been used to investigate the pathogenesis of filoviral disease, identify immune responses to infection and evaluate antiviral drugs and vaccines. We also discuss the strengths and weaknesses of murine models for filovirus research, and identify important questions for further study.

Correlates of immunity to filovirus infection

Filoviruses can cause severe, often fatal hemorrhagic fever in humans. Recent advances in vaccine and therapeutic drug development have provided encouraging data concerning treatment of these infections. However, relatively little is known about immune responses in fatal versus non-fatal filovirus infection. This review summarizes the published literature on correlates of immunity to filovirus infection, and highlights deficiencies in our knowledge on this topic. It is likely that there are several types of successful immune responses, depending on the type of filovirus, and the presence and timing of vaccination or drug treatment.

Progress in filovirus vaccine development: evaluating the potential for clinical use

Marburg and Ebola viruses cause severe hemorrhagic fever in humans and nonhuman primates. Currently, there are no effective treatments and no licensed vaccines; although a number of vaccine platforms have proven successful in animal models. The ideal filovirus vaccine candidate should be able to provide rapid protection following a single immunization, have the potential to work postexposure and be cross-reactive or multivalent against all Marburg virus strains and all relevant Ebola virus species and strains. Currently, there are multiple platforms that have provided prophylactic protection in nonhuman primates, including DNA, recombinant adenovirus serotype 5, recombinant human parainfluenza virus 3 and virus-like particles. In addition, a single platform, recombinant vesicular stomatitis virus, has demonstrated both prophylactic and postexposure protection in nonhuman primates. These results demonstrate that achieving a vaccine that is protective against filoviruses is possible; the challenge now is to prove its safety and efficacy in order to obtain a vaccine that is ready for human use.

A novel single cDNA amplicon pyrosequencing method for high-throughput, cost-effective sequence-based HLA class I genotyping

Human leukocyte antigen (HLA) genotype influences the immune response to pathogens and transplanted tissues; accurate HLA genotyping is critical for clinical and research applications. Sequence-based HLA typing is limited by the cost of Sanger sequencing genomic DNA (gDNA) and resolving cis/trans ambiguities, hindering both studies correlating high-resolution genotype with clinical outcomes, and population-specific allele frequency surveys. We present an assay for sequence-based HLA genotyping by titanium read length clonal Roche/454 pyrosequencing of a single, universally diagnostic polymerase chain reaction (PCR) amplicon from HLA class I cDNA that captures most of exons 2, 3, and 4 used for traditional sequence-based typing. The amplicon is predicted to unambiguously resolve 85% of known alleles. A panel of 48 previously HLA-typed samples was assayed with this method, demonstrating 100% non-null allele typing concordance. We show that this technique can multiplex at least 768 patients per sequencing run with multiplex identifier sequence bar-coding. Unprecedented typing throughput results from a novel single cDNA-PCR amplicon strategy requiring only 1 PCR amplification per sample. This method dramatically reduces cost for genotyping of large cohorts.

High-throughput high-resolution class I HLA genotyping in East Africa

HLA, the most genetically diverse loci in the human genome, play a crucial role in host-pathogen interaction by mediating innate and adaptive cellular immune responses. A vast number of infectious diseases affect East Africa, including HIV/AIDS, malaria, and tuberculosis, but the HLA genetic diversity in this region remains incompletely described. This is a major obstacle for the design and evaluation of preventive vaccines. Available HLA typing techniques, that provide the 4-digit level resolution needed to interpret immune responses, lack sufficient throughput for large immunoepidemiological studies. Here we present a novel HLA typing assay bridging the gap between high resolution and high throughput. The assay is based on real-time PCR using sequence-specific primers (SSP) and can genotype carriers of the 49 most common East African class I HLA-A, -B, and -C alleles, at the 4-digit level. Using a validation panel of 175 samples from Kampala, Uganda, previously defined by sequence-based typing, the new assay performed with 100% sensitivity and specificity. The assay was also implemented to define the HLA genetic complexity of a previously uncharacterized Tanzanian population, demonstrating its inclusion in the major East African genetic cluster. The availability of genotyping tools with this capacity will be extremely useful in the identification of correlates of immune protection and the evaluation of candidate vaccine efficacy.

Correlates of protective immunity for Ebola vaccines: implications for regulatory approval by the animal rule

Ebola is a rare but deadly disease caused by a filovirus for which no treatment or vaccine is available. Vaccine development for such diseases is hampered by the inability to test vaccines in volunteers or a target population.

The Food and Drug Administration (FDA) has instituted the 'animal rule' to allow approval of vaccines and drugs that cannot be tested in humans based on immune correlates in animal models.

In the case of Ebola, the relevant animal models are non-human primates and mice.

For Ebola, immune correlates consist of immunoglobulin G responses, although other factors, such as T cells, are also likely to be important in a successful immune response.

Vaccine candidates for Ebola vaccine include the glycoprotein and nucleocapsid proteins.

Initial testing of Ebola vaccines has shown a protective effect in non-human primates and positive antibody titres in humans.

For diseases that are both rare and lethal, it is difficult to test vaccines. Sullivan and colleagues describe the use of immune correlates and the animal rule for the licensing of Ebola vaccines.

Ebola virus infection is a highly lethal disease for which there are no effective therapeutic or preventive treatments. Several vaccines have provided immune protection in laboratory animals, but because outbreaks occur unpredictably and sporadically, vaccine efficacy cannot be proven in human trials, which is required for traditional regulatory approval. The Food and Drug Administration has introduced the 'animal rule', to allow laboratory animal data to be used to show efficacy when human trials are not logistically feasible. In this Review, we describe immune correlates of vaccine protection against Ebola virus in animals. This research provides a basis for bridging the gap from basic research to human vaccine responses in support of the licensing of vaccines through the animal rule.

Recombinant human activated protein C for the postexposure treatment of Ebola hemorrhagic fever

BACKGROUND

Infection of primates with Zaire ebolavirus (ZEBOV) leads to hypotension, coagulation disorders, and an impaired immune response and, in many ways, resembles severe sepsis. Rapid decreases in plasma levels of protein C are a prominent feature of severe sepsis and ZEBOV hemorrhagic fever (ZHF). Currently, recombinant human activated protein C (rhAPC [Xigris; Eli Lilly]) is licensed for treating human patients with severe sepsis who are at high risk of death. The aim of this study was to test the efficacy of rhAPC as a potential treatment for ZHF.

METHODS

Fourteen rhesus macaques were challenged with a uniformly lethal dose of ZEBOV; 11 of these monkeys were treated by intravenous infusion with rhAPC beginning 30-60 min after challenge and continuing for 7 days. Three control monkeys received sterile saline in parallel.

RESULTS

All 3 control monkeys died on day 8, whereas 2 of the 11 rhAPC-treated monkeys survived. The mean time to death for the rhAPC-treated monkeys that did not survive ZEBOV challenge was 12.6 days. The difference in survival was significant when the rhAPC-treated monkeys were compared with historical controls.

CONCLUSIONS

The experimental findings provide evidence that ZHF and severe sepsis share underlying mechanisms and may respond to the same therapies.