Potential vaccines and post-exposure treatments for filovirus infections

A Historical Review of Military Medical Strategies for Fighting Infectious Diseases: From Battlefields to Global Health

The environmental conditions generated by war and characterized by poverty, undernutrition, stress, difficult access to safe water and food as well as lack of environmental and personal hygiene favor the spread of many infectious diseases. Epidemic typhus, plague, malaria, cholera, typhoid fever, hepatitis, tetanus, and smallpox have nearly constantly accompanied wars, frequently deeply conditioning the outcome of battles/wars more than weapons and military strategy. At the end of the nineteenth century, with the birth of bacteriology, military medical researchers in Germany, the United Kingdom, and France were active in discovering the etiological agents of some diseases and in developing preventive vaccines. Emil von Behring, Ronald Ross and Charles Laveran, who were or served as military physicians, won the first, the second, and the seventh Nobel Prize for Physiology or Medicine for discovering passive anti-diphtheria/tetanus immunotherapy and for identifying mosquito Anopheline as a malaria vector and plasmodium as its etiological agent, respectively. Meanwhile, Major Walter Reed in the United States of America discovered the mosquito vector of yellow fever, thus paving the way for its prevention by vector control. In this work, the military relevance of some vaccine-preventable and non-vaccine-preventable infectious diseases, as well as of biological weapons, and the military contributions to their control will be described. Currently, the civil-military medical collaboration is getting closer and becoming interdependent, from research and development for the prevention of infectious diseases to disasters and emergencies management, as recently demonstrated in Ebola and Zika outbreaks and the COVID-19 pandemic, even with the high biocontainment aeromedical evacuation, in a sort of global health diplomacy.

The Ebola virus glycoprotein and its immune responses across multiple vaccine platforms

Introduction: For over 40 years, ebolaviruses have been responsible for sporadic outbreaks of severe and often fatal hemorrhagic fever in humans and nonhuman primates across western and central Africa. In December 2013, an unprecedented Ebola virus (EBOV) epidemic began in West Africa and resulted in the largest outbreak to date. The past and current epidemics in West Africa and the Democratic Republic of the Congo has focused attention on the potential vaccine platforms developed over the past 20 years.Areas covered: This review summarizes the extraordinary progress using a variety of vaccination platforms including DNA, subunit, and several viral vector approaches, replicating and non-replicating, incorporating the primary antigen of EBOV, the glycoprotein. These vaccine constructs have shown varying degrees of protective efficacy in the 'gold-standard' nonhuman primate model for EBOV infections and were immunogenic in human clinical trials.Expert commentary: A number of these vaccine platforms have moved into phase III clinical trials over the past years and with the recent approval of the first EBOV vaccine in the European Union and the USA there is a strong potential to prevent future outbreaks/epidemics of EBOV infections on the scale of the West African epidemic.

UK vaccines network: Mapping priority pathogens of epidemic potential and vaccine pipeline developments

During the 2013-2016 Ebola outbreak in West Africa an expert panel was established on the instructions of the UK Prime Minister to identify priority pathogens for outbreak diseases that had the potential to cause future epidemics. A total of 13 priority pathogens were identified, which led to the prioritisation of spending in emerging diseases vaccine research and development from the UK. This meeting report summarises the process used to develop the UK pathogen priority list, compares it to lists generated by other organisations (World Health Organisation, National Institutes of Allergy and Infectious Diseases) and summarises clinical progress towards the development of vaccines against priority diseases. There is clear technical progress towards the development of vaccines. However, the availability of these vaccines will be dependent on sustained funding for clinical trials and the preparation of clinically acceptable manufactured material during inter-epidemic periods.

Vaccines against Ebola virus and Marburg virus: recent advances and promising candidates

The filoviruses Ebola virus and Marburg virus are among the most dangerous pathogens in the world. Both viruses cause viral hemorrhagic fever, with case fatality rates of up to 90%. Historically, filovirus outbreaks had been relatively small, with only a few hundred cases reported. However, the recent West African Ebola virus outbreak underscored the threat that filoviruses pose. The three year-long outbreak resulted in 28,646 Ebola virus infections and 11,323 deaths. The lack of Food and Drug Administration (FDA) licensed vaccines and antiviral drugs hindered early efforts to contain the outbreak. In response, the global scientific community has spurred the advanced development of many filovirus vaccine candidates. Novel vaccine platforms, such as viral vectors and DNA vaccines, have emerged, leading to the investigation of candidate vaccines that have demonstrated protective efficacy in small animal and nonhuman primate studies. Here, we will discuss several of these vaccine platforms with a particular focus on approaches that have advanced into clinical development.

Distinct Immunogenicity and Efficacy of Poxvirus-Based Vaccine Candidates against Ebola Virus Expressing GP and VP40 Proteins

Zaire and Sudan ebolavirus species cause a severe disease in humans and nonhuman primates (NHPs) characterized by a high mortality rate. There are no licensed therapies or vaccines against Ebola virus disease (EVD), and the recent 2013 to 2016 outbreak in West Africa highlighted the need for EVD-specific medical countermeasures. Here, we generated and characterized head-to-head the immunogenicity and efficacy of five vaccine candidates against Zaire ebolavirus (EBOV) and Sudan ebolavirus (SUDV) based on the highly attenuated poxvirus vector modified vaccinia virus Ankara (MVA) expressing either the virus glycoprotein (GP) or GP together with the virus protein 40 (VP40) forming virus-like particles (VLPs). In a human monocytic cell line, the different MVA vectors (termed MVA-EBOVs and MVA-SUDVs) triggered robust innate immune responses, with production of beta interferon (IFN-β), proinflammatory cytokines, and chemokines. Additionally, several innate immune cells, such as dendritic cells, neutrophils, and natural killer cells, were differentially recruited in the peritoneal cavity of mice inoculated with MVA-EBOVs. After immunization of mice with a homologous prime/boost protocol (MVA/MVA), total IgG antibodies against GP or VP40 from Zaire and Sudan ebolavirus were differentially induced by these vectors, which were mainly of the IgG1 and IgG3 isotypes. Remarkably, an MVA-EBOV construct coexpressing GP and VP40 protected chimeric mice challenged with EBOV to a greater extent than a vector expressing GP alone. These results support the consideration of MVA-EBOVs and MVA-SUDVs expressing GP and VP40 and producing VLPs as best-in-class potential vaccine candidates against EBOV and SUDV.IMPORTANCE EBOV and SUDV cause a severe hemorrhagic fever affecting humans and NHPs. Since their discovery in 1976, they have caused several sporadic epidemics, with the recent outbreak in West Africa from 2013 to 2016 being the largest and most severe, with more than 11,000 deaths being reported. Although some vaccines are in advanced clinical phases, less expensive, safer, and more effective licensed vaccines are desirable. We generated and characterized head-to-head the immunogenicity and efficacy of five novel vaccines against EBOV and SUDV based on the poxvirus MVA expressing GP or GP and VP40. The expression of GP and VP40 leads to the formation of VLPs. These MVA-EBOV and MVA-SUDV recombinants triggered robust innate and humoral immune responses in mice. Furthermore, MVA-EBOV recombinants expressing GP and VP40 induced high protection against EBOV in a mouse challenge model. Thus, MVA expressing GP and VP40 and producing VLPs is a promising vaccine candidate against EBOV and SUDV.

Vesicular Stomatitis Virus Pseudotyped with Ebola Virus Glycoprotein Serves as a Protective, Noninfectious Vaccine against Ebola Virus Challenge in Mice

The recent Ebola virus (EBOV) epidemic in West Africa demonstrates the potential for a significant public health burden caused by filoviral infections. No vaccine or antiviral is currently FDA approved. To expand the vaccine options potentially available, we assessed protection conferred by an EBOV vaccine composed of vesicular stomatitis virus pseudovirions that lack native G glycoprotein (VSVΔG) and bear EBOV glycoprotein (GP). These pseudovirions mediate a single round of infection. Both single-dose and prime/boost vaccination regimens protected mice against lethal challenge with mouse-adapted Ebola virus (ma-EBOV) in a dose-dependent manner. The prime/boost regimen provided significantly better protection than a single dose. As N-linked glycans are thought to shield conserved regions of the EBOV GP receptor-binding domain (RBD), thereby blocking epitopes within the RBD, we also tested whether VSVΔG bearing EBOV GPs that lack GP1 N-linked glycans provided effective immunity against challenge with ma-EBOV or a more distantly related virus, Sudan virus. Using a prime/boost strategy, high doses of GP/VSVΔG partially or fully denuded of N-linked glycans on GP1 protected mice against ma-EBOV challenge, but these mutants were no more effective than wild-type (WT) GP/VSVΔG and did not provide cross protection against Sudan virus. As reported for other EBOV vaccine platforms, the protection conferred correlated with the quantity of EBOV GP-specific Ig produced but not with the production of neutralizing antibodies. Our results show that EBOV GP/VSVΔG pseudovirions serve as a successful vaccination platform in a rodent model of Ebola virus disease and that GP1 N-glycan loss does not influence immunogenicity or vaccination success.IMPORTANCE The West African Ebola virus epidemic was the largest to date, with more than 28,000 people infected. No FDA-approved vaccines are yet available, but in a trial vaccination strategy in West Africa, recombinant, infectious VSV encoding the Ebola virus glycoprotein effectively prevented virus-associated disease. VSVΔG pseudovirion vaccines may prove as efficacious and have better safety, but they have not been tested to date. Thus, we tested the efficacy of VSVΔG pseudovirions bearing Ebola virus glycoprotein as a vaccine platform. We found that wild-type Ebola virus glycoprotein, in the context of this platform, provides robust protection of EBOV-challenged mice. Further, we found that removal of the heavy glycan shield surrounding conserved regions of the glycoprotein does not enhance vaccine efficacy.

Antiviral therapeutics for the treatment of Ebola virus infection

There have been significant developments in Ebola virus therapeutics. While the efficacy of several products was evaluated in the recent West Africa outbreak, a licensed treatment for EBOV disease remains elusive. Factors that negatively impacted the execution of clinical trials included an overall lack of world readiness to conduct clinical trials in an outbreak setting, ethical concerns limiting implementation of the randomized controlled trials in an outbreak setting, and a decline in case numbers by the time resources were mobilized to conduct clinical trials. We summarize relevant therapeutics that underwent clinical trials during the West Africa outbreak and highlight promising candidates under advanced development.

Will There Be a Cure for Ebola?

Despite the unprecedented Ebola virus outbreak response in West Africa, no Ebola medical countermeasures have been approved by the US Food and Drug Administration. However, multiple valuable lessons have been learned about the conduct of clinical research in a resource-poor, high risk-pathogen setting. Numerous therapeutics were explored or developed during the outbreak, including repurposed drugs, nucleoside and nucleotide analogues (BCX4430, brincidofovir, favipiravir, and GS-5734), nucleic acid-based drugs (TKM-Ebola and AVI-7537), and immunotherapeutics (convalescent plasma and ZMapp). We review Ebola therapeutics progress in the aftermath of the West Africa Ebola virus outbreak and attempt to offer a glimpse of a path forward.

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.

Transmission of ebola virus disease: an overview

Ebola is a viral illness of which the initial symptoms can include a sudden fever, intense weakness, muscle pain and a sore throat, according to the World Health Organization (WHO). Airborne transmission of Ebola virus has been hypothesized but not demonstrated in humans. Ebola is not spread through the air or by water, or in general, by food. However, in Africa, Ebola may be spread as a result of handling bushmeat (wild animals hunted for food) and contact with infected bats. The disease infects humans through close contact with infected animals, including chimpanzees, fruit bats, and forest antelope. Ebola virus can be transmitted by direct contact with blood, bodily fluids, or skin of patients with or who died of Ebola virus disease. As of late October 2014, the World Health Organization reported 13,567 suspected cases and 4922 deaths, although the agency believes that this substantially understates the magnitude of the outbreak. Experimental vaccines and treatments for Ebola are under development, but they have not yet been fully tested for safety or effectiveness.

Ebola virus disease and critical illness

As of 20 May 2016 there have been 28,646 cases and 11,323 deaths resulting from the West African Ebola virus disease (EVD) outbreak reported to the World Health Organization. There continue to be sporadic flare-ups of EVD cases in West Africa.EVD presentation is nonspecific and characterized initially by onset of fatigue, myalgias, arthralgias, headache, and fever; this is followed several days later by anorexia, nausea, vomiting, diarrhea, and abdominal pain. Anorexia and gastrointestinal losses lead to dehydration, electrolyte abnormalities, and metabolic acidosis, and, in some patients, acute kidney injury. Hypoxia and ventilation failure occurs most often with severe illness and may be exacerbated by substantial fluid requirements for intravascular volume repletion and some degree of systemic capillary leak. Although minor bleeding manifestations are common, hypovolemic and septic shock complicated by multisystem organ dysfunction appear the most frequent causes of death.Males and females have been equally affected, with children (0-14 years of age) accounting for 19 %, young adults (15-44 years) 58 %, and older adults (≥45 years) 23 % of reported cases. While the current case fatality proportion in West Africa is approximately 40 %, it has varied substantially over time (highest near the outbreak onset) according to available resources (40-90 % mortality in West Africa compared to under 20 % in Western Europe and the USA), by age (near universal among neonates and high among older adults), and by Ebola viral load at admission.While there is no Ebola virus-specific therapy proven to be effective in clinical trials, mortality has been dramatically lower among EVD patients managed with supportive intensive care in highly resourced settings, allowing for the avoidance of hypovolemia, correction of electrolyte and metabolic abnormalities, and the provision of oxygen, ventilation, vasopressors, and dialysis when indicated. This experience emphasizes that, in addition to evaluating specific medical treatments, improving the global capacity to provide supportive critical care to patients with EVD may be the greatest opportunity to improve patient outcomes.

Post-exposure treatment of Ebola virus disease in guinea pigs using EBOTAb, an ovine antibody-based therapeutic

Ebola virus (EBOV) is highly pathogenic, with a predisposition to cause outbreaks in human populations accompanied by significant mortality. An ovine polyclonal antibody therapy has been developed against EBOV, named EBOTAb. When tested in the stringent guinea pig model of EBOV disease, EBOTAb has been shown to confer protection at levels of 83.3%, 50% and 33.3% when treatment was first started on days 3, 4 and 5 post-challenge, respectively. These timepoints of when EBOTAb treatment was initiated correspond to when levels of EBOV are detectable in the circulation and thus mimic when treatment would likely be initiated in human infection. The effects of EBOTAb were compared with those of a monoclonal antibody cocktail, ZMapp, when delivered on day 3 post-challenge. Results showed ZMapp to confer complete protection against lethal EBOV challenge in the guinea pig model at this timepoint. The data reported demonstrate that EBOTAb is an effective treatment against EBOV disease, even when delivered late after infection.

Ebola Virus Makona Shows Reduced Lethality in an Immune-deficient Mouse Model

Ebola virus Makona (EBOV-Makona; from the 2013-2016 West Africa outbreak) shows decreased virulence in an immune-deficient mouse model, compared with a strain from 1976. Unlike other filoviruses tested, EBOV-Makona may be slightly more virulent by the aerosol route than by the injected route, as 2 mice died following aerosol exposure, compared with no mortality among mice that received intraperitoneal injection of equivalent or higher doses. Although most mice did not succumb to infection, the detection of an immunoglobulin G antibody response along with observed clinical signs suggest that the mice were infected but able to clear the infection and recover. We hypothesize that this may be due to the growth rates and kinetics of the virus, which appear slower than that for other filoviruses and consequently give more time for an immune response that results in clearance of the virus. In this instance, the immune-deficient mouse model is unlikely to be appropriate for testing medical countermeasures against this EBOV-Makona stock but may provide insight into pathogenesis and the immune response to virus.

Recent advances in the development of vaccines for Ebola virus disease

Ebola virus is one of the most dangerous microorganisms in the world causing hemorrhagic fevers in humans and non-human primates. Ebola virus (EBOV) is a zoonotic infection, which emerges and re-emerges in human populations. The 2014 outbreak was caused by the Zaire strain, which has a kill rate of up to 90%, though 40% was recorded in the current outbreak. The 2014 outbreak is larger than all 20 outbreaks that have occurred since 1976, when the virus was first discovered. It is the first time that the virus was sustained in urban centers and spread beyond Africa into Europe and USA. Thus far, over 22,000 cases have been reported with about 50% mortality in one year. There are currently no approved therapeutics and preventive vaccines against Ebola virus disease (EVD). Responding to the devastating effe1cts of the 2014 outbreak and the potential risk of global spread, has spurred research for the development of therapeutics and vaccines. This review is therefore aimed at presenting the progress of vaccine development. Results showed that conventional inactivated vaccines produced from EBOV by heat, formalin or gamma irradiation appear to be ineffective. However, novel vaccines production techniques have emerged leading to the production of candidate vaccines that have been demonstrated to be effective in preclinical trials using small animal and non-human primates (NHP) models. Some of the promising vaccines have undergone phase 1 clinical trials, which demonstrated their safety and immunogenicity. Many of the candidate vaccines are vector based such as Vesicular Stomatitis Virus (VSV), Rabies Virus (RABV), Adenovirus (Ad), Modified Vaccinia Ankara (MVA), Cytomegalovirus (CMV), human parainfluenza virus type 3 (HPIV3) and Venezuelan Equine Encephalitis Virus (VEEV). Other platforms include virus like particle (VLP), DNA and subunit vaccines.

Immune evasion in ebolavirus infections

Ebola virus (EBOV) infects humans as well as several animal species. It can lead to a highly lethal disease, with mortality rates approaching 90% in primates. Recent advances have deepened our understanding of how this virus is able to prevent the development of protective immune responses. The EBOV genome encodes eight proteins, four of which were shown to interact with the host in ways that counteract the immune response. The viral protein 35 (VP35) is capable of capping dsRNA and interacts with IRF7 to prevent detection of the virus by immune cells. The main role of the soluble glycoprotein (sGP) is still unclear, but it is capable of subverting the anti-GP1,2 antibody response. The GP1,2 protein has shown anti-tetherin activity and the ability to hide cell-surface proteins. Finally, VP24 interferes with the production of interferons (IFNs) and with IFN signaling in infected cells. Taken together, these data point to extensive adaptation of EBOV to evade the immune system of dead end hosts. While our understanding of the interactions between the human and viral proteins increases, details of those interactions in other hosts remain largely unclear and represent a gap in our knowledge.

VSVΔG/EBOV GP-induced innate protection enhances natural killer cell activity to increase survival in a lethal mouse adapted Ebola virus infection

Members of the species Zaire ebolavirus cause severe hemorrhagic fever with up to a 90% mortality rate in humans. The VSVΔG/EBOV GP vaccine has provided 100% protection in the mouse, guinea pig, and nonhuman primate (NHP) models, and has also been utilized as a post-exposure therapeutic to protect mice, guinea pigs, and NHPs from a lethal challenge of Ebola virus (EBOV). EBOV infection causes rapid mortality in human and animal models, with death occurring as early as 6 days after infection, suggesting a vital role for the innate immune system to control the infection before cells of the adaptive immune system can assume control. Natural killer (NK) cells are the predominant cell of the innate immune response, which has been shown to expand with VSVΔG/EBOV GP treatment. In the current study, an in vivo mouse model of the VSVΔG/EBOV GP post-exposure treatment was used for a mouse adapted (MA)-EBOV infection, to determine the putative VSVΔG/EBOV GP-induced protective mechanism of NK cells. NK depletion studies demonstrated that mice with NK cells survive longer in a MA-EBOV infection, which is further enhanced with VSVΔG/EBOV GP treatment. NK cell mediated cytotoxicity and IFN-γ secretion was significantly higher with VSVΔG/EBOV GP treatment. Cell mediated cytotoxicity assays and perforin knockout mice experiments suggest that there are perforin-dependent and -independent mechanisms involved. Together, these data suggest that NK cells play an important role in VSVΔG/EBOV GP-induced protection of EBOV by increasing NK cytotoxicity, and IFN-γ secretion.

AVI-7288 for Marburg Virus in Nonhuman Primates and Humans

BACKGROUND

AVI-7288 is a phosphorodiamidate morpholino oligomer with positive charges that targets the viral messenger RNA that encodes Marburg virus (MARV) nucleoprotein. Its safety in humans is undetermined.

METHODS

We assessed the efficacy of AVI-7288 in a series of studies involving a lethal challenge with MARV in nonhuman primates. The safety of AVI-7288 was evaluated in a randomized, multiple-ascending-dose study in which 40 healthy humans (8 humans per dose group) received 14 once-daily infusions of AVI-7288 (1 mg, 4 mg, 8 mg, 12 mg, or 16 mg per kilogram of body weight) or placebo, in a 3:1 ratio. We estimated the protective dose in humans by comparing pharmacokinetic variables in infected nonhuman primates, uninfected nonhuman primates, and uninfected humans.

RESULTS

Survival in infected nonhuman primates was dose-dependent, with survival rates of 0%, 30%, 59%, 87%, 100%, and 100% among monkeys treated with 0 mg, 3.75 mg, 7.5 mg, 15 mg, 20 mg, and 30 mg of AVI-7288 per kilogram, respectively (P<0.001 with the use of the log-rank test for the comparison of survival across groups). No safety concern was identified at doses up to 16 mg per kilogram per day in humans. No serious adverse events were reported. Drug exposure (the area under the curve) was dose-dependent in both nonhuman primates and humans; drug clearance was independent of dose but was higher in nonhuman primates than in humans. The protective dose in humans was initially estimated, on the basis of exposure, to be 9.6 mg per kilogram per day (95% confidence interval, 6.6 to 12.5) for 14 days. Monte Carlo simulations supported a dose of 11 mg per kilogram per day to match the geometric mean protective exposure in nonhuman primates.

CONCLUSIONS

This study shows that, on the basis of efficacy in nonhuman primates and pharmacokinetic data in humans, AVI-7288 has potential as postexposure prophylaxis for MARV infection in humans. (Funded by the Department of Defense; ClinicalTrials.gov number, NCT01566877.).

Experimental Respiratory Infection of Marmosets (Callithrix jacchus) With Ebola Virus Kikwit

Ebola virus (EBOV) causes a highly infectious and lethal hemorrhagic fever in primates with high fatality rates during outbreaks and EBOV may be exploited as a potential biothreat pathogen. There is therefore a need to develop and license appropriate medical countermeasures against this virus. To determine whether the common marmoset (Callithrix jacchus) would be an appropriate model to assess vaccines or therapies against EBOV disease (EVD), initial susceptibility, lethality and pathogenesis studies were performed. Low doses of EBOV-Kikwit, between 4 and 27 times the 50% tissue culture infectious dose, were sufficient to cause a lethal, reproducible infection. Animals became febrile between days 5 and 6, maintaining a high fever before succumbing to EVD between 6 and 8 days after challenge. Typical signs of EVD were observed. Pathogenesis studies revealed that virus was isolated from the lungs of animals beginning on day 3 after challenge and from the liver, spleen and blood beginning on day 5. The most striking features were observed in animals that succumbed to infection, including high viral titers in all organs, increased levels of liver function enzymes and blood clotting times, decreased levels of platelets, multifocal moderate to severe hepatitis, and perivascular edema.

Development of Small-Molecule Antivirals for Ebola

Ebola hemorrhagic fever is a deadly disease caused by infection with one of the Ebola virus species. Although a significant progress has recently been made in understanding of Ebola virus biology and pathogenesis, development of effective anti-Ebola treatments has not been very productive, compared to other areas of antiviral research (e.g., HIV and HCV infections). No approved vaccine or medicine is available for Ebola but several are currently under development. This review summarises attempts in identification, evaluation, and development of small-molecule candidates for treatment of Ebola viral disease, including the most promising experimental drugs brincidofovir (CMX001), BCX4430, and favipiravir (T-705).

Pathophysiology of Ebola Virus Infection: Current Challenges and Future Hopes

The filoviruses, Ebola virus (EBOV) and Marburg virus (MARV), are among the deadliest viruses that cause disease in humans, with reported case fatality rates of up to 90% in some outbreaks. The high virulence of EBOV and MARV is largely attributed to the ability of these viruses to interfere with the host immune response. Currently, there are no approved vaccines or postexposure therapeutics, and treatment options for patients infected with EBOV are limited to supportive care. In this review, we discuss mechanisms of EBOV pathogenesis and its ability to subvert host immunity as well as several vaccines and therapeutics with respect to their evaluation in small animal models, nonhuman primates, and human clinical trials.

Three minimal sequences found in Ebola virus genomes and absent from human DNA

Motivation: Ebola virus causes high mortality hemorrhagic fevers, with more than 25 000 cases and 10 000 deaths in the current outbreak. Only experimental therapies are available, thus, novel diagnosis tools and druggable targets are needed.

Results: Analysis of Ebola virus genomes from the current outbreak reveals the presence of short DNA sequences that appear nowhere in the human genome. We identify the shortest such sequences with lengths between 12 and 14. Only three absent sequences of length 12 exist and they consistently appear at the same location on two of the Ebola virus proteins, in all Ebola virus genomes, but nowhere in the human genome. The alignment-free method used is able to identify pathogen-specific signatures for quick and precise action against infectious agents, of which the current Ebola virus outbreak provides a compelling example.

Availability and Implementation: EAGLE is freely available for non-commercial purposes at http://bioinformatics.ua.pt/software/eagle.

Contact:raquelsilva@ua.pt; pratas@ua.pt

Supplementary Information:Supplementary data are available at Bioinformatics online.

Ebola virus. Two-pore channels control Ebola virus host cell entry and are drug targets for disease treatment

Ebola virus causes sporadic outbreaks of lethal hemorrhagic fever in humans, but there is no currently approved therapy. Cells take up Ebola virus by macropinocytosis, followed by trafficking through endosomal vesicles. However, few factors controlling endosomal virus movement are known. Here we find that Ebola virus entry into host cells requires the endosomal calcium channels called two-pore channels (TPCs). Disrupting TPC function by gene knockout, small interfering RNAs, or small-molecule inhibitors halted virus trafficking and prevented infection. Tetrandrine, the most potent small molecule that we tested, inhibited infection of human macrophages, the primary target of Ebola virus in vivo, and also showed therapeutic efficacy in mice. Therefore, TPC proteins play a key role in Ebola virus infection and may be effective targets for antiviral therapy.

Ebola and Marburg haemorrhagic fever

Ebolaviruses and Marburgviruses (family Filoviridae) are among the most virulent pathogens for humans and great apes causing severe haemorrhagic fever and death within a matter of days. This group of viruses is characterized by a linear, non-segmented, single-stranded RNA genome of negative polarity. The overall burden of filovirus infections is minimal and negligible compared to the devastation caused by malnutrition and other infectious diseases prevalent in Africa such as malaria, dengue or tuberculosis. In this paper, we review the knowledge gained on the eco/epidemiology, the pathogenesis and the disease control measures for Marburg and Ebola viruses developed over the last 15 years. The overall progress is promising given the little attention that these pathogen have achieved in the past; however, more is to come over the next decade given the more recent interest in these pathogens as potential public and animal health concerns. Licensing of therapeutic and prophylactic options may be achievable over the next 5-10 years.

What clinicians should know about the 2014 Ebola outbreak

The ongoing Ebola outbreak that began in Guinea in February 2014 has spread to Liberia, Sierra Leone, Nigeria, Senegal, Spain, and the United States and has become the largest Ebola outbreak in recorded history. It is important for frontline medical providers to understand key aspects of Ebola virus disease (EVD) to quickly recognize an imported case, provide appropriate medical care, and prevent transmission. Furthermore, an understanding of the clinical presentation, clinical course, transmission, and prevention of EVD can help reduce anxiety about the disease and allow health care providers to calmly and confidently provide medical care to patients suspected of having EVD.

Ebolavirus in West Africa, and the use of experimental therapies or vaccines

Response to the current ebolavirus outbreak based on traditional control measures has so far been insufficient to prevent the virus from spreading rapidly. This has led to urgent discussions on the use of experimental therapies and vaccines untested in humans and existing in limited quantities, raising political, strategic, technical and ethical questions.

Post-exposure efficacy of oral T-705 (Favipiravir) against inhalational Ebola virus infection in a mouse model

Filoviruses cause disease with high case fatality rates and are considered biological threat agents. Licensed post-exposure therapies that can be administered by the oral route are desired for safe and rapid distribution and uptake in the event of exposure or outbreaks. Favipiravir or T-705 has broad antiviral activity and has already undergone phase II and is undergoing phase III clinical trials for influenza. Here we report the first use of T-705 against Ebola virus. T-705 gave 100% protection against aerosol Ebola virus E718 infection; protection was shown in immune-deficient mice after 14 days of twice-daily dosing. T-705 was also shown to inhibit Ebola virus infection in cell culture. T-705 is likely to be licensed for use against influenza in the near future and could also be used with a new indication for filovirus infection.

Sustained protection against Ebola virus infection following treatment of infected nonhuman primates with ZMAb

Ebola virus (EBOV) is one of the most lethal filoviruses, with mortality rates of up to 90% in humans. Previously, we demonstrated 100% and 50% survival of EBOV-infected cynomologus macaques with a combination of 3 EBOV-GP-specific monoclonal antibodies (ZMAb) administered at 24 or 48 hours post-exposure, respectively. The survivors demonstrated EBOV-GP–specific humoral and cell-mediated immune responses. In order to evaluate whether the immune response induced in NHPs during the ZMAb treatment and EBOV challenge is sufficient to protect survivors against a subsequent exposure, animals that survived the initial challenge were rechallenged at 10 or 13 weeks after the initial challenge. The animals rechallenged at 10 weeks all survived whereas 4 of 6 animals survived a rechallenge at 13 weeks. The data indicate that a robust immune response was generated during the successful treatment of EBOV-infected NHPs with EBOV, which resulted in sustained protection against a second lethal exposure.

A novel mechanism of immune evasion mediated by Ebola virus soluble glycoprotein

Ebola viruses encode two glycoproteins (GPs): a membrane-associated GP that is present in the viral membrane and mediates viral attachment and entry into host cells; and a secreted, nonstructural glycoprotein (sGP) that is identical to GP over approximately 90% of its length. A recent study by Mohan and colleagues attributes a novel immune evasion mechanism dubbed 'antigenic subversion' to sGP. Using DNA immunization in mice, the authors demonstrate that sGP elicits antibodies that crossreact with GP, but these antibodies are non-neutralizing. Coimmunization with sGP plus GP or sequential immunizations with GP and sGP direct the host antibody response toward non-neutralizing epitopes. Therefore, the production of sGP may prevent effective neutralization of the virus during Ebola virus infection, and may reduce the effectiveness of vaccines that rely upon neutralizing antibody responses.

Animal models for Ebola and Marburg virus infections

Ebola and Marburg hemorrhagic fevers (EHF and MHF) are caused by the Filoviridae family, Ebolavirus and Marburgvirus (ebolavirus and marburgvirus), respectively. These severe diseases have high mortality rates in humans. Although EHF and MHF are endemic to sub-Saharan Africa. A novel filovirus, Lloviu virus, which is genetically distinct from ebolavirus and marburgvirus, was recently discovered in Spain where filoviral hemorrhagic fever had never been reported. The virulence of this virus has not been determined. Ebolavirus and marburgvirus are classified as biosafety level-4 (BSL-4) pathogens and Category A agents, for which the US government requires preparedness in case of bioterrorism. Therefore, preventive measures against these viral hemorrhagic fevers should be prepared, not only in disease-endemic regions, but also in disease-free countries. Diagnostics, vaccines, and therapeutics need to be developed, and therefore the establishment of animal models for EHF and MHF is invaluable. Several animal models have been developed for EHF and MHF using non-human primates (NHPs) and rodents, which are crucial to understand pathophysiology and to develop diagnostics, vaccines, and therapeutics. Rhesus and cynomolgus macaques are representative models of filovirus infection as they exhibit remarkably similar symptoms to those observed in humans. However, the NHP models have practical and ethical problems that limit their experimental use. Furthermore, there are no inbred and genetically manipulated strains of NHP. Rodent models such as mouse, guinea pig, and hamster, have also been developed. However, these rodent models require adaptation of the virus to produce lethal disease and do not mirror all symptoms of human filovirus infection. This review article provides an outline of the clinical features of EHF and MHF in animals, including humans, and discusses how the animal models have been developed to study pathophysiology, vaccines, and therapeutics.

Human monoclonal antibodies as candidate therapeutics against emerging viruses and HIV-1

More than 40 monoclonal antibodies (mAbs) have been approved for a number of disease indications with only one of these (Synagis) - for a viral disease, and not for therapy but for prevention. However, in the last decade novel potent mAbs have been discovered and characterized with potential as therapeutics against viruses of major importance for public health and biosecurity including Hendra virus (HeV), Nipah virus (NiV), severe acute respiratory syndrome coronavirus (SARS-CoV), Ebola virus (EBOV), West Nile virus (WNV), influenza virus (IFV) and human immunodeficiency virus type 1 (HIV-1). Here, we review such mAbs with an emphasis on antibodies of human origin, and highlight recent results as well as technologies and mechanisms related to their potential as therapeutics.