Filovirus pathogenesis and immune evasion: insights from Ebola virus and Marburg virus

Marburg Virus Disease: A Narrative Review

Background and Aims

Given the recent deadly outbreaks of the Marburg virus (MARV), in early 2023 in Tanzania and Equatorial Guinea, and the most recent one in Rwanda in 2024, there has been renewed attention across Africa on the threat posed by the re-emergence of MARV as a growing concern for public health. Therefore, it needs to provide a comprehensive overview of the virus and its related infections, encompassing virus classification, historical outbreaks, transmission dynamics, the intricate interface between the virus and its hosts, the methods of diagnosis, core prevention strategies, and current therapeutic options, to better understand the virus and the disease characteristics in responding to future outbreaks.

Methods

For this review, four scientific online databases, including PubMed, Google Scholar, Scopus, and Web of Science were thoroughly searched for peer-reviewed journal papers (original, case reports/series, and review studies) published in English language using the following keywords: Filovirus, Marburg virus, Marburg Haemorrhagic Fever, Marburg virus disease, and Marburg virus outbreak.

Results

MARV shares similarities with its close cousin -the Ebola virus [EBOV]-in terms of viral characteristics and most clinical features. These two viruses are of animal origin and primarily spread to humans through infected bats (both direct and indirect close contact), which serve as the common natural host reservoirs. The potential for interhuman transmission, coupled with the ability to cross borders of endemic regions combined with the absence of a licensed vaccine and effective treatment, have made MARV a significant threat to human health. This virus is clinically characterized by a range of symptoms and organ dysfunctions. The disease is often fatal in a significant proportion of infected individuals. This viral infection is diagnosed by various diagnostic tools, prevented mainly through personal protective measures, and treated usually with clinical management and supportive care.

Conclusion

The outbreaks of MARV are continuously threaten public health; therefore, the world must be alert and well-prepared. For MVD, taking precautions along with investing in research and preparedness at regional, national, and global levels is of crucial importance and should be prioritized.

Refining early detection of Marburg Virus Disease (MVD) in Rwanda: Leveraging predictive symptom clusters to enhance case definitions

BACKGROUND

Marburg Virus Disease (MVD) poses a significant global health risk due to its high case fatality rates (24%-88%) and the diagnostic challenges posed by its nonspecific early symptoms, which overlap with other febrile illnesses like malaria. This study analyzed symptom patterns from the 2024 MVD outbreak in Rwanda to refine case definitions and enhance early detection.

METHODS

A retrospective analysis was conducted of 6613 suspected MVD cases (66 positive, 6547 negative) reported between September 27 and December 20, 2024. Symptom prevalence and predictive value were assessed using multiple logistic regression models with L1 and L2 regularization to identify the most predictive symptoms. Models were validated using 5-fold cross-validation, with performance assessed through ROC analysis and standard accuracy metrics.

RESULTS

Fever (78.8%), fatigue (63.6%), and headache (57.6%) were identified as the most common early symptoms, while hemorrhagic signs were rare (3.0%). The model achieved high accuracy (99.04%) and an area under the receiver operating characteristic curve of 0.824, identifying fever, fatigue, nausea/vomiting, joint pain, and sore throat as key predictors.

CONCLUSION

Early symptom clusters, especially constitutional and gastrointestinal signs outperformed hemorrhagic symptoms for MVD detection. Findings challenge current case definitions, emphasizing the need for revised public health messaging and healthcare worker training. Integrating symptom-based models into surveillance could enhance detection, especially in resource-limited settings.

Molecular virulence determinants of human-pathogenic filoviruses

The Filoviridae family encompasses Ebola virus (EBOV) and Marburg virus (MARV), some of the most lethal viruses known to cause sporadic, recurring outbreaks of severe hemorrhagic fever mainly throughout central Africa. However, other lesser-known viruses also belong to the filovirus family as they are closely related, such as Bundibugyo, Reston and Taï Forest virus. These viruses differ in their virulence in humans significantly: while EBOV and MARV show lethality in humans of up to 90 %, Reston virus appears to be avirulent in humans. Here, underlying molecular factors leading to differences in virulence via changes in filovirus entry, replication and immune evasion strategies are summarized and assessed. While the filovirus glycoprotein contributes towards virulence by facilitating entry into a wide variety of tissues, differences in virus-host interactions and replication efficacies lead to measurable variances of progeny virus production. Additionally, immune evasion strategies lead to alterations in replication efficacy thus changing who has the upper hand between the virus and the host. Understanding and unraveling the contributions of these molecular determinants on filovirus virulence provide insights into the processes causing the underlying pathogenesis. It will further help to assess the pathogenicity of newly discovered filoviruses. Finally, these molecular determinants and processes present attractive targets for therapeutic intervention and development of novel antiviral countermeasures.

A comparative analysis of the dendritic cell response upon exposure to different rabies virus strains

Rabies is a viral zoonotic disease that causes over 60,000 human deaths annually worldwide. Natural infections lack a virus-specific immune response, leading to a near 100% fatality rate unless immediately treated. Rabies virus (RABV) is typically transmitted through bites from rabid dogs or other carnivores to humans and may initially interact with innate immune cells such as dendritic cells at the site of infection. This study investigates the in vitro response of human monocyte-derived dendritic cells (moDCs) exposed to two pathogenic RABV strains-silver-haired bat rabies virus (SHBRV) and dog-related rabies virus (dogRV)-and an attenuated vaccine strain (SAD P5). MoDCs were susceptible only to high doses of SHBRV and SAD P5, resulting in a more mature and migratory phenotype within the infected moDC populations. No infection was observed in moDCs exposed to dogRV. In co-culture with T cells, the presence of RABV-exposed moDCs, regardless of the strain, did not enhance T cell activation. Additionally, RABV exposure did not hinder LPS-induced moDC maturation; instead, high doses of SHBRV and SAD P5 even boosted activation levels. Overall, the findings suggest varied capabilities of RABV strains to infect and activate moDCs in vitro. However, exposure to any RABV strain did not provoke a clear antiviral state or suppression of moDC responsiveness. This lack of activation may contribute to the absence of an effective adaptive immune response in natural RABV infections.

Rational design of next-generation filovirus vaccines with glycoprotein stabilization, nanoparticle display, and glycan modification

Filoviruses pose a significant threat to human health with frequent outbreaks and high mortality. Although two vector-based vaccines are available for Ebola virus, a broadly protective filovirus vaccine remains elusive. In this study, we evaluate a general strategy for stabilizing glycoprotein (GP) structures of Ebola, Sudan, and Bundibugyo ebolaviruses and Ravn marburgvirus. A 3.2 Å-resolution crystal structure provides atomic details for the redesigned Ebola virus GP, and cryo-electron microscopy reveals how a pan-ebolavirus neutralizing antibody targets a conserved site on the Sudan virus GP (3.13 Å-resolution), in addition to a low-resolution model of antibody-bound Ravn virus GP. A self-assembling protein nanoparticle (SApNP), I3-01v9, is redesigned at the N-terminus to allow the optimal surface display of filovirus GP trimers. Following detailed in vitro characterization, the lymph node dynamics of Sudan virus GP and GP-presenting SApNPs are investigated in a mouse model. Compared with soluble GP trimer, SApNPs show ~112 times longer retention in lymph node follicles, up-to-28 times greater presentation on follicular dendritic cell dendrites, and up-to-3 times stronger germinal center reactions. Functional antibody responses induced by filovirus GP trimers and SApNPs bearing wildtype and modified glycans are assessed in mice. Our study provides a foundation for next-generation filovirus vaccine development.

Metabolically purified human stem cell-derived hepatocytes reveal distinct effects of Ebola and Lassa viruses

Ebola and Lassa viruses require biosafety-level-4 (BSL4) containment, infect the liver, and cause deadly hemorrhagic fevers. The cellular effects of these viruses, and whether different families of hemorrhagic-fever viruses elicit similar effects, remain fundamental questions in BSL4 virology. Here, we introduce a new metabolic selection approach to create nearly-pure hepatocytes from human pluripotent stem cells, killing non-liver cells by withholding essential nutrients. Unexpectedly, Ebola and Lassa exerted starkly different effects on human hepatocytes. Ebola infection activated the integrated stress response (ISR) and WNT pathways in hepatocytes in vitro and killed them, whereas Lassa did not. Within non-human primates, Ebola likewise infected hepatocytes and activated ISR signaling in vivo . In summary, we present a single-cell transcriptional and chromatin accessibility roadmap of human hepatocyte differentiation, purification, and viral infection.

Ginkgolic acid inhibits Ebola virus transcription and replication by disrupting the interaction between nucleoprotein and VP30 protein

The Ebola virus, a filovirus, has been responsible for significant human fatalities since its discovery. Despite extensive research, effective small-molecule drugs remain elusive due to its complex pathogenesis. Inhibition of RNA synthesis is a promising therapeutic target, and the VP30 protein plays a critical role in this process. The interaction between VP30 and the nucleoprotein (NP) is essential for viral replication. We identified ginkgolic acid as a small molecule with strong affinity for VP30, which was validated through multiple assays, including thermal shift, surface plasmon resonance, fluorescence polarization, pull-down, and co-immunoprecipitation. The antiviral efficacy of ginkgolic acid was demonstrated in the EBOV transcription- and replication-competent virus-like particle (trVLP) system. Furthermore, we resolved the crystal structure of the VP30-ginkgolic acid complex, revealing two ginkgolic acid molecules located at the VP30/NP interaction interface. This structural information provides insight into the molecular basis of ginkgolic acid's antiviral activity and suggests a novel therapeutic strategy targeting the VP30/NP interaction.

Intracellular Ebola virus nucleocapsid assembly revealed by in situ cryo-electron tomography

Filoviruses, including the Ebola and Marburg viruses, cause hemorrhagic fevers with up to 90% lethality. The viral nucleocapsid is assembled by polymerization of the nucleoprotein (NP) along the viral genome, together with the viral proteins VP24 and VP35. We employed cryo-electron tomography of cells transfected with viral proteins and infected with model Ebola virus to illuminate assembly intermediates, as well as a 9 Å map of the complete intracellular assembly. This structure reveals a previously unresolved third and outer layer of NP complexed with VP35. The intrinsically disordered region, together with the C-terminal domain of this outer layer of NP, provides the constant width between intracellular nucleocapsid bundles and likely functions as a flexible tether to the viral matrix protein in the virion. A comparison of intracellular nucleocapsids with prior in-virion nucleocapsid structures reveals that the nucleocapsid further condenses vertically in the virion. The interfaces responsible for nucleocapsid assembly are highly conserved and offer targets for broadly effective antivirals.

Emerging and reemerging infectious diseases: global trends and new strategies for their prevention and control

To adequately prepare for potential hazards caused by emerging and reemerging infectious diseases, the WHO has issued a list of high-priority pathogens that are likely to cause future outbreaks and for which research and development (R&D) efforts are dedicated, known as paramount R&D blueprints. Within R&D efforts, the goal is to obtain effective prophylactic and therapeutic approaches, which depends on a comprehensive knowledge of the etiology, epidemiology, and pathogenesis of these diseases. In this process, the accessibility of animal models is a priority bottleneck because it plays a key role in bridging the gap between in-depth understanding and control efforts for infectious diseases. Here, we reviewed preclinical animal models for high priority disease in terms of their ability to simulate human infections, including both natural susceptibility models, artificially engineered models, and surrogate models. In addition, we have thoroughly reviewed the current landscape of vaccines, antibodies, and small molecule drugs, particularly hopeful candidates in the advanced stages of these infectious diseases. More importantly, focusing on global trends and novel technologies, several aspects of the prevention and control of infectious disease were discussed in detail, including but not limited to gaps in currently available animal models and medical responses, better immune correlates of protection established in animal models and humans, further understanding of disease mechanisms, and the role of artificial intelligence in guiding or supplementing the development of animal models, vaccines, and drugs. Overall, this review described pioneering approaches and sophisticated techniques involved in the study of the epidemiology, pathogenesis, prevention, and clinical theatment of WHO high-priority pathogens and proposed potential directions. Technological advances in these aspects would consolidate the line of defense, thus ensuring a timely response to WHO high priority pathogens.

Mapping knowledge landscapes and emerging trends of Marburg virus: A text-mining study

Background

Marburg virus (MARV), a close relative of Ebola virus, could induce hemorrhagic fevers in humans with high mortality rate. In recent years, increasing attention has been paid to this highly lethal virus due to sporadic outbreaks observed in various African nations. This bibliometric analysis endeavors to elucidate the trends, dynamics, and focal points of knowledge that have delineated the landscape of research concerning MARV.

Methods

Relevant literature on MARV from 1968 to 2023 was extracted from the Web of Science Core Collection database. Following this, the data underwent bibliometric analysis and visualization procedures utilizing online analysis platform, CiteSpace 6.2R6, and VOSviewer 1.6.20. Three different types of bibliometric indicators including quantitative indicator, qualitative indicators, and structural indicators were used to gauge a researcher's productivity, assess the quality of their work, and analyze publication relationships, respectively.

Results

MARV is mainly prevalent in Africa. And approximately 643 confirmed cases have been described in the literature to date, and mortality observed was 81.2 % in overall patients. A total of 1014 papers comprising 869 articles and 145 reviews were included. The annual publications showed an increasing growth pattern from 1968 to 2023 (R2 = 0.8838). The United States stands at the forefront of this discipline, having dedicated substantial financial and human resources to scientific inquiry. However, co-authorship analysis showed the international research collaboration needs to be further strengthened. Based on reference and keywords analysis, contemporary MARV research encompasses pivotal areas: primarily, prioritizing the creation of prophylactic vaccines to impede viral spread, and secondarily, exploring targeted antiviral strategies, including small-molecule antivirals or MARV-specific monoclonal antibodies. Additionally, a comprehensive grasp of viral transmission, transcription, and replication mechanisms remains a central focus in ongoing investigations. And future MARV studies are expected to focus on evaluating clinical trial safety and efficacy, developing inhibitors to contain viral spread, exploring vaccine immunogenicity, virus-host association studies, and elucidating the role of neutralizing antibodies in MARV treatment.

Conclusion

The present study offered comprehensive insights into the contemporary status and trajectories of MARV over the past decades. This enables researchers to discern novel collaborative prospects, institutional partnerships, emerging topics, and research forefronts within this domain.

Heterologous cAd3-Ebola and MVA-EbolaZ vaccines are safe and immunogenic in US and Uganda phase 1/1b trials

Ebola virus disease (EVD) is a filoviral infection caused by virus species of the Ebolavirus genus including Zaire ebolavirus (EBOV) and Sudan ebolavirus (SUDV). We investigated the safety and immunogenicity of a heterologous prime-boost regimen involving a chimpanzee adenovirus 3 vectored Ebola vaccine [either monovalent (cAd3-EBOZ) or bivalent (cAd3-EBO)] prime followed by a recombinant modified vaccinia virus Ankara EBOV vaccine (MVA-EbolaZ) boost in two phase 1/1b randomized open-label clinical trials in healthy adults in the United States (US) and Uganda (UG). Trial US (NCT02408913) enrolled 140 participants, including 26 EVD vaccine-naïve and 114 cAd3-Ebola-experienced participants (April-November 2015). Trial UG (NCT02354404) enrolled 90 participants, including 60 EVD vaccine-naïve and 30 DNA Ebola vaccine-experienced participants (February-April 2015). All tested vaccines and regimens were safe and well tolerated with no serious adverse events reported related to study products. Solicited local and systemic reactogenicity was mostly mild to moderate in severity. The heterologous prime-boost regimen was immunogenic, including induction of durable antibody responses which peaked as early as two weeks and persisted up to one year after each vaccination. Different prime-boost intervals impacted the magnitude of humoral and cellular immune responses. The results from these studies demonstrate promising implications for use of these vaccines in both prophylactic and outbreak settings.

Repurposing of SARS-CoV-2 compounds against Marburg Virus using MD simulation, mm/GBSA, PCA analysis, and free energy landscape

The significant mortality rate associated with Marburg virus infection made it the greatest hazard among infectious diseases. Drug repurposing using in silico methods has been crucial in identifying potential compounds that could prevent viral replication by targeting the virus's primary proteins. This study aimed at repurposing the drugs of SARS-CoV-2 for identifying potential candidates against the matrix protein VP40 of the Marburg virus. Virtual screening was performed where the control compound, Nilotinib, showed a binding score of -9.99 kcal/mol. Based on binding scores, hit compounds 9549298, 11960895, 44545852, 51039094, and 89670174 were selected that had a lower binding score than the control. Subsequent molecular dynamics (MD) simulation revealed that compound 9549298 consistently formed a hydrogen bond with the residue Gln290. This was observed both in molecular docking and MD simulation poses, indicating a strong and significant interaction with the protein. 11960895 had the most stable and consistent RMSD pattern exhibited in 100 ns simulation, while 9549298 had the most identical RMSD plot compared to the control molecule. MM/PBSA analysis showed that the binding free energy (ΔG) of 9549298 and 11960895 was lower than the control, with -30.84 and -38.86 kcal/mol, respectively. It was observed by the PCA (principal component analysis) and FEL (free energy landscape) analysis that compounds 9549298 and 11960895 had lesser conformational variation. Overall, this study proposed 9549298 and 11960895 as potential binders of VP40 MARV that can cause its inhibition, however it inherently lacks experimental validation. Furthermore, the study proposes in-vitro experiments as the next step to validate these computational findings, offering a practical approach to further explore these compounds' potential as antiviral agents.

O-glycosylation in viruses: A sweet tango

O-glycosylation is an ancient yet underappreciated protein posttranslational modification, on which many bacteria and viruses heavily rely to perform critical biological functions involved in numerous infectious diseases or even cancer. But due to the innate complexity of O-glycosylation, research techniques have been limited to study its exact role in viral attachment and entry, assembly and exit, spreading in the host cells, and the innate and adaptive immunity of the host. Recently, the advent of many newly developed methodologies (e.g., mass spectrometry, chemical biology tools, and molecular dynamics simulations) has renewed and rekindled the interest in viral-related O-glycosylation in both viral proteins and host cells, which is further fueled by the COVID-19 pandemic. In this review, we summarize recent advances in viral-related O-glycosylation, with a particular emphasis on the mucin-type O-linked α-N-acetylgalactosamine (O-GalNAc) on viral proteins and the intracellular O-linked β-N-acetylglucosamine (O-GlcNAc) modifications on host proteins. We hope to provide valuable insights into the development of antiviral reagents or vaccines for better prevention or treatment of infectious diseases.

Coordinated inflammatory responses dictate Marburg virus control by reservoir bats

Bats are increasingly recognized as reservoirs of emerging zoonotic pathogens. Egyptian rousette bats (ERBs) are the known reservoir of Marburg virus (MARV), a filovirus that causes deadly Marburg virus disease (MVD) in humans. However, ERBs harbor MARV asymptomatically, likely due to a coadapted and specific host immunity-pathogen relationship. Recently, we measured transcriptional responses in MARV-infected ERB whole tissues, showing that these bats possess a disease tolerant strategy that limits pro-inflammatory gene induction, presumably averting MVD-linked immunopathology. However, the host resistant strategy by which ERBs actively limit MARV burden remains elusive, which we hypothesize requires localized inflammatory responses unresolvable at bulk-tissue scale. Here, we use dexamethasone to attenuate ERB pro-inflammatory responses and assess MARV replication, shedding and disease. We show that MARV-infected ERBs naturally mount coordinated pro-inflammatory responses at liver foci of infection, comprised of recruited mononuclear phagocytes and T cells, the latter of which proliferate with likely MARV-specificity. When pro-inflammatory responses are diminished, ERBs display heightened MARV replication, oral/rectal shedding and severe MVD-like liver pathology, demonstrating that ERBs balance immunoprotective tolerance with discreet MARV-resistant pro-inflammatory responses. These data further suggest that natural ERB immunomodulatory stressors like food scarcity and habitat disruption may potentiate viral shedding, transmission and therefore outbreak risk.

Ebola virus sequesters IRF3 in viral inclusion bodies to evade host antiviral immunity

Viral inclusion bodies (IBs) commonly form during the replication of Ebola virus (EBOV) in infected cells, but their role in viral immune evasion has rarely been explored. Here, we found that interferon regulatory factor 3 (IRF3), but not TANK-binding kinase 1 (TBK1) or IκB kinase epsilon (IKKε), was recruited and sequestered in viral IBs when the cells were infected by EBOV transcription- and replication-competent virus-like particles (trVLPs). Nucleoprotein/virion protein 35 (VP35)-induced IBs formation was critical for IRF3 recruitment and sequestration, probably through interaction with STING. Consequently, the association of TBK1 and IRF3, which plays a vital role in type I interferon (IFN-I) induction, was blocked by EBOV trVLPs infection. Additionally, IRF3 phosphorylation and nuclear translocation induced by Sendai virus or poly(I:C) stimulation were suppressed by EBOV trVLPs. Furthermore, downregulation of STING significantly attenuated VP35-induced IRF3 accumulation in IBs. Coexpression of the viral proteins by which IB-like structures formed was much more potent in antagonizing IFN-I than expression of the IFN-I antagonist VP35 alone. These results suggested a novel immune evasion mechanism by which EBOV evades host innate immunity.

Peripheral immune responses to filoviruses in a reservoir versus spillover hosts reveal transcriptional correlates of disease

Several filoviruses, including Marburg virus (MARV), cause severe disease in humans and nonhuman primates (NHPs). However, the Egyptian rousette bat (ERB, Rousettus aegyptiacus), the only known MARV reservoir, shows no overt illness upon natural or experimental infection, which, like other bat hosts of zoonoses, is due to well-adapted, likely species-specific immune features. Despite advances in understanding reservoir immune responses to filoviruses, ERB peripheral blood responses to MARV and how they compare to those of diseased filovirus-infected spillover hosts remain ill-defined. We thus conducted a longitudinal analysis of ERB blood gene responses during acute MARV infection. These data were then contrasted with a compilation of published primate blood response studies to elucidate gene correlates of filovirus protection versus disease. Our work expands on previous findings in MARV-infected ERBs by supporting both host resistance and disease tolerance mechanisms, offers insight into the peripheral immunocellular repertoire during infection, and provides the most direct known cross-examination between reservoir and spillover hosts of the most prevalently-regulated response genes, pathways and activities associated with differences in filovirus pathogenesis and pathogenicity.

Structural and Dynamical Basis of VP35-RBD Inhibition by Marine Fungi Compounds to Combat Marburg Virus Infection

The Marburg virus (MBV), a deadly pathogen, poses a serious threat to world health due to the lack of effective treatments, calling for an immediate search for targeted and efficient treatments. In this study, we focused on compounds originating from marine fungi in order to identify possible inhibitory compounds against the Marburg virus (MBV) VP35-RNA binding domain (VP35-RBD) using a computational approach. We started with a virtual screening procedure using the Lipinski filter as a guide. Based on their docking scores, 42 potential candidates were found. Four of these compounds-CMNPD17596, CMNPD22144, CMNPD25994, and CMNPD17598-as well as myricetin, the control compound, were chosen for re-docking analysis. Re-docking revealed that these particular compounds had a higher affinity for MBV VP35-RBD in comparison to the control. Analyzing the chemical interactions revealed unique binding properties for every compound, identified by a range of Pi-cation interactions and hydrogen bond types. We were able to learn more about the dynamic behaviors and stability of the protein-ligand complexes through a 200-nanosecond molecular dynamics simulation, as demonstrated by the compounds' consistent RMSD and RMSF values. The multidimensional nature of the data was clarified by the application of principal component analysis, which suggested stable conformations in the complexes with little modification. Further insight into the energy profiles and stability states of these complexes was also obtained by an examination of the free energy landscape. Our findings underscore the effectiveness of computational strategies in identifying and analyzing potential inhibitors for MBV VP35-RBD, offering promising paths for further experimental investigations and possible therapeutic development against the MBV.

Recent Advances in Therapeutic Approaches Against Ebola Virus Infection

BACKGROUND

Ebola virus (EBOV) is a genus of negative-strand RNA viruses belonging to the family Filoviradae that was first described in 1976 in the present-day Democratic Republic of the Congo. It has intermittently affected substantial human populations in West Africa and presents itself as a global health menace due to the high mortality rate of patients, high transmission rate, difficult patient management, and the emergence of complicated autoimmune disease-like conditions post-infection.

OBJECTIVE

EBOV or other EBOV-like species as a biochemical weapon pose a significant risk; hence, the need to develop both prophylactic and therapeutic medications to combat the virus is unquestionable.

METHODS

In this review work, we have compiled the literature pertaining to transmission, pathogenesis, immune response, and diagnosis of EBOV infection. We included detailed structural details of EBOV along with all the available therapeutics against EBOV disease. We have also highlighted current developments and recent advances in therapeutic approaches against Ebola virus disease (EVD).

DISCUSSION

The development of preventive vaccines against the virus is proving to be a successful effort as of now; however, problems concerning logistics, product stability, multi- dosing, and patient tracking are prominent in West Africa. Monoclonal antibodies that target EBOV proteins have also been developed and approved in the clinic; however, no small drug molecules that target these viral proteins have cleared clinical trials. An understanding of clinically approved vaccines and their shortcomings also serves an important purpose for researchers in vaccine design in choosing the right vector, antigen, and particular physicochemical properties that are critical for the vaccine's success against the virus across the world.

CONCLUSION

Our work brings together a comprehensive review of all available prophylactic and therapeutic medications developed and under development against the EBOV, which will serve as a guide for researchers in pursuing the most promising drug discovery strategies against the EBOV and also explore novel mechanisms of fighting against EBOV infection.

Pathogenicity and virulence of human respiratory syncytial virus: Multifunctional nonstructural proteins NS1 and NS2

Human respiratory syncytial virus (hRSV) is a major cause of acute lower respiratory tract infections in children under the age of two as well as in the elderly and immunocompromised worldwide. Despite its discovery over 60 years ago and the global impact on human health, limited specific and effective prophylactic or therapeutic options have been available for hRSV infections. Part of the lack of treatment options is attributed to the legacy of vaccine failure in the 1960s using a formalin-inactivated RSV (FI-RSV), which led to enhancement of disease post exposure to hRSV infection and hampered subsequent development of vaccine candidates. Recent FDA approval of a vaccine for older adults and impending approval for a maternal vaccine are major advancements but leaves children between 6 months and 5 years of age unprotected. Part of this limitation can be attributed to a lack of complete understanding of the factors that contribute to hRSV pathogenesis. The nonstructural proteins NS1 and NS2 are multifunctional virulence factors that are unique to hRSV and that play critical roles during hRSV infection, including antagonizing interferon (IFN) signalling to modulate host responses to hRSV infection. However, the molecular mechanisms by which the nonstructural proteins mediate their IFN inhibitory functions have not been completely defined. Current progress on the characterization of NS1 and NS2 during infection provides deeper insight into their roles. Furthermore, reverse genetics systems for hRSV provide a viable strategy to generate attenuated viruses by introduction of select mutations while maintaining immunogenicity required to elicit a long-term protective response. Here we will review the current state of knowledge of the nonstructural proteins, their contributions to RSV pathogenesis, and their potential as targets for therapeutic development.

An Antiviral Role for TRIM14 in Ebola Virus Infection

Ebola virus (EBOV) is a highly pathogenic virus that encodes 7 multifunctional structural proteins. Multiple host factors have been reported to interact with the EBOV proteins. Here, we found that tripartite motif-containing 14 (TRIM14), an interferon-stimulated gene that mediates cellular signaling pathways associated with type I interferon and inflammatory cytokine production, interacts with EBOV nucleoprotein to enhance interferon-β (IFN-β) and nuclear factor-κB (NF-κB) promotor activation. Moreover, TRIM14 overexpression reduced viral replication in an infectious but biologically contained EBOVΔVP30 system by approximately 10-fold without affecting viral protein expression. Furthermore, TRM14-deficient mice were more susceptible to mouse-adapted EBOV infection than wild-type mice. Our data suggest that TRIM14 is a host factor with anti-EBOV activity that limits EBOV pathogenesis.

Extracellular vesicle storm during the course of Ebola virus infection in primates

Introduction

Ebola virus (EBOV) is an RNA virus of the Filoviridae family that is responsible for outbreaks of hemorrhagic fevers in primates with a lethality rate as high as 90%. EBOV primarily targets host macrophages leading to cell activation and systemic cytokine storm, and fatal infection is associated with an inhibited interferon response, and lymphopenia. The EBOV surface glycoprotein (GP) has been shown to directly induce T cell depletion and can be secreted outside the virion via extracellular vesicles (EVs), though most studies are limited to epithelial cells and underlying mechanisms remain poorly elucidated.

Methods

To assess the role of GP on EBOV-induced dysregulation of host immunity, we first utilized EBOV virus-like particles (VLPs) expressing VP40 and NP either alone (Bald-VLP) or in conjunction with GP (VLP-GP) to investigate early inflammatory responses in THP-1 macrophages and in a murine model. We then sought to decipher the role of non-classical inflammatory mediators such as EVs over the course of EBOV infection in two EBOV-infected rhesus macaques by isolating and characterizing circulatory EVs throughout disease progression using size exclusion chromatography, nanoparticle tracking-analysis, and LC-MS/MS.

Results

While all VLPs could induce inflammatory mediators and recruit small peritoneal macrophages, pro-inflammatory cytokine and chemokine gene expression was exacerbated by the presence of GP. Further, quantification of EVs isolated from infected rhesus macaques revealed that the concentration of vesicles peaked in circulation at the terminal stage, at which time EBOV GP could be detected in host-derived exosomes. Moreover, comparative proteomics conducted across EV populations isolated from serum at various time points before and after infection revealed differences in host-derived protein content that were most significantly pronounced at the endpoint of infection, including significant expression of mediators of TLR4 signaling.

Discussion

These results suggest a dynamic role for EVs in the modification of disease states in the context of EBOV. Overall, our work highlights the importance of viral factors, such as the GP, and host derived EVs in the inflammatory cascade and pathogenesis of EBOV, which can be collectively further exploited for novel antiviral development.

The Inability of Marburg Virus to Cause Disease in Ferrets Is Not Solely Linked to the Virus Glycoprotein

Ebola virus (EBOV) causes lethal disease in ferrets, whereas Marburg virus (MARV) does not. To investigate this difference, we first evaluated viral entry by infecting ferret spleen cells with vesicular stomatitis viruses pseudotyped with either MARV or EBOV glycoprotein (GP). Both viruses were capable of infecting ferret spleen cells, suggesting that lack of disease is not due to a block in MARV entry. Next, we evaluated replication kinetics of authentic MARV and EBOV in ferret cell lines and demonstrated that, unlike EBOV, MARV was only capable of low levels of replication. Finally, we inoculated ferrets with a recombinant EBOV expressing MARV GP in place of EBOV GP. Infection resulted in uniformly lethal disease within 7-9 days postinfection, while MARV-inoculated animals survived until study endpoint. Together these data suggest that the inability of MARV to cause disease in ferrets is not entirely linked to GP.

Filoviruses: Scientific Gaps and Prototype Pathogen Recommendation

Viruses in the family Filoviridae, including the commonly known Ebola (EBOV) and Marburg (MARV) viruses, can cause severe hemorrhagic fever in humans and nonhuman primates. Sporadic outbreaks of filovirus disease occur in sub-Saharan Africa with reported case fatality rates ranging from 25% to 90%. The high mortality and increasing frequency and magnitude of recent outbreaks along with the increased potential for spread from rural to urban areas highlight the importance of pandemic preparedness for these viruses. Despite their designation as high-priority pathogens, numerous scientific gaps exist in critical areas. In this review, these gaps and an assessment of potential prototype pathogen candidates are presented for this important virus family.

Disruption of Ebola NP0VP35 Inclusion Body-like Structures reduce Viral Infection

Viral inclusion bodies (IBs) are potential sites of viral replication and assembly. How viral IBs form remains poorly defined. Here we describe a combined biophysical and cellular approach to identify the components necessary for IB formation during Ebola virus (EBOV) infection. We find that the eNP0VP35 complex containing Ebola nucleoprotein (eNP) and viral protein 35 (eVP35), the functional equivalents of nucleoprotein (N) and phosphoprotein (P) in non-segmented negative strand viruses (NNSVs), phase separates to form inclusion bodies. Phase separation of eNP0VP35 is reversible and modulated by ionic strength. The multivalency of eVP35, and not eNP, is also critical for phase separation. Furthermore, overexpression of an eVP35 peptide disrupts eNP0VP35 complex formation, leading to reduced frequency of IB formation and limited viral infection. Together, our results show that upon EBOV infection, the eNP0VP35 complex forms the minimum unit to drive IB formation and viral replication.

Antimicrobial Properties of Capsaicin: Available Data and Future Research Perspectives

Capsaicin is a phytochemical derived from plants of the genus Capsicum and subject of intensive phytochemical research due to its numerous physiological and therapeutical effects, including its important antimicrobial properties. Depending on the concentration and the strain of the bacterium, capsaicin can exert either bacteriostatic or even bactericidal effects against a wide range of both Gram-positive and Gram-negative bacteria, while in certain cases it can reduce their pathogenicity by a variety of mechanisms such as mitigating the release of toxins or inhibiting biofilm formation. Likewise, capsaicin has been shown to be effective against fungal pathogens, particularly Candida spp., where it once again interferes with biofilm formation. The parasites Toxoplasma gondi and Trypanosoma cruzi have been found to be susceptible to the action of this compound too while there are also viruses whose invasiveness is significantly dampened by it. Among the most encouraging findings are the prospects for future development, especially using new formulations and drug delivery mechanisms. Finally, the influence of capsaicin in somatostatin and substance P secretion and action, offers an interesting array of possibilities given that these physiologically secreted compounds modulate inflammation and immune response to a significant extent.

Reemergence of Marburgvirus disease: Update on current control and prevention measures and review of the literature

In 1967, the very first case of the Marburgvirus disease (MVD) was detected in Germany and Serbia sequentially. Since then, MVD has been considered one of the most serious and deadly infectious diseases in the world with a case-fatality rate between 23% and 90% and a substantial number of recorded deaths. Marburgvirus belongs to the family of Filoviridae (filoviruses), which causes severe viral hemorrhagic fever (VHF). Some major risk factors for human infections are close contact with African fruit bats, MVD-infected non-human primates, and MVD-infected individuals. Currently, there is no vaccine or specific treatment for MVD, which emphasizes the seriousness of this disease. In July 2022, the World Health Organization reported outbreaks of MVD in Ghana after two suspected VHF cases were detected. This was followed in February and March 2023 with the emergence of the virus in two countries new to the virus: Equatorial Guinea and Tanzania, respectively. In this review, we aim to highlight the characteristics, etiology, epidemiology, and clinical symptoms of MVD, along with the current prevention measures and the possible treatments to control this virus.

VP24 matrix proteins of eight filoviruses downregulate innate immune response by inhibiting the interferon-induced pathway

Filoviruses encode viral protein 24 (VP24) which effectively inhibit the innate immune responses in infected cells. Here we systematically analysed the effects of nine mammalian filovirus VP24 proteins on interferon (IFN)-induced immune response. We transiently expressed Ebola, Bombali, Bundibugyo, Reston, Sudan and Taï Forest ebolavirus (EBOV, BOMV, BDBV, RESTV, SUDV, TAFV, respectively), Lloviu virus (LLOV), Mengla dianlovirus (MLAV) and Marburgvirus (MARV) VP24 proteins and analysed their ability to inhibit IFN-α-induced activation of myxovirus resistance protein 1 (MxA) and interferon-induced transmembrane protein 3 (IFITM3) promoters. In addition, we analysed the expression of endogenous MxA protein in filovirus VP24-expressing cells. Eight filovirus VP24 proteins, including the VP24s of the recently discovered MLAV, BOMV and LLOV, inhibited IFN-induced MxA and IFITM3 promoter activation. MARV VP24 was the only protein with no inhibitory effect on the activation of either promoter. Endogenous MxA protein expression was impaired in cells transiently expressing VP24s with the exception of MARV VP24. We mutated nuclear localization signal (NLS) of two highly pathogenic filoviruses (EBOV and SUDV) and two putatively non-pathogenic filoviruses (BOMV and RESTV), and showed that the inhibitory effect on IFN-induced expression of MxA was dependent on functional cluster 3 of VP24 nuclear localization signal. Our findings suggest that filovirus VP24 proteins are both genetically and functionally conserved, and that VP24 proteins of most filovirus species are capable of inhibiting IFN-induced antiviral gene expression thereby efficiently downregulating the host innate immune responses.

Ebolavirus Species-Specific Interferon Antagonism Mediated by VP24

Members of the Ebolavirus genus demonstrate a marked differences in pathogenicity in humans with Ebola (EBOV) being the most pathogenic, Bundibugyo (BDBV) less pathogenic, and Reston (RESTV) is not known to cause a disease in humans. The VP24 protein encoded by members of the Ebolavirus genus blocks type I interferon (IFN-I) signaling through interaction with host karyopherin alpha nuclear transporters, potentially contributing to virulence. Previously, we demonstrated that BDBV VP24 (bVP24) binds with lower affinities to karyopherin alpha proteins relative to EBOV VP24 (eVP24), and this correlated with a reduced inhibition in IFN-I signaling. We hypothesized that modification of eVP24-karyopherin alpha interface to make it similar to bVP24 would attenuate the ability to antagonize IFN-I response. We generated a panel of recombinant EBOVs containing single or combinations of point mutations in the eVP24-karyopherin alpha interface. Most of the viruses appeared to be attenuated in both IFN-I-competent 769-P and IFN-I-deficient Vero-E6 cells in the presence of IFNs. However, the R140A mutant grew at reduced levels even in the absence of IFNs in both cell lines, as well as in U3A STAT1 knockout cells. Both the R140A mutation and its combination with the N135A mutation greatly reduced the amounts of viral genomic RNA and mRNA suggesting that these mutations attenuate the virus in an IFN-I-independent attenuation. Additionally, we found that unlike eVP24, bVP24 does not inhibit interferon lambda 1 (IFN-λ1), interferon beta (IFN-β), and ISG15, which potentially explains the lower pathogenicity of BDBV relative to EBOV. Thus, the VP24 residues binding karyopherin alpha attenuates the virus by IFN-I-dependent and independent mechanisms.

A Bivalent Bacterium-like Particles-Based Vaccine Induced Potent Immune Responses against the Sudan Virus and Ebola Virus in Mice

Ebola virus disease (EVD) is an acute viral hemorrhagic fever disease causing thousands of deaths. The large Ebola outbreak in 2014-2016 posed significant threats to global public health, requiring the development of multiple medical measures for disease control. Sudan virus (SUDV) and Zaire virus (EBOV) are responsible for severe disease and occasional deadly outbreaks in West Africa and Middle Africa. This study shows that bivalent bacterium-like particles (BLPs)-based vaccine, SUDV-EBOV BLPs (S/ZBLP + 2 + P), generated by mixing SUDV-BLPs and EBOV-BLPs at a 1 : 1 ratio, is immunogenic in mice. The SUDV-EBOV BLPs induced potent immune responses against SUDV and EBOV and elicited both T-helper 1 (Th1) and T-helper 2 (Th2) immune responses. The results indicated that SUDV-EBOV BLPs-based vaccine has the potential to be a promising candidate against SUDV and EBOV infections and provide a strategy to develop universal vaccines for EVD.

Inhibiting the transcription and replication of Ebola viruses by disrupting the nucleoprotein and VP30 protein interaction with small molecules

Ebola virus (EBOV) causes hemorrhagic fever in humans with high morbidity and fatality. Although over 45 years have passed since the first EBOV outbreak, small molecule drugs are not yet available. Ebola viral protein VP30 is a unique RNA synthesis cofactor, and the VP30/NP interaction plays a critical role in initiating the transcription and propagation of EBOV. Here, we designed a high-throughput screening technique based on a competitive binding assay to bind VP30 between an NP-derived peptide and a chemical compound. By screening a library of 8004 compounds, we obtained two lead compounds, Embelin and Kobe2602. The binding of these compounds to the VP30-NP interface was validated by dose-dependent competitive binding assay, surface plasmon resonance, and thermal shift assay. Moreover, the compounds were confirmed to inhibit the transcription and replication of the Ebola genome by a minigenome assay. Similar results were obtained for their two respective analogs (8-gingerol and Kobe0065). Interestingly, these two structurally different molecules exhibit synergistic binding to the VP30/NP interface. The antiviral efficacy (EC₅₀) increased from 1 μM by Kobe0065 alone to 351 nM when Kobe0065 and Embelin were combined in a 4:1 ratio. The synergistic anti-EBOV effect provides a strong incentive for further developing these lead compounds in future studies.

Computational Modeling and Evaluation of Potential mRNA and Peptide-Based Vaccine against Marburg Virus (MARV) to Provide Immune Protection against Hemorrhagic Fever

A hemorrhagic fever caused by the Marburg virus (MARV) belongs to the Filoviridae family and has been classified as a risk group 4 pathogen. To this day, there are no approved effective vaccinations or medications available to prevent or treat MARV infections. Reverse vaccinology-based approach was formulated to prioritize B and T cell epitopes utilizing a numerous immunoinformatics tools. Potential epitopes were systematically screened based on various parameters needed for an ideal vaccine such as allergenicity, solubility, and toxicity. The most suitable epitopes capable of inducing immune response were shortlisted. Epitopes with population coverage of 100% and fulfilling set parameters were selected for docking with human leukocyte antigen molecules, and binding affinity of each peptide was analyzed. Finally, 4 CTL and HTL each while 6 B cell 16-mers were used for designing multiepitope subunit (MSV) and mRNA vaccine joined via suitable linkers. Immune simulations were used to validate the constructed vaccine's capacity to induce a robust immune response whereas molecular dynamics simulations were used to confirm epitope-HLA complex stability. Based on these parameter's studies, both the vaccines constructed in this study offer a promising choice against MARV but require further experimental verification. This study provides a rationale point to begin with the development of an efficient vaccine against Marburg virus; however, the findings need further experimental validation to confirm the computational finding of this study.

Ebola Virus Activates IRE1α-Dependent XBP1u Splicing

Ebola (EBOV) and Marburg virus (MARV) are highly pathogenic filoviruses that influence cellular signaling according to their own needs. MARV has been shown to regulate the IRE1α-dependent unfolded protein response (UPR) to ensure optimal virus replication. It was not known whether EBOV affects this signaling cascade, which can be beneficial or detrimental for viruses. Activation of IRE1α leads to the expression of the transcription factor XBP1s, which binds to cis-acting UPR elements (UPRE), resulting in the expression of genes aimed at restoring homeostasis in the endoplasmic reticulum. We observed that EBOV infection, in contrast to MARV infection, led to UPR activation by IRE1α-dependent but not ATF6-dependent signaling. We showed an activation of IRE1α, XBP1s and UPRE target genes upon EBOV infection. ATF6, another UPRE transcription factor, was not activated. UPRE activation was mainly attributed to the EBOV nucleoprotein NP and the soluble glycoprotein sGP. Finally, activation of UPR by thapsigargin, a potent ER-stress inducer, in parallel to infection as well as knock-out of XBP1 had no effect on EBOV growth, while MARV proliferation was affected by thapsigargin-dependent UPR activation. Taken together EBOV and MARV differ in their strategy of balancing IRE1α-dependent signaling for their own needs.

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.

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.

Single Nucleotide Variants of the Human TIM-1 IgV Domain with Reduced Ability to Promote Viral Entry into Cells

Human T-cell immunoglobulin mucin 1 (hTIM-1) is known to promote cellular entry of enveloped viruses. Previous studies suggested that the polymorphisms of hTIM-1 affected its function. Here, we analyzed single nucleotide variants (SNVs) of hTIM-1 to determine their ability to promote cellular entry of viruses using pseudotyped vesicular stomatitis Indiana virus (VSIV). We obtained hTIM-1 sequences from a public database (Ensembl genome browser) and identified 35 missense SNVs in 3 loops of the hTIM-1 immunoglobulin variable (IgV) domain, which had been reported to interact with the Ebola virus glycoprotein (GP) and phosphatidylserine (PS) in the viral envelope. HEK293T cells transiently expressing wildtype hTIM-1 or its SNV mutants were infected with VSIVs pseudotyped with filovirus or arenavirus GPs, and their infectivities were compared. Eleven of the thirty-five SNV substitutions reduced the efficiency of hTIM-1-mediated entry of pseudotyped VSIVs. These SNV substitutions were found not only around the PS-binding pocket but also in other regions of the molecule. Taken together, our findings suggest that some SNVs of the hTIM-1 IgV domain have impaired ability to interact with PS and/or viral GPs in the viral envelope, which may affect the hTIM-1 function to promote viral entry into cells.

Ebola virus protein VP40 stimulates IL-12- and IL-18-dependent activation of human natural killer cells

Accumulation of activated natural killer (NK) cells in tissues during Ebola virus infection contributes to Ebola virus disease (EVD) pathogenesis. Yet, immunization with Ebola virus-like particles (VLPs) comprising glycoprotein and matrix protein VP40 provides rapid, NK cell–mediated protection against Ebola challenge. We used Ebola VLPs as the viral surrogates to elucidate the molecular mechanism by which Ebola virus triggers heightened NK cell activity. Incubation of human peripheral blood mononuclear cells with Ebola VLPs or VP40 protein led to increased expression of IFN-γ, TNF-α, granzyme B, and perforin by CD3^–CD56⁺ NK cells, along with increases in degranulation and cytotoxic activity of these cells. Optimal activation required accessory cells like CD14⁺ myeloid and CD14^– cells and triggered increased secretion of numerous inflammatory cytokines. VP40-induced IFN-γ and TNF-α secretion by NK cells was dependent on IL-12 and IL-18 and suppressed by IL-10. In contrast, their increased degranulation was dependent on IL-12 with little influence of IL-18 or IL-10. These results demonstrate that Ebola VP40 stimulates NK cell functions in an IL-12– and IL-18–dependent manner that involves CD14⁺ and CD14^– accessory cells. These potentially novel findings may help in designing improved intervention strategies required to control viral transmission during Ebola outbreaks.

Discovery of potent ebola entry inhibitors with (3S,4aS,8aS)-2-(3-amino-2-hydroxypropyl) decahydroisoquinoline-3-carboxamide scaffold

Ebola virus (EBOV), one member of the family Filoviridae, can causes hemorrhagic fever and other severe diseases in humans with a high mortality rate (25-90%). Until recently, there were no approved drugs and very limited treatment method for Ebola virus disease. In this study, we discovered a series of potent Ebola entry inhibitors with the (3S,4aS,8aS)-2-(3-amino-2-hydroxypropyl)decahydroisoquinoline-3-carboxamide scaffold from high-throughput screening in reported pseudotyped virus system. Further optimization resulted a most potent compound 28 (IC₅₀= 0.05 μM, SI = 98), which displayed 3-fold potency compared to the known inhibitor Toremifene (IC₅₀= 0.17 μM, SI = 55). Moreover, compound 28 exhibited the remarkable selectivity between EBOV-GP and VSV-G (Spec. Index = 58), thus could exclude nonspecific effects. Structure-activity relationship and molecular docking analysis of the new chemical scaffold provided more information on the binding modes and the spare volume at the binding cavity, thus can guide the design of the further potent compounds.

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.

Transient Liver Damage and Hemolysis Are Associated With an Inhibition of Ebola Virus Glycoprotein-Specific Antibody Response and Lymphopenia

Numerous studies have demonstrated the importance of the adaptive immunity for survival following Ebola virus (EBOV) infection. To evaluate the contribution of tissue damage to EBOV-induced immune suppression, acute liver damage or hemolysis, 2 symptoms associated with lethal EBOV infection, were chemically induced in vaccinated mice. Results show that either liver damage or hemolysis was sufficient to inhibit the host humoral response against EBOV glycoprotein and to drastically reduce the level of circulating T cells. This study thus provides a possible mechanism for the limited specific antibody production and lymphopenia in individuals with lethal hemorrhagic fever infections.

TRIM25 and ZAP target the Ebola virus ribonucleoprotein complex to mediate interferon-induced restriction

Ebola virus (EBOV) causes highly pathogenic disease in primates. Through screening a library of human interferon-stimulated genes (ISGs), we identified TRIM25 as a potent inhibitor of EBOV transcription-and-replication-competent virus-like particle (trVLP) propagation. TRIM25 overexpression inhibited the accumulation of viral genomic and messenger RNAs independently of the RNA sensor RIG-I or secondary proinflammatory gene expression. Deletion of TRIM25 strongly attenuated the sensitivity of trVLPs to inhibition by type-I interferon. The antiviral activity of TRIM25 required ZAP and the effect of type-I interferon was modulated by the CpG dinucleotide content of the viral genome. We find that TRIM25 interacts with the EBOV vRNP, resulting in its autoubiquitination and ubiquitination of the viral nucleoprotein (NP). TRIM25 is recruited to incoming vRNPs shortly after cell entry and leads to dissociation of NP from the vRNA. We propose that TRIM25 targets the EBOV vRNP, exposing CpG-rich viral RNA species to restriction by ZAP.

A cryptic pocket in Ebola VP35 allosterically controls RNA binding

Protein-protein and protein-nucleic acid interactions are often considered difficult drug targets because the surfaces involved lack obvious druggable pockets. Cryptic pockets could present opportunities for targeting these interactions, but identifying and exploiting these pockets remains challenging. Here, we apply a general pipeline for identifying cryptic pockets to the interferon inhibitory domain (IID) of Ebola virus viral protein 35 (VP35). VP35 plays multiple essential roles in Ebola's replication cycle but lacks pockets that present obvious utility for drug design. Using adaptive sampling simulations and machine learning algorithms, we predict VP35 harbors a cryptic pocket that is allosterically coupled to a key dsRNA-binding interface. Thiol labeling experiments corroborate the predicted pocket and mutating the predicted allosteric network supports our model of allostery. Finally, covalent modifications that mimic drug binding allosterically disrupt dsRNA binding that is essential for immune evasion. Based on these results, we expect this pipeline will be applicable to other proteins.

Protein Folding Interdiction Strategy for Therapeutic Drug Development in Viral Diseases: Ebola VP40 and Influenza A M1

In a recent paper, we proposed the folding interdiction target region (FITR) strategy for therapeutic drug design in SARS-CoV-2. This paper expands the application of the FITR strategy by proposing therapeutic drug design approaches against Ebola virus disease and influenza A. We predict target regions for folding interdicting drugs on correspondingly relevant structural proteins of both pathogenic viruses: VP40 of Ebola, and matrix protein M1 of influenza A. Identification of the protein targets employs the sequential collapse model (SCM) for protein folding. It is explained that the model predicts natural peptide candidates in each case from which to start the search for therapeutic drugs. The paper also discusses how these predictions could be tested, as well as some challenges likely to be found when designing effective therapeutic drugs from the proposed peptide candidates. The FITR strategy opens a potential new avenue for the design of therapeutic drugs that promises to be effective against infectious diseases.

Recombinant Lloviu virus as a tool to study viral replication and host responses

Next generation sequencing has revealed the presence of numerous RNA viruses in animal reservoir hosts, including many closely related to known human pathogens. Despite their zoonotic potential, most of these viruses remain understudied due to not yet being cultured. While reverse genetic systems can facilitate virus rescue, this is often hindered by missing viral genome ends. A prime example is Lloviu virus (LLOV), an uncultured filovirus that is closely related to the highly pathogenic Ebola virus. Using minigenome systems, we complemented the missing LLOV genomic ends and identified cis-acting elements required for LLOV replication that were lacking in the published sequence. We leveraged these data to generate recombinant full-length LLOV clones and rescue infectious virus. Similar to other filoviruses, recombinant LLOV (rLLOV) forms filamentous virions and induces the formation of characteristic inclusions in the cytoplasm of the infected cells, as shown by electron microscopy. Known target cells of Ebola virus, including macrophages and hepatocytes, are permissive to rLLOV infection, suggesting that humans could be potential hosts. However, inflammatory responses in human macrophages, a hallmark of Ebola virus disease, are not induced by rLLOV. Additional tropism testing identified pneumocytes as capable of robust rLLOV and Ebola virus infection. We also used rLLOV to test antivirals targeting multiple facets of the replication cycle. Rescue of uncultured viruses of pathogenic concern represents a valuable tool in our arsenal for pandemic preparedness.

Due to increasing utilization of high-throughput sequencing technologies, RNA sequences of many unknown viruses have been discovered in bats and other animal species. Research on the pathogenic potential of these viruses is hampered by incomplete viral genome sequences and difficulties in isolating infectious virus from the animal hosts. One example of these potentially zoonotic pathogens is Lloviu virus (LLOV), a filovirus which is closely related to Ebola virus. Here we applied molecular virological approaches, including minigenome assays, to complement the incomplete LLOV genome ends with sequences from related viruses and identify cis-acting elements required for LLOV replication and transcription that were missing in the published LLOV sequence. The resulting full-length clones were used to generate infectious recombinant LLOV. We used this virus for electron microscopic analyses, infection studies in human cells, host response analysis, and antiviral drug testing. Our results provide new insights into the pathogenic potential of LLOV and delineate a roadmap for studying uncultured viruses.

Filovirus VP24 Proteins Differentially Regulate RIG-I and MDA5-Dependent Type I and III Interferon Promoter Activation

Filovirus family consists of highly pathogenic viruses that have caused fatal outbreaks especially in many African countries. Previously, research focus has been on Ebola, Sudan and Marburg viruses leaving other filoviruses less well studied. Filoviruses, in general, pose a significant global threat since they are highly virulent and potentially transmissible between humans causing sporadic infections and local or widespread epidemics. Filoviruses have the ability to downregulate innate immunity, and especially viral protein 24 (VP24), VP35 and VP40 have variably been shown to interfere with interferon (IFN) gene expression and signaling. Here we systematically analyzed the ability of VP24 proteins of nine filovirus family members to interfere with retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated antigen 5 (MDA5) induced IFN-β and IFN-λ1 promoter activation. All VP24 proteins were localized both in the cell cytoplasm and nucleus in variable amounts. VP24 proteins of Zaire and Sudan ebolaviruses, Lloviu, Taï Forest, Reston, Marburg and Bundibugyo viruses (EBOV, SUDV, LLOV, TAFV, RESTV, MARV and BDBV, respectively) were found to inhibit both RIG-I and MDA5 stimulated IFN-β and IFN-λ1 promoter activation. The inhibition takes place downstream of interferon regulatory factor 3 phosphorylation suggesting the inhibition to occur in the nucleus. VP24 proteins of Mengla (MLAV) or Bombali viruses (BOMV) did not inhibit IFN-β or IFN-λ1 promoter activation. Six ebolavirus VP24s and Lloviu VP24 bound tightly, whereas MARV and MLAV VP24s bound weakly, to importin α5, the subtype that regulates the nuclear import of STAT complexes. MARV and MLAV VP24 binding to importin α5 was very weak. Our data provides new information on the innate immune inhibitory mechanisms of filovirus VP24 proteins, which may contribute to the pathogenesis of filovirus infections.

Immune Response to Viruses

Viruses are essentially, obligate intracellular parasites. They require a host to replicate their genetic material, spread to other cells, and eventually to other hosts. For humans, most viral infections are not considered lethal, regardless if at the cellular level, the virus can obliterate individual cells. Constant genomic mutations, (which can alter the antigenic content of viruses such as influenza or coronaviruses), zoonosis or immunosuppression/immunocompromisation, is when viruses achieve higher host mortality. Frequent examples of the severe consequenses of viral infection can be seen in children and the elderly. In most instances, the immune system will take a multifaceted approach in defending the host against viruses. Depending on the virus, the individual, and the point of entry, the immune system will initiate a robust response which involves multiple components. In this chapter, we expand on the total immune system, breaking it down to the two principal types: Innate and Adaptive Immunity, their different roles in viral recognition and clearance. Finally, how different viruses activate and evade different arms of the immune system.

Domain-specific biochemical and serological characterization of SARS-CoV-2 nucleocapsid protein

Nucleocapsid proteins are essential for SARS-CoV-2 life cycle. Here, we describe protocols to gather domain-specific insights about essential properties of nucleocapsids. These assays include dynamic light scattering to characterize oligomerization, fluorescence polarization to quantify RNA binding, hydrogen-deuterium exchange mass spectrometry to map RNA binding regions, negative-stain electron microscopy to visualize oligomeric species, interferon reporter assay to evaluate interferon signaling modulation, and a serology assay to reveal insights for improved sensitivity and specificity. These assays are broadly applicable to RNA-encapsidated nucleocapsids. For complete details on the use and execution of this protocol, please refer to Wu et al. (2021).

Quantification of Type I Interferon Inhibition by Viral Proteins: Ebola Virus as a Case Study

Type I interferons (IFNs) are cytokines with both antiviral properties and protective roles in innate immune responses to viral infection. They induce an antiviral cellular state and link innate and adaptive immune responses. Yet, viruses have evolved different strategies to inhibit such host responses. One of them is the existence of viral proteins which subvert type I IFN responses to allow quick and successful viral replication, thus, sustaining the infection within a host. We propose mathematical models to characterise the intra-cellular mechanisms involved in viral protein antagonism of type I IFN responses, and compare three different molecular inhibition strategies. We study the Ebola viral protein, VP35, with this mathematical approach. Approximate Bayesian computation sequential Monte Carlo, together with experimental data and the mathematical models proposed, are used to perform model calibration, as well as model selection of the different hypotheses considered. Finally, we assess if model parameters are identifiable and discuss how such identifiability can be improved with new experimental data.

The MAVS Immune Recognition Pathway in Viral Infection and Sepsis

Significance: It is estimated that close to 50 million cases of sepsis result in over 11 million annual fatalities worldwide. The pathognomonic feature of sepsis is a dysregulated inflammatory response arising from viral, bacterial, or fungal infections. Immune recognition of pathogen-associated molecular patterns is a hallmark of the host immune defense to combat microbes and to prevent the progression to sepsis. Mitochondrial antiviral signaling protein (MAVS) is a ubiquitous adaptor protein located at the outer mitochondrial membrane, which is activated by the cytosolic pattern recognition receptors, retinoic acid-inducible gene I (RIG-I) and melanoma differentiation associated gene 5 (MDA5), following binding of viral RNA agonists. Recent Advances: Substantial progress has been made in deciphering the activation of the MAVS pathway with its interacting proteins, downstream signaling events (interferon [IFN] regulatory factors, nuclear factor kappa B), and context-dependent type I/III IFN response. Critical Issues: In the evolutionary race between pathogens and the host, viruses have developed immune evasion strategies for cleavage, degradation, or blockade of proteins in the MAVS pathway. For example, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) M protein and ORF9b protein antagonize MAVS signaling and a protective type I IFN response. Future Directions: The role of MAVS as a sensor for nonviral pathogens, host cell injury, and metabolic perturbations awaits better characterization in the future. New technical advances in multidimensional single-cell analysis and single-molecule methods will accelerate the rate of new discoveries. The ultimate goal is to manipulate MAVS activities in the form of immune-modulatory therapies to combat infections and sepsis. Antioxid. Redox Signal. 35, 1376-1392.