Search Results (921)

Functional antibody-dependent enhancement (ADE) represents a fundamental and context-dependent characteristic of antiviral antibody responses, reflecting the dual capacity of antibodies to mediate both the neutralization and Fc receptor-dependent enhancement of infection. In flavivirus research, this duality complicates the interpretation of conventional serological metrics and limits the reliability of single-parameter correlates of immunity, particularly in populations with complex exposure histories. Over the past decade, functional ADE assays have evolved from specialized mechanistic tools into integrated immune assessment platforms supporting translational immunology, vaccine evaluation, and population-level immune surveillance. These platforms incorporate Fcγ receptor-relevant target cell systems, standardized viral inputs, dilution series-based profiling, quantitative enhancement metrics, and structured quality control frameworks to enable reproducible, comparable, and context-aware functional measurements across cohorts and laboratories. A central concept emerging from these developments is that ADE reflects a dynamic functional immune state rather than an intrinsic property of antibodies or a direct indicator of pathological risk. Accordingly, functional ADE platforms support the contextual interpretation of antibody activity across physiologically relevant conditions, facilitating discrimination between transient functional enhancement and clinically meaningful immunological risk. By integrating functional ADE metrics with serological, cellular, and epidemiological data, these platforms provide a structured framework for interpreting immune profiles in vaccine evaluation, booster strategy design, and population-level risk stratification. This review synthesizes the development, standardization, and global dissemination of functional ADE platforms and discusses key principles governing biological relevance, analytical robustness, and inter-site transferability. Emerging directions integrating functional ADE profiling with systems immunology, immunogenomics, and computational modeling are highlighted as pathways toward predictive, decision-support-oriented frameworks. By positioning ADE platforms as immune assessment infrastructures rather than isolated assays, this review underscores their value for mechanistic inquiry, translational interpretation, and preparedness-oriented responses to emerging viral threats in the absence of definitive correlates of protection. Full article

NS4A plays a role in forming the flavivirus replication complex, which inhibits apoptosis in host cells by inducing autophagy, thereby promoting viral replication. The host protein ENO1 interacts with NS4A, but the precise mechanism underlying this interaction and its role in viral replication remain unclear. In this study, we identified ZIKV NS4A^1–73 as a key regulator of replication and infection cycles in both temporal and spatial dimensions. Through surface plasmon resonance (SPR) analysis, we demonstrated that ENO1 directly interacts with NS4A^1–73. This critical binding inhibits the enzymatic activity of ENO1 and reduces cellular lactate and ATP production. Our findings suggest that ZIKV NS4A may effectively impede cellular metabolism by targeting the host factor ENO1, thus disrupting the glycolytic process. This insight could open new avenues for targeting ZIKV and similar viruses in therapeutic strategies. Full article

Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) represent fundamental cellular adaptive mechanisms that maintain protein homeostasis and metabolic balance. Many RNA viruses, particularly flaviviruses such as dengue virus (DENV), Zika virus (ZIKV), West Nile virus (WNV), yellow fever virus (YFV), and Japanese encephalitis virus (JEV), extensively remodel the ER to establish replication compartments and assemble progeny virions. This massive reorganization disrupts ER homeostasis, leading to UPR activation. Emerging evidence reveals that flaviviruses not only trigger but also manipulate the three UPR branches—PERK, IRE1, and ATF6—to optimize viral translation, replication, and egress. In parallel, flavivirus infection profoundly alters host lipid metabolism and promotes dynamic changes in lipid droplets (LDs), key organelles that mediate lipid storage and serve as scaffolds for viral replication and assembly. The UPR intimately connects to LD biogenesis through transcriptional and translational programs mediated by XBP1, ATF4, and ATF6, thereby coupling ER stress responses to lipid remodeling and energy homeostasis. This intricate crosstalk between UPR and LDs creates a metabolic and structural niche favorable for viral replication but detrimental to host cell integrity. This review provides a comprehensive analysis of the molecular mechanisms by which flaviviruses exploit ER stress and the UPR to reprogram lipid metabolism and LD dynamics. We highlight the dual role of UPR signaling in promoting adaptive lipid synthesis and initiating cell death under prolonged stress, discuss recent insights into ER–LD interactions during flavivirus infection, and explore therapeutic opportunities targeting UPR–lipid metabolic pathways as broad-spectrum antiviral strategies. Understanding this interconnected network will advance our knowledge of viral pathogenesis and identify new avenues for host-directed antiviral intervention. Full article

West Nile virus (WNV) is a mosquito-borne flavivirus of growing importance for both human and equine health in Europe. Horses are highly susceptible to neurological disease and, because they share ecological exposure with humans, they represent valuable sentinels for detecting local viral circulation within a One Health framework. However, diagnosis of WNV infection in equines is complicated by the short and low-level viraemia, which limits the sensitivity of molecular assays, and by serological cross-reactivity with related flaviviruses and the confounding effects of vaccination. In this narrative review, we summarise the current diagnostic tools for WNV in horses, including direct detection methods (RT-qPCR, virus isolation, antigen detection) and indirect serological approaches (IgM and IgG ELISA, virus neutralisation tests), and discuss their practical performance and constraints in clinical and surveillance settings. We further examine equine surveillance systems, passive clinical reporting, active serosurveys and sentinel cohorts, and their integration with vector, avian and environmental monitoring. Key challenges include methodological heterogeneity, limited access to confirmatory testing and variable cross-sector data sharing. Finally, we outline future directions, highlighting the need for harmonised laboratory protocols, innovative field-deployable diagnostics, genomic surveillance and integrated, multi-source monitoring systems to strengthen early warning capacity and improve preparedness for WNV outbreaks in equine populations. Full article

Background/Objectives: Chimpanzee adenoviral-vectored vaccines have proven to be both safe and effective, with a manufacturing and distribution pipeline capable of rapid global supply, as demonstrated during the COVID-19 pandemic. Yellow fever is a mosquito-borne viral hemorrhagic disease endemic in parts of Africa and Latin America, and although an effective live attenuated vaccine exists, its use is limited by safety and eligibility restrictions. Moreover, large outbreaks continue to expose critical challenges, such as an insufficient vaccine supply, reliance on fractional dosing, and slow and difficult-to-scale manufacturing processes. Here, we report the design, development and in vivo immunogenicity of multiple yellow fever virus (YFV) antigen constructs based on the pre-membrane (prM) and envelope (E) proteins—with or without the transmembrane domain (TM or ΔTM)—delivered using the ChAdOx1 adenoviral vector. Methods: Four ChAdOx1 YF vaccines were developed, and immunogenicity was evaluated. The efficacy of the full-length YF envelope vaccine was also tested in Balb/c mice. Results/Conclusions: In contrast to previously described orthoflavivirus vaccines on the same platform, the full-length antigen elicited superior immunogenicity and conferred protection against intracranial challenge with the YF17D virus in mice. Notably, this protection was comparable to that induced by the licensed YF17D vaccine, highlighting the promise of this platform as a next-generation yellow fever vaccine candidate. Full article

The zoonotic Orthoflavivirus Usutu virus (USUV) is distributed throughout Germany, putting hosts at a considerable risk of infection nationwide. Besides birds as reservoir hosts, a broad range of accidental hosts is suspected. However, there are few reports documenting the progression of USUV-associated disease. This case report describes the course of fatal USUV infections in three harbor seals (Phoca vitulina) from a rescue center on the North Sea coast in Germany. Corresponding samples were analyzed using (histo-)pathological, immunohistochemical, molecular and phylogenetic methods. The most prevalent findings in clinically affected animals were neurological signs and non-suppurative encephalitis. All animals were found dead or had been euthanized due to animal welfare reasons within 30 h after the onset of clinical signs. Blood samples taken from another 37 young harbor seals from the same rescue center in the same year revealed two further asymptomatic USUV RNA and antibody-positive animals. The sequences were found to belong to USUV lineages Europe 2 and Africa 3, which are known to circulate in birds in Germany. This case report highlights the importance of USUV as a potential diagnosis for neurological impairments in marine mammals and documents the first cases of USUV infection in harbor seals. Full article

Zoonotic diseases account for approximately one billion cases of illness and millions of deaths globally each year. Increasing contact between humans and competent wildlife hosts elevates the risk of zoonotic spillover. Synanthropic bird species are key players in the transmission of zoonotic pathogens, including flaviviruses such as West Nile virus (WNV) and influenza A viruses like Avian Influenza Virus (AIV). Active surveillance of sentinel birds inhabiting urban areas allows for early detection of emerging pathogens before they cause zoonotic outbreaks. Despite nesting in close proximity to humans, the role of the house martin (Delichon urbicum) in the circulation of flaviviruses and AIV remains poorly understood. Here, we analyzed the presence of antibodies against flaviviruses and AIV in a colony of house martins from southwestern Spain. In addition, we aimed to detect amplicons of the matrix and nucleoprotein genes of AIV using RT-qPCR. While none of the samples tested positive for AIV by RT-qPCR, we observed an AIV seroprevalence of 2.13% based on non-subtyped ELISA. Notably, this is the first report of AIV-seropositive D. urbicum individuals captured in Spain. Moreover, we detected a flavivirus-group seroprevalence of 24.34%, similar to rates reported in the same house martin population between 2018 and 2020, suggesting widespread circulation of flaviviruses within this synanthropic species. These results support the hypothesis that house martins may participate in the transmission of these viruses between wild bird populations and humans in urban environments. Full article

West Nile virus (WNV) is a mosquito-borne flavivirus that remains an important public and veterinary health concern across Europe. Periodic outbreaks affecting humans, horses, and wildlife highlight the complex ecological interactions underlying viral circulation. This narrative review aims to synthesize current knowledge regarding WNV epidemiology, transmission dynamics, and surveillance strategies in Europe, with particular attention to the Romanian context. Available surveillance data indicate recurrent seasonal transmission in several European regions; however, reported case numbers may be influenced by differences in diagnostic capacity, reporting practices, and surveillance intensity among countries. Recent studies suggest that environmental variability, vector adaptation, and host community composition play important roles in shaping regional transmission risk, although the relative contribution of these factors remains incompletely quantified. Despite expanding surveillance networks and One Health initiatives, important knowledge gaps persist regarding the integration of environmental risk indicators, vector ecology, and operational preparedness into coherent risk-assessment frameworks. This review therefore examines current epidemiological patterns, evaluates surveillance approaches, and discusses emerging drivers of WNV transmission in Europe. As a narrative synthesis based on published literature and surveillance reports, this review is subject to limitations related to heterogeneity in available data and differences in national reporting systems. Nevertheless, a clearer understanding of these interacting factors may support improved surveillance strategies and more adaptive public health responses to future WNV transmission events. Reported surveillance data should be interpreted cautiously, as differences in national surveillance intensity, diagnostic capacity, and reporting frameworks across Europe may influence notified case numbers. Consequently, reported outbreaks do not necessarily reflect proportional differences in transmission intensity. Full article

Background: Zika virus (ZIKV) is a mosquito-borne flavivirus associated with severe neurological disease, including congenital Zika syndrome (CZS) following utero infection and Guillain–Barré syndrome in adults. The 2015–2016 epidemic in the Americas highlighted the profound maternal and neonatal consequences of ZIKV infection. Although reported transmission has declined, ongoing circulation of competent vectors and population susceptibility sustain a substantial risk of future outbreaks, underscoring the need for effective vaccines. Methods: We developed a recombinant Modified Vaccinia Ankara (MVA)-based vaccine candidate expressing the ZIKV pre-membrane (prM) and envelope (E) proteins and evaluated its immunogenicity and protective efficacy in interferon receptor-deficient AG129 mice. Results: Vaccination induced strong humoral and cellular immune responses and conferred significant protection against viral replication in key target organs, including the brain and testes, following ZIKV challenge. Conclusions: These preclinical findings support further development of this MVA-based ZIKV vaccine as a promising strategy to prevent ZIKV infection and its associated neurological complications. Full article

Japanese encephalitis virus (JEV) is an important flavivirus that causes zoonotic and arboviral diseases. Infection with JEV not only induces acute central nervous system (CNS) infectious diseases but also leads to reproductive disorders. Currently, research on the pathogenic mechanism of JEV has mainly focused on CNS inflammation caused by infection, while studies on the pathogenic mechanism of JEV targeting the reproductive system are relatively scarce. This study used TM3 cells as a model to investigate the regulatory role of the CD4 molecule in JEV infection, the STAT1 signaling pathway, and inflammatory factors. Firstly, we found that CD4 knockdown significantly inhibited JEV replication in TM3 cells. Further virus adsorption and internalization experiments confirmed that CD4 knockdown specifically impaired the early stages of JEV invasion into cells. Additionally, CD4 knockdown also drastically attenuated JEV infection-induced STAT1 phosphorylation (p-STAT1) and the production of downstream inflammatory factors. To distinguish whether CD4 affects p-STAT1 through an indirect effect of reduced viral load or its direct involvement in signal transduction, we performed experiments using RO8191, a specific agonist of the STAT1 signaling pathway. The results showed that RO8191 treatment increased the expression levels of p-STAT1 protein and inflammatory factor mRNA in both normal cells and CD4 knockdown cells, but the recovery amplitude in the CD4 knockdown group was significantly lower. In contrast, CD4 complementation significantly elevated the expression levels of p-STAT1 protein and inflammatory factor mRNA. In conclusion, this study demonstrates that the CD4 molecule positively regulates JEV proliferation in TM3 cells, while also modulating STAT1—a key factor in the STAT signaling pathway—and downstream inflammatory cytokines. Notably, this regulatory effect operates independently of viral replication. These findings provide a theoretical foundation for further elucidation of JEV pathogenic mechanisms and offer a scientific basis for the prevention and control of JEV. Full article

Zika virus (ZIKV), a unique flavivirus with neurotropic and teratogenic potential, can cross the blood–brain barrier and persist in human brain microvascular endothelial cells (BMECs); however, no approved vaccines or specific antivirals exist, and its barrier-crossing and neuroinvasive mechanisms remain elusive. Innovative strategies to identify additional host factors mediating ZIKV infection could yield key insights and help address these challenges. To uncover novel host factors, we established the first tree shrew (Tupaia belangeri) genome-wide CRISPR/Cas9 knockout (GeCKO) library and performed a screen in BMECs, identifying ring finger protein 6 (RNF6) as a novel proviral factor for ZIKV. ZIKV infection in BMECs was significantly reduced following RNF6 knockout or knockdown but enhanced upon RNF6 overexpression or rescue. Mechanistically, RNF6 interacts with the ZIKV NS5 protein and acts as a potential negative regulator of the type I interferon and MAPK signaling pathways. Evolutionary and structural analyses revealed that RNF6 is highly conserved between humans and tree shrews; molecular docking further identified shared NS5-binding residues (Gln-59, Arg-140), supporting the conserved proviral role of human RNF6 in ZIKV infection. Our findings highlight tree shrew GeCKO screening as an efficient approach for identifying novel host factors and establish RNF6 as a critical proviral factor for ZIKV replication in BMECs, providing new insights into ZIKV neurotropic pathogenesis and informing potential antiviral strategies. Full article

West Nile virus (WNV) is a mosquito-borne flavivirus with one of the widest global distributions. Since its discovery in Uganda in 1937, it has become a major zoonotic pathogen, and after its introduction into the United States in 1999, it spread rapidly across the Americas, becoming the leading cause of neuroinvasive arboviral disease. Its expansion illustrates a remarkable ecological adaptability, further intensified by climate change. In Latin America and the Caribbean, WNV circulation has been consistently documented in birds, horses, and mosquitoes; however, confirmed human cases remain disproportionately scarce compared with North America and Europe. Reports include sporadic human cases in Brazil (>100 since 2014), Mexico (~13), Argentina (2006–2007), Puerto Rico (2007), Nicaragua, and Haiti, while animal and vector evidence extends to Guatemala, El Salvador, Belize, Costa Rica, Bolivia, Paraguay, Colombia, Venezuela, Cuba, and Ecuador. This paradox likely reflects structural limitations within regional health systems, including underdiagnosis, restricted diagnostic capacity, and significant surveillance gaps, particularly in contexts where mild febrile syndromes may be misclassified as dengue, Zika, or Chikungunya. The regional risk of emergence is further amplified by climatic variability, ecological change, and intensifying human–wildlife interactions. Experiences from Europe highlight the importance of early detection, transfusion safety, and integrated surveillance within a One Health framework. Strengthening preparedness in Latin America will require investments in diagnostic infrastructure, implementation of standardized seroepidemiological surveys, development of predictive models tailored to local ecological contexts, and robust intersectoral collaboration. Full article

Human Pegivirus (HPgV) is an understudied flavivirus that is highly prevalent and often persists in the blood and tissues of humans. HPgV-infected brain tissue from individuals with Parkinson’s disease has shown significant transcriptomic and immune signaling differences compared to non-infected Parkinson’s brains. The HPgV genome is similar to Hepatitis C Virus (HCV), a well-characterized flavivirus with multiple approved small-molecule therapeutics. Here, we used HCV crystal structures to create homology models for two HPgV non-structural (NS) proteins, the serine protease (NS3) and the RNA-dependent RNA polymerase (NS5B), and performed molecular dynamic simulations. HCV and HPgV proteins had minimal structural differences, as seen by the Root Mean Square Deviation (RMSD) difference between NS3 (1.00 Å) and NS5B (1.26 Å). FDA-approved small molecules were then docked in silico to the NS3 and NS5B subunits of HCV and HPgV. HCV had weak to moderate correlated docking scores with HPgV NS3 (R² = 0.21, p < 0.001) and NS5B (R² = 0.58, p < 0.001). The predicted protein–ligand interactions showed potential binding between HCV antivirals and conserved residues of HPgV, including the catalytic triad for NS3 or the GDD motif for NS5B. Together, these results provide structural insights for key HPgV proteins and highlight possibilities for therapeutic repurposing of HCV antivirals. Full article

Emerging mosquito-borne flaviviruses, such as Dengue virus (DENV) and Zika virus (ZIKV), pose major global public health threats due to their geographic expansion, climate change, and the absence of effective antiviral therapies. Antiviral development against these pathogens has primarily focused on two complementary strategies. On the one hand, the blocking of viral replication by directly inhibiting essential viral enzymes, and on the other, enhancing the host’s innate immune defenses via targeted activation of intracellular antiviral pathways. Among the viral proteins required for replication, the NS2B–NS3 protease complex is one of the most conserved and druggable targets, prompting extensive efforts to design both covalent and non-covalent inhibitors. Covalent inhibitors, such as boronic acids, aldehydes, trifluoromethyl ketones, phenoxymethylphenyl derivatives, and α-ketoamides, form irreversible or slowly reversible bonds with the catalytic serine residue (Ser 135), producing long-lasting and high-affinity suppression of protease activity. In parallel, several classes of non-covalent, particularly allosteric, inhibitors have emerged as promising alternatives with improved specificity and reduced off-target reactivity. A complementary antiviral strategy involves the use of agonists of key innate immune sensors such as TLRs, RIG-I, and the cGAS–STING axis, which mediate the release of interferons (IFNs). This review brings together current knowledge on these two mechanistically distinct yet convergent approaches, highlighting how both can ultimately restrict flavivirus replication. Future opportunities involving modified peptide scaffolds, advanced delivery systems, and drug-repurposing strategies are finally discussed for the development of next-generation therapeutics against DENV and ZIKV. Full article