Search Results (108)

Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV), members of the family Pneumoviridae, represent a foremost global cause of acute lower respiratory tract infection in infants, young children, the elderly, and immunocompromised individuals. Despite the recent approval of preventive vaccines and monoclonal antibody prophylactics targeting the viral fusion protein, no widely adopted, RSV-specific direct-acting antiviral is currently approved for routine post-infection treatment. The large (L) protein of the viral RNA polymerase complex, which catalyzes genome replication and mRNA transcription in concert with its obligate cofactor, the phosphoprotein (P), constitutes an ideal drug target owing to its essential and multifunctional enzymatic activities and its absence from host cells. Over the past decade, Cryo-electron microscopy (Cryo-EM) has yielded a series of landmark structures of Pneumoviridae L–P complexes, including apo forms of RSV (at 3.2–3.67 Å) and hMPV (at 3.7 Å) polymerases, among the first promoter-bound non-segmented negative-sense (nsNSV) RNA virus polymerase structures (at 3.40–3.41 Å), and inhibitor-bound complexes that illuminate the molecular basis of non-nucleoside inhibitor (NNI) action at sub-nanomolar potency. This review synthesizes the structural biology of Pneumoviridae RNA polymerases from a chronological and mechanistic perspective, compares RSV and hMPV L protein active sites at near-atomic resolution, and critically evaluates how structural insights are being translated into next-generation antiviral drug candidates, including nucleoside analog inhibitors, allosteric non-nucleoside inhibitors, and emerging candidates at various stages of preclinical and clinical investigation. Full article

Human metapneumovirus (HMPV) is a major cause of respiratory infections, but its impact on macrophage antibacterial functions remains poorly understood. Macrophages play a crucial role in host defense through phagocytosis, and impairment of this function may increase susceptibility to secondary infections. Here, we show that HMPV infection of THP-1-derived macrophages significantly reduces bacterial uptake in a replication-dependent manner. This effect was restricted to infected cells and was not recapitulated by cell-free supernatants, indicating a cell-intrinsic mechanism. HMPV infection was also associated with reduced expression of the scavenger receptor CD36. Viral gene knockdown studies further implicated the HMPV G protein in this phenotype, as silencing the G protein restored phagocytic function. Analysis of single-cell RNA-sequencing datasets from HMPV-infected mouse lungs revealed reduced CD36 expression and broader alterations in phagocytosis-associated gene programs across lung macrophage subsets. Supporting these observations, expression of Cd36 and Marco was reduced in lung tissue from HMPV-infected mice. Overall, these findings demonstrate that HMPV impairs macrophage-mediated bacterial uptake through a replication-dependent, cell-intrinsic mechanism and identify reduced scavenger receptor expression and the viral G protein as factors associated with this phenotype. These alterations may contribute to increase susceptibility to secondary bacterial infections during HMPV infection. Full article

Background/Objectives: Respiratory syncytial virus (RSV), human metapneumovirus (hMPV), and parainfluenza virus type 3 (PIV3) are leading causes of acute respiratory infections in children and the elderly, yet no licensed T-cell vaccines are available. This study aimed to develop multivalent T-cell vaccine candidates against these pathogens using a live attenuated influenza virus (LAIV) vector platform. Methods: Conserved F, N, and M proteins of RSV, hMPV, and PIV3 were identified through multiple sequence alignments. Fragments enriched with experimentally confirmed and predicted T-cell epitopes were selected using the IEDB and NetMHCpan servers. These fragments were assembled into polyepitope immunogenic cassettes, and their selected order was determined by thermodynamic analysis of mRNA secondary structures using the RNAfold Web Server. The selected cassettes were cloned into the neuraminidase (NA) gene of a cold-adapted LAIV vector. Recombinant viruses were rescued by reverse genetics and assessed for replicative fitness in embryonated chicken eggs and MDCK cells, NA enzymatic activity and genetic stability upon serial passaging. Results: Four cassettes were designed for RSV, three for hMPV, and one for PIV3, all containing fragments with multiple T-cell epitopes. Three recombinant viruses of LAIV/RSV type and three of LAIV/hMPV type were successfully rescued, while attempts to recover the remaining recombinant viruses, i.e., LAIV/RSV and LAIV/PIV3, were not successful. All rescued recombinant viruses replicated to titers comparable to the parental LAIV strain and retained the full-length insert for at least eight passages in eggs. Importantly, NA enzymatic activity of the LAIV vector was not compromised by the insertion of the polyepitope T-cell cassettes. Conclusions: We developed a panel of recombinant T cell-based vaccine candidates against RSV and hMPV using the LAIV vector platform. These recombinant viruses encode conserved T-cell epitopes of the target viruses while retaining the biological properties of LAIV strains. Taken together, these characteristics warrant further evaluation of these recombinant viruses in appropriate relevant in vitro models to directly assess their immunogenicity in terms of stimulating a T-cell response against target pathogens. Full article

Human metapneumovirus (HPMV) is a significant pathogen that causes lower respiratory tract infections. Given the weak immunogenicity thereof, and the few relevant studies, the utility of the viral membrane protein G as a vaccine remains controversial. In this study, the G extracellular domain (RMG) of HMPV was expressed either alone or fused with the cholera toxin B subunit (CTB) and “cross-reacting material 197” (CRM197) carrier proteins (giving G-CTB/G and CRM197), to enhance immunogenicity. The non-glycosylated G protein (REG) expressed in Escherichia coli served as a control. SDS-PAGE and anti-His tag Western blotting verified that each protein was successfully expressed and correctly identified. BALB/c mice were immunized with each protein and subjected to challenge with HMPV. The results showed that, although immunization with RMG alone failed to induce potent neutralizing antibodies, it modestly reduced viral loads in the lungs of mice. However, the pathological damage caused by lung inflammation was more aggravated than that of the control challenge group. The level of specific IgG antibody induced by the recombinant G-CTB was significantly higher than that elicited by RMG. Compared to the RMG group, the viral load in the lungs of the G-CTB group tended to be reduced. Also, the damage caused by lung inflammation was significantly alleviated. Our study proves that HMPV G may be a valuable antigen in terms of HMPV vaccine development and offers a promising strategy for modulating the immunogenicity and safety thereof. Full article

Human metapneumovirus or HMPV is an important respiratory pathogen of public health significance that primarily affects the immunocompromised, the very old, and young infants. However, recent studies have long since dispelled the idea that healthy adults are not at risk for serious sequelae, though it seems that HMPV has a particular affinity to infect children rather than adults. HMPV was first identified in 2001 and is implicated in a range of respiratory illnesses, from less severe upper respiratory infections to more severe pneumonia. This review compiles the recent literature on the epidemiology, molecular virology, and clinical characteristics of HMPV with an emphasis on, importantly, the virus’s significant contribution to respiratory morbidity and the requirement for better diagnostic capabilities and public health measures against this very much underappreciated viral pathogen. Full article

Background: Respiratory viral infections remain a major cause of morbidity and hospitalization in children. The increased use of multiplex molecular assays has improved the detection of simultaneous viral pathogens, raising questions about the clinical relevance of pediatric viral co-infections. Objective: The aim of this study is to synthesize recent evidence on respiratory viral co-infections in children, focusing on clinical severity, healthcare burden, mechanisms, and interpretation of multiplex detections. Methods: This narrative review included studies published between 1 January 2022 and 30 September 2025, identified through PubMed and Web of Science. Eligible studies involved children and adolescents (0–18 years) with laboratory-confirmed respiratory viral co-infections, mainly detected by multiplex PCR. Evidence was synthesized qualitatively across severity, neutral or inconsistent impact, viral interference, and post-acute implications. Results: Forty-five studies were included. The most frequently reported viruses were respiratory syncytial virus (RSV), rhinovirus, adenovirus, influenza virus, and human metapneumovirus (HMPV). Clinical impact was heterogeneous and depended more on specific viral pairings and host factors than on the number of detected viruses. RSV-containing combinations, particularly with HMPV, adenovirus, or rhinovirus, were more often linked to increased respiratory burden, whereas some rhinovirus-associated combinations appeared compatible with viral interference. Conclusions: Pediatric respiratory viral co-infection is clinically relevant but context-dependent. Multiplex results should be interpreted together with clinical, laboratory, and radiological findings. Full article

Background/Objectives: Viral respiratory tract infections (VRTIs) in patients with diabetes mellitus (DM) are characterized by a severity gap rather than an infection gap. This review synthesizes evidence from the 2023–2026 respiratory seasons to provide a post-pandemic framework for managing the synergistic metabolic and viral threats in this population. Materials and Methods: A scoping review of literature from PubMed, Scopus, and Embase (2023–2026) was conducted, focusing on clinical outcomes and mechanistic interactions between DM and emerging respiratory pathogens. Results: Recent data identify human Metapneumovirus (hMPV) and adenovirus as significant threats to diabetic hosts, with mortality risks equivalent to seasonal influenza (HR 1.00 for hMPV vs. influenza). The two-hit model combines a baseline of innate immune paralysis, characterized by impaired neutrophil chemo-taxis and mechanical SP-D dysfunction, with a cellular signaling environment primed for cytokine overreaction by epigenetic metabolic memory. The stress hyperglycemia ratio (SHR) has emerged as a promising predictor of mortality compared to absolute glucose or HbA1c, with a proposed threshold of ≥1.14 identifying patients at 3.5-fold increased risk for mechanical ventilation. Precision management should consider the prudent suspension of SGLT2 inhibitors to mitigate euglycemic DKA risks and considering the early use of GLP-1 receptor agonists for their hypothesized pulmonary anti-inflammatory properties. Conclusions: Closing the mortality gap may require a shift from generic viral care to a precision model that treats metabolic susceptibility with high clinical priority alongside the treatment of the viral pathogen. Full article

The coronavirus disease 19 pandemic disrupted pediatric respiratory infections through non-pharmaceutical interventions and altered contact patterns. Long-term comparisons across the pandemic timeline in children remain limited. In this study, we analyzed 15,657 respiratory specimens from patients ≤ 18 years at Dankook University Hospital (2007–2023) using multiplex polymerase chain reaction assays targeting 15 viruses. Age-stratified positivity rates were compared across pandemic phases. Children ≤ 6 years comprised 88.61% of the study population. Human rhinovirus showed the highest detection rate (24.06%), followed by adenovirus (12.33%), respiratory syncytial virus-subtypes A and B (RSV-A: 11.13%; RSV-B: 8.65%), human parainfluenza virus-type 3 (HPIV-3; 6.21%), human metapneumovirus (HMPV; 5.33%), and enterovirus (2018–2023; EV; 10.96%). Monthly distributions differed (p < 0.001). RSV peaked in late autumn and winter; influenza and seasonal coronaviruses in winter and spring; HMPV, HPIV-3, EV, and human bocavirus in summer and fall. Positivity declined during the pandemic, rebounding in 2023, most prominently among children aged 1–6 years (84.91%). HPIV-3 and EV increased (p < 0.001). RSV-A predominated pre-pandemic, whereas RSV-B showed a non-significant relative increase post-pandemic; no subtype differences occurred during the pandemic. Findings demonstrate pathogen-specific shifts in predominance and seasonality and support ongoing surveillance and pediatric care planning. Full article

Recent reports have advocated the global resurgence of human metapneumovirus (hMPV) infections in the post-COVID-19 era. Considering the absence of relevant data from Greece, the present study aimed to explore the molecular epidemiology and possible resurgence of significant genotypic variants. Whole genome and F gene-specific sequencing were implemented in order to obtain complete information on the genotype and lineage distribution of circulating hMPV strains in Greece. The results showed a statistically significant increase in monthly positivity rates in 2025, especially from February to April, compared to the respective period in 2024. Overall, 21 strains were classified as genotype A2.2.2 (42.9%) and 27 as genotype B2 (55.1%), whereas only one strain belonged to genotype B1. The G gene of most completely sequenced A2.2.2 strains harbored a 111nt duplication sequence and a genotype-specific pattern of N-glycosylation sites. Maximum likelihood and time-scaled, Bayesian phylogenetic analyses demonstrated the dominance of specific sub-lineages at the regional level and international transmission events. This complex epidemic pattern in conjunction with the differential evolutionary pressure exerted on the hMPV genes, advocates continuous surveillance of hMPV epidemiology with multiple genes, or complete genome sequencing methodologies. Full article

The human metapneumovirus (HMPV) Fusion (F) glycoprotein is a high-priority target for “fusion-locking” agents that stabilize its metastable prefusion state. While monomeric catechins like EGCG are known antivirals, the molecular basis for the superior activity of structurally complex dimeric catechins remains poorly understood. We employed an advanced biophysical workflow, integrating 100 ns all-atom molecular dynamics (MD), free energy landscape (FEL) analysis, and MM/GBSA thermodynamic integration to decode the Structure–Dynamics Relationship (SDR) of 210 Camellia sinensis (Green tea) phytochemicals. The results reveal a “Galloylation-Driven Anchoring” mechanism: the galloyl moiety of prodelphinidin A2 3′-gallate provides critical electrostatic complementarity to the Asp325-Asp336 acidic ridge. FEL analysis quantitatively demonstrates that this anchoring leads to pronounced stabilization of the F protein in a deep, kinetically favored global minimum (ΔG = 9.357 kJ/mol), effectively raising the energy barrier for the fusogenic conformational shift. This study provides a comparative and mechanistically informed computational proof-of-concept for the use of dimeric natural scaffolds as precision fusion-locking agents, offering a roadmap for experimental biophysical validation. In this workflow, molecular docking was employed exclusively as a qualitative structure-based filtering step, while all quantitative conclusions regarding stabilization and binding energetics were derived from post-docking MD, FEL, and MM/GBSA analyses. Full article

Metapneumoviruses comprise a genus of negative-sense RNA viruses that cause significant respiratory disease across human and avian hosts. Human metapneumovirus (hMPV) is a globally prevalent pathogen associated with acute lower respiratory tract infections in infants, older adults, and immunocompromised individuals. Avian metapneumovirus (aMPV) imposes substantial economic losses on the poultry industry through respiratory disease, reproductive impairment, and high mortality in the presence of secondary infections. Despite their distinctive host ranges, hMPV and aMPV share a conserved genomic architecture and encode homologous structural and non-structural proteins that mediate viral entry, replication, assembly, and evasion of host innate immunity. Comparative analysis highlights that both have deeply conserved polymerase and nucleocapsid functions, and yet have a wide range of diversity in the attachment glycoprotein (G) and small hydrophobic protein (SH), reflecting divergent evolutionary pressures in human versus avian hosts that have led to such distinctive differences. The recent emergence and detection of aMPV/A and aMPV/B across the previously aMPV-free United States beginning in late 2023, combined with rising cases globally of hMPV post-SARS-CoV-2 pandemic, underscore the continued challenges of metapneumovirus surveillance and control in humans and animals. This review aims to highlight the current knowledge on the history, molecular virology, pathogenesis, epidemiology, diagnostics, and control strategies for aMPV while drawing mechanistic parallels to hMPV. By contextualizing shared biology and structure alongside host-specific adaptations, we aim to identify key gaps that shape vaccine design, antiviral development, and future research priorities aimed at mitigating the health and economic burden posed by metapneumoviruses found in both birds and humans. Full article

Nirsevimab is a long-acting monoclonal antibody designed to prevent infections due to respiratory syncytial virus (RSV). Here we report on a retrospective, multicenter study encompassing a total of 19 Italian neonatal and pediatric centers evaluating the epidemiology of lower respiratory tract infection (LRTI)-related hospitalizations in infants younger than 2 years during the first RSV season following the introduction of nirsevimab prophylaxis. A total of 401 hospitalizations were reported, with 40.4% being in children with previous prophylaxis with nirsevimab. Respiratory syncytial virus was the most frequently identified pathogen (47.5%), followed by rhinovirus/enterovirus (20.2%) and human metapneumovirus (hMPV; 6.9%). In multivariable analyses adjusted for age, sex, and month of diagnosis, prior nirsevimab immunization was associated with a significantly reduced likelihood of RSV-related hospitalization (adjusted odds ratio [aOR], 0.259; 95% CI, 0.157–0.427), corresponding to an estimated effectiveness of 74.1% (95% CI, 57.3–84.3). Conversely, nirsevimab-immunized infants showed increased odds of hospitalization due to hMPV (aOR, 2.490; 95% CI, 1.019–6.085) and rhinovirus/enterovirus (aOR, 2.573; 95% CI, 1.424–4.650). Lower respiratory tract infections associated with hMPV predominantly occurred outside the typical RSV season, being associated with moderate-to-severe clinical presentations. These findings confirm the real-world effectiveness of nirsevimab against RSV hospitalizations, also highlighting the need for the continued surveillance of non-RSV respiratory pathogens in the context of universal RSV immunoprophylaxis. Full article

In recent years, wastewater (WW)-based epidemiology has been increasingly used for surveillance of SARS-CoV-2 and has emerged as a potential tool for monitoring other respiratory viruses. Most evidence on the use of WW for detecting multiple respiratory viruses comes from developed countries. In this study, we assessed the feasibility of multi-respiratory virus sewage surveillance in a middle-income country and explored signals that may be potentially used as early warning signs for Public Health authorities. We examined the presence of SARS-CoV-2, influenza virus, respiratory syncytial virus (RSV), and human metapneumovirus (hMPV) in 238 WW samples collected from three treatment plants in San Luis Potosí, Mexico, over one year. The weekly detection of each virus was compared with the weekly number of hospital admissions for respiratory infections caused by that virus in pediatric patients. SARS-CoV-2, influenza, hMPV, and RSV were detected in 152 (63.9%), 108 (45.4%), 95 (39.9%), and 24 (10.1%) samples, respectively. There was no significant correlation between viral detection in WW and the number of hospitalizations during that week. However, analyses of WW viral detection with hospitalizations in subsequent weeks showed an increasing correlation reaching a maximum correlation for a lag of 12 weeks for SARS-CoV-2 (r_s = 0.63, p = 0.001), 9 weeks for influenza (r_s 0.62, p = 0.0001), 2 weeks for RSV (r_s = 0.30, p = 0.05), and 3 weeks for hMPV (r_s = 0.39, p = 0.009). In addition, we identified time-periods of SARS-CoV-2, influenza, and RSV widespread circulation (several consecutive weeks in which viruses were detected in the three treatment plants); most hospitalizations caused by these viruses occurred after widespread circulation was detected in WW, suggesting this may be used as an early alert for public health systems. Overall, our results show that WW-based surveillance of multiple respiratory viruses is feasible and has potential applications as an early warning system in middle-income countries. Full article

Human metapneumovirus (hMPV) is an important cause of acute respiratory tract infections. This study aimed to describe the clinical characteristics, outcomes, and molecular features of hMPV infection among hospitalized patients in Romania. We performed an analysis of prospectively collected surveillance data from patients hospitalized with influenza-like illness or severe acute respiratory infection and tested by RT-PCR for the presence of respiratory viruses between November 2023 and May 2025. Only cases of hMPV monoinfection were analyzed. Clinical, laboratory, and outcome data were analyzed, and a subset of samples with high viral load underwent genetic sequencing of the hMPV fusion (F) gene. A total of 71 patients met the criteria. Children accounted for 62.0% of cases. The clinical features were nonspecific, dominated by cough (87.3%), fever (80.3%), and nasal congestion (47.9%). Adults were significantly more likely to develop dyspnea and respiratory failure requiring oxygen supplementation (51.9% vs. 6.8%, p < 0.001). The median length of hospital stay was 5 days (interquartile range: 2, 7 days), and dyspnea at admission was the strongest factor associated with prolongation of hospitalization. The rate of intensive care unit admission was 4.2%, and overall outcomes were favorable, with no deaths recorded. Molecular analysis revealed the circulation of different hMPV subclades across consecutive seasons, with A2b1 predominating in 2023–2024 and A2b2 in 2024–2025. hMPV infection in hospitalized patients presents with nonspecific clinical features and shows distinct age-related patterns of severity and complications. Early identification of respiratory involvement, particularly dyspnea at presentation, may support risk stratification and optimized clinical management. Preliminary molecular data indicate dynamic circulation of hMPV subclades, underscoring the value of integrated clinical and molecular surveillance. These findings support the inclusion of hMPV in the differential diagnosis of severe acute respiratory infections and highlight the importance of continued monitoring in the post-pandemic period. Full article

Human metapneumovirus genotype B (HMPV-B) is an important respiratory pathogen, requiring detailed elucidation of the evolutionary and antigenic features of its fusion (F) gene. Using 500 sequences collected between 1982 and 2024, we investigated the molecular evolution, phylodynamics, and structural epitope landscape of the HMPV-B F gene. Time-scaled phylogeny dated the divergence of sublineages B1 and B2 to around 1937, and Bayesian Skyline Plot analysis showed that these sublineages exhibited distinct demographic trajectories over time. The F gene evolved at a rate of 1.01 × 10⁻³ substitutions/site/year; however, amino acid variation remained limited, consistent with pervasive purifying selection, with 39% of codons under strong negative selection and little consensus evidence for positive selection. Conformational B-cell epitope prediction demonstrated a high degree of conservation across neutralizing antibody binding regions (sites Ø and I–V), and amino acid substitutions occurring within these sites were not predicted to substantially alter epitope architecture. Together, these findings indicate that the HMPV-B F gene evolves under strong evolutionary constraint while maintaining stable antigenic features, supporting the potential for antibody-based strategies that target neutralizing antibody binding regions of the F protein. Full article