Human metapneumovirus - what we know now

An overview of progress in human metapneumovirus (hMPV) research: Structure, function, and therapeutic opportunities

The human metapneumovirus (hMPV), a member of the Pneumoviridae family, is a significant respiratory pathogen that causes severe infections in infants, children, the elderly, adults with chronic illnesses, and individuals with immunocompromised conditions. Globally, hMPV is recognized as the second leading cause of bronchiolitis and pneumonia among children under five. The absence of targeted antiviral treatments or vaccines for hMPV significantly strains the global health-care system. This review summarizes recent advances and scientific findings on hMPV by reviewing the current literature on its life cycle, structure, function, prevention, and treatment options.

Interplay between endogenous hormones and immune systems in human metapneumovirus pathogenesis and management

The present review explores the role of endogenous hormones, such as cortisol, melatonin, thyroid hormones, sex hormones, and insulin, in the modulation of the immune response to a human metapneumovirus (hMPV) infection. hMPV is a respiratory pathogen responsible for severe infections, particularly in vulnerable populations like children and the elderly. The virus triggers inflammatory responses through various molecular processes, including cytokine production and immune signaling pathways. Notably, these processes can be influenced by endocrine factors, such as hormones. Cortisol, through hypothalamic-pituitary-adrenal (HPA) axis activation, modulates inflammation but may contribute to immunosuppression. Melatonin inhibits the NLRP3 inflammasome, reducing lung inflammation. Thyroid hormones regulate immune responses via nuclear factor kappa B (NF-κB) and JAK/STAT pathways, while hypothyroidism may alter infection severity. Sex hormones, particularly estrogens, enhance antiviral immunity, whereas androgens may have variable effects on immune modulation. Insulin influences inflammation through NF-κB suppression, with insulin resistance potentially worsening viral pathogenesis. Therapeutic implications suggest that modulating these hormonal pathways could aid in hMPV management. Strategies such as hormone therapy, glucocorticoid regulation, and nanoparticle-based drug delivery are potential routes of intervention. The aim of the present review is to understand the complex interplay between endogenous hormones and the immune system during an hMPV infection by describing the complex molecular mechanisms associated with these processes.

Human Metapneumovirus: an emerging respiratory pathogen and the urgent need for improved Diagnostics, surveillance, and vaccine development

Human Metapneumovirus (HMPV) is a re-emerging respiratory pathogen causing significant morbidity and mortality, particularly among young children, the elderly, and immunocompromised individuals. First identified in 2001, HMPV has since been recognised as a leading cause of acute respiratory tract infections (ARTIs) worldwide. Its transmission occurs through droplets, direct contact, and surface contamination, with crowded spaces and healthcare facilities serving as key environmental amplifiers. HMPV's clinical manifestations, ranging from mild cold-like symptoms to severe pneumonia, often overlap with those of other respiratory pathogens like RSV and COVID-19, complicating timely diagnosis and management. Despite advancements in molecular diagnostics, the limited accessibility of these tools in low-resource settings presents a challenge. Preventive measures, such as hygiene practices and physical distancing, remain critical, as no approved vaccines or targeted antiviral therapies are currently available. However, promising innovations, including AI-guided vaccine design and portable diagnostic tools, highlight the potential for future breakthroughs. This article highlights the urgent need for enhanced surveillance, scalable diagnostics, and intensified research into vaccines and therapeutic strategies. By addressing these gaps, HMPV's global burden can be significantly mitigated, improving outcomes for high-risk populations, and strengthening preparedness against respiratory virus outbreaks.

The role of M2 proteins of pneumoviruses in transcription regulation, prevention of hypermutation, and activation of the type I interferon pathway

Human metapneumovirus (HMPV) is an important causative agent of respiratory tract disease. Fundamental knowledge of the interaction between HMPV and the innate immune system could lead to the design of novel antiviral therapies. Previously, we demonstrated that HMPV M2-2 deletion mutants had hypermutated genomes and contained defective interfering particles (DIs), which are potent inducers of the IFN response. Here, we investigated the role of the HMPV M2-2 protein as IFN antagonist using chimeric HMPV expressing M2 proteins of other pneumoviruses: respiratory syncytial virus (RSV) and avian metapneumovirus type C (AMPV/C). Chimeric HMPVs expressing the M2 proteins of RSV or AMPV/C were attenuated in HEp-2 cells but did not activate the IFN response, and their genomes were not hypermutated. In contrast, chimeric HMPVs expressing the M2-2 proteins of RSV and AMPV/C, in combination with HMPV M2-1, did activate the IFN response, and their genomes were hypermutated. Investigation of the role of the pneumovirus M2 proteins in transcription regulation demonstrated that the M2-2 protein, only in concerted action with autologous M2-1 protein, acted as a transcription elongation factor. As a second approach, chimeric RSV in which the IFN antagonists NS1 and NS2 were replaced by the HMPV M2-2 gene failed to suppress an IFN response, indicating that the HMPV M2-2 protein is not a potent IFN antagonist. These data indicate that expression of autologous M2-1 and M2-2 proteins is important for the fidelity of the RNA-dependent RNA polymerase, necessary to prevent the accumulation of mutations, and possibly DIs, thereby preventing activation of the IFN responses.IMPORTANCEThe M2-2 protein of human metapneumovirus is suggested to function as a type I interferon antagonist, a function so far not assigned to the M2 proteins of other pneumoviruses. Although M2-2 deletion mutants of HMPV activate the type I interferon pathway, these mutants have hypermutated genomes and contain defective interfering RNAs, known to activate the interferon pathway. Here, we show that the M2-2 protein, in concerted action with autologous M2-1 protein, acts as a transcription elongation factor, which could explain the accumulation of DIs in M2-2 deletion mutants. Additionally, chimeric RSV in which the IFN antagonists NS1 and NS2 were replaced by the HMPV M2-2 gene failed to suppress an IFN response. These data indicate that expression of autologous M2-1 and M2-2 proteins is required for the fidelity of the RNA-dependent RNA polymerase to prevent genome hypermutation and activation of the type I IFN pathway.

A Re-emerging Respiratory Virus: Human Metapneumovirus (hMPV)

Human metapneumovirus (hMPV) is identified as a pathogenic agent responsible for respiratory tract infections in paediatric, adult and elderly populations. It is a spherical, enveloped virus with a diameter of 209nm, consisting of a single-stranded, non-segmented, and negative-sense RNA genome of around 13.3 kb in length. hMPV infection is prevalent all around the globe, with peak positivity rates detected mostly during later winter and spring seasons. Mostly transmitted through droplet or aerosol contamination, this viral infection may manifest clinical characteristics indicative of both upper and lower respiratory tract infections like fever, cough, rhinorrhea, pneumonia, bronchiolitis, and croup. The recommended laboratory diagnostic approach is reverse transcription polymerase chain reaction, given the challenges associated with culturing the virus. This review article focuses on the structure, replication, genotype, epidemiology, seasonality, transmission methods, clinical manifestations in humans, treatment methodology, and outbreaks of hMPV that have been reported worldwide.

The Silent Threat of Human Metapneumovirus: Clinical Challenges and Diagnostic Insights from a Severe Pneumonia Case

BACKGROUND

Human metapneumovirus (hMPV) is a respiratory pathogen that has gained increasing recognition due to advancements in molecular diagnostic tools, which have improved its detection and characterization. While severe disease manifestations are traditionally associated with pediatric, elderly, or immunocompromised patients, hMPV-related pneumonia in immunocompetent adults remains underexplored.

METHODS

This case report describes a 68-year-old male who developed severe community-acquired pneumonia (CAP) caused by hMPV despite being immunocompetent and having no significant comorbidities. The diagnosis was confirmed via multiplex RT-PCR, excluding bacterial and viral coinfections. Laboratory and imaging findings supported a viral etiology, while empirical antibiotics were initially prescribed due to diagnostic uncertainty.

RESULTS

The patient presented with respiratory symptoms that progressed to hypoxia, productive cough, and fatigue, requiring hospitalization. Imaging revealed bilateral ground-glass opacities and consolidations typical of viral pneumonia. Molecular diagnostics enabled accurate pathogen identification and guiding appropriate management, and the patient fully recovered with supportive care.

CONCLUSION

This case underscores the importance of rapid molecular diagnostics for hMPV, reducing unnecessary antibiotics and enhancing management. Routine incorporation of hMPV testing into clinical protocols could improve the diagnosis and resource use. The development of vaccines, such as the IVX-A12 in phase II trials, offers hope for targeted prevention, underscoring the need for further research and therapeutic innovations.

Clinical Insights and Advancements in Human Metapneumovirus Management and Prognosis

Human metapneumovirus is a respiratory pathogen that infects children, the elderly, and immunocompromised individuals. Despite its global prevalence, underdiagnosis persists because of clinical overlap with other respiratory viruses. The current approach is mostly supportive, with oxygen therapy and hydration being crucial interventions. Ribavirin contains antiviral properties but has little clinical application. Vaccine development is moving forward, with prospects including live-attenuated, subunit-based, and virus-like particle vaccines. Molecular diagnostics, such as RT-PCR and metagenomic sequencing, have increased detection rates, which aids epidemiological monitoring. Monoclonal antibodies targeting the fusion (F) protein are being studied for passive immunity, while immunomodulatory treatments such as corticosteroids and intravenous immunoglobulins may help treat severe cases. Emerging treatments include fusion inhibitors and pan-pneumovirus vaccinations that protect against HMPV and RSV. Future research should concentrate on optimizing antiviral methods, increasing vaccination trials, and improving surveillance to detect outbreaks. A multidisciplinary approach that combines virology, immunology, and epidemiology is required to reduce HMPV's effect and improve patient outcomes. This review serves as a comprehensive literature about HMPV which provides all the crucial clinical perspectives and the latest advancements in management, antivirals, patient prognosis as well and diagnostic modalities.

Exploring Chemical Space to Identify Partial Binders Against hMPV Nucleocapsid Protein

Human metapneumovirus (hMPV) has gained prominence in recent times as the predominant etiological agent of acute respiratory tract infections. This virus targets children, the elderly, and individuals with compromised immune systems. Given the protracted duration of hMPV transmission, it is probable that the majority of children will have acquired the virus by the age of 5. In individuals with compromised immune systems, recurrence of hMPV infection is possible. As hMPV matures, it remains latent from the time of acquisition. The genome of hMPV encompasses a pivotal protein referred to as the nucleocapsid protein (N). This protein assumes the form of a left-handed helical nucleocapsid, enveloping the viral RNA genome. The primary function of this structure is to protect nucleases, rendering it a potentially promising target for therapeutic advancements. The present study employs a methodology that involves structure-based virtual screening, followed by molecular dynamics simulation at a 250-ns time scale, to identify potential natural molecules or their derivatives from the ZINC Database. These molecules are investigated for their binding properties against the hMPV nucleoprotein. Based on an evaluation of the docking score, binding site interaction, and molecular dynamics studies, it has been found that two naturally occurring molecules, namely M1 (ZINC85629735) and M3 (ZINC85569125), have shown notable docking scores of -9.6 and -10.7 kcal/mol, acceptable RMSD, RMSF, Rg, and so on calculated from molecular dynamics trajectory associated with MMGBSA binding energy of -81.94 and -99.63 kcal/mol, respectively. These molecules have shown the highest binding affinity toward nucleocapsid protein and demonstrated promising attributes as potential binders against hMPV.

The Molecular Basis of Asthma Exacerbations Triggered by Viral Infections: The Role of Specific miRNAs

Viral respiratory infections are a significant clinical problem among the pediatric population and are one of the leading causes of hospitalization. Most often, upper respiratory tract infections are self-limiting. Still, those that involve the lower respiratory tract are usually associated with asthma exacerbations, leading to worsening or even the initiation of the disease. A key role in regulating the immune response and inflammation during viral infections and their impact on the progression of asthma has been demonstrated for miRNA molecules (microRNA). Their interaction with mRNA (messenger RNA) regulates gene expression in innate and acquired immune responses, making them valuable biomarkers for diagnostics, monitoring, and predicting asthma exacerbations. The following paper presents changes in the expression of miRNAs during the five most common viral infections causing asthma worsening, with particular emphasis on the pediatric population. In addition, we describe the molecular mechanisms by which miRNAs influence the pathogenesis of viral infection, immune responses, and asthma exacerbations. These molecules represent promising targets for future innovative therapeutic strategies, paving the way for developing personalized medicine for patients with viral-induced asthma exacerbations.

Fumarprotocetraric acid and geraniin were identified as novel inhibitors of human respiratory syncytial virus infection in vitro

Introduction

Respiratory syncytial virus (RSV) remains a major international public health concern. However, disease treatment is limited to preventive care with monoclonal antibodies and supportive care. In this study, natural products were screened to identify novel anti-RSV inhibitors.

Methods

The antiviral effect of 320 compounds on RSV in HEp-2 cells was tested using a Cytopathic effect (CPE) inhibition assay. The antiviral effect of fumarprotocetraric acid (FUM) and geraniin (GE) were confirmed by Real-time reverse transcription quantitative PCR (Real-time RT-PCR), plaque reduction test, immunofluorescence assay, and Western blot analysis. Real-time PCR was used to detect inflammatory factor expression. ATP assay and JC-1 stain were used to evaluate mitochondrial protection function. The experiment of administration time was used to determine the stages in the RSV life cycle inhibited by FUM and GE. Human metapneumovirus (HMPV) and human rhinovirus (HRV) were used to evaluate the antiviral activities of other respiratory viruses of FUM and GE. Finally, Air-liquid interface human airway epithelium (ALI-HAE) cells were used to evaluate the antiviral effect and mechanism of FUM and GE to RSV.

Results

The results showed that FUM and GE can inhibit the replication of RSV in multiple-cell models. Both compounds could dose-dependent inhibit the viral load, RSV nucleic acids level, and RSV-F protein level. Besides, FUM and GE showed good anti-inflammatory activity, mitochondrial protection, and antiviral activity to HMPV and HRV. Meanwhile, our result indicated that FUM and GE can inhibit RSV replication in ALI-HAE cells.

Conclusions

FUM and GE were identified as new inhibitors of RSV infection. At the same time, FUM and GE have anti-inflammatory activity, mitochondrial protection function, and broad-spectrum antiviral activity. These results provide evidence that FUM and GE are potential candidates for the development of novel anti-RSV drugs.

Human metapneumovirus SH protein promotes JAK1 degradation to impair host IL-6 signaling

Human metapneumovirus (HMPV) is a leading cause of respiratory infections in children, older adults, and those with underlying conditions (K. M. Edwards et al., N Engl J Med 368:633-643, 2013, https://doi.org/10.1056/NEJMoa1204630; A. R. Falsey et al., J Infect Dis 187:785-790, 2003, https://doi.org/10.1086/367901; J. S. Kahn, Clin Microbiol Rev 19:546-557, 2006, https://doi.org/10.1128/CMR.00014-06; N. Shafagati and J. Williams, F1000Res 7:135, 2018, https://doi.org/10.12688/f1000research.12625.1). HMPV must evade immune defenses to replicate successfully; however, the viral proteins used to accomplish this are poorly characterized. The HMPV small hydrophobic (SH) protein has been reported to inhibit signaling through type I and type II interferon (IFN) receptors in vitro in part by preventing STAT1 phosphorylation (A. K. Hastings et al., Virology (Auckl) 494:248-256, 2016, https://doi.org/10.1016/j.virol.2016.04.022). HMPV infection also inhibits IL-6 signaling. However, the mechanisms by which SH inhibits signaling and its involvement in IL-6 signaling inhibition are unknown. Here, we used transfection of SH expression plasmids and SH-deleted virus (ΔSH) to show that SH is the viral factor responsible for the inhibition of IL-6 signaling during HMPV infection. Transfection of SH-expression vectors or infection with wild-type, but not ΔSH virus, blocked IL-6-mediated STAT3 activation. Furthermore, JAK1 protein (but not RNA) was significantly reduced in cells infected with wild-type, but not ΔSH virus. The SH-mediated reduction of JAK1 was partially restored by the addition of proteasome inhibitors, suggesting proteasomal degradation of JAK1. Confocal microscopy indicated that infection relocalized JAK1 to viral replication factories. Co-immunoprecipitation showed that SH interacts with JAK1 and ubiquitin, further linking SH to proteasomal degradation machinery. These data indicate that SH inhibits IL-6 and IFN signaling in infected cells in part by promoting proteasomal degradation of JAK1 and that SH is necessary for IL-6 and IFN signaling inhibition in infection. These findings enhance our understanding of the immune evasion mechanisms of an important respiratory pathogen.IMPORTANCEHuman metapneumovirus (HMPV) is a common cause of severe respiratory illness, especially in children and older adults, in whom it is a leading cause of hospitalization. Prior research suggests that severe HMPV infection is driven by a strong immune response to the virus, especially by inflammatory immune signals like interferons (IFN). HMPV produces a small hydrophobic (SH) protein that is known to block IFN signaling, but the mechanism by which it functions and its ability to inhibit other important immune signals remains unexplored. This paper demonstrates that SH can inhibit another related immune signal, IL-6, and that SH depletes JAKs, which are critical proteins involved in both IL-6 and IFN signaling. A robust understanding of how HMPV and related viruses interfere with immune signals important for disease could pave the way for future treatments aimed at mitigating severe infections.

Interferon Epsilon-Mediated Antiviral Activity Against Human Metapneumovirus and Respiratory Syncytial Virus

BACKGROUND

Interferon epsilon (IFN-ε) is a type I IFN that plays a critical role in the host immune response against pathogens. Despite having demonstrated antiviral activity in macrophages and mucosal tissues such as the female reproductive tract and the constitutive expression in mucosal tissues such as the lung, the relevance of IFN-ε against respiratory viral infections remains elusive.

RESULTS

We present, for the first time, the expression of IFN-ε in alveolar epithelial cells and primary human bronchial epithelial cells grown in an air-liquid interface (ALI) in response to human metapneumovirus (HMPV) and respiratory syncytial virus (RSV) infection. The molecular characterization of the IFN-ε induction by the viruses indicates that the expression of RIG-I is necessary for an optimal IFN-ε expression. Furthermore, treatment of the airway epithelial cells with rhIFN-ε induced the expression of IFN-stimulated genes (ISGs) and significantly restricted the viral replication of HMPV and RSV.

CONCLUSIONS

These findings underscore the relevance of IFN-ε against viral infections in the respiratory tract.

Small hydrophobic (SH) proteins of Pneumoviridae and Paramyxoviridae: small but mighty

Small hydrophobic (SH) proteins are a class of viral accessory proteins expressed by many members of the negative-stranded RNA viral families Paramyxoviridae and Pneumoviridae. Identified SH proteins are type I or II transmembrane (TM) proteins with a single-pass TM domain. Little is known about the functions of SH proteins; however, several possess viroporin activity, enhancing membrane permeability of infected cells or those expressing SH protein. Moreover, several SH proteins inhibit apoptosis and immune signaling pathways within infected cells, including TNF and interferon signaling, or activate inflammasomes. SH proteins are generally nonessential for viral replication in vitro, but loss of SH is often associated with reduced replication in vivo, suggesting a role in enhancing viral replication or evading host immunity. Analogous proteins are expressed by a variety of pathogens of public health importance; thus, understanding the functional importance and mechanisms of SH proteins provides insight into the pathogenesis and replication of negative-sense RNA viruses.

Rapid and one-tube detection of human metapneumovirus using the RT-RPA and CRISPR/Cas12a

Human metapneumovirus (HMPV) is a common pathogen that can cause acute respiratory tract infections and is prevalent worldwide. There is yet no effective vaccine or specific treatment for HMPV. Early, rapid, and accurate detection is essential to treat the disease and control the spread of infection. In this study, we created the One-tube assay by combining Reverse Transcription-Recombinase Polymerase Amplification (RT-RPA) with the CRISPR/Cas12a system. By targeting the nucleoprotein (N) gene of HMPV to design specific primers and CRISPR RNAs (crRNAs), combining RT-RPA and CRISPR/Cas12a, established the One-tube assay. Meanwhile, the reaction conditions of the One-tube assay were optimized to achieve rapid and visual detection of HMPV. This assay could detect HMPV at 1 copy/μL in 30 min, without cross-reactivity with nine other respiratory pathogens. We validated the detection performance using clinical specimens and showed that the coincidence rate was 98.53 %，compared to the quantitative reverse-transcription polymerase chain reaction. The One-tube assay reduced the detection time and simplified the manual operation, while maintaining the detection performance and providing a new platform for HMPV detection.

Epidemiological characteristics of human metapneumovirus among children in Nanjing, China

PURPOSE

The objective of this study was to examine the molecular epidemiology and clinical characteristics of HMPV infection among children with ARIs in Nanjing.

METHODS

The respiratory samples were collected from 2078 children (≤ 14 years) with acute respiratory infections and were tested for HMPV using real-time RT-PCR. Amplification and sequencing of the HMPV G gene were followed by phylogenetic analysis using MEGA 7.0.

RESULT

The detection rate of HMPV among children was 4.7% (97/2078), with a concentration in those under 5 years of age. Notably, the peak season for HMPV prevalence was observed in winter. Among the 97 HMPV-positive samples, 51.5% (50/97) were available for characterization of the HMPV G protein gene. Phylogenetic analysis indicated that the sequenced HMPV strains were classified into three sublineages: A2c111nt - dup (84.0%), B1 (2.0%), and B2 (14.0%).

CONCLUSION

There was an incidence of HMPV among hospitalized children during 2021-2022 in Nanjing with A2c111nt - dup being the dominant strain. This study demonstrated the molecular epidemiological characteristics of HMPV among children with respiratory infections in Nanjing, China.

Burden of respiratory syncytial virus, human metapneumovirus and influenza virus infections in Japanese adults in the Hospitalized Acute Respiratory Tract Infection study

BACKGROUND

Respiratory syncytial virus (RSV), human metapneumovirus (hMPV), and influenza virus are responsible for acute respiratory tract infections (ARTIs) in adults. We assessed the clinical burden of RSV, hMPV and influenza virus infection among Japanese adults hospitalized with ARTIs.

METHODS

The Hospitalized Acute Respiratory Tract Infection (HARTI) study was a multinational, prospective cohort study in adults with ARTIs across the 2017-2019 epidemic seasons. Enrolment in Japan began in Sept 2018 and ran until Oct 2019. The clinical diagnosis of ARTI and the decision to hospitalize the patient were made according to local standard of care practices. Viral testing was performed by reverse transcription polymerase chain reaction.

RESULTS

Of the 173 adults hospitalized with ARTI during this period at the Japan sites, 7 (4.0%), 9 (5.2%), and 11 (6.4%) were positive for influenza virus, RSV, and hMPV, respectively. RSV season was observed from Oct 2018 to Jan 2019, followed by influenza from Dec 2018 to Apr 2019. hMPV was detected across both the RSV and influenza seasons. Two patients with RSV and 1 patient with hMPV required ICU admission whereas none with influenza. Use of antibiotics, bronchodilators and inhaled corticosteroids was high amongst patients with RSV and hMPV at 1, 2, and 3 months' post-discharge compared with patients with influenza, with few exceptions.

CONCLUSION

These findings highlight the need for a high degree of clinical suspicion for RSV and hMPV infection in adults hospitalized with ARTIs.

Household transmission of human metapneumovirus and seasonal coronavirus

We analyzed data from a community-based acute respiratory illness study involving K-12 students and their families in southcentral Wisconsin and assessed household transmission of two common seasonal respiratory viruses - human metapneumovirus (HMPV) and human coronaviruses OC43 and HKU1 (HCOV). We found secondary infection rates of 12.2% (95% CI: 8.1%-17.4%) and 19.2% (95% CI: 13.8%-25.7%) for HMPV and HCOV, respectively. We performed individual- and family-level regression models and found that HMPV transmission was positively associated age of the index case (individual model: p = .016; family model: p = .004) and HCOV transmission was positively associated with household density (family model: p = .048). We also found that the age of the non-index case was negatively associated with transmission of both HMPV (individual model: p = .049) and HCOV (individual model: p = .041), but we attributed this to selection bias from the original study design. Understanding household transmission of common respiratory viruses like HMPV and HCOV may help to broaden our understanding of the overall disease burden and establish methods to prevent the spread of disease from low- to high-risk populations.

Human metapneumovirus SH protein promotes JAK1 degradation to impair host IL-6 signaling

Human metapneumovirus (HMPV) is a leading cause of respiratory infections in children, older adults, and those with underlying conditions 1,2,3,4. HMPV must evade immune defenses to replicate successfully; however, the viral proteins used to accomplish this are poorly characterized. The HMPV small hydrophobic (SH) protein has been reported to inhibit signaling through type I and type II interferon (IFN) receptors in vitro, in part by preventing STAT1 phosphorylation5. HMPV infection also inhibits IL-6 signaling. However, the mechanisms by which SH inhibits signaling, and its involvement in IL-6 signaling inhibition are unknown. Here, we used transfection of SH expression plasmids and SH-deleted virus (ΔSH) to show that SH is the viral factor responsible for inhibition of IL-6 signaling during HMPV infection. Transfection of SH-expression vectors or infection with wildtype, but not ΔSH virus, blocked IL-6 mediated STAT3 activation. Further, JAK1 protein (but not RNA) was significantly reduced in cells infected with wildtype but not ΔSH virus. The SH-mediated reduction of JAK1 was partially restored by addition of proteasome inhibitors, suggesting proteasomal degradation of JAK1. Confocal microscopy indicated that infection relocalized JAK1 to viral replication factories. Co-immunoprecipitation showed that SH interacts with JAK1 and ubiquitin, further linking SH to proteasomal degradation machinery. These data indicate that SH inhibits IL-6 and IFN signaling in infected cells in part by promoting proteasomal degradation of JAK1 and that SH is necessary for IL-6 and IFN signaling inhibition in infection. These findings enhance our understanding of the immune evasion mechanisms of an important respiratory pathogen.

IFN-λ drives distinct lung immune landscape changes and antiviral responses in human metapneumovirus infection

Human metapneumovirus (HMPV) is a primary cause of acute respiratory infection, yet there are no approved vaccines or antiviral therapies for HMPV. Early host responses to HMPV are poorly characterized, and further understanding could identify important antiviral pathways. Type III interferon (IFN-λ) displays potent antiviral activity against respiratory viruses and is being investigated for therapeutic use. However, its role in HMPV infection remains largely unknown. Here, we show that IFN-λ is highly upregulated during HMPV infection in vitro in human and mouse airway epithelial cells and in vivo in mice. We found through several immunological and molecular assays that type II alveolar cells are the primary producers of IFN-λ. Using mouse models, we show that IFN-λ limits lung HMPV replication and restricts virus spread from upper to lower airways but does not contribute to clinical disease. Moreover, we show that IFN-λ signaling is predominantly mediated by CD45- non-immune cells. Mice lacking IFN-λ signaling showed diminished loss of ciliated epithelial cells and decreased recruitment of lung macrophages in early HMPV infection along with higher inflammatory cytokine and interferon-stimulated gene expression, suggesting that IFN-λ may maintain immunomodulatory responses. Administration of IFN-λ for prophylaxis or post-infection treatment in mice reduced viral load without inflammation-driven weight loss or clinical disease. These data offer clinical promise for IFN-λ in HMPV treatment.

IMPORTANCE

Human metapneumovirus (HMPV) is a common respiratory pathogen and often contributes to severe disease, particularly in children, immunocompromised people, and the elderly. There are currently no licensed HMPV antiviral treatments or vaccines. Here, we report novel roles of host factor IFN-λ in HMPV disease that highlight therapeutic potential. We show that IFN-λ promotes lung antiviral responses by restricting lung HMPV replication and spread from upper to lower airways but does so without inducing lung immunopathology. Our data uncover recruitment of lung macrophages, regulation of ciliated epithelial cells, and modulation of inflammatory cytokines and interferon-stimulated genes as likely contributors. Moreover, we found these roles to be distinct and non-redundant, as they are not observed with knockout of, or treatment with, type I IFN. These data elucidate unique antiviral functions of IFN-λ and suggest IFN-λ augmentation as a promising therapeutic for treating HMPV disease and promoting effective vaccine responses.

Clinical human metapneumovirus isolates show distinct pathogenesis and inflammatory profiles but similar CD8+ T cell impairment

Human metapneumovirus (HMPV) is a negative-sense single-stranded RNA virus in the Pneumoviridae family and a leading cause of acute upper and lower respiratory infections, particularly in children, immunocompromised patients, and the elderly. Although nearly every person is infected with HMPV during early childhood, re-infections occur often, highlighting difficulty in building long-term immunity. Inflammatory responses, including PD-1-mediated impairment of virus-specific CD8+ T cells (TCD8), contribute to HMPV disease severity. HMPV strains are divided into four lineages: A1, A2, B1, and B2. However, little is known about immune responses to different viral subtypes. Here, we characterize responses to four HMPV clinical isolates-TN/94-344 (A1), TN/94-49 (A2), C2-202 (B1), and TN/96-35 (B2)-in vivo in C57BL/6 (B6) mice. TN/94-49 was avirulent, while TN/94-344, C2-202, and TN/96-35 showed varying degrees of weight loss and clinical disease. Differences in disease did not correlate to virus burden in upper or lower tracts. TN/94-49 HMPV exhibited highest nose titers and delayed lung clearance. Cytokine profiles differed between HMPV isolates, with TN/96-35 inducing the broadest lung inflammatory cytokines. TN/96-35 also showed lower HMPV burden and less weight loss than other virulent isolates, suggesting a more efficient antiviral response. Interestingly, disease correlated with higher expression of T-cell chemoattractant CXCL9. All isolates elicited PD-1 upregulation and decreased IFNγ and CD107a expression in virus-specific TCD8, with little difference between HMPV subtypes. This work uncovers previously uncharacterized variations in immune responses to clinical HMPV isolates of different lineages.IMPORTANCEThis study extensively explored differences in T-cell-mediated immunity between human metapneumovirus (HMPV) clinical isolates. Much existing HMPV research has been done with strains passaged extensively in cell lines, likely acquiring mutations advantageous to in vitro replication. Clinical isolates are collected directly from human patients and have undergone <10 passages, serving as more physiologically relevant models of HMPV infection. Additionally, existing animal studies of HMPV disease mainly focus on lung pathogenesis, while HMPV infects both upper and lower airways of humans. This work highlights distinct differences in HMPV burden in upper and lower tracts between clinical isolates. Lastly, this study uniquely explores differences in host immunity between all four HMPV genetic lineages. The predominant HMPV subtype in circulation varies seasonally; thus, understanding host responses to all subgroups is critical for developing effective HMPV vaccines.

Upper and/or Lower Respiratory Tract Infection Caused by Human Metapneumovirus After Allogeneic Hematopoietic Stem Cell Transplantation

BACKGROUND

Human metapneumovirus (hMPV) epidemiology, clinical characteristics and risk factors for poor outcome after allogeneic stem cell transplantation (allo-HCT) remain a poorly investigated area.

METHODS

This retrospective multicenter cohort study examined the epidemiology, clinical characteristics, and risk factors for poor outcomes associated with human metapneumovirus (hMPV) infections in recipients of allo-HCT.

RESULTS

We included 428 allo-HCT recipients who developed 438 hMPV infection episodes between January 2012 and January 2019. Most recipients were adults (93%). hMPV infections were diagnosed at a median of 373 days after allo-HCT. The infections were categorized as upper respiratory tract disease (URTD) or lower respiratory tract disease (LRTD), with 60% and 40% of cases, respectively. Patients with hMPV LRTD experienced the infection earlier in the transplant course and had higher rates of lymphopenia, neutropenia, corticosteroid use, and ribavirin therapy. Multivariate analysis identified lymphopenia and corticosteroid use (>30 mg/d) as independent risk factors for LRTD occurrence. The overall mortality at day 30 after hMPV detection was 2% for URTD, 12% for possible LRTD, and 21% for proven LRTD. Lymphopenia was the only independent risk factor associated with day 30 mortality in LRTD cases.

CONCLUSIONS

These findings highlight the significance of lymphopenia and corticosteroid use in the development and severity of hMPV infections after allo-HCT, with lymphopenia being a predictor of higher mortality in LRTD cases.

Cytokine Storm Syndrome Associated with Hemorrhagic Fever and Other Viruses

A wide variety of infections can trigger cytokine storm syndromes including those caused by bacteria, viruses, fungi and parasites. The most frequent viral trigger is Epstein-.Barr virus which is covered in Chapter 16. CSS associated with COVID-19 is also discussed separately (Chapter 22). This chapter will focus on other viruses including the hemorrhagic fever viruses, influenza, parainfluenza, adenovirus, parvovirus, hepatitis viruses, measles, mumps, rubella, enterovirus, parechovirus, rotavirus, human metapneumovirus and human T-lymphotropic virus. The published literature consists of many single case reports and moderate-sized case series reporting CSS, in most circumstances meeting the 2004 diagnostic criteria for hemophagocytic lymphohistiocytosis (HLH). There is no published clinical trial evidence specifically for management of HLH associated with these viruses. In some situations, patients received supportive therapy and blood product transfusions only but in most cases, they were treated with one or more of intravenous corticosteroids, intravenous immunoglobulin and/or etoposide. These were successful in many patients although in significant numbers progression of infection to CSS was associated with mortality.

Bronchial reactivity and asthma at school age after early-life metapneumovirus infection

Background

The association between early-life lower respiratory tract infection (LRTI) and asthma is well established. Knowledge about bronchial hyperresponsiveness (BHR) and asthma after metapneumovirus (MPV) LRTI is scarce. The aim of this study was to assess BHR and current asthma in school-aged children after hospital admission for early-life LRTI with MPV, and to compare with more well-known viruses, rhinovirus (RV) and respiratory syncytial virus (RSV), and with controls.

Methods

A cohort consisting of children admitted for LRTI and controls was followed-up at school age with a clinical research assessment and lung function tests, including a methacholine provocation test. Current asthma was defined based on objective variable airway obstruction and clinical symptoms. BHR and asthma were compared according to viral groups.

Results

135 children (median age 9.3 years) were included (16 MPV, 34 RV, 51 RSV, 13 mixed infections and 21 controls). Compared with controls there was increased BHR after MPV and RV LRTI (provocative dose causing a 20% fall in forced expiratory volume in 1 s and dose-response slope; p<0.05). Using Kaplan-Meier statistics, BHR was increased for MPV compared with both controls and RSV (p=0.02 and p=0.01). The proportion of children with current asthma at follow-up was higher in the LRTI children compared with the controls (46% versus 24%; p=0.06). Among children who had undergone MPV and RV infection, 50% fulfilled the asthma criteria compared with 43% in the RSV group (p=0.37).

Conclusion

We found increased BHR and a high prevalence of asthma in school-aged children after early-life MPV infection, and findings were similar to RV, and less to RSV, compared with controls.

Tunneling Nanotubes: The Cables for Viral Spread and Beyond

Multicellular organisms require cell-to-cell communication to maintain homeostasis and thrive. For cells to communicate, a network of filamentous, actin-rich tunneling nanotubes (TNTs) plays a pivotal role in facilitating efficient cell-to-cell communication by connecting the cytoplasm of adjacent or distant cells. Substantial documentation indicates that diverse cell types employ TNTs in a sophisticated and intricately organized fashion for both long and short-distance communication. Paradoxically, several pathogens, including viruses, exploit the structural integrity of TNTs to facilitate viral entry and rapid cell-to-cell spread. These pathogens utilize a "surfing" mechanism or intracellular transport along TNTs to bypass high-traffic cellular regions and evade immune surveillance and neutralization. Although TNTs are present across various cell types in healthy tissue, their magnitude is increased in the presence of viruses. This heightened induction significantly amplifies the role of TNTs in exacerbating disease manifestations, severity, and subsequent complications. Despite significant advancements in TNT research within the realm of infectious diseases, further studies are imperative to gain a precise understanding of TNTs' roles in diverse pathological conditions. Such investigations are essential for the development of novel therapeutic strategies aimed at leveraging TNT-associated mechanisms for clinical applications. In this chapter, we emphasize the significance of TNTs in the life cycle of viruses, showcasing the potential for a targeted approach to impede virus-host cell interactions during the initial stages of viral infections. This approach holds promise for intervention and prevention strategies.

Development of a novel multi-epitope mRNA vaccine candidate to combat HMPV virus

Human metapneumovirus (HMPV) is one of the main pathogens causing severe respiratory infections in children, as a common cause of immunodeficiency-related deaths in children and elderly individuals, the prevalence of HMPV has been showing an increasing trend during the last years. However, no vaccines or effective treatment plans are available currently. In this present, based on candidate proteins highly associated with viral virulence and has promising protective potential, we screened for immunodominant cytotoxic T cells, helper T cells, and Linear B-cell epitopes from the most promising candidate Fusion protein, together with G, SH, M, and M2. All epitopes were predicted to have strong antigenicity by Vaxijen and pose no potential toxicity, allergenicity, or hormonology to human proteins by Toxinpred, Allerpred, and Blast analysis, meanwhile, high conservancy is demanded to cover different subtypes. adjuvants β-defensin II and Pam2Cys was attached with EAAAK linkers to improve vaccine's efficiency. Then, calculation of physicochemical properties proved the protein vaccine as a product can stably exist in the human body. Besides, we assessed the docking between the vaccine and immune receptors to evaluate its ability to stimulate immune responses, and the dynamic simulation further confirmed that the vaccine can tightly bind with immune receptors, which approved that the construction has the potential to induce strong humoral and cellular immune response. Finally, the vaccine was constructed into a multi-epitope mRNA vaccine, the immune simulations suggest that this is a vaccine candidate for controlling HMPV infection.

Epidemiology, genetic characteristics, and association with meteorological factors of human metapneumovirus infection in children in southern China: A 10-year retrospective study

OBJECTIVES

This study aimed to determine the epidemiological and genetic features of human metapneumovirus (HMPV) infection in children in southern China, and the effect of meteorological factors on infection.

METHODS

14,817 children (≤14 years) with acute respiratory tract infections from 2010 to 2019 were examined for HMPV and other respiratory viruses by real-time quantitative polymerase chain reaction. Full-length F gene of 54 positive samples were sequenced and subjected to phylogenetic analysis. The correlation between the HMPV-positive rate and meteorological factors was analyzed by linear regression analysis.

RESULTS

HMPV was detected in 524 (3.5%) children, who were mostly younger than 1 year. The seasonal peak of HMPV prevalence mainly occurred in spring. Respiratory syncytial virus was the most common virus coinfected with HMPV (5.3%). Phylogenetic analysis revealed that the sequenced HMPV strains belonged to four sublineages, including A2b (1.9%), A2c (31.5%), B1 (50.0%), and B2 (16.7%). After adjusting for all meteorological factors, sunshine duration was inversely correlated with the HMPV-positive rate.

CONCLUSION

HMPV is an important respiratory pathogen that causes acute respiratory tract infections in children in southern China, particularly in children ≤5 years old. The prevalence peak of HMPV in this area appeared in spring, and the predominant subtype was B1. Meteorological factors, especially long sunshine duration, might decrease the HMPV prevalence.

The effects of weather and mobility on respiratory viruses dynamics before and during the COVID-19 pandemic in the USA and Canada

The flu season is caused by a combination of different pathogens, including influenza viruses (IVS), that cause the flu, and non-influenza respiratory viruses (NIRVs), that cause common colds or influenza-like illness. These viruses exhibit similar dynamics and meteorological conditions have historically been regarded as a principal modulator of their epidemiology, with outbreaks in the winter and almost no circulation during the summer, in temperate regions. However, after the emergence of SARS-CoV2, in late 2019, the dynamics of these respiratory viruses were strongly perturbed worldwide: some infections displayed near-eradication, while others experienced temporal shifts or occurred "off-season". This disruption raised questions regarding the dominant role of weather while also providing an unique opportunity to investigate the roles of different determinants on the epidemiological dynamics of IVs and NIRVs. Here, we employ statistical analysis and modelling to test the effects of weather and mobility in viral dynamics, before and during the COVID-19 pandemic. Leveraging epidemiological surveillance data on several respiratory viruses, from Canada and the USA, from 2016 to 2023, we found that whereas in the pre-COVID-19 pandemic period, weather had a strong effect, in the pandemic period the effect of weather was strongly reduced and mobility played a more relevant role. These results, together with previous studies, indicate that behavioral changes resulting from the non-pharmacological interventions implemented to control SARS-CoV2, interfered with the dynamics of other respiratory viruses, and that the past dynamical equilibrium was disturbed, and perhaps permanently altered, by the COVID-19 pandemic.

SARS-CoV-2 antibodies from children exhibit broad neutralization and belong to adult public clonotypes

From the beginning of the COVID-19 pandemic, children have exhibited different susceptibility to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, reinfection, and disease compared with adults. Motivated by the established significance of SARS-CoV-2-neutralizing antibodies in adults, here we characterize SARS-CoV-2-specific antibody repertoires in a young cohort of individuals aged from 5 months to 18 years old. Our results show that neutralizing antibodies in children possess similar genetic features compared to antibodies identified in adults, with multiple antibodies from children belonging to previously established public antibody clonotypes in adults. Notably, antibodies from children show potent neutralization of circulating SARS-CoV-2 variants that have cumulatively resulted in resistance to virtually all approved monoclonal antibody therapeutics. Our results show that children can rely on similar SARS-CoV-2 antibody neutralization mechanisms compared to adults and are an underutilized source for the discovery of effective antibody therapeutics to counteract the ever-evolving pandemic.

PD-1 Impairs CD8+ T Cell Granzyme B Production in Aged Mice during Acute Viral Respiratory Infection

CD8+ T cell dysfunction contributes to severe respiratory viral infection outcomes in older adults. CD8+ T cells are the primary cell type responsible for viral clearance. With increasing age, CD8+ T cell function declines in conjunction with an accumulation of cytotoxic tissue-resident memory (TRM) CD8+ T cells. We sought to elucidate the role of PD-1 signaling on aged CD8+ T cell function and accumulation of CD8+ TRM cells during acute viral respiratory tract infection, given the importance of PD-1 regulating CD8+ T cells during acute and chronic infections. PD-1 blockade or genetic ablation in aged mice yielded improved CD8+ T cell granzyme B production comparable to that in young mice during human metapneumovirus and influenza viral infections. Syngeneic transplant and adoptive transfer strategies revealed that improved granzyme B production in aged Pdcd1-/- CD8+ T cells was primarily cell intrinsic because aged wild-type CD8+ T cells did not have increased granzyme B production when transplanted into a young host. PD-1 signaling promoted accumulation of cytotoxic CD8+ TRM cells in aged mice. PD-1 blockade of aged mice during rechallenge infection resulted in improved clinical outcomes that paralleled reduced accumulation of CD8+ TRM cells. These findings suggest that PD-1 signaling impaired CD8+ T cell granzyme B production and contributed to CD8+ TRM cell accumulation in the aged lung. These findings have implications for future research investigating PD-1 checkpoint inhibitors as a potential therapeutic option for elderly patients with severe respiratory viral infections.

Human metapneumovirus infection in the cardiac paediatric ICU before and during COVID-19 pandemic: a retrospective cohort analysis

INTRODUCTION

This study investigates the hygiene standards in the context of the COVID-19 pandemic and their impact on the perioperative incidence of human metapneumovirus as well as the typical symptom burden of human metapneumovirus-infected children with CHDs.

MATERIALS AND METHODS

Between March 2018 and July 2021, all patients of a cardiac paediatric ICU of a German university hospital were included in this retrospective cohort analysis.

RESULTS

A total of 589 patients with CHD were included in the analysis. Three hundred and fifty-two patients (148 females and 204 males) were admitted before the introduction of social distancing and face masks between March 2018 and 15 April 2020 (cohort A). Two hundred and thirty-seven patients (118 females and 119 males) were admitted after the introduction between April 16 and July 2021 (cohort B). In cohort A, human metapneumovirus was detected in 11 out of 352 patients (3.1%) during their stay at cardiac paediatric ICU. In cohort B, one patient out of 237 (0.4%) tested positive for human metapneumovirus. Patients who tested positive for human metapneumovirus stayed in cardiac paediatric ICU for a median of 17.5 days (range, 2-45 days). Patients without a detected human metapneumovirus infection stayed in the cardiac paediatric ICU for a median of 4 days (range, 0.5-114 days). Nine out of 12 (75%) human metapneumovirus-positive patients showed atelectasis.

CONCLUSION

Perioperative human metapneumovirus infections prolong cardiac paediatric ICU stay in children with CHD. In affected patients, pulmonary impairment with typical symptoms appears. Under certain circumstances, a complication-rich perioperative infection with human metapneumovirus could be prevented in paediatric cardiac high-risk patients by prophylactic hygiene intervention.

Burden of human metapneumovirus infections among children with acute respiratory tract infections attending a Tertiary Care Hospital, Kathmandu

BACKGROUND

Acute respiratory infections (ARIs) are one of the most common causes of mortality and morbidity worldwide. Every year millions of children suffer from viral respiratory tract infections (RTIs) ranging from mild to severe illnesses. Human Metapneumovirus (HMPV) is among the most frequent viruses responsible for RTIs. However, HMPV infections and their severity among children have not been explored yet in Nepal.

PURPOSE

Therefore, the study was focused on HMPV infections and other potential viral etiologies or co-infections using multiplex PCR among children attending Kanti Children's Hospital and assessed the clinical characteristics of the infections as well as found the co-infections. A hospital-based cross-sectional study was designed and a convenience sampling method was used to enroll children of less than 15 years with flu-like symptoms from both outpatients and inpatients departments over three months of the study period.

RESULTS

HMPV infection (13.3%) was the most predominant infection among the different viral infections in children with ARIs in Kanti Children's Hospital. The HMPV was more prevalent in the age group less than three years (21.8%). Cough and fever were the most common clinical features present in all children infected with HMPV followed by rhinorrhea, sore throat, and wheezing. HMPV-positive children were diagnosed with pneumonia (42.9%), bronchiolitis (28.5%), upper respiratory tract infections (14.3%), and asthma (14.3%). The prevalence of HMPV was high in late winter (14.3%) followed by early spring (13.5%).

CONCLUSIONS

This study provides the baseline information on HMPV and associated co-infection with other respiratory viruses for the differential diagnosis based on molecular methods and also the comparison of clinical presentations among the different respiratory syndromes.

Viral load: We need a new look at an old problem?

The concept of viral load was introduced in the 1980s to measure the amount of viral genetic material in a person's blood, primarily for human immunodeficiency virus (HIV). It has since become crucial for monitoring HIV infection progression and assessing the efficacy of antiretroviral therapy. However, during the coronavirus disease 2019 pandemic, the term "viral load" became widely popularized, not only for the scientific community but for the general population. Viral load plays a critical role in both clinical patient management and research, providing valuable insights for antiviral treatment strategies, vaccination efforts, and epidemiological control measures. As measuring viral load is so important, why don't researchers discuss the best way to do it? Is it simply acceptable to use raw Ct values? Relying solely on Ct values for viral load estimation can be problematic due to several reasons. First, Ct values can vary between different quantitative polymerase chain reaction assays, platforms, and laboratories, making it difficult to compare data across studies. Second, Ct values do not directly measure the quantity of viral particles in a sample and they can be influenced by various factors such as initial viral load, sample quality, and assay sensitivity. Moreover, variations in viral RNA extraction and reverse-transcription steps can further impact the accuracy of viral load estimation, emphasizing the need for careful interpretation of Ct values in viral load assessment. Interestingly, we did not observe scientific articles addressing different strategies to quantify viral load. The absence of standardized and validated methods impedes the implementation of viral load monitoring in clinical management. The variability in cell quantities within samples and the variation in viral particle numbers within infected cells further challenge accurate viral load measurement and interpretation. To advance the field and improve patient outcomes, there is an urgent need for the development and validation of tailored, standardized methods for precise viral load quantification.

Terminally exhausted CD8+ T cells contribute to age-dependent severity of respiratory virus infection

BACKGROUND

Lower respiratory infections are a leading cause of severe morbidity and mortality among older adults. Despite ubiquitous exposure to common respiratory pathogens throughout life and near universal seropositivity, antibodies fail to effectively protect the elderly. Therefore, we hypothesized that severe respiratory illness in the elderly is due to deficient CD8+ T cell responses.

RESULTS

Here, we establish an aged mouse model of human metapneumovirus infection (HMPV) wherein aged C57BL/6 mice exhibit worsened weight loss, clinical disease, lung pathology and delayed viral clearance compared to young adult mice. Aged mice generate fewer lung-infiltrating HMPV epitope-specific CD8+ T cells. Those that do expand demonstrate higher expression of PD-1 and other inhibitory receptors and are functionally impaired. Transplant of aged T cells into young mice and vice versa, as well as adoptive transfer of young versus aged CD8+ T cells into Rag1-/- recipients, recapitulates the HMPV aged phenotype, suggesting a cell-intrinsic age-associated defect. HMPV-specific aged CD8+ T cells exhibit a terminally exhausted TCF1/7- TOX+ EOMES+ phenotype. We confirmed similar terminal exhaustion of aged CD8+ T cells during influenza viral infection.

CONCLUSIONS

This study identifies terminal CD8+ T cell exhaustion as a mechanism of severe disease from respiratory viral infections in the elderly.

Human metapneumovirus driven IFN-β production antagonizes macrophage transcriptional induction of IL1-β in response to bacterial pathogens

Human metapneumovirus (HMPV) is a pneumovirus that may cause severe respiratory disease in humans. HMPV infection has been found to increase susceptibility to bacterial superinfections leading to increased morbidity and mortality. The molecular mechanisms underlying HMPV-mediated increase in bacterial susceptibility are poorly understood and largely understudied. Type I interferons (IFNs), while critical for antiviral defenses, may often have detrimental effects by skewing the host immune response and cytokine output of immune cells. It is currently unknown if HMPV skews the inflammatory response in human macrophages triggered by bacterial stimuli. Here we report that HMPV pre-infection impacts production of specific cytokines. HMPV strongly suppresses IL-1β transcription in response to LPS or heat-killed Pseudomonas aeruginosa and Streptococcus pneumonia, while enhancing mRNA levels of IL-6, TNF-α and IFN-β. We demonstrate that in human macrophages the HMPV-mediated suppression of IL-1β transcription requires TANK-binding kinase 1 (TBK1) and signaling via the IFN-β-IFNAR axis. Interestingly, our results show that HMPV pre-infection did not impair the LPS-stimulated activation of NF-κB and HIF-1α, transcription factors that stimulate IL-1β mRNA synthesis in human cells. Furthermore, we determined that sequential HMPV-LPS treatment resulted in accumulation of the repressive epigenetic mark H3K27me3 at the IL1B promoter. Thus, for the first time we present data revealing the molecular mechanisms by which HMPV shapes the cytokine output of human macrophages exposed to bacterial pathogens/LPS, which appears to be dependent on epigenetic reprogramming at the IL1B promoter leading to reduced synthesis of IL-1β. These results may improve current understanding of the role of type I IFNs in respiratory disease mediated not only by HMPV, but also by other respiratory viruses that are associated with superinfections.

Common cold

The common cold is a unique human disease, as it is arguably the most common disease and because of the large number of respiratory viruses causing colds it is one of the most complex of human diseases. This review discusses the respiratory viruses and notes that all these viruses may cause the illness complex recognised as the common cold. The common cold is discussed as part of the "iceberg concept" of disease which ranges from asymptomatic infection to severe illness and death. The factors influencing the incidence of colds are discussed: crowding and sociability, stress, smoking and alcohol, immune status, sex, age, sleep, season, chilling, nutrition and exercise. The mechanism of symptoms related to the innate immune response is explained and symptomatic treatments are tabulated. Morbidity associated with common cold is discussed and possible vaccines.

Conserved allosteric inhibitory site on the respiratory syncytial virus and human metapneumovirus RNA-dependent RNA polymerases

Respiratory syncytial virus (RSV) and human metapneumovirus (HMPV) are related RNA viruses responsible for severe respiratory infections and resulting disease in infants, elderly, and immunocompromised adults^1-3. Therapeutic small molecule inhibitors that bind to the RSV polymerase and inhibit viral replication are being developed, but their binding sites and molecular mechanisms of action remain largely unknown⁴. Here we report a conserved allosteric inhibitory site identified on the L polymerase proteins of RSV and HMPV that can be targeted by a dual-specificity, non-nucleoside inhibitor, termed MRK-1. Cryo-EM structures of the inhibitor in complexes with truncated RSV and full-length HMPV polymerase proteins provide a structural understanding of how MRK-1 is active against both viruses. Functional analyses indicate that MRK-1 inhibits conformational changes necessary for the polymerase to engage in RNA synthesis initiation and to transition into an elongation mode. Competition studies reveal that the MRK-1 binding pocket is distinct from that of a capping inhibitor with an overlapping resistance profile, suggesting that the polymerase conformation bound by MRK-1 may be distinct from that involved in mRNA capping. These findings should facilitate optimization of dual RSV and HMPV replication inhibitors and provide insights into the molecular mechanisms underlying their polymerase activities.

Human Metapneumovirus Reinfection in Aged Mice Recapitulates Increased Disease Severity in Elderly Humans Infected with Human Metapneumovirus

Human metapneumovirus (HMPV) is a leading cause of respiratory infection in adults >65 y. Nearly all children worldwide are seropositive for HMPV by age 5 y, but reinfections occur throughout life, and there is no licensed vaccine. Recurrent HMPV infection is mild and self-resolving in immunocompetent individuals. However, elderly individuals develop severe respiratory disease on HMPV reinfection that leads to a high risk for morbidity and mortality. In this study, we developed a mouse model to mirror HMPV reinfection in elderly humans. C57BL/6J mice were infected with HMPV at 6-7 wk old, aged in-house, and rechallenged with high-dose virus at 70 wk. Aged rechallenged mice had profound weight loss similar to primary infected mice, increased lung histopathology, and accumulated cytotoxic CD8+CD44+CD62L-CD69+CD103+ memory cells despite having undetectable lung virus titer. When aged mice 14 mo postinfection (p.i.) or young mice 5 wk p.i. were restimulated with HMPV cognate Ag to mimic epitope vaccination, aged mice had an impaired CD8+ memory response. Convalescent serum transfer from young naive or 5 wk p.i. mice into aged mice on day of infection did not protect. Aged mice vaccinated with UV-inactivated HMPV also exhibited diminished protection and poor CD8+ memory response compared with young mice. These results suggest aged individuals with HMPV reinfection have a dysregulated CD8+ memory T cell response that fails to protect and exacerbates disease. Moreover, aged mice exhibited a poor memory response to either epitope peptide or UV-inactivated vaccination, suggesting that aged CD8+ T cell dysfunction presents a barrier to effective vaccination strategies.

Specific Residues in the C-Terminal Domain of the Human Metapneumovirus Phosphoprotein Are Indispensable for Formation of Viral Replication Centers and Regulation of the Function of the Viral Polymerase Complex

Human metapneumovirus (HMPV) is a negative-strand RNA virus that frequently causes respiratory tract infections in infants, the elderly, and the immunocompromised. A hallmark of HMPV infection is the formation of membraneless, liquid-like replication and transcription centers in the cytosol termed inclusion bodies (IBs). The HMPV phosphoprotein (P) and nucleoprotein (N) are the minimal viral proteins necessary to form IB-like structures, and both proteins are required for the viral polymerase to synthesize RNA during infection. HMPV P is a homotetramer with regions of intrinsic disorder and has several known and predicted phosphorylation sites of unknown function. In this study, we found that the P C-terminal intrinsically disordered domain (CTD) must be present to facilitate IB formation with HMPV N, while either the N-terminal intrinsically disordered domain or the central oligomerization domain was dispensable. Alanine substitution at a single tyrosine residue within the CTD abrogated IB formation and reduced coimmunoprecipitation with HMPV N. Mutations to C-terminal phosphorylation sites revealed a potential role for phosphorylation in regulating RNA synthesis and P binding partners within IBs. Phosphorylation mutations which reduced RNA synthesis in a reporter assay produced comparable results in a recombinant viral rescue system, measured as an inability to produce infectious viral particles with genomes containing these single P mutations. This work highlights the critical role HMPV P plays in facilitating a key step of the viral life cycle and reveals the potential role for phosphorylation in regulating the function of this significant viral protein. IMPORTANCE Human metapneumovirus (HMPV) infects global populations, with severe respiratory tract infections occurring in infants, the elderly, and the immunocompromised. There are currently no FDA-approved therapeutics available to prevent or treat HMPV infection. Therefore, understanding how HMPV replicates is vital for the identification of novel targets for therapeutic development. During HMPV infection, viral RNA synthesis proteins localize to membraneless structures called inclusion bodies (IBs), which are sites of genome replication and transcription. The HMPV phosphoprotein (P) is necessary for IBs to form and for the virus to synthesize RNA, but it is not known how this protein contributes to IB formation or if it is capable of regulating viral replication. We show that the C-terminal domain of P is the location of a molecular interaction driving IB formation and contains potential phosphorylation sites where amino acid charge regulates the function of the viral polymerase complex.

Emergence and Potential Extinction of Genetic Lineages of Human Metapneumovirus between 2005 and 2021

Human metapneumovirus (HMPV) is one of the leading causes of respiratory illness (RI), primarily in infants. Worldwide, two genetic lineages (A and B) of HMPV are circulating that are antigenically distinct and can each be further divided into genetic sublineages. Surveillance combined with large-scale whole-genome sequencing studies of HMPV are scarce but would help to identify viral evolutionary dynamics. Here, we analyzed 130 whole HMPV genome sequences obtained from samples collected from individuals hospitalized with RI and partial fusion (n = 144) and attachment (n = 123) protein gene sequences obtained from samples collected from patients with RI visiting general practitioners between 2005 and 2021 in the Netherlands. Phylogenetic analyses demonstrated that HMPV continued to group in the four sublineages described in 2004 (A1, A2, B1, and B2). However, one sublineage (A1) was no longer detected in the Netherlands after 2006, while the others continued to evolve. No differences were observed in dominant (sub)lineages between samples obtained from patients with RI being hospitalized and those consulting general practitioners. In both populations, viruses of lineage A2 carrying a 180-nucleotide or 111-nucleotide duplication in the attachment protein gene became the most frequently detected genotypes. In the past, different names for the newly energing lineages have been proposed, demonstrating the need for a consistent naming convention. Here, criteria are proposed for the designation of new genetic lineages to aid in moving toward a systematic HMPV classification. IMPORTANCE Human metapneumovirus (HMPV) is one of the major causative agents of human respiratory tract infections. Monitoring of virus evolution could aid toward the development of new antiviral treatments or vaccine designs. Here, we studied HMPV evolution between 2005 and 2021, with viruses obtained from samples collected from hospitalized individuals and patients with respiratory infections consulting general practitioners. Phylogenetic analyses demonstrated that HMPV continued to group in the four previously described sublineages (A1, A2, B1, and B2). However, one sublineage (A1) was no longer detected after 2006, while the others continued to evolve. No differences were observed in dominant (sub)lineages between patients being hospitalized and those consulting general practitioners. In both populations, viruses of lineage A2 carrying a 180-nucleotide or 111-nucleotide duplication in the attachment protein gene became the most frequently detected genotypes. These data were used to propose criteria for the designation of new genetic lineages to aid toward a systematic HMPV classification.

Opportunistic etiological agents causing lung infections: emerging need to transform lung-targeted delivery

Lung diseases continue to draw considerable attention from biomedical and public health care agencies. The lung with the largest epithelial surface area is continuously exposed to the external environment during exchanging gas. Therefore, the chances of respiratory disorders and lung infections are overgrowing. This review has covered promising and opportunistic etiologic agents responsible for lung infections. These pathogens infect the lungs either directly or indirectly. However, it is difficult to intervene in lung diseases using available oral or parenteral antimicrobial formulations. Many pieces of research have been done in the last two decades to improve inhalable antimicrobial formulations. However, very few have been approved for human use. This review article discusses the approved inhalable antimicrobial agents (AMAs) and identifies why pulmonary delivery is explored. Additionally, the basic anatomy of the respiratory system linked with barriers to AMA delivery has been discussed here. This review opens several new scopes for researchers to work on pulmonary medicines for specific diseases and bring more respiratory medication to market.

Human metapneumovirus in hospitalized children with acute respiratory tract infections in Beijing, China

BACKGROUND

This study aims to described the epidemiology and genotypic diversity of Human metapneumovirus (HMPV) and the impact of SARS-CoV-2 on the prevalence of HMPV in hospitalized children with Acute respiratory tract infections (ARTIs) in Beijing, China.

METHODS

From April 2018 to March 2019 and from September 2020 to August 2021, nasopharyngeal aspirates (NPAs) from hospitalized children with ARTIs in Beijing were collected and subjected to real-time polymerase chain reaction tests for HMPV. Then genotyping, detection of 15 common respiratory viruses and clinical characteristics were analyzed on HMPV positive samples.

RESULTS

7.9% (124/1572) enrolled pediatric patients were identified as having HMPV infection, and the majority of children under the age of 5 (78.2%, 92/124), From April 2018 to March 2019. The detection rate of HMPV in spring and winter is significantly higher than that in summer and autumn. The co-infection rate were 37.1% (46/124), the most common co-infected virus were parainfluenza virus type 3 (HPIV-3). The main diagnosis of HMPV infection was pneumonia (92.7%,115/124), most patient have cough and fever. Of 78 HMPV-positive specimens, A2b (82.1%,64/78) were the main epidemic subtypes. Hospitalized children with HMPV genotype A infection had a higher viral load compared to genotype B. During the COVID-19 outbreak, Among 232 samples, only 4 cases were HMPV-positive. After statistical test, the detection rate of HMPV during the COVID-19 pandemic has decreased significantly compared with that before the epidemic (p = 0.001).

CONCLUSIONS

HMPV is an important cause of ARTIs in children under 5 years old. The epidemic peak is generally in winter and spring, and the A2b subtype is the most common. However, under the prevention and control of the COVID-19 pandemic, the HMPV infection of hospitalized children with ARTIs has decreased significantly.

Respiratory illness virus infections with special emphasis on COVID-19

Viruses that emerge pose challenges for treatment options as their uniqueness would not know completely. Hence, many viruses are causing high morbidity and mortality for a long time. Despite large diversity, viruses share common characteristics for infection. At least 12 different respiratory-borne viruses are reported belonging to various virus taxonomic families. Many of these viruses multiply and cause damage to the upper and lower respiratory tracts. The description of these viruses in comparison with each other concerning their epidemiology, molecular characteristics, disease manifestations, diagnosis and treatment is lacking. Such information helps diagnose, differentiate, and formulate the control measures faster. The leading cause of acute illness worldwide is acute respiratory infections (ARIs) and are responsible for nearly 4 million deaths every year, mostly in young children and infants. Lower respiratory tract infections are the fourth most common cause of death globally, after non-infectious chronic conditions. This review aims to present the characteristics of different viruses causing respiratory infections, highlighting the uniqueness of SARS-CoV-2. We expect this review to help understand the similarities and differences among the closely related viruses causing respiratory infections and formulate specific preventive or control measures.

Female offspring gestated in hypothyroxinemia and infected with human Metapneumovirus (hMPV) suffer a more severe infection and have a higher number of activated CD8+ T lymphocytes

Maternal thyroid hormones (THs) are essential for the appropriate development of the fetus and especially for the brain. Recently, some studies have shown that THs deficiency can also alter the immune system development of the progeny and their ability to mount an appropriate response against infectious agents. In this study, we evaluated whether adult mice gestated under hypothyroxinemia (Hpx) showed an altered immune response against infection with human metapneumovirus (hMPV). We observed that female mice gestated under Hpx showed higher clinical scores after seven days of hMPV infection. Besides, males gestated under Hpx have higher lung viral loads at day seven post-infection. Furthermore, the female offspring gestated in Hpx have already reduced the viral load at day seven and accordingly showed an increased proportion of activated (CD71⁺ and FasL⁺) CD8⁺ T cells in the lungs, which correlated with a trend for a higher histopathological clinical score. These results support that T₄ deficiency during gestation might condition the offspring differently in males and females, enhancing their ability to respond to hMPV.

Interactions among common non-SARS-CoV-2 respiratory viruses and influence of the COVID-19 pandemic on their circulation in New York City

BACKGROUND

Non-pharmaceutical interventions (NPIs) and voluntary behavioral changes during the COVID-19 pandemic have influenced the circulation of non-SARS-CoV-2 respiratory infections. We aimed to examine interactions among common non-SARS-CoV-2 respiratory virus and further estimate the impact of the COVID-19 pandemic on these viruses.

METHODS

We analyzed incidence data for seven groups of respiratory viruses in New York City (NYC) during October 2015 to May 2021 (i.e., before and during the COVID-19 pandemic). We first used elastic net regression to identify potential virus interactions and further examined the robustness of the found interactions by comparing the performance of Seasonal Auto Regressive Integrated Moving Average (SARIMA) models with and without the interactions. We then used the models to compute counterfactual estimates of cumulative incidence and estimate the reduction during the COVID-19 pandemic period from March 2020 to May 2021, for each virus.

RESULTS

We identified potential interactions for three endemic human coronaviruses (CoV-NL63, CoV-HKU, and CoV-OC43), parainfluenza (PIV)-1, rhinovirus, and respiratory syncytial virus (RSV). We found significant reductions (by ~70-90%) in cumulative incidence of CoV-OC43, CoV-229E, human metapneumovirus, PIV-2, PIV-4, RSV, and influenza virus during the COVID-19 pandemic. In contrast, the circulation of adenovirus and rhinovirus was less affected.

CONCLUSIONS

Circulation of several respiratory viruses has been low during the COVID-19 pandemic, which may lead to increased population susceptibility. It is thus important to enhance monitoring of these viruses and promptly enact measures to mitigate their health impacts (e.g., influenza vaccination campaign and hospital infection prevention) as societies resume normal activities.

Structural basis for ultrapotent antibody-mediated neutralization of human metapneumovirus

Human metapneumovirus (hMPV) is a leading cause of morbidity and hospitalization among children worldwide, however, no vaccines or therapeutics are currently available for hMPV disease prevention and treatment. The hMPV fusion (F) protein is the sole target of neutralizing antibodies. To map the immunodominant epitopes on the hMPV F protein, we isolated a panel of human monoclonal antibodies (mAbs), and the mAbs were assessed for binding avidity, neutralization potency, and epitope specificity. We found the majority of the mAbs target diverse epitopes on the hMPV F protein, and we discovered multiple mAb binding approaches for antigenic site III. The most potent mAb, MPV467, which had picomolar potency, was examined in prophylactic and therapeutic mouse challenge studies, and MPV467 limited virus replication in mouse lungs when administered 24 h before or 72 h after viral infection. We determined the structure of MPV467 in complex with the hMPV F protein using cryo-electron microscopy to a resolution of 3.3 Å, which revealed a complex novel prefusion-specific epitope overlapping antigenic sites II and V on a single protomer. Overall, our data reveal insights into the immunodominant antigenic epitopes on the hMPV F protein, identify a mAb therapy for hMPV F disease prevention and treatment, and provide the discovery of a prefusion-specific epitope on the hMPV F protein.

Global Extension and Predominance of Human Metapneumovirus A2 Genotype with Partial G Gene Duplication

Human metapneumovirus (HMPV) is an important respiratory pathogen and is divided in two main groups (A and B). HMPV strains with partial duplications (111-nt and 180-nt duplication) of the G gene have been reported in recent years. Since the initial reports, viruses with these characteristics have been reported in several countries. We analyzed all complete HMPV G gene ectodomain sequences available at GenBank to determine if viruses with 111-nt or 180-nt duplication have become the leading HMPV strains worldwide, and to describe their temporal and geographic distribution. We identified 1462 sequences that fulfilled study criteria (764 HMPV A and 698 HMPV B) reported from 37 countries. The most frequent HMPV A genotype was A2b2 (n = 366), and the most frequent B genotype was B2 (n = 374). A total of 84 sequences contained the 111-nt duplication, and 90 sequences contained the 180-nt duplication. Since 2016, viruses with a partial duplication comprise the most frequent HMPV A sequences globally and have displaced other HMPV A viruses in Asia, Europe, and South America; no sequences of viruses with partial duplication have been reported in North America or Africa so far. Continued surveillance of HMPV is required to identify the emergence and spread of epidemiologically relevant variants.

Prevalence of viral pathogens in a sample of hospitalized Egyptian children with acute lower respiratory tract infections: a two-year prospective study

BACKGROUND

Viral pneumonias are a major cause of childhood mortality. Proper management needs early and accurate diagnosis. This study objective is to investigate the viral etiologies of pneumonia in children.

RESULTS

This prospective study enrolled 158 and 101 patients in the first and second year, respectively, and their mean age was 4.72 ± 2.89. Nasopharyngeal swabs were collected and subjected to virus diagnosis by reverse transcription polymerase chain reaction (RT-PCR). Viral etiologies of pneumonia were evidenced in 59.5% of the samples in the first year, all of them were affirmative for influenza A, 2 samples were affirmative for Human coronavirus NL63, and one for Human coronavirus HKU1. In the second year, 87% of patients had a viral illness. The most prevalent agents are human metapneumovirus which was detected in 44 patients (43.6%) followed by human rhinovirus in 35 patients (34.7%) and then parainfluenza-3 viruses in 33 patients (32.7%), while 14 patients had a confirmed diagnosis for both Pan coronavirus and Flu-B virus.

CONCLUSIONS

Viral infection is prevalent in the childhood period; however, the real magnitude of viral pneumonia in children is underestimated. The reverse transcriptase polymerase chain reaction has to be a vital tool for epidemiological research and is able to clear the gaps in-between clinical pictures and final diagnoses.