Antigenic and genetic variability of human metapneumoviruses

Isolation of Human Metapneumovirus from clinical specimen in human organoid-derived bronchial cell cultures is superior to isolation in monolayer cell line cultures

BACKGROUND

Human Metapneumovirus (HMPV) is a causative agent of respiratory tract infections (RTI) in children and adults. HMPV is a member of the Pneumoviridae family for which circulation of two serotypes, A and B, has been reported. HMPV isolation in standard monolayer cell lines is not always successful. Recently, it was shown that upon inoculation of human organoid-derived bronchial (ODB) cultures, HMPV primarily targeted the ciliated cells, similar as observed in experimentally infected animals. These observations lead to the hypothesis that isolation of virus from clinical specimen in this ODB model could be more successful than in standard monolayer cultures.

METHODS

This study compared the efficiency of isolation of HMPV from 36 clinical samples in human ODB cultures with that in monolayers of Vero-118 cells.

RESULTS

A total of 27 isolates (8 HMPV A and 19 HMPV B) were obtained in the ODB cultures, after one passage, whereas 21 isolates (9 HMPV A and 12 HMPV B) were obtained after one or two passages in Vero-118 cells.

CONCLUSIONS

Overall, the isolation efficiency of serotype A HMPV was comparable in both models, while isolation of serotype B viruses was profoundly more efficient in the ODB cultures than in Vero-118 cells, suggesting that primary cultures expressing ciliated cells should be considered as a superior isolation method for HMPV from clinical specimens.

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.

Design and validation of a semi-quantitative microneutralization assay for human Metapneumovirus A1 and B1 subtypes

Since 2001, human Metapneumovirus has been a significant cause of human respiratory disease worldwide, and no vaccine or preventive treatment is currently available. The ELISA-based live virus microneutralization assay is a method to detect neutralizing antibodies against a target pathogen. The aim of this study was to demonstrate the suitability of this approach to quantifying neutralizing antibodies against A1 and B1 virus subtypes in human serum samples. To standardize and validate this microneutralization assay, we carried out analytical procedures according to the International Council of Harmonization guidelines; these procedures are described in detail. In addition, we compared the validated method with the indirect ELISA, and confirmed that the ELISA-based microneutralization assay provides reliable, accurate and reproducible results. The use of this high-throughput method for large-scale serological studies could effectively support the evaluation of the immunogenicity of new vaccines, thereby improving therapeutical strategies against human Metapneumovirus.

The global burden of human metapneumovirus-associated acute respiratory infections in older adults: a systematic review and meta-analysis

BACKGROUND

The human metapneumovirus (hMPV)-associated disease burden in older adults remains under-researched. We aimed to systematically estimate the global burden of hMPV-associated disease in older adults.

METHODS

We searched MEDLINE, Embase, Global Health, CINAHL, Web of Science, and Global Index Medicus in February, 2023, November, 2023, and October, 2024; and CNKI, Wanfang, and CQVip, in April, 2024, and October, 2024. We included studies conducted over at least 12 consecutive months, reporting on adults aged 60 years or older, and with laboratory-confirmed hMPV infections. Critical appraisal of included studies was conducted using the Joanna Briggs Institute critical appraisal tools. To estimate the hMPV pooled proportions positive in acute respiratory infections (ARIs), random effects meta-analyses were conducted. Using Monte Carlo simulation, we estimated the hMPV-associated hospitalisations globally and separately in high-income countries, low-income and middle-income countries, and the USA in individuals aged 65 years or older in 2019, as most studies reported on this age group. The hMPV-associated ARI incidence in countries other than the USA and in outpatient or community settings in the USA was summarised narratively due to scarcity of data. The review protocol was registered on PROSPERO (CRD42023422325).

FINDINGS

46 studies conducted between 2005 and 2023, and reporting on hMPV proportion positive estimates (n=36, with 29 866 laboratory tests), hospitalisation rates in the USA (n=4), and hMPV incidence (n=6) were included. We estimated 473 000 (95% CI 396 000-777 000) hMPV-associated hospitalisations globally, of which 185 000 (105 000-340 000) were in high-income countries (n=6 studies), and 288 000 (193 000-436 000) in low-income and middle-income countries (n=10 studies) in people aged 65 years or older in 2019. In the USA, the pooled hMPV-associated hospitalisation rate was 231 (95% CI 41-421) per 100 000 people in adults aged 65 years or older, representing approximately 122 000 (41 000-398 000) hospital admissions in this population in 2019.

INTERPRETATION

hMPV-associated ARIs contribute to a substantial disease and hospitalisation burden in older adults. However, more large-scale surveillance studies and greater investment in research and diagnostic methods are required to develop reliable estimates.

FUNDING

Icosavax, a member of the AstraZeneca group.

Harnessing Epigenetics: Innovative Approaches in Diagnosing and Combating Viral Acute Respiratory Infections

Acute respiratory infections (ARIs) caused by viruses such as SARS-CoV-2, influenza viruses, and respiratory syncytial virus (RSV), pose significant global health challenges, particularly for the elderly and immunocompromised individuals. Substantial evidence indicates that acute viral infections can manipulate the host's epigenome through mechanisms like DNA methylation and histone modifications as part of the immune response. These epigenetic alterations can persist beyond the acute phase, influencing long-term immunity and susceptibility to subsequent infections. Post-infection modulation of the host epigenome may help distinguish infected from uninfected individuals and predict disease severity. Understanding these interactions is crucial for developing effective treatments and preventive strategies for viral ARIs. This review highlights the critical role of epigenetic modifications following viral ARIs in regulating the host's innate immune defense mechanisms. We discuss the implications of these modifications for diagnosing, preventing, and treating viral infections, contributing to the advancement of precision medicine. Recent studies have identified specific epigenetic changes, such as hypermethylation of interferon-stimulated genes in severe COVID-19 cases, which could serve as biomarkers for early detection and disease progression. Additionally, epigenetic therapies, including inhibitors of DNA methyltransferases and histone deacetylases, show promise in modulating the immune response and improving patient outcomes. Overall, this review provides valuable insights into the epigenetic landscape of viral ARIs, extending beyond traditional genetic perspectives. These insights are essential for advancing diagnostic techniques and developing innovative treatments to address the growing threat of emerging viruses causing ARIs globally.

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.

Safety and Immunogenicity of an mRNA-Based hMPV/PIV3 Combination Vaccine in Seropositive Children

OBJECTIVES

Human metapneumovirus (hMPV) and parainfluenza virus type 3 (PIV3) are common respiratory illnesses in children. The safety and immunogenicity of an investigational mRNA-based vaccine, mRNA-1653, encoding membrane-anchored fusion proteins of hMPV and PIV3, was evaluated in hMPV/PIV3-seropositive children.

METHODS

In this phase 1b randomized, observer-blind, placebo-controlled, dose-ranging study, hMPV/PIV3-seropositive children were enrolled sequentially into 2 dose levels of mRNA-1653 administered 2 months apart; children aged 12 to 36 months were randomized (1:1) to receive 10-μg of mRNA-1653 or placebo and children aged 12 to 59 months were randomized (3:1) to receive 30-μg of mRNA-1653 or placebo.

RESULTS

Overall, 27 participants aged 18 to 55 months were randomized; 15 participants received 10-μg of mRNA-1653 (n = 8) or placebo (n = 7), whereas 12 participants received 30-μg of mRNA-1653 (n = 9) or placebo (n = 3). mRNA-1653 was well-tolerated at both dose levels. The only reported solicited local adverse reaction was tenderness at injection site; solicited systemic adverse reactions included grade 1 or 2 chills, irritability, loss of appetite, and sleepiness. A single 10-μg or 30-μg mRNA-1653 injection increased hMPV and PIV3 neutralizing antibody titers (geometric mean fold-rise ratio over baseline: hMPV-A = 2.9-6.1; hMPV-B = 6.2-13.2; PIV3 = 2.8-3.0) and preF and postF binding antibody concentrations (geometric mean fold-rise ratio: hMPV preF = 5.3-6.1; postF = 4.6-6.5 and PIV3 preF = 13.9-14.2; postF = 11.0-12.1); a second injection did not further increase antibody levels in these seropositive children. Binding antibody responses were generally preF biased.

CONCLUSIONS

mRNA-1653 was well-tolerated and boosted hMPV and PIV3 antibody levels in seropositive children aged 12 to 59 months, supporting the continued development of mRNA-1653 or its components for the prevention of hMPV and PIV3.

Molecular Epidemiology of Human Metapneumovirus in East Japan before and after COVID-19, 2017-2022

Human metapneumovirus (hMPV) is genetically classified into two major subgroups, A and B, based on attachment glycoprotein (G protein) gene sequences. The A2 subgroup is further separated into three subdivisions, A2a, A2b (A2b1), and A2c (A2b2). Subgroup A2c viruses carrying 180- or 111-nucleotide duplications in the G gene (A2c 180nt-dup or A2c 111nt-dup ) have been reported in Japan and Spain. The coronavirus disease 2019 (COVID-19) pandemic disrupted the epidemiological kinetics of other respiratory viruses, including hMPV. In this study, we analyzed the sequences of hMPV isolates in Tokyo and Fukushima obtained from 2017 to 2022, i.e., before and after the COVID-19 pandemic. Subgroup A hMPV strains were detected from 2017 to 2019, and most cases were A2c 111nt-dup, suggesting ongoing transmission of this clade, consistent with global transmission dynamics. Subgroup B viruses, but not subgroup A viruses, were detected in 2022 after the COVID-19 peak. Phylogenetic analysis showed that the subgroup B viruses were closely related to strains detected in Yokohama from 2013 to 2016, and strains detected in Fukushima in 2019, suggesting the reappearance of local endemic viruses in East Japan.

Human metapneumovirus infection of organoid-derived human bronchial epithelium represents cell tropism and cytopathology as observed in in vivo models

Human metapneumovirus (HMPV), a member of the Pneumoviridae family, causes upper and lower respiratory tract infections in humans. In vitro studies with HMPV have mostly been performed in monolayers of undifferentiated epithelial cells. In vivo studies in cynomolgus macaques and cotton rats have shown that ciliated epithelial cells are the main target of HMPV infection, but these observations cannot be studied in monolayer systems. Here, we established an organoid-derived bronchial culture model that allows physiologically relevant studies on HMPV. Inoculation with multiple prototype HMPV viruses and recent clinical virus isolates led to differences in replication among HMPV isolates. Prolific HMPV replication in this model caused damage to the ciliary layer, including cilia loss at advanced stages post-infection. These cytopathic effects correlated with those observed in previous in vivo studies with cynomolgus macaques. The assessment of the innate immune responses in three donors upon HMPV and RSV inoculation highlighted the importance of incorporating multiple donors to account for donor-dependent variation. In conclusion, these data indicate that the organoid-derived bronchial cell culture model resembles in vivo findings and is therefore a suitable and robust model for future HMPV studies.

IMPORTANCE

Human metapneumovirus (HMPV) is one of the leading causative agents of respiratory disease in humans, with no treatment or vaccine available yet. The use of primary epithelial cultures that recapitulate the tissue morphology and biochemistry of the human airways could aid in defining more relevant targets to prevent HMPV infection. For this purpose, this study established the first primary organoid-derived bronchial culture model suitable for a broad range of HMPV isolates. These bronchial cultures were assessed for HMPV replication, cellular tropism, cytopathology, and innate immune responses, where the observations were linked to previous in vivo studies with HMPV. This study exposed an important gap in the HMPV field since extensively cell-passaged prototype HMPV B viruses did not replicate in the bronchial cultures, underpinning the need to use recently isolated viruses with a controlled passage history. These results were reproducible in three different donors, supporting this model to be suitable to study HMPV infection.

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.

A chimeric influenza virus vaccine expressing fusion protein epitopes induces protection from human metapneumovirus challenge in mice

Human metapneumovirus (HMPV) is a common virus associated with acute respiratory distress syndrome in pediatric patients. There are no HMPV vaccines or therapeutics that have been approved for prevention or treatment. In this study, we constructed a novel recombinant influenza virus carrying partial HMPV fusion protein (HMPV-F), termed rFLU-HMPV/F-NS, utilizing reverse genetics, which contained (HMPV-F) in the background of NS segments of influenza virus A/PuertoRico/8/34(PR8). The morphological characteristics of rFLU-HMPV/F-NS were consistent with the wild-type flu virus. Additionally, immunofluorescence results showed that fusion proteins in the chimeric rFLU-HMPV/F-NS could work well, and the virus could be stably passaged in SPF chicken embryos. Furthermore, intranasal immunization with rFLU-HMPV/F-NS in BALB/c mice induced robust humoral, mucosal and Th1-type dominant cellular immune responses in vivo. More importantly, we discovered that rFLU-HMPV/F-NS afforded significant protective efficacy against the wild-type HMPV and influenza virus challenge, with significantly attenuated pathological changes and reduced viral titers in the lung tissues of immunized mice. Collectively, these findings demonstrated that chimeric recombinant rFLU-HMPV/F-NS as a promising HMPV candidate vaccine has potentials for the development of HMPV vaccine.

Development of a duplex real-time RT-PCR assay for the detection and identification of two subgroups of human metapneumovirus in a single tube

Human metapneumovirus (hMPV) is a common cause of respiratory infections in children. Many genetic diagnostic assays have been developed, but most detect hMPV regardless of the subgroup. In this study, we developed a real-time RT-PCR assay that can detect and identify the two major subgroups of hMPV (A and B) in one tube. Primers and probes were designed based on the sequences of recent clinical isolates in Japan. The assay showed comparable analytical sensitivity to a previously reported real-time RT-PCR assay and specific reactions to hMPV subgroups. The assay also showed no cross-reactivity to clinical isolates of 19 species of other respiratory viruses. In a validation assay using post-diagnosed clinical specimens, 98% (167/170) positivity was confirmed for the duplex assay, and the three specimens not detected were of low copy number. The duplex assay also successfully distinguished the two major subgroups for all 12 clinical specimens, for which the subgroup had already been determined by genomic sequencing analysis. The duplex assay described here will contribute to the rapid and accurate identification and surveillance of hMPV infections.

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.

Meeting Ferret Enrichment Needs in Infectious Disease Laboratory Settings

Environmental enrichment is a necessary component of all research vivarium settings. However, appropriate enrichment decisions vary greatly depending on the species involved and the research use of the animals. The increasing use of ferrets in research settings-notably for modeling the pathogenicity and transmissibility of viral pathogens that require containment in ABSL-2 to -4 environments-presents a particular challenge for veterinary and research staff to ensure that enrichment needs for these animals are met consistently. Here, we discuss the species-specific enrichment needs of ferrets, enrichment considerations for ferrets housed in research settings, and the challenges and importance of providing appropriate enrichment during experimentation, including when ferrets are housed in high-containment facilities. This article is organized to support the easy availability of information that will facilitate the design and implementation of optimal environmental enrichment for ferrets used in diverse research efforts in vivarium settings.

Re-Emergence of HMPV in Gwangju, South Korea, after the COVID-19 Pandemic

The non-pharmaceutical interventions implemented to prevent the spread of COVID-19 have affected the epidemiology of other respiratory viruses. In South Korea, Human metapneumovirus (HMPV) typically occurs from winter to the following spring; however, it was not detected for two years during the COVID-19 pandemic and re-emerged in the fall of 2022, which is a non-epidemic season. To examine the molecular genetic characteristics of HMPV before and after the COVID-19 pandemic, we analyzed 427 HMPV-positive samples collected in the Gwangju area from 2018 to 2022. Among these, 24 samples were subjected to whole-genome sequencing. Compared to the period before the COVID-19 pandemic, the incidence rate of HMPV in 2022 increased by 2.5-fold. Especially in the age group of 6-10 years, the incidence rate increased by more than 4.5-fold. In the phylogenetic analysis results, before the COVID-19 pandemic, the A2.2.2 lineage was predominant, while in 2022, the A2.2.1 and B2 lineage were observed. The non-pharmaceutical interventions implemented after COVID-19, such as social distancing, have reduced opportunities for exposure to HMPV, subsequently leading to decreased acquisition of immunity. As a result, HMPV occurred during non-epidemic seasons, influencing the age distribution of its occurrences.

A decade of human metapneumovirus in hospitalized children with acute respiratory infection: molecular epidemiology in central Vietnam, 2007-2017

Human metapneumovirus (hMPV) can cause severe acute respiratory infection (ARI). We aimed to clarify the clinical and molecular epidemiological features of hMPV. We conducted an ARI surveillance targeting hospitalized children aged 1 month to 14 years in Nha Trang, Vietnam. Nasopharyngeal swabs were tested for respiratory viruses with PCR. We described the clinical characteristics of hMPV patients in comparison with those with respiratory syncytial virus (RSV) and those with neither RSV nor hMPV, and among different hMPV genotypes. Among 8822 patients, 278 (3.2%) were hMPV positive, with a median age of 21.0 months (interquartile range: 12.7-32.5). Among single virus-positive patients, hMPV cases were older than patients with RSV (p < 0.001) and without RSV (p = 0.003). The proportions of clinical pneumonia and wheezing in hMPV patients resembled those in RSV patients but were higher than in non-RSV non-hMPV patients. Seventy percent (n = 195) were genotyped (A2b: n = 40, 20.5%; A2c: n = 99, 50.8%; B1: n = 37, 19%; and B2: n = 19, 9.7%). The wheezing frequency was higher in A2b patients (76.7%) than in those with other genotypes (p = 0.033). In conclusion, we found a moderate variation in clinical features among hMPV patients with various genotypes. No seasonality was observed, and the multiple genotype co-circulation was evident.

[Respiratory infections: Additional transmission-based precautions in healthcare facilities]

INTRODUCTION

In health care, measures against cross-transmission of microorganisms are codified by standard precautions, and if necessary, they are supplemented by additional precautions.

STATE OF THE ART

Several factors impact transmission of microorganisms via the respiratory route: size and quantity of the emitted particles, environmental conditions, nature and pathogenicity of the microorganisms, and degree of host receptivity. While some microorganisms necessitate additional airborne or droplet precautions, others do not.

PROSPECTS

For most microorganisms, transmission patterns are well-understood and transmission-based precautions are well-established. For others, measures to prevent cross-transmission in healthcare facilities remain under discussion.

CONCLUSIONS

Standard precautions are essential to the prevention of microorganism transmission. Understanding of the modalities of microorganism transmission is essential to implementation of additional transmission-based precautions, particularly in view of opting for appropriate respiratory protection.

Structure-based design of a single-chain triple-disulfide-stabilized fusion-glycoprotein trimer that elicits high-titer neutralizing responses against human metapneumovirus

The Pneumoviridae family of viruses includes human metapneumovirus (HMPV) and respiratory syncytial virus (RSV). The closely related Paramyxoviridae family includes parainfluenza viruses (PIVs). These three viral pathogens cause acute respiratory tract infections with substantial disease burden in the young, the elderly, and the immune-compromised. While promising subunit vaccines are being developed with prefusion-stabilized forms of the fusion glycoproteins (Fs) of RSV and PIVs, for which neutralizing titers elicited by the prefusion (pre-F) conformation of F are much higher than for the postfusion (post-F) conformation, with HMPV, pre-F and post-F immunogens described thus far elicit similar neutralizing responses, and it has been unclear which conformation, pre-F or post-F, would be the most effective HMPV F-vaccine immunogen. Here, we investigate the impact of further stabilizing HMPV F in the pre-F state. We replaced the furin-cleavage site with a flexible linker, creating a single chain F that yielded increased amounts of pre-F stabilized trimers, enabling the generation and assessment of F trimers stabilized by multiple disulfide bonds. Introduced prolines could increase both expression yields and antigenic recognition by the pre-F specific antibody, MPE8. The cryo-EM structure of a triple disulfide-stabilized pre-F trimer with the variable region of antibody MPE8 at 3.25-Å resolution confirmed the formation of designed disulfides and provided structural details on the MPE8 interface. Immunogenicity assessments in naïve mice showed the triple disulfide-stabilized pre-F trimer could elicit high titer neutralization, >10-fold higher than elicited by post-F. Immunogenicity assessments in pre-exposed rhesus macaques showed the triple disulfide-stabilized pre-F could recall high neutralizing titers after a single immunization, with little discrimination in the recall response between pre-F and post-F immunogens. However, the triple disulfide-stabilized pre-F adsorbed HMPV-directed responses from commercially available pooled human immunoglobulin more fully than post-F. Collectively, these results suggest single-chain triple disulfide-stabilized pre-F trimers to be promising HMPV-vaccine antigens.

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.

Epidemiology and genetic characterization of human metapneumovirus in pediatric patients from Hangzhou China

Human metapneumovirus (HMPV), which is distributed worldwide, is a significant viral respiratory pathogen responsible for causing acute respiratory tract infections (ARTIs) in children. The aim of the present study was to investigate the epidemiological and genetic characteristics of HMPV in pediatric patients in Hangzhou China following the peak of onset of coronavirus disease 2019 (COVID-19). A total of 1442 throat swabs were collected from the pediatric patients with a diagnosis of ARTI from November 2020 to March 2021. The following viruses were detected by real-time polymerase chain reaction analysis: HMPV, RSV, adenovirus, hPIV1-3, influenza A, and influenza B. A two-step method was used to amplify the F genes of the HMPV-positive samples. Following sequencing, phylogenetic analyses were conducted using the MEGA version 7 software package. Among the 1442 samples, 103 (7.14%) were positive for HMPV. No significant differences were observed in the gender distribution. The highest incidence of HMPV occurred in children older than 6 years and the lowest was noted in children younger than 6 months. Lower respiratory tract infections were diagnosed at a higher rate than upper respiratory tract infections in HMPV-infected children. Only 10 HMPV-infected children (5.41%) were inpatients compared with 93 outpatients (7.39%). Co-infection was observed in 31 HMPV-positive samples including 24 samples of double infection and seven samples of triple infection. A total of 61F gene fragments of HMPV, which were approximately 727 bp in length were successfully sequenced. All the HMPVs belonged to the genotype B and were clustered into subgenotypes B1 (1.6%, 1/61) and B2 (98.4%, 60/61). A total of four specific amino acid substitutions were noted as follows: aa280, aa296, aa392, and aa396. These substitutions were present between sequences derived from the subgenotypes B1 and B2 in the fusion open reading frame from position 244 to 429. In conclusion, the present study provided significant information regarding the epidemiological and genetic characteristics of HMPV in children living in Hangzhou. Following the first peak of the COVID-19 pandemic, HMPV was considered an important viral respiratory pathogen present in children with ARTI.

Characterization of prefusion-F-specific antibodies elicited by natural infection with human metapneumovirus

Human metapneumovirus (hMPV) is a major cause of acute respiratory infections in infants and older adults, for which no vaccines or therapeutics are available. The viral fusion (F) glycoprotein is required for entry and is the primary target of neutralizing antibodies; however, little is known about the humoral immune response generated from natural infection. Here, using prefusion-stabilized F proteins to interrogate memory B cells from two older adults, we obtain over 700 paired non-IgM antibody sequences representing 563 clonotypes, indicative of a highly polyclonal response. Characterization of 136 monoclonal antibodies reveals broad recognition of the protein surface, with potently neutralizing antibodies targeting each antigenic site. Cryo-EM studies further reveal two non-canonical sites and the molecular basis for recognition of the apex of hMPV F by two prefusion-specific neutralizing antibodies. Collectively, these results provide insight into the humoral response to hMPV infection in older adults and will help guide vaccine development.

Antiviral strategies against human metapneumovirus: Targeting the fusion protein

Human metapneumoviruses have emerged in the past decades as an important global pathogen that causes severe upper and lower respiratory tract infections. Children under the age of 2, the elderly and immunocompromised individuals are more susceptible to HMPV infection than the general population due to their suboptimal immune system. Despite the recent discovery of HMPV as a novel important respiratory virus, reports have rapidly described its epidemiology, biology, and pathogenesis. However, progress is still to be made in the development of vaccines and drugs against HMPV infection as none are currently available. Herein, we discuss the importance of HMPV and review the reported strategies for anti-HMPV drug candidates. We also present the fusion protein as a promising antiviral drug target due to its multiple roles in the HMPV lifecycle. This key viral protein has previously been targeted by a range of inhibitors, which will be discussed as they represent opportunities for future drug design.

Fetal Transfer of Human Metapneumovirus-Neutralizing Antibodies Is Reduced From Mothers Living With HIV-1

Transplacental hMPV-neutralizing antibody transfer was reduced from mothers living with HIV-1. However, a comparison of antibody titers at birth between hMPV hospitalization cases at <6 months and matched controls suggested that reduced maternal antibody might not be the primary cause of the previously reported elevated hMPV risk in HIV-1-exposed infants.

The A2c 111nt-dup Variants of Human Metapneumovirus Predominantly Circulating in Qingdao, China, during 2018 and 2019

BACKGROUND

Human metapneumovirus (HMPV) plays an important role in acute respiratory tract infections, especially in children. We investigated the epidemiology of HMPV associated with acute respiratory tract infections (ARTIs) among pediatric inpatients and identified HMPV genetic variations in Qingdao, China, from January 2018 to June 2019.

METHODS

HMPV-positive samples were identified from throat swabs by multiplex real-time RT-PCR. The G gene sequences of HMPV were obtained, followed by phylogenetic analysis.

RESULTS

As a result, 71 out of 1051 (6.76%) patients were HMPV positive, and the HMPV-positive rate in children under 5 years of age was three times higher than that in those aged 5-17 years. The epidemic season of HMPV was in spring, with a peak mainly in March. Thirty-two nucleotide sequences of the HMPV G gene successfully obtained were clustered into 3 genotypes, A2c (25/32, 78.13%), B1 (3/32, 9.38%) and B2 (4/32, 12.50%). In addition, 76% (19/25) of A2c viruses were identified as the emerging A2c_111nt-dup variants, which were predominantly circulating among pediatric inpatients with ARTIs between January 2018 and June 2019 in Qingdao.

CONCLUSIONS

The emerging A2c_111nt-dup variants have spread between countries and cities and might spread more widely in the future. Further prevalence monitoring of this duplication variant is needed to clarify the potentially expanding transmission and to provide a scientific basis for disease control and vaccine development. This article is protected by copyright. All rights reserved.

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.

Profiling of hMPV F-specific antibodies isolated from human memory B cells

Human metapneumovirus (hMPV) belongs to the Pneumoviridae family and is closely related to respiratory syncytial virus (RSV). The surface fusion (F) glycoprotein mediates viral fusion and is the primary target of neutralizing antibodies against hMPV. Here we report 113 hMPV-F specific monoclonal antibodies (mAbs) isolated from memory B cells of human donors. We characterize the antibodies' germline usage, epitopes, neutralization potencies, and binding specificities. We find that unlike RSV-F specific mAbs, antibody responses to hMPV F are less dominant against the apex of the antigen, and the majority of the potent neutralizing mAbs recognize epitopes on the side of hMPV F. Furthermore, neutralizing epitopes that differ from previously defined antigenic sites on RSV F are identified, and multiple binding modes of site V and II mAbs are discovered. Interestingly, mAbs that bind preferentially to the unprocessed prefusion F show poor neutralization potency. These results elucidate the immune recognition of hMPV infection and provide novel insights for future hMPV antibody and vaccine development.

Safety and immunogenicity of an mRNA-based human metapneumovirus and parainfluenza virus type 3 combined vaccine in healthy adults

Background

Human metapneumovirus (hMPV) and parainfluenza virus type 3 (PIV3) cause respiratory tract illness in children and the elderly. No licensed vaccines are available.

Methods

In this phase 1, randomized, dose-ranging, first-in-human study, the safety, reactogenicity, and humoral immunogenicity of an investigational mRNA-based hMPV and PIV3 combination vaccine, mRNA-1653, were evaluated in healthy adults aged 18–49 years. Sentinel participants (n = 20) received 2 doses of mRNA-1653 (25, 75, 150, or 300 μg) in the dose escalation phase, and participants (n = 104) received 2 doses of mRNA-1653 (75, 150, or 300 μg) or placebo in the dose selection phase; injections were 28 days apart.

Results

The most common solicited reactogenicity events were injection site pain, headache, fatigue, and myalgia, the majority of which were grade 1 or 2. A single mRNA-1653 dose increased neutralization titers against hMPV and PIV3 1 month after vaccination compared with baseline. No notable increases in neutralizing antibody titers were observed with escalating dose levels after mRNA-1653, although no statistical inferences were made; a second mRNA-1653 dose had little observable impact on antibody titers. Neutralizing titers through 1 year remained above baseline for hMPV and returned to baseline for PIV3.

Conclusions

mRNA-1653 was well tolerated, with an acceptable safety profile and increased hMPV and PIV3 neutralization titers in healthy adults.

Zoonotic Origins of Human Metapneumovirus: A Journey from Birds to Humans

Metapneumoviruses, members of the family Pneumoviridae, have been identified in birds (avian metapneumoviruses; AMPV’s) and humans (human metapneumoviruses; HMPV’s). AMPV and HMPV are closely related viruses with a similar genomic organization and cause respiratory tract illnesses in birds and humans, respectively. AMPV can be classified into four subgroups, A–D, and is the etiological agent of turkey rhinotracheitis and swollen head syndrome in chickens. Epidemiological studies have indicated that AMPV also circulates in wild bird species which may act as reservoir hosts for novel subtypes. HMPV was first discovered in 2001, but retrospective studies have shown that HMPV has been circulating in humans for at least 50 years. AMPV subgroup C is more closely related to HMPV than to any other AMPV subgroup, suggesting that HMPV has evolved from AMPV-C following zoonotic transfer. In this review, we present a historical perspective on the discovery of metapneumoviruses and discuss the host tropism, pathogenicity, and molecular characteristics of the different AMPV and HMPV subgroups to provide increased focus on the necessity to better understand the evolutionary pathways through which HMPV emerged as a seasonal endemic human respiratory virus.

Molecular investigation of human metapneumovirus in children with acute respiratory infections in Chennai, South India, from 2016-2018

Human metapneumovirus (hMPV) has emerged as a frequent cause of acute respiratory infections (ARI) among young children. The prevalence and genetic diversity of hMPV circulating in Chennai, Southern India, has not been studied yet. Hence, this study was aimed to investigate the prevalence, co-infection with other respiratory viruses like HRSV A and B, influenza A and B, hRV and HPIV 1-4 viruses, socio-demographic associations, and genotypes of hMPV among children in Chennai. A total of 350 nasal swab specimens were collected from children with ARI during April 2016 to August 2018 and tested for hMPV by real time PCR method. In this study, hMPV was detected in 4% (14/350) of the samples. One hMPV positive sample was found to be co-infected with influenza B virus. The mean and median ages of the children with hMPV infection were 61.5 months (5.1 years) and 83 months (6.9 years), respectively. Phylogenetic analysis of the partial F gene revealed the presence of A2c subcluster among the study strains as well as with B1 and B2 lineages. The prevalence data obtained in this study is important in evaluating the role of hMPV in childhood ARI and emphasizes the importance of routine viral diagnosis in hospitals. To the best of our knowledge, this is the first study to report the prevalence, seasonality, and genetic diversity of hMPV in Chennai as well as the first study to report A2c subcluster of hMPV among children in India.

Molecular typing and epidemiologic profiles of human metapneumovirus infection among children with severe acute respiratory infection in Huzhou, China

Background

Human metapneumovirus (hMPV) is one of the important pathogens in infant respiratory tract infection. However, the molecular epidemiology of hMPV among children < 14 years of age hospitalized with severe acute respiratory infection (SARI) is unclear. We investigated the hMPV infection status and genotypes of children hospitalized with SARI from January 2016 to December 2020 in Huzhou, China.

Methods

A nasopharyngeal flocked swab, nasal wash, or nasopharyngeal swab/or opharyngeal swab combination sample was collected from children with SARI in Huzhou from January 2016 to December 2020. Quantitative reverse transcription-polymerase chain reaction was performed to detect hMPV RNA. The hMPV F gene was amplified and sequenced, followed by analysis using MEGA software (ver. 7.0). Epidemiological data were analyzed using Microsoft Excel 2010 and SPSS (ver. 22.0) software.

Results

A total of 1133 children with SARI were recruited from 2016 to 2020. Among them, 56 (4.94%) were positive for hMPV-RNA. Children < 5 years of age accounted for 85.71% of the positive cases. The hMPV incidence was high in spring and winter, especially in December and January to March. Phylogenetic analysis of the F-gene sequences of 28 hMPV strains showed that the A1, B1, and B2 genotypes were prevalent in Huzhou, and the dominant hMPV genotype varied according to surveillance year.

Conclusions

HMPV is an important respiratory pathogen in children in Huzhou, with a high incidence in winter and spring in children < 5 years of age. In this study, genotypes A1, B1, and B2 were the most prevalent.

Avian Cell Line DuckCelt®-T17 Is an Efficient Production System for Live-Attenuated Human Metapneumovirus Vaccine Candidate Metavac®

The development of a live-attenuated vaccine (LAV) for the prevention of human metapneumovirus (HMPV) infection is often hampered by the lack of highly efficient and scalable cell-based production systems that support eventual global vaccine production. Avian cell lines cultivated in suspension compete with traditional cell platforms used for viral vaccine manufacture. We investigated whether the DuckCelt^®-T17 avian cell line (Vaxxel), previously described as an efficient production system for several influenza strains, could also be used to produce a new HMPV LAV candidate (Metavac^®, SH gene-deleted A1/C-85473 HMPV). To that end, we characterized the operational parameters of MOI, cell density, and trypsin addition to achieve the optimal production of Metavac^®, and demonstrated that the DuckCelt^®-T17 cell line is permissive and well-adapted to the production of the wild-type A1/C-85473 HMPV and the Metavac^® vaccine candidate. Moreover, our results confirmed that the LAV candidate produced in DuckCelt^®-T17 cells conserves its advantageous replication properties in LLC-MK2 and 3D-reconstituted human airway epithelium models, and its capacity to induce efficient neutralizing antibodies in a BALB/c mouse model. Our results suggest that the DuckCelt^®-T17 avian cell line is a very promising platform for the scalable in-suspension serum-free production of the HMPV-based LAV candidate Metavac^®.

Structure, Immunogenicity, and Conformation-Dependent Receptor Binding of the Postfusion Human Metapneumovirus F Protein

Human metapneumovirus (hMPV) is an important cause of acute viral respiratory infection. As the only target of neutralizing antibodies, the hMPV fusion (F) protein has been a major focus for vaccine development and targeting by drugs and monoclonal antibodies (MAbs). While X-ray structures of trimeric prefusion and postfusion hMPV F proteins from genotype A, and monomeric prefusion hMPV F protein from genotype B have been determined, structural data for the postfusion conformation for genotype B is lacking. We determined the crystal structure of this protein and compared the structural differences of postfusion hMPV F between hMPV A and B genotypes. We also assessed the receptor binding properties of the hMPV F protein to heparin and heparan sulfate (HS). A library of HS oligomers was used to verify the HS binding activity of hMPV F, and several compounds showed binding to predominantly prefusion hMPV F, but had limited binding to postfusion hMPV F. Furthermore, MAbs to antigenic sites III and the 66-87 intratrimeric epitope block heparin binding. In addition, we evaluated the efficacy of postfusion hMPV B2 F protein as a vaccine candidate in BALB/c mice. Mice immunized with hMPV B2 postfusion F protein showed a balanced Th1/Th2 immune response and generated neutralizing antibodies against both subgroup A2 and B2 hMPV strains, which protected the mice from hMPV challenge. Antibody competition analysis revealed the antibodies generated by immunization target two known antigenic sites (III and IV) on the hMPV F protein. Overall, this study provides new characteristics of the hMPV F protein, which may be informative for vaccine and therapy development. IMPORTANCE Human metapneumovirus (hMPV) is an important cause of viral respiratory disease. In this paper, we report the X-ray crystal structure of the hMPV fusion (F) protein in the postfusion conformation from genotype B. We also assessed binding of the hMPV F protein to heparin and heparan sulfate, a previously reported receptor for the hMPV F protein. Furthermore, we determined the immunogenicity and protective efficacy of postfusion hMPV B2 F protein, which is the first study using a homogenous conformation of the protein. Antibodies generated in response to vaccination give a balanced Th1/Th2 response and target two previously discovered neutralizing epitopes.

The Prevalence and Genetic Characterization of Human Metapneumovirus in Bulgaria, 2016-2019

INTRODUCTION

We investigated the prevalence of human metapneumovirus (hMPV) among patients with acute respiratory infections in Bulgaria, and performed genetic characterization of the F gene of these strains.

METHODS

Nasopharyngeal swabs collected from patients of a range of ages were tested by using real-time PCR for 12 respiratory viruses. The F gene was sequenced, and phylogenetic and amino acid analyses of the F gene/protein were performed.

RESULTS

A total of 1,842 patients were examined during a 3-year period; 1,229 patients (66.7%) were positive for at least one respiratory virus. hMPV was identified in 83 (4.5%) patient samples. Eleven (13%) of hMPV-positive patients were coinfected with another respiratory virus. The hMPV incidence rate in the 2016/2017, 2017/2018, and 2018/2019 winter seasons was 5.4, 5.4, and 3.1%, respectively. hMPV was mainly detected in specimens collected between January and May (89.2% of cases). The incidence of hMPV infection was highest (5.1%) among the youngest age-group (0-4 years), where hMPV was a causative agent in 8.1 and 4.8% of bronchiolitis and pneumonia cases, respectively. Among the patients aged ≥5 years, hMPV was detected in 2.2 and 3.2% of cases of pneumonia and central nervous system infections, respectively. Phylogenetic analysis of the F gene showed that the sequenced hMPV strains belonged to the A2b, B1, and B2 genotypes. Numerous amino acid substitutions were identified compared with the NL00/1 prototype strain.

CONCLUSION

This study revealed the significant role of hMPV as a causative agent of serious respiratory illnesses in early childhood, and also demonstrated year-to-year changes in hMPV prevalence and genetic diversity in circulating strains.

Emerging Human Metapneumovirus Gene Duplication Variants in Patients with Severe Acute Respiratory Infection, China, 2017-2019

We detected human metapneumovirus (HMPV) in 72 (7.1%) of 1,021 patients hospitalized with severe acute respiratory infection in Luohe, China, during 2017–2019. We detected HMPV most frequently in young children and less often in adults. HMPV genotype A2c variants 111 nt and 180 nt duplications predominated, demonstrating their continuing geographic spread.

Whole genome sequencing of human metapneumoviruses from clinical specimens using MinION nanopore technology

Human metapneumovirus (HMPV), a member of the Pneumoviridae family, is a causative agent of respiratory illness in young children, the elderly, and immunocompromised individuals. Globally, viruses belonging to two main genetic lineages circulate, A and B, which are further divided into four genetic sublineages (A1, A2, B1, B2). Classical genotyping of HMPV is based on the sequence of the fusion (F) and attachment (G) glycoprotein genes, which are under direct antibody-mediated immune pressure. Whole genome sequencing provides more information than sequencing of subgenomic fragments and is therefore a powerful tool for studying virus evolution and disease epidemiology and for identifying transmission events and nosocomial outbreaks. Here, we report a robust method to obtain whole genome sequences for HMPV using MinION Nanopore technology. This assay is able to generate HMPV whole genome sequences from clinical specimens with good coverage of the highly variable G gene and is equally sensitive for strains of all four genetic HMPV sublineages. This method can be used for studying HMPV genetics, epidemiology, and evolutionary dynamics.

Comparative analysis of spatial-temporal patterns of human metapneumovirus and respiratory syncytial virus in Africa using genetic data, 2011-2014

BACKGROUND

Human metapneumovirus (HMPV) and respiratory syncytial virus (RSV) are leading causes of viral severe acute respiratory illnesses in childhood. Both the two viruses belong to the Pneumoviridae family and show overlapping clinical, epidemiological and transmission features. However, it is unknown whether these two viruses have similar geographic spread patterns which may inform designing and evaluating their epidemic control measures.

METHODS

We conducted comparative phylogenetic and phylogeographic analyses to explore the spatial-temporal patterns of HMPV and RSV across Africa using 232 HMPV and 842 RSV attachment (G) glycoprotein gene sequences obtained from 5 countries (The Gambia, Zambia, Mali, South Africa, and Kenya) between August 2011 and January 2014.

RESULTS

Phylogeographic analyses found frequently similar patterns of spread of RSV and HMPV. Viral sequences commonly clustered by region, i.e., West Africa (Mali, Gambia), East Africa (Kenya) and Southern Africa (Zambia, South Africa), and similar genotype dominance patterns were observed between neighbouring countries. Both HMPV and RSV country epidemics were characterized by co-circulation of multiple genotypes. Sequences from different African sub-regions (East, West and Southern Africa) fell into separate clusters interspersed with sequences from other countries globally.

CONCLUSION

The spatial clustering patterns of viral sequences and genotype dominance patterns observed in our analysis suggests strong regional links and predominant local transmission. The geographical clustering further suggests independent introduction of HMPV and RSV variants in Africa from the global pool, and local regional diversification.

Human Metapneumovirus Infection and Genotyping of Infants in Rural Nepal

BACKGROUND

Acute respiratory tract infections are a serious clinical burden in infants; human metapneumovirus (HMPV) is an important etiological agent. We investigated genotypic variation and molecular epidemiological patterns among infants infected with HMPV in Sarlahi, Nepal, to better characterize infection in a rural, low-resource setting.

METHODS

Between May 2011 and April 2014, mid-nasal swabs were collected from 3528 infants who developed respiratory symptoms during a longitudinal maternal influenza vaccine study. Sequencing glycoprotein genes permitted genotyping and analyses among subtypes.

RESULTS

HMPV was detected by reverse-transcriptase polymerase chain reaction (RT-PCR) in 187 (5%) infants, with seasonality observed during fall and winter months. Phylogenetic investigation of complete and partial coding sequences for the F and G genes, respectively, revealed that 3 genotypes were circulating: A2, B1, and B2. HMPV-B was most frequently detected with a single type predominating each season. Both HMPV genotypes exhibited comparable median viral loads. Clinically significant differences between genotypes were limited to increased cough duration and general respiratory symptoms for type B.

CONCLUSIONS

In rural Nepal, multiple HMPV genotypes circulate simultaneously with an alternating predominance of a single genotype and definitive seasonality. No difference in viral load was detected by genotype and symptom severity was not correlated with RT-PCR cycle threshold or genotype.

Host Components That Modulate the Disease Caused by hMPV

Human metapneumovirus (hMPV) is one of the main pathogens responsible for acute respiratory infections in children up to 5 years of age, contributing substantially to health burden. The worldwide economic and social impact of this virus is significant and must be addressed. The structural components of hMPV (either proteins or genetic material) can be detected by several receptors expressed by host cells through the engagement of pattern recognition receptors. The recognition of the structural components of hMPV can promote the signaling of the immune response to clear the infection, leading to the activation of several pathways, such as those related to the interferon response. Even so, several intrinsic factors are capable of modulating the immune response or directly inhibiting the replication of hMPV. This article will discuss the current knowledge regarding the innate and adaptive immune response during hMPV infections. Accordingly, the host intrinsic components capable of modulating the immune response and the elements capable of restricting viral replication during hMPV infections will be examined.

Epidemiology and genotypic diversity of human metapneumovirus in paediatric patients with acute respiratory infection in Beijing, China

BACKGROUND

Acute respiratory tract infections (ARTIs) causes high amounts of morbidity and mortality worldwide every year. Human metapneumovirus (HMPV) is a major pathogen of ARTIs in children. In this study, we aimed to investigate the epidemiology and genotypic diversity of HMPV in children hospitalized with ARTIs in Beijing, China.

METHODS

Hospitalized children aged < 14 years with ARTIs were enrolled from April 2017 to March 2018; nasopharyngeal aspirates were collected and subjected to real-time polymerase chain reaction tests for HMPV. HMPV-positive samples were genotyped based on a partial N gene. Whole genome sequences were determined for samples with high viral loads.

RESULTS

4.08% (52/1276) enrolled paediatric patients were identified as having HMPV infection. The epidemic season is winter and early spring, children aged ≤ 4 years were more susceptible to HMPV infection (47/52, 90.38%). The co-infection rate were 36.54% (19/52), the most common co-infected virus were influenza and respiratory syncytial virus. The main diagnoses of HMPV infection were pneumonia (29/52, 55.77%) and bronchitis (23/52, 44.23%), while the main clinical manifestations were cough, fever, rhinorrhoea, and sneeze. Among 48 HMPV-positive specimens, A2b (19/48, 39.58%) and B1 (26/48, 54.17%) were the main epidemic subtypes. Patients with HMPV genotype A infection had a higher viral load compared to genotype B patients (6.07 vs. 5.37 log₁₀ RNA copies/ml). Five complete sequences of HMPV were obtained. This is the first report of a whole genome sequence of HMPV-B1 isolated in China.

CONCLUSIONS

HMPV is an important respiratory pathogen in paediatric patients. Cases of HMPV infection could burden hospitals in the epidemic season. HMPV viral loads and genotypes have no correlation with co-infection or clinical characteristics.

Human Metapneumovirus: Epidemiology and genotype diversity in children and adult patients with respiratory infection in Córdoba, Argentina

Human Metapneumovirus (hMPV) is responsible for acute respiratory infections in humans, with clinical and epidemiological relevance in pediatric, elderly, and immunocompromised populations. These features are largely unknown in Córdoba, Argentina and in adults in general. Hence, our goal was to broadly characterize hMPV infection in patients of all ages hospitalized with acute respiratory infections in Córdoba, Argentina, including epidemiology, clinical features and genetic diversity. Nasopharyngeal secretions were obtained from 795 patients during 2011-2013, 621 patients were 0-25 years old and 174 were 26-85 years old. HMPV was assayed by RT-PCR and other respiratory viruses by indirect immunofluorescence. Local strains were identified by sequence analysis. Human Metapneumovirus was detected in 20.3% (161/795) patients, 13.1% as single infections and 7.2% in co-infections, more frequently with Respiratory Syncytial Virus. HMPV circulated during late winter and spring in all age patients, but mainly in children under 4 years old in 71.4% (115/161) and adults between 26 and 59 years old in 12.4% (20/161). The most prevalent diagnosis was mild acute respiratory infection in 59.6% (96/161) and bronchiolitis in 9.3% (15/161). Local strains were clustered within A2 subtype; they presented 73-100% identities among them, showing a high degree of homology compared to isolations from neighboring countries. We demonstrate that hMPV circulated among all age patients with respiratory infection during 2011-2013 in Córdoba, contributing to the understanding of this virus, its diagnosis and patient handling in local health-care centers.

Antibody recognition of the Pneumovirus fusion protein trimer interface

Human metapneumovirus (hMPV) is a leading cause of viral respiratory infection in children, and can cause severe lower respiratory tract infection in infants, the elderly, and immunocompromised patients. However, there remain no licensed vaccines or specific treatments for hMPV infection. Although the hMPV fusion (F) protein is the sole target of neutralizing antibodies, the immunological properties of hMPV F remain poorly understood. To further define the humoral immune response to the hMPV F protein, we isolated two new human monoclonal antibodies (mAbs), MPV458 and MPV465. Both mAbs are neutralizing in vitro and were determined to target a unique antigenic site using competitive biolayer interferometry. We determined both MPV458 and MPV465 have higher affinity for monomeric hMPV F than trimeric hMPV F. MPV458 was co-crystallized with hMPV F, and the mAb primarily interacts with an alpha helix on the F2 region of the hMPV F protein. Surprisingly, the major epitope for MPV458 lies within the trimeric interface of the hMPV F protein, suggesting significant breathing of the hMPV F protein must occur for host immune recognition of the novel epitope. In addition, significant glycan interactions were observed with a somatically mutated light chain framework residue. The data presented identifies a novel epitope on the hMPV F protein for epitope-based vaccine design, and illustrates a new mechanism for human antibody neutralization of viral glycoproteins.

Recent Molecular Evolution of Human Metapneumovirus (HMPV): Subdivision of HMPV A2b Strains

Human metapneumovirus (HMPV) is a major etiological agent of acute respiratory infections in humans. HMPV has been circulating worldwide for more than six decades and is currently divided into five agreed-upon subtypes: A1, A2a, A2b, B1, and B2. Recently, the novel HMPV subtypes A2c, A2b1, and A2b2 have been proposed. However, the phylogenetic and evolutionary relationships between these recently proposed HMPV subtypes are unclear. Here, we report a genome-wide phylogenetic and evolutionary analysis of 161 HMPV strains, including unique HMPV subtype A2b strains with a 180- or 111-nucleotide duplication in the G gene (nt-dup). Our data demonstrate that the HMPV A2b subtype contains two distinct subtypes, A2b1 and A2b2, and that the HMPV subtypes A2c and A2b2 may be different names for the same subtype. HMPV A2b strains with a nt-dup also belong to subtype A2b2. Molecular evolutionary analyses indicate that subtypes A2b1 and A2b2 diverged from subtype A2b around a decade after the subtype A2 was divided into the subtypes A2a and A2b. These data support the A2b1 and A2b2 subtypes proposed in 2012 and are essential for the unified classification of HMPV subtype A2 strains, which is important for future HMPV surveillance and epidemiological studies.

Phylogenetic analysis and circulation pattern of human metapneumovirus strains in children with acute respiratory infection in Iran, 2014–2015

Aim: The aim of the present study was to investigate the prevalence and genetic variation of the human metapneumovirus (HMPV) G gene in children less than 8 years old with acute respiratory tract infections in Iran during 2014–2015. Materials & methods: To this end, 110 nasal swabs were tested for HMPV F gene. All positive samples were tested for the full length of HMPV G gene, then sequenced and analyzed for phylogenetic grouping. Results: Six (5.45%) out of 110 samples were positive for HMPV gene. Our HMPV sequences clustered into two main clusters: A2b (five isolates) and B1 (one isolate). The dN/dS ratio showed the presence of negative selective pressure. Conclusion: A2b was the predominant genotype during the study period in southwest of Iran.

Cell-Mediated Responses to Human Metapneumovirus Infection

Viruses are the most common cause of acute respiratory tract infections (ARTI). Human metapneumovirus (hMPV) frequently causes viral pneumonia which can become life-threatening if the virus spreads to the lungs. Even though hMPV was only isolated in 2001, this negative-stranded RNA virus has probably been circulating in the human population for many decades. Interestingly, almost all adults have serologic evidence of hMPV infection. A well-established host immune response is evoked when hMPV infection occurs. However, the virus has evolved to circumvent and even exploit the host immune response. Further, infection with hMPV induces a weak memory response, and re-infections during life are common. In this review, we provide a comprehensive overview of the different cell types involved in the immune response in order to better understand the immunopathology induced by hMPV. Such knowledge may contribute to the development of vaccines and therapeutics directed against hMPV.

Cell-Mediated Responses to Human Metapneumovirus Infection

Viruses are the most common cause of acute respiratory tract infections (ARTI). Human metapneumovirus (hMPV) frequently causes viral pneumonia which can become life-threatening if the virus spreads to the lungs. Even though hMPV was only isolated in 2001, this negative-stranded RNA virus has probably been circulating in the human population for many decades. Interestingly, almost all adults have serologic evidence of hMPV infection. A well-established host immune response is evoked when hMPV infection occurs. However, the virus has evolved to circumvent and even exploit the host immune response. Further, infection with hMPV induces a weak memory response, and re-infections during life are common. In this review, we provide a comprehensive overview of the different cell types involved in the immune response in order to better understand the immunopathology induced by hMPV. Such knowledge may contribute to the development of vaccines and therapeutics directed against hMPV.

Cell-Mediated Responses to Human Metapneumovirus Infection

Viruses are the most common cause of acute respiratory tract infections (ARTI). Human metapneumovirus (hMPV) frequently causes viral pneumonia which can become life-threatening if the virus spreads to the lungs. Even though hMPV was only isolated in 2001, this negative-stranded RNA virus has probably been circulating in the human population for many decades. Interestingly, almost all adults have serologic evidence of hMPV infection. A well-established host immune response is evoked when hMPV infection occurs. However, the virus has evolved to circumvent and even exploit the host immune response. Further, infection with hMPV induces a weak memory response, and re-infections during life are common. In this review, we provide a comprehensive overview of the different cell types involved in the immune response in order to better understand the immunopathology induced by hMPV. Such knowledge may contribute to the development of vaccines and therapeutics directed against hMPV.

Phylogenetic variability of Human Metapneumovirus in patients with acute respiratory infections in Cameroon, 2011-2014

BACKGROUND

Identified in 2001, Human Metapneumovirus (HMPV) is a Pneumovirus associated with acute lower and upper respiratory infections in all age groups and especially in newborns, elderly and immunocompromised subjects. Data are still limited in sub-Saharan African countries genetic characterization of this respiratory virus. This study reports the genetic variability of HMPV strains in Cameroonian children for 3 consecutive epidemic seasons (September 2011-October 2014).

METHODS

A prospective surveillance was conducted to identify inpatient and outpatient children less than 15 years with respiratory symptoms ≤5 days. The nasopharyngeal samples were tested for HMPV using a multiplex polymerase chain reaction. Viral distribution and demographic data were analyzed statistically. Positive samples for HMPV were amplified by semi-nested polymerize chain reaction and then partially sequenced at the G gene. Phylogenetic analyzes were performed on the partial nucleotide and protein sequences of the G gene.

RESULTS

From September 2011 to October 2014, 822 children under 15 years were enrolled in the study. HMPV was identified in each of 3.9% (32/822) of children. HMPV were detected throughout the year. HMPV-A (73.3%; 11/15) was predominant compared to HMPV-B (26.7; 4/15). Cameroonian HMPV strains are grouped among the members of genotype A2b (for HMPV-A), B1 and B2 (for HMPV-B).

CONCLUSION

This study suggests that about 4% of ARI recorded in children in Cameroon are caused by HMPV. The present study is also the first report on the genetic variability of the G gene of HMPV strains in the region. Although this work partially fills gaps for some information, additional studies are required to clarify the molecular epidemiology and evolutionary pattern of HMPV in sub-Saharan Africa in general and more particularly in Cameroon.

Engineering of Live Chimeric Vaccines against Human Metapneumovirus

Human metapneumovirus (HMPV) is an important human pathogen that, along with respiratory syncytial virus (RSV), is a major cause of respiratory tract infections in young infants. Development of an effective vaccine against Pneumoviruses has proven to be particularly difficult; despite over 50 years of research in this field, no vaccine against HMPV or RSV is currently available. Recombinant chimeric viruses expressing antigens of other viruses can be generated by reverse genetics and used for simultaneous immunization against more than one pathogen. This approach can result in the development of promising vaccine candidates against HMPV, and several studies have indeed validated viral vectors expressing HMPV antigens. In this review, we summarize current efforts in generating recombinant chimeric vaccines against HMPV, and we discuss their potential optimization based on the correspondence with RSV studies.