The two major human metapneumovirus genetic lineages are highly related antigenically, and the fusion (F) protein is a major contributor to this antigenic relatedness

Novel insights into the host cell glycan binding profile of human metapneumovirus

Numerous viruses have been found to exploit glycoconjugates expressed on human cells as their initial attachment factor for viral entry and infection. The virus-cell glycointeractome, when characterized, may serve as a template for antiviral drug design. Heparan sulfate proteoglycans extensively decorate the human cell surface and were previously described as a primary receptor for human metapneumovirus (HMPV). After respiratory syncytial virus, HMPV is the second most prevalent respiratory pathogen causing respiratory tract infection in young children. To date, there is neither vaccine nor drug available to prevent or treat HMPV infection. Using a multidisciplinary approach, we report for the first time the glycointeractome of the HMPV fusion (F) protein, a viral surface glycoprotein that is essential for target-cell recognition, attachment, and entry. Our glycan microarray and surface plasmon resonance results suggest that Galβ1-3/4GlcNAc moieties that may be sialylated or fucosylated are readily recognized by HMPV F. The bound motifs are highly similar to the N-linked and O-linked glycans primarily expressed on the human lung epithelium. We demonstrate that the identified glycans have the potential to compete with the cellular receptors used for HMPV entry and consequently block HMPV infection. We found that lacto-N-neotetraose demonstrated the strongest HMPV binding inhibition in a cell infection assay. Our current findings offer an encouraging and novel avenue for the design of anti-HMPV drug candidates using oligosaccharide templates.IMPORTANCEAll cells are decorated with a dense coat of sugars that makes a sugar code. Many respiratory viruses exploit this sugar code by binding to these sugars to cause infection. Human metapneumovirus is a leading cause for acute respiratory tract infections. Despite its medical importance, there is no vaccine or antiviral drug available to prevent or treat human metapneumovirus infection. This study investigates how human metapneumovirus binds to sugars in order to more efficiently infect the human host. We found that human metapneumovirus binds to a diverse range of sugars and demonstrated that these sugars can ultimately block viral infection. Understanding how viruses can take advantage of the sugar code on our cells could identify new intervention and treatment strategies to combat viral disease.

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.

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.

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.

Cross-protective antibodies against common endemic respiratory viruses

Respiratory syncytial virus (RSV), human metapneumovirus (HMPV), and human parainfluenza virus types one (HPIV1) and three (HPIV3) can cause severe disease and death in immunocompromised patients, the elderly, and those with underlying lung disease. A protective monoclonal antibody exists for RSV, but clinical use is limited to high-risk infant populations. Hence, therapeutic options for these viruses in vulnerable patient populations are currently limited. Here, we present the discovery, in vitro characterization, and in vivo efficacy testing of two cross-neutralizing monoclonal antibodies, one targeting both HPIV3 and HPIV1 and the other targeting both RSV and HMPV. The 3 × 1 antibody is capable of targeting multiple parainfluenza viruses; the MxR antibody shares features with other previously reported monoclonal antibodies that are capable of neutralizing both RSV and HMPV. We obtained structures using cryo-electron microscopy of these antibodies in complex with their antigens at 3.62 Å resolution for 3 × 1 bound to HPIV3 and at 2.24 Å for MxR bound to RSV, providing a structural basis for in vitro binding and neutralization. Together, a cocktail of 3 × 1 and MxR could have clinical utility in providing broad protection against four of the respiratory viruses that cause significant morbidity and mortality in at-risk individuals.

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.

Prospects of and Barriers to the Development of Epitope-Based Vaccines against Human Metapneumovirus

Human metapneumovirus (HMPV) is a major cause of respiratory illnesses in children, the elderly and immunocompromised patients. Although this pathogen was only discovered in 2001, an enormous amount of research has been conducted in order to develop safe and effective vaccines to prevent people from contracting the disease. In this review, we summarize current knowledge about the most promising experimental B- and T-cell epitopes of human metapneumovirus for the rational design of HMPV vaccines using vector delivery systems, paying special attention to the conservation of these epitopes among different lineages/genotypes of HMPV. The prospects of the successful development of an epitope-based HMPV vaccine are discussed in the context of recent findings regarding HMPV’s ability to modulate host immunity. In particular, we discuss the lack of data on experimental human CD4 T-cell epitopes for HMPV despite the role of CD4 lymphocytes in both the induction of higher neutralizing antibody titers and the establishment of CD8 memory T-cell responses. We conclude that current research should be focused on searching for human CD4 T-cell epitopes of HMPV that can help us to design a safe and cross-protective epitope-based HMPV vaccine.

Metapneumovirus humano: epidemiología y posibles tratamientos profilácticos

In 2001 in the Netherlands, Human metapneumovirus (hMPV) was identified as a “new” etiologic agent causing acute respiratory infections in children younger than 5 years old; however, it has also been isolated in the elderly and immunocompromised people. This virus is considered the second etiological agent in acute diseases of the respiratory tract. Currently, the estimated cost of IRAs in our country is of 9,000USD per inpatient. hMPV is a member of the genus Metapneumovirus, family Pneumoviridae, and it belongs to the order Mononegavirales that is part of the negative single-stranded ribonucleic acid (RNA) virus, consisting of eight genes ordered: 3’-N-P-M-FM2-SH-G-L-5 ‘, and which encodes for 9 proteins. Of these proteins, the F fusion glycoprotein is highly conserved in the genus Metapneumovirus, and is the major antigenic determinant, and because an approved vaccine doesn’t exist, it has been used as a candidate epitope for the design of a vaccine that confers host immunity or as a therapeutic target in the creation of antiviral peptides that inhibit the fusion of the virus to its target cell and to avoid infection in subjects at high risk of contagion since there is currently none accepted by COFEPRIS as a prophylactic treatment against hMPV. Key words: hMPV; respiratory infections; epitopes; protein F;vaccines.

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.

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.

Human metapneumovirus prevalence and patterns of subgroup persistence identified through surveillance of pediatric pneumonia hospital admissions in coastal Kenya, 2007-2016

BACKGROUND

Human metapneumovirus (HMPV) is an important respiratory pathogen that causes seasonal epidemics of acute respiratory illness and contributes significantly to childhood pneumonia. Current knowledge and understanding on its patterns of spread, prevalence and persistence in communities in low resource settings is limited.

METHODS

We present findings of a molecular-epidemiological analysis of nasal samples from children < 5 years of age admitted with syndromic pneumonia between 2007 and 2016 to Kilifi County Hospital, coastal Kenya. HMPV infection was detected using real-time RT-PCR and positives sequenced in the fusion (F) and attachment (G) genes followed by phylogenetic analysis. The association between disease severity and HMPV subgroup was assessed using Fisher's exact test.

RESULTS

Over 10 years, 274/6756 (4.1%) samples screened were HMPV positive. Annual prevalence fluctuated between years ranging 1.2 to 8.7% and lowest in the recent years (2014-2016). HMPV detections were most frequent between October of one year to April of the following year. Genotyping was successful for 205/274 (74.8%) positives revealing clades A2b (41.0%) and A2c (10.7%), and subgroups B1 (23.4%) and B2 (24.9%). The dominance patterns were: clade A2b between 2007 and 11, subgroup B1 between 2012 and 14, and clade A2c in more recent epidemics. Subgroup B2 viruses were present in all the years. Temporal phylogenetic clustering within the subgroups for both local and global sequence data was seen. Subgroups occurring in each epidemic season were comprised of multiple variants. Pneumonia severity did not vary by subgroup (p = 0.264). In both the F and G gene, the sequenced regions were found to be predominantly under purifying selection.

CONCLUSION

Subgroup patterns from this rural African setting temporally map with global strain distribution, suggesting a well-mixed global virus transmission pool of HMPV. Persistence in the local community is characterized by repeated introductions of HMPV variants from the global pool. The factors underlying the declining prevalence of HMPV in this population should be investigated.

Phylogenetic evidence of a novel lineage of canine pneumovirus and a naturally recombinant strain isolated from dogs with respiratory illness in Thailand

BACKGROUND

Canine pneumovirus (CPV) is a pathogen that causes respiratory disease in dogs, and recent outbreaks in shelters in America and Europe have been reported. However, based on published data and documents, the identification of CPV and its variant in clinically symptomatic individual dogs in Thailand through Asia is limited. Therefore, the aims of this study were to determine the emergence of CPV and to consequently establish the genetic characterization and phylogenetic analysis of the CPV strains from 209 dogs showing respiratory distress in Thailand.

RESULTS

This study identified and described the full-length CPV genome from three strains, designated herein as CPV_CP13 TH/2015, CPV_CP82 TH/2016 and CPV_SR1 TH/2016, that were isolated from six dogs out of 209 dogs (2.9%) with respiratory illness in Thailand. Phylogenetic analysis suggested that these three Thai CPV strains (CPV TH strains) belong to the CPV subgroup A and form a novel lineage; proposed as the Asian prototype. Specific mutations in the deduced amino acids of these CPV TH strains were found in the G/glycoprotein sequence, suggesting potential substitution sites for subtype classification. Results of intragenic recombination analysis revealed that CPV_CP82 TH/2016 is a recombinant strain, where the recombination event occurred in the L gene with the Italian prototype CPV Bari/100-12 as the putative major parent. Selective pressure analysis demonstrated that the majority of the nucleotides in the G/glycoprotein were under purifying selection with evidence of positive selection sites.

CONCLUSIONS

This collective information on the CPV TH strains is the first evidence of CPV emergence with genetic characterization in Thailand and as first report in Asia, where homologous recombination acts as a potential force driving the genetic diversity and shaping the evolution of canine pneumovirus.

Simultaneous outbreaks of respiratory disease in wild chimpanzees caused by distinct viruses of human origin

Respiratory viruses of human origin infect wild apes across Africa, sometimes lethally. Here we report simultaneous outbreaks of two distinct human respiratory viruses, human metapneumovirus (MPV; Pneumoviridae: Metapneumovirus) and human respirovirus 3 (HRV3; Paramyxoviridae; Respirovirus, formerly known as parainfluenza virus 3), in two chimpanzee (Pan troglodytes schweinfurthii) communities in the same forest in Uganda in December 2016 and January 2017. The viruses were absent before the outbreaks, but each was present in ill chimpanzees from one community during the outbreak period. Clinical signs and gross pathologic changes in affected chimpanzees closely mirrored symptoms and pathology commonly observed in humans for each virus. Epidemiologic modelling showed that MPV and HRV3 were similarly transmissible (R₀ of 1.27 and 1.48, respectively), but MPV caused 12.2% mortality mainly in infants and older chimpanzees, whereas HRV3 caused no direct mortality. These results are consistent with the higher virulence of MPV than HRV3 in humans, although both MPV and HRV3 cause a significant global disease burden. Both viruses clustered phylogenetically within groups of known human variants, with MPV closely related to a lethal 2009 variant from mountain gorillas (Gorilla beringei beringei), suggesting two independent and simultaneous reverse zoonotic origins, either directly from humans or via intermediary hosts. These findings expand our knowledge of human origin viruses threatening wild chimpanzees and suggest that such viruses might be differentiated by their comparative epidemiological dynamics and pathogenicity in wild apes. Our results also caution against assuming common causation in coincident outbreaks.

Genetic characterization of human metapneumovirus identified through community and facility-based surveillance of infants in Dhaka, Bangladesh

BACKGROUND

Acute respiratory infection (ARI) is a leading cause of morbidity and mortality in children in low and middle-income countries. Human metapneumovirus (hMPV) is one of the most common viral etiological agents for ARIs in children.

OBJECTIVES

In this study, we explored the genotypic diversity and the epidemiology of hMPV among infants in Dhaka, Bangladesh.

STUDY DESIGN

Between December 2014 and August 2016, a total of 3810 mid-turbinate nasal swab samples were collected from infants (0 to 6 months of age) who met clinical ARI criteria, as a part of a prospective ARI cohort study. hMPV was detected using polymerase chain reaction, and genotyped by sequencing and phylogenetic analysis.

RESULTS

hMPV was identified in 206 (5.4%) nasal swab specimens. One-tenth of the hMPV-positive swabs (n = 19) were also positive for other respiratory viruses. hMPV activity peaked in January and September in 2015; however, no seasonal pattern of hMPV infection was detected. Phylogenetic analyses of the N and F gene-fragments revealed that the hMPV strains circulating in Dhaka, Bangladesh, belonged to three genotypes: A2b, A2c, and B1. Genotype A (57%) was the predominant hMPV genotype circulating in Bangladesh during the study period.

CONCLUSION

This study describes both the epidemiology of hMPV infection and its genotypic strain diversity in Dhaka, Bangladesh.

Human metapneumovirus - what we know now

Human metapneumovirus (HMPV) is a leading cause of acute respiratory infection, particularly in children, immunocompromised patients, and the elderly. HMPV, which is closely related to avian metapneumovirus subtype C, has circulated for at least 65 years, and nearly every child will be infected with HMPV by the age of 5. However, immunity is incomplete, and re-infections occur throughout adult life. Symptoms are similar to those of other respiratory viral infections, ranging from mild (cough, rhinorrhea, and fever) to more severe (bronchiolitis and pneumonia). The preferred method for diagnosis is reverse transcription-polymerase chain reaction as HMPV is difficult to culture. Although there have been many advances made in the past 16 years since its discovery, there are still no US Food and Drug Administration-approved antivirals or vaccines available to treat HMPV. Both small animal and non-human primate models have been established for the study of HMPV. This review will focus on the epidemiology, transmission, and clinical manifestations in humans as well as the animal models of HMPV pathogenesis and host immune response.

Evidence for Human Streptococcus pneumoniae in wild and captive chimpanzees: A potential threat to wild populations

Habituation of wild great apes for tourism and research has had a significant positive effect on the conservation of these species. However, risks associated with such activities have been identified, specifically the transmission of human respiratory viruses to wild great apes, causing high morbidity and, occasionally, mortality. Here, we investigate the source of bacterial-viral co-infections in wild and captive chimpanzee communities in the course of several respiratory disease outbreaks. Molecular analyses showed that human respiratory syncytial viruses (HRSV) and human metapneumoviruses (HMPV) were involved in the etiology of the disease. In addition our analysis provide evidence for coinfection with Streptococcus (S.) pneumoniae. Characterisation of isolates from wild chimpanzees point towards a human origin of these bacteria. Transmission of these bacteria is of concern because - in contrast to HRSV and HMPV - S. pneumoniae can become part of the nasopharyngeal flora, contributing to the severity of respiratory disease progression. Furthermore these bacteria have the potential to spread to other individuals in the community and ultimately into the population. Targeted vaccination programs could be used to vaccinate habituated great apes but also human populations around great ape habitats, bringing health benefits to both humans and wild great apes.

Role of human metapneumovirus and respiratory syncytial virus in asthma exacerbations: where are we now?

Since its discovery in 2001, human metapneumovirus (hMPV) has been identified as an important cause of respiratory tract infection in young children, second only to the closely related respiratory syncytial virus (RSV). Clinical evidence suggests that hMPV is associated with acute exacerbations of asthma in both children and adults, and may play a role in initiating asthma development in children. Animal models have demonstrated that airway hyperresponsiveness (AHR) and inflammation are triggered following hMPV infection, and hMPV is able to persist in vivo by inhibiting innate immune responses and causing aberrant adaptive responses. In this review, we discuss the prevalence of hMPV infection in pediatric and adult populations and its potential role in asthma exacerbation. We also review recent advances made in animal models to determine immune responses following hMPV infection, and compare to what is known about RSV.

Modulation of Host Immunity by the Human Metapneumovirus

Globally, as a leading agent of acute respiratory tract infections in children <5 years of age and the elderly, the human metapneumovirus (HMPV) has gained considerable attention. As inferred from studies comparing vaccinated and experimentally infected mice, the acquired immune response elicited by this pathogen fails to efficiently clear the virus from the airways, which leads to an exaggerated inflammatory response and lung damage. Furthermore, after disease resolution, there is a poor development of T and B cell immunological memory, which is believed to promote reinfections and viral spread in the community. In this article, we discuss the molecular mechanisms that shape the interactions of HMPV with host tissues that lead to pulmonary pathology and to the development of adaptive immunity that fails to protect against natural infections by this virus.

Current developments and prospects on human metapneumovirus vaccines

INTRODUCTION

Human metapneumovirus (hMPV) has become one of the major pathogens causing acute respiratory infections (ARI) mainly affecting young children, immunocompromised patients, and the elderly. Currently there are no licensed vaccines against this virus. Areas covered: Since the discovery of hMPV in 2001, many groups have focused on developing vaccines against this pathogen. This review presents the outcomes and perspectives derived from preclinical studies performed in cell cultures and animals as well as the only candidate that has reached evaluation in a clinical trial. Limitations of the current vaccine candidates are discussed and perspectives for the development of plant-based vaccines are analyzed. Expert commentary: Several hMPV vaccine candidates are under development with the potential to progress into clinical trials. In parallel, the molecular farming field offers new opportunities to generate innovative vaccines that will offer several advantages in the fight against hMPV.

Metapneumovirus Infections and Respiratory Complications

Acute respiratory tract infections (ARTIs) are the most common illnesses experienced by people of all ages worldwide. In 2001, a new respiratory pathogen called human metapneumovirus (hMPV) was identified in respiratory secretions. hMPV is an RNA virus of the Paramyxoviridae family, and it has been isolated on every continent and from individuals of all ages. hMPV causes 7 to 19% of all cases of ARTIs in both hospitalized and outpatient children, and the rate of detection in adults is approximately 3%. Symptoms of hMPV infection range from a mild cold to a severe disease requiring a ventilator and cardiovascular support. The main risk factors for severe disease upon hMPV infection are the presence of a high viral load, coinfection with other agents (especially human respiratory syncytial virus), being between 0 and 5 months old or older than 65 years, and immunodeficiency. Currently, available treatments for hMPV infections are only supportive, and antiviral drugs are employed in cases of severe disease as a last resort. Ribavirin and immunoglobulins have been used in some patients, but the real efficacy of these treatments is unclear. At present, the direction of research on therapy for hMPV infection is toward the development of new approaches, and a variety of vaccination strategies are being explored and tested in animal models. However, further studies are required to define the best treatment and prevention strategies.

Human metapneumovirus in the preterm neonate: current perspectives

Premature birth (<37 weeks gestation) occurs in ~11% of all births in the US. These infants are at risk of chronic lung disease and respiratory conditions, including bronchopulmonary dysplasia. Respiratory viruses are important causes of acute respiratory illness (ARI) in preterm infants, leading to rehospitalization, increased health care burden, and long-term morbidity. Human metapneumovirus (HMPV) is a paramyxovirus discovered in 2001 that is related to respiratory syncytial virus. Epidemiologic studies show that HMPV is a leading cause of ARI in children and adults worldwide. Prematurity is a major risk factor for severe HMPV disease, requiring hospitalization. Moreover, limited data suggest that HMPV infection during infancy is associated with asthma and recurrent wheezing, which are common long-term pulmonary complication of prematurity. HMPV causes nosocomial outbreaks of ARI in hospitals and long-term care facilities, although there are few studies of the prevalence of HMPV in neonatal intensive care unit populations. HMPV is a common and important virus in premature infants, and caregivers for preterm infants should consider this virus in patients with acute respiratory symptoms.

Human Metapneumovirus

Human metapneumovirus (HMPV), a paramyxovirus identified in 2001, is a leading cause of respiratory tract infections in both children and adults. Seroprevalence studies demonstrate that the primary infection occurs before the age of 5 years, and humans are reinfected throughout life. The four subgroups of HMPV occur with year-to-year variability, and infection with one subgroup confers some serologic cross-protection. Experimental vaccines elicit a humoral response in both animal and human models and have been used to identify antigenic determinants. The main target of protective antibodies is the fusion (F) protein, although many of the remaining eight proteins are immunogenic. Monoclonal antibodies (mAbs) targeting the F protein are both protective and therapeutic in animal models. Most recently, the identification of broadly neutralizing antibodies against HMPV and respiratory syncytial virus demonstrates that common epitopes are present between the two viruses. Broadly neutralizing mAbs have significant clinical implications for prophylaxis and treatment of high-risk hosts as well as vaccine development.

Human metapneumovirus infection in chimpanzees, United States

Zoonotic disease transmission and infections are of particular concern for humans and closely related great apes. In 2009, an outbreak of human metapneumovirus infection was associated with the death of a captive chimpanzee in Chicago, Illinois, USA. Biosecurity and surveillance for this virus in captive great ape populations should be considered.

New Approaches for Immunization and Therapy against Human Metapneumovirus

Human metapneumovirus (HMPV) is a paramyxovirus discovered in 2001 in the Netherlands. Studies have identified HMPV as an important causative agent of acute respiratory disease in infants, the elderly, and immunocompromised individuals. Clinical signs of infection range from mild upper respiratory illness to more serious lower respiratory illness, including bronchiolitis and pneumonia. There are currently no licensed therapeutics or vaccines against HMPV. However, several research groups have tested vaccine candidates and monoclonal antibodies in various animal models. Several of these approaches have shown promise in animal models. This minireview summarizes the current therapies used to treat HMPV infection as well as different approaches for immunization.

Serologic cross-reactions between nucleocapsid proteins of human respiratory syncytial virus and human metapneumovirus

Human respiratory syncytial virus (hRSV) and human metapneumovirus (hMPV) share virologic and epidemiologic features and cause clinically similar respiratory illness predominantly in young children. In a previous study of acute febrile respiratory illness in Bangladesh, we tested paired serum specimens from 852 children presenting fever and cough for diagnostic increases in titers of antibody to hRSV and hMPV by enzyme immunoassay (EIA). Unexpectedly, of 93 serum pairs that showed a ≥ 4-fold increase in titers of antibody to hRSV, 24 (25.8%) showed a concurrent increase in titers of antibody to hMPV; of 91 pairs showing an increase to hMPV, 13 (14.3%) showed a concurrent increase to hRSV. We speculated that common antigens shared by these viruses explain this finding. Since the nucleocapsid (N) proteins of these viruses show the greatest sequence homology, we tested hyperimmune antisera prepared for each virus against baculovirus-expressed recombinant N (recN) proteins for potential cross-reactivity. The antisera were reciprocally reactive with both proteins. To localize common antigenic regions, we first expressed the carboxy domain of the hMPV N protein that was the most highly conserved region within the hRSV N protein. Although reciprocally reactive with antisera by Western blotting, this truncated protein did not react with hMPV IgG-positive human sera by EIA. Using 5 synthetic peptides that spanned the amino-terminal portion of the hMPV N protein, we identified a single peptide that was cross-reactive with human sera positive for either virus. Antiserum prepared for this peptide was reactive with recN proteins of both viruses, indicating that a common immunoreactive site exists in this region.

The Pneumovirinae fusion (F) protein: A common target for vaccines and antivirals

The Pneumovirinae fusion (F) protein mediates fusion of the virus and cell membrane, an essential step for entry of the viral genome in the cell cytoplasm and initiation of a new infectious cycle. Accordingly, potent inhibitors of virus infectivity have been found among antibodies and chemical compounds that target the Pneumovirinae F protein. Recent developments in structure-based vaccines have led to a deeper understanding of F protein antigenicity, unveiling new conformations and epitopes which should assist in development of efficacious vaccines. Similarly, structure-based studies of potent antiviral inhibitors have provided information about their mode of action and mechanisms of resistance. The advantages and disadvantages of the different options to battle against important pathogens, such as human respiratory syncytial virus (hRSV) and human metapneumovirus (hMPV) are summarized and critically discussed in this review.

Programmed death-1 impairs secondary effector lung CD8⁺ T cells during respiratory virus reinfection

Reinfections with respiratory viruses are common and cause significant clinical illness, yet precise mechanisms governing this susceptibility are ill defined. Lung Ag-specific CD8(+) T cells (T(CD8)) are impaired during acute viral lower respiratory infection by the inhibitory receptor programmed death-1 (PD-1). To determine whether PD-1 contributes to recurrent infection, we first established a model of reinfection by challenging B cell-deficient mice with human metapneumovirus (HMPV) several weeks after primary infection, and found that HMPV replicated to high titers in the lungs. A robust secondary effector lung TCD8 response was generated during reinfection, but these cells were more impaired and more highly expressed the inhibitory receptors PD-1, LAG-3, and 2B4 than primary T(CD8). In vitro blockade demonstrated that PD-1 was the dominant inhibitory receptor early after reinfection. In vivo therapeutic PD-1 blockade during HMPV reinfection restored lung T(CD8) effector functions (i.e., degranulation and cytokine production) and enhanced viral clearance. PD-1 also limited the protective efficacy of HMPV epitope-specific peptide vaccination and impaired lung T(CD8) during heterotypic influenza virus challenge infection. Our results indicate that PD-1 signaling may contribute to respiratory virus reinfection and evasion of vaccine-elicited immune responses. These results have important implications for the design of effective vaccines against respiratory viruses.

Structural insights into the human metapneumovirus glycoprotein ectodomain

Human metapneumovirus is a major cause of respiratory tract infections worldwide. Previous reports have shown that the viral attachment glycoprotein (G) modulates innate and adaptive immune responses, leading to incomplete immunity and promoting reinfection. Using bioinformatics analyses, static light scattering, and small-angle X-ray scattering, we show that the extracellular region of G behaves as a heavily glycosylated, intrinsically disordered polymer. We discuss potential implications of these findings for the modulation of immune responses by G.

A broadly neutralizing human monoclonal antibody exhibits in vivo efficacy against both human metapneumovirus and respiratory syncytial virus

BACKGROUND

Human metapneumovirus (HMPV) is a leading cause of acute respiratory tract infection, with significant morbidity and mortality. No licensed vaccines or therapeutic agents exist. Monoclonal antibodies (mAbs) are effective at preventing other infectious diseases and could be used against HMPV in high-risk hosts.

METHODS

In vitro assays were performed to assess the neutralizing activity and affinity kinetics of human mAb 54G10. A new mouse model was developed to assess prophylactic and therapeutic efficacy in vivo. The epitope of 54G10 was identified by generating mAb-resistant mutants (MARMs).

RESULTS

At low concentrations, 54G10 neutralized all 4 subgroups of HMPV in vitro and had subnanomolar affinity for the fusion protein. DBA/2 mice were permissive for all 4 HMPV subgroups, and 54G10 was effective both prophylactically and therapeutically against HMPV in vivo. Sequencing of HMPV MARMs identified the 54G10 epitope, which was similar to an antigenic site on respiratory syncytial virus (RSV). 54G10 also exhibited in vitro neutralizing activity and in vivo protective and therapeutic efficacy against RSV.

CONCLUSIONS

Human mAb 54G10 has broad neutralizing activity against HMPV and could have prophylactic and therapeutic utility clinically. The conserved epitope could represent a structural vaccine target for HMPV and RSV.

Viral replication and lung lesions in BALB/c mice experimentally inoculated with avian metapneumovirus subgroup C isolated from chickens

Avian metapneumovirus (aMPV) emerged as an important respiratory pathogen causing acute respiratory tract infection in avian species. Here we used a chicken aMPV subgroup C (aMPV/C) isolate to inoculate experimentally BALB/c mice and found that the aMPV/C can efficiently replicate and persist in the lungs of mice for at least 21 days with a peak viral load at day 6 postinoculation. Lung pathological changes were characterized by increased inflammatory cells. Immunochemical assay showed the presence of viral antigens in the lungs and significant upregulation of pulmonary inflammatory cytokines and chemokines including MCP-1, MIP-1α, RANTES, IL-1β, IFN-γ, and TNF-α were detected following inoculation. These results indicate for the first time that chicken aMPV/C may replicate in the lung of mice. Whether aMPV/C has potential as zoonotic pathogen, further investigation will be required.

Molecular analysis of human metapneumovirus detected in patients with lower respiratory tract infection in upper egypt

Introduction. Since 2001, when Human metapneumovirus (HMPV) was isolated in the Netherlands, the virus has been detected in several continents. Although reports have confirmed the prevalence of HMPV worldwide, data from Egypt remain limited. HMPV plays an important role in respiratory tract infections in individuals of all ages particularly in children. This study was aimed at estimating the prevalence of HMPV in patients with community-acquired lower respiratory infection in Upper Egypt and characterizing the circulating Egyptian HMPV strains for the first time. Materials and Methods. From 2005 to 2008, respiratory samples from 520 patients were analyzed for the presence of HMPV by real-time RT-PCR. Molecular and phylogenetic analyses were performed on partial fusion gene sequences of HMPV-positive patients. Results. HMPV-positive patients were detected in 2007-2008. The overall infection rate was 4%, while 57% of the patients were children. Sequence analysis demonstrated circulation of subgroup B viruses with predominance of lineage B2. Nucleotide sequence identity within lineage B1 was 98.8%–99.7% and higher than that in lineage B2 (94.3%–100%). Three new amino acid substitutions (T223N, R229K, and D280N) of lineage B2 were observed. Conclusion. HMPV is a major viral pathogen in the Egyptian population especially in children. During 2007-2008, predominantly HMPV B2 circulated in Upper Egypt.

Human Metapneumovirus

Name of Virus: Human metapneumovirus

Identification of human metapneumovirus genotypes A and B from clinical specimens by reverse transcription loop-mediated isothermal amplification

Human metapneumovirus (hMPV) has been recognized as an important pathogen for acute respiratory infections in children worldwide and classified into genotypes A and B. Reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay is a rapid diagnostic method for detecting nucleic acids with a single step under isothermal conditions in less than 1h. RT-LAMP targeting the M gene of hMPV was developed for detecting and identifying hMPV genotypes A and B. The detection limit of the genotype-specific hMPV RT-LAMP assay was 10 times greater than that of conventional reverse transcription polymerase chain reaction (RT-PCR). No cross-reactivity was found with respiratory syncytial virus, parainfluenza virus 1-3, adenovirus, human bocavirus, human rhinovirus, influenza virus A and B, human coronaviruses and enteroviruses. One hundred and fifteen clinical specimens were detected for hMPV genotypes A and B with RT-LAMP, RT-PCR and real-time SYBR PCR. Kappa coefficients showed that there was a good agreement among these three methods. Compared with RT-PCR and real-time SYBR PCR, the genotype-specific RT-LAMP showed better specificity, sensitivity and is more convenient to perform with reduced turn-around time.

A live attenuated human metapneumovirus vaccine strain provides complete protection against homologous viral infection and cross-protection against heterologous viral infection in BALB/c mice

A live attenuated vaccine candidate strain (M2) of human metapneumovirus (hMPV) was generated by removing the N-linked carbohydrate at amino acid 172 in the fusion (F) protein. Previously, replication of M2 in mouse lungs could be detected by molecular assays but not by viral titration. In the present study, the protective effects of M2 against infection by homologous or heterologous viruses were evaluated in BALB/c mice. Immunization with M2 produced a high titer of serum virus-neutralizing antibodies in BALB/c mice at 4 and 8 weeks postimmunization, with the titers against the homologous virus being higher than those against the heterologous virus. Challenges at 4 and 8 weeks postinoculation with M2 or wild-type virus led to no replication when mice were challenged with a homologous virus and extremely reduced replication when mice were challenged with a heterologous virus, as determined by the detection of viral genomic RNA copies in the lungs, as well as significantly milder pulmonary pathology. Thus, M2, with only one N-linked carbohydrate removed in the F protein, provides complete protection from homologous virus infection and substantial cross-protection from heterologous virus infection for at least 56 days after inoculation. This vaccine strain may therefore be a candidate for further preclinical study. Furthermore, this attenuating strategy (changing the glycosylation of a major viral protein) may be useful in the development of other viral vaccines.

Virus-like particle vaccine induces cross-protection against human metapneumovirus infections in mice

Human metapneumovirus (HMPV) is a paramyxovirus that causes acute respiratory-tract infections in children and adults worldwide. A safe and effective vaccine could decrease the burden of disease associated with this novel pathogen. We engineered HMPV viral-like particles (HMPV-VLPs) derived from retroviral core particles that mimic the properties of the viral surface of two HMPV viruses of either lineage A or B. These VLPs functionally display F and G HMPV surface glycoproteins. When injected in mice, HMPV-VLPs induce strong humoral immune response against both homologous and heterologous strains. Moreover, the induced neutralizing antibodies prevented mortality upon subsequent infection of the lungs with both homologous and heterologous viruses. Upon challenge, viral titers in the lungs of immunized animals were significantly reduced as compared to those of control animals. In conclusion, a HMPV-VLP vaccine that induces cross-protective immunity in mice is a promising approach to prevent HMPV infections.

Burden of human metapneumovirus infection in young children

BACKGROUND

The inpatient and outpatient burden of human metapneumovirus (HMPV) infection among young children has not been well established.

METHODS

We conducted prospective, population-based surveillance for acute respiratory illness or fever among inpatient and outpatient children less than 5 years of age in three U.S. counties from 2003 through 2009. Clinical and demographic data were obtained from parents and medical records, HMPV was detected by means of a reverse-transcriptase polymerase-chain-reaction assay, and population-based rates of hospitalization and estimated rates of outpatient visits associated with HMPV infection were determined.

RESULTS

HMPV was detected in 200 of 3490 hospitalized children (6%), 222 of 3257 children in outpatient clinics (7%), 224 of 3001 children in the emergency department (7%), and 10 of 770 asymptomatic controls (1%). Overall annual rates of hospitalization associated with HMPV infection were 1 per 1000 children less than 5 years of age, 3 per 1000 infants less than 6 months of age, and 2 per 1000 children 6 to 11 months of age. Children hospitalized with HMPV infection, as compared with those hospitalized without HMPV infection, were older and more likely to receive a diagnosis of pneumonia or asthma, to require supplemental oxygen, and to have a longer stay in the intensive care unit. The estimated annual burden of outpatient visits associated with HMPV infection was 55 clinic visits and 13 emergency department visits per 1000 children. The majority of HMPV-positive inpatient and outpatient children had no underlying medical conditions, although premature birth and asthma were more frequent among hospitalized children with HMPV infection than among those without HMPV infection.

CONCLUSIONS

HMPV infection is associated with a substantial burden of hospitalizations and outpatient visits among children throughout the first 5 years of life, especially during the first year. Most children with HMPV infection were previously healthy. (Funded by the Centers for Disease Control and Prevention and the National Institutes of Health.).

Human metapneumovirus in adults

Human metapneumovirus (HMPV) is a relative newly described virus. It was first isolated in 2001 and currently appears to be one of the most significant and common human viral infections. Retrospective serologic studies demonstrated the presence of HMPV antibodies in humans more than 50 years earlier. Although the virus was primarily known as causative agent of respiratory tract infections in children, HMPV is an important cause of respiratory infections in adults as well. Almost all children are infected by HMPV below the age of five; the repeated infections throughout life indicate transient immunity. HMPV infections usually are mild and self-limiting, but in the frail elderly and the immunocompromised patients, the clinical course can be complicated. Since culturing the virus is relatively difficult, diagnosis is mostly based on a nucleic acid amplification test, such as reverse transcriptase polymerase chain reaction. To date, no vaccine is available and treatment is supportive. However, ongoing research shows encouraging results. The aim of this paper is to review the current literature concerning HMPV infections in adults, and discuss recent development in treatment and vaccination.

Diversity in glycosaminoglycan binding amongst hMPV G protein lineages

We have previously shown that hMPV G protein (B2 lineage) interacts with cellular glycosaminoglycans (GAGs). In this study we examined subtypes A1, A2 and B1 for this interaction. GAG-dependent infectivity of available hMPV strains was demonstrated using GAG-deficient cells and heparin competition. We expressed the G protein ectodomains from all strains and analysed these by heparin affinity chromatography. In contrast to the B2 lineage, neither the A2 or B1 G proteins bound to heparin. Sequence analysis of these strains indicated that although there was some homology with the B2 heparin-binding domains, there were less positively charged residues, providing a likely explanation for the lack of binding. Although sequence analysis did not demonstrate well defined positively charged domains in G protein of the A1 strain, this protein was able to bind heparin, albeit with a lower affinity than G protein of the B2 strain. These results indicate diversity in GAG interactions between G proteins of different lineages and suggest that the GAG-dependency of all strains may be mediated by interaction with an alternative surface protein, most probably the conserved fusion (F) protein. Analysis of both native and recombinant F protein confirmed that F protein binds heparin, supporting this conclusion.

Expeditious neutralization assay for human metapneumovirus based on a recombinant virus expressing Renilla luciferase

BACKGROUND

Human metapneumovirus (HMPV) is a common cause of respiratory diseases in persons of all ages. Because of its slow replication and weak cytopathic effect in cultured cells, conventional neutralization assays for HMPV require around one week for completion.

OBJECTIVES

The purpose of this study is to establish a rapid neutralization assay based on a recombinant virus expressing Renilla luciferase (Rluc).

STUDY DESIGN

A recombinant HMPV expressing both Rluc and green fluorescent protein (GFP) was created by reverse genetics method. Two-fold serial dilutions of human 23 sera were made in a 96-well plate and incubated with 50 pfu/well of the recombinant virus at 4°C for 1 h. The mixtures were then transferred to LLC-MK2 cells in a 96-well plate, incubated for 2 h, and replaced with trypsin-free fresh media. After incubation at 32°C for 24 h, the cells were lysed and measured for Rluc activity. The neutralization titer was defined as the reciprocal of the highest serum dilution that resulted in 50% reduction of Rluc activity.

RESULTS

The novel assay could be completed within 24 h and eliminated the requirement of trypsin supporting multistep replication in cultured cells, as well as laborious processes including the plaque assay with immunostaining. Neutralization titers correlated well with those determined by a GFP-based assay previously developed.

CONCLUSIONS

The neutralization assay based on Rluc activity is the fastest and the most straightforward of all previous assays, and may be available for high throughput screening of neutralizing antibodies.

Seroprevalence of human respiratory syncytial virus and human metapneumovirus in healthy population analyzed by recombinant fusion protein-based enzyme linked immunosorbent assay

Background

Human respiratory syncytial virus (hRSV) and human metapneumovirus (hMPV) are two of the most frequent respiratory pathogens that circulate worldwide. Infection with either virus can lead to hospitalization of young children, immunocompromised people and the elderly.

A better understanding of the epidemiological aspects, such as prevalence of these viruses in the population will be of significant importance to the scientific community. The aim of this study was to gain some detailed knowledge on the humoral immune response to both viruses in different populations of individuals.

Findings

The fusion protein (F) of hRSV and hMPV was expressed in the baculovirus and Escherichia coli systems, respectively, and used as antigen in two independent enzyme-linked immunosorbent assays (ELISAs) for detection of specific antibodies in human sera. The seroprevalence of each virus in a large cohort of individuals with ages ranging from 0 to 89 years old was determined. Although the general distribution of the antibody response to each virus in the different age group was similar, the prevalence of hRSV appeared to be higher than that of hMPV in most of them. The group of children with ages between 0 and 2 showed the highest seronegative rates. After this age, an increase in the antibody response was observed, most likely as the result of new infections or even due to reinfections.

Conclusions

The use of these specific F-ELISAs in seroepidemiological studies might be helpful for a better understanding of the human antibody response to these viruses.

Human Metapneumovirus: lessons learned over the first decade

It has been 10 years since human metapneumovirus (HMPV) was identified as a causative agent of respiratory illness in humans. Since then, numerous studies have contributed to a substantial body of knowledge on many aspects of HMPV. This review summarizes our current knowledge on HMPV, HMPV disease pathogenesis, and disease intervention strategies and identifies a number of areas with key questions to be addressed in the future.

Detection and genetic diversity of human metapneumovirus in hospitalized children with acute respiratory infections in India

Human metapneumovirus (hMPV) causes acute respiratory infections in children and adults. It is classified into two major genetic lineages and each lineage into two sublineages. The purpose of the study was to identify and characterize hMPV in children who presented to the All India Institute of Medical Sciences, New Delhi, India with acute respiratory infection from April 2005 to March 2007. By reverse-transcription polymerase chain reaction, hMPV was detected in 21 (3%) of the 662 nasopharyngeal samples from children with acute respiratory infection and in none of the 120 control children. Seven of the 21 (33%) children infected with hMPV required hospital admission for pneumonia or bronchiolitis. Most hMPV detections were during the winter and spring seasons. The majority (67%, 11/21) of children positive for hMPV were within 24 months of age. Phylogenetic analysis of partial F and N gene and the full G gene sequences showed three sub-lineages of hMPV circulated during the study period, B1, B2, and the novel sub-lineage A2b. The circulation pattern of hMPV genotypes varied by season. Comparison of the F and G genes of eight strains revealed incongruencies in lineage assignments, raising the possibility that recombination had occurred. Sequence analysis also revealed the F gene was relatively conserved whereas the G gene was more variable between the A and B lineages. This study demonstrates that hMPV is an important contributor to acute respiratory infection in children in India, resulting in both outpatient visits and hospitalizations.

Progress in the development of human parainfluenza virus vaccines

In children under 5 years of age, human parainfluenza viruses (HPIVs) as a group are the second most common etiology of acute respiratory illness leading to hospitalization, surpassed only by respiratory syncytial virus but ahead of influenza viruses. Using reverse genetics systems for HPIV serotypes 1, 2 and 3 (HPIV1, 2 and 3), several live-attenuated HPIVs have been generated and evaluated as intranasal vaccines in adults and in children. Two vaccines against HPIV3 were found to be well tolerated, infectious and immunogenic in Phase I trials in HPIV3-seronegative infants and children and should progress to proof-of-concept trials. Vaccines against HPIV1 and HPIV2 are less advanced and have just entered pediatric trials.

Ten years of human metapneumovirus research

Described for the first time in 2001, human metapneumovirus (hMPV) has become one of the main viral pathogens responsible for acute respiratory tract infections in children but also in the elderly and immuno-compromised patients. The pathogen most closely related to hMPV is human respiratory syncytial virus (hRSV), the most common cause of bronchiolitis and pneumonia in young children. hMPV has been classified into two main viral groups A and B and has a seasonal distribution in temperate countries with most cases occurring in winter and spring. Given the difficulties encountered in culturing hMPV in vitro, diagnosis is generally achieved using real-time polymerase chain reaction. Like other Paramyxoviridae, hMPV has a negative-sense single-stranded RNA genome that includes 8 genes coding for 9 different proteins. The genomic organization and functions of surface attachment and fusion glycoproteins are relatively similar to those of hRSV. Although many groups have studied the viral life cycle of hMPV, many questions remain unanswered concerning the exact roles of the viral proteins in the attachment, fusion and replication of hMPV. To date, there remains no approved modality to combat hMPV infections. The majority of treatments that have been tested on hMPV have already demonstrated activity against hRSV infections. Some innovative approaches based on RNA interference and on fusion inhibitors have shown efficacy in vitro and in animal studies and could be beneficial in treating human hMPV disease. Difficulties faced inducing a durable immune response represent the biggest challenge in the development of an effective hMPV vaccine. Several strategies, such as the use of live-attenuated viruses generated by reverse genetics or recombinant proteins, have been tested in animals with encouraging results.