Analysis of the genomic sequence of a human metapneumovirus

The cotton rat (Sigmodon hispidus) is a permissive small animal model of human metapneumovirus infection, pathogenesis, and protective immunity

Human metapneumovirus (hMPV) is a newly described paramyxovirus that is an important cause of acute respiratory tract disease. We undertook to develop a small animal model of hMPV infection, pathogenesis, and protection. Hamsters, guinea pigs, cotton rats, and nine inbred strains of mice were inoculated intranasally with hMPV. The animals were sacrificed, and nasal and lung tissue virus yields were determined by plaque titration. None of the animals exhibited respiratory symptoms. The quantity of virus present in the nasal tissue ranged from 4.6 x 10(2) PFU/gram tissue (C3H mice) to greater than 10(5) PFU/gram (hamster). The amount of virus in the lungs was considerably less than in nasal tissue in each species tested, ranging from undetectable (<5 PFU/g; guinea pigs) to 1.8 x 10(5) PFU/gram (cotton rat). The peak virus titer in cotton rat lungs occurred on day 4 postinfection. hMPV-infected cotton rat lungs examined on day 4 postinfection exhibited histopathological changes consisting of peribronchial inflammatory infiltrates. Immunohistochemical staining detected virus only at the luminal surfaces of respiratory epithelial cells throughout the respiratory tract. hMPV-infected cotton rats mounted virus-neutralizing antibody responses and were partially protected against virus shedding and lung pathology on subsequent rechallenge with hMPV. Viral antigen was undetectable in the lungs on challenge of previously infected animals. This study demonstrates that the cotton rat is a permissive small animal model of hMPV infection that exhibits lung histopathology associated with infection and that primary infection protected animals against subsequent infection. This model will allow further in vivo studies of hMPV pathogenesis and evaluation of vaccine candidates.

Human metapneumovirus in infants and young children in Thailand with lower respiratory tract infections; molecular characteristics and clinical presentations

Human metapneumovirus (hMPV) is a recently identified Paramyxovirus. The clinical features and molecular characteristics of hMPV in Asian populations have so far remained obscure.

OBJECTIVE

The present study was designed to investigate the prevalence of hMPV in infants and young children presented with acute lower respiratory tract infection (ALRI) and to identify the molecular characteristics and clinical presentations.

METHODS

There were 236 nasopharyngeal secretions (NPs) collected from infants and children presented with ALRI at King Chulalongkorn Memorial hospital between March 2001 and September 2003. Reverse transcriptase-polymerase chain reaction (RT-PCR) applying specific primers was done to identify hMPV and hRSV. Phylogenetic analysis of hMPV N, F and L genes was also performed.

RESULTS

Of the 220 (236) infants and young children tested, positive results were found in 12 specimens (5.4%). The mean age of children with hMPV infections was 22+/-11 months. They mostly presented with fever with cough (100%) and upper respiratory tract symptoms (10/12, 83%). Eleven of twelve infants (92%) were hospitalized. Additionally, phylogenetic analysis identified two distinct lineages of hMPV.

CONCLUSION

Our results demonstrated the prevalence, molecular characterization and clinical spectrum of hMPV infection in infants and young children presented with lower respiratory tract infections in Thailand.

An S101P substitution in the putative cleavage motif of the human metapneumovirus fusion protein is a major determinant for trypsin-independent growth in vero cells and does not alter tissue tropism in hamsters

Human metapneumovirus (hMPV), a recently described paramyxovirus, is a major etiological agent for lower respiratory tract disease in young children that can manifest with severe cough, bronchiolitis, and pneumonia. The hMPV fusion glycoprotein (F) shares conserved functional domains with other paramyxovirus F proteins that are important for virus entry and spread. For other paramyxovirus F proteins, cleavage of a precursor protein (F0) into F1 and F2 exposes a fusion peptide at the N terminus of the F1 fragment, a likely prerequisite for fusion activity. Many hMPV strains have been reported to require trypsin for growth in tissue culture. The majority of these strains contain RQSR at the putative cleavage site. However, strains hMPV/NL/1/00 and hMPV/NL/1/99 expanded in our laboratory contain the sequence RQPR and do not require trypsin for growth in Vero cells. The contribution of this single amino acid change was verified directly by generating recombinant virus (rhMPV/NL/1/00) with either proline or serine at position 101 in F. These results suggested that cleavage of F protein in Vero cells could be achieved by trypsin or S101P amino acid substitution in the putative cleavage site motif. Moreover, trypsin-independent cleavage of hMPV F containing 101P was enhanced by the amino acid substitution E93K. In hamsters, rhMPV/93K/101S and rhMPV/93K/101P grew to equivalent titers in the respiratory tract and replication was restricted to respiratory tissues. The ability of these hMPV strains to replicate efficiently in the absence of trypsin should greatly facilitate the generation, preclinical testing, and manufacturing of attenuated hMPV vaccine candidates.

Activity and regulation of alpha interferon in respiratory syncytial virus and human metapneumovirus experimental infections

Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) cause a similar spectrum of respiratory infections in humans. Classified within the Paramyxoviridae family, Pneumovirinae subfamily, RSV and hMPV present a significant degree of divergence in genome constellation, organization, and protein sequences. RSV has been reported to be a poor inducer of alpha/beta interferons (IFN-alpha/beta) and partially resistant to its antiviral activity. The nature of the innate immune response to hMPV is currently unknown. Herein, an experimental mouse model was used to investigate the interplay between RSV and hMPV infections and IFN-alpha in the airways. RSV-infected BALB/c mice treated intranasally with either poly-ICLC, a potent inducer of IFN-alpha, or directly with recombinant IFN-alpha showed significantly reduced lung viral titers, inflammation, and clinical disease than untreated controls. However, RSV was significantly less sensitive to the antiviral activity of IFN-alpha than hMPV. Similarly, when the ability to directly induce IFN-alpha production was assessed, RSV was clearly a weaker inducer of IFN-alpha than hMPV, as shown by both kinetics and the absolute amount of IFN-alpha secreted into the bronchoalveolar lavage. To further investigate the putative inhibitory effect of these viruses on IFN-alpha production, mice were infected for 48 h prior to treatment with poly-ICLC or a specific Toll-like receptor 9 ligand, CpG oligodeoxynucleotides. Strikingly, both poly-ICLC- and CpG-mediated IFN-alpha production was abrogated by either RSV or MPV infection. These results suggest that a complex interplay between virus-specific and host-mediated responses regulates IFN-alpha in the lung during infection by members of the Pneumovirinae family.

Perspective on the host response to human metapneumovirus infection: what can we learn from respiratory syncytial virus infections?

Human metapneumovirus (HMPV) is a recently discovered pathogen first identified in respiratory specimens from young children suffering from clinical respiratory syndromes ranging from mild to severe lower respiratory tract illness. HMPV has worldwide prevalence, and is a leading cause of respiratory tract infection in the first years of life, with a spectrum of disease similar to respiratory syncytial virus (RSV). The disease burden associated with HMPV infection has not been fully elucidated; however, studies indicate that HMPV may cause upper or lower respiratory tract illness in patients between ages 2 months and 87 years, may co-circulate with RSV, and HMPV infection may be associated with asthma exacerbation. The mechanisms and effector pathways contributing to immunity or disease pathogenesis following infection are not fully understood; however, given the clinical significance of HMPV, there is a need for a fundamental understanding of the immune and pathophysiological processes that occur following infection to provide the foundation necessary for the development of effective vaccine or therapeutic intervention strategies. This review provides a current perspective on the processes associated with HMPV infection, immunity, and disease pathogenesis.

Development and validation of an enzyme-linked immunosorbent assay for human metapneumovirus serology based on a recombinant viral protein

The human metapneumovirus (hMPV) is a newly reported respiratory virus belonging to the Paramyxoviridae family that has been associated with bronchiolitis and pneumonia in young children. We developed a simple enzyme-linked immunosorbent assay (ELISA) for hMPV serological testing using the nucleoprotein (N) from group A or B (N-A or N-B) as the antigen, and we evaluated it in both children and adults. The N proteins were first used in a Western immunoblot assay to identify hMPV-negative sera, which were then used to determine the cutoff value of the ELISA test. Subsequent evaluation of the ELISA-N test revealed that the mean reciprocal antibody titer of 20 randomly selected seropositive children was 143, compared to 69 for 20 seropositive adults. In a prospective evaluation of 71 adults with acute exacerbations of chronic obstructive pulmonary disease, 58 (81.6%) had prior hMPV antibodies and 3 (4.2%) had evidence of recent hMPV infection. In testing paired sera from adults (n = 4) with recent hMPV group A infection confirmed by reverse transcriptase PCR (RT-PCR), ELISAs using the N-A or N-B proteins were able to detect hMPV seroconversion. Moreover, testing of paired sera from three adults with a recent infection by the human respiratory syncytial virus confirmed by RT-PCR and serology did not reveal any increase in hMPV antibodies over time. The ELISA-N is a simple, objective, and specific serological test useful for detecting anti-hMPV antibodies following group A or B viral infections, which should permit a better understanding of the epidemiology of this virus.

Detection and pathogenicity of human metapneumovirus respiratory infection in pediatric Italian patients during a winter--spring season

Background

Some diagnostic, epidemiological and clinical features of the recently discovered human metapneumovirus remain to be investigated.

Objectives

To study the best approach for the diagnosis of human metapneumovirus infections by both conventional and molecular methods, along with the human metapneumovirus circulation rate in northern Italy and the severity of human metapneumovirus respiratory infections in a pediatric patient population.

Study design

Nasopharyngeal aspirates (NPA) were taken from 306 pediatric patients during the winter–spring season 2003–2004, and examined for conventional respiratory viruses by direct fluorescent staining and cell culture, while human coronavirus and human metapneumovirus were sought by RT-PCR.

Results

RT-PCR detected human metapneumovirus in 40/306 (13.1%) children positive for respiratory viruses, with an incidence intermediate between that of respiratory syncytial virus (58 patients, 18.9%) and that of influenzavirus infections (29 patients, 9.5%). Phylogenetic analysis showed cocirculation of both human metapneumovirus types (A and B) as well as their relevant subtypes (A1–A2 and B1–B2). Clinically, human metapneumovirus was found to be second to human respiratory syncytial virus alone, as a cause of respiratory tract infections, while duration of virus excretion appeared to correlate with severity of infection, and virus load in NPA with the stage of respiratory infection.

Conclusion

(i) Human metapneumovirus is a major viral pathogen in the Italian pediatric patient population; (ii) the severity of lower respiratory tract infections approaches that of human respiratory syncytial virus; (iii) there are preliminary indications that the duration of virus excretion may reach 2–3 weeks and that the level of viral load in NPA correlates with the clinical stage of human metapneumovirus infection.

Human metapneumovirus genetic variability, South Africa

The molecular epidemiology and genetic diversity of the human metapneumovirus (hMPV) were characterized for a 3-year period (2000-2002) from viruses that were identified in South Africa. Two major genetic groups (A and B) and 2 subgroups (1 and 2) of hMPV were identified, as well as 2-6 possible genotypes within the subgroups. A shift in the predominant group was documented in successive seasons. Whereas the F gene was relatively conserved between subgroups, a high degree of variation was observed in the extracellular domain of the G gene of the virus. The G protein identities between groups A and B were 45.1%-53.1% at the nucleotide level and 22.4%-27.6% at the amino acid level. These results provide evidence for the diversity of both surface glycoproteins of hMPV in Africa, which may be a prerequisite to understanding protective immunity against hMPV.

Changing circulation rate of human metapneumovirus strains and types among hospitalized pediatric patients during three consecutive winter-spring seasons. Brief report

From 2001 through 2004, 808 pediatric patients admitted to hospital because of acute respiratory infections were examined for presence of respiratory viruses by either direct fluorescent staining using monoclonal antibodies or RT-PCR during three consecutive winter-spring seasons. On the whole, 336 (42%) patients were detected as positive for one or more respiratory viruses. The most widely circulating virus was human respiratory syncytial virus (hRSV) infecting 50% of positive patients, followed by human metapneumovirus (hMPV) found in 13% of patients, and then by influenza virus type A, human parainfluenzaviruses and coinfections. Significant variations in the circulation rate of hRSV, hMPV and influenzavirus type A were observed during the individual seasons. In addition, the circulation rates of the different types of hMPV changed yearly. In 2001-2002 and 2002-2003 hMPV circulated at a significant lower proportion than hRSV, while in 2003-2004 the circulation rates of the two viruses were closer. In conclusion, the 4 hMPV subtypes circulated yearly in Northern Italy flanking hRSV as major respiratory pathogens in the infantile patient population.

The immune response to human metapneumovirus is associated with aberrant immunity and impaired virus clearance in BALB/c mice

Human metapneumovirus (HMPV), recently identified in isolates from children hospitalized with acute respiratory tract illness, is associated with clinical diagnosis of pneumonia, asthma exacerbation, and acute bronchiolitis in young children. HMPV has been shown to cocirculate with respiratory syncytial virus (RSV) and mediate clinical disease features similarly to RSV. Little is known regarding the pathophysiology or immune response associated with HMPV infection; thus, animal models are needed to better understand the mechanisms of immunity and disease pathogenesis associated with infection. In this study, we examine features of the innate and adaptive immune response to HMPV infection in a BALB/c mouse model. Primary HMPV infection elicits weak innate and aberrant adaptive immune responses characterized by induction of a Th2-type cytokine response at later stages of infection that coincides with increased interleukin-10 expression and persistent virus replication in the lung. Examination of the cytotoxic T lymphocyte and antibody response to HMPV infection revealed a delayed response, but passive transfer of HMPV-specific antibodies provided considerable protection. These features are consistent with virus persistence and indicate that the immune response to HMPV is unique compared to the immune response to RSV.

Immunofluorescence assay for detection of human metapneumovirus-specific antibodies by use of baculovirus-expressed fusion protein

Human metapneumovirus (hMPV) has recently been identified as an etiological agent of acute respiratory infections. The hMPV fusion (F) protein has been indicated to be a major antigenic determinant that mediates effective neutralization and protection against hMPV infection. We developed a new immunofluorescence assay (IFA) using Trichoplusia ni (Tn5) insect cells infected with a recombinant baculovirus-expressing hMPV F protein (Bac-F IFA). A total of 200 serum samples from Japanese people 1 month to 41 years old were tested for immunoglobulin G antibodies to hMPV F protein by Bac-F IFA. The results were compared with those of the conventional IFA based on hMPV-infected LLC-MK2 cells (hMPV IFA). The titers obtained by the two IFAs correlated well (correlation coefficient of 0.88), and the concordance of seroreactivities between the two IFAs was 91% (kappa=0.76). For 192 of the 200 serum samples, the titers obtained by the Bac-F IFA were equal to or higher than those obtained by the hMPV IFA. These results indicated that the Bac-F IFA was more sensitive than the hMPV IFA and that the majority of the antibodies detected by the hMPV IFA reacted with the hMPV F protein. The Bac-F IFA is a more reliable, sensitive, and specific method for the detection of hMPV antibodies than is the hMPV IFA.

Deletion of M2 gene open reading frames 1 and 2 of human metapneumovirus: effects on RNA synthesis, attenuation, and immunogenicity

The M2 gene of human metapneumovirus (HMPV) contains two overlapping open reading frames (ORFs), M2-1 and M2-2. The expression of separate M2-1 and M2-2 proteins from these ORFs was confirmed, and recombinant HMPVs were recovered in which expression of M2-1 and M2-2 was ablated individually or together [rdeltaM2-1, rdeltaM2-2, and rdeltaM2(1+2)]. Each M2 mutant virus directed efficient multicycle growth in Vero cells. The ability to recover HMPV lacking M2-1 contrasts with human respiratory syncytial virus, for which M2-1 is an essential transcription factor. Expression of the downstream HMPV M2-2 ORF was not reduced when translation of the upstream M2-1 ORF was silenced, indicating that it is initiated separately. The rdeltaM2-2 mutants exhibited a two- to fivefold increase in the accumulation of mRNA, normalized to the genome template, suggesting that M2-2 has a role in regulating RNA synthesis. Replication and immunogenicity were tested in hamsters. Animals infected intranasally with rdeltaM2-1 or rdeltaM2(1+2) did not have recoverable virus in the lungs or nasal turbinates on days 3 or 5 postinfection and did not develop HMPV-neutralizing serum antibodies or resistance to HMPV challenge. Thus, M2-1 appears to be essential for significant virus replication in vivo. In animals infected with rdeltaM2-2, virus was recovered from only 1 of 12 animals and only in the nasal turbinates on a single day. However, all of the animals developed a high titer of HMPV-neutralizing serum antibodies and were highly protected against challenge with wild-type HMPV. The HMPV rdeltaM2-2 virus is a promising and highly attenuated HMPV vaccine candidate.

Newer respiratory virus infections: human metapneumovirus, avian influenza virus, and human coronaviruses

PURPOSE OF REVIEW

Recently, several previously unrecognized respiratory viral pathogens have been identified and several influenza A virus subtypes, previously known to infect poultry and wild birds, were transmitted to humans. Here we review the recent literature on these respiratory viruses.

RECENT FINDINGS

Human metapneumovirus has now been detected worldwide, causing severe respiratory tract illnesses primarily in very young, elderly and immunocompromised individuals. Animal models and reverse genetic techniques were designed for human metapneumovirus, and the first vaccine candidates have been developed. Considerable genetic and antigenic diversity was observed for human metapneumovirus, but the implication of this diversity for vaccine development and virus epidemiology requires further study. Two previously unrecognized human coronaviruses were discovered in 2004 in The Netherlands and Hong Kong. Their clinical impact and epidemiology are largely unknown and warrant further investigation. Several influenza A virus subtypes were transmitted from birds to humans, and these viruses continue to constitute a pandemic threat. The clinical symptoms associated with these zoonotic transmissions range from mild respiratory illnesses and conjunctivitis to pneumonia and acute respiratory distress syndrome, sometimes resulting in death. More basic research into virus ecology and evolution and development of effective vaccines and antiviral strategies are required to limit the impact of influenza A virus zoonoses and the threat of an influenza pandemic.

SUMMARY

Previously unknown and emerging respiratory viruses are an important threat to human health. Development of virus diagnostic tests, antiviral strategies, and vaccines for each of these pathogens is crucial to limit their impact.

A host-range restricted parainfluenza virus type 3 (PIV3) expressing the human metapneumovirus (hMPV) fusion protein elicits protective immunity in African green monkeys

Human metapneumovirus (hMPV) infection causes respiratory tract disease similar to that observed during human respiratory syncytial virus infection (hRSV). hMPV infections have been reported across the entire age spectrum although the most severe disease occurs in young children. No vaccines, chemotherapeutics or antibodies are presently available for preventing or treating hMPV infections. In this study, a bovine/human chimeric parainfluenza virus type 3 (b/h PIV3) expressing the human parainfluenza type 3 (hPIV3) fusion (F) and hemagglutinin-neuraminidase (HN) proteins was engineered to express hMPV fusion (F) protein from the second genome position (b/h PIV3/hMPV F2) with the goal of generating a novel hMPV vaccine. b/h PIV3/hMPV F2 was previously shown to protect hamsters from challenge with wt hMPV (Tang RS, Schickli JH, Macphail M, Fernandes F, Bicha L, Spaete J, et al. Effects of human metapneumovirus and respiratory syncytial virus antigen insertion in two 3' proximal genome positions of bovine/human parainfluenza virus type 3 on virus replication and immunogenicity. J Virol 2003;77:10819-28) and is here further evaluated for efficacy and immunogenicity in African green monkeys (AGMs). AGMs immunized intranasally and intratracheally with b/h PIV3/hMPV F2 generated hMPV- and hPIV3-specific humoral and cellular immune responses and were protected from wt hMPV infection. In a separate study, the host-range restriction of b/h PIV3/hMPV F2 replication relative to wt hPIV3 was performed in rhesus monkeys to demonstrate attenuation. These studies showed that b/h PIV3/hMPV F2 was immunogenic, protective and attenuated in non-human primates and warrants further evaluation in humans as a vaccine candidate for prevention of hMPV-associated respiratory tract diseases.

Seroepidemiology of human metapneumovirus (hMPV) on the basis of a novel enzyme-linked immunosorbent assay utilizing hMPV fusion protein expressed in recombinant vesicular stomatitis virus

Human metapneumovirus (hMPV) is a newly identified human respiratory virus now recognized as a major respiratory pathogen of infants and children. To define the seroepidemiology of hMPV, we developed a novel enzyme-linked immunosorbent assay (ELISA) based on expression of the fusion protein of hMPV (hMPV F) in recombinant vesicular stomatitis virus (VSV). Western blot analysis using an hMPV F-specific antiserum confirmed the expression of hMPV in recombinant VSV. The ELISA is specific for hMPV F; antibody specific for the most closely related human paramyxovirus, respiratory syncytial virus, does not bind to hMPV F. Overall, 216 serum specimens were tested. The percentages of seropositive individuals were 89.1% in children < or =5 months old, 55.0% in children 6 to 11 months old, 36.0% in children 12 to 23 months old, 45.0% in children 24 to 47 months old, 77.3% in children 48 to 59 months old, 91.3% in children 5 to 10 years old, and 95.5% for individuals 11 to 20 years old. This is the first seroepidemiological survey of hMPV in the United States and the first analysis to determine the prevalence of antibody to a specific hMPV protein. The data suggest that exposure to hMPV is common in childhood and that hMPV F is an antigenic determinant of hMPV.

Comparison of the full-length genome sequence of avian metapneumovirus subtype C with other paramyxoviruses

We determined the nucleotide (nt) sequence of the small hydrophobic (SH), attachment glycoprotein (G), and RNA polymerase (L) genes, plus the leader and trailer regions of the Colorado strain of Avian metapneumovirus subtype C (aMPV/C) in order to complete the genome sequencing. The complete genome comprised of 13,134 nucleotides, with a 40 nt leader at its 3' end and a 45 nt trailer at its 5' end. The aMPV/C L gene was the largest with 6173 nt and consisting of a single open reading frame encoding a 2005 amino acids (aa) protein. Comparison of the aMPV/C SH, G, and L nt and predicted aa sequences with those of Human metapneumoviruses (hMPV) revealed higher nt and aa sequence identities than the sequence identities between the aMPV subtypes A, B, C, and D, supporting earlier finding that aMPV/C was closer evolutionary to hMPV than the other aMPV subtypes.

Sequence analysis of the large polymerase (L) protein of the US strain of avian metapneumovirus indicates a close resemblance to that of the human metapneumovirus

The complete nucleotide sequence of the large polymerase (L) protein of the avian metapneumovirus subgroup C strain Colorado was determined. The L protein gene of avian pneumovirus Colorado isolate (APV-C) was 6173 nucleotides in length from the gene-start to the gene-end and encoded a polypeptide of 2005 amino acids in length. The length of the L protein of APV-C was exactly the same as that of human metapneumovirus (hMPV) and one amino acid longer than the L protein of APV subgroup A. The L protein of APV-C showed 80% amino acid identity with the L protein of hMPV, but only 64% amino acid identity with the L protein of APV-A. The nucleotide and deduced amino acid sequences were compared with the corresponding sequences of eleven other paramyxoviruses. All six domains characteristic of paramyxovirus L proteins were also observed in the L protein of APV-C. All the polymerase core motifs in domain III were conserved to nearly 100% in the metapneumoviruses. Similarly, the putative ATP-binding motif in domain VI was completely conserved among the metapneumoviruses and differed in length, by one intermediate residue, from other paramyxoviruses. Phylogenetic analysis of the different L proteins also revealed a closer relationship between APV-C and hMPV.

Serological cross-reactivity of members of the Metapneumovirus genus

Respiratory tract infections are a leading cause of morbidity and mortality worldwide. Human metapneumovirus (HMPV) is a recently discovered respiratory pathogen of the Paramyxovirus family in the Metapneumovirus genus. HMPV was first isolated from young children in The Netherlands with respiratory illness similar to human respiratory syncytial virus (RSV) infection. Epidemiological data indicates that HMPV co-circulates with RSV in the community. Few immunological tools are available to study the virological features of HMPV infection, thus current studies rely on reverse-transcription (RT) polymerase chain reaction (PCR) for detection. In this study, we examine serological cross-reactivity of RSV, HMPV and other Metapneumovirus members, i.e. avian metapneumovirus (AMPV), and show that polyclonal and monoclonal antibodies reactive to a conserved region in AMPV nucleoprotein (N) cross-react with HMPV N protein, but not with RSV N protein by ELISA, Western blot and immunohistochemical assays. In addition, we show that HMPV infection in the lungs of BALB/c mice can be detected using anti-N protein antibody. These reagents provide new tools and methods for investigating HMPV infection, for differentiating HMPV from RSV infection, and may be useful for characterizing potential links between HMPV with other respiratory complications.

Monoclonal antibodies versus reverse transcription-PCR for detection of respiratory viruses in a patient population with respiratory tract infections admitted to hospital

In the winter season 2001–2002, 239 nasopharyngeal aspirate and 15 bronchoalveolar lavage samples from 208 patients (135 pediatric and 73 adults, including 19 lung transplant recipients) admitted to hospital because of an acute respiratory tract infection were examined for rapid diagnosis of respiratory viruses by two diagnostic approaches: immunological, using specific monoclonal antibodies (MAb); and molecular, using specific reverse transcription (RT)‐PCR assays. Both methods detected influenza viruses A (H1N1 and H3N2) and B, human parainfluenza virus types 1 to 3, human respiratory syncytial virus (hRSV) types A and B, and human adenoviruses. In addition, human coronavirus (hCoV) groups I (229E‐like) and II (OC43‐like), as well as the new human metapneumovirus (hMPV), types A and B, were searched for by RT‐PCR alone. When results obtained by both methods were added, the overall percentage of patients positive for at least one respiratory virus peaked at 44.2%, involving 92/208 patients (81 pediatric, and 11 adults), while 116 patients (55.8%) were negative for any respiratory virus tested. The most common circulating virus was hRSV, infecting 54 (25.9%) patients (24 type A, and 30 type B strains), followed by hMPV, infecting 12 (5.8%) patients (7 type A and 5 type B strains). Coinfections by two respiratory viruses interested 11 (5.3%) patients, and 9 (81.8%) of these were infected by hRSV in association with another respiratory virus. In the great majority of infected children, hRSV and hMPV were associated with lower respiratory tract infections. In lung transplant recipients, viruses present in bronchoalveolar lavage appeared to be associated frequently with lower respiratory tract infections. In conclusion: the combination of immunological and molecular assays is the most sensitive approach to the diagnosis of respiratory viral infections; and infections caused by the less investigated hCoVs and hMPVs represent a fair proportion of respiratory infections. J. Med. Virol. 75:336–347, 2005. © 2004 Wiley‐Liss, Inc.

Analysis of Replication Kinetics of the Human Metapneumovirus in Different Cell Lines by Real-Time PCR

Human metapneumovirus (hMPV) is associated with acute respiratory tract disease especially in young children. Using a quantitative real-time TaqMan PCR, we analyzed the replication kinetics of hMPV in different cell lines. Our results indicate that hMPV replicates slightly more efficiently in LLC-MK2 than in Vero cells and poorly in HEp-2 cells.

Prospective study of human metapneumovirus infection in children less than 3 years of age

Most lower respiratory tract infections (LRTIs) in children under the age of 3 years are due to respiratory syncytial virus (RSV). Epidemiological, host, and viral factors eventually account for the severity of LRTIs, but they do not completely explain it. Human metapneumovirus (hMPV) was recently identified in children with LRTIs. In a population-based prospective multicenter study (the PRI.DE study, conducted in Germany over 2 years), we tested 3,369 nasopharyngeal secretions from children younger than 3 years of age with LRTIs for RSV A and B, influenza viruses (IVs) A and B, and parainfluenza viruses (PIVs) 1 to 3. Of the children requiring intensive care (n = 85), 18% had hMPV infections, and 60% of these children were infected with hMPV in combination with RSV. We did not detect hMPV in a randomly selected subset of RSV-positive nasopharyngeal secretions (n = 120) from children not requiring intensive care support. hMPV was detected in <1% of virus-negative samples from patients without intensive care support (n = 620). Our data support the hypothesis that coinfections with RSV and hMPV are more severe than infections with either RSV or hMPV alone, at least in children younger than 3 years of age.

Human metapneumovirus persists in BALB/c mice despite the presence of neutralizing antibodies

Human metapneumovirus (HMPV) has emerged as an important human respiratory pathogen causing upper and lower respiratory tract infections in young children and older adults. Recent epidemiological evidence indicates that HMPV may cocirculate with respiratory syncytial virus, and HMPV infection has been associated with other respiratory diseases. In this study, we show that BALB/c mice are susceptible to HMPV infection, the virus replicates in the lungs with biphasic growth kinetics in which peak titers occur at days 7 and 14 postinfection (p.i.), and infectious HMPV can be recovered from lungs up to day 60 p.i. In addition, we show that genomic HMPV RNA can be detected in the lungs for >/=180 days p.i. by reverse transcription-PCR; however, neither HMPV RNA nor infectious virus can be detected in serum, spleen, kidneys, heart, trachea, and brain tissue. Lung histopathology revealed prevalent mononuclear cell infiltration in the interstitium beginning at day 2 p.i. and peaking at day 4 p.i. which decreased by day 14 p.i. and was associated with airway remodeling. Increased mucus production evident at day 2 p.i. was concordant with increased bronchial and bronchiolar inflammation. HMPV-specific antibodies were detected by day 14 p.i., neutralizing antibody titers reached >/=6.46 log(2) end-point titers by day 28 p.i., and depletion of T cells or NK cells resulted in increased HMPV titers in the lungs, suggesting some immune control of viral persistence. This study shows that BALB/c mice are amenable for HMPV studies and indicates that HMPV persists as infectious virus in the lungs of normal mice for several weeks postinfection.

Complete sequence of the G glycoprotein gene of avian metapneumovirus subgroup C and identification of a divergent domain in the predicted protein

The complete nucleotide sequences of the attachment glycoprotein (G) genes of three strains of avian metapneumovirus subgroup C (AMPV-C) were determined from the viral genomic and mRNAs. The G gene of AMPV-C was 1798 nt (1015 nt longer than previously reported) and the derived polypeptide had 585 aa. The deduced amino acid sequence of the predicted G protein of AMPV-C strain Colorado (AMPV-CO) showed 21-25 % amino acid identity to the G proteins of human metapneumoviruses, but only 14-16 % amino acid identity to those of other AMPV subgroups. The predicted G protein of AMPV-CO showed 98 and 81 % amino acid identity to those of AMPV-C strains Mn-1a and Mn-2a, respectively, indicating considerable sequence variation in the G proteins of AMPV-C isolates. Comparison of the G protein sequences of AMPV-CO and Mn-2a identified a highly divergent domain (48 % amino acid identity) at aa 300-450.

Development of a reverse-genetics system for Avian pneumovirus demonstrates that the small hydrophobic (SH) and attachment (G) genes are not essential for virus viability

Avian pneumovirus (APV) is a member of the genus Metapneumovirus of the subfamily Pneumovirinae. This study describes the development of a reverse-genetics system for APV. A minigenome system was used to optimize the expression of the nucleoprotein, phosphoprotein, M2 and large polymerase proteins when transfected into Vero cells under the control of the bacteriophage T7 promoter. Subsequently, cDNA was transcribed from the virion RNA to make a full-length antigenome, which was also cloned under the control of the T7 promoter. Transfection of the full-length genome plasmid, together with the plasmids expressing the functional proteins in the transcription and replication complex, generated APV in the transfected cells. The recombinant virus was passaged and was identified by cytopathic effect (CPE) that was typical of APV, the presence of a unique restriction-endonuclease site in the cDNA copy of the genome and immunofluorescence staining with anti-APV antibodies. Replacement of the full-length wild-type antigenome with one lacking the small hydrophobic (SH) protein and the attachment (G) genes generated a virus that grew more slowly and produced atypical CPE with syncytia much larger than those seen with wild-type virus.

Recombinant human Metapneumovirus lacking the small hydrophobic SH and/or attachment G glycoprotein: deletion of G yields a promising vaccine candidate

Human metapneumovirus (HMPV) has recently been identified as a significant cause of serious respiratory tract disease in humans. In particular, the emerging information on the contribution of HMPV to pediatric respiratory tract disease suggests that it will be important to develop a vaccine against this virus for use in conjunction with those being developed for human respiratory syncytial virus and the human parainfluenza viruses. A recently described reverse genetic system (S. Biacchesi, M. H. Skiadopoulos, K. C. Tran, B. R. Murphy, P. L. Collins, and U. J. Buchholz, Virology 321:247-259, 2004) was used to generate recombinant HMPVs (rHMPVs) that lack the G gene, the SH gene, or both. The DeltaSH, DeltaG, and DeltaSH/G deletion mutants were readily recovered and were found to replicate efficiently during multicycle growth in cell culture. Thus, the SH and G proteins are not essential for growth in cell culture. Apart from the absence of the deleted protein(s), the virions produced by the gene deletion mutants were similar by protein yield and gel electrophoresis protein profile to wild-type HMPV. When administered intranasally to hamsters, the DeltaG and DeltaSH/G mutants replicated in both the upper and lower respiratory tracts, showing that HMPV containing F as the sole viral surface protein is competent for replication in vivo. However, both viruses were at least 40-fold and 600-fold restricted in replication in the lower and upper respiratory tract, respectively, compared to wild-type rHMPV. They also induced high titers of HMPV-neutralizing serum antibodies and conferred complete protection against replication of wild-type HMPV challenge virus in the lungs. Surprisingly, G is dispensable for protection, and the DeltaG and DeltaSH/G viruses represent promising vaccine candidates. In contrast, DeltaSH replicated somewhat more efficiently in hamster lungs compared to wild-type rHMPV (20-fold increase on day 5 postinfection). This indicates that SH is completely dispensable in vivo and that its deletion does not confer an attenuating effect, at least in this rodent model.

[Human metapneumovirus pneumonia in an adult patient hospitalized for suspected severe acute respiratory syndrome (SARS)]

Introduction

Le métapneumovirus humain (hMPV) est un virus récemment identifié chez l’homme, responsable d’infections respiratoires parfois sévères que l’on observe surtout chez l’enfant.

Observation

Un patient âgé de 59 ans a été hospitalisé pour une atteinte respiratoire fébrile 3 jours après le retour d’un voyage en Chine effectué pendant l’épidémie de syndrome respiratoire aigu sévère (Sras). En dehors de la fièvre (>38 °C), étaient notées une toux sèche, des myalgies, des arthralgies, une opacité paracardiaque droite et une lymphopénie modérée. Les recherches virologiques conventionnelles étaient négatives. La recherche du nouveau coronavirus responsable du Sras était négative, mais la recherche de métapneumovirus humain (hMPV) était positive.

Discussion

Cette observation indique que le hMPV peut être responsable d’une atteinte respiratoire fébrile pouvant initialement évoquer un Sras chez un patient ayant séjourné en zone d’endémie.

Conclusion

La recherche de hMPV paraît indiquée dans les infections respiratoires aiguës de l’adulte.

Human metapneumovirus as a major cause of human respiratory tract disease

BACKGROUND

Human metapneumovirus (hMPV) is a newly identified paramyxovirus that appears to be one of the most significant and common viral infections in humans. The virus, first isolated in 2001, is a clear cause of lower respiratory tract disease in both the very young and the frail elderly. The virus causes acute wheezing in children or, less commonly, croup or pneumonia.

METHODS/RESULTS

Molecular epidemiology studies have shown that field strains exhibit sufficient sequence diversity to designate 2 subgroups of circulating viruses. Small animal and nonhuman primate models of infection have been described, which will allow studies of pathogenesis and immunity. Recombinant viruses have already been generated by several groups using reverse genetics, which facilitates the study of the biology of the virus and the generation of live attenuated vaccine candidates.

CONCLUSIONS

Ongoing research promises to elucidate the molecular basis for pathogenesis and immunity of human metapneumovirus infections and to pave the way for rapid vaccine development.

Duration of immunity produced by a live attenuated vaccine against avian pneumovirus type C

A recently developed live, attenuated vaccine against avian pneumovirus (APV) was found to be safe and protective in experimental birds. Duration of immunity following a single dose of this experimental vaccine in 1-week-old turkey poults is described. Two groups each of 60 poults were housed in separate isolation rooms. Birds in group one were inoculated oculonasally at 1 week of age with the vaccine. The second group served as a non-vaccinated group and was inoculated with mock-infected cell culture fluid. At 3, 7, 10, and 14 weeks post vaccination, 15 birds from each of the groups were removed to separate isolation rooms and challenged with virulent APV. Taken together, data on clinical signs and virus detection in choanal swabs following each challenge indicated that the vaccine was able to protect birds for up to 14 weeks post vaccination. Peak antibody levels were attained 7 weeks post vaccination and declined thereafter. These results indicated that this experimental vaccine induced protection against APV even in the absence of high antibody titres.

Recovery of human metapneumovirus genetic lineages a and B from cloned cDNA

Human metapneumovirus (hMPV) is a newly discovered pathogen associated with respiratory tract illness, primarily in young children, immunocompromised individuals, and the elderly. The genomic sequence of the prototype hMPV isolate NL/1/00 without the terminal leader and trailer sequences has been reported previously. Here we describe the leader and trailer sequences of two hMPV isolates, NL/1/00 and NL/1/99, representing the two main genetic lineages of hMPV. Minigenome constructs in which the green fluorescent protein or chloramphenicol acetyltransferase genes are flanked by the viral genomic ends derived from both hMPV lineages and transcribed using a T7 RNA polymerase promoter-terminator cassette were generated. Cotransfection of minigenome constructs with plasmids expressing the polymerase complex components L, P, N, and M2.1 in 293T or baby hamster kidney cells resulted in expression of the reporter genes. When the minigenome was replaced by a sense or antisense full-length cDNA copy of the NL/1/00 or NL/1/99 viral genomes, recombinant virus was recovered from transfected cells. Viral titers up to 10(7.2) and 10(5.7) 50% tissue culture infective dose/ml were achieved with the sense and antisense plasmids, respectively. The recombinant viruses replicated with kinetics similar to those of the parental viruses in Vero cells. This reverse genetics system provides an important new tool for applied and fundamental research.

High genetic diversity of the attachment (G) protein of human metapneumovirus

Complete genes encoding the predicted nucleoprotein (N), phosphoprotein (P), matrix protein (M), fusion protein (F), M2-1protein, M2-2protein, small hydrophobic protein (SH), and attachmentprotein (G) of seven newly isolated human metapneumoviruses (hMPVs) were analyzed and compared with previously published data for hMPV genes. Phylogenetic analysis of the nucleotide sequences indicated that there were two genetic groups, tentatively named groups 1 and 2, similar to the grouping of human respiratory syncytial virus. Although the predicted amino acid sequences of N, P, M, F, and M2 were highly conserved between the two groups (amino acid identities, 96% for N, 85% for P, 97% for M, 94% for F, 95% for M2-1, and 90% for M2-2), the amino acid identities of the SH and G proteins were low (SH, 58%; G, 33%). Furthermore, each group could be subdivided into two subgroups by phylogenetic analysis, tentatively named subgroups 1A and 1B and subgroups 2A and 2B. The predicted amino acid sequences of G within members of each subgroup were highly conserved (amino acid identities, 88% for group 1A, 93% for group 1B, and 96% for group 2B). The G of hMPV is thought to be the major antigenic determinant and to play an important role in the production of neutralizing antibodies. Clarification of the antigenic diversity of G is important for epidemiological analysis and for establishment of strategies to prevent hMPV infection.

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

The growth properties and antigenic relatedness of the CAN98-75 (CAN75) and the CAN97-83 (CAN83) human metapneumovirus (HMPV) strains, which represent the two distinct HMPV genetic lineages and exhibit 5 and 63% amino acid divergence in the fusion (F) and attachment (G) proteins, respectively, were investigated in vitro and in rodents and nonhuman primates. Both strains replicated to high titers (> or =6.0 log(10)) in the upper respiratory tract of hamsters and to moderate titers (> or =3.6 log(10)) in the lower respiratory tract. The two lineages exhibited 48% antigenic relatedness based on reciprocal cross-neutralization assay with postinfection hamster sera, and infection with each strain provided a high level of resistance to reinfection with the homologous or heterologous strain. Hamsters immunized with a recombinant human parainfluenza virus type 1 expressing the fusion F protein of the CAN83 strain developed a serum antibody response that efficiently neutralized virus from both lineages and were protected from challenge with either HMPV strain. This result indicates that the HMPV F protein is a major antigenic determinant that mediates extensive cross-lineage neutralization and protection. Both HMPV strains replicated to low titers in the upper and lower respiratory tracts of rhesus macaques but induced high levels of HMPV-neutralizing antibodies in serum effective against both lineages. The level of HMPV replication in chimpanzees was moderately higher, and infected animals developed mild colds. HMPV replicated the most efficiently in the respiratory tracts of African green monkeys, and the infected animals developed a high level of HMPV serum-neutralizing antibodies (1:500 to 1:1,000) effective against both lineages. Reciprocal cross-neutralization assays in which postinfection sera from all three primate species were used indicated that CAN75 and CAN83 are 64 to 99% related antigenically. HMPV-infected chimpanzees and African green monkeys were highly protected from challenge with the heterologous HMPV strain. Taken together, the results from hamsters and nonhuman primates support the conclusion that the two HMPV genetic lineages are highly related antigenically and are not distinct antigenic subtypes or subgroups as defined by reciprocal cross-neutralization in vitro.

Human Metapneumovirus as a causative agent of acute bronchiolitis in infants

Background: Human Metapneumovirus (hMPV), has been recently isolated from children with acute respiratory tract infections (RTIs), including bronchiolitis, and classified in the Pneumovirinae subfamily within the Paramyxoviridae family. Objectives: Since most bronchiolitis studies fail to detect any viral pathogen in part of the samples, we sought for the presence of hMPV in a well characterized bronchiolitis cohort. Study design: Nasal washes were obtained from 56 children admitted to the hospital for acute bronchiolitis. RNA extraction and subsequent RT-PCR were used to detect hMPV, and correlated the presence of the virus with clinical characteristics of the disease. Results and conclusions: PCR revealed the presence of hMPV in 16% of bronchiolitis cases, whereas respiratory syncytial virus (RSV; 67.9%) was the most frequently encountered viral pathogen. hMPV was identified either as a unique viral pathogen or co-existed with RSV, with whom they shared a similar seasonal distribution. There were no differences in disease characteristics, either clinical or laboratory, between bronchiolitis cases where hMPV was present and those caused by RSV or other viral pathogens.

These findings suggest that hMPV is a common and important causative agent in infants with bronchiolitis, with clinical characteristics similar to that of RSV.

Human metapneumovirus infection among children hospitalized with acute respiratory illness

Recent studies have associated human Metapneumovirus (HMPV) infection in children with respiratory disease of similar severity as respiratory syncytial virus (RSV) infection. We studied 668 banked swab specimens (one per admission) collected from a population-based, prospective study of acute respiratory illness among inpatient children from two U.S. cities. Specimens were tested for HMPV, RSV, influenza, and parainfluenza viruses by reverse transcription–polymerase chain reaction assays. Twenty-six (3.9%) were positive for HMPV; 125 (18.7%) for RSV; 45 (6.7%) for parainfluenza 1, 2, or 3; and 23 (3.4%) for influenza. HMPV-positive children were significantly older than RSV-positive children. HMPV-positive children required medical intensive care and received supplemental oxygen in similar frequencies to RSV-positive children. Among children hospitalized with respiratory illness, the incidence of HMPV infection was less than RSV, but clinical disease severity mirrored that of RSV infection. Further investigations to better characterize HMPV infection and its clinical effect are needed.

Antigenic and genetic variability of human metapneumoviruses

Human metapneumovirus (HMPV) is a member of the subfamily Pneumovirinae within the family Paramyxoviridae. Other members of this subfamily, respiratory syncytial virus and avian pneumovirus, can be divided into subgroups based on genetic or antigenic differences or both. For HMPV, the existence of different genetic lineages has been described on the basis of variation in a limited set of available sequences. We address the antigenic relationship between genetic lineages in virus neutralization assays. In addition, we analyzed the genetic diversity of HMPV by phylogenetic analysis of sequences obtained for part of the fusion protein (n = 84) and the complete attachment protein open reading frames (n = 35). On the basis of sequence diversity between attachment protein genes and the differences in virus neutralization titers, two HMPV serotypes were defined. Each serotype could be divided into two genetic lineages, but these did not reflect major antigenic differences.

Experimental human metapneumovirus infection of cynomolgus macaques (Macaca fascicularis) results in virus replication in ciliated epithelial cells and pneumocytes with associated lesions throughout the respiratory tract

A substantial proportion of hitherto unexplained respiratory tract illnesses is associated with human metapneumovirus (hMPV) infection. This virus also was found in patients with severe acute respiratory syndrome (SARS). To determine the dynamics and associated lesions of hMPV infection, six cynomolgus macaques (Macaca fascicularis) were inoculated with hMPV and examined by pathological and virological assays. They were euthanized at 5 (n = 2) or 9 (n = 2) days post-infection (dpi), or monitored until 14 dpi (n = 2). Viral excretion peaked at 4 dpi and decreased to zero by 10 dpi. Viral replication was restricted to the respiratory tract and associated with minimal to mild, multi-focal erosive and inflammatory changes in conducting airways, and increased numbers of macrophages in alveoli. Viral expression was seen mainly at the apical surface of ciliated epithelial cells throughout the respiratory tract, and less frequently in type 1 pneumocytes and alveolar macrophages. Both cell tropism and respiratory lesions were distinct from those of SARS-associated coronavirus infection, excluding hMPV as the primary cause of SARS. This study demonstrates that hMPV is a respiratory pathogen and indicates that viral replication is short-lived, polarized to the apical surface, and occurs primarily in ciliated respiratory epithelial cells.

Identification of small-animal and primate models for evaluation of vaccine candidates for human metapneumovirus (hMPV) and implications for hMPV vaccine design

Human metapneumovirus (hMPV), a recently identified paramyxovirus, is the causative agent of respiratory tract disease in young children. Epidemiological studies have established the presence of hMPV in retrospective as well as current clinical samples in Europe, USA, Canada, Hong Kong and Australia. The hMPV disease incidence rate varied from 7 to 12 %. This rate of disease attack places hMPV in severity between respiratory syncytial virus and human parainfluenza virus type 3, two common respiratory pathogens of young children, the elderly and immunosuppressed individuals. To evaluate the effectiveness and safety of future hMPV antiviral drugs, therapeutic and prophylactic monoclonal antibodies (mAbs), and vaccine candidates, it was necessary to identify small-animal and primate models that efficiently supported hMPV replication in the respiratory tract and produced neutralizing serum antibodies, commonly a clinical correlate of protection in humans. In this study, various rodents (mice, cotton rats, hamsters and ferrets) and two primate species, rhesus macaques and African green monkeys (AGMs), were evaluated for hMPV replication in the respiratory tract. The results showed that hamsters, ferrets and AGMs supported hMPV replication efficiently and produced high levels of hMPV-neutralizing antibody titres. Hamsters vaccinated with subgroup A hMPV were protected from challenge with subgroup A or subgroup B hMPV, which has implications for hMPV vaccine design. Although these animal models do not mimic human hMPV disease signs, they will nevertheless be invaluable for the future evaluation of hMPV antivirals, mAbs and vaccines.

Recovery of human metapneumovirus from cDNA: optimization of growth in vitro and expression of additional genes

Human metapneumovirus (HMPV) is a recently recognized causative agent of respiratory tract disease in individuals of all ages and especially young infants. HMPV remains poorly characterized and has been reported to replicate inefficiently in vitro. Complete consensus sequences were recently determined for two isolates representing the two proposed HMPV genetic subgroups. We have developed a reverse genetic system to produce one of these isolates, CAN97-83, entirely from cDNA. We also recovered a version, rHMPV-GFP, in which the enhanced green fluorescent protein (GFP) was expressed from a transcription cassette inserted as the first gene, leaving the 41-nt leader region and first 16 nt of the N gene undisturbed. The ability to monitor GFP expression in living cells greatly facilitated the initial recovery of this slow-growing virus. In addition, the ability to express a foreign gene from an engineered transcription cassette confirmed the identification of the HMPV transcription signals and identified the F gene-end signal as being highly efficient for transcription termination. The ability to recover virus containing a foreign insert in this position indicated that the viral promoter is contained within the 3'-terminal 57 nt of the genome. Recombinant HMPV replicated in vitro as efficiently as biologically derived HMPV, whereas the kinetics and final yield of rHMPV-GFP were reduced several-fold. Conditions for trypsin treatment were investigated, providing for improved virus yields. Another version of HMPV, rHMPV+G1F23, was recovered that contained a second copy of the G gene and two extra copies of F in promoter-proximal positions in the order G1-F2-F3. Thus, this recombinant genome would encode 11 mRNAs rather than eight and would be 17.3 kb long, 30% longer than that of the natural virus. Nonetheless, the rHMPV+G1F23 virus replicated in vitro with an efficiency that was only modestly reduced compared to rHMPV and was essentially the same as rHMPV-GFP. Northern blot analysis showed that the increased number and promoter-proximal location of the added copies of the F and G genes resulted in a more than 6- and 14-fold increase in the expression of F and G mRNA, respectively, and sequence analysis confirmed the intactness of the added genes in recovered virus. Thus, it should be feasible to construct an HMPV vaccine virus containing extra copies of the G and F putative protective antigen genes to increase antigen expression or to provide representation of additional antigenic lineages or subgroups of HMPV.

Human respiratory syncytial virus matrix protein is an RNA-binding protein: binding properties, location and identity of the RNA contact residues

The human respiratory syncytial virus (HRSV) matrix (M) protein is a structural internal membrane protein. Here we have shown that, like its orthomyxovirus and rhabdovirus counterparts, it has RNA-binding capacity, as determined by retardation of (32)P-labelled riboprobes in gel electrophoresis, cross-linking with UV light and Northern-Western assays. Its binding to RNA was neither sequence-specific nor showed a length requirement, although it had cooperative kinetics with a K(d) of 25 nM and probably two different types of RNA-binding sites. After preparative cross-linking of (32)P-labelled riboprobes with purified, renatured HRSV Long strain M protein (256 residues), the residues in contact with RNA were located between amino acids 120 and 170, in the central part of the molecule. Lysine (positions 121, 130, 156 and 157) and arginine (position 170) residues located within this region and conserved among pneumovirus M proteins of different origins were found to be essential for RNA contact. M protein expression did not affect the replication and transcription of HRSV RNA analogues in vivo (except when expressed in large amounts), in contrast to the in vitro transcription inhibition described previously. In addition, M protein was found to aggregate into high-molecular-mass oligomers, both in the presence and absence of its RNA-binding activity. The formation of these structures has been related in other viruses to either viral or host-cell RNA metabolism.

Sequence polymorphism of the predicted human metapneumovirus G glycoprotein

The putative G glycoprotein genes of 25 human metapneumovirus (hMPV) field isolates obtained during five consecutive epidemic seasons (1997 to 2002) were sequenced. Sequence alignments identified two major genetic groups, designated groups 1 and 2, and two minor genetic clusters within each major group, designated subgroups A and B. Extensive nucleotide and deduced amino acid sequence variability was observed, consisting of high rates of nucleotide substitutions, use of alternative transcription-termination codons and insertions that retained the reading frame. Deduced amino acid sequences showed the greatest variability, with most differences located in the extracellular domain of the protein: nucleotide and amino acid sequence identities for the entire open reading frame ranged from 52 to 58 % and 31 to 35 %, respectively, between the two major groups. Like the closely related avian pneumovirus and human and bovine respiratory syncytial viruses, the predicted G protein of hMPV shared the basic features of a type II mucin-like glycosylated protein. However, differences from these related viruses were also observed, e.g. lack of conserved cysteine clusters as seen in human respiratory syncytial virus and avian pneumovirus. The displacement of genetic groups of hMPV observed during the study period suggests that potential antigenic differences in the G glycoprotein, which have evolved in response to immune-mediated pressure, may influence the circulation patterns of hMPV strains.

Evidence of human metapneumovirus in children in Argentina

Human metapneumovirus (hMPV) is a virus, which was first associated with acute lower respiratory infection in children but is detected currently in all age groups. Clinical symptoms are similar to those described for respiratory syncytial virus (RSV) infections, ranging from mild respiratory illness to severe bronchiolitis and pneumonia in children. To date, no cases of hMPV have been reported in Argentina. In this study, 440 respiratory samples obtained during the period 1998-2002 from children under 5 years old with acute respiratory infection were evaluated. Routine detection for RSV, adenovirus, influenza, and parainfluenza was undertaken by immunofluorescent assay. Of the samples negative for these viruses, only 100 were available. All these samples were tested for hMPV by RT-PCR using primers for the L gene. Eleven out of 100 (11%) respiratory samples were positive for hMPV by RT-PCR. A higher frequency of detection was observed in spring. hMPV was detected in all the years studied, except in 2001. Ten out of 11 children positive for hMPV were hospitalized. Median age was 5 months. Of seven patients, five (71%) required oxygen supplementation. The most frequent diagnosis was bronchiolitis (86%), sometimes accompanied by conjunctivitis and otitis media. The present study showed that hMPV was associated with acute lower respiratory infections in children in Buenos Aires, Argentina. This evidence strongly suggests that hMPV is a common pathogen with a wide geographical distribution, which should be included in the routine diagnosis of respiratory viruses in young children.

Comparison of the seroprevalence of human metapneumovirus and human respiratory syncytial virus

Human metapneumovirus (hMPV) is a virus that induces human respiratory syncytial virus (hRSV)-like illnesses, ranging from upper respiratory tract infection to severe bronchiolitis and pneumonia. The 100 serum samples from children aged 1 month to 5 years were tested for the presence of hMPV and hRSV antibodies using an indirect immunofluorescence assay and a neutralizing-antibody assay, respectively. The seroprevalence of hMPV was significantly lower than that of hRSV in children over 4-months-old (43% vs. 60%, P < 0.025), and the difference was particularly notable between the ages of 4 months and 1 year (11% vs. 48%, P = 0.006). The results suggest that primary infection with hMPV occurs somewhat later than that with hRSV.

Real-time reverse transcriptase PCR assay for detection of human metapneumoviruses from all known genetic lineages

The discovery of human metapneumovirus and its implications for respiratory tract disease have emphasized the need for a sensitive, specific, and rapid assay to detect this virus in a clinical setting. It recently became clear that human metapneumovirus can be grouped into at least four genetic lineages. Previously described assays for the detection of human metapneumovirus were developed by using limited sequence information and failed to detect viruses from all four genetic lineages with comparable sensitivities. Here we describe the development and evaluation of a real-time reverse transcriptase PCR assay that detects human metapneumovirus from the four known genetic lineages with equal specificities and sensitivities.

Human metapneumovirus and respiratory syncytial virus, Brazil

We describe the epidemiologic and clinical characteristics of 111 children attending clinics and hospitals in Aracaju, northeast Brazil, with acute respiratory infections attributable to human metapneumovirus (HMPV), respiratory syncytial virus (RSV), or both in May and June 2002. Fifty-three (48%) children were infected with RSV alone, 19 (17%) with HMPV alone, and 8 (7%) had RSV/HMPV co-infections.

A 1-year experience with human metapneumovirus in children aged <5 years

Human metapneumovirus (hMPV) is a recently discovered respiratory pathogen. We tested respiratory specimens for the presence of hMPV by reverse-transcription polymerase chain reaction. These specimens were obtained over a 1-year period from children aged <5 years and had negative results by the direct fluorescent antibody test for respiratory syncytial virus, influenza A and B, parainfluenza viruses 1-3, and adenovirus. Overall, 54 (8.1%) of 668 individuals tested positive for hMPV. During March and April of the study period, hMPV was detected in 17.6% and 25.0% of specimens tested, respectively. At least 2 distinct genotypes of hMPV circulated during the study period. Fever, tachypnea, cough, rhinorrhea, retractions of the chest wall, and wheezing were common findings. Of hMPV-positive children, 60.4% were aged <12 months. hMPV accounted for a small but significant proportion of respiratory-tract disease in infants and children.

Animal pneumoviruses: molecular genetics and pathogenesis

Pneumoviruses are single-stranded, negative-sense, nonsegmented RNA viruses of the family Paramyxoviridae, subfamily Pneumovirinae, and include pathogens that infect humans (respiratory syncytial virus and human metapneumovirus), domestic mammals (bovine, ovine, and caprine respiratory syncytial viruses), rodents (pneumonia virus of mice), and birds (avian metapneumovirus). Among the topics considered in this review are recent studies focused on the roles of the individual virus-encoded components in promoting virus replication as well as in altering and evading innate antiviral host defenses. Advances in the molecular technology of pneumoviruses and the emergence of recombinant pneumoviruses that are leading to improved virus-based vaccine formulations are also discussed. Since pneumovirus infection in natural hosts is associated with a profound inflammatory response that persists despite adequate antiviral therapy, we also review the recent experimental treatment strategies that have focused on combined antiviral, anti-inflammatory, and immunomodulatory approaches.

Human metapneumovirus: a new player among respiratory viruses

The human metapneumovirus (hMPV) is a newly described member of the Paramyxoviridae family belonging to the Metapneumovirus genus. Since its initial description in 2001, hMPV has been reported in most parts of the world and isolated from the respiratory tract of subjects from all age groups. Despite the fact that prospective and case-control studies have been limited, the epidemiology and clinical manifestations associated with hMPV have been found to be reminiscent of those of the human respiratory syncytial virus, with most severe respiratory tract infections occurring in infants, elderly subjects, and immunocompromised hosts. Additional research is needed to define the pathogenesis of this viral infection and the host's specific immune response.

Human metapneumovirus infection in Japanese children

Human metapneumovirus (hMPV) has been recently discovered as an etiological agent of acute respiratory infections. Our purpose was to asses the virological and clinical features of children with respiratory infections caused by hMPV. We examined 658 nasopharyngeal swab samples obtained from 637 children with respiratory infections for hMPV by using reverse transcription-PCR (RT-PCR). A total of 268 samples from 637 children were inoculated onto tertiary monkey kidney cells. A total of 36 serum samples (26 in the acute phase and 10 in the convalescent phase) from the 26 hMPV-positive children were tested for immunoglobulin G (IgG) and IgM antibodies to hMPV by using an indirect immunofluorescence assay. We detected hMPV in 57 (8.9%) of the 637 samples by using RT-PCR and isolated 7 (2.6%) hMPV strains of the 268 samples in cell cultures. A total of 12 (46.2%) of 26 hMPV-positive children were suspected to have primary infection with hMPV as determined by an indirect immunofluorescence assay. The infected children were diagnosed as having wheezy bronchitis (36.8%), upper respiratory tract infection (26.3%), bronchitis (22.8%), and pneumonia (14.0%). We showed that two hMPV groups were circulating in different regions during the same period and that reinfection with hMPV frequently occurs in childhood. The RT-PCR test is the most sensitive test for detection of hMPV, and a serological test may be useful to differentiate between primary infection and reinfection with hMPV.

[Acute respiratory tract infections due to a human metapneumovirus in children: descriptive study and comparison with respiratory syncytial virus infections]

BACKGROUND

A new paramyxovirus, the human metapneumovirus was recently isolated. We report the first French cases collected between 2000 and 2002.

MATERIAL AND METHODS

Samples were obtained from nasopharyngeal aspirates from children hospitalised for acute respiratory tract infection in hospitals of Caen and Flers in Basse-Normandie. Human metapneumovirus was studied by polymerase chain reaction on negative samples for respiratory syncytial virus, influenza A and B virus, parainfluenza (1, 2 and 3) virus, adenovirus, coronavirus and rhinovirus. Comparison between metapneumovirus virus and respiratory syncytial virus infections was done after matching sex, age and infection month.

RESULTS

Twenty-six human metapneumovirus infections were identified. A comparative study of a matched group of children infected by respiratory syncytial virus found no significative difference for hospitalisation motive, clinical criteria and treatment.

CONCLUSION

The human metapneumovirus is responsible for typical acute bronchiolitis in children.