Antigenic and genetic variability of human metapneumoviruses

An alphavirus replicon-based human metapneumovirus vaccine is immunogenic and protective in mice and cotton rats

Human metapneumovirus (hMPV) is a recently discovered paramyxovirus that causes upper and lower respiratory tract infections in infants, the elderly, and immunocompromised individuals worldwide. Here, we developed Venezuelan equine encephalitis virus replicon particles (VRPs) encoding hMPV fusion (F) or attachment (G) glycoproteins and evaluated the immunogenicity and protective efficacy of these vaccine candidates in mice and cotton rats. VRPs encoding hMPV F protein, when administered intranasally, induced F-specific virus-neutralizing antibodies in serum and immunoglobulin A (IgA) antibodies in secretions at the respiratory mucosa. Challenge virus replication was reduced significantly in both the upper and lower respiratory tracts following intranasal hMPV challenge in these animals. However, vaccination with hMPV G protein VRPs did not induce neutralizing antibodies or protect animals from hMPV challenge. Close examination of the histopathology of the lungs of VRP-MPV F-vaccinated animals following hMPV challenge revealed no enhancement of inflammation or mucus production. Aberrant cytokine gene expression was not detected in these animals. Together, these results represent an important first step toward the use of VRPs encoding hMPV F proteins as a prophylactic vaccine for hMPV.

Antiviral therapy for respiratory tract infections

Viruses are important pathogens causing respiratory tract infections both in the community and health-care facility settings. They are extremely common causes of morbidity in the competent hosts and some are associated with significant mortality in the compromised individuals. With wider application of molecular techniques, novel viruses are being described and old viruses are found to have new significance in different epidemiological and clinical settings. Some of these emerging pathogens may have the potential to cause pandemics or global spread of a severe disease, as exemplified by severe acute respiratory syndrome and avian influenza. Antiviral therapy of viral respiratory infections is often unnecessary in the competent hosts because most of them are selflimiting and effective agents are not always available. In the immunocompromised individuals or for infections caused by highly pathogenic viruses, such as avian influenza viruses (AIV), antiviral treatment is highly desirable, despite the fact that many of the agents may not have undergone stringent clinical trials. In immunocompetent hosts, antiviral therapy can be stopped early because adaptive immune response can usually be mounted within 5-14 days. However, the duration of antiviral therapy in immunosuppressed hosts depends on clinical and radiological resolution, the degree and duration of immunosuppression, and therefore maintenance therapy is sometimes needed after the initial response. Immunotherapy and immunoprophylaxis appear to be promising directions for future research. Appropriate and targeted immunomodulation may play an important adjunctive role in some of these infections by limiting the extent of end-organ damage and multi-organ failure in some fulminant infections.

New respiratory viruses of humans

Acute respiratory viruses are a major cause of morbidity and mortality in humans worldwide and most acute respiratory infections are caused by viruses. Many of these viruses cause the highest burden of disease in specific risk groups such as young infants, the elderly, and immune-compromised individuals. Although the most important respiratory viruses of humans have been identified in the last century, in the past decade about a dozen "new" viruses have been discovered that may cause a high burden of acute respiratory disease in humans. Not only viruses were discovered that must have been with humans for many decades or centuries, such as human metapneumovirus and 2 different human coronaviruses, but also viruses that are truly new for humans and have emerged as a result of recent interspecies transmissions from other mammalian or avian reservoirs. The latter include highly pathogenic avian influenza viruses, severe acute respiratory syndrome (SARS) coronavirus, and Nipah virus. The discovery, etiologic role, and burden of disease caused by these infections are described.

Human metapneumovirus infection in adults

Human metapneumovirus (hMPV) was first identified in 2001 in Dutch children with bronchiolitis. The virus is an RNA virus in the Pneumovirinae subfamily and is most closely related to respiratory syncytial virus. hMPV has been shown to have worldwide circulation with nearly universal infection by age 5. Similar to influenza and respiratory syncytial virus, activity is greatest during the winter in temperate climates. Most of the available data on the clinical manifestations of hMPV infection are from studies of children where the virus causes upper respiratory tract infections, bronchiolitis, and pneumonia. Reinfections with hMPV occur throughout adult life and hMPV infection has been documented in 1-9% of adults each year using RT-PCR and serology for diagnosis. Illness is generally mild in young adults with serologic evidence of asymptomatic infection in many cases. Adults at highest risk of serious sequelae as a result of hMPV include the elderly, adults with underlying pulmonary disease, and those who are immunocompromised. Outbreaks of hMPV have been documented in long term care facilities with mortality of up to 50% in frail elderly residents. In addition, 6-12% of exacerbations of chronic obstructive pulmonary disease have been associated with hMPV and underlying lung disease is common in patients hospitalized with hMPV. Lastly, hMPV has been linked with severe idiopathic pneumonia in recipients of hematopoietic stem cell transplants. Although the true spectrum of adult hMPV remains to be defined, it is clear that hMPV can result in severe illness the frail elderly and adults with underlying diseases.

Detection of four genetic subgroup-specific antibodies to human metapneumovirus attachment (G) protein in human serum

Human metapneumovirus (hMPV) strains are classified into two genetic groups, A and B, each of which is further divided in two genetic subgroups, A1, A2, B1 and B2. hMPV encodes two major surface glycoproteins, the fusion (F) and attachment (G) proteins, which may be immunogenic and protective antigens. Although the amino acid sequences of hMPV F protein are highly conserved, those of the G protein are highly variable with low amino acid identity between the two groups. To address the antigenic variation between the genetic subgroups, we developed an immunofluorescence assay (IFA) method using Trichoplusia ni (Tn5) insect cells infected with each recombinant baculovirus-expressed hMPV G (Bac-G) protein of the four genetic subgroups. The titre of each antibody to the four Bac-G proteins was measured by the IFA in 12 paired serum samples obtained from children infected with hMPV of each genetic subgroup. Although 11 of the 12 acute-phase serum samples in paired samples were negative for the antibody to any Bac-G proteins, all of the convalescent-phase serum samples in those paired samples were positive for the antibody to only one of the four Bac-G proteins of the infecting genotype of hMPV. Since the antibody response to hMPV G protein was transient and genetic subgroup-specific without cross-reactivity, four genetic subgroups on the basis of hMPV G protein could be identified as different serotypes. This assay may be useful for the study of immune responses of humans to different hMPV strains, especially for clarifying the risk of reinfection with hMPV.

Prevalence of human metapneumovirus among hospitalized children younger than 1 year in Catalonia, Spain

Human metapneumovirus was discovered recently respiratory virus implicated in both upper and lower respiratory tract infection. In children, the clinical symptoms of human metapneumovirus are similar to those produced by respiratory syncytial virus, ranging from mild to severe diseases such as bronchiolitis and pneumonia. The aim of the present study was to describe the prevalence of human metapneumovirus and other common respiratory viruses among admitted to hospital infants. From January 2006 to June 2006, 99 nasopharyngeal aspirates were collected from hospitalized children younger than 12 months in order to study respiratory viruses. Human metapneumovirus detection was performed by cell culture and two RT‐PCR targeting on polymerase and fusion genes. The latter gene was used for phylogenetic analysis. In 67/99 children (67%) at least one viral pathogen was identified, the viruses detected most frequently were respiratory syncytial virus (35%), human metapneumovirus (25%) and rhinovirus (19%). The results obtained in this study, show that: (1) human metapneumovirus is one of the most important viruses among children less than 12 months; (2) children infected with human metapneumovirus were significantly older than those infected by respiratory syncytial virus; (3) human metapneumovirus was associated more frequently with pneumonia whereas respiratory syncytial virus was only detected in patients with bronchiolitis; (4) there was a clear epidemiological succession pattern with only a small overlap among the viruses detected most frequently; (5) all human metapneumovirus samples were clustered within sublineage A2. J. Med. Virol. 80:1452–1460, 2008. © 2008 Wiley‐Liss, Inc.

Generation of temperature-sensitive human metapneumovirus strains that provide protective immunity in hamsters

Human metapneumovirus (HMPV) causes acute respiratory tract illness primarily in young children, immunocompromised individuals and the elderly. Vaccines would be desirable to prevent severe illnesses in these risk groups. Here, we describe the generation and evaluation of cold-passage (cp) temperature-sensitive (ts) HMPV strains as vaccine candidates. Repeated passage of HMPV at low temperatures in Vero cells resulted in the accumulation of mutations in the viral genome. Introduction of these mutations in a recombinant HMPV by reverse genetics resulted in a ts-phenotype, judged on the decreased shut-off temperature for virus replication in vitro. As an alternative approach, three previously described cp-respiratory syncytial virus (cp-HRSV) mutations were introduced in a recombinant HMPV, which also resulted in a low shut-off temperature in vitro. Replication of these ts-viruses containing either the cp-HMPV or cp-HRSV mutations was reduced in the upper respiratory tract (URT) and undetectable in the lower respiratory tract (LRT) of hamsters. Nevertheless, high titres of HMPV-specific antibodies were induced by both ts-viruses. Upon immunization with the ts-viruses, the LRT of hamsters were completely protected against challenge infection with a heterologous HMPV strain, and URT viral titres were reduced by 10 000-fold. In conclusion, we provide proof-of-principle for two candidate live-attenuated HMPV vaccines that induce cross-protective immunity to prevent infection of the LRT in Syrian golden hamsters. Further mapping of the molecular determinants of attenuation of HMPV should be the subject of future studies.

Low-pH-induced membrane fusion mediated by human metapneumovirus F protein is a rare, strain-dependent phenomenon

Membrane fusion promoted by human metapneumovirus (HMPV) fusion (F) protein was suggested to require low pH (R. M. Schowalter, S. E. Smith, and R. E. Dutch, J. Virol. 80:10931-10941, 2006). Using prototype F proteins representing the four HMPV genetic lineages, we detected low-pH-dependent fusion only with some lineage A proteins and not with lineage B proteins. A glycine at position 294 was found responsible for the low-pH requirement in lineage A proteins. Only 6% of all HMPV lineage A F sequences have 294G, and none of the lineage B sequences have 294G. Thus, acidic pH is not a general trigger of HMPV F proteins for activity.

The emergence of human metapneumovirus

Until relatively recently there had been episodes when children had been admitted into hospitals with symptoms that were similar to those expected for human respiratory syncytial virus (HRSV), but the available diagnostic procedures failed to detect the presence of HRSV, and the causative disease agent remained unidentified. Dutch scientists examined nasopharyngeal aspirates from similar patients in Holland using advanced molecular biology and imaging techniques. The conclusions of this study were published in 2001, revealing that a previously unidentified paramyxovirus was responsible for these infections. This agent was grouped within the subfamily Pneumovirinae, genus metapneumovirus, and given the name human metapneumovirus (HMPV) to distinguish it from other members of the genus Metapneumovirus that are of avian origin. Although HMPV is associated with upper respiratory tract infection, it is now recognized as a major cause of lower respiratory infection (LRTI) in children in a variety of different geographical regions. Furthermore, retrospective studies have detected the presence of HMPV in archived clinical material dating from the 1950s, suggesting that this was not a new virus, but it had remained undetected for several decades until its ‘emergence’ in 2001. This review will discuss the increasing global importance of HMPV as a cause of LRTI among young children.

Specificity and functional interaction of the polymerase complex proteins of human and avian metapneumoviruses

Human metapneumovirus (HMPV) and avian metapneumovirus (AMPV) have a similar genome organization and protein composition, but a different host range. AMPV subgroup C (AMPV-C) is more closely related to HMPV than other AMPVs. To investigate the specificity and functional interaction of the polymerase complex proteins of human and avian metapneumoviruses, a minireplicon system was generated for AMPV-C and used in combination with minireplicon systems for HMPV lineages A1 and B1. Viral RNA-like molecules representing HMPV-A1 and -B1, AMPV-A and -C and human respiratory syncytial virus were replicated efficiently by polymerase complexes of HMPV-A1 and -B1 and AMPV-C, but not by polymerase complexes of bovine parainfluenza virus 3. Upon exchange of HMPV and AMPV-C polymerase complex components, all chimeric polymerase complexes were functional; exchange between HMPVs did not result in altered polymerase activity, whereas exchange between HMPVs and AMPV-C did. Recombinant HMPV-B1 viruses in which polymerase genes were exchanged with those of HMPV-A1 replicated with normal kinetics in vitro, whilst replacement with AMPV-C genes resulted in moderate differences in virus replication. In hamsters, recombinant HMPV-B1 viruses in which individual polymerase genes were exchanged with those of AMPV-C were attenuated, irrespective of the results obtained with minireplicon systems or in vitro replication assays. This study provides insight into the specificity and functional interaction of polymerase complex proteins of human and avian metapneumoviruses, but neither minireplicon systems nor in vitro replication kinetics were found to be predictive for attenuation in permissive animals.

Efficient multiplication of human metapneumovirus in Vero cells expressing the transmembrane serine protease TMPRSS2

Human metapneumovirus (HMPV) is a major causative agent of severe bronchiolitis and pneumonia. Its fusion (F) protein must be cleaved by host proteases to cause membrane fusion, a critical step for virus infection. By generating Vero cells constitutively expressing the transmembrane serine protease TMPRSS2 and green fluorescent protein-expressing recombinant HMPV, we show that TMPRSS2, which is expressed in the human lung epithelium, cleaves the HMPV F protein efficiently and supports HMPV multiplication. The results indicate that TMPRSS2 is a possible candidate protease involved in the development of lower respiratory tract illness in HMPV-infected patients.

Clinical impact of human metapneumovirus genotypes and genotype-specific seroprevalence in Yamagata, Japan

The clinical impact of human metapneumovirus (hMPV) genotypes and the relation between the hMPV genotype in circulation and genotype-specific seroprevalence are yet to be clarified. We determined the genotypes of 93 hMPV strains that were isolated between 2004 and 2006 in Yamagata, Japan, and identified 35 genotype A2, 14 genotype B1, and 44 genotype B2 isolates. Children infected with genotype A2 hMPV were significantly older than those infected with genotype B1 hMPV. Diagnosis of laryngitis was more common in children with genotype B1 hMPV infection and wheezing was more prevalent in children with genotype B1 and B2 hMPV infection than in those with genotype A2 hMPV infection. We then examined genotype-specific seroprevalence by neutralization assay. The higher seropositive rate for the B2 genotype among the children aged 1-2 years is likely to reflect the outbreak of B2 genotype strains in the previous year in this community. The low seropositive rate for the B1 genotype among children aged 1-2 years appears to be associated with a finding that more than 70% of children infected with the B1 genotype were less than 3 years old. In conclusion, we found that the different clinical characteristics of hMPV infection may be associated with hMPV genotype, and the predominant genotype during a season and the affecting age may be closely related to genotype-specific immune status within a community.

Immunogenicity and efficacy of two candidate human metapneumovirus vaccines in cynomolgus macaques

Human metapneumovirus (HMPV) is an important cause of acute respiratory tract disease for which the development of vaccine candidates is warranted. We have previously described the generation of an iscom matrix-adjuvanted HMPV fusion protein subunit vaccine (Fsol) and a live-attenuated vaccine (HMPVM11). Here, we evaluate the immunogenicity and efficacy of these vaccines in cynomolgus macaques. Immunization with Fsol induced HMPV F-specific antibody responses, virus neutralizing antibody titers, and cellular immune responses, but the induced humoral immune response waned rapidly over time. HMPVM11 was strongly attenuated and displayed limited immunogenicity, although immunization with this virus primed for a good secondary HMPV-specific lymphoproliferative response after challenge infection. The duration of virus shedding in HMPVM11-immunized animals was reduced compared to sham-immunized animals. Both vaccines induced HMPV-specific immune responses, but the rapid waning of immunity is a challenging obstacle for vaccine development.

[Human metapneumovirus]

Le métapneumovirus humain (hMPV) est un nouveau Pneumovirinae apparenté au métapneumovirus aviaire du type C. Le génome du hMPV diffère de celui du virus respiratoire syncytial humain (RSV) par l’ordre des gènes et le manque des gènes non structuraux. Deux sous-groupes génétiques de hMPV et quatre sous-types ont été identifiés. Les infections à hMPV évoluent sous forme d’épidémies hivernales régulières, superposées à celle du RSV et d’importance à peu près égale d’une année sur l’autre. Chez les enfants hospitalisés à Caen, le hMPV est détecté dans 9,7 % des cas, après le RSV (37 %), les rhinovirus (18 %), les virus influenza (15,4 %), les adénovirus (9 %) et les virus parainfluenza (5 %). La plupart des infections à hMPV sont observées chez des enfants atteints de bronchiolites, mais par comparaison à l’infection à RSV, l’atteinte respiratoire basse et les signes de gravité sont moins fréquents. Le hMPV est très difficile à isoler en cultures des cellules. Le diagnostic a reposé jusqu’ici sur la détection moléculaire par RT–PCR. L’apparition récente des tests antigéniques permet de disposer aujourd’hui d’un test de diagnostic rapide, simple et économique.

Association between high nasopharyngeal viral load and disease severity in children with human metapneumovirus infection

Background

Previous studies have shown that viral genotype and viral load may play a significant role in the pathogenesis of viral infections.

Objectives

The aim of this study was to evaluate these aspects of hMPV infections in children and their household contacts.

Study design

Between 1 November 2003 and 31 March 2004, we prospectively studied 2060 children attending our Emergency Department for acute reasons. Nasopharyngeal swabs were collected upon enrolment and then tested with real-time PCR assays for the major viral causes of respiratory illness.

Results

Sixty children (2.9%) were infected by hMPV: 24 (1.2%) by hMPV A, 14 (0.7%) by hMPV B, 11 (0.5%) by untyped hMPV, and 11 (0.5%) by hMPV and an additional respiratory virus. There were no differences in disease presentation or in clinical or socioeconomic impact in relation to viral genotypes. HMPV viral load was significantly higher in children with lower respiratory tract involvement (p < 0.05), hospitalised children (p < 0.05), and the prevalence of secondary cases of a similar disease in the household of index cases (p < 0.05).

Conclusion

A high hMPV viral load correlated with disease presentation, whereas the overall clinical and socioeconomic burden caused by the two hMPV genotypes was similar.

Emerging pathogens: challenges and successes of molecular diagnostics

More than 50 emerging and reemerging pathogens have been identified during the last 40 years. Until 1992 when the Institute of Medicine issued a report that defined emerging infectious diseases, medicine had been complacent about such infectious diseases despite the alarm bells of infections with human immunodeficiency virus. Molecular tools have proven useful in discovering and characterizing emerging viruses and bacteria such as Sin Nombre virus (hantaviral pulmonary syndrome), hepatitis C virus, Bartonella henselae (cat scratch disease, bacillary angiomatosis), and Anaplasma phagocytophilum (human granulocytotropic anaplasmosis). The feasibility of applying molecular diagnostics to dangerous, fastidious, and uncultivated agents for which conventional tests do not yield timely diagnoses has achieved proof of concept for many agents, but widespread use of cost-effective, validated commercial assays has yet to occur. This review presents representative emerging viral respiratory infections, hemorrhagic fevers, and hepatitides, as well as bacterial and parasitic zoonotic, gastrointestinal, and pulmonary infections. Agent characteristics, epidemiology, clinical manifestations, and diagnostic methods are tabulated for another 22 emerging viruses and five emerging bacteria. The ongoing challenge to the field of molecular diagnostics is to apply contemporary knowledge to facilitate agent diagnosis as well as to further discoveries of novel pathogens.

WU polyomavirus in children with acute lower respiratory tract infections, South Korea

In South Korea, WU polyomavirus (WUPyV) was detected in 34 (7%) of 486 children with acute lower respiratory tract infections, 3 (4.2%) of 72 asymptomatic children, and as coinfection with other respiratory viruses in 23 (67.6%) children. Although WUPyV was frequently detected, its clinical role has not been distinguished from that of coinfecting viruses.

Human metapneumovirus in children, Singapore

Four hundred specimens were collected from pediatric patients hospitalized in Singapore; 21 of these specimens tested positive for human metapneumovirus (HMPV), with the A2 genotype predominating. A 5% infection rate was estimated, suggesting that HMPV is a significant cause of morbidity among the pediatric population of Singapore.

Clinical evaluation of NucliSENS magnetic extraction and NucliSENS analyte-specific reagents for real-time detection of human metapneumovirus in pediatric respiratory specimens

In this study, we evaluated the NucliSENS miniMAG (MM) and easyMAG (EM) nucleic acid extraction platforms (bioMérieux, Durham, NC) in combination with the NucliSENS EasyQ basic kit and analyte-specific reagents (ASRs) (bioMérieux) for the detection of human metapneumovirus (hMPV) in respiratory samples. Total nucleic acids from pediatric clinical samples (n = 653) and an hMPV-specific inhibition control (h-IC) were coextracted using the MM and/or the EM. Nucleic acid sequence-based amplification and real-time molecular beacon detection of hMPV were performed using a NucliSENS EasyQ analyzer (bioMérieux). Positive results were confirmed using an in-house-validated reverse transcriptase PCR ASR-based assay. The inclusion of the h-IC monitored the entire process, including the efficiency of nucleic acid extraction, amplification, and detection. The percentages of samples with inhibited amplification of the h-IC after initial NA extraction by EM and MM were 1.88% and 3.17%, respectively. After reprocessing of a new aliquot, the final h-IC inhibition rates were 0% (EM) and 1.06% (MM). The limit of detection of the assay was between 2 (EM extraction) and 10 (MM extraction) RNA copies/reaction, and specificity was 100% when testing viral respiratory isolates and clinical samples. hMPV was detected in 5.6% of pediatric samples tested and was also detected in three coinfections with respiratory syncytial virus (RSV). hMPV was the second most frequently detected respiratory virus in children of 0 to 2 years of age, after RSV. In summary, NucliSENS extraction and ASRs provided a sensitive and specific method for the detection of hMPV in respiratory samples.

The Prophylactic Administration of a Monoclonal Antibody against Human Metapneumovirus Attenuates viral Disease and Airways Hyperresponsiveness in Mice

Background

Human metapneumovirus (hMPV) is one of the most frequent causes of respiratory tract infections in children. Our objective was to assess the prophylactic benefit of a monoclonal antibody (mAb) against the hMPV fusion protein in a murine model.

Methods

BALB/c mice received one intramuscular injection of either 5 or 10 mg/kg of mAb 338 (MedImmune, Inc.) and were infected intranasally 24 h later with 1x108 TCID50 (50% tissue culture infectious dose) of hMPV. On days 5 and 42 post-infection, lung samples were collected for determination of viral titres and for histopathological studies. Pulmonary function was characterized by plethysmography.

Results

Mean lung viral titres were significantly lower in mice treated with 5 or 10 mg/kg of mAb 338 compared with infected controls on day 5 (283, 45.6 and 1.49x105 TCID50/g, respectively; P<0.05). Similarly, lung viral RNA copies were significantly reduced in treated mice on day 42 (292, 101 and 607 copies per 0.01 g of lungs for mice that received 5 mg/kg, 10 mg/kg or no mAb, respectively; P<0.05). Histopathological changes characterized by important alveolar and interstitial inflammation were less severe in treated mice on days 5 and 42 compared with control. Airways obstruction was also significantly reduced in both treated groups on days 5 and 42, but development of hyperresponsiveness following the acute phase of infection was only significantly reduced in 10 mg/kg treated mice.

Conclusions

Prophylactic administration of mAb 338 attenuates acute and late consequences of hMPV disease in this mouse model.

Vaccination approaches to combat human metapneumovirus lower respiratory tract infections

Human metapneumovirus (hMPV) was discovered in 2001 as a causative agent of respiratory disease in young children, immunocompromised individuals and the elderly. Clinical signs of hMPV infection range from mild respiratory illness to bronchiolitis and pneumonia. Two main genetic lineages of hMPV that circulate worldwide were found to be antigenically different, but antibodies against the F protein, the major determinant of protection, were shown to be cross-protective. Since the discovery of hMPV in 2001, several research groups have developed vaccine candidates that may be used to protect different risk groups against hMPV-induced respiratory disease. The studies in rodent and non-human primate models look promising, but none of the vaccine candidates has been tested yet in human volunteers. Here we give an overview of the immunogenicity and protective efficacy of a variety of live attenuated, virus vectored, inactivated virus and subunit vaccines that have been tested in animal models.

A PCR-restriction fragment length polymorphism assay to genotype human metapneumovirus

Human metapneumovirus (hMPV) genotypes A and B show epidemiological and probably clinical differences. This report describes a fast and simple PCR-restriction fragment length polymorphism (PCR-RFLP) assay, involving digestion of the fusion protein gene with Tsp509I, that allows lineages A1, A2, B1 and B2 to be distinguished. The assay should help in elucidating the epidemiology of hMPV, and possibly in predicting the severity of clinical infection.

Diagnosis of human metapneumovirus by immunofluorescence staining with monoclonal antibodies in the North-East of England

BACKGROUND

Since its discovery in 2001 human metapneumovirus (hMPV) has been shown to be a significant cause of human respiratory disease, responsible for 5-8% of respiratory infections in hospitalised children. Diagnosis hitherto has been largely carried out by reverse tanscriptase polymerase chain reaction (RT-PCR) but immunofluorescence staining of cells from nasopharyngeal secretions (IF) offers advantages for some laboratories and may produce a more rapid result in urgent cases. We have recently demonstrated that IF with a rabbit antiserum gave sensitivity equal to that of RT-PCR. However, monoclonal antibodies offer a more plentiful, uniform IF reagent.

OBJECTIVES

Here we have evaluated a pool of anti-hMPV monoclonal antibodies in the routine diagnosis of respiratory infections in hospitalised infants and children.

STUDY DESIGN

Eight hundred and fifty-seven routine respiratory specimens were tested by IF with rabbit polyclonal antiserum and monoclonal antibody pool in parallel. A further 1003 specimens were tested with the monoclonal antibody pool alone. All specimens were also tested for a panel of other respiratory viruses by IF.

RESULTS

Both rabbit polyclonal antiserum and monoclonal antibody pool gave positive results in 56 and negative results in 797 specimens. The rabbit polyclonal antibody detected virus in a further two specimens which were negative when tested with the monoclonal pool giving a concordance of 96.6% and a specificity of 100% for the monoclonal antibody pool. Overall hMPV was detected in 5% of specimens whilst 18.4% were positive for hRSV.

CONCLUSIONS

The monoclonal antibody pool-based IF is a robust assay suitable for routine use with a sensitivity only slightly less than that of the other major diagnostic methodologies available.

Identification and evaluation of a highly effective fusion inhibitor for human metapneumovirus

Human metapneumovirus (hMPV) can cause acute upper and lower respiratory tract infections that are particularly severe in young children, elderly subjects, and immunocompromised patients. To date, no treatments or vaccines are available for hMPV infections. Our objective was to assess the inhibitory potential of several peptides derived from the heptad repeat A and B (HRA and HRB) domains of the hMPV fusion protein. Nine candidate peptides were expressed in Escherichia coli or obtained synthetically and tested in vitro and in an animal model. Excellent in vitro inhibition of an hMPV strain of the A1 subgroup was obtained with five peptides, with 50% inhibitory concentrations ranging from 1.4 nM to 3.3 microM. One peptide, HRA2, displayed very potent activity against all four hMPV subgroups. It was also moderately active against human respiratory syncytial virus (strain A2) but displayed no activity against human parainfluenza virus type 3. BALB/c mice that received the HRA2 peptide and a lethal hMPV intranasal challenge simultaneously were completely protected from clinical symptoms and mortality. On day 5 postinfection, HRA2-treated mice had undetectable lung viral loads which were significantly less than those of untreated mice (3 x 10(4) 50% tissue culture infective doses/lung). Pulmonary inflammation, levels of proinflammatory cytokines/chemokines (RANTES, gamma interferon, and monocyte chemoattractant protein 1) and airway obstruction were also significantly decreased in HRA2-treated mice. The results of this study demonstrate that potent antivirals can be derived from the hMPV fusion protein HR domains. Moreover, hMPV, compared to other paramyxoviruses and to the human immunodeficiency virus, seems to be more susceptible to HRA- than HRB-derived peptides.

Immunization of Syrian golden hamsters with F subunit vaccine of human metapneumovirus induces protection against challenge with homologous or heterologous strains

Human metapneumovirus (hMPV), a newly discovered paramyxovirus, is associated with acute respiratory-tract illness, primarily in young children, individuals with underlying disease and the elderly. Two genetic lineages of hMPV circulate around the world, and viruses from these two lineages demonstrate antigenic differences. The clinical impact of hMPV warrants the development of vaccines. Recombinant soluble fusion (F) proteins of prototype viruses of the two main lineages of hMPV that can be produced in high yields have been constructed. In this study, the antigenicity, immunogenicity and protective efficacy of these soluble F subunit vaccines were evaluated in Syrian golden hamsters (Mesocricetus auratus). Immunization of hamsters with the soluble F proteins, adjuvanted with Specol or iscom matrix, induced high virus-neutralization titres, with higher titres against the homologous than the heterologous virus. The neutralizing antibodies protected from subsequent infection of the lungs with both homologous and heterologous virus. Upon challenge, viral titres in the nasal turbinates of immunized animals were reduced significantly compared with those of PBS-immunized animals. In conclusion, a soluble F subunit vaccine for hMPV that induces cross-protective immunity for infection of the lower respiratory tract in Syrian golden hamsters has been generated.

Immunization of macaques with formalin-inactivated human metapneumovirus induces hypersensitivity to hMPV infection

Human metapneumovirus (hMPV), a member of the family Paramyxoviridae, is an important cause of acute respiratory tract disease. In the 1960s, vaccination with formalin-inactivated paramyxovirus preparations--respiratory syncytial virus (RSV) and measles virus (MV)--resulted in predisposition for enhanced disease upon natural infection. We have produced a formalin-inactivated hMPV preparation (FI-hMPV), which was used to immunize young cynomolgus macaques. Six days after challenge FI-hMPV-primed monkeys had developed eosinophilic bronchitis and bronchiolitis, indicative of a hypersensitivity response. This study indicates that formalin-inactivated hMPV vaccines have the same propensity to predispose for immune-mediated disease as inactivated RSV and MV vaccines.

Positive natural selection in the evolution of human metapneumovirus attachment glycoprotein

Human metapneumovirus (hMPV), a newly discovered virus of the family Paramyxoviridae, has been associated with upper and lower respiratory tract infections in different age groups in many countries. The putative attachment (G) glycoprotein of this virus was previously reported to have shown more extensive nucleotide and deduced amino acid sequence polymorphism than any other genomic regions of this virus, leading to four sub-lineages. Using a maximum likelihood-based codon substitution model of sequence evolution, here we report that sequences of extracellular domain of 8 amino acid sites in lineage 1a, and 3 amino acid sites each in lineage 1b, 2a, and 2b have a higher rate of nonsynonymous substitutions (d(N)) than the synonymous substitutions (d(S)) with a posterior probability above 0.95, thus suggesting the evidence of adaptive evolution driven by Darwinian selection. Although it is unclear whether these amino acid adaptations are driven by differential immune pressure or some other factors, identification of these positively selected amino acid sites would help in better screening using epitope mapping technology to identify and localize the sites that can be recognized by the immune system. We also observed surprisingly higher nucleotide substitution rates per site, per year for each lineage of hMPV than the rates that were previously reported for the human respiratory syncytial virus, suggesting rapid evolutionary dynamics of hMPV.

Diagnosis and epidemiological studies of human metapneumovirus using real-time PCR

Background

Human metapneumovirus (hMPV) is prevalent in children, the elderly and immunocompromised individuals, but available epidemiological data is limited.

Objectives

(1) To develop and validate a real-time PCR method for hMPV diagnosis. (2) To determine the percentage of hMPV in respiratory specimens from the community and its association with outbreaks in our geographic area. (3) To provide epidemiological data in terms of age distribution, seasonality and co-infections.

Study design

A real-time PCR assay was designed for detection of hMPV lineages A and B. Prospective testing for hMPV over a 22-month period was then undertaken.

Results

The real-time PCR was sensitive and specific for detection of both lineages of hMPV. hMPV was detected in 9.5% (n = 8239) of the specimens and 25% of the outbreaks (n = 100) tested. The hMPV-positive patients ranged in age from 18 days to 99 years with a median age of 24 months. The number of positive samples peaked during the winter months of December, January and February. A high rate of co-infections was noted in the samples tested.

Conclusions

hMPV is common in the community and is associated with outbreaks. Including hMPV in routine testing improves etiological diagnosis of acute respiratory infections.

Prospective study of human metapneumovirus infection: diagnosis, typing and virus quantification in nasopharyngeal secretions from pediatric patients

STUDY DESIGN

During the winter-spring seasons 2004-2005 and 2005-2006, 965 nasopharyngeal aspirates from 871 patients were examined for human metapneumovirus (hMPV) by both monoclonal antibodies (MAbs) and reverse transcription (RT)-PCR.

RESULTS

Overall, 46 samples (4.8%) from 37 patients were positive for hMPV. Of these, 39 were positive by RT-PCR, and 35 by MAbs. Thus, using RT-PCR as a reference assay, the sensitivity, specificity, positive and negative predictive values of MAbs were 71.8%, 99.2%, 80.0% and 98.8%, respectively. Typing showed that concordant results were obtained in 32/46 (69.6%) strains (five untyped), whereas three strains were typed by MAbs only, and 11 by RT-PCR only. Finally, quantification of hMPV RNA allowed to correlate high viral load in nasopharyngeal secretions with acute respiratory symptoms in a group of 11 infants with acute lower respiratory tract infection examined upon admission and discharge from hospital, and a group of nine infants examined upon admission only. Conversely, hMPV etiology was questioned in a group of 14 infants with low viral load.

CONCLUSIONS

MAbs may represent an alternative to or a complement to RT-PCR for detection and typing of hMPV strains, while hMPV RNA quantification may help in associating viral load with clinical symptoms.

Newly discovered respiratory viruses: significance and implications

With the recent advances in molecular biology and the ability to amplify viral genomes in a non-sequence-dependent manner, several previously unidentified human respiratory viruses have been discovered. There are accumulating data that some of these new pathogens are responsible for a substantial proportion of respiratory tract diseases, particularly in children. This review will focus on several of these newly identified pathogens for which there are clinical data implicating a role of these viruses in respiratory tract disease specifically, human metapneumovirus, human coronaviruses NL63 and HKU1, and the human bocavirus. Antivirals and effective vaccines for these new agents may decrease the burden of respiratory tract diseases.

Detection of viruses identified recently in children with acute wheezing

The etiologic role of recently identified respiratory viruses for acute wheezing in children is not yet clear. The purpose of this study was to investigate the prevalence of recently identified viruses, including human metapneumovirus (hMPV), human bocavirus (hBoV), human coronavirus NL63 (hCoV‐NL63), and human coronavirus HKU1 (hCoV‐HKU1) in children with acute wheezing. Viral etiology was identified in 231 children hospitalized with acute wheezing, aged from 1 month to 5 years. Viral antigens for common respiratory viruses were detected by IFA or multiplex PCR. RT‐PCR was used to detect respiratory rhinoviruses, hCoV‐NL63, hCoV‐HKU1, and hMPV. PCR assays for hBoV DNA were performed using the primer sets for noncapsid protein (NP1) and nonstructural protein (NS1) genes. Viruses were found in 61.5% (142/231) of the study population and a single virus was detected in 45.5% (105/231) of the study population. Rhinovirus (33.3%), human respiratory syncytial virus (hRSV; 13.8%), and hBoV (13.8%) were the most frequently detected viruses. hMPV and hCoV‐NL63 were detected in 7.8% and 1.3% of wheezing children, respectively. HCoV‐HKU1 was not detected. In 16.0% of the study population, more than one virus was detected. In children with acute wheezing, rhinovirus, hRSV, and hBoV were most frequently detected. Further studies including healthy control subjects are needed to define the clinical significance of hBoV in acute wheezing. J. Med. Virol. 79: 1238–1243, 2007. © 2007 Wiley‐Liss, Inc.

Comparison of different cell lines and incubation times in the isolation by the shell vial culture of human metapneumovirus from pediatric respiratory samples

We report a prospective study concerning the efficacy of LLC-MK2 (continuous monkey kidney cell), Hep-2, MDCK (Madin-Darby Canine Kidney), Vero and MRC-5 cell lines, by shell vial assay, and incubation time in the isolation of hMPV from pediatric respiratory samples. The overall sensitivity of the cell lines studied were: 100% for the LLC-MK2, 68.7% for the Hep-2, 28.1% for the Vero, 3.1% for the MDCK and 0% for the MRC-5. Only one strain (3.1%) showed growth in the four cell lines studied and 10 (31.2%) strains only grew in the LLC-MK2 cell line. The analysis of incubation times showed that only 14 strains (43.7%) were able to grow after 3 days of incubation, while all strains (100%) showed growth after 5 days. The use of shell vials with commercial LLC-MK2 cells could be a method for isolating hMPV from respiratory samples in the pediatric population.

Respiratory picornavirus infections in Korean children with lower respiratory tract infections

Recently, human rhinoviruses (RVs) and enteroviruses have been suggested as important etiological agents in young children with lower respiratory tract infections (LRTIs). We investigated the role of respiratory picornaviruses in hospitalized children with LRTI. A total of 233 nasopharyngeal samples were collected from hospitalized children with LRTIs from July 2004 to January 2006. All specimens were tested for the presence of human respiratory syncytial virus (hRSV), influenza virus A, influenza B, parainfluenzavirus, and adenovirus using direct immunofluorescent assay, and for human metapneumovirus (HMPV) by RT-PCR. Detection of RV was performed in nasopharyngeal samples by a RT-PCR assay that incorporated a BglI restriction enzyme digestion of the picornavirus RT-PCR amplicon, and detection of enterovirus was accomplished by hemi-nested RT-PCR using specific primers. Viral agents were detected in 70.4% (164/233) of the study population. The most frequently detected viruses were RV (64/233, 27.4%), hRSV (48/233, 20.6%), and enterovirus (43/233, 18.4%). Picornaviruses were detected as the sole viral agents in 27.0% (63/233) of children, whereas mixed viral infection was detected in 12.0%. These results suggest that picronavirus infection is an important etiological cause of LRTIs in Korean children.

A recombinant human monoclonal antibody to human metapneumovirus fusion protein that neutralizes virus in vitro and is effective therapeutically in vivo

Human metapneumovirus (hMPV) is a recently discovered paramyxovirus that is a major cause of lower-respiratory-tract disease. hMPV is associated with more severe disease in infants and persons with underlying medical conditions. Animal studies have shown that the hMPV fusion (F) protein alone is capable of inducing protective immunity. Here, we report the use of phage display technology to generate a fully human monoclonal antibody fragment (Fab) with biological activity against hMPV. Phage antibody libraries prepared from human donor tissues were selected against recombinant hMPV F protein with multiple rounds of panning. Recombinant Fabs then were expressed in bacteria, and supernatants were screened by enzyme-linked immunosorbent assay and immunofluorescent assays. A number of Fabs that bound to hMPV F were isolated, and several of these exhibited neutralizing activity in vitro. Fab DS7 neutralized the parent strain of hMPV with a 60% plaque reduction activity of 1.1 mug/ml and bound to hMPV F with an affinity of 9.8 x10(-10) M, as measured by surface plasmon resonance. To test the in vivo activity of Fab DS7, groups of cotton rats were infected with hMPV and given Fab intranasally 3 days after infection. Nasal turbinates and lungs were harvested on day 4 postinfection and virus titers determined. Animals treated with Fab DS7 exhibited a >1,500-fold reduction in viral titer in the lungs, with a modest 4-fold reduction in the nasal tissues. There was a dose-response relationship between the dose of DS7 and virus titer. Human Fab DS7 may have prophylactic or therapeutic potential against severe hMPV infection.

Experimental infection of macaques with human metapneumovirus induces transient protective immunity

Human metapneumovirus (hMPV), a member of the family Paramyxoviridae, is a causative agent of acute respiratory-tract illness. Two main hMPV lineages circulate worldwide and reinfections occur frequently. It is unclear what level of protection is induced by natural hMPV infection, what the durability of this protection is and whether it differs for reinfection with homologous or heterologous viruses. Here, protective immunity in cynomolgus macaques at different time points after inoculation with molecularly cloned prototype viruses of the two main lineages of hMPV has been addressed. Animals received a homologous challenge at 4, 6 or 12 weeks after the primary infection. In addition, animals that had been inoculated three times within 10 weeks were challenged with homologous or heterologous virus 8 months later. Primary infection with 10(7) TCID(50) resulted in virus shedding and induction of virus-neutralizing antibody responses, with higher titres against the homologous than the heterologous virus. Infections associated with virus shedding and seroconversion protected completely from homologous reinfection within 6 weeks, and partly at 12 weeks, after primary infection. Eight months later, protection had waned to virtually undetectable levels. This study demonstrates that experimental hMPV infection induces transient protective immunity.

Acute respiratory infection by human metapneumovirus in children in southern Brazil

BACKGROUND

Human metapneumovirus (hMPV) has been described as an etiologic agent of acute respiratory infections (ARI), mainly in pediatric patients. Viral isolation is difficult and has low sensitivity, and consequently RT-PCR assays are currently used for detection.

OBJECTIVES

Detect hMPV in ARI in hospitalized children in Southern Brazil; standardize a RT-PCR for routine hMPV diagnosis; validate a positive control for molecular tests; and perform phylogenetics analyses.

STUDY DESIGN

Nasopharyngeal aspirates (NPA) from 156 hospitalized children were studied. A conserved region of the nucleoprotein gene was cloned, characterized and used to standardize an RT-PCR assay. Phylogenetic analyses were performed. Clinical data were obtained from medical records.

RESULTS

hMPV was detected in 6.4% of the samples. Dyspnea and wheezing were frequently reported symptoms and the most common diagnoses were bronchiolitis, acute respiratory insufficiency or laryngotracheobronchitis. Nucleotide sequence alignment revealed 97.7% identity with genotype A1 of hMPV. The detection limit of hMPV genomes by RT-PCR in clinical samples was 180 copies/microL.

CONCLUSION

This is the first report of the detection and genetic characterization of hMPV infections in children with lower ARI in Southern Brazil.

Outbreak of human metapneumovirus detected by use of the Vero E6 cell line in isolates collected in Yamagata, Japan, in 2004 and 2005

A number of epidemiological studies have shown human metapneumovirus (hMPV) to be one of the most important viral agents associated with acute respiratory infections in humans. However, due to the difficulty in growing the virus, all epidemiological studies of hMPV infection have been performed on the basis of the molecular method. Thus, the development of a cell line suitable for the isolation of hMPV from clinical specimens is a crucial step for further research. Using the Vero E6 cell line, which could be stably maintained for 1 month without passage or medium change, we succeeded in isolating 79 strains from 4,112 specimens obtained in Yamagata, Japan, in 2004 and 2005. The total isolation rate was 1.9% (79/4,112). The monthly distribution revealed that hMPV infections occurred between February and April in 2004 and throughout most of the year in 2005. Phylogenetic analysis indicated that subgenogroup B2 was predominant in 2004, whereas three subgenogroups, A2, B1, and B2, had cocirculated in 2005. Although multiple subgenogroups cocirculated in 2005, each individual subgenogroup strain was found to predominate at specific sites. An infectivity assay of hMPV strains also indicated that the infection efficiency in Vero E6 cells was better than that in LLC-MK2 cells. Finally, we found that Vero E6 cells are useful for the isolation of hMPVs and that this utility might aid further research into hMPVs beyond the epidemiological data shown in this study.

An improved plaque reduction virus neutralization assay for human metapneumovirus

Virus-neutralizing antibodies against human metapneumovirus (hMPV) have been shown to be important indicators for protection in experimental animal models. An improved plaque reduction virus neutralization assay to detect hMPV-specific neutralizing antibodies was designed using two prototype recombinant hMPV strains expressing green fluorescent protein (GFP). These prototypes represented each of the main antigenic variants of hMPV, because antigenic variability could have implications for vaccine development. The utility of mutations in the F gene resulting in trypsin-independent replication was also tested. Although these mutant hMPV strains could replicate in the absence of trypsin, bigger plaque size was achieved with the addition of trypsin. Insertion of the GFP gene in the genome of hMPV did not affect replication of the virus in vitro. Plaques could be detected by measuring expression of GFP after 5 days by automated scanning. Ferret, hamster, and macaque sera positive for hMPV were compared in a conventional virus neutralization assay and the plaque reduction virus neutralization assay. The results obtained with the two assays were in agreement but the improved plaque reduction virus neutralization assay was faster, more suitable for high throughput testing, and 10-fold more sensitive than the conventional virus neutralization assay.

Detection of human metapneumovirus in hospitalized children with acute respiratory tract infection using real-time RT-PCR in a hospital in northern Taiwan

Background/purpose

Human metapneumovirus (hMPV) is a newly discovered respiratory pathogen. This prospective hospital-based study investigated the clinical role and features of hMPV in Taiwan.

Methods

Respiratory specimens collected from hospitalized children with acute respiratory tract infection between September 1, 2003 and April 10, 2005 were screened for metapneumovirus using real-time reverse transcription-polymerase chain reaction (RT-PCR).

Results

During the study period, 930 specimens were obtained from 926 hospitalized children. After exclusion of 200 cases due to lack of clinical evidence of airway infection or diseases with known etiology, 726 were included in the analysis. Among these, 33 children had a positive result for hMPV infection. The majority of these patients were admitted during spring and early summer. Twenty-one (63.6%) were younger than 2 years of age. hMPV accounted for 13.3% of respiratory infections occurring between the ages of 18 and 24 months and was as common a respiratory pathogen as respiratory syncytial virus (RSV) in that age group. The 11 patients (33.3%) with underlying diseases had a similar disease course to those without underlying diseases. A co-pathogen was found in 11 patients (33.3%). Infected children between 2 and 5 years of age had significantly higher titers of hMPV in their respiratory specimens (10^3.88 copies/mL) than children younger than 2 years (10^2.26 copies/mL) (p = 0.013) and children older than 5 years (10^2.25 copies/mL) (p = 0.005). hMPV positive cases were significantly older than those with RSV infection (p = 0.002) and had a shorter duration of hospitalization (p = 0.001), fewer days of oxygen use (p = 0.001) and higher levels of C-reactive protein (p = 0.004).

Conclusion

Metapneumovirus circulates in children in northern Taiwan during spring and early summer. hMPV was the most common respiratory pathogen in children aged between 18 and 24 months hospitalized with acute respiratory tract infection. Real-time RT-PCR is a sensitive method for investigating the epidemiology and diseases associated with hMPV. [J Formos Med Assoc 2007;106(1):16-24]

Live vaccines for human metapneumovirus designed by reverse genetics

Human metapneumovirus (HMPV) was first described in 2001 and has quickly become recognized as an important cause of respiratory tract disease worldwide, especially in the pediatric population. A vaccine against HMPV is required to prevent severe disease associated with infection in infancy. The primary strategy is to develop a live-attenuated virus for intranasal immunization, which is particularly well suited against a respiratory virus. Reverse genetics provides a means of developing highly characterized 'designer' attenuated vaccine candidates. To date, several promising vaccine candidates have been developed, each using a different mode of attenuation. One candidate involves deletion of the G glycoprotein, providing attenuation that is probably based on reduced efficiency of attachment. A second candidate involves deletion of the M2-2 protein, which participates in regulating RNA synthesis and whose deletion has the advantageous property of upregulating transcription and increasing antigen synthesis. A third candidate involves replacing the P protein gene of HMPV with its counterpart from the related avian metapneumovirus, thereby introducing attenuation owing to its chimeric nature and host range restriction. Another live vaccine strategy involves using an attenuated parainfluenza virus as a vector to express HMPV protective antigens, providing a bivalent pediatric vaccine. Additional modifications to provide improved vaccines will also be discussed.

Epidemiological and clinical features of hMPV, RSV and RVs infections in young children

BACKGROUND

Human metapneumovirus (hMPV) has recently been isolated from children with acute respiratory tract infections (RTIs). The epidemiological and clinical characteristics of hMPV infection need further investigation.

OBJECTIVES

The purpose of this study was to compare the clinical features of hMPV, respiratory syncytial virus (RSV) and rhinoviruses (RV) infections in children less than 3 years of age presenting to an emergency department with acute respiratory illness.

STUDY DESIGN

From December 2002 to April 2004, all children under age three (n=931) admitted for acute respiratory illness to Dijon Hospital, France, were investigated for respiratory viruses in nasal washes.

RESULTS

hMPV was detected in 6% of children (in 10.1% (n=38) the first winter and in 3.3% (n=17) the second winter); RSV was detected in 28.5% of the children, while rhinoviruses were found in 18.3%. Five hMPV-infected children had evidence of dual infection, two with RSV and three others with RV. The median age of the patients with hMPV infection was 6 months, and the main clinical symptoms were rhinorrhea (74.5%) and cough (67%). A lower tract disease occurred in 66% of hMPV-positive patients. Gene sequencing of hMPV isolates revealed co-circulation of the two major groups of hMPV during the study period; no difference in pathogenicity was found. There was no difference in the prevalence of bronchiolitis where hMPV, RSV or rhinoviruses were present. Asthma was found more often in hospitalized children with hMPV and rhinoviruses than among those with RSV (p<0.001).

CONCLUSIONS

These results provide further evidence of the importance of hMPV as a pathogen associated with respiratory tract infection in children.

Human metapneumovirus infection

Initially, human metapneumovirus (hMPV) was isolated from children with clinical symptoms of respiratory syncytial virus (RSV) infection in whom RSV could not be detected. Since then, numerous reports have described the detection of hMPV in clinical specimens from children, adults and the elderly (both immunocompetent and immunocompromised patients), diagnosed with an acute respiratory illness all over the world. hMPV is associated with a substantial number of respiratory tract infections in otherwise healthy children, with clinical illnesses similar to those associated with other common respiratory viruses. Serological surveys have shown that hMPV is a ubiquitous virus that infects all children by the age of 5–10 years and has been circulating in humans for at least 50 years. hMPV is a member of the Metapneumovirus genus of the Paramyxoviridae family, a group of negative-stranded RNA viruses. Genetic studies on hMPV have demonstrated the presence of two distinct hMPV serotypes each divided in two subgroups. Diagnosis is made by RT-PCR assays on respiratory secretions. Rapid antigen detection tests are not yet available and its growth in cell cultures is fastidious. No vaccines, antibodies (monoclonal or polyclonal), or chemotherapeutic agents are currently licensed for use to prevent or treat hMPV infections. The contribution of hMPV to pediatric respiratory tract infections suggests that it will be important to develop a vaccine against this virus in combination with those being developed for RSV and parainfluenza viruses. Reverse genetics technology is currently used to develop multivalent vaccines against hMPV and a variety of other important respiratory viruses such as RSV. Additional research to define the pathogenesis of this viral infection and the host’ specific immune response will enhance our knowledge to guide the search for preventive and therapeutical strategies.

Serosurvey of human metapneumovirus infection in Croatia

AIM

To assess the seroprevalence of human metapneumovirus (hMPV) in Croatia.

METHODS

During 2005, a total of 137 serum specimens from Croatian patients aged from 6 days to 51 years, without respiratory symptoms, were collected at the Croatian National Institute of Public Health. The sera were examined using the indirect immunofluorescent assay.

RESULTS

The overall hMPV seropositivity rate in the samples tested was 77.4% (106/137). The seropositivity rate increased from 18.7% in children aged between 6 months and 1 year to 100% in people older than 20 years of age. The highest proportion of titers > or =1:512 was found in children aged from 1 to 2 years.

CONCLUSION

Our results suggest that hMPV infection is present in Croatia, with primary infection occurring in early childhood. This is the first study that indicates the circulation of hMPV in Croatia.

[Human metapneumovirus]

Human metapneumovirus (hMPV), first isolated in the Netherlands in 2001, is a member of the genus Metapneumovirus of the sub-family Pneumovirinae of the family Paramyxoviridae. The genomic organization of hMPV is 3'-N-P-M-F-M2-SH-G-L-5'. hMPV resembles the sole member of this genus, avian pneumovirus. hMPV is the most closely related human pathogen to respiratory syncytial virus. Phylogenetic analysis of the nucleotide sequences indicated that there were two genetic groups. Furthermore, each group could be subdivided into two subgroups. hMPV encodes three surface proteins, F, G and SH proteins. The majority of antibodies to hMPV in serum were antibody against F protein, which mediates cross-group neutralization and protection. The incidences of hMPV-associated respiratory infection estimate 5 to 10% in children and 2 to 4% in adults. hMPV generally causes upper respiratory tract infection and flu-like illness, the virus can be associated with lower tract infections, such as wheezy bronchitis, bronchitis, bronchiolitis and pneumonia, in very young children, elderly persons, and immunocompromised patients. hMPV has a seasonal peak during the spring in Japan. Reinfection with hMPV frequently occurs in children, implying that the host immune response induced by natural infection provides incomplete protection. The RT-PCR test is the most sensitive test for detection of hMPV.