Human metapneumovirus: a not so new virus

Comparison of human metapneumovirus, respiratory syncytial virus and Rhinovirus respiratory tract infections in young children admitted to hospital

Respiratory Syncytial Virus (RSV), Human metapneumovirus (HMPV), and Rhinoviruses (RV) are frequent causes of respiratory tract infections in young children. We compared laboratory and clinical findings in children with comparable age distribution and hospitalized due to RSV, HMPV or RV infections. Viral pathogens were detected by a quantitative real time PCR from nasopharyngeal aspirates. No significant differences in the admission diagnosis, laboratory parameters, patient demographics and treatment measures between the three viral causes of respiratory illness were found. No correlation between viral load and disease severity was observed however, there was a significantly lower concentration of the nasopharyngeal interleukin 8 (IL‐8) in children with RV compared to HMPV and RSV, indicating a milder proinflammatory reaction. Moreover, RV‐infected children had significantly lower body temperature, higher leucocyte counts in peripheral blood, and a tendency to have a shorter stay in hospital than children with either HMPV or RSV infection. Taken together, clinical presentation of the infections with RSV, HMPV, and RV is similar among children of the same age group and not clearly distinguishable by standard clinical or laboratory findings. Therefore, virus specific testing should be included regularly for routine diagnosis of children with respiratory tract infections. J. Med. Virol. 87:275–280, 2015. © 2014 Wiley Periodicals, Inc.

Human metapneumovirus infections are associated with severe morbidity in hospitalized children of all ages

The impact of human metapneumovirus (HMPV) in children aged >5 years and the risk factors associated with disease severity for all ages have not been well characterized. A retrospective cohort study of 238 children aged 0–15 years hospitalized over a 3-year period was performed. Medical records were reviewed for demographic information, clinical parameters and outcomes. Multivariable analyses were performed to identify independent factors associated with worse disease severity assessed by length of hospital stay (LOS), need for ICU care, respiratory support, and a disease severity score. Pulmonary diseases were associated with all outcomes of care, while congenital heart disease (CHD) and neuromuscular disorders were associated with longer LOS, and CHD and trisomy 21 were associated with worse severity scores independent of other covariables. Fever, retractions, use of steroids and albuterol were also associated with enhanced disease severity. Understanding the determinants of HMPV disease in children may help design targeted preventive strategies.

Epidemiological and phylogenic study of human metapneumovirus infections during three consecutive outbreaks in Normandy, France

Human metapneumovirus (hMPV) is responsible for respiratory tract disease, particularly in the young and elderly population. An epidemiological and phylogenic study was performed on children admitted to hospital with an acute lower respiratory tract infection (LRI). Data were obtained and analyzed over three consecutive winters, from 2002–2003 to 2004–2005. Each year during the winter period, from November to March, 2,415 nasal swabs were tested by a direct immunofluorescence assay (DFA) for influenza viruses A and B, respiratory syncytial virus, parainfluenza viruses, and adenoviruses. Rhinoviruses, enteroviruses, and coronaviruses OC43 and 229E were detected by RT‐PCR. A RT‐PCR designed for the M gene was performed on negative samples for hMPV detection and phylogenic analyses. For the three consecutive winters, hMPV represented 10%, 22.6%, and 8.8% of virus‐negative samples, respectively. In most cases, clinical symptoms indicated a LRI with a final diagnosis of bronchiolitis. During the winter of 2003–2004, all viral clusters (A1, A2, B1, and B2) that circulated in France shifted progressively from the A group to the B group. This study determined the prevalence of hMPV in Normandy, its clinical impact and permitted the analysis of the molecular evolution during the successive outbreaks. J. Med. Virol. 83:517–524, 2011. © 2011 Wiley‐Liss, Inc.

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.

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]

Human metapneumovirus and respiratory syncytial virus infections in older children with cystic fibrosis

BACKGROUND

Human metapneumovirus (hMPV) has been isolated from children with acute respiratory infection worldwide. Its epidemiology remains to be defined in children with cystic fibrosis (CF). We describe the epidemiology and clinical impact of hMPV in CF children and compared it to respiratory syncytial virus (RSV).

METHODS

CF children ages 7-18 years were studied prospectively during the 1998 -1999 RSV season. Nasopharyngeal specimens were collected during acute respiratory illnesses and tested for respiratory viruses. Blood specimens were drawn early, mid, and end of the RSV season, and tested for serological evidence of hMPV and RSV infections. Rates of lower respiratory tract illnesses (LRTI) and hospitalizations for pulmonary exacerbations were compared during the time intervals they developed serological evidence of infection to their non-infection intervals.

RESULTS

Six of 44 CF children had a virus positive respiratory illness in 56 LTRI events and 18 hospitalizations. Serological evidence of hMPV and RSV infections occurred in 16 and 20 CF children, respectively; 8 had infections with both viruses. A greater proportion of CF children had >or=1 LRTI during their infection intervals compared to their non-infection intervals (13/25 vs. 5/25; P=0.03). A trend for higher rates of LRTI was observed in the infection intervals compared to non-infection intervals (9.5 +/- 11.0 vs. 4.2 +/- 9.9 per 1,000 child-days; P=0.06), and it was significantly greater with a more conservative estimate (one event per child per interval; 7.4 +/- 7.7 vs. 2.6 +/- 5.4 per 1,000 child-days; P <or=0.01). No differences in hospitalizations rates were detected.

CONCLUSION

The infection rates and clinical impact observed for hMPV were comparable to that for RSV in CF children 7-18 years of age.

Human metapneumovirus infection in a hematopoietic stem cell transplant recipient with relapsed multiple myeloma and rapidly progressing lung cancer

Human metapneumovirus (HMPV) was isolated from a 63-year-old multiple myeloma patient who had undergone hematopoietic stem cell transplantation and who presented with lower respiratory tract infection several weeks prior to the diagnosis of lung cancer. The isolate was phylogenetically and biologically characterized and compared to HMPV prototypes and recent pediatric isolates. Remarkably, it belonged to the novel genomic subgroup A2b.

Isolation and characterization of monoclonal antibodies which neutralize human metapneumovirus in vitro and in vivo

Human metapneumovirus (hMPV) is a recently described member of the Paramyxoviridae family/Pneumovirinae subfamily and shares many common features with respiratory syncytial virus (RSV), another member of the same subfamily. hMPV causes respiratory tract illnesses that, similar to human RSV, occur predominantly during the winter months and have symptoms that range from mild to severe cough, bronchiolitis, and pneumonia. Like RSV, the hMPV virus can be subdivided into two genetic subgroups, A and B. With RSV, a single monoclonal antibody directed at the fusion (F) protein can prevent severe lower respiratory tract RSV infection. Because of the high level of sequence conservation of the F protein across all the hMPV subgroups, this protein is likely to be the preferred antigenic target for the generation of cross-subgroup neutralizing antibodies. Here we describe the generation of a panel of neutralizing monoclonal antibodies that bind to the hMPV F protein. A subset of these antibodies has the ability to neutralize prototypic strains of both the A and B hMPV subgroups in vitro. Two of these antibodies exhibited high-affinity binding to the F protein and were shown to protect hamsters against infection with hMPV. The data suggest that a monoclonal antibody could be used prophylactically to prevent lower respiratory tract disease caused by hMPV.

Modification of the trypsin-dependent cleavage activation site of the human metapneumovirus fusion protein to be trypsin independent does not increase replication or spread in rodents or nonhuman primates

The contribution of cleavage activation of the fusion F protein of human metapneumovirus (HMPV) to replication and pathogenicity in rodents and nonhuman primates was investigated. Recombinant HMPVs were generated in which the naturally occurring trypsin-dependent cleavage sequence (R-Q-S-R downward arrow) was replaced by each of three sequences whose cleavage in vitro does not depend upon added trypsin. Two of these were multibasic sequences derived from avian metapneumovirus type A (R-R-R-R) or type C (R-K-A-R), with the former containing the consensus furin protease cleavage motif (R-X-R/K-R downward arrow). The third one (R-Q-P-R) was derived from a recently described trypsin independent HMPV isolate (J. H. Schickli, J. Kaur, N. Ulbrandt, R. R. Spaete, and R. S. Tang, J. Virol. 79:10678-10689, 2005). To preclude the possibility of conferring even greater virulence to this significant human pathogen, the modifications were done in an HMPV variant that was attenuated by the deletion of two of the three envelope glycoproteins, SH and G. Each of the introduced cleavage sequences conferred trypsin independent F cleavage and growth to HMPV in vitro. However, they differed in the efficiency of trypsin independent growth and plaque formation in vitro: R-R-R-R > R-K-A-R > R-Q-P-R > R-Q-S-R. The R-R-R-R mutant was the only one whose growth in vitro was not augmented by added trypsin, indicative of highly efficient trypsin independent cleavage. When inoculated intranasally into hamsters, there was essentially no difference in the magnitude of replication in the upper or lower respiratory tract between the mutants, and virus was not detected in organs outside of the respiratory tract. Evaluation of the most cleavage-efficient mutant, R-R-R-R, in African green monkeys showed that there was no detectable change in the magnitude of replication in the upper and lower respiratory tract or in immunogenicity and protective efficacy against HMPV challenge. These results suggest that cleavage activation is not a major determinant of HMPV virulence.

Human metapneumovirus in paediatric patients

Acute respiratory tract infections (ARTIs) are a leading cause of morbidity and mortality in children worldwide, but the aetiology of many ARTIs is still unknown. In 2001, researchers in The Netherlands reported the discovery of a previously unidentified pathogen called human metapneumovirus (hMPV). Since its initial description, hMPV has been associated with ARTI in Europe (Italy, France, Spain, the UK, Germany, Denmark, Finland and Norway), America (the USA, Canada, Argentina and Brazil), Asia (India, Japan, China and Singapore), Australia and South Africa in individuals of all ages. The incidence of infection varies from 1.5% to 25%, indicating that hMPV is a ubiquitous virus with a worldwide distribution. hMPV seems to play an important role as a cause of paediatric upper and lower respiratory tract infection, with similar, but not identical, epidemiological and clinical features to those of respiratory syncytial virus and influenza virus. Moreover, the socio‐economic impact of hMPV‐infected children on their families seems to be considerable, which suggests that, like influenza virus, hMPV infection may be a substantial public health problem for the community. It may be associated with significant morbidity and mortality in pre‐term infants and children with underlying clinical conditions, although more adequately controlled studies are needed to confirm its importance in such patients. Many fundamental questions concerning the pathogenesis of hMPV disease and the host's specific immune response remain to be answered. Further studies are also required to properly define hMPV diagnosis, treatment and prevention strategies.

Human metapneumovirus induces a profile of lung cytokines distinct from that of respiratory syncytial virus

Lung cytokine and chemokine production by BALB/c mice infected with human metapneumovirus (hMPV) was compared to respiratory syncytial virus (RSV)-infected mice. hMPV infection induced lower levels of the inflammatory cytokines interleukin-1 (IL-1), IL-6 and tumor necrosis factor alpha but was a more potent inducer of granulocyte-macrophage colony-stimulating factor and triggered a more sustained production of the CXC chemokine KC compared to RSV. hMPV was a stronger inducer of both alpha interferon (IFN-alpha) and IFN-gamma responses than RSV. In regard to immunomodulatory cytokines, hMPV failed to induce detectable IL-10 or IL-12p70 but was a potent inducer of IL-12 p40 subunit. The implications for hMPV pathogenesis are discussed.

Real-time PCR in clinical microbiology: applications for routine laboratory testing

Real-time PCR has revolutionized the way clinical microbiology laboratories diagnose many human microbial infections. This testing method combines PCR chemistry with fluorescent probe detection of amplified product in the same reaction vessel. In general, both PCR and amplified product detection are completed in an hour or less, which is considerably faster than conventional PCR detection methods. Real-time PCR assays provide sensitivity and specificity equivalent to that of conventional PCR combined with Southern blot analysis, and since amplification and detection steps are performed in the same closed vessel, the risk of releasing amplified nucleic acids into the environment is negligible. The combination of excellent sensitivity and specificity, low contamination risk, and speed has made real-time PCR technology an appealing alternative to culture- or immunoassay-based testing methods for diagnosing many infectious diseases. This review focuses on the application of real-time PCR in the clinical microbiology laboratory.

Community-acquired pathogens associated with prolonged coughing in children: a prospective cohort study

A 2-year prospective study was performed of children with prolonged coughing to investigate the frequency of different respiratory pathogens, the rate of mixed infections, and possible differences in severity of disease between single and mixed infections. Sera from 135 children (136 episodes of prolonged coughing lasting 1-6 weeks) were tested for antibodies to different viruses and bacteria. Swabs were taken for culture and PCR to detect different viral and bacterial pathogens. One or more pathogens were found in 91 (67%) patients. One infectious agent was found in 49 (36%) patients, two agents in 35 (26%) patients, and more than two agents in seven (5%) patients. The most frequent pathogens encountered were rhinovirus (n = 43; 32%), Bordetella pertussis (n = 23; 17%) and respiratory syncytial virus (n = 15; 11%). The most frequent mixed infection was B. pertussis and rhinovirus (n = 14; 10%). No significant differences in clinical symptoms were observed between patients with or without pathogens; however, patients with mixed infections were significantly older. There was a strong seasonal influence on the number of infections, but not on the number of mixed infections. In children with prolonged coughing, there was a high frequency of mixed infections regardless of the season. However, mixed infection was not associated with increased disease severity. No clinical symptoms were found that allowed discrimination between specific pathogens.

Prevalence of human metapneumovirus and influenza virus infections among Japanese children during two successive winters

BACKGROUND

Human metapneumoviruses (hMPVs) are recognized as a leading cause of respiratory infections in young infants in many countries. The objective of this study was to identify links between hMPV and influenza virus infections among children with influenza-like illness.

METHOD

This study was conducted in 2 influenza seasons (2002-2003 and 2003-2004) at 2 pediatric outpatient clinics in Niigata city, Japan. Nasopharyngeal swabs or aspirates were collected from influenza-like illness patients, and hMPV and influenza were detected by reverse transcription-polymerase chain reaction (RT-PCR). A nucleotide sequence of 352 nucleotides segment of the F gene was performed.

RESULTS

A total of 765 influenza viruses and 84 hMPV were identified from 1498 nasopharyngeal swabs or aspirates by virus isolation and RT-PCR, respectively. hMPV-positive rates in patients with influenza-like illness were 5.7 and 5.2% in the 2002-2003 and 2003-2004 seasons, respectively. Epidemic curves of influenza and hMPV patients showed similar patterns with peaks in February in 2 influenza seasons. hMPV infections occurred frequently in infants and school children. Approximately 46% of hMPV patients were coinfected with influenza A viruses, but those coinfected cases were not clinically distinct from the others. No coinfection with influenza B viruses was found. Phylogenetic analysis of the hMPV fusion gene sequences revealed that 2 distinct hMPV cocirculated and that completely identical strains in subgroup A were observed over 2 years.

CONCLUSIONS

HMPV plays an important pathogenic role in patients with influenza-like illness in winter seasons, often in coinfections with influenza A viruses.

Rapid human metapneumovirus microneutralization assay based on green fluorescent protein expression

We describe a simple and expedited microneutralization assay for human metapneumovirus virus (HMPV) based on a recombinant HMPV expressing the enhanced green fluorescent protein (rHMPV-GFP). Test serum dilutions were incubated with fixed amounts of rHMPV-GFP and inoculated onto Vero cells, and the growth of non-neutralized rHMPV-GFP was visualized by fluorescent microscopy of living cells. A preliminary titer could be determined following 3 days of incubation. GFP expression was sufficient to be read by an automated scanner after 4-5 days of incubation, which also provided a permanent record. In comparison, the conventional serum neutralization assay requires a longer incubation time plus the additional steps of fixation and staining or immunostaining. rHMPV-GFP-based titers could be determined by the 50% infectivity endpoint method of Reed and Muench [Reed, L.J., Muench, H., 1938. A simple method of estimating fifty per cent endpoint. Am. J. Hyg. 27, 493-497], or by automated scanning and non-linear regression to determine the 50% endpoint of GFP fluorescence. The latter method was two- to three-fold more sensitive. This assay also permits automation and up-scaling, making it suitable for broad HMPV seroepidemiology studies and experiments that require large scale serology, such as vaccine studies.

Community-acquired pneumonia in children

PURPOSE OF REVIEW

This review highlights recent developments in the diagnosis, etiology, therapy, and prevention of community-acquired pneumonia in children.

RECENT FINDINGS

Sensitive new diagnostic methods have increased the detection rate of the causative agent up to 94%. Streptococcus pneumoniae is the most prevalent bacterial pathogen in all ages. Polymerase chain reaction is a rapid and sensitive method for the detection of Chlamydia pneumoniae and Mycoplasma pneumoniae, which have gained greater importance in recent years. During the period covered by this review, two new agents causing pneumonia were extensively studied. Human metapneumonovirus detected in young children is a leading cause of respiratory disease during the first years of life. A novel coronavirus was identified as the causative agent of severe respiratory syndrome, a new respiratory illness that affects adults and children. One multicenter trial concluded that nonsevere pneumonia can be treated with a short course of oral amoxicillin and a multicenter international study showed that children with severe pneumonia have similar outcomes whether treated with oral amoxicillin or parenteral penicillin, but more data are needed to demonstrate the safety and efficacy of such regimens.

SUMMARY

The continued evolution of bacterial resistance highlights the need for appropriate use of antibacterials. Improved diagnostic techniques will aid the treatment of children with community-acquired pneumonia. Aggressive vaccination with the pneumococcal conjugate vaccine and other available vaccines as well as the development of new vaccines will aid the prevention of respiratory disease in children.

Seasonality and clinical features of human metapneumovirus infection in children in Northern Alberta

Human metapneumovirus (hMPV) causes respiratory tract infections in all age groups. The characteristics of pediatric hMPV infection in Northern Alberta have not been studied. The objectives of this study were to determine the seasonality of pediatric hMPV infections over a 13-month period, the genetic relationship of hMPV isolates to hMPV detected in other parts of Canada, and the burden of illness and possible risk factors for pediatric hMPV hospitalization. Detection of hMPV by polymerase chain reaction was performed on nasopharyngeal specimens collected from outpatients and inpatients at the Stollery Children's Hospital in Edmonton, Alberta, November 12, 2002-December 31, 2003. Forty-two of 1,079 specimens were positive for hMPV (3.9%) from 41 patients (14 outpatients and 27 inpatients), with a peak incidence during January-April, but isolates were detected 10 months of the year. Co-infection was not detected in 39 specimens from which RSV had been detected. Two hMPV genetic clusters were detected, and the isolates were homologous to those of previous Canadian isolates. Four of the 14 outpatients had reactive airways disease. Possible risk factors in the 27 inpatients included prematurity (n = 8), congenital heart disease (n = 6), gastroesophageal reflux disease or aspiration (n = 6), global developmental delay (n = 5), and multiple congenital anomalies (n = 4). Risk factors for hospitalization appear to be similar to risk factors for respiratory syncytial virus hospitalization.

Impact of human metapneumovirus in childhood: comparison with respiratory syncytial virus and influenza viruses

This study evaluated the overall impact of human metapneumovirus (hMPV) infection in 1,505 children and their households, and compared it with infections due to respiratory syncytial virus (RSV) and influenza viruses. Nasopharyngeal swabs were used at enrollment to collect specimens for the detection of hMPV, RSV, and influenza virus RNA by reverse-transcriptase polymerase chain reaction (RT-PCR). hMPV was detected in 42 children (2.8%), RSV in 143 (9.5%; P < 0.0001 vs. hMPV), and influenza viruses in 230 (15.3%; P < 0.0001 vs. hMPV). Of the 42 hMPV-positive samples, one was also positive for RSV and six for influenza viruses, for a co-infection rate of 16.7%. Clinically, hMPV was identified only in patients with acute respiratory infection, whereas RSV and influenza viruses were also detected in patients with different clinical manifestations. Symptoms with statistically significant different proportions at presentation were fever (more frequent in the hMPV- and influenza-positive children) and wheezing with bronchiolitis or asthma exacerbation (more frequent among hMPV- and RSV-positive cases). The households of the hMPV- and the influenza-positive children had significantly more illnesses, needed significantly more medical visits, received more antipyretics, and missed significantly more work or school days than those of the RSV-positive children. Results show that hMPV is an emerging cause of acute respiratory infection in childhood, and may have a significant clinical and socioeconomic impact on children and their families.

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.