Metapneumovirus

Abstracts & Commentary

Synopsis: Evidence indicates that a novel paramyxovirus, the human metapneumovirus, may be an important cause of respiratory tract infection.

Sources: Jartti T, et al. Metapneumovirus and acute wheezing in children. Lancet. 2002;360:1393-1394; Boivin G, et al. Virological features and clinical manifestations associated with human metapneumovirus: A new paramyxovirus responsible for acute respiratory-tract infections in all age groups. J Infect Dis. 2002;186:1330-1334.

Jartti and colleagues determined the viral etiologies of respiratory tract infections in 132 children enrolled in a clinical trial in Turku, Finland. The trial was designed to determine the efficacy of systemically administered glucocorticoids. A diagnosis of bronchiolitis was made in 15, "wheezy bronchitis" in 59, and acute asthma in 48. The children ranged from 4 months to 13.5 years in age, while their median age was 2 years.

Culture and/or PCR evidence of a viral infection was found in 88%: 27% with rhinovirus, 22% with enterovirus, 16% with nontypeable picornavirus, 14% with respiratory syncytial virus (RSV), and 9% with human metapneumovirus (HMPV). Three of the 10 children with HMPV infection were coinfected with another virus. Of those without coinfection, 2 had acute otitis media as part of their illness. The 10 ranged in age from 4-25 months; their median age was 7 months. Five had bronchiolitis, 4 wheezy bronchitis, and 1 had acute asthma. Cough had persisted for a mean of 9 (±10) days at the time of enrollment, rhinitis for 4, wheezing and fever for 3 each. From January to April 2001, 10 of 32 (32%) children with wheezing had metapneumovirus infection.

Boivin and colleagues retrospectively evaluated previously unidentified viruses that had been isolated from specimens submitted to the Quebec City Regional Virology Laboratory. Thirty-eight of these, all from samples of respiratory secretions, demonstrated CPE in LLC-MK2 cells, an established cell line used to identify parainfluenza viruses, but could not be identified as a common respiratory pathogen with hemadsorption testing and immunofluorescence. Those 38 contained HMPV genes when tested by RT-PCR. Six of the 38 (16%) had evidence, by antigen testing, of the presence of a second respiratory virus.

During the 2000-2001 winter season, HMPV was isolated as frequently as parainfluenza viruses (2.3% each), but less frequently than adenoviruses (3.4%), RSV (4.8%), or influenza A or B (19.8%). HMPV was isolated from 7.1% of all respiratory samples obtained from patients during the winter seasons studied, including 4.1% of patients younger than 5 years of age, 2.8% of those 5-65, and 29.3% of those older than 65 years of age. Children younger than 5 years of age and individuals older than 65 years of age accounted for 35.1% and 45.9%, respectively, of HMPV infections.

Among HMPV-infected children who were hospitalized, 66.7% had pneumonitis and 58.3% had bronchiolitis, while 60% of the elderly had bronchitis and/or bronchospasm, and 40% had pneumonitis. Approximately one-fourth of patients with pneumonitis were immunocompromised, and 40% were younger than 15 months of age. Acute and convalescent sera were available from only 2 patients; both had evidence of seroconversion.

Comment by Stan Deresinski, MD, FACP

Metapneumovirus, a member of the Paramyxoviridae family, was first described in 2001 after its isolation from 28 epidemiologically unrelated children over a 20-year period in The Netherlands.1 HMPV was identified in respiratory secretions of 2.2% of patients with acute respiratory illness in England and Wales.2 It appears that few children escape infection; 100% of 20 children aged 5-10 years were seropositive in an immunofluorescence assay for antibodies to HPMV.1

While Koch’s postulates have not been fulfilled, the accumulating evidence strongly points to the role of this virus as a human pathogen. HMPV was identified in respiratory secretions of 1.5% of children with otherwise unexplained respiratory tract infections in Australia and approximately 10% in The Netherlands.1,3 HMPV has been associated with a range of respiratory illness, including pneumonitis. However, the associated symptoms, especially bronchiolitis, most closely parallel those caused by RSV. Like RSV, HMPV is commonly associated with bronchiolitis in young children.

In the absence of ready availability of other methods, the diagnosis of metapneumovirus infection requires culture in LLC-MK2 cells and a great deal of patience, since the mean time to detection of CPE in the Olvin study was 17.3 days (range, 3-23 days).

Dr. Deresinski is Editor of Infectious Disease Alert, Clinical Professor of Medicine at Stanford, and Associate Chief of Infectious Diseases at Santa Clara Valley Medical Center.

References

1. van den Hoogen BG, et al. A newly discovered human pneumovirus isolated from young children with respiratory tract disease. Nature Med. 2001;7:719-724.

2. Stockton J, et al. Human metapneumovirus as a cause of community-acquired respiratory illness. Emerg Infect Dis. 2002;8:897-901.

3. Nissen MD, et al. Evidence of human metapneumovirus in Australian children. Med J Aust. 2002;176 (4):188.