Pediatric Human Metapneumovirus 

Updated: May 02, 2018
Author: Joseph Domachowske, MD; Chief Editor: Russell W Steele, MD 

Overview

Background

Human metapneumovirus (hMPV) is a respiratory viral pathogen that causes a spectrum of illnesses that range from asymptomatic infection to severe bronchiolitis. In 2001, van den Hoogen et al described the identification of this new human viral pathogen from respiratory samples submitted for viral culture during the winter season.[1] Half of the initial 28 human metapneumovirus isolates were cultured from patients younger than 1 year, and 96% were isolated from children younger than 6 years.

Seroprevalence studies revealed that 25% of all children aged 6-12 months who were tested in the Netherlands had detectable antibodies to human metapneumovirus; by age 5 years, 100% of patients showed evidence of past infection. Separate reports from all areas of the world support the early contention that this newly discovered virus is ubiquitous, and, like human respiratory syncytial virus (RSV) infection, is seasonal in nature.[2]

Although the description of this viral pathogen was first described in children, subsequent reports have highlighted the importance of human metapneumovirus as a cause of respiratory illness in adults of all ages,[3, 4] in patients with cancer,[5] in the elderly population (as a cause of serious lower respiratory tract infection),[6] and in adults with underlying chronic medical conditions.[7]

Pathophysiology

The pathophysiology of human metapneumovirus infection is thought to be closely related to the other common human pneumovirus, RSV. Like RSV, human metapneumovirus has a tropism for the respiratory epithelium. The patient may be asymptomatic, or symptoms may range from mild upper respiratory tract symptoms to severe bronchiolitis and pneumonia. More than 20% of infants with bronchiolitis have been found to be infected with two or more respiratory pathogens at the same time. Of these, more than 10% have been described to be co-infected with human metapneumovirus.[8, 9] Viremia from human metapneumovirus infection has not yet been demonstrated, but a 2005 reported case of human metapneumovirus encephalitis with concurrent lung disease supports the possibility that the virus may (rarely) enter the bloodstream.

Epidemiology

Frequency

United States

Human metapneumovirus infection is very common. Estimates suggest that this virus is the causative agent of infant bronchiolitis in 5-15% of cases. Children infected with respiratory viruses, such as human metapneumovirus, are frequently co-infected with other common respiratory viruses.[8, 9]

International

Seroprevalence studies revealed that 25% of all children aged 6-12 months who were tested in the Netherlands had detectable antibodies to human metapneumovirus; by age 5 years, 100% of patients showed evidence of past infection. In Australia, 3 of 200 (1.5%) randomly chosen respiratory samples with negative results for the presence of known respiratory pathogens had positive results for human metapneumovirus on culture, polymerase chain reaction, or both.

Race

To date, no racial predilection has been described.

Sex

Females accounted for 31% of the patients originally described to have human metapneumovirus infection.

Age

Human metapneumovirus infection is prevalent during infancy and early childhood.[10]  By age 5 years, seroprevalence data suggest infection in all (or nearly all) individuals. Available demographic data are limited to the Netherlands, where the virus was originally identified in 2001. Further epidemiologic investigation is needed to determine prevalence in other areas of the world. The role of human metapneumovirus in causing respiratory illness in adults has been explored in detail, highlighting the potential severity of human metapneumovirus infection in elderly patients,[6] including outbreaks of severe illness among elderly persons in long-term care facilities.[11]

 

Presentation

History

Patient history in suspected cases of human metapneumovirus (hMPV) should focus on respiratory symptoms, such as rhinorrhea, congestion, cough, dyspnea, and tachypnea.

Physical

A complete physical examination may reveal rhinorrhea, congestion, cough, tachypnea, wheezing, or rales. A high fever with myalgias has been described in some patients. Respiratory failure may ensue, requiring mechanical ventilation.

Causes

The respiratory viral pathogen human metapneumovirus causes a spectrum of illnesses, which range from asymptomatic infection to severe bronchiolitis. Human respiratory syncytial virus (RSV), parainfluenza virus type 1, human metapneumovirus, and human parainfluenza virus type 3 are all known to cause clinical bronchiolitis. Although RSV has been reported to cause as many as 90% of bronchiolitis cases in infants, the relative contribution of human metapneumovirus remains undetermined.

Human metapneumovirus is a negative-sense nonsegmented RNA virus that has been categorized in the pneumovirus subfamily, family Paramyxoviridae, based on genomic sequence and gene constellation.

Phylogenetic tree showing sequence analysis of hum Phylogenetic tree showing sequence analysis of human metapneumovirus (HMPV).
 

DDx

Differential Diagnoses

 

Workup

Laboratory Studies

A general respiratory virus culture obtained by nasal wash or nasopharyngeal swab should be performed in patients with clinical symptoms of lower respiratory tract viral infections.

Human metapneumovirus (hMPV) has proven to be difficult to identify using common clinical virologic procedures.[12] Human metapneumovirus replicates slowly in primary cynomolgus monkey kidney cells and poorly in Vero cells and A549 cells (a human respiratory epithelial cell line). Other cell lines commonly used in viral diagnostic laboratories do not appear to support the replication of human metapneumovirus.

Commercial reagents to confirm the presence of human metapneumovirus infection are available. Detection techniques that have been developed include virus identification by reverse transcriptase-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), and the rapid culture technique known as shell vial amplification. The clinical sample appropriate for submission to the laboratory may include nasal wash or aspirate fluid, nasopharyngeal flock swab culture, endotracheal tube aspirate, and/or bronchoalveolar lavage fluid.[13] To determine the optimal biologic sample, consult directly with the local clinical virology team because the best sample types vary according to the specific tests offered.

Multiplex PCR assays are more generally available than in recent years, often including the ability to diagnose hMPV and more than a dozen other respiratory viruses from a single panel. Since some of the respiratory viral pathogens do not grow well, or at all, in standard tissue culture, nucleic acid–based testing provides the ability to detect their presence, or co-presence with another virus.[14, 15] Co-infection with more than one respiratory virus in hospitalized children with acute respiratory illness is as high as 28% when all common respiratory viruses are taken into account.

Further diagnostic evaluation, including a CBC count and a blood culture, may be necessary to exclude invasive bacterial disease.

Imaging Studies

Chest radiography is appropriate in patients who present with symptoms of lower respiratory tract disease.

A systematic review that included 215 children with HMPV reported that parahilar opacities were the most common (87%) chest radiographic abnormality seen followed by hyperinflation (69%), atelectasis (40%) and consolidation (18%).[16]

Histologic Findings

Currently, histologic findings are unknown.

 

Treatment

Medical Care

Treatment of human metapneumovirus (hMPV) infection is supportive. Maintain hydration and provide supplemental oxygen if necessary. Supplemental oxygen may be required in patients with moderate-to-severe infection. In patients with respiratory failure, mechanical ventilation is necessary. Clinical trials of anti–human metapneumovirus monoclonal antibodies for the prevention of human metapneumovirus infection in high risk infants are planned but not yet open for enrollment.

Consultations

Patients with severe bronchiolitis or pneumonia may require admission to an intensive care unit. Consultation with a pediatric infectious disease specialist or pulmonologist may also be necessary.

 

Medication

Medication Summary

Drug therapy is not currently a treatment component in human metapneumovirus (hMPV) infection. See Treatment.

 

Follow-up

Deterrence/Prevention

See the list below:

  • Until more information becomes available, using contact precautions in all hospitalized patients with bronchiolitis is prudent, whether or not human respiratory syncytial virus (RSV) is present. Guidelines are available for the diagnosis and treatment of bronchiolitis in children.[17]

  • Development of anti–human metapneumovirus (hMPV) monoclonal antibodies continues. In the future, such preparations may become available for the passive prevention of human metapneumovirus infection in high-risk infants.

Complications

See the list below:

  • Respiratory failure may develop.

Prognosis

See the list below:

  • Prognosis appears excellent, but further information is needed.