Human metapneumovirus: a ubiquitous and long-standing respiratory pathogen.

BACKGROUND: Human metapneumovirus (hMPV) is a recently described human pathogen first identified in respiratory specimens of young children suffering from respiratory syndromes ranging from mild to severe.

METHODS AND RESULTS: Virological studies have reported the presence of hMPV infections in many countries from all continents. Seroprevalence studies have indicated that the virus has been circulating in humans for more than 50 years and that it infects virtually all children by the ages of 5-10 years. In young children, hMPV has been mainly associated with bronchiolitis but also with pneumonitis, otitis media and acute exacerbation of asthma. The contribution of hMPV in respiratory syndromes of adults has been studied considerably less; initial studies have indicated a role for this pathogen in flu-like syndromes and in significant percentages of chronic obstructive pulmonary disease exacerbations and cases of community-acquired pneumonia during the winter-spring period. Both primate and rodent experimental models have been used to characterize the pathogenesis of this respiratory virus. In some of these models, intranasal hMPV inoculation has elicited not only important viral replication but also significant pulmonary inflammation and clinical disease. Recently a few groups have developed reverse genetic systems for hMPV, allowing a better understanding of viral pathogenesis and generation of attenuated viral strains for immunization.

CONCLUSIONS: Recent studies on hMPV have provided a better understanding of the epidemiology and pathogenesis associated with this viral infection, and have enhanced the prospect of developing efficient therapeutic agents and vaccine candidates.