Human metapneumovirus (hMPV) is an enveloped, non segmented, negative‑sense RNA virus in the family Pneumoviridae that infects the respiratory tract of humans and other mammals.
Virology & Pathogenesis
Human metapneumovirus belongs to the order Mononegavirales and forms the genus Metapneumovirus within the family Pneumoviridae. Its ~13 kilobase genome encodes nucleocapsid, phosphoprotein, matrix, fusion (F), glycoprotein (G), small hydrophobic protein (SH) and large polymerase proteins. Two major genetic lineages, A and B, with subgroups A1, A2a, A2b, B1 and B2 circulate worldwide. The virion is enveloped and pleomorphic; attachment is mediated by the G glycoprotein and entry is driven by the F protein that triggers membrane fusion. After cytoplasmic replication, progeny bud from the host cell membrane. hMPV targets ciliated epithelial cells of the nasopharynx and lower airways and downregulates innate immune responses through interference with interferon signalling. Natural infection does not induce robust long‑lasting immunity, which allows reinfections later in life.
Clinical significance and epidemiology
Since its discovery in 2001, hMPV has been recognised as an important cause of acute respiratory tract infections in all age groups. It accounts for about 5–10 % of hospitalisations for acute respiratory infections in children. Clinical manifestations range from mild cold‑like symptoms to bronchiolitis and pneumonia; severe disease is most often observed in infants, older adults and immunocompromised patients. Reinfections occur throughout life because immunity wanes. Outbreaks typically arise in late winter and spring, and coinfections with respiratory syncytial virus or influenza can exacerbate severity. There is currently no licensed vaccine, although fusion protein–based candidates and monoclonal antibodies are under evaluation. Management remains supportive, emphasising oxygen therapy and hydration. Human metapneumovirus is a ubiquitous respiratory pathogen with worldwide distribution. Understanding its virology and immune evasion mechanisms is essential for developing vaccines and therapeutics. Related Terms: Paramyxoviridae, Pneumoviridae, Bronchiolitis, Respiratory infection, Pediatric hospitalisations