Human metapneumovirus (hMPV), first discovered in the Netherlands in the year 2001[1], belongs to the genus Metapneumovirus in the Pneumoviridae family[2]. hMPV is characterized as a spherical enveloped virus with a diameter of approximately 209 nanometers. hMPV consists of a single-stranded, non-segmented and negative-sense RNA genome approximately 13.3 kb in length[3]. The HMPV genome contains eight genes that encode nine proteins: nucleoprotein (N), phosphoprotein (P), matrix protein (M), fusion protein (F), matrix-2 proteins (M2-1 and M2-2), small hydrophobic (SH) protein, glycoprotein (G), and large (L) polymerase protein[4].
According to the genetic features of the F and G genes, hMPV strains are classified into four genotypes (A1, A2, B1 and B2) and further divided into six lineages (A1, A2a, A2b, A2c, B1, and B2)[5, 6]. It’s worth noting that the genotypes or lineages of hMPV may vary from one region to another[7]. In China, at least five hMPV lineages (A1, A2b, A2 c, B1, and B2) have been identified, while the lineages and proportions of hMPV vary greatly from province to province or region to region. Overall, the A2b, B1, and B2 lineages have become the predominant strains in China, while the A1 lineage was seldom detected in the regions under investigation[8].
Worldwide distribution of hMPV has been recorded with seasonal peak in infection noticed during peak winter seasons. The virus is propagated from one individual to another primarily through aerosol transmission or by direct contact with an infected individual with an incubation period ranging from three to five days. After transmission, the virus infects the nasopharyngeal mucous membrane and then spreads rapidly into the respiratory tract infecting the host cells. Initial infection typically manifests as mild upper respiratory tract illness with symptoms ranging from fever, malaise, and vomiting to severe clinical features like wheezing, pneumonia, croup, bronchiolitis and uncommon features like conjunctivitis, otitis media, diarrhea, rash, seizures, and altered liver function tests following hMPV infection[9]. The main treatment procedure involves supportive care[8, 10] involving oxygen supplementation, antipyretic and anti-inflammatory medication along with fluid supplementation if necessary.
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[1] VAN DEN HOOGEN B G, DE JONG J C, GROEN J, et al. A newly discovered human pneumovirus isolated from young children with respiratory tract disease [J]. Nature medicine, 2001, 7(6): 719-24.
[2] AMARASINGHE G K, ARéCHIGA CEBALLOS N G, BANYARD A C, et al. Taxonomy of the order Mononegavirales: update 2018 [J]. Archives of virology, 2018, 163(8): 2283-94.
[3] SOTO J A, GáLVEZ N M S, BENAVENTE F M, et al. Human Metapneumovirus: Mechanisms and Molecular Targets Used by the Virus to Avoid the Immune System [J]. Frontiers in immunology, 2018, 9: 2466.
[4] VAN DEN HOOGEN B G, BESTEBROER T M, OSTERHAUS A D, et al. Analysis of the genomic sequence of a human metapneumovirus [J]. Virology, 2002, 295(1): 119-32.
[5] TULLOCH R L, KOK J, CARTER I, et al. An Amplicon-Based Approach for the Whole-Genome Sequencing of Human Metapneumovirus [J]. Viruses, 2021, 13(3): 499.
[6] YI L, ZOU L, PENG J, et al. Epidemiology, evolution and transmission of human metapneumovirus in Guangzhou China, 2013-2017 [J]. Sci Rep, 2019, 9(1): 14022.
[7] DIVARATHNA M V M, RAFEEK R A M, NOORDEEN F. A review on epidemiology and impact of human metapneumovirus infections in children using TIAB search strategy on PubMed and PubMed Central articles [J]. Reviews in medical virology, 2020, 30(1): e2090.
[8] FENG Y, HE T, ZHANG B, et al. Epidemiology and diagnosis technologies of human metapneumovirus in China: a mini review [J]. Virology journal, 2024, 21(1): 59.
[9] BARRERA-BADILLO G, OLIVARES-FLORES B, RUIZ-LóPEZ A, et al. Human Metapneumovirus: Etiological Agent of Severe Acute Respiratory Infections in Hospitalized and Deceased Patients with a Negative Diagnosis of Influenza [J]. Pathogens (Basel, Switzerland), 2020, 9(2): 85.
[10] MISHRA B, MOHAPATRA D, TRIPATHY M, et al. A Re-emerging Respiratory Virus: Human Metapneumovirus (hMPV) [J]. Cureus, 2025, 17(2): e78354.