Human metapneumovirus: a new player among respiratory viruses

Abstract

The human metapneumovirus (hMPV) is a newly described member of the Paramyxoviridae family belonging to the Metapneumovirus genus. Since its initial description in 2001, hMPV has been reported in most parts of the world and isolated from the respiratory tract of subjects from all age groups. Despite the fact that prospective and case-control studies have been limited, the epidemiology and clinical manifestations associated with hMPV have been found to be reminiscent of those of the human respiratory syncytial virus, with most severe respiratory tract infections occurring in infants, elderly subjects, and immunocompromised hosts. Additional research is needed to define the pathogenesis of this viral infection and the host's specific immune response.

Figure 1

Negative-stain electron micrographs of human metapneumovirus (hMPV). Center image shows 5 pleomorphic hMPV particles; note the projections along the periphery of the viruses. Upper right and lower left insets show the nucleocapsid and the filamentous rodlike particle, respectively. Staining was done with 2% phosphotungstic acid. Bar markers represent 100 nm. From [6]; reproduced with permission from The University of Chicago Press.

Figure 2

Schematic representation of the genomic organization of members of the Pneumovirus genus (represented by the human respiratory syncytial virus [hRSV]; GenBank accession no. NC 001781) and the Metapneumovirus genus (represented by the human metapneumovirus [hMPV]; GenBank accession no. AF371337). The lengths of the genomes are ∼15 Kb and ∼13 Kb for hRSV and hMPV, respectively. Length of each gene (in nucleotides) is also indicated. The overlap between the M2 and L genes of hRSV is not indicated.

Table 1

Incidence of human metapneumovirus (hMPV) infection in several studies.

Table 2

Clinical findings in 28 human metapneumovirus (hMPV)—infected Canadian subjects, by age group.

Figure 3

Microscopic studies of uninfected (A) and human metapneumovirus (hMPV)—infected LLC-MK2 cells. Note the various cytopathic effects induced by different hMPV strains consisting of small round cells (B) and large, respiratory syncytial virus—like syncytia (C).