Metapneumovirus

Metapneumovirus
Virus classification
Group:	Group V ((-)ssRNA)
Order:	Mononegavirales
Family:	Paramyxoviridae
Genus:	Metapneumovirus
Type species
Avian metapneumovirus
Species
Human metapneumovirus

Human metapneumovirus (hMPV) is a negative single-stranded RNA virus of the family Paramyxoviridae and is closely related to the avian metapneumovirus (AMPV) subgroup C. It was isolated for the first time in 2001 in the Netherlands by using the RAP-PCR (RNA arbitrarily primed PCR) technique for identification of unknown viruses growing in cultured cells. It may be the second most common cause (after the respiratory syncytial virus) of lower respiratory infection in young children.

Compared with respiratory syncytial virus, infection with human metapneumovirus tends to occur in slightly older children and to produce disease that is less severe. Co-infection with both viruses can occur, and is generally associated with worse disease.

Epidemiology

Human metapneumovirus accounts for approximately 10% of respiratory tract infections that are not related to previously known etiologic agents. The virus seems to be distributed worldwide and to have a seasonal distribution with its incidence comparable to that for the influenza viruses during winter. Serologic studies have shown that by the age of five, virtually all children have been exposed to the virus and reinfections appear to be common. Human metapneumovirus may cause mild respiratory tract infection. However, small children, elderly and immunocompromised individuals are at risk of severe disease and hospitalization.

Genome

The genomic organisation of hMPV is analogous to RSV, however hMPV lacks the non-structural genes, NS1 and NS2, and the hMPV antisense RNA genome contains eight open reading frames in slightly different gene order than RSV (viz. 3’-N-P-M-F-M2-SH-G-L-5’). hMPV is genetically similar to the avian pneumoviruses A, B and in particular type C. Phylogenetic analysis of hMPV has demonstrated the existence of two main genetic lineages termed subtype A and B containing within them the subgroups A1/A2 and B1/B2 respectively.

Identification

The identification of hMPV has predominantly relied on reverse-transcriptase polymerase chain reaction (RT-PCR) technology to amplify directly from RNA extracted from respiratory specimens. Alternative more cost effective approaches to the detection of hMPV by nucleic acid-based approaches have been employed and these include:

• 1) detection of hMPV antigens in nasopharyngeal secretions by immunofluorescent-antibody test
• 2) the use of immunofluorescence staining with monoclonal antibodies to detect hMPV in nasopharyngeal secretions and shell vial cultures
• 3) immunofluorescence assays for detection of hMPV-specific antibodies
• 4) the use of polyclonal antibodies and direct isolation in cultured cells.

Transmission

There are no conclusive studies to date, however, it is likely that transmission occurs by contact with contaminated secretions, via droplet, aerosol, or fomite vectors. Hospital acquired infections with Human Metapneumovirus have been reported.

Treatment

No treatment is yet known, but ribavirin has shown effectiveness in an animal model.

External links

• hMPV EIA kit
• hMPV, Human Metapnuemovirus
• Virus Pathogen Database and Analysis Resource (ViPR): Paramyxoviridae