Budding human metapneumovirus particles. Coloured transmission electron micrograph (TEM) of a host cell with particles of the human metapneumovirus (hMPV, green) budding from its surface. The virus is a type of paramyxovirus, consisting of RNA (ribonucleic acid) genetic material enclosed in a protein coat (capsid). The proteins enable the particles to penetrate a host cell and use its mechanisms to produce many copies of the virus, which then leave the cell by forming buds. hMPV is a respiratory virus that affects almost all children by the age of 5. It will only cause a mild respiratory infection in healthy adults but small children, elderly and immunocompromised individuals are at risk of severe disease. Magnification: x170,000 when printed 10 centimetres tall.