Human metapneumovirus particles. Coloured transmission electron micrograph (TEM) of particles of the human metapneumovirus (hMPV), a respiratory virus that affects almost all children by the age of 5. The virus is a type of paramyxovirus, consisting of RNA (ribonucleic acid) genetic material enclosed in a protein coat, or capsid, within a phospholipid envelope. The envelope (white) is covered in protein spikes, which are seen here as the virus' outermost layer (orange and green). hMPV will only cause a mild respiratory tract infection in healthy adults but small children, elderly and immunocompromised individuals are at risk of severe disease and hospitalisation. Magnification: x170,000 when printed 10 centimetres wide.