Respiratory syncytial virus. Coloured transmission electron micrograph (TEM) of a respiratory syncytial virus (RSV). This pneumovirus, a type of paramyxovirus, is a major cause of human respirat- ory tract infections in temperate climates, especially in winter. The virus consists of RNA (ribonucleic acid) genetic material enclosed in a protein coat, or capsid, within a phospholipid envelope. The envelope is covered in protein spikes, seen as the yellow lines around the edge of the virus. In adults, the virus only affects the upper respiratory tract, but in infants bronchiolitis (bronchiole inflammation) or bron- chopneumonia can result. Magnification unknown.