False-colour transmission electron micrograph of a group of rhinoviruses. The rhinovirus is one of the causes of the common cold, as well as other respiratory disease. It belongs in the Picornaviridae family, a group of small icosahedral viruses, 22 nanometres in diameter, which are sub-grouped according to their acid sensitivity. The genus rhinovirus is adapted to low temperatures but cannot invade the gut since it is inactivated by moderately acid conditions. The virus is spread readily in droplets produced by talking, coughing and sneezing. Magnification: x70,000 at 6x4.5cm size.