Rhinoviruses. Coloured Transmission Electron Micrograph (TEM) of a cluster of rhinoviruses. These viruses are a cause of the common cold, as well as other respiratory diseases. Rhinoviruses belong to the Picornaviridae family. These icosa- hedral forms are very small and sub-grouped according to their acid sensitivity. They are adapted to low temperatures but cannot invade the gut since they are inactivated by moderately acid conditions. Rhinoviruses are spread readily in the air by droplets produced by talking, coughing and sneezing. The virus may infect mucous membranes of the nose, and also the lungs causing bronchitis. Magnification: x220,000 at 6x6cm size.