Influenza virus. Coloured Transmission Electron Micrograph (TEM) of a cluster of variously-shaped influenza (flu) viruses. This contagious virus belongs to the orthomyxovirus group. Each is made up of a core of ribonucleic acid (RNA), surrounded by a spiked protein envelope of haemagglutinin. The tiny external spikes stick to host cells when the virus invades the body. The virus has an affinity for mucus, and is spread in droplets from coughs or sneezes. Influenza infection is usually short-lived. However, the spikes on the virus can change structure to create a new strain of influenza that may spread as an epidemic. Magnification: x30,600 at 35mm size.