Influenza virus. Coloured transmission electron micrograph of a cluster of five spherical-shaped influenza (flu) viruses. Each virus is made up of a core of ribonucleic acid (RNA, not seen here), surrounded by a spiked protein envelope. 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. These contagious viruses belongs to the orthomyxovirus group. 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: x76,800 at 6x7cm size. x200,000 at 7x9"~PORTRAIT"