Caption

Influenza viruses. Coloured transmission electron micrograph (TEM) of Beijing influenza viruses. Each virus contains a core of ribonucleic acid (RNA, orange), surrounded by a spiked protein envelope of haemagglutinin (yellow dots). Spikes adhere to host cells during infection. The virus has an affinity for mucus, and is transmitted by coughed or sneezed droplets inhaled into the respiratory tract. Influenza infection is usually short-lived. The haemagglutinin spikes of the virus, however, can change structure to create a new influenza strain such as this Beijing strain which spread as an epidemic in 1993. Magnification: x66,000 at 6x4.5cm size.