Asian flu virus. Coloured transmission electron micrograph of Asian influenza (flu) viruses. In appearance they are typical of the strains which cause Asian flu epidemics, such as Beijing or Hong Kong influenza. Each virus contains a core of ribonucleic acid (RNA), surrounded by a spiked protein envelope of haemagglutinin. The spikes adhere to host cells during infection. The virus has an affinity for mucus, and is transmitted by coughed or sneezed droplets. Influenza infection causes fever, headache and weakness. Spikes on the virus, however, change their structure to form new potent viral strains. Magnification: x42,340 at 6x4.5cm size.