Hong Kong flu viruses. Colored transmission electron micrograph (TEM) of Hong Kong influenza (flu) viruses. In appearance these are typical of the strains which cause other Asian flu epidemics including Beijing influenza. Each virus is rounded in shape, some larger than others. They contain a core of ribonucleic acid (RNA), surrounded by a spiked protein envelope of hemagglutinin. The spikes adhere to host cells during infection. The virus is transmitted by coughed mucus 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: x54,000 at 6x4.5cm size. x30,000 at 35mm