False-colour transmission electron micrograph (TEM) of influenza virus particles, the cause of Hong Kong 'flu". The influenza virus belongs to the orthomyxovirus class of RNA viruses, all of which possess an affinity for mucus. Spikes projecting from the envelope (gold coloured) surrounding the viruses are used as a means of attachment to the mucoprotein receptors on the surface of host cells that form the respiratory epithelia. Influenza is usually short-lived & generally not serious, although virus-induced pneumonia or secondary bacterial infection can prove fatal. Magnification: x120,000 at 35mm size, x240,000 at 6x7cm size."