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Adenoviruses. Coloured transmission electron micrograph (TEM) of three adenovirus particles. There are many kinds of adenoviruses which are all icosahedral (20-sided) viruses. They infect the respiratory tract, causing common cold-like symptoms, and also infect the eyes and gut, particularly in children. The orange ball-and- stick objects seen are fibres that have become detached from the surface of the particles. Virus particles consist of a protein coat which contains DNA. They replicate by invading cells, inserting their own DNA and causing the cell to produce more virus particles. Magnification unknown. (KEYSTONE/SCIENCE PHOTO LIBRARY/DR LINDA STANNARD, UCT)