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Coronavirus particles. Coloured transmission electron micrograph (TEM) of three coronavirus particles. Different strains of coronavirus are responsible for diseases such as the common cold, gastroenteritis and SARS (severe acute respiratory syndrome). SARS is a fatal disease that first appeared in China in 2002. The coronaviruses take their name from their crown (corona) of surface proteins, which are used to attach and penetrate their host cells. Once inside the cells, the particles use the cells' machinery to make more copies of the virus. Magnification unknown. (KEYSTONE/SCIENCE PHOTO LIBRARY/DR LINDA STANNARD, UCT)