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SARS virus. Artwork of a SARS virus particle inside a cell. SARS (severe acute respiratory syndrome) is a fatal lung disease that first appeared in China in late 2002, and spread throughout the world through air travel. The disease is caused by the inhalation of virus particles, which are carried in tiny water droplets in the air. The SARS virus is a type of coronavirus, other types of which cause the common cold and a type of gastroenteritis. Like all viruses it cannot replicate by itself, instead infecting a cell and using the machinery of the cell to produce more copies of the virus (some seen at lower left). (KEYSTONE/SCIENCE PHOTO LIBRARY/RUSSELL KIGHTLEY)