SARS virus particles. Coloured transmission electron micrograph (TEM) of numerous SARS virus particles (red) in a host cell. Severe acute respiratory syndrome (SARS) is a fatal lung disease that first appeared in China in 2002. The SARS virus is a coronavirus. The coronaviruses are RNA (ribonucleic acid) viruses that take their name from their crown (corona) of surface proteins, which are used to attach to and penetrate their host cells. Once inside a cell, the virus particles use the cell machinery to replicate themselves. Magnification: x58000 when printed at 10 centimetres tall.