Coronavirus infection. Coloured transmission electron micrograph (TEM) of several coronavirus particles (red) with host cells (blue and green). The surface proteins embedded in the virus membrane form a crown (corona) covering the surface. The surface proteins are used to attach to host cells and enter them. The particles then use the cell machinery to make copies of themselves. Coronavirus strains cause diseases such as the common cold and SARS (severe acute respiratory syndrome). Magnification: x19,000 when printed 10cm high.