Measles virus. Coloured transmission electron micrograph (TEM) of measles virus particles (various shapes) budding out from an infected cell (at bottom). The virus, which causes measles, replicates within the cell. As each new infectious particle is released from the cell surface, it become enclosed in a lipid envelope derived from the cell's surface membrane (brown). The core of the viral particle is helical and is composed of protein and the genetic material RNA (ribonucleic acid). Measles virus is highly infectious and mainly affects children, producing fever and rash. Infection results in life-long immunity. Magnification: x21,000 at 5x7cm size. x84,000 at 6x11 inch size.