Measles virus. Coloured transmission electron micrograph (TEM) of measles viruses (morbillivirus group) budding off the surface of an infected cell (bottom, pink/yellow). The lipoprotein envelopes of the viruses (red) surround the nucleocapsid (blue). The envelopes are acquired from the host cell's cytoplasmic membrane as the viruses bud from the surface. They enclose the nucleocapsid: a helical structure consisting of a single-stranded RNA core (genetic material) surrounded by protein. Measles is very infectious and mainly affects children, producing fever and rash. One attack usually gives life-long immunity. Magnification: x14,400 at 6x6cm size.