Transmission Electron Micrograph (TEM) of a cluster of polio virus particles. Each particle is composed of a protein coat (capsid) around a core containing RNA genetic material, and is only 27 nanometers across. This virus infects children and causes the disease poliomyelitis or infantile paralysis. Although it normally causes a mild illness, in some cases it causes damage to the nervous system, which can lead to paralysis or death. Vaccination, starting in the 1950s, has been effective in controlling the disease. Magnification: x130,500.