False-colour transmission electron micrograph (TEM) of numerous virions (virus particles) of the polio virus, the causative agent of poliomyelitis. Polioviruses belong to the enterovirus sub-group of the picornaviruses (small RNA viruses) and occur as 3 antigenically-distinct types; type 1 is the cause of most polio epidemics. Infection occurs through the mouth; the virus travels via lymph nodes in the gut & upper respiratory tract to the central nervous system, where viral replication (especially in horn cells of the spinal cord) may produce paralytic poliomyelitis (causing death or severe & permanent disability). Magnification: x64,000 at 6x4.5cm size.