Poliomyelitis, often called polio or infantile paralysis, is a virally induced infectious disease which spreads via the fecal-oral route. It may proceed to the blood stream and into the central nervous system causing muscle weakness and often paralysis. Polio is a communicable disease which is categorized as a disease of civilization. Polio spreads through human-to-human contact, usually entering the body through the mouth due to fecally contaminated water or food (fecal-oral transmission). The incubation period of polio, from the time of first exposure to first symptoms, ranges from three to 35 days. During the late 1940's and early 1950's, a research group headed by Dr. John Enders at Boston's Children's Hospital successfuly cultivated the polio virus in human tissue. This highly significant breakthrough ultimately allowed for the development of vaccines against polio.