Polio is a disease caused by a virus that attacks the central nervous system and causes paralysis
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. The poliovirus is spread by direct person-to-person contact by contact with infected mucus or feces and leads to the disease, poliomyelitis
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. Like all viruses, the poliovirus works by infecting human cells. The poliovirus enters the body through the mouth and nose where it travels through the digestive system and multiplies
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. Once it reaches the intestinal tract, the virus is absorbed into the blood stream and spread to the lymphatic system
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. While polio has been largely eradicated, lack of immunization and exposure to the poliovirus will cause a person to contract the disease. The people that are most likely to be infected by the poliovirus are children, pregnant women, and the elderly
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Polio was a worldwide epidemic between 1840 and 1950, before the polio vaccine was developed. The development of the vaccine was aided largely by the discovery of HeLa cells and the incidence of the disease has been greatly reduced
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. In fact, the disease has been completely eradicated in some countries. In 1948, Dr. Jonas Salk began researching the poliovirus at a virology lab at the University of Michigan
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. HeLa cells were easily infected by the poliovirus and therefore were perfect for vaccine testing and development. Since HeLa cells were easily grown and cultured in the laboratory, Salk was able to infect large amounts of HeLa cells and develop a vaccine that was viable for human use. In 1950 he began working to create an inactivated poliovirus vaccine, and by 1952 Dr. Salk had created what he considered a safe and effective vaccine against the poliovirus
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