Poliomyelitis, often called polio or infantile paralysis, is a viral paralytic disease. The causative agent, a virus called poliovirus (PV), enters the body orally, infecting the intestinal wall. It may proceed to the blood stream and into the central nervous system causing muscle weakness and often paralysis. An ancient disease, it was first recognized as a medical entity by Jakob Heine in 1840. Eradication efforts led by the World Health Organization and The Rotary Foundation of Rotary International have reduced the number of annual diagnosed cases from the hundreds of thousands to around a thousand.

Infection

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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. The poliovirus is a small RNA (ribonucleic acid) virus that has three different strains and is extremely infectious. The virus invades the nervous system, and the onset of paralysis can occur in a matter of hours. While polio can strike a person at any age, over fifty percent of the cases occur in children between the ages of three and five.

The incubation period of polio, from the time of first exposure to first symptoms, ranges from three to thirty five days, thus Polio can spread widely before a polio outbreak is apparent. Most people infected with the poliovirus have no symptoms or outward signs of the illness and are thus never aware they have been infected. After initial infection with poliovirus, virus particles are excreted in the feces for several weeks and are highly transmissible to others in a community. In all forms of polio, the early symptoms of infection are fatigue, fever, vomiting, headache and pain in the neck and extremities. Around 1% of unimmunized people develop paralytic complications, in some cases bulbar paralysis.

The cause of the disease

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Initial infection is of cells in the lining of the small intestine. Immunization interrupts the process here. After multiplication there, viraemia occurs, with distribution of virus to other parts of the body. Flu-like symptoms are typical of viraemia from any cause. The virus has an affinity for the cell bodies of motor neurones, which carry commands to the muscles.

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