Polio is an infectious disease caused by a virus. It can strike at any age, but affects mainly children under three (over 50% of all cases). The disease causes paralysis, which is almost always irreversible. In the most severe cases, polio paralysis can lead to death by asphyxiation.
Once established in the intestines, poliovirus can enter the blood stream and invade the central nervous system - spreading along nerve fibres. As it multiplies, the virus destroys nerve cells (motor neurons) which activate muscles. These nerve cells cannot be regenerated and the affected muscles no longer function. The muscles of the legs are affected more often than the arm muscles.
Poliovirus is spread through person-to-person or faecal-oral contact. Where hygiene and sanitation are poor, young children are especially at risk. Young children who are not yet toilet-trained are a ready source of transmission, regardless of their environment. Polio can be spread when food or drink is contaminated by faeces. There is also evidence that flies can passively transfer poliovirus from faeces to food.
Because no drug developed so far has proven effective, treatment is entirely symptomatic. Moist heat is coupled with physical therapy to stimulate the muscles and antispasmodic drugs are given to produce muscular relaxation.