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The Disease

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. Polio follows infection with any one of three related enteroviruses: poliovirus types 1, 2, or 3. The virus enters through the mouth and then multiplies inside the throat and intestines. The incubation period is 4 to 35 days and the initial symptoms include fever, fatigue, headaches, vomiting, constipation (or less commonly diarrhea), stiffness in the neck, and pain in the limbs. 
 

Polio Paralysis

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. The limb becomes floppy and lifeless - a condition known as acute flaccid paralysis (AFP). More extensive paralysis, involving the trunk and muscles of the thorax and abdomen, can result in quadriplegia. In the most severe cases (bulbar polio), poliovirus attacks the motor neurons of the brain stem - reducing breathing capacity and causing difficulty in swallowing and speaking. Without respiratory support, bulbar polio can result in death.

Large polio epidemics caused panic every summer during the 1940s and 50s in industrialized countries (United States and Western Europe). At that time, people with polio affecting the respiratory muscles were immobilized inside "iron lungs" - huge metal cylinders that operated like a pair of bellows to regulate their breathing and keep them alive. Today, the iron lung has largely been replaced by the positive pressure ventilator; nevertheless, it is still in use in some countries. 

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. 
 

(Text and Photos Courtesy of the World Health Organization)