Poliomyelitis is a crippling disease that results from infection with any one of the three related poliovirus types (referred to as types P1, P2, and P3), members of the enterovirus (picornavirus) family. Poliovirus is transmitted from one person to another by oral contact with secretions or faecal material from an infected person. Once viral reproduction is established in the mucosal surfaces of the nasopharynx, poliovirus can multiply in specialized cells in the intestines and enter the blood stream to invade the central nervous system, where it spreads along nerve fibres. When it multiplies in the nervous system, the virus can destroy nerve cells (motor neurons) which activate skeletal muscles. These nerve cells cannot regenerate, and the affected muscles lose their function due to a lack of nervous enervation - a condition known as acute flaccid paralysis (AFP). Typically, in patients with poliomyelitis muscles of the legs are affected more often than the arm muscles. 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. It can strike at any age, but affects mainly children under three (over 50% of all cases).
In May 1988, at its annual meeting in Geneva, the World Health Assembly, the governing body of the World Health Organization (WHO), resolved to eradicate polio from the world. The global eradication initiative is concerned both with stopping new cases of poliomyelitis caused by poliovirus throughout the world as well as implementing mechanisms to prevent its reintroduction. In the ensuing years, the number of poliomyelitis cases have been reduced by over 99%, and as of the beginning of 2003, only 7 countries world wide had any detectable level of poliovirus transmission.
Technical report series
- Meeting Reports
- WHO International biological reference preparations catalogue