Polio  common name for the disease poliomyelitis, a viral disease caused by poliovirus, which belongs to the Enterovirus group, so called because of their enteric route of entry into the body. After entry through contaminated food and water, the poliovirus infects the blood through rapid multiplication within the blood cells. The virus then spreads through the axons of peripheral nerves to the central nervous system where it causes destruction of myelin, the fatty material insulating nerve fibres that helps in the transmission of nerve impulses, which is present in the motor neurones (hence myelitis). The resulting clinical outcome is flaccid paralysis. It is a major childhood disease of global distribution although in the industrialised countries the disease has almost been eradicated. About 70% of the world's polio cases occur in India; contribution of Bangladesh in world's polio burden was considerable even about fifteen years back.

In 1983, incidence of polio in Bangladesh was 52 cases per 100,000 children under the age of five years. But the picture has been rapidly changing with the use of oral polio vaccine (OPV) as part of polio eradication programme. The vaccine consists of live attenuated virus which is given as oral drops as a part of a programme carried out during the national immunisation day (NID) observed every year when millions of eligible infants under the age of one year are given two drops of the vaccine. The first and the second dose of the three-dose vaccine are given about one month apart, while the third dose is usually given through the routine immunisation programme of the government. In Bangladesh World Health Organisation sponsored extended programme on immunisation (EPI) where six vaccines are given. These are: the triple vaccine diphtheria- pertussis- tetanus (DPT), OPV, measles and BCG. Since the launching of the programme in the mid-1980s, the incidence of polio cases began to drop sharply. In 1988, the incidence was found to be 14 per 100,000 children under five years of age. During the year 1999, a total of 26 wild type polio cases were detected in 17 of the 64 districts. It is likely that in a couple of years Bangladesh will be a polio-free country. [Zia Uddin Ahmed]