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Cholera a diarrhoeal disease characterised by profuse watery stool and rapid and severe dehydration of the body due to loss of large quantities of fluid and electrolytes with the stool. In the Gangetic delta of which Bangladesh is a part, cholera has been known to wreck havoc, and to wipe out villages after villages killing men, women and children by the thousands. The causative agent of cholera is a comma-shaped bacteria, Vibrio cholerae which was discovered by Robert Koch in 1883. The pathogen is water-borne and is almost always ingested by human subjects with food and water that have been contaminated with the bacteria through the faecal material of cholera patient. After entry into the gut, the bacteria attaches to the small intestine, multiplies rapidly, and in the process produces cholera toxin. The toxin binds with carbohydrate receptors called gangliosides located in the villi of the small intestine. It causes a large increase in the activity of the enzyme adenylate cyclase at the site of colonisation. The result is massive watery diarrhoea. So potent is the secretogenic effect of cholera toxin that as much as 30 litres of fluid may be lost by a cholera patient in one day or, during the course of a full blown episode, twice the body weight of the patient. Dehydration caused by fluid loss during cholera can be readily corrected by intra-venous administration of a fluid containing a mixture of electrolytes such as sodium, potassium, and chloride together with glucose and a small quantity of bicarbonate. It is a self-limiting disease lasting for three to six days and other than rehydration no drug therapy is usually necessary, although use of antibiotics may shorten the duration of cholera.

At one time cholera used to appear as explosive epidermics in the Bengal delta and caused death to thousands of men, women and children. The disease was ascribed by villagers to the emergence of Ola or deity and hence was given the name 'Rise of Ola'. People in the villages resorted to various prejudice and practices to prevent the coming of the Ola Bibi.

Bangladesh has to its credit several pioneering contributions towards scientific understanding of the disease, including development of oral rehydration therapy (ORT) to correct fluid loss by the administration of oral rehydration solution (ORS) instead of intra-venous fluid injection, and development of anti-cholera vaccines and diagnostic tools. The International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) has been singularly responsible for many of these discoveries and is internationally acclaimed for many of its contributions in the field of cholera and other diarrhoeal diseases. [Zia Uddin Ahmed]