FOR the long-suffering people of Bangladesh, India and more recently Latin America, who have to contend with frequent outbreaks of cholera, here is a message of hope from Rita Colwell, a researcher at the Maryland Universit), Washington. Her research has revealed that a major outbreak of cholera can be prevented by keeping a watch on the growth of a type of aquatic plant known as the phytoplankton.

Cholera is a threat whenever clean water is scarce and is caused by a kind of bacteria called -,qbrio cholerae. Colwell has discovered that a kind of microscopic aquatic animal, the zooplankton which also thrives in cold water, is the primary carrier of the cholera virus. An individual zooplankton can carry as many as 10,000 vibrios and can enter a human body through water or even through fish or shellfish picked up from a pond or river. Colwell has further observed that the population of zooplankton increases - usually in the summers - when an aquatic plant, the phytoplankton, which forms the primary diet of the little animals, grows in abundance. This is inevitably followed by an outbreak of cholera. Colwell suggests that the bloom of phytoplankton should be monitored by keeping a close watch on the satellite images of the earth. And the alarm signals should be sent vigorously ringing whenever there is a significant change in the growth of the phytoplanktons.