Both countries have achieved spectacular success in prevention of the disease by releasing into stagnant water bodies organisms that feed on mosquito larvae.

The Vietnam programme used mesocyclops, a tiny one-eyed shrimp-like creature that can eliminate 96-100 per cent of mosquito larvae in a water body.

The programme, carried out from 1998 to 2003, was reported in the February 2005 issue of The Lancet. It said over 3.80 lakh people had been protected from dengue fever in 12 provinces.

Mesocylops was introduced in all water bodies likeliest to allow large-scale breeding of the Aedes mosquito. This was backed with a community education campaign that told people to take care so as to prevent mosquito breeding in water containers.

The authors, Brian Kay and Vu Sihn Nam, reported that the mosquito had been eradicated in most villages in the programme and no case of dengue had been reported since 2002. They said such a strategy could be used wherever the major breeding ground for A. aegypti is water bodies and containers. This could well apply to the current outbreak in India.

Experts here say the strategy is “not a universal answer, but has the potential to make an important difference in rural communities.” Says Dr A P Dash, director of the Malaria Research Centre, “There’s no vaccine for the disease and the only way to stop it is to prevent mosquito breeding. One of the most important strategies is biological control.”

He explains that biological control is the use of other organisms, not themselves harmful, to check the breeding of one that does cause harm, such as the strategy adopted in Vietnam.

The following are some of the chief forms biological control could take:

Fish: The Chinese have used many species of fish to prevent the growth of A. aegypti · Tadpoles: The tadpoles of the Cuban tree frog have been found an effect check against all kind of insects and algae growing in water·

Zooprophylactics: Animals that attract mosquitoes, and thereby keep them off humans. Some scientists have found that a kind of mosquito common in Hawaii prefers cats to humans.

Predators: The Culex, Psorophora, and Toxorhynchitis species of mosquito sparked interest as their larvae feed on the larvae of A. aegypti.