A controversial US-funded mosquito-control project in Delhi which was closed down by the Indian government 20 years ago (Nature 256, 355-357; 1975) is now likely to be revived.
International efforts are under way to relaunch a sterile-insect technology (SIT) project, despite scepticism in parts of India's scientific community, with the aim of eradicating Anopheles stephensi — the principal vector for urban malaria — from towns in southern India.
SIT relies on the fact that female mosquitoes mate only once. If this single mating occurs with sterilized males, it results in eggs that do not hatch. So releasing sterilized males in numbers far greater than those of the wild male population could eradicate the targeted vector mosquitoes — provided the area is not reinfested by mosquitoes from the surrounding region.
The move to revive the technique is being led by Christopher Curtis of the London School of Hygiene and Tropical Medicine, Alan Robinson, head of the entomology unit of the Vienna-based International Atomic Energy Agency (IAEA), and Vinod Prakash Sharma, who is due to retire shortly as director of India's Malaria Research Centre (MRC) in New Delhi.
The group presented the idea to last month's global meeting on malaria in Hyderabad, sponsored by the Malaria Foundation, which is based in New York. They are also preparing a report on it for India's Department of Biotechnology, which is said to be sympathetic to the project, provided that environmental and biosafety concerns are met.
Both Curtis and Sharma were prominent scientists of the Delhi project that was terminated in 1975 following an uproar in the Indian parliament about reports that the project was part of US efforts to develop yellow fever as a biological weapon.
These allegations were prompted by the fact that project scientists had been genetically manipulating the Aedes aegypti mosquitoes which spread yellow fever — a disease that does not exist in India — and were planning a massive release of sterile males of this species.
Curtis denies that anything sinister took place, and says that the project fell victim to an “ill-informed press and political campaign”. The new project proposed for southern India will use mosquitoes sterilized by radiation and will not involve genetic manipulation.
Robinson says the IAEA, with backing from the World Health Organization and the United States, plans to raise the $12 million needed to start the project by holding a series of donor meetings, and to start work next year. Meanwhile, the search is on for an Indian scientist to act as local project leader.
Curtis says that towns such as Salem, in the state of Tamil Nadu in southern India, are ideal sites for SIT because A. stephensi, the only vector spreading malaria in these towns, is totally absent in surrounding rural areas. “If we get rid of A. stephensi in towns using SIT, no replacement is possible and the area can remain free of malaria for ever,” he says.
Some scientists are sceptical, however, citing potential problems with cost, efficiency of separation of the sexes, and what they predict would be the temporary nature of any eradication. “This technology is not workable,” warns P. K. Rajagopalan, the former director of the Vector Control Research Centre in Pondicherry, who was involved in the Delhi project. “It is a mystery to me why it is coming back after two decades.” P. K. Das, current director of the Pondicherry centre, says India does not need high-technology mosquito control. “What we need is political will to implement low-cost techniques that already exist,” he says.
It is true that the long-term efficacy of SIT in eradicating mosquitoes has not been demonstrated. But Robinson says that recent success in controlling screw worm, tsetse and Mediterranean fruitflies “gives us hope we can use this technology in human health”.
On the question of separation of the sexes — no females can be released because they are the ones that bite — Robinson also argues that techniques for sexing Anopheles mosquitoes have been refined. He says he is confident that “the changed political atmosphere in India” will not allow the 1975 episode to be repeated.
And on the third argument, cost, an official from the MRC told the Hyderabad malaria conference: “Delhi spends $9 million each year on malaria control without any success. Can't we spend this money just once to eliminate the malaria mosquitoes for ever, using SIT?”
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