The tiny agent that kills up to 3 million people in Africa and Asia each year is the plasmodium parasite that uses the Anopheles mosquito. The mosquito ingests blood from an infected human, then spreads the disease to the next victim.

Scientists in Ohio recently reported that they have modified a species of malarial mosquito to put paid to the parasites. They modified a gene -� SM1, to make a protein to interfere with the development of the parasite in the mosquito. The scientists are also looking for a way of stopping the parasite from getting to the mosquito's salivary glands, where it multiplies.

Neither approach is expected to be totally effective. "The value of this research is that it will provide an extra weapon. Drugs and insecticides are not very effective because of resistance. Vaccines are hard to develop. What we need is a multi-pronged approach," said Marcelo Jacobs-Lorena, of Case Western Reserve University school of medicine.

The insect chosen for modification transmits the parasite in India. The next step would be to test the gene on African mosquitoes. Around the world the parasite infects between 300 million and 500 million people a year.