Malaria kills one to three million people every year in tropical and subtropical countries such as Africa and India. Traditional attempts to eliminate the scourge are failing: insecticides, including DDT, can be hazardous to both human health and the environment, and the malarial parasite is becoming resistant to many medications. Findings announced today may offer new hope, however: researchers writing in the journal Nature report that inserting laboratory-created genes into mosquito DNA reduced transmission of the disease in mice. Scientists hope that such genetically modified mosquitoes could one day be used in the wild to combat the spread of the malarial parasite from infected mosquitoes to unsuspecting humans.

The malarial parasite's life cycle is a complex one. After a mosquito consumes parasite-laden blood from an infected mammal, the malaria grows and reproduces inside the mosquitos midgut. After several transformations, it binds to the wall of the midgut and then moves to the salivary gland, where it lies in wait, ready to infect the next mammal the mosquito decides to bite. Preventing the parasite from completing its life cycle within the mosquito could thus stop the spread of the disease. To do that, Marcelo Jacobs-Lorena of Case Western Reserve University and his colleagues created a gene called SM1 that encodes a protein that binds to the midgut wall just as the parasite does. In subsequent experiments, the team found, insertion of SM1 into a mosquitos DNA led to the insect producing so much SM1 protein that the midgut wall was covered with it, leaving no surface for the malarial parasite to bind to. As a result, the malarial mosquitoes were 80 percent less effective at transmitting the disease-causing organism to mice.

But will this approach work in the wild? Researchers caution that introducing transgenic mosquitoes into malaria-infected regions is years away. Scientists not only need to test these new genetic techniques on different mosquito and mammal species, they also must better understand the potential effects of releasing genetically modified mosquitoes into the environment. "I think the value of this research is that it will provide an extra weapon," Jacobs-Lorena remarks. "Drugs and insecticides exist and help, but they are not very effective because of resistance. Vaccines are very hard to develop. What we need is a multipronged approach. The more weapons we have, the more effective we will be in our fight against malaria."