THE first step has been taken towards altering mosquitoes so they can鈥檛 pass on malaria. But it鈥檚 not clear whether genetically modified mosquitoes could displace natural populations, or if we should even try to make this happen.
For decades, researchers have been trying to enhance the Anopheles mosquito鈥檚 resistance to the parasite that causes malaria, one of the world鈥檚 most prolific killers. In 2000, a technique for inserting genes into these mosquitoes was finally developed.
Now Marcelo Jacobs-Lorena of Case Western Reserve University in Ohio and his colleagues have managed to add a gene to Anopheles that codes for a protein that binds to the walls of their guts and salivary glands. This makes it difficult for the parasite to pass through. 鈥淚t鈥檚 a watershed,鈥� says Fotis Kafatos, whose commentary accompanies the Nature paper (vol 417, p 452).
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But it鈥檚 only the first step on a long road. The modified mosquitoes have only a fifth as many plasmodium parasites in their saliva, but that鈥檚 still enough to pass on the disease. And in the wild, those parasites that do make it through to the saliva might be selected for, making the scheme completely useless. 鈥淔or this to work, it would have to be 100 per cent,鈥� says Kafatos, who works at the European Molecular Biology Laboratory in Heidelberg. The solution may be to add several resistance genes.
Finding these genes will be the easy bit. What no one has worked out is how to get them to spread throughout wild populations of Anopheles. The altered mosquitoes don鈥檛 seem to be any fitter than their wild relatives so they wouldn鈥檛 naturally replace them. To increase the chances of the resistance genes being passed on to offspring, researchers hope to tag them onto a transposon, a piece of DNA that jumps around the genome.
But no one has yet found a suitable transposon to attach them to. Even if researchers do find a way to promote the spread of the resistance genes, modified mosquitoes would still have to be bred and released on a massive scale after a campaign to decimate the wild population. 鈥淚 think there鈥檚 a less than 50 per cent chance that this is ever going to happen,鈥� says Chris Curtis, who works on malaria control at the London School of Hygiene and Tropical Medicine.
If and when the perfect mosquito can be developed, it will still take years to prove that it is safe to release into the environment, adds Jacobs-Lorena, though scientists can鈥檛 think of any reason why these transgenic mosquitoes should be more dangerous than wild ones. In the meantime, other less controversial options are being pursued, says Kafatos, such as developing human vaccines against the parasite.