Scientists have created genetically modified (GM) mosquitoes resistant to the malaria parasite, which could provide a new method to combat the disease.

Research published in the Proceedings of the National Academy of Sciences today (20 March) shows how the malaria-resistant mosquitoes out-compete natural mosquitoes to dominate a population exposed to the malaria parasite.

The malaria-causing plasmodium parasite is commonly spread by the bite of an infected mosquito. In theory, dominance of resistant mosquitoes would reduce infection rates.

Scientists engineered mosquitoes to carry a gene that prevents the malaria parasite from infecting them. They then introduced equal numbers of GM and non-GM mosquitoes into a cage to feed on malaria-infected mice.

The GM mosquitoes eventually dominated the population, making up 70 per cent of the mosquitoes after nine generations. They had a higher survival rate and laid more eggs than the non-GM mosquitoes when fed malaria infected blood.

Lead researcher Marcelo Lorena, from the US-based John Hopkins University, told SciDev.Net that the advantage is not large enough to insure that wild populations are entirely replaced by the GM mosquitoes. In the wild the percentage of mosquitoes exposed to the malaria parasite is too small for resistance to be a major survival advantage.

He added that a current research priority is to devise a means to drive GM mosquitoes into natural populations where malaria is prevalent.

Trials in sub-Saharan Africa could be conducted within five years, according to the Guardian newspaper. But further research is needed to show that the resistance genes will not lead to a more infectious form of the disease.

Richard Tren, director of the South Africa-based Africa Fighting Malaria, said the idea of using GM mosquitoes to fight malaria has been around for some time.

He said the intervention is best suited to islands or areas where there are pockets of malaria, allowing the GM mosquitoes to dominate the wild population. But he stressed that even if the strategy proved successful, it would need to be part of a comprehensive anti-malaria program.

He also pointed out that for this strategy to be adopted in southern African countries, it would have to be both more effective and cheaper than indoor residual spraying, which has recorded enormous success as a malaria prevention measure.

According to the World Health Organization, malaria kills more than a million people globally; around 90 per cent of these deaths occur in Africa, mostly in young children.

Link to abstract in Proceedings of the National Academy of Sciences

Reference: Proceedings of the National Academy of Sciences 104, 5580 (2007)