A gene may explain why mosquitoes do not develop malaria even though they carry the disease, say US scientists.
The female mosquito spreads malaria
Female mosquitoes become infected with the malaria parasite when they draw blood from humans with malaria.
The insects can then pass this on to other humans they bite, but do not get sick themselves.
The Johns Hopkins University team believe a gene called SPRN6 enables a mosquito to defend itself - a discovery that could help fight human infection.
Scientist Dr Marcelo Jacobs-Lorena told Proceedings of the National Academy of Sciences: "More research is needed, but we plan to apply this knowledge in the development of new approaches to control the disease."
The scientists hope to develop chemical sprays that would enhance the switching on of the SPRN6 gene in infected mosquitoes.
These mosquitoes would no longer be a real threat to humans when biting them, because they would not transmit the malaria parasite Plasmodium, they believe.
By looking at two types of mosquito, Anopheles stephensi and Anopheles gambiae, Dr Jacobs-Lorena and colleagues found that the SPRN6 gene is normally switched off.
However, when mosquitoes are infected with the malaria parasite the gene is switched on.
To find out the function of SPRN6 they looked at what happened when they forced the gene to stay switched off.
The number of malaria parasites that developed in the stephensi mosquitoes increased three-fold.
Removing the SPRN6 gene completely delayed the natural process by which gambiae mosquitoes rid themselves of the malaria parasite.
Dr Alister Craig, from the Liverpool School of Tropical Medicine, said a number of genes had been found that appeared to help mosquitoes defend themselves against the malaria parasite.
"Having multiple ways of stopping malaria is important. This type of research is really helpful in that area. It's nice to use mosquito immunity as well as other approaches, such as bed nets and anti-malarial drugs, to beat the disease."
Professor Paul Eggleston, professor of molecular entomology at Keele University, said: "This latest piece of work offers new and important insights into the mechanisms by which mosquitoes deal with malaria parasites.
"However, it remains to be seen whether manipulating the activity of SRPN6 in Anopheles gambiae could play a role in controlling transmission of the human disease.
"These organisms have had millions of years to refine their game-play and we, as scientists, must expect to be equally ambitious in our attempts to outwit them."
Dr Jo Lines, of the London School of Hygiene and Tropical Medicine, said it was possible that the parasite might evolve and find a way to overcome such a mechanism.