July 17, 2010 -- A "malaria-proof" mosquito has been created by scientists who have engineered a genetic "on" switch that permanently activates a malaria-destroying response, according to their report in the journal Public Library of Science Pathogens.
If these mosquitoes are successfully introduced into the wild, they could prevent millions of people from becoming infected with life-threatening Plasmodium -- the parasite that causes malaria.
"We were surprised how well this works," said Michael Riehle, a professor at the University of Arizona and a co-author of the new PLoS Pathogens paper. "We were just hoping to see some effect on the mosquitoes' growth rate, lifespan or their susceptibility to the parasite. But it was great to see that our construct blocked the infection process completely."
An estimated 250 million people are infected by the four kinds of Plasmodium each year, but each infection comes from female Anopheles mosquitoes. While sucking blood to feed her brood, the mosquito ingests an average of 40 Plasmodium parasites.
The parasites develop on the mosquitoes mid-gut, while the insect's immune system does its best to thin the herd. A few parasites escape and eventually migrate to the mosquito's salivary glands, where they sit, ready to infect the next unfortunate victim.
Age Might Be a Factor in Malaria-Proofing Mosquitoes
The scientists focused on the parasites as they develop by targeting the Akt gene. Previous studies have shown that Akt affects a mosquito's longevity, immune system and digestion -- all of which could affect the bug's susceptibility to malaria.
As a result, the team engineered a special version of the Akt gene into the eggs of Anopheles stephensi mosquitoes.
After infecting the mosquitoes with Plasmodium parasites and allowing them to develop, the scientists examined the mosquitoes. They found no trace of the malaria parasites in mosquitoes that had the amped up version of Akt.
Exactly how Akt eliminates malaria in mosquitoes is unknown.
Older mosquitoes are more likely to carry malaria than younger mosquitoes, and Akt mosquitoes die sooner. That suggests age might be a factor.
New Mosquito Won't Be Introduced Into the Wild Soon
The mosquito's immune system naturally destroys many malaria parasites so it stands to reason that a beefed up immune system could destroy all of the parasites. The mosquito's digestive system could also simply consume the parasites as it digests its blood meal.
"What they've done is take a key point in the insulin signaling pathway, and expressed an active form of it in the gut," said Mark Brown, a doctor at the University of Georgia who is familiar with the new research. Akt, said Brown, "could be activated at any step along that process."
Regardless of how Akt works, it won't be working for any mosquitoes in the wild any time soon.
"We are at least a decade away from actually releasing mosquitoes into the wild," said Riehle. The engineered mosquitoes could mate with wild mosquitoes, but that the team still needs a more effective way to drive the inserted genes through the entire population.
Research labs across the world are trying to solve that exact problem, but so far no solution has been developed.