Malaria is one of the world's deadliest diseases, infecting millions annually. More than a million children die each year from the disease, which is spread by mosquitoes. But mosquitoes are starting to become resistant to the insecticides used to control them. Now researchers have found some genes in mosquitoes that allow them to survive the chemicals.
Hilary Ranson from the Liverpool School of Tropical Medicine says one of the most effective weapons against the spread of malaria has been the use of bednets. But bednets need to be treated several times a year, soaked in an insecticide, most commonly a pyrethroid-type insecticide.
"These insecticides have been very successful for malaria control, but in recent years, we are seeing a growing trend of increasing resistance to this insecticide class," Ranson says. "This is really worrying because we don't have many other alternatives."
Ranson says there are some areas in Africa where more and more malaria-carrying mosquitoes are becoming resistant to the pyrethroid insecticides.
So she and an international team looked for what made some mosquitoes more resistant.
"We identified two enzymes that are found at much higher levels in the resistant insects that we were studying than in the general susceptible population," Ranson says. "We were able to show that these enzymes are able to break down the insecticide..."
Ranson says since the resistant mosquitoes break down insecticide very rapidly, the insecticide becomes less toxic. The result is that it no longer has the desired effect of killing a mosquito.
Ranson and her team were also able to determine which genes in the mosquitoes create these enzymes. She says this is important information.
"Now we can think about modifying that insecticide so that it's still toxic even to resistant insects," Ranson says.
She explains that the way scientists could approach making new insecticides is to change the property of the chemical. Instead of trying to kill the insect directly, a new insecticide would also stop the action of these enzymes, allowing the pyrethrin-type insecticides to last longer even in resistant insects. Ranson says this approach would effectively restore efficacy to the pyrethrin insecticides.
Ranson says this information will help keep a powerful weapon in the anti-malaria arsenal.
Her research is published in the journal Genome Research.