BRIEF: Mosquitoes Bite Back Against Malaria Control

(Inside Science) -- Throughout sub-Saharan Africa, public health officials are locked in an arms race with mosquitoes -- one in which some fear the mosquitoes may be poised to take the upper hand. A new study published today in PLOS Genetics looked at one common species of mosquito in large areas of Mozambique and Malawi and found evidence of widespread resistance among them to chemicals known as pyrethroid insecticides, one of humanity’s key weapons against malaria transmission.

Those chemicals are used to make insecticide treated bed nets, which are a front-line preventative tool in the fight against malaria in Africa and throughout the world. According to the researchers who authored the new study, pyrethroid-infused bed nets are responsible for averting hundreds of millions of cases of malaria since 2000.

The new study suggests the widespread use of these chemicals in the last 15 years put evolutionary pressure on the insects and led directly to the large-scale emergence of mosquitoes able to resist them.

The researchers already knew which mutated gene gave the mosquitoes the power to break down pyrethroids. For the new study, they compared DNA from mosquitoes collected in Malawi and Mozambique in 2002, before the widespread use of insecticide-treated bed nets, with DNA from mosquitoes collected in those same countries in 2009 and 2010. In 2002, only a small proportion of mosquitoes in the population carried genetic markers showing resistance to the treated nets. But by 2009, nearly all of them had it.

While nearly all of this type of mosquito in the southern African population studied are now resistant to pyrethroids, there is still hope for the rest of the continent. The researchers found that mosquitoes from other parts of Africa rarely interbreed with the southern population, so the resistance may not spread any further, at least not immediately. Nevertheless, say the researchers, the new study highlights the danger of relying too heavily on any one weapon in the fight against malaria and emphasizes the need for new insecticides and other methods for controlling mosquitoes.