New way to ward off malaria mosquitoes

QIMR Berghofer Medical Research Institute scientists, as part of an international team, have identified a way to maintain the long-term effectiveness of the world’s best weapon against malaria infection.

Associate Professor Greg Devine, head of the Mosquito Control Laboratory, said the team had shown that using a new combination of chemicals on insecticide-treated bed nets (ITNs) could mean the nets would continue to protect people from malaria-carrying mosquitoes.

“We know that ITNs dramatically reduce malaria infection and deaths in endemic regions by forming a protective barrier,” Associate Professor Devine said.

“At the moment, though, only pyrethroid insecticides are approved by the World Health Organisation for ITNs, and there have been increasing, worrying signs that mosquitoes are developing pyrethroid resistance, potentially undermining the effectiveness of the nets.”

This study showed the value of combining a pyrethroid insectide with a powerful chemosterilant, known as PPF, which makes adult mosquitoes sterile.

“Resistant mosquitoes spend more time at the nets, get a bigger dose of the PPF, and are sterilised. Over time, that reduces the proportion of pyrethroid-resistant insects in the population,” Associate Professor Devine said.

“PPF doesn’t kill adult mosquitoes, so we don’t want to use it on its own because even a sterile mosquito might transmit malaria. But when you combine PPF with pyrethroids it ensures that those really important, mosquito-killing insecticides retain their efficacy.

“That’s crucial for the continued success of malaria control in large parts of sub Saharan Africa where insecticide resistance is now emerging”.

The chemosterilant PPF is already available for mosquito control and is approved as safe for humans.

“What this finding might do is get us off the treadmill – the treadmill where for decades we’ve developed insecticides, used them universally because they’re effective, and then seen mosquitoes develop a resistance to them,” Associate Professor Devine said.

“By combining the chemicals, we can prevent the development of resistance, protect effective chemistries and conserve the sustainability of our best malaria control tools.”

This research was undertaken with colleagues from Imperial College, London, and the Ifakara Health Institute in Tanzania.

It is published online in the current issue of PLOS ONE and can be viewed at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0095640

This research was made possible by a Tanzanian-based grant from the Bill and Melinda Gates Foundation.