Malaria-carrying mosquitoes detect insecticides with their legs
Scientists at the Liverpool School of Tropical Medicine (LSTM) have found that two species of malaria-bearing mosquitoes can identify insecticides with their legs. Genetic studies of the West African mosquitoes Anopheles gambiae and Anopheles coluzzii show that binding proteins on the insects' legs help them avoid bed nets that have been treated with mosquito-killing chemicals.
Ever since the Anopheline mosquito was identified as the culprit that spreads the deadly malaria parasite, scientists have waged a decades-long arms race trying to come up with effective, environmentally safe insecticides against mosquitoes that continue to develop resistance to them.
Led by Professor Hilary Ranson of the LSTM, the latest round in this battle that kills about half a million people per year involved some clever genetic manipulation. The team took the Anopheline mosquitoes and partially silenced the gene that allows them to express the protein SAP2, which resulted in a restoration of susceptibility to pyrethroids, which is the class of insecticides used on bed nets. Conversely, when the researchers elevated the binding protein in mosquito populations, they displayed increased resistance to pyrethroid insecticides.
According to the LSTM, the rise in insecticide resistance amongst mosquito populations has led to the introduction of bed nets treated with insecticides containing the synergist piperonyl butoxide (PBO) as well as pyrethroid insecticides. The synergist targets what was once one of the most potent resistance mechanisms, but mosquitoes continue to evolve new ones, and the researchers say their new discovery could help identify synergists with the potential to restore insecticide susceptibility.
"Long-lasting insecticide-treated bed nets remain one of the key interventions in malaria control," says Ranson. "It is vital that we understand and mitigate for resistance within mosquito populations in order to ensure that the dramatic reductions in disease rates in previous decades are not reversed. This newly discovered resistance mechanism could provide us with an important target for both the monitoring of insecticide resistance and the development of novel compounds able to block pyrethroid resistance and prevent the spread of malaria."
The research was published in Nature.