Malaria carrying mosquitoes are using their legs to fight off insecticides

Mosquito varieties that are known vectors of malaria have started to come up with new ways to fend off the effects of insecticides that are commonly used against them.

Researchers from Liverpool School of Tropical Medicine have observed a higher than usual expression of a specific category of binding proteins in the legs of insecticide-resistant populations of Anopheles gambiae and Anopheles coluzzii, the two most well-known carriers of the Malaria.

The first author of the paper published in the journal Nature, Dr Victoria Ingham explains: "We have found a completely new insecticide resistance mechanism that we think is contributing to the lower than expected efficacy of bed nets."

"The protein, which is based in the legs, comes into direct contact with the insecticide as the insect lands on the net, making it an excellent potential target for future additives to nets to overcome this potent resistance mechanism."

Examining the anopheline mosquitoes, the team demonstrated that the binding protein, SAP2, was found elevated in resistant populations and further elevated following contact with pyrethroids, the insecticide class used on all bed nets.

They found that when levels of this protein were reduced, by partial silencing of the gene, susceptibility to pyrethroids was restored; conversely when the protein was expressed at elevated levels, previously susceptible mosquitoes became resistant to pyrethroids.

The increase in insecticide resistance across mosquito populations has led to the introduction of new insecticide-treated bed nets containing the synergist piperonyl butoxide (PBO) as well as pyrethroid insecticides. The synergist targets one of the most widespread and previously most potent resistance mechanisms caused by the cytochrome P450s.

However, mosquitoes are continually evolving new resistance mechanisms and the discovery of this new resistance mechanism provides an excellent opportunity to identify additional synergists that could be used to restore susceptibility

Prof Hilary Ranson, a senior author of the paper, said: "Long-lasting insecticide-treated bed nets remain one of the key interventions in malaria control. It is vital that we understand and mitigate 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," added Prof Ranson.