Research proposes repellent/insecticide combination to fight malaria

After 15 years of research findings on efforts to fight malaria, a researcher has proposed a combination of insect repellents and insecticides to combat malaria scourge.
Michael Boots, a University of California, Berkeley, professor of integrative biology, who worked with his colleagues at Exeter University in the United Kingdom on the project, disclosed this on Monday in San Francisco, United States of America.
Boots said the finding suggested that the combination therapy would extend the lifetime of the available insecticides and, paradoxically, evolve mosquitoes with greater aversion to the repellent.
He said the combination of both substances would give better repellents and give slower resistance to the insecticide that would last longer or forever.
Boots said research has indicated that insecticides do not kill 100 per cent of mosquitoes, those with some resistance survive and come to dominate the population, rendering the insecticide ineffective.
Boots said: “Repellents, which can be as simple as a scent that insects avoid, can help protect humans by keeping homes free of malarial mosquitoes.
“Many of the mosquitoes that carry the malaria parasite have evolved to bite humans indoors at night.”
Penny Lynch, first author of the research findings said the proposed technique doesn’t require an initially very effective repellent to work.
Lynch, who is also a postdoctoral fellow with joint appointments at the two universities, said that mediocre repellent would drive mosquitoes to evolve, so that the repellent becomes more effective.
Lynch said: “That is the premise, evolution should be selecting for the ones that are repelled, because they don’t get killed by the insecticide.
“As fewer mosquitoes encounter the insecticide, there is less pressure for the mosquitoes to develop resistance to it.
“The idea is, if you combine a spatial repellent that is not particularly good initially, with an effective insecticide in the house, then a certain proportion of the mosquitoes will be repelled and some proportion will go inside the house and get killed.
“So populations that aren’t going into the house are under selection for increased repellence or deflection, and as that happens you get less selection for insecticide resistance.”
Lynch said the finding has assisted in driving malaria cases down almost to levels achieved decades ago with the insecticide DDT.
Boots, however, said now that DDT has been phased out almost everywhere, however, there are fewer fallback options when current insecticides become ineffective because of resistance.
A researcher said the idea of repellent/insecticide combination came to Lynch as she was working on her Ph.D. thesis on insecticides that kill older mosquitoes, the ones that actually spread malaria.
He said she teamed up with Boots to use mathematical models of evolutionary competition between vectors and hosts, the malaria parasite and the mosquito, to test whether the strategy would work.
The researcher said much of the 15 years work, was funded by the Gates Foundation.
He said residents of many countries in Africa and Asia now have access to bed nets impregnated with insecticides such as pyrethroid compounds.
He said one advantage of the strategy is that it can be implemented without interrupting current mosquito control programs, such as spraying insecticides around homes and using bed nets.
He said a repellent could easily be applied in a home at the same time as insecticides are sprayed.
The researcher said plan is underway to test the hypothesis that mosquitoes can actually evolve to be more repelled by mediocre repellents in Africa or Asia, and determine what levels of effectiveness are necessary for both repellent and insecticide.

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