Scientists to exploit mosquito's genetic Achilles heel in fight against malaria
Thursday 08 May 2003
SCientists Have discovered the Achilles' heel of insecticide-resistant mosquitoes which could lead to the invention of new pesticides to wipe out the carrier of malaria, yellow fever and other dangerous diseases.
A team of researchers from Montpellier in France has found what it takes to turn a vulnerable mosquito into a super-resistant strain that can survive a dousing with the most toxic pesticides. A single mutation in the insect's DNA – the smallest possible change in the mosquito's genetic code – is almost certainly responsible for the pesticide resistance seen across the globe over the past 25 years, the scientists said.
Resistance, and the consequent failure to control mosquito numbers, is one of the biggest problems in the fight against malaria, which kills an estimated 2 million people a year, most of them children in developing countries.
Malaria affects between 300 million and 500 million people in the world at any one time and its effects can cut economic performance by 1.5 per cent in the worst-hit nations.
Mylène Weill, who led the University of Montpellier team, said the mutation occurred in a gene called Ace-1 which is responsible for producing a chemical enzyme found in the tips of the insect's nerves. Normally the enzyme, called acetylcholinesterase, mops up a neurotransmitter that causes a nerve impulse to jump from one cell to another, so the enzyme prevents the over-stimulation of nerves. Organophosphates – which are effectively nerve agents – work by binding to acetylcholinesterase thereby blocking the enzyme's activity and preventing the removal of spare neurotransmitter, which quickly kills the insect.
Dr Weill and her colleagues show in a study published today in the journal Nature that the mutation in the Ace-1 gene of resistant mosquitoes prevents organophosphates from binding to the acetylcholinesterase, rendering the insecticides redundant. Dr Weill said: "We found the target for insecticides and we found the mutation that makes them resistant. There is resistance almost everywhere and this is a big problem. Our identification of this mutation may pave the way for designing new insecticides and opens the way to new strategies for pest management."
Dr Weill said by knowing how a change in the mosquito's DNA results in the emasculation of organophosphate pesticides, scientists will be able to screen for chemicals that can work against the mutated form of the gene, overcoming the problem of resistance. She said: "This is really crucial. There are not many other ways to combat malaria. Vaccines are still years away so the only way we can fight the disease it to limit the number of mosquitoes."
The Montpellier team found the mutation was present in all 10 highly resistant strains of Culex pipiens, the species that transmits West Nile fever, as well as a resistant strain of the malaria mosquito, Anopheles gambiae.
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