Mutation may explain mosquito resistance to many insecticides

Scientists have discovered the same genetic mutation in 11 types of West Nile- and malaria-spreading mosquitoes -- a mutation that may explain their growing immunity to insecticides.

The findings could give chemical companies a molecular target for new insecticides to combat mosquitoes no longer kept in check by existing chemicals.

French scientists who discovered the mutation in the ace-1 gene said it appears to endow the mosquitoes with an immunity to two potent chemicals that cause a fatal paralysis in other mosquitoes.

Researchers from the University of Montpellier II, in Montpellier, France, found the mutated gene in 10 insecticide-resistant strains of the mosquito Culex pipiens, which spreads the West Nile virus in Europe, Africa and the Caribbean.

They also found it in resistant populations of the Anopheles gambiae mosquito -- which transmits the malaria parasite -- that were collected in the Ivory Coast.

The scientists said the mutation in the ace-1 gene, which normally encodes a key enzyme targeted by some insecticides, makes the mosquitoes resistant to those chemicals.

Surfaced 25 years ago

Molecular biologist Mylene Weill led the Montpellier team in scrutinizing the genetics behind mosquito insecticide resistance, a problem that surfaced about 25 years ago and continues to grow.

Normally, insecticides containing either of two families of chemicals, organophosphates and carbamates, paralyzes and kills mosquitoes by blocking an enzyme that regulates nerve signals.

In the case of A. gambiae, its insecticide resistance has allowed malaria's deadly scourge to rebound in African nations where the parasite's courier was once controlled by spraying.

Since finding the mutation in 10 populations of insecticide-resistant C. pipiens, the researchers have found it in additional strains of that species, and expect to find it in others.

"We have looked at something like 15 resistant populations of C. pipiens and every time we've tested them we find the same mutation," Weill said.

While the findings are intriguing, much work remains to determine the precise genetic basis of mosquitoes' insecticide resistance, said Dyann Wirth, a microbiologist who directs the Harvard Malaria Initiative.

She said there may well be other genes that play a role in making the mosquitoes immune to many insecticides.

"I think it's a very good lead but there clearly needs to be more work done," Wirth said.

'Completely unpredictable'

Dr. Joseph Vinetz of the University of Texas Medical Branch, chief spokesman for the Infectious Diseases Society of America, agrees. "Just finding a mutation, which is completely predictable, however, has no relation to the development of new insecticides."

Weill said she and her colleagues, whose discovery was aided by the recently mapped genome of the A. gambiae mosquito, are now collecting other resistant populations of the same species from Africa to test them for the same mutation.

Weill said she hopes concern about malaria and West Nile -- which killed 284 people in the United States -- can convince chemical companies to devote more resources to new insecticides.

"Malaria is seen as an African problem, but with West Nile it's an American problem now," she said.

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On the Net

National Institute of Allergy and Infectious Diseases: www.niaid.nih.gov