This is life | Mosquitoes are highly resistant to insecticides identified in Asia

A recently published Japanese study shows that mosquitoes that transmit dengue and other severe viral diseases have developed high resistance to insecticides in parts of Asia, and new ways to stop their spread are urgently needed.

Spraying insecticides in mosquito-infested areas is a common practice in tropical and subtropical regions. Resistance was indeed a concern, but the exact scale of the problem was not yet known precisely.

Japanese scientist Shinji Kasai and his team studied mosquitoes from several Asian countries and Ghana, and found genetic mutations that make some of them immune to widely used insecticides like permethrin.

“In Cambodia, more than 90% of the Aedes aegypti mosquitoes — the main vectors of dengue, Zika, chikungunya and yellow fever viruses — have a set of mutations that lead to an extremely high level of resistance,” said Kasai, in an interview with Mr. Kasai. France Press agency.

The director of the Department of Medical Entomology at Japan’s National Institute of Infectious Diseases discovered that certain types of mosquitoes that were supposed to be 100% eradicated with insecticides are now only 7% dead. Even a toxic dose ten times higher killed only 30%.

Resistance levels vary by region. They are “quite different” between Cambodia and Vietnam, for example, according to Mr. Kasai.

His work also revealed that pesticides found in Ghana and parts of Indonesia and Taiwan still work today.

Insecticide resistance has also been observed in Aedes albopictus, but at lower levels.

– New Parises to find –

This study, published at the end of December by the journal Science Advances, shows that “commonly used strategies may no longer be effective” in controlling harmful mosquito populations, according to Professor Cameron Webb, an expert from the University of Sydney who gave an interview to AFP. .

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New chemicals are needed, but authorities and scientists should also consider new methods of prevention, such as vaccines, according to Webb.

There are currently only a few dengue vaccines available – Japanese pharmaceutical group Takeda’s vaccines were approved last year by Indonesia and then the European Union, while use of France’s Sanofi vaccine is severely limited because it can exacerbate the disease in people who have never had it. that. This virus was before.

Dengue cases have increased dramatically worldwide over the past 20 years, with between 100 and 400 million infections annually, according to the World Health Organization (WHO). More than 80% of cases are mild or asymptomatic, but life-threatening complications are present.

Kasai, who worries that the highly resistant mosquitoes he discovered could spread elsewhere in the world “in the near future,” recommends further diversification in insecticides, but the problem is that their modes of action are often similar.

Alternatives are to step up efforts to eradicate mosquito breeding grounds or to sterilize male mosquitoes using Wolbachia bacteria, an innovative method that has already yielded encouraging results locally.

Where the insecticide resistance mutations appear in mosquitoes remains a mystery.

Mr Kasai is now expanding his research to other parts of Asia and is also looking at more recent samples from Cambodia and Vietnam to see if anything has changed from his previous study which looked in 2016-2019.

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