Asia’s super-resistant mosquitoes pose a growing threat: study

Mosquitoes that transmit dengue and other viruses have developed increasing resistance to insecticides in parts of Asia, and new ways to control them are desperately needed, new research warns.

Health authorities commonly spray mosquito-infested areas with clouds of insecticide, and resistance has long been a concern, but the scale of the problem was not well understood.

Japanese scientist Shinji Kasai and his team examined mosquitoes from several countries in Asia, as well as Ghana, and found that a series of mutations had made some virtually impervious to popular pyrethroid-based chemicals such as permethrin.

“In Cambodia, more than 90 percent of Aedes aegypti mosquitoes have a combination of mutations that results in an extremely high level of resistance,” Kasai told the AFP news agency.

He found that some strains of mosquitoes had 1,000 times greater resistance, compared to the 100 times previously seen.

That meant that insecticide levels that would normally kill nearly 100 percent of the mosquitoes in a sample killed only about seven percent of the insects.

Even a 10 times stronger dose killed only 30 percent of the super-resistant mosquitoes.

“The level of resistance we found in mosquitoes from Cambodia and Vietnam is totally different,” said Kasai, director of the Department of Medical Entomology at Japan’s National Institute of Infectious Diseases.

Dengue can cause hemorrhagic fever and infects between 100 and 400 million people a year, although more than 80 percent of cases are mild or asymptomatic, according to the World Health Organization.

Several dengue vaccines have been developed, and researchers have also used a bacterium that sterilizes mosquitoes to fight the virus.

But neither option is yet close to eradicating dengue, and Aedes aegypti mosquitoes carry other diseases, including Zika and yellow fever.

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New formulas are needed

Resistance has also been detected in another type of mosquito, Aedes albopictus, although at lower levels, possibly because it tends to feed outdoors, often on animals, and may be less exposed to insecticides than its Aedes aegypti counterparts, which love insects. humans.

The research found that several genetic changes were linked to resistance, including two that occur near the part of mosquitoes targeted by pyrethroids and several other insecticides.

Resistance levels differed, with mosquitoes from Ghana, as well as parts of Indonesia and Taiwan, still relatively susceptible to existing chemicals, particularly at higher doses.

But research shows that “commonly employed strategies may no longer be effective,” said Cameron Webb, associate professor and mosquito researcher at NSW Health Pathology and the University of Sydney.

“There is increasing evidence that current insecticide formulations may have no place in controlling populations of key mosquito pests,” Webb told AFP.

He said new chemicals are needed, but authorities and researchers must also think about other ways to protect communities, including vaccinations.

“We have to think about rotating insecticides… that have different target sites,” added Kasai, whose research was published last month in the journal Science Advances.

“The problem is that we don’t have as many different types that we can use.”

Other options include more efforts to eliminate breeding sites.

When and where the resistance mutations arose remains a mystery, but Kasai is now expanding the research to other parts of Asia and examining more recent samples from Cambodia and Vietnam to see if anything has changed since the 2016-2019 study period. .

“We are concerned that mosquitoes with the mutations we found in this study will spread to the rest of the world in the near future,” he said.

“Before that, we have to think of a solution.”

Source: AFP