Southeast Asia warned of insecticide-resistant dengue mosquitoes

- A team of researchers led by Shinji Kasai, director of the Department of Medical Entomology at Japan's National Institute of Infectious Diseases, has warned about an increasing number of insecticide-resistant mosquitoes in Southeast Asia.

The warning comes after the team found a new genetic mutation that makes Aedes aegypti mosquitoes -- also known as yellow fever or dengue mosquitoes -- more resistant to common insecticides.

Aedes aegypti mosquitoes are known as a vector of the Zika virus, as well as yellow fever and dengue fever.

More than 80% of Aedes aegypti mosquitoes in Vietnam and Cambodia were found to have this genetic mutation, necessitating review of mosquito control methods and increased caution about a proliferation of insecticide-resistant mosquitoes.

The team led by Kasai collected mosquitoes in Vietnam and elsewhere and examined how they were resistant to commonly used "pyrethroid" insecticides.

The study showed that even when the concentration of insecticides was raised to 10 times the level that can kill ordinary mosquitoes, about 80% of mosquitoes collected in Hanoi survived.

Kasai's team identified a new genetic mutation called L982W, which makes mosquitoes more resistant to common insecticides.

Between 78% and 99% of mosquitoes in three cities -- Hanoi in the north of Vietnam and Ho Chi Minh City in the south, as well as the Cambodian capital Phnom Penh across the border -- had this genetic mutation.

Including L982W, four genetic mutations have so far been found to show resistance to insecticides. The percentage of mosquitoes with two of the four genetic mutations reached 91% in Phnom Penh, showing how resistance is strengthening there.

According to Kasai's team, there is a possibility that insecticide-resistant mosquitoes spread from Cambodia to neighboring Vietnam.

Although no mosquitoes with the L982W genetic mutation were found in Laos, Thailand and China, the mosquitoes might be gradually spreading across Indochina and to other regions in Asia.

Even in Japan, there are concerns about Aedes aegypti mosquitoes taking hold, as regions in the country where they can survive winter are expanding due to warming temperatures.

Kasai stressed the need to closely examine how insecticide-resistant mosquitoes are spreading across Indochina and how to reduce the use of pyrethroid insecticides, or use them with other mosquito control methods.


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