Rising Mosquito Insecticide Resistance in Asia and Africa: Implications for Disease Control

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A team of scientists from several Asian nations reported that mosquitoes in parts of Vietnam and Cambodia show high resistance to common insecticides. This is not the first time such a finding has emerged. Earlier warnings had noted that disease-spreading mosquitoes with pesticide resistance were arriving in East Africa.

Mosquitoes transmit a wide range of infections, from dengue and yellow fever to Zika and malaria. To combat this, researchers have developed various chemical families, including pyrethroids, which target the insect’s nervous system. The current study provides evidence that mosquito populations in Vietnam and Cambodia have evolved strong resistance to pyrethroids, with implications for disease control in the region.

Scientists collected mosquitoes from Vietnam, Indonesia, Ghana, and Taiwan. Permethrin, a widely used pyrethroid, was sprayed in all sampling areas. The results showed that only about 20% of Vietnamese mosquitoes died after exposure, while mortality rates in other samples aligned with expectations.

Photographs accompany the report to illustrate the presence of mosquitoes that act as disease carriers. The study highlights the broader public-health stakes of pesticide resistance and the challenges it poses to prevention efforts.

The researchers then examined the genomes of individuals that survived pesticide exposure and identified a mutation in the L982W gene, a genetic change previously linked to resistance in mosquitoes. Following this, they expanded sampling to Singapore and Cambodia and analyzed the L982W gene across ten distinct species. Most of these resistant species were found in Cambodia, suggesting a regional spread.

Across the data set, the team estimated that up to 78% of mosquitoes in Cambodia or Vietnam could resist pyrethroids. Mosquitoes carrying the pyrethroid-associated mutation showed a 50- to 100-fold increase in tolerance. The study also explored combinations of mutations and found that mosquitoes with the L982W mutation plus additional genetic changes could survive pyrethroid exposure levels hundreds to thousands of times higher than normal lethal doses.

In light of these findings, the researchers urged other countries to begin stress-testing their local mosquito populations to determine the true scale of resistance and to inform future control strategies.

Concerning Trends in Africa

Similar resistance patterns have emerged in Africa. Scientists identified a strain of mosquito, Anopheles stephensi, linked to a malaria outbreak in East Africa and beginning to resist insecticides. This complicates eradication efforts in a region where most malaria infections occur. The emergence of this species, which behaves differently from other malaria vectors, has prompted renewed concern among researchers.

In East Africa, Anopheles stephensi has become more common and may be contributing to recent fluctuations in malaria cases. Data presented at major tropical-medicine meetings in late 2023 and early 2024 indicate that this species is involved in outbreaks in urban and peri-urban settings.

Prior to the appearance of Anopheles stephensi in Dire Dawa and nearby areas, malaria cases were relatively low. Since 2019, reported infections surged dramatically, reaching thousands in the current year. The mosquitoes responsible can pick up malaria parasites from the blood of infected individuals and pass them to others in close proximity.

Researchers sampled breeding sites and captured adult mosquitoes around the homes of participants involved in the study. They found the vast majority of adult specimens clustered near residences where malaria cases were detected, underscoring the link between local breeding conditions and transmission risk.

Note: Findings are consistent with ongoing work across multiple laboratories and are being discussed within the broader context of vector-control strategy assessments. Attribution: Science Advances and related presentations.

End of report. The study highlights the importance of robust surveillance and the need for diversified control approaches that do not rely solely on chemical pesticides. Ongoing research aims to identify alternative methods and integrate genetic, environmental, and community-based interventions to reduce disease transmission while managing resistance.

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