Researchers in Japan say they have discovered “super” resistant mosquitoes in Asia. In a study published this week, they detail the discovery of populations of Aedes aegypti Mosquitoes – a common disease vector – in Vietnam and Cambodia carry several mutations thought to confer strong protection against the most widely used insecticides. The discovery should merit urgent action to prevent these mutations from spreading globally, they say.
A. aegypti Mosquitoes are one of the most prolific sources of human misery in the world, thanks in part to the wide range of germs they can transmit to us. These mosquito-borne diseases include yellow fever, dengue fever, Zika, and chikungunya, to name a few. The global presence of A. aegypti (with a related species, A. albopictus) and the diseases they spread has expanded in recent years. Many experts expect their range will only expand in the coming decades as the climate continues to warm, including in the southern and eastern United States. So these new discoveries, published Wednesday in Science Advances could add yet another concern to an already serious problem.
The research was led by scientists from Japan’s National Institute of Infectious Diseases, the national equivalent of the National Institute of Allergy and Infectious Diseases (NIAID) in the United States. They studied samples of A. aegypti mosquitoes recently collected from across Asia, specifically looking for mutations in their voltage-gated sodium channel gene. Certain mutations in this gene, called knock-down mutations, can help mosquitoes and other insects survive exposure to pyrethroids, a class of chemicals commonly used to control insect populations. To test whether any of the mutations the researchers found really protected mosquitoes, they also compared their survival rates against insecticides to non-resistant mosquitoes in the lab.
The team eventually identified 10 previously unknown substrains of A. aegypti mosquitoes that appeared to carry one or more of these knockdown mutations. One new mutation in particular, called the L982W substitution, was found in more than 78% of mosquitoes in both countries. And in one specific area of Cambodia, around 90% of mosquitoes carried one of two pairs of mutations identified as particularly troubling.
Laboratory experiments also revealed that these mosquitoes with combined mutations were much harder to kill, with “significantly higher levels of pyrethroid resistance than any other field population ever reported,” the team wrote. In the title of their paper, they describe their findings as the “discovery of super-insecticide-resistant dengue mosquitoes in Asia.”
Other studies In recent years, evidence of increasing resistance to pyrethroids has been found among them. A. aegypti mosquitoes in Asia and the Americas, both in the laboratory and the real world. And the new study is the latest in the team’s ongoing research project to understand pyrethroid resistance in A. aegypti globally. They say it is the first to attempt to unravel the molecular mechanisms that led to these emerging mutations, particularly in mosquitoes from Cambodia.
There is development non-insecticidal technologies that could one day better keep mosquitoes indoors check, as sterile insect techniques that sabotage the population from within, but none of these interventions are expected to be in widespread use any time soon. There is also a new class of insecticides, called neonicotinoids, which is beginning to be deployed more often against mosquitoes. But these chemicals are controversial because of their harmful effects on important pollinating insects, and they are there. sign already that mosquitoes have also begun to adapt to it. There are also no very effective and/or inexpensive vaccines and treatments for many of the common diseases spread by these mosquitoes, especially dengue fever.
All this means that pyrethroids will remain a widely used tool against A. aegypti mosquitoes at the moment. Given this, much more needs to be done to prevent these disturbing mutations from spreading around the world before it’s too late. The L982W mutation has yet to be found in mosquitoes outside Vietnam and Cambodia, for example. But “it may spread to other parts of Asia, which may pose an unprecedented threat to the control of dengue fever as well as other infectious diseases transmitted by Aedes”, warn the researchers.
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