Researchers in Japan report discovering “super” resistant mosquitoes in Asia. In a study published this week, they detailed finding populations of Aedes aegypti mosquitoes, a common disease vector in Vietnam and Cambodia, carrying several mutations that are believed to offer strong protection against the most widely used pesticides. They note that this discovery shows that urgent action is needed to prevent the global spread of mutations.
A. aegypti mosquitoes stand out as one of the biggest sources of disease for humans, partly because of the wide variety of microbes they can transmit to us. These mosquito-borne diseases include many different diseases such as yellow fever, dengue fever, zika and chikungunya. The global presence of A. aegypti (along with a related species, A. albopictus) and the diseases they spread have increased considerably in recent years, and many experts think it will increase even more in the coming years. Therefore, the new findings provide new reasons to worry about an already serious problem.
The research was led by scientists from Japan’s National Institute of Infectious Diseases, the country’s equivalent of the US’s National Institute of Allergy and Infectious Diseases (NIAID).
The results of the study identified 10 previously unknown subspecies of A. aegypti mosquitoes that appear to carry one or more of these extinction mutations. A new mutation specifically called the L982W substitution was found in more than 78% of mosquitoes in both countries. And in one particular region of Cambodia, about 90% of mosquitoes carried one of two pairs of mutations identified as particularly worrisome.
In addition, the team reported that laboratory experiments found mosquitoes carrying these combination mutations were much more difficult to kill and had “significantly higher levels of pyrethroid resistance than any other field population reported so far.” Other studies in recent years have found evidence of increased pyrethroid resistance among A. aegypti mosquitoes in Asia and the Americas, both in the lab and in the real world. And the new study is the latest addition to the team’s ongoing research project to understand pyrethroid resistance in A. aegypti globally.
None of these interventions are expected to be widely used in the near future, although there may someday be non-insecticide technologies that could better control mosquitoes, such as sterile insect techniques that sabotage the population from within. There is also a newer class of pesticides called neonicotinoids that are starting to be applied more frequently against mosquitoes. But these chemicals are controversial for their harmful effects on important pollinator insects, and there are signs that mosquitoes are starting to adapt. There are also no highly effective and/or low-cost vaccines and treatments for the most common diseases spread by these mosquitoes, particularly dengue.
All this means that pyrethroids will remain a widely used tool against A. aegypti mosquitoes for now. So more research and testing is needed to prevent these alarming mutations from spreading around the world before it’s too late. For example, the L982W mutation has not yet been found in mosquitoes outside of Vietnam and Cambodia. However, the researchers warn that it “could be spreading to other parts of Asia, posing an unprecedentedly serious threat to the control of dengue fever and other Aedes-borne infectious diseases.”
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