Infecting Mosquitoes With Natural Bacteria Slashed Dengue Fever Cases by 70% in Gold-Standard City Trial

A gold-standard scientific trial has revealed that an existing mosquito control method works not only to reduce insect numbers, but also dramatically cuts diagnoses of dengue fever — a severe viral infection that can be debilitating when caught and lethal if caught again. In Singapore, populations of Aedes aegypti, the Nile mosquito, are controlled by releasing captive-bred male mosquitoes carrying a type of bacteria called Wolbachia, found naturally on many insect genera. The Wolbachia in this case have been modified to make any eggs born via breeding with the infected mosquitoes sterile — a technique known as Wolbachia-mediated incompatible insect technique–sterile insect technique (IIT-SIT). Even though IIT-SIT is practiced in different parts of the world, there had never been a randomized controlled trial on its effectiveness at controlling or reducing the transmission of mosquito-borne diseases — until now. Researchers at Singapore's National Environment Agency selected 15 densely populated areas of the city-state and randomly divided them into groups that would receive a transplanted swarm of IIT-SIT male mosquitoes, and others that would receive none. The scientists didn't know which areas saw the mosquito release when they began using traps to estimate insect populations, and national health statistics to observe dengue fever cases over 20 months. By the study's end in 2024, the amount of mosquitoes recorded in traps set in wards where Wolbachia-infected males were released plummeted by 77%. Of residents who tested positive for dengue fever, 21% were recorded in control areas, while just 6% were found in the study areas — a roughly 70% reduction in disease risk. The results, published in the New England Journal of Medicine, represent the strongest evidence yet that this biological approach to mosquito control can dramatically reduce the burden of one of the world's most dangerous tropical diseases. Dengue affects an estimated 390 million people per year worldwide, with cases rising sharply due to climate change expanding mosquito habitats. This trial offers a proven, scalable, and environmentally friendly tool in the fight against it — no pesticides required.