Distributing mosquito eggs infected with Wolbachia bacteria led to a dramatic fall in dengue cases and hospitalizations in areas that got the intervention compared with those that didn’t, researchers report today (June 10) in The New England Journal of Medicine. While research on Wolbachia as a potential public health tool for combating dengue dates back more than a decade, this is the first randomized trial of the strategy. 

“That provides the gold standard of evidence that Wolbachia is a highly effective intervention against dengue,” Oliver Brady, a dengue expert at the London School of Hygiene and Tropical Medicine who was not involved in the study, tells The Atlantic. “It has the potential to revolutionize mosquito control.” 

Wolbachia is present in numerous arthropod species, where it manipulates reproduction in its hosts to ensure it becomes widespread in the population. Lab experiments indicated that once in mosquitos, Wolbachia competes for resources with the virus that causes dengue, preventing the virus from taking hold in the host. (This principle also holds with other viruses, such as Zika.) 

Wolbachia isn’t naturally present in the dengue vector Aedis aegypti, so more than a decade ago the researchers developed a method to introduce the bacteria to the mosquitoes in a way that would be transmitted from females to their offspring. Then, to see whether Wolbachia could counter dengue in the real world, researchers with the nonprofit World Mosquito Program (WMP) released A. aegypti infected with the bacteria in northern Australia and in several other countries in 2011. The number of dengue infections in the Australian release area dropped by 96 percent after the introduction and results from the other sites were also encouraging, but the work was observational and couldn’t definitively prove that the Wolbachia caused the reductions. 

In the current study, the WMP randomly assigned 24 geographic areas in the city of Yogyakarta, Indonesia, to either receive infected mosquito eggs or to serve as controls. The researchers enrolled participants with fever who visited clinics in the treated and untreated areas, and found that 9.4 percent of those who lived in the control areas had dengue, while only 2.3 percent of the people with fever living in the egg-release zones had the disease. The researchers reported this 77 percent reduction in dengue incidence in a press release last year. In the new paper, they also report a decrease in hospitalizations due to dengue of 86 percent in the treated areas.  

“That’s really the big thing,” study coauthor Cameron Simmons of Monash University in Melbourne and the WMP, tells Science. “It’s the weight of hospitalization . . . that really stretches health systems.”  

According to The Atlantic, the WMP is now working in 11 countries, where 7 million people now live in areas with Wolbachia-infected A. aegypti. The organization aims to protect at least 500 million people by 2030.