These Mosquitoes Were Released Into a City. Then Dengue Cases Dropped.

Researchers have struck a powerful blow against the deadly dengue virus after a groundbreaking experiment in Indonesia in which specially bred mosquitoes released in communities led to a dramatic decline in cases, according to results of the yearslong trial published this week.

Dengue is the most common mosquito-borne illness in the world. Every year, up to 400 million people are infected with the virus and more than 20,000 die from it, according to the U.S. Centers for Disease Control. It is transmitted by bites from the Aedes aegypti mosquito, which also carries the Zika and chikungunya viruses among others. 

But researchers working with the World Mosquito Program (WMP) over a three-year period in the Indonesian city of Yogyakarta documented a stunning 77 percent decline in infections and an 86 percent drop in hospitalizations by releasing mosquitoes carrying a bacterium called Wolbachia to breed in the wild, the study in the New England Journal of Medicine said.

“Wolbachia is naturally occurring and it is not genetically modified,” Katie Anders, WMP’s impact assessment director, told VICE World News. “It lives inside the cells of mosquitoes and we think what it does is use the resources available there and limits the ability of the mosquito to carry dengue.”

Scientists described it as a safe and effective long-term solution. The so-called Wolbachia method is also being used to tackle other mosquito-borne diseases.

The team worked in Yogyakarta in part because dengue is endemic there. In the randomized control trial, the World Mosquito Program, working with local health authorities and researchers, divided the city into 24 areas. To start, some six million Wolbachia-carrying mosquitoes were released in randomly selected places encompassing the homes of an estimated 300,000 people. After positive results, the coverage area expanded.

“We are very optimistic about local elimination of dengue in the years to come for the reason that the whole city is now covered and because of these really positive results, the team is now releasing these mosquitoes in the districts outside Yogyakarta this year,” Anders said. 

However, it is still possible to import dengue into the city as people travel outside and return. But Anders said that the establishment of a Wolbachia population will curtail local transmission.

The study could have huge implications for other communities struggling with dengue. Indonesia, a tropical country in Southeast Asia, records some seven million cases each year in a country of 270 million people. 

“This is a great success for the people of Yogyakarta,” Adi Utarini, lead investigator and professor at the University of Gadjah Mada, said in a statement. “We think there is a possible future where residents of Indonesian cities can live free of dengue.”

Anders said having community participation was key to success and that the WMP is now in the process of scaling up the experiment to bigger places with one or two million people in 11 countries such as Brazil and Columbia. 

Similar experiments involving the Wolbachia method have been conducted in Singapore as well as the U.S. state of Florida.

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