They still bite, but recent research shows lab-grown mosquitoes are fighting dangerous dengue fever that they would normally spread.
Dengue infections appear to be dropping fast in communities in Indonesia, Vietnam, Brazil, and Australia that are buzzing with specially bred mosquitoes, according to a report by an international research team.
Scientists infected the mosquitoes with a bacteria called Wolbachia, aiming to block their ability to transmit viruses. The researchers say Wolbachia is a naturally occurring bacteria that is harmless to people and carried by 60 percent of insect species including fruit flies, dragon flies and moths.
The scientists specifically targeted Aedes aegypti mosquitoes, which are the primary carriers of dengue around the world.
Results of an Indonesian study, published in the New England Journal of Medicine on Wednesday, confirms that infecting the mosquitoes with Wolbachia not only reduced the incidence of dengue by 77 percent, but the number of people who would normally need hospital treatment decreased by 86 percent.
Researchers found a similar drop in a community near the southern Vietnamese city of Nha Trang.
Preliminary results suggest large declines in dengue and a related virus, chikungunya, in a few neighborhoods in Brazil, near Rio de Janeiro.
The Indonesian trial enrolled 8,144 participants who attended primary care clinics with acute fever lasting up to four days.
Over a 27-month period, researchers found that in areas where Wolbachia was introduced, dengue was present in only 2.3 percent of participants, compared to 9.4 percent in non-Wolbachia areas.
The studies have been led by an international collaboration of scientists in the World Mosquito Program, formerly known as Eliminate Dengue.
One of the laboratories leading the research is based at the Fundacao Oswaldo Cruz (FIOCRUZ), Brazil's main biological research institution, in Rio de Janeiro. FIOCRUZ researchers prepare tubes containing the Wolbachia-infected mosquito larvae, which they then release in specially marked out areas of Rio.
Wolbachia blocks the mosquitoes' ability to pass on diseases like dengue, chikungunya and Zika, according to researchers, but it doesn't affect malaria.
"Wolbachia is an intracellular bacteria, and the discovery was that when it was injected in the Aedes Aegypti, it reduced the capacity of the mosquito to transmit the virus," FIOCRUZ's Dr. Betina Durovni told the AP in 2019.
"The first experiments were with dengue; more recently studies have been published showing that it also has the capacity to reduce the transmission of Zika and Chikungunya."
Trials expanding around the world
In several labs around the world, teams are breeding new generations of mosquitoes from the mosquitoes originally infected with Wolbachia. Subsequent generations carry the same characteristics as their parents, blocking their ability to pass on diseases.
Wolbachia-infected mosquitoes were first released in Queensland, Australia a decade ago, and the World Mosquito Program claims they've led to a 96 percent reduction in dengue transmission. The organization says trials are ongoing and are currently being expanded to Colombia, Sri Lanka, India and places in the Western Pacific.
Some researchers worry that releasing large numbers of modified insects in this way could affect the ecosystem, and that we may not realize the full ramifications until it's too late.
But Durovni said no evidence so far points in this direction. She said scientists continue to monitor mosquito populations in places like Queensland where the Wolbachia mosquitoes were first released and that they hadn't observed any changes in the mosquitoes' behavior or environments.
"Of course, all this needs to be monitored - we are talking about innovation that still needs to be monitored for some years. But so far, we have not observed any changes from the presence of Wolbachia in these mosquitoes," she said in 2019.
The same studies ongoing in Brazil and Vietnam are yet to pronounce final results.
(FRANCE 24 with AP)