Brazil’s massive mosquito factory fights dengue 2023


Over the next decade, the non-profit World Mosquito Program (WMP) will release modified mosquitoes in numerous Brazilian urban areas to protect up to 70 million people from dengue. In chosen locations in Australia, Brazil, Colombia, Indonesia, and Vietnam, researchers have released this mosquito, which carries a Wolbachia bacterium that prevents virus transmission. The technology will be nationwide for the first time.

In conjunction with Rio de Janeiro’s Oswaldo Cruz Foundation (Fiocruz), the WMP will build a mosquito factory in Brazil. The factory will produce five billion mosquitoes annually starting in 2024. “This will be the biggest facility in the world” to breed Wolbachia-infected mosquitoes, says Scott O’Neill, a microbiologist at Monash University in Melbourne, Australia, and WMP head. “And it will enable us to cover more people faster than any other country.” In 2022, Brazil had almost two million dengue cases.

Despite positive mosquito releases, experts predict it to be difficult to run the technology at such a large scale.

Competing bacteria

About half of bug species natively carry Wolbachia pipientis. However, Aedes aegypti mosquitoes, which spread dengue, Zika, chikungunya, and other viruses, rarely carry the bacterium. After discovering that Wolbachia-infected A. aegypti disseminated less disease, O’Neill and his colleagues created the WMP mosquitoes. Bacteria outperform insect viruses.

The transgenic mosquitoes steadily transfer the bacterium to wild A. aegypti when released.

Insects have succeeded in several experiments. The most complete one, a randomized, controlled experiment in Yogyakarta, Indonesia, revealed that the technique might lower dengue incidence by 77%1. Epidemiologists were enthusiastic.

Rapidly advancing

The modified mosquitoes have been tested in five Brazilian towns with less promising outcomes. The intervention reduced dengue cases 69% in Niterói2. Rio de Janeiro reduced 38%.3

Wolbachia may spread slower in cities with more wild mosquitoes due to environmental variables. Social setting matters too. Violence in several Rio de Janeiro neighborhoods slowed deployment. “While we’ve worked very closely with people in those communities, it can be slow work to build trust and operationalize plans,” O’Neill says.

As the project grows, this will be crucial. “We’re interested in automating mosquito distribution in communities to cover ground faster,” he explains. The WMP is investigating mosquito-dispersal tactics with drones, motorbikes, and vehicles.

The facility will create five billion bacteria-infected mosquitoes annually.

In Belo Horizonte, Brazil, a big randomized, controlled study is comparing dengue rates in Wolbachia-infected mosquito sites and other places. Previous research in Niterói and Rio de Janeiro used national database health data instead of enrolling individuals.

“We have good indications that the WMP mosquitoes are an efficient tool, but this must be proved beyond any doubt,” says Brazilian microbiologist Maurício Nogueira.

Brazilian regulators allowed Wolbachia-infected mosquitoes. However, the WHO has not yet endorsed the technique, which may prevent its adoption in other nations. The WHO’s Vector Control Advisory Group will consider the modified mosquitoes at its next meeting this month.

Despite the mosquitoes’ effectiveness, Fiocruz senior scientist Luciano Moreira, one of WMP’s colleagues in Brazil, advises governments not to forgo dengue vaccines. “The Wolbachia method is complementary, and we should use integrated methods to control dengue, Zika, and chikungunya,” he says. “This doesn’t work.”

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