World Mosquito Programme | Impact

Releasing mosquitoes to fight dengue

In Joinville, a city in southern Brazil, Noel Maciel watched dengue arrive and take hold within a few short years. His community had barely seen the disease before 2011. By 2024, the city had recorded more than 80,000 cases and 83 deaths. People he knew were dying.

Then one morning, a white minivan began making its way through his quiet streets. The team inside were not spraying insecticide to limit mosquitoes. Instead, they were releasing them, each one carrying a natural bacterium that blocks their ability to transmit dengue.

"Many people thought it was very strange," says Maciel. "How can you release more mosquitoes? But my thought was that it would work. I just didn't imagine it would work in such a short time."

Noel Maciel sat in a cafe in Joinville, Brazil — Noel Maciel, a cafe owner who told of the impact of dengue on his community in Joinville, Brazil.
Credit:
Léo Mello/Camisa Preta Filmes
Licence: All Rights Reserved

Watch: inside Brazil's fight against dengue

From the world’s largest mosquito biofactory in Curitiba to the streets of Joinville, this film – produced in collaboration with Devex – follows the scientists, health workers and communities turning a bold idea into real-world protection against dengue.

In Brazil, scientists and communities are teaming up to release mosquitoes that block dengue transmission. This video follows the journey from lab to neighborhood, showing how R&D protects communities from disease.

Noel Maciel: Suddenly, things started to increase, increase, increase. Outbreaks began to appear, and it ended up becoming an epidemic. I have acquaintances who contracted dengue and ended up dying. It was very scary and very fast, right? I believe that in less than five years this thing rose exponentially.

Luciano Moreira: In Brazil especially, we are seeing dengue spreading all over the country and places that never had dengue before. So when we challenged these mosquitoes with dengue, we discovered that Wolbachia was actually blocking the virus inside the cells of Aedes aegypti. So that was a huge discovery. The idea was to produce 100 million eggs per week, so more than 5 billion eggs per year. So it took one year to build this structure, almost 2000 square meters for production sites.

Gabriel Sylvestre: The offspring has Wolbachia, and then generation for generation they are replaced by mosquitoes that cannot transmit. And when the eggs reach the city, the local health agents, they produce mosquitoes and release mosquitoes in the field. So Wolbito do Brasil is now managing and delivering eggs and training people how to do it.

Tamila Klein: We need to explain this to the population. So, our first contact is really about explaining, using simple language and playful methods so that everyone understands, addressing all queries, because I believe that people don't accept what they don't understand. We explain that it's temporary, that we won't be doing it forever. That for a short period there will be more mosquitoes on the streets, but then it stops, and everything returns to normal. The release is done by car. The production process involves placing adult Wolbachia mosquitoes in containers. At each point, the release agents open a container, release the mosquitoes, and let them fly out.

Luciano Moreira: So, in Indonesia, we have around 86% reduction in hospitalizations with the RCT (randomized controlled trials) that happened there. And we also see from cities that they say, yeah, dengue is no longer a problem.

William Garrood: For a technique like Wolbachia, you need to have a greatly increased operational capacity, you need to be able to manufacture so you can produce these mosquitoes at scale. You need to have the logistics in place to actually be able to deploy these in the communities that need them the most, and you need the technical expertise within your workforce to bring this all together. So what you need is long-term secure financing, and then what you would also need is, you need it to be integrated into a health program, controlled methods.

Gabriel Sylvestre: So at Wolbito do Brasil, we have a commitment with the minister of health to cover 7 million people every six months. So for every year we will be covering close to 14 million people. So we have a plan to cover close to half of Brazil in 10 years.

Mathias Gonçalves: It's so important we have the partnership with government and acceptance of government and approval of the government in terms to implement the structure and to organize things.

Noel Maciel: Many people thought it was very strange. "But how can you release more mosquitoes?" I thought that it would work — I just didn't think it would work so quickly. This year, dengue has decreased dramatically. People stopped commenting, stopped saying, "Oh, so-and-so has it, another so-and-so got sick." So, it really became very noticeable.

Why is dengue getting worse?

The Aedes aegypti mosquito transmits dengue, chikungunya, yellow fever and Zika. It breeds in small pools of standing water, bites during the day and is growing resistant to insecticides. Traditional control methods are struggling to keep pace.

For Maciel, the speed of the crisis was terrifying. Outbreaks in Joinville surged in the space of just a few years. “I have acquaintances who contracted dengue and ended up dying. It was very scary and very fast. I believe that in less than five years this thing rose exponentially.”

For those who have had dengue, the memory stays. Adrielly Amarante, a hotel worker from Joinville, contracted the disease four years ago.

It took her almost 60 days to recover. "I wasn't very active, but I used to ride my bike," she says. "Even pedalling slowly or doing daily activities was difficult. I had joint pain, especially behind my knees, and pain behind my eyes.”

Adrielly a hotel receptionist in Joinville, Brazil — Adrielly Amarante, a hotel receptionist in Joinville, Brazil, who spoke of her experience with dengue fever.
Credit:
Léo Mello/Camisa Preta Filmes
Licence: All Rights Reserved

In 2024, the world experienced its worst year for dengue on record – more than 14 million cases and over 10,000 deaths globally. Brazil bore the heaviest burden, with more than 10 million cases and over 6,300 deaths. Climate change is a driving factor: rising temperatures and shifting rainfall are expanding the mosquito’s range into higher altitudes and latitudes previously too cool for it to survive, while lengthening transmission seasons in regions already affected.

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How does the Wolbachia method work?

Scientists at Monash University in Australia, working through what became the World Mosquito Program, made a pivotal discovery in 2009. They found that that a naturally occurring bacterium called Wolbachia – found in roughly half of all insect species, but not in Aedes aegypti – could block dengue from replicating inside the mosquito. If the virus cannot replicate, the mosquito cannot pass it to a person.

The method is self-sustaining. When an infected female mates, she passes Wolbachia to all her offspring. Once enough of the local mosquito population carries the bacterium, it maintains itself generation after generation. Public-health and regulatory agencies say there is no data suggesting Wolbachia mosquitoes harm people, animals or the environment.

How effective is Wolbachia against dengue?

The strongest evidence comes from a randomised controlled trial in Yogyakarta, Indonesia, which showed a 77 percent reduction in dengue incidence and an 86 percent reduction in hospitalisations in areas where the method was deployed. Long-term surveillance in Yogyakarta has since recorded the lowest three-year average of dengue cases in more than 30 years.

Outside of clinical trials, the results are being confirmed in country after country. In Niterói, Brazil, the first city to achieve full coverage, dengue cases dropped by roughly 90 percent. In Colombia’s Aburrá Valley, cities including Medellín recorded their lowest incidence in 20 years in 2024, even as the rest of the country faced a national epidemic. Across all sites, the World Mosquito Program’s internal modelling estimates that they have prevented 1.5 million dengue cases and 93,000 hospitalisations, saving an estimated US$455.7 million in healthcare costs.

The World Mosquito Program has released Wolbachia mosquitoes to protect almost 16.1 million people worldwide

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How is the World Mosquito Program scaling up?

External view of the Wolbito do Brasil biofactory in Curitiba, Brazil

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Turning a laboratory discovery into a national health tool takes more than good science. In Curitiba, Brazil, a joint venture between the World Mosquito Program, the Oswaldo Cruz Foundation (Fiocruz) and the Institute of Molecular Biology of Paraná has built one of the world’s largest mosquito-rearing facilities, designed to produce more than five billion Wolbachia mosquito eggs a year.