Deir Silva rolls down the back seat window.
He stretches an oblong plastic container out of the moving car and carefully pulls off the lid.
Then he shakes the can.
Mosquitoes buzz from the container into the sky of Niterói, the twin city of Rio de Janeiro.
“Fly and do your job!” says Silva.
After about 50 meters he holds the next can out the window.
Silva, 57, plump, wearing blue plastic gloves, works for the World Mosquito Program, an organization founded in Australia.
The mosquitoes released are Aedes aegypti, Egyptian tiger mosquitoes.
They could help tackle one of today's biggest health problems.
At first glance this may sound absurd.
Because Aedes aegypti are actually the problem, not the solution.
The dashed mosquito species transmits tropical diseases such as Zika, chikungunya and dengue.
Fever is the fastest spreading viral disease.
Today there are eight times as many infections every year as there were 20 years ago.
The World Health Organization recently sounded the alarm: half of the world's population is at risk of infection.
Even France and the USA reported cases of the tropical disease, which is nicknamed bone crusher fever.
But a few years ago, researchers in Australia made a groundbreaking discovery.
They infected mosquito eggs with a naturally occurring bacteria called Wolbachia.
“To our surprise, we were able to prove that Wolbachia blocks the viruses of dengue and other diseases,” says Luciano Moreira in a video conversation.
It was more difficult for the infected mosquitoes to reproduce in the host.
This means that the likelihood of mosquitoes transmitting viruses to humans decreased.
They quickly found a name for the mosquitoes infected with Wolbachia: Wolbitos.
The Brazilian Moreira was part of the research team at the time.
In 2010 he returned to Brazil.
A year later, the mosquito eggs arrived from Australia.
With support from the Ministry of Health, he and his colleagues at the state research institute Fundação Oswaldo Cruz, or Fiocruz for short, began breeding their own Wolbitos.
There were the first model tests.
Mosquitoes have been released in six municipalities so far, but only one town has used the Wolbachia method throughout the area: Niterói.
The city has just over 500,000 inhabitants and is located opposite Rio de Janeiro on the other side of Guanabara Bay.
In the east of Niterói, a narrow road winds up the hill to the Morro da Atalaia.
At the foot of the favela there is a flat functional building, it is a health center.
Inside, Raissa de Souza Vieira, 25, with braces and pigtails, bustles around.
She grew up in the favela.
This is important for her job because she is a community worker who mediates between the health station and the population.
In 2022, the World Mosquito Program approached the station.
There was a project, they said, about releasing mosquitoes.
Before that happens, however, the consent of the residents is required.
Favelas are worlds of their own, with their own laws.
Just show up and release mosquitoes?
Impossible.
This is where Vieira came into play.
At the beginning, she says, many residents were skeptical.
There are already enough mosquitoes here, she heard.
Vieira replied: These mosquitoes are different, they help fight diseases.
Together with her colleagues, she went from house to house, distributed flyers and hung up posters.
Not everyone was thrilled.
Because suddenly there were a lot more mosquitoes flying through the alleys of the favela.
“The residents slowly understood the benefits of the initiative,” says Vieira.
Today, success can also be recorded in numbers.
A scientific study shows that in Niterói, dengue cases were reduced by 70 percent and chikungunya cases by 50 percent.
Niterói currently reports four times fewer dengue cases than the neighboring city of Rio de Janeiro.
“It worked,” says Vieira.
"Without the program, we would now have the same problems as other cities." Niterói is considered a flagship project and has aroused interest across the country.
Super mosquitoes will soon be buzzing in seven more cities.
A woman should help that happen.
In a stuffy, dark room, Cátia Cabral walks to a trolley.
Several trays are stacked on top, filled with water.
It's full of black dots.
“It all starts with the egg,” says Cabral, 46, with dyed blonde hair.
She is the head of the biofactory in Rio de Janeiro.
Here they produce ten million mosquito eggs per week.
The factory is located on the grounds of the Fiocruz research institute in the north of the city.
Cabral pulls out another tray and examines it closely.
Thousands of tiny creatures twitch and curl around inside.
"These are larvae, they'll need a while." It's scorching hot in the room.
“The Aedes is a tropical mosquito,” explains Cabral.
Hence these temperatures.
It smells like a pet store.
When the eggs hatch into larvae, they are fed fish food.
After around a week, the larvae pupate.
The dolls move on to a windowless room that Cabral calls a “nursery.”
There are numerous white boxes with mesh walls here, filled with hundreds of thousands of mosquitoes.
In the cage-like containers there are small pots of water with strips of paper on the edge.
The mosquitoes are supposed to lay their eggs there.
There are blood lobes on the head of the boxes because female Aedes Aegypti need blood to form eggs.
“They like human blood best,” says Cabral.
Where does it come from?
Donations from blood banks, leftovers from the hospital.
If necessary, animal blood can also be used.
Cabral started here as a laboratory assistant and is now the head of the factory.
She is proud to work here.
“We are doing something good for society.” She emphasizes: The goal is not to eliminate mosquitoes from the environment.
Mosquito populations that carry viruses should be replaced by those that are no longer able to do so or to a lesser extent thanks to Wolbachia.
They call it a “mosquito replacement strategy.”
Brazil has big plans.
A new biofactory, the largest in the world, will open next year.
100 million eggs per week, that is the goal.
70 million Brazilians are expected to be protected using the Wolbachia method in the next ten years.
However, there is also criticism; some researchers believe that sooner or later the virus will find a way to overcome the Wolbachia effect.
Moreira doesn't want to rule that out.
However, many studies have shown the resistance of the bacterium.
And the method is very sustainable.
"In some areas we released mosquitoes nine years ago and 90 percent of the population are still Wolbitos."
Logistically, releasing the mosquitoes is a challenge, and there were problems in Rio de Janeiro in particular.
In many favelas, dealers armed to the teeth stand on the street corners, and there are regular skirmishes with the police.
For weeks, program employees were unable to enter the neighborhoods.
People in densely populated areas become infected particularly often: Aedes aegypti is not born with the virus.
When mosquitoes suck the blood of a sick person, the virus multiplies in their bodies and is transmitted to the next person with a bite.
The disease can quickly get out of control.
Before 1970, dengue was reported in only seven countries.
For most scientists, the reason for the rapid spread is also related to climate change: mosquitoes like it hot and humid.
This is why they feel particularly comfortable in countries like Brazil.
This year the country is experiencing record temperatures due to El Niño, a natural climate phenomenon.
More than 1.3 million dengue cases have been reported since the beginning of the year - four times as many as in the same period in 2023. Many states have declared states of emergency.
Soldiers were deployed to detect the mosquito's breeding grounds.
Brazil also started a vaccination campaign, initially giving priority to children and young people.
The Qdenga vaccine, developed by the Japanese drug manufacturer Takeda, is injected.
Brazil has a long tradition of vaccination and a well-functioning public health system.
But it will hardly be possible to slow down the current outbreak.
That's why people like Vieira are needed.
She trudges up a steep street in her favela.
Motorcycles rattle by, older men sit in front of tiled bars.
Typical favela scenes.
6,000 people live here – and Vieira seems to know almost everyone personally.
“Oi, meu amor,” she greets a woman as she passes by, “Hello, my love.”
She stops in front of a knee-deep puddle, takes out her cell phone and takes a photo: “A perfect nest.” Mosquitoes prefer to lay their eggs in stagnant water.
She will report the position to the city administration.
Vieira stops in front of a heavy metal gate: “Hello, is anyone home?” A tanned man opens the door.
Bertoldo Pereira Monteiro, 72, wears casual clothing and flip-flops.
Yes, he says, dengue worries him.
He lifts a plant pot.
"I poured sand into all the coasters so that water doesn't collect there," he explains.
“Exemplary,” says Vieira.
Many of the residents of her favela take the disease seriously, which is why she believes they will defeat dengue.
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