Scientists hope that the revolutionary trial will see these ‘good’ mosquitoes multiply, breed and help reduce the cases of dengue fever.
The initiative is part of a global program that is also taking place in Australia, Vietnam and Indonesia.
Unbeknown to most, the programme started in 2012, said the study’s lead researcher Luciano Moreira, of the Brazilian research institute Fiocruz.
“Our teams performed weekly visits to the four neighbourhoods in Rio being targeted. Mosquitoes were analysed after collection in special traps,” he said.
“Transparency and proper information for the households is a priority. “
Every month, for four months, 10,000 mosquitoes will be released.
But don’t be alarmed; the intracellular bacteria – called Wolbachia – that the mosquitoes are carrying cannot be transmitted to humans.
The bacterium is found in more than half of all insects and acts like a vaccine for the mosquito, which carries dengue fever and stops the virus from multiplying in its body.
Wolbachia also has an important role in the reproduction for mosquitoes. If a contaminated male fertilises the eggs of a female without the bacteria, the eggs do not turn into larvae.
If both male and female are contaminated, or if just the female is, all of the subsequent future generations of mosquito will carry the bacteria.
As a result, the mosquitoes with Wolbachia quickly become predominant without researchers having to release more of the contaminated insects.
In Australia, where research began in 2008, it only took 10 weeks for the contaminated mosquitoes to take over.
Australian researchers even let the mosquitoes feed on their own arms for five years to be certain that the bacteria could not infect humans and domestic animals.
In Brazil, dengue fever re-emerged in 1981 after being absent for more than 20 years. Since then, seven million new cases were reported.
Brazil leads the world tally in dengue fever cases, with 3.2 million access and 800 deaths reported between 2009-2014.