As Brazil grapples with a severe dengue fever outbreak, the country is turning to an innovative strategy that involves releasing mosquitoes infected with bacteria to combat the spread of the viral disease. In the coming months, this approach, known as the Wolbachia method, will be rolled out to six additional Brazilian cities, expanding its reach to an additional 1.7 million people.
The current dengue outbreak in Brazil has been fueled by factors such as hotter and wetter weather due to the climate crisis, as well as the circulation of previously absent subtypes of the virus. Since January, the country has already recorded 1.6 million probable cases of dengue – the same number reported for the entire year of 2022 – and 491 confirmed deaths, with an additional 889 deaths under investigation as of March 14th.
Local and national health authorities have ramped up their response, including deploying community health agents to scour cities for potential mosquito breeding grounds in stagnant water. However, as Ethel Maciel, the secretary for health surveillance at the health ministry, notes, “Our strategies are old and heavily focused on vector control.” With “a significant change in the pattern of dengue,” marked by earlier and larger spikes in infections, the government is embracing newer technologies with medium-term results, such as vaccines and the Wolbachia method.
The Wolbachia method takes its name from a type of bacteria found in about 60% of insects but not naturally present in the Aedes aegypti mosquito, which is the primary vector for transmitting dengue, chikungunya, and Zika viruses to humans. By releasing Aedes aegypti mosquitoes infected with Wolbachia bacteria, the method aims to reduce the transmission of these viruses to humans.
The technique has already been introduced in five Brazilian cities, providing protection to 3.2 million people. The expansion to six new municipalities will be supported by a laboratory in Rio de Janeiro, run by the public health institute Fiocruz, which manages the Wolbachia method in partnership with the NGO World Mosquito Program (WMP) and with support from the health ministry.
The Rio lab, which houses approximately 1.5 million adult mosquitoes and produces 10 million eggs each week, has grown significantly from its humble beginnings a decade ago. “We started off in a tiny room, with just three small cages. And now we have these big rearing cages which can hold 32,000 mosquitoes,” says Cátia Cabral, the lab’s supervisor and a biologist who has worked with the WMP since its Brazil-based projects began.
Niterói, a city across the Guanabara Bay from Rio, was one of the initial pilot project sites in 2015 and later became the first city with full Wolbachia coverage. Despite the severe dengue outbreak in the state of Rio, which declared an official emergency last month, Niterói has recorded just 689 probable cases as of March 14th, compared to 61,779 in neighboring Rio de Janeiro.
“There is no doubt that the application of the Wolbachia strategy has been decisive for our results,” says Axel Grael, the mayor of Niterói. A 2021 study associated the deployment of Wolbachia-infected mosquitoes in the city with a 69% decrease in dengue, as well as a 56% and 37% decrease in the incidence of chikungunya and Zika, respectively.
The low cost, self-sustaining nature, and proven efficacy of the Wolbachia method have appealed to city authorities across Brazil. According to Luciano Moreira, a Fiocruz researcher who leads the WMP in Brazil, “We have a list of more than 50 municipalities that have got in touch requesting [‘wolbitos’].”
However, the current bottleneck is the production of mosquitoes. A new mosquito-breeding lab, set to be operational by 2025, will increase the current production capacity tenfold, to 100 million eggs per week. “Our projections show that within 10 years, we will be able to protect around 70 million Brazilians across various cities,” says Moreira.
As Brazil confronts this severe dengue outbreak, the Wolbachia method offers a promising solution to limit the transmission of the viral disease and other Aedes-borne illnesses. By harnessing the power of bacteria-infected mosquitoes, the country aims to gain control over a public health crisis exacerbated by climate change and introduce a sustainable, long-term strategy to protect its citizens.
