Brazil to release millions of anti-dengue mosquitoes as the death toll from the outbreak rises

A dengue control strategy that involves releasing mosquitoes infected with bacteria will be rolled out in six Brazilian cities in the coming months as the country faces a serious outbreak of dengue, a viral disease transmitted by the Aedes aegypti mosquito.

Factors such as the warmer and wetter weather caused by the climate crisis and the circulation of previously absent subtypes of the virus are fueling an explosion of dengue in Brazil. 1.6m probable cases since January – the same number reported for all of last year – and 491 deaths, with a further 889 deaths under investigation, as of March 14.

Local and national health authorities have stepped up their response, particularly by ramping up prevention measures, including community health officers crisscrossing cities in search of containers of stagnant water in which mosquitoes can breed.

“Our strategies are old and heavily focused on vector control,” said Ethel Maciel, secretary for health surveillance at the Ministry of Health. But amid “a significant change in the pattern of dengue” – with earlier and larger peaks in infections – the government is turning to newer technologies with medium-term results, such as vaccines and releasing mosquitoes infected with bacteria that limit the transmission of dengue. dengue and other arboviruses for humans.

The Wolbachia method – named after a type of bacteria that occurs in about 60% of insects, but does not occur naturally there Aedes aegypti – has already been introduced five Brazilian citiesand provides protection to 3.2 million people. An 80 million reais (£12.5 million) expansion to six new municipalities will cover a further 1.7 million people.

Eggs and larvae of Wolbachia-infected mosquitoes – which the Brazilians nicknamewool bitos” – will be supplied by a laboratory in Rio de Janeiro in a public health institute run by the health science organization Fiocruz, which manages the Wolbachia method in Brazil in collaboration with the NGO World Mosquito Program (WMP) and with support from the Ministry of Health.

“We started in a small room, with only three small cages. And now we have these large breeding cages that can hold 32,000 mosquitoes,” said Cátia Cabral, supervisor of the laboratory, during a recent tour of the 397-square-meter facility, which houses about 1.5 million adult mosquitoes and produces 10 million eggs every week produces. . There are plans to build a larger mosquito breeding laboratory in another state.

Cabral, a biologist who has worked with the WMP since the start of the Brazil-based projects a decade ago, leads a team of seventeen people responsible for keeping the wolbitos colony alive in a continuous reproductive cycle. They also monitor the implementation of the Wolbachia method in target areas through diagnoses Aedes aegypti eggs collected in the field.

Niterói, a city of half a million inhabitants across Guanabara Bay from Rio de Janeiro, hosted one of the first pilot projects in 2015 and later became the first city with full Wolbachia coverage. This appears to have helped keep dengue numbers low, even as Rio state declared an official state of emergency last month.

Just now 689 by March 14, Niterói had recorded probable cases, compared to 61,779 in neighboring Rio de Janeiro, where the Wolbachia method was being trialled on a smaller scale and in areas that presented specific challenges, such as violence-plagued favelas.

“Rio is a city with twelve times as many inhabitants, but (almost) a hundred times more cases of dengue than Niterói,” says Axel Grael, the mayor of Niterói. “There is no doubt that the application of the Wolbachia strategy has been decisive for our results.”

New research is expected to be published later this year, but a A 2021 study linked the deployment of Wolbachia-infected mosquitoes in Niterói with a 69% decrease in dengue, as well as a 56% and 37% decrease in the incidence of chikungunya and Zika, respectively – two other Aedes-borne diseases.

The low cost, self-sustaining nature and proven effectiveness of the Wolbachia method appeal to city governments, said Luciano Moreira, a Fiocruz researcher who leads the WMP in Brazil.

“We have a list of more than fifty municipalities that have contacted us with requests for (‘wolbitos’),” he said, adding: “Our biggest bottleneck at the moment is mosquito production.”

The new mosquito breeding laboratory, which should be operational in 2025, will increase the current production capacity tenfold, to 100 million eggs per week.

“Our forecasts show that within ten years we can protect approximately 70 million Brazilians in different cities,” Moreira said.