April 16, 2024

A dengue-fighting strategy involving the release of bacteria-infected mosquitoes will be rolled out to six Brazilian cities in the coming months as the country grapples with a serious outbreak of dengue fever, a viral disease transmitted by the Aedes aegypti mosquito.

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

Local and national health authorities have stepped up their response, particularly boosting prevention measures, which include community health agents criss-crossing cities on the lookout for containers of stagnant water that could allow mosquitoes to breed.

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

The Wolbachia method – named after a type of bacteria found in around 60% of insects, but not naturally present in Aedes aegypti – has already been introduced in five Brazilian cities, which 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.

A staff member at the World Mosquito Program releases Wolbachia mosquitoes in Niterói. The car contains 900 tubes that it will release every 50 meters. Photo: Adrienne Surprenant/Collectif/Welkom

Eggs and larvae of Wolbachia-infected mosquitoes – nicknamed by Brazilianswolbitos” – will be provided by a Rio de Janeiro laboratory in a public health institute managed by the health scientific organization Fiocruz, which manages the Wolbachia method in Brazil in partnership 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 huge rearing cages that can hold 32,000 mosquitoes,” lab supervisor Cátia Cabral said during a recent tour of the 397 sq m (4,273 sq ft) facility that houses about 1.5 million adult mosquitoes and produce 10 m eggs every week. There are plans to build a larger mosquito-counting laboratory in another state.

Cabral, a biologist who has worked with the WMP since the start of his Brazil-based projects 10 years ago, leads a team of 17 people responsible for keeping the colony of wolbitos alive in a continuous cycle of reproduction. They also monitor the implementation of the Wolbachia method in targeted areas through diagnosis Aedes aegypti collect eggs in the field.

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

Only 689 Probable cases were recorded in Niterói as of March 14, compared to 61,779 in neighboring Rio de Janeiro, where the Wolbachia method has been tried on a smaller scale and in areas that present specific challenges, such as favelas ravaged by violence.

Aedes aegypti mosquitoes, which transmit dengue and Zika virus, in a jar at the International Atomic Energy Agency Insect Pest Control Laboratory in Seibersdorf, Austria. Photo: Christian Bruna/EPA

“Rio is a city with 12 times the population [nearly] 100 times more dengue cases than Niterói,” said Axel Grael, the mayor of Niterói. “There is no doubt that the application of the Wolbachia strategy was decisive for our results.”

New research is expected to be published later this year, but a 2021 study associated 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 Zikarespectively – two other Aedes-transmitted diseases.

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

“We have a list of more than 50 municipalities that have contacted and requested [‘wolbitos’],” he said, adding: “Our biggest bottleneck right now is the production of mosquitoes.”

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

“Our projections show that within 10 years we will be able to protect around 70 million Brazilians across several cities,” Moreira said.

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