Bacteria-based mosquito program shields Brazilian city from record dengue outbreak

Dengue has been a public health problem in the tropical world for decades and 2024 saw a global dengue surge, with more than 14 million cases and 10 thousand deaths reported worldwide – more than more double the figures for dengue epidemics previously recorded in 2023 and 2019.

In the middle of the world's worst global dengue epidemic – the city of Niterói, Brazil, was effectively protected against the deadly disease by an innovative program that introduced a bacteria called Wolbachia into the local mosquito population, reducing their ability to transmit dengue and lowering the rate of dengue by almost 90 per cent.

According to the authors, the study findings "suggest that Wolbachia prevented at least three-quarters of the dengue case burden that may have otherwise occurred in Niterói in 2024, corresponding to thousands of cases averted."

The study, led by the World Mosquito Program and researchers at Monash University in Melbourne, Australia, and published in the journal Tropical Medicine and Infectious Diseases, involved the release of Aedes aegypti mosquitoes infected with the wMel-strain Wolbachia bacteria throughout Niterói, a city of half a million people in Rio de Janeiro state, Brazil. Within five years of the introduction, the majority of Aedes aegypti mosquitoes in Niterói carried Wolbachia, lowering the incidence of dengue by 89 per cent.

Associate Professor Katherine Anders from Monash University and Professor Luciano Moreira, from the World Mosquito Program and now CEO of Wolbito do Brasil, led the study evaluating the long-term public health impact of the Wolbachia deployments in Niterói.

Of particular significance was the finding that dengue incidence Niterói in 2024 – which was a period of record high incidence of the disease in Brazil – was 374 per 100,000 population, substantially lower than overall in Rio de Janeiro state (1884 per 100,000) and nationwide in Brazil (3157 per 100,000).

According to Associate Professor Anders, the study adds to the accumulating evidence that successful introduction of Wolbachia into mosquito populations is a sustainable intervention that provides ongoing protection to communities. This sets it apart from traditional ways of controlling the mosquitoes that transmit dengue – such as the use of insecticide, which has led to resistance and is challenging to deliver in complex urban environments.

In July, Brazil has unveiled the world's largest biofactory, Wolbito do Brasil, located in Curibita, dedicated to breeding mosquitoes infected with Wolbachia bacteria, described by Professor Moreira as "an innovative method poised to safeguard an estimated 140 million people from dengue fever across the nation in the coming years."