Common bacterium protects Brazilian city from dengue storm

ByDr. Tim Sandle
December 22, 2024
DIGITAL JOURNAL

Aedes aegypti, a common vector of dengue fever and yellow fever. Image by Muhammad Mahdi Karim. — GNU License, V1.2

With climate change acting as an accelerant fuelling dengue’s surge, new findings presented at the American Society of Tropical Medicine and Hygiene (ASTMH) Annual Meeting provide evidence that releasing mosquitoes (Aedes aegypti) carrying a common bacterium of the family Wolbachia offers a tool to fend off intense outbreaks of the viral disease.

The study was conducted by researchers from the World Mosquito Program and it found that in 2024, as Brazil battled its largest dengue outbreak on record, there was only a small rise in Niterói, a city of half a million people close to Rio de Janeiro.

The study credits the fact that five years ago, a partnership between the World Mosquito Program and Brazil’s Ministry of Health blanketed three-quarters of Niterói with mosquitoes infected with Wolbachia, a naturally occurring bacteria that has been shown to inhibit a mosquito’s ability to transmit dengue and other viruses.

Deployments into the remaining areas were completed in May 2023.

According to lead researcher Katie Anders: “We already saw infections essentially flatline in Niterói after the Wolbachia deployment, and while there was a small increase in 2024, the caseload was still 90 percent lower than before the deployment — and nothing like what was happening in the rest of Brazil.”

Anders adds: “The fact that Wolbachia has sustained itself in the mosquito population for years now and remained effective during a record year for dengue outbreaks shows that Wolbachia can provide long-term protection for communities against the increasingly frequent surges in dengue that we’re seeing globally.”

Anders explains that since Wolbachia has been rolled out across Niterói, dengue incidence has dropped to an average of 84 cases per 100,000 people per year, compared to an average rate of 913 cases per 100,000 people per year in the 10 years pre-Wolbachia.

The 1,736 dengue cases reported in Niterói from January to June 2024 represent a rate of 336 per 100,000 in 2024. This is compared to a rate of 3,121 nationwide and 1,816 in Rio de Janeiro state during the same period. Overall, in 2024, Brazil has recorded 9.6 million dengue cases — more than twice as many as in 2023 — and 5,300 dengue-related deaths.

Other trials spearheaded by the World Mosquito Program, including large-scale releases in urban areas of Colombia and Indonesia, have reported significant reductions in dengue. They also have shown that Wolbachia is safe for humans, animals and the surrounding environment. But Anders said the protective effect documented in Niterói stands out for occurring amid such an intense wave of disease.

Anders noted that the production facility in Brazil is a significant step because one the biggest barriers to using Wolbachia on a large scale is that it requires releasing a large number of infected mosquitoes to spread the bacteria into the local mosquito population.