Wolbachia Mosquito Releases Dramatically Curb Dengue in Brazilian City Amid National Epidemic Surge

As Brazil faced its deadliest dengue outbreak on record in 2024—with more than 6.6 million cases and 6,200 deaths— Niterói, in Rio de Janeiro state, reported an 89% reduction in dengue incidence following a city-wide deployment of Wolbachia-infected mosquitoes, according to a new study published in Tropical Medicine and Infectious Disease.

Researchers from the World Mosquito Program, Monash University, and Brazilian public health institutions documented the long-term public health effects of releasing Aedes aegypti mosquitoes infected with the wMel strain of Wolbachia, a symbiotic bacterium that inhibits viral replication within the mosquito. Between 2017 and 2023, staggered releases covered the entire urban population of Niterói.

By the end of 2023, wMel prevalence exceeded 95% in the local Aedes aegypti population across all monitored neighborhoods. This entomological success was sustained even in areas where initial post-release monitoring had shown uneven coverage. Notably, no re-releases were necessary to maintain Wolbachia stability.

Epidemiologically, the impact was striking. From 2007 to 2016, Niterói averaged over 4,300 dengue cases annually. In the five years following full Wolbachia deployment (2019–2024), average annual cases plummeted to just 439. Even during the massive 2024 epidemic, Niterói's dengue incidence was 374 per 100,000 people—significantly lower than the state (1,884) and national (3,157) rates.

Interrupted time series analysis estimated an 88.8% reduction in dengue incidence post-intervention. Researchers conservatively projected that between 5,200 and 11,600 cases were averted in Niterói in 2024 alone, amounting to a 74–87% decrease in expected case burden.

The success in Niterói contrasts with less favorable outcomes in nearby Rio de Janeiro, where Wolbachia prevalence collapsed in some neighborhoods just 2.5 years after release. While the same mosquito line and production protocols were used in both cities, Niterói’s more uniform urban environment and consistent release coverage may have contributed to the superior outcome.

This study underscores Wolbachia's potential not as a silver bullet but as a robust, self-sustaining tool within an integrated vector management strategy. While occasional breakthrough dengue cases are expected due to imperfect viral blocking, the significant reduction in transmission—even during peak epidemic conditions—demonstrates meaningful public health value.

Niterói’s experience provides compelling evidence that innovative biological control strategies like Wolbachia can offer lasting protection—even during periods of intense viral pressure—when deployed at scale and monitored rigorously. As arboviral threats grow in frequency and severity across the tropics, this model may offer a blueprint for resilient, scalable dengue prevention.