A Model of Mosquito-Borne Disease Control
Brazil’s first fully protected city sees over 90% drop in dengue cases following WMP’s Wolbachia releases.
The surge of dengue cases has been unrelenting this year, and nowhere else in the world has felt the brunt of dengue as much as Brazil has in 2024. The country has so far registered a record-breaking 9.9 million cases and more than 5,726 deaths, with the World Health Organisation (WHO) warning that all four dengue serotypes have been detected in the Americas this year in at least six countries, including Brazil.
Following 2023’s record numbers, which saw 3 million cases and 1,188 dengue-related deaths, the Brazilian government had forecast disheartening case numbers at the start of the year. The Ministry of Health estimated the worst-case scenario would be five million cases, a figure surpassed in the first four months alone.
The worrying trend is even more stark when looking back at historical records. After an absence of more than 20 years, dengue re-emerged in the country in 1981. Over the next 30 years, seven million cases were reported. Today, Brazil has the greatest number of dengue cases in the world, and accounts for more than 80% of the total global burden this year alone.
Niterói fights dengue with Wolbachia
However, one city in Brazil is dramatically bucking the trend. Home to roughly half a million people, Niterói, just across the Guanabara Bay from neighbouring Rio de Janeiro, has seen its lowest number of dengue cases in more than 20 years between 2020 and 2023.
Health officials credited the successful impact of WMP’s Wolbachia method, which was first deployed in the city to help battle dengue in 2015. Nine years on, it is the first Brazilian city to be fully protected by Wolbachia. Long-term monitoring in Niterói, showed that at least 97% of Aedes aegypti mosquitoes carried Wolbachia up to eight years after release efforts ended.
“The sustained absence of dengue, chikungunya and Zika outbreaks in Niterói during the past four years has provided an increasingly clear signal of the real-world effectiveness of large-scale Wolbachia deployments," says Dr Katie Anders, WMP’s Director Integrated Evidence.
In the ten years prior to the start of the city-wide roll-out of Wolbachia mosquito releases in Niterói in 2017, more than 46,000 dengue cases resident in Niterói were reported to Brazil’s national disease surveillance system (SINAN). Large dengue outbreaks numbering thousands of cases were an almost annual occurrence in the city, and more than 12,000 cases were reported in 2013 alone. By comparison, in the first four years 2020 - 2023 after Wolbachia was rolled out across Niterói, there were a total of 326 dengue cases reported in the city - lower than any previous period on record.
Record year of dengue
While surging dengue transmission in 2024 has seen case numbers creep up also in Niterói, the 1,754 cases recorded so far this year are dramatically lower than historical outbreaks.
"This year has provided the litmus test,” adds Anders. “To see dengue incidence remain low in Niterói while dengue is inflicting a public health emergency on so much of Brazil and the region really highlights the extraordinary impact that Wolbachia is having in preventing illness and deaths and protecting health systems.”
Anders notes that while cases have increased this year, the caseload is still 90 per cent lower than before the deployment of WMP’s Wolbachia method.
Ana Eppinghaus remembers when WMP first approached the city with its novel method in 2015. “The first contact we had with the project was a little surprising," says the Health Surveillance Coordinator at the Municipal Health Foundation of Niterói. “It’s not often you come across a proposal to release mosquitoes when our entire history of disease prevention was to fight against the mosquitoes. But… we accepted the challenge.”
The project first began in Jurujuba before expanding to another 33 neighbourhoods in 2017. The final 19 neighbourhoods were completed in May 2023, with scientific results from other areas already showing a drop in dengue cases.
“We were used to seeing dengue epidemics in the city every three to five years, with tens of thousands of cases,” adds Eppinghaus. “And today, we see the impact of Wolbachia all over the city, with at most a hundred or so cases. The impact was clear, cases were decreasing.”
Since Wolbachia has been rolled out across the city, Anders says 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 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 this year. This compares to the national rate of 3,121 and 1,816 in Rio de Janeiro state during the same period.
Anders points out that historically Niterói has ranked among the highest dengue incidence cities in Brazil, so this protective effect of Wolbachia in the city translates into thousands of dengue cases prevented that would otherwise have occurred during this year's unprecedented dengue surge in Brazil.
Replicating Niterói’s success
At the end of last year, the city’s symbolic Museum of Contemporary Art (Mac), hosted an exhibition entitled: Wolbachia pipientis: Niterói em Três Tempos, which told the story of how WMP implemented the Wolbachia method across the city over eight years.
“It gives me much joy and I’m really proud of our city being the first Brazilian municipality to be 100% protected by Wolbachia,” says Juliana Martins, the Education, Sustainability, Sport and Health Coordinator from the City Education Secretariat of Niterói.
“We are really proud to be part of this project and to see how effective it has been — and in such a sustainable way. It’s wonderful to see that science is not meant to stay in a drawer and with WMP, it has benefited those who most need it. It’s fantastic.”
It is hoped the success of Niterói will be replicated across much of the country in the coming years. WMP, alongside Fiocruz and the Ministry of Health, have great ambitions to protect more than 100 million people in Brazil over the next decade.
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Alongside previous releases in other cities including Petrolina, Campo Grande and a randomised controlled trial in Belo Horizonte, with results expected in mid-2025, Joinville, Foz do Iguaçu and Londrina are currently in the midst of Wolbachia releases. Uberlândia, Presidente Prudente and Natal, will also commence deployments early next year.
Ethel Maciel, the Ministry of Health’s Secretary for Health and Environment Surveillance, emphasises the importance of these new initiatives to protect more people from mosquito-borne diseases.
“Expanding the number of cities that use the Wolbachia method and building new factories are of great importance if we are to face future epidemics and better protect the Brazilian population,” she says.
“This technology is proof that science needs to be increasingly fostered and valued.”
The factory, which is owned by IBMP/Fiocruz and WMP, is part of the formal partnership between the two organisations to dramatically expand access across the country. It will produce about five billion mosquito eggs annually at a rate of up to 100 million per week in the initial stages.
“In Brazil, we’re in the process of moving past Wolbachia as an experimental measure to its use as a cornerstone of dengue control,” says Luciano Moreira, WMP’s project leader in Brazil. “We’ve partnered with the Brazilian government to build a Wolbachia mosquito production facility that will enable deployment in multiple cities simultaneously — with the goal of protecting millions of people.”
Anders concludes: “In a record year for dengue outbreaks, Niterói has shown that Wolbachia can provide long-term protection for communities against the increasingly frequent surges in dengue we’re seeing globally.”
