The city of Rio de Janeiro has taken extensive measures to address the recent outbreak of dengue fever, including increasing testing capabilities, setting up multiple health centers specifically for dengue, and providing training for medical personnel to meet the increasing demands of the population.

However, in Niteroi, the sister city of Rio located on the other side of Guanabara Bay, the situation is quite different. Despite a population of approximately 500,000, Niteroi has only reported 403 suspected cases of dengue thus far this year. In fact, its rate of incidence per capita is one of the lowest in the state, with only 69 confirmed cases per 100,000 people.

The rate of incidence in the city of Rio is 700 for every 100,000 people, resulting in over 42,000 cases.

The transmission of the dengue virus among humans is caused by infected mosquitoes. However, a particular type of bacteria known as Wolbachia can disrupt the spread of the disease.

Public health authorities report that a trial initiative initiated in Niteroi in the year 2015, where researchers intentionally reproduce mosquitoes that harbor the Wolbachia bacteria, has proven beneficial in the city’s fight against dengue.

The nonprofit organization, World Mosquito Program, has pioneered the use of the Wolbachia strategy in the past decade. Beginning with a trial in Australia in 2011, the group has conducted experiments in over a dozen countries, including Brazil. This approach offers a promising alternative as the World Health Organization reports a tenfold increase in reported cases of dengue worldwide in recent years.

The mayor of Niteroi, Axel Grael, requested assistance following a dengue outbreak in 2012 where the city received numerous notifications and one fatality occurred. To combat this, a collaboration was established between the city, the state-run Fiocruz Institute, the World Mosquito Program, and the Health Ministry, resulting in a decrease in cases.

“In an interview with The Associated Press in Niteroi on Friday, Grael recounted a moment of great worry in the country and in Rio. Now, with the implementation of the Wolbachia technique, we have seen significant improvements.”

Dengue is a viral infection transmitted to humans through infected mosquitoes. Many who are infected never develop symptoms, but others get a high fever, headaches, body aches, nausea and a rash. While most get better after a week or so, some develop a severe form that requires hospitalization and can be fatal.

The combination of regular rainfalls and hot weather speeds up the hatching of mosquito eggs and the growth of larvae in the notoriously warm city of Rio. This makes the city particularly vulnerable. Every few years, these outbreaks become full-blown epidemics.

Despite the small number of cases, the city of Niteroi, along with its neighboring areas, continues to prioritize prevention efforts. On a daily basis, hundreds of city health employees are dispatched to conduct surveys in communities, streets, rooftops, wooded areas, local establishments, and junkyards, with the goal of promoting effective measures. Their main focus is to eliminate any standing water sources that could potentially serve as breeding grounds for mosquitoes.

Last Friday, Augusto Cesar, who is 63 years old, ascended the Morro da Penha – also called Penha Hill – in a low-income community referred to as a favela in Brazil. As a city representative for over 20 years, he has been visiting the houses of local residents, scaling roofs, collecting waste, and examining all areas of the Penha neighborhood to search for any stagnant water. He mentioned that even a plastic bottle cap, if filled with rainwater, can serve as a breeding spot for larvae.

“The main obstacle is gaining entry,” stated Cesar as he wiped away beads of sweat from his forehead. Favelas, typically constructed without formal blueprints, can be difficult to maneuver, resembling intricate mazes. Despite his determination to reach a large water tank he spotted on a rooftop, Cesar struggled to find a passage through a cramped alley, sandwiched between sturdy walls of concrete and red bricks.

As he continues on his journey, he comes across an additional pair of uncovered water tanks. He scales a wall in order to access them and begins to remove the flimsy metal panels that were concealing them. Utilizing mosquito nets, he installs them and replaces the metal panels. In a dim alleyway, he opens the lids of two water tanks, retrieving a flashlight to thoroughly examine the surface for any indication of mosquito larvae.

Fiocruz researcher Luciano Moreira mentioned that there is another obstacle to overcome – security, as large portions of the city are controlled by drug lords or militias. Moreira is in charge of the Wolbachia initiative in Brazil.

Multiple cities have contacted national and local government officials, Cesar and Moreira revealed, eager to utilize the Wolbachia method in their own areas. The Ministry of Health recently revealed plans to construct a sizable factory for cultivating Wolbachia-carrying mosquitoes, with the goal of producing 100 million eggs per week over the course of 10 years – a tenfold increase from Fiocruz’s current capacity.