According to World Mosquito Program (WMP), a worldwide program to combat diseases caused by mosquitoes, it is possible to reduce the transmission of dengue through a technique called the Wolbachia Method. A survey conducted in Indonesia, which used the method of introducing Wolbachia bacteria into mosquitoes Aedes aegypti, proved the effectiveness of the strategy, raising hopes of containing the disease that infected more than 1 million people in Brazil in 2020.

WMP is an international not-for-profit initiative that works to protect the global community from mosquito-borne diseases such as dengue, yellow fever, chikungunya and zika. WMP's first location was in Northern Australia in 2011, and the program currently operates in 11 countries: Australia, Brazil, Colombia, Mexico, Indonesia, Sri Lanka, Vietnam, Kiribati, Fiji, Vanuatu and New Caledonia. 

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Female Aedes aegypti lays, on average, 100 eggs at a time, distributing them to different points. Image: Celso Margraf – Shutterstock

In Brazil, the Wolbachia Method is conducted by Oswaldo Cruz Foundation (Fiocruz), with funding from the Ministry of Health, in partnership with local governments. “Currently, we operate in Rio de Janeiro (RJ), Niterói (RJ), Campo Grande (MS), Belo Horizonte (MG) and Petrolina (PE)”, informs the program's Brazilian website.

An experiment published by the scientific journal The New England Journal of Medicine, carried out for the first time in Yogyakarta, Indonesia, and also carried out in Brazil by Fiocruz, managed to reduce dengue cases by 77%. In addition, a 60% reduction in chikungunya cases was identified in areas that received Aedes aegypti with Wolbachia, when compared to areas that did not. 

"The expectation is that within four years, which is the time of the study, it will be possible to know the impact of the Wolbachia Method in the control of arboviruses in Belo Horizonte", said in a statement the researcher from Fiocruz and leader of the Wolbachia method in Brazil, Luciano Moreira.

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How the Wolbachia method works 

One of the researchers in the Indonesian experiment, Katie Anders, describes the Wolbachia bacteria as a “natural miracle”. This is because the microorganism does not harm the mosquito by taking care of the same parts of the body that the dengue virus needs to be spread by the vector. 

Through this method, the bacteria compete for resources and make it much more difficult for the dengue virus to replicate, which makes it far less likely that the mosquito will cause infection when it bites someone. 

In Yogyakarta, the experiment used 5 million eggs from mosquitoes infected with Wolbachia. The eggs were placed in water containers in the city every two weeks, and the process of building an infected mosquito population took nine months. 

The city, which has about 300 inhabitants, has been divided by scientists into 24 zones, and Wolbachia-infected mosquitoes have been released in half of them. As a result, in addition to the reduction in the number of dengue cases, there was a reduction of 86% in the number of people who needed hospital care.

"This is very encouraging," Anders told BBC News. "To be honest, it's better than we expected." 

The researcher, who is also the WMP's impact assessment director, believes the strategy "may have an even greater impact when deployed on a large scale in the world's big cities, where dengue is a major public health problem." 

According to the research, the Wolbachia bacteria proved to be quite manipulable and also capable of altering the fertility of their hosts to ensure that they pass the micro-organism to the next generation of mosquitoes. 

This means that once established, the bacteria can continue to help control infections for a long time. This strategy contrasts with other attempts to control the disease, such as insecticides or release of infertile male mosquitoes, which need to be redone.

The experiment represents an important milestone after years of research, since Wolbachia is a bacterium present in about 60% of insects, including some mosquitoes, but it does not usually appear naturally in Aedes aegypti. Studies with mathematical models that try to calculate and understand the spread of diseases predict that the bacteria could be enough to completely suppress dengue, if it were to establish itself in the mosquito population.

Fight against Aedes aegypti in Brazil has lasted over a century

Considered by the European Agency for Disease Control and Prevention (ECDC, its acronym in English) one of the most widespread species of mosquito on the planet, Aedes aegypti has been fought in Brazil since the beginning of the last century. Some factors contribute to making it such an efficient agent for transmitting these viruses. One of them is its ability to adapt to the environment, in addition to its proximity to man. 

Arisen in Africa, in wild places, the mosquito arrived in the Americas on ships, still at the time of colonization. Over the years, he found in the urban environment an ideal space for his proliferation. “He specialized in sharing space with man,” says Fabiano Carvalho, entomologist and researcher at Fiocruz Minas. “The mosquito prefers clean water to lay its eggs, and any object or place serves as a breeding ground. Even in an orange peel or a bottle cap, if there is even a minimum of standing water, your eggs will develop.”

Another aspect that also favors mosquito reproduction is the fact that the female lays an average of 100 eggs at a time, but not in a single location, distributing them to different points. 

According to the US Centers for Disease Control and Prevention, Aedes aegypti is "very resistant", which causes "its population to return to its original state quickly after natural or human interventions". 

In Brazil, the dengue mosquito was eradicated twice

At the beginning of the XNUMXth century, Brazilian epidemiologist Oswaldo Cruz led an intense campaign against him in the fight against yellow fever. 

In 1958, the World Health Organization declared the country free from Aedes aegypti. But, as the same did not happen in neighboring countries, the mosquito returned to be noticed here in the late 60s. In 1973, it was eradicated again, returning again three years later.

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