2023-11-02 16:39:37
In three cities in Colombian Aburra Valley are the infections with Dengue fever decreased by 97 percent. This might have something to do with mosquitoes that have been infected with Wolbachia bacteria. This means that the mosquitoes themselves can hardly transmit dangerous viruses. Researchers from the non-profit organization gave these results “World Mosquito Program” (WMP) at the end of October at the annual meeting of the American Society for Tropical Medicine and Hygiene known.
The World Mosquito Program seeks to stop the spread of a number of life-threatening diseases transmitted by vectors such as mosquitoes. It does this by releasing millions of mosquitoes infected with Wolbachia bacteria into places where diseases such as Dengue, Zika and yellow fever happens often.
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How can the Wolbachia bacteria prevent dengue?
The Wolbachia bacteria reduces the ability of the Aedes aegypti mosquito to transmit disease. This insect species is one of the most notorious spreaders of dangerous vector-borne diseases.
After a pilot test in 2015 in the Colombian city of Bello, the researchers expanded their activities to the nearby cities of Medellín and Itagua. Although they have conducted such experiments around the world, these releases were the largest they have conducted within this program to date.
In April 2022, the researchers found that around 80 percent of all mosquitoes in Bello and Itagui were infected with Wolbachia mosquitoes through cross-breeding, and in Medellíin the figure was around 60 percent.
Promising results
In order to find out whether this infiltration actually had an impact on the number of dengue cases in the three cities, the researchers evaluated the results during the experiment, which lasted until July 2022.
Dengue fever usually breaks out in wavesImage: Mortuza Rashed/DW
The researchers found that the introduction of the infected mosquitoes into local mosquito populations was associated with a significant decrease in dengue cases. Compared to the ten years before the experiment began, they recorded a decline of up to 97 percent.
They also conducted a case-control study in Medellín. They found a causal connection between the use of infected mosquitoes and the decline Dengue-Cases. According to the researchers, dengue cases fell by 47 percent in the neighborhoods where the mosquitoes were released.
The positive results “underscore the feasibility and true effectiveness of such deployment in large urban areas. They also demonstrated that the public health benefits are reproducible in different ecological settings.”
A single application is enough
The releases in Colombia are the largest to date. The researchers from the “World Mosquito Program” had already carried out similar experiments around the world. Previous studies have shown that in Yogyakarta, Indonesia, for example, dengue cases fell by 77 percent as a result of this program. In Brazil, the disease burden has (so far) been reduced by 38 percent.
Similar experiments with Wolbachia mosquitoes took place in Indonesia as in BrazilImage: World Mosquito Program
Numerous options are currently being investigated to successfully combat diseases transmitted by vectors such as mosquitoes. According to experts, the method used by the World Mosquito Program is a big plus. “Once you introduce the Wolbachia mosquitoes into the native mosquito populations, they stay there. You don’t have to release more mosquitoes,” biologist Rafael Maciel de Freitas told DW in April 2023. Freitas is for the Brazilian Oswaldo-Cruz-Stiftungand on Bernhard Nocht Institute for Tropical Medicineemployed.
However, according to Freitas, there is concern that the method will not work forever. It is very likely that the dengue pathogen would find a way to adapt to the Wolbachia bacteria and then bypass them. “I wouldn’t say that the Wolbachia method is the solution to dengue, but I think this way we have a better chance of dealing with the disease,” said Freitas.
Mosquito eggs infected with Wolbachia bacteriaImage: Dwi Oblo/REUTERS
Its a lot to do
This all sounds like good news. However, there are some caveats: Firstly, the methods of the “World Mosquito Program” are expensive to implement. On the other hand, it is currently unclear whether the decline in dengue cases observed in Colombia and other places can be attributed solely to Wolbachia-infected mosquitoes. Sometimes a city located in a dengue-prone area may not experience an outbreak for years.
Additionally, there are certain areas where Wolbachia-infected mosquitoes do not appear to be causing a decline in dengue cases, or a much smaller decline than in other regions. Researchers are still not sure why mosquitoes in some areas appear to be resistant to this approach.
The World Mosquito Program wants to expand its activities over the next ten years. Earlier this year, plans were announced to build a factory in Brazil that would infect around 5 billion mosquitoes with Wolbachia every year.
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