The sky over El Manchén is as blue as ever. This suburb of Honduras’ capital, Tegucigalpa, is still bustling with people jostling to get to work and cars honking in the heavy traffic. To the naked eye, this densely populated area seems much like it did a year ago. But a Médecins Sans Frontières (MSF) team has been working hard to make a microscopic change that could save lives.

A recent test found that eight out of 10 mosquitoes caught in El Manchén carry Wolbachia, a harmless bacterium that’s found in over 50 per cent of insects. One year ago, almost none of the local mosquitoes were carrying it.

This matters because Wolbachia dramatically reduces the likelihood that mosquitoes will transmit diseases like dengue fever, a potentially deadly disease which affects an estimated 100–400 million people worldwide each year.

The team at the MSF Arbovirus Prevention Project released over 8 million mosquitoes deliberately infected with the bacteria in El Manchén last year. Their hope was that the mosquitoes would thrive, reproducing and passing Wolbachia down through the generations, radically reducing the rate of dengue in the area.

However, a lot could go wrong.

“As we continued to release mosquitos, this meant there were more and more of them in the area, which caused distress to the local communities,” says Edgard Boquín, coordinator of the project. “At the same time, another dengue epidemic broke out in the capital. This made it more difficult to approach people about dengue. But by engaging them directly in the activities, we were able to do everything as planned.” 

“We’ve been working in partnership with local communities, Honduran health authorities, the National Autonomous University of Honduras and the World Mosquito Program. It’s been a real team effort,” says Boquín. “This is the first time that MSF and the World Mosquito Program have worked together on arbovirus prevention like dengue. Our strength in community involvement and their technical expertise complemented each other to make this a reality.”

So, has it worked?

El Manchén previously had among the highest rates of dengue fever in the city. However, in the past year there have been fewer cases than in previous years, and lower rates compared to other areas of the city.

“It’s still too early to claim victory,” Boquín says cautiously. “We tested 294 mosquitoes in September, and we were really pleased that 85.7% were carriers of Wolbachia. However, these are preliminary results. In the first quarter of 2025, definitive tests will be carried out that will tell us to what extent this strategy has served to reduce the impact of dengue in El Manchén”.

Although he’s careful about showing too much excitement too soon, Boquín is hopeful.

“This is undoubtedly promising,” he says. 

“If we continue this path, the Wolbachia method will be a positive tool to reduce dengue in the country,” Boquín says. “For a long time, we have seen how people have suffered from dengue but now we hear positive stories from the community that something is changing after the Wolbachia release; this gives hope to people who have experienced dengue or have seen someone close to them get sick.”