The Lamen

Columbia is beating dengue with bacteria-infected mosquitoes

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Brazilian scientists figured out a way to curb dengue transmission: letting bacteria-infected mosquitoes run free. And their strategy has already shown promising results.

Photo: Bing AI

Published on Nov 1, 2023

Armed with the microscopic bacterium Wolbachia pipientis, modified mosquitoes released in three cities in Columbia have led to a dramatic fall in the incidence of dengue: up to a 97 percent decrease, reported Nature.

Context: Dengue, a viral fever, is transmitted by mosquitoes of the Aedes species. While approximately 80 percent of the infections are asymptomatic, others experience flu-like symptoms: high fever, headache, and excruciating joint and body pain that has earned it the nickname “breakbone fever.”

  • Dengue has periods of high transmission — most prominent during the rainy season. Higher temperatures, a consequence of climate change, have exacerbated the impact of dengue fever.
  • The World Health Organization recently warned that dengue is reaching a pandemic-level threat.

Dengue is unlikely to become a serious problem for the United States, but the condition can be deadly in tropical countries like Brazil and Columbia. This is where the “mosquito factories” come in.

The World Mosquito Program has collaborated with several countries to curb the incidence of dengue with these modified mosquitoes — and their effectiveness has been promising.

What is Wolbachia and how is it helping slow down the spread of dengue?

Wolbachia is a bacteria found in about half of all insects, but not in the Aedes mosquito. The bacteria can have a “virus-blocking” effect — reducing the transmission of human viruses like dengue, Zika, chikungunya, and yellow fever.

  • The bacterium prevents the dengue virus from replicating and being infected into a new host when a mosquito bites.
  • Wolbachia is safe for humans, animals, and the environment since the bacterium cannot survive outside the insect hosts.

Scientists began injecting Wolbachia into the eggs of Aedes mosquitoes in 2011, and the bacterium spread into their offspring naturally — making for a cost-effective approach.

Microinjecting the eggs of Aedes mosquito to control the spread of dengue.

Scientists breed mosquitoes and inject the eggs — using microscopic needles — with the Wolbachia bacterium. The larvae then grow infected.

Photo: World Mosquito Program

Mosquitoes are growing increasingly resistant to insecticides, and initial efforts from the Wolbachia program show that these mosquitoes could be established as part of the local population — requiring no further intervention.

  • Interest in Wolbachia has grown since the 1970s when researchers noticed it could prevent mosquito eggs from hatching and shorten an insect’s life span.
  • A study found Wolbachia-infected mosquitoes to have a protective efficacy of 77 percent against dengue. The incidence of hospitalization was lowered by 86 percent.
  • Mosquito factories producing hundreds of millions of these modified mosquitoes have since been established — backed by the likes of the Bill and Melinda Gates Foundation.

The World Mosquito Program is currently leading this Wolbachia effort in 14 countries: Brazil, Columbia, Mexico, Honduras, El Salvador, Indonesia, Laos, Sri Lanka, Vietnam, Australia, Fiji, Kiribati, New Caledonia, and Vanuatu.

Challenges ahead: The WMP plans to build a factory in Brazil that produces 5 billion bacteria-infected mosquitoes per year. However, they still require strategies that function for different geographical conditions.

  • Wolbachia can be less effective in hotter environments. Aedes aegypti larvae that develop in hotter environments have lower levels of the bacterium, noted Science.
  • New data suggests that intensified heat waves may pose a risk to Wolbachia-carrying mosquitoes, with their population likely to decline by the 2050s.
  • Researchers are currently looking into a more heat-resistant strain of Wolbachia — followed by conducting larger, randomized trials.

What the officials hope is for their multi-million dollar bet on mosquito control to pay off — at least in the short term.