While North Americans don’t have to worry about dengue fever, people in the rest of the world do; it kills about 25,000 people each year, and infects about 390 million a year, and the World Health Organization regards it as one of the top 10 threats to global health. 

That is why a recent experiment in Indonesia is almost miraculous, as if (to use pandemic terms) a whole population had achieved herd immunity when only a few people had been vaccinated. But in this case, it’s the mosquitoes that are ‘vaccinated’ using a microbe that spreads quickly and prevents them from being infected by dengue viruses.

Science journalist Ed Yong wrote a wonderfully clear article about it in Atlantic Magazine, and I do recommend that you read it. Or you can watch his equally wonderful video about it:

But in case you don’t, here are the highlights.

Dengue fever is spread by mosquito bites, especially the species Aedes aegypti, which also spreads Zika, chikungunya, and yellow fever. (Malaria is spread by a different mosquito species.)

Aedes aegypti quickly develops resistance to insecticides, and removing standing water doesn’t deter them. Something new was needed, and quickly – dengue has increased each year over the past few decades.

That something new was Wolbachia, discovered in 1924 in a different species of mosquito. When scientists began studying it in the 1980s, they realized it made hosts resistant to viruses and had an amazing ability to reproduce itself.

The World Mosquito Project, after decades of work, managed to get Wolbachia to infect Aedes aegypti in 2006. In 2011, it released 300,000 treated mosquitoes in two suburbs of the northern Australian city of Cairns. Within four months, 80 to 90% of the local mosquitoes were full of Wolbachia, and dengue cases fell. It also released treated mosquitoes in several other parts of the world.

But to prove that the drop in dengue was due to Wolbachia, they needed to carry out a randomized controlled trial. And for that, they headed for the world’s dengue ‘capital’ – Yogyakarta, Indonesia.

It wasn’t just a matter of injecting mosquitoes and turning those loose. Because they rely on peoples’ participation, they had to earn peoples’ trust, and that took time and effort. They set up community meetings and WhatsApp hotlines and let people visit the laboratory to see the technology for themselves.

When they started the trial in 2017, they divided much of the city into 24 zones. Almost 10,000 volunteers  distributed egg-filled containers to local backyards in 12 zones. Within a year, about 95%  of the Aedes mosquitoes in the 12 release zones harbored Wolbachia.

For the next 27 months, consenting patients presenting with fever were enrolled at a network of primary care clinics across the study area, and were tested for dengue. “In June 2021, the New England Journal of Medicine published the peer reviewed results of the trial which show that Wolbachia deployments reduced dengue incidence by 77% and dengue hospitalisations by 86%.”

The trial’s results were so encouraging that the researchers have released Wolbachia-carrying mosquitoes over all of central Yogyakarta—a 32-square-kilometer zone that’s home to more than 400,000 people. They’re now expanding into surrounding provinces, aiming to protect four million people by the end of 2022 and prevent more than 10,000 dengue infections every year, Yong says. And the team is optimistic enough to think about eliminating dengue from the city altogether.

The World Mosquito Project is now working in 11 countries and territories. Seven million people now live under Wolbachia’s ‘net’, protected against Aedes aegypti’s viruses. The organization aims to cover at least 75 million by 2025, and at least half a billion by 2030. 

This is such a good news story, and Yong tells it so well….so please help spread it 🙂

Updates:

Massive mosquito factory in Brazil aims to halt dengue. Nature, Apr. 14, 2023