In the northeastern Australian city of Townsville, about 7000 families recently became nannies—for mosquitoes. Each hosted a tub of Aedes aegypti eggs in their yard, stocked with fish food to nourish their little charges as they grew and took flight. The insects were part of a project by the nonprofit World Mosquito Program, with regional hubs at Monash University in Melbourne, Australia, and Ho Chi Minh City, Vietnam, to fight annual outbreaks of dengue fever, familiar to the residents of this tropical region. The released mosquitoes—about 4 million in all—were infected with a bacterium called Wolbachia, which reduces their ability to transmit dengue, Zika, and chikungunya viruses, and which can spread quickly through the population as these mosquitoes mate with wild ones.
The sprawling effort—covering 66 square kilometers—wasn’t designed to test how well the mosquitoes prevent the spread of dengue. Instead, the project, described in a paper published today on the Gates Open Research platform, was a study of how to deploy disease-fighting mosquitoes on a city-wide scale, with the blessing of local residents. Over a muffled phone connection from Ho Chi Minh City, World Mosquito Program Director Scott O'Neill, a medical entomologist at Monash University, told Science about building support for a mosquito release in his own backyard. This interview has been edited for clarity and length.
Q: What was unique about this mosquito release effort?
A: Firstly, the size of it: Most other releases have been done on the scale of 1 or 2 square kilometers. And here, for most of the land area covered, the releases were undertaken by the community itself, not by us. Often there are questions about, “Is the community accepting?” In this study, we are able to show that not only is the community accepting … the community actually deployed the mosquitoes on its own behalf.
Q: You gave mosquito-rearing kits to individual households, but you also distributed them in school programs that sent them home with about 1000 kids. How did that work?
A: We gave them a container, like you might buy takeout Chinese food [in], with some fish food and some mosquito eggs in a little Ziploc bag, and they’d mix it with water and leave it in their backyard. It’s a bit like a “sea monkeys” kit. The schoolchildren would then be able to look at the natural history of the mosquito, and the life cycle, and then watch them progress.
Q: Do people ever have a problem with hosting mosquitoes in their backyard?
A: If the community is feeling like there’s too many mosquitoes around, then we would usually pull back or stop. But there was no organized opposition to the project in Townsville. If you’re living in a place where there’s regular, annual transmission of a disease like dengue, and there’s nothing actually working to prevent it, then people can be quite fearful of it.
Q: Is it different trying to sell suburban Australians on this concept than people in poor countries?
A: We’re currently operating in 12 countries, and undertaking releases at the moment in six. When we talk to the communities—whether it’s Townsville or a subsistence fishing village in central Vietnam—we find there’s very little difference from the perspective of what people are concerned about. The top two concerns are nearly always “Is it safe for me and my children if the mosquitoes bite us?” and “Could there be some environmental impact that’s not really understood by releasing the mosquito?”
Q: It ended up costing about $13 per person to establish Wolbachia in Townsville, and the microbe remains in the population now that you’ve stopped releasing mosquitoes. Is that what you expect this strategy to cost elsewhere?
A: It’s a pretty good price, but we think that price could be much lower. For example, if you were just to put more people into the city of Townsville, into the area we covered, that would drive the per-person cost down. Other cities we’re working in, in Brazil or Indonesia, because the population density is so much higher … that already brings our cost down to below $3 per person. And we’re hoping that over the next 18 months or so to be able to drop that price down to below $1 a person.
Q: Why do you think your effort faced less opposition than proposed mosquito releases that involve genetically modified (GM) mosquitoes?
A: I think that we probably put much more emphasis on community engagement than any of the other teams I’ve seen working with other technologies. I think it also helps us that we are not GM, so it’s easier for people to see this as a more natural intervention. There’s also, I think, a distrust of for-profit operations.
Q: Did the mosquitoes prevent the spread of dengue in Townsville?
A: Townsville had experienced local transmission outbreaks every year for 10 years preceding us doing an intervention, and in Townsville now, Wolbachia is maintaining itself quite nicely and we’ve seen no dengue transmission occurring since we started [in 2014]. This study was not set up as an experimental, epidemiological trial. We’re actually doing that in Indonesia at the moment—a randomized, controlled trial, which will read out in about 18 months. But this is showing extremely encouraging evidence as we lead up to that piece of work.