[music playing] ED YONG: Mosquitoes are... [mosquito buzzing, smack] Mosquitoes... [mosquito buzzing, smack] Mosquitoes are a scourge.

They annoy us, they suck our blood, and they spread all kinds of horrible diseases.

[mosquito buzzing] Of the thousands of species of mosquitoes one of the worst from our perspective is called Aedes aegypti.

There is something almost beautiful about the way Aedes aegypti feeds and fills up with blood.

But these things also spread the viruses that cause diseases like yellowfever, Zika, and dengue fever.

And dengue infects 400 million people around the world every year.

They're afflicted by severe joint and muscle pains.

Fevers.

Rashes.

Headaches.

Many of them die.

There is a long history oftrying to control mosquitoes by draining wetlands, using bednets, spraying them with insecticides.

All of these measures are imperfect, and some can be hazardous.

Scott O'Neill, a microbiologist at Monash University in Australia, had a new idea for how to protect the world from dengue fever.

SCOTT O'NEILL: When you explainthat you're working on dengue, everybody's got a personal story about, you know, being sick themselves, or a child, or knowing somebody that's sick.

So, you've spent --years and years and years trying to find ways of stoppingAedes aegypti from spreading the viruses behinddiseases like dengue fever.

And your big idea is to inject them with a bacterium from the group Wolbachia.

SCOTT: Yeah, so Wolbachia I've been fascinated with for many years, ever since I learned about Wolbachia.

Hey me too!

In fact, if I had to pick myfavorite group of bacteria, it would probably be Wolbachia.

These things live inside the cells of insects, and something like fortypercent of arthropod species carry Wolbachia, which means it's arguably one of the mostsuccessful groups of microbes on the planet.

But, Wolbachia only passes down the female line.

Males are a dead end to it, and it has many ways of dealing with them.

In some species like thebeautiful blue moon butterfly, it kills male embryos outrightso that the adult population can have a hundred females for every male.

In others, like wood lice or pill bugs it actually transforms males into females.

And this thing is so good at manipulating the sexual lives of its hoststhat it spreads like wildfire.

Which incidentally is why ScottO'Neill is so interested in it.

So how could we harnessthat ability of Wolbachia to spread into insects todo something good for us?

ED: So Scott set out in searchof a way of using Wolbachia to keep Aedes mosquitoes fromspreading dengue viruses.

He started when the firstGeorge Bush was still President, and he tried a dozen tricksincluding genetic engineering, but nothing seemed to work.

But then you had a lucky break.

Yeah, something dropped out of the blue from Seymour Benzer's lab in Caltech.

ED: Now most people haven't heard of Seymour Benzer, but he was a titan of 20th century science.

He was one of the first to lookat the link between genetics and behavior and his animalof choice was the fruit fly.

SCOTT: He found a strain ofWolbachia in the fruit fly... ED: It causes the neurons inthe insects head to explode - [flies buzzing, corn popping] SCOTT: Like a bag of microwave popcorn.

[mosquito buzzing, corn popping] ED: So they named the strain "popcorn".

SCOTT: It was one of those rare light bulb moments.

We could stop disease transmission without needing to genetically engineer Wolbachia, without needing to do any fancy tricks.

ED: If the mosquitoeswere infected with popcorn they would die before getting a chance to spread the viruses into people.

But remember: Wolbachia only transmits from mothers to offspring.

Which means that if you wantto infect Aedes with Wolbachia, you need to inject the bacteria directly into a mosquitos embryo.

You know, a young embryois a very delicate thing.

So a way to think about this is to imagine a balloon full of water that you need to insert a knitting needle into that and then pull the knitting needle out and the balloon can't break.

[Stretching rubber, water balloon popping] That's a difficult thing to do.

Very few people in the world can do it, uh, reliably, and I think we've gotten better over time, but it's a certain skill.

You need dexterity, patience, obsession.

It's like the art of science.

But after all that work the team discovered that their plan had a fatal flaw: popcorn was just too virulent.

It was killing mosquitoes beforethey had a chance to reproduce, so if ever unleashed into thewild it just wouldn't spread.

[mosquito buzzing, corn popping] And that was a crushing blow.

You know I think we were all ready to give up.

But then you finally had a spot of good luck?

Yeah the sequence of eventswere quite incredible for us.

Some of his colleagues madea really surprising discovery about Wolbachia.

They found that the bacteria can actually prevent the growth of virusesin the insects that it infects.

Now they found that in fruitflies-- so the question was, would it also do the same in mosquitoes?

SCOTT: And so we took these mosquitoes that, that had popcorn inthem and we infected them with dengue virus to see what would happen.

And we actually found Wolbachiawould prevent the viruses from growing, and if these viruses can't grow in the mosquitothen it can't be transmitted.

It meant that the teamdidn't need popcorn at all.

Almost any strain ofWolbachia would stop Aedes from spreading dengue virus.

It was that sort of feeling.

You know when you'vebeen working on something that doesn't work and then suddenly you get a big breakthrough.

[swarm of mosquitos buzzing] Finally, after decades of effort it was time to release thosemosquitos and their microbes into the world.

So, Scott.

This plan involves askingpeople to release mosquitoes that you've loaded with a microbe that's really good at spreading rapidly, and those mosquitoes will probably bite them, and no one has ever doneanything like this before.

Was it hard to convince people to do this?

People are frightened of dengue and they're frightened of the impact itmight have on their children, they're frightened that they can't control transmission of it.

Everybody knows people that havebeen terribly sick from dengue.

People are desperate for a solution.

I think that helps facilitate them coming on the journey with us.

[Swarm of mosquitos buzzing along to music] ED: Since 2011 Scott's team have set up trial tests in Australia, Vietnam, Indonesia, Columbia, and Brazil.

Their mosquitos have spreadWolbachia as they predicted, but the big question remains.

Has the number of denguecases actually gone down?

Those experiments are long.

Probably we will get theresults in two or three years.

But, in every location that we've put it out now even though allthese locations are relatively small, we're not seeing any disease transmission occurring in those communities.

Scientists are still figuring out the details of how Wolbachia blocks the transmission of viruses.

But they know that it's not just Dengue.

It's also the virusesbehind Zika, yellow fever, and chikungunya.

And they're trying to use bacteria to control other insect pests-- like the tsetse flies thatspread sleeping sickness, and bedbugs.

I hate bedbugs.

This is just part of a whole new approach to thinking about microbes,and realizing that they not only kill, they can also save.