Mosquitoes Engineered To Kill Their Own Kind

Reporting in Nature Biotechnology, researchers write of genetically engineering mosquitoes to pass lethal genes to their offspring, in hopes of crashing populations of one dengue-transmitting species. Science writer Bijal Trivedi talks about recent tests of the bugs, and the concerns of critics.

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IRA FLATOW, host: This is SCIENCE FRIDAY. I'm Ira Flatow. Mosquitoes infect up to 100 million people with Dengue fever every year, according to CDC estimates. There's no vaccine. There is no cure. Other than keeping the person hydrated, there's little the doctors can do.

So to control Dengue fever today, we eliminate standing water where mosquitoes lay their eggs. We use insecticides and for all our efforts, cause - cases of Dengue are still on the rise. But there may be a better solution, which my next guest writes about in Scientific American this month, a way to get at the problem using the mosquitoes themselves, by engineering them to pass on lethal genes to their children, killing off new generations of the bloodsuckers one batch of eggs at a time.

One company has already conducted tests of these mosquitoes in the wild, reducing the number of mosquitoes, they say. How safe is this technique? Might there be some unintended consequences to releasing these genetically engineered bugs? And is this tactic effective enough to warrant the risk?

Bijal Trivedi is a freelance science writer and author of that feature on engineering mosquitoes in the current issue of Scientific American. You can find a link to her article on our website, at sciencefriday.com. Bijal joins us from NPR in Washington. Welcome back to SCIENCE FRIDAY, Bijal.

BIJAL TRIVEDI: Oh hi, Ira, thank you.

FLATOW: Good to have you back, no longer just an intern.

TRIVEDI: Nope.

FLATOW: Tell us about the - this is an interesting study. They genetically modify the mosquitoes.

TRIVEDI: That's right. The paper that actually just came out in Nature by Technology is the first one that the - the company is publishing about open field trials. And with their mosquitoes, the progeny die. So it's basically a death gene that they're passing down, and they - the mosquitoes lay the eggs, and - but, you know, there are no offspring.

They sent me down to Mexico to observe field trials of a - field cage trials of another type of anti-Dengue mosquito, and with those mosquitoes, they are engineered to just kill off the female offspring. So the idea is that you send out genetically modified males, they mate with the wild females, and when the offspring are born, the females don't make it. So it crashes the population very quickly.

FLATOW: So they have two different techniques then?

TRIVEDI: There are two different techniques. They - the British biotech company Oxitec did their trials in the Cayman Islands, and the field trials that I observed, which were all within cages, very large cages in the middle of a farming community on the edge of Tapichulo, which is right near the Guatemalan border, those were in cage trials, and that was sort of the female-specific kill switch.

FLATOW: Does one kind, one technique have an advantage over the other?

TRIVEDI: In terms of the genetic capabilities of the mosquitoes, I don't think they know yet. But in terms of practicality, the females kill switch might better because with Aedes aegypti, which are the mosquitoes, the species that primarily spread Dengue virus, you can literally dry these eggs, the mosquito eggs, and with the ones that were done in the Grand Caymans, you know, you have to pick out the sterile males and only release them.

With the ones with the female kill switch, you can release - you know, you can release these mosquitoes. They'll mate with the wild females. They'll lay their eggs. And the males will survive, and the females will just die in the water. They don't develop their wings, and they can't fly, and they just squat on the water, and they die.

So from a practical, you know, point, you don't have to just release males. You can let everybody out there, and, you know, only the males will survive.

FLATOW: Because it's the females that do the biting.

TRIVEDI: Yeah, they do the biting, they spread disease. They're the ones that you really don't want.

FLATOW: So the other ones, if males survive, we don't care because they're not...

TRIVEDI: Because they don't bother us.

(SOUNDBITE OF LAUGHTER)

FLATOW: I guess when speaking about males, that's a good thing sometimes.

(SOUNDBITE OF LAUGHTER)

TRIVEDI: Those genetically sterile males don't bother us, let's put it that way.

FLATOW: Let's not go there.

(SOUNDBITE OF LAUGHTER)

FLATOW: Let's talk about the trials, the field trials. There are no international laws that prevent them from trying these field trials out there?

TRIVEDI: No, I mean, and this is the really tricky thing here. The trials that were done in the Cayman Islands, on Grand Cayman Island by the British biotech firm Oxitec, they released these mosquitoes. Now, they said they did some community engagement, and I'll tell you what that means. That means they sent out a pamphlet that they were releasing sterile mosquitoes, and they had basically a five-minute spot on the daily nightly news that they were doing these experiments.

And then they started releasing them in this plot at, you know, sort of an isolated end of the island, and no, there is no body that sort of polices these trials. And, you know, when you're dealing with genetically engineered organisms, I mean, this is a very, very touchy issue.

And for the trials in Mexico, you know, they haven't done an open release yet. Everything is still in these gigantic, huge cages with a lot of biosecurity measures on the cages. And you know, Mexico has signed the Cartagena Protocol, which, you know, governs how you move genetically modified organisms around.

And so they're doing everything very by-the-book there, and it was only sort of after the trials were being done and were in progress on Grand Cayman that the scientists really sort of came out and said, hey, we've been doing this, and these are the results, that they took a lot of people, including a lot of people in the field, by surprise.

FLATOW: Well, what could be unintended consequences, the side effects of this?

TRIVEDI: They claim that the technology is very safe. And you know, the fact that, you know, these mosquitoes do not do well after - basically, I mean, they are engineered to die, which is, you know, if there's a problem, that's a good thing. You know, they'll die off pretty quickly.

Some people have said, you know, you could be hurting some organism that depends on mosquitoes for food, and you could be affecting food webs. But the - what the proponents of the technology argue is that, you know, this Aedes aegypti mosquito, you know, it is native only to parts of West Africa, and it sort of hitched a ride on slave ships and on trade vessels about 400 years ago and spread everywhere.

So it's really an invasive species. So what the, you know, what the scientists argue is, you know, nobody's going to miss this mosquito if we drop the levels a bit. I mean, it's very, very hard to eradicate something. So what we're talking about is suppressing the population such that, you know, you don't transmit the disease. It's - I mean, we all know it's really hard to get rid of mosquitoes.

FLATOW: Well, how effective are these engineered mosquitoes at crashing that population?

TRIVEDI: Well, you know, not the recent paper, but, you know, at a meeting a year ago, Oxitec announced - and this hasn't to my knowledge been published yet - that, you know, they had released not just a few mosquitoes but three million mosquitoes in this area of the island over a period of six months, and they had managed to crash the mosquito population by 80 percent.

And this is what they announced at the - it was the American Society for Tropical Medicine and Hygiene, the annual meeting about a year ago. And so that's pretty dramatic. You know, crashing a population by 80 percent. But like I said, you know, they haven't published that release yet, that research yet.

FLATOW: Let me to go to Jackie(ph) in Arlington. Hi, welcome to SCIENCE FRIDAY.

JACKIE: Hi, thanks. You kind of almost touched on what I was going to bring up, which is, you know, if you kill mosquitoes, are you eradicating an ecological niche? I mean, I'm a molecular biologist. I'm not afraid of transgenic organisms, but it does sound like this - and I've read just in the past few weeks about several others that are really targeting mosquitoes for eradication. I'm not sure that that's really smart.

But you did kind of just touch on that you're not going to eradicate all of them, I guess.

What about in areas where that's an indigenous species, though? I mean, maybe that's helpful in areas where it's invasive, but what about the areas that are maybe the worst affected?

FLATOW: Good question, thank you, Jackie.

TRIVEDI: Well, these - the places that they're talking about are places where, you know, insecticides have failed, public health measures have failed, and you had this rising and falling of the population of mosquitoes. So like I said, they're not talking - it's not eradication. It's something that could be done at peak mosquito season to really stem the population at a low level so that you wouldn't get disease transmission.

FLATOW: And when you say peak mosquito season, we're not talking about a mosquito here and there, right? It's really flying all over the...

TRIVEDI: No, we - we are - I mean, when I was down in Tapichula, I visited the community where these trial cages are installed. And they did a very broad - because, you know, GM has such a stigma attached to it that they wanted to go very by-the-book. They wanted to be very open with the community, get feedback from the community in terms of what they thought of having genetically modified organisms near them.

And I sat with a family in their - well, the houses are all open. So you can't prevent mosquitoes from coming in and out. I sat at the kitchen table with a family, and there wasn't a moment when I wasn't swatting myself. And I'm sure I looked ridiculous. But it was low mosquito season, and I was slapping myself probably every 10 seconds. I mean, it was swarming.

FLATOW: And so the family welcomed this.

TRIVEDI: The family welcomed this. I mean, they had - I mean, they couldn't tell you - I mean, you know, you'd be hard-pressed to find somebody who could understand the genetics, you know, very well at the molecular level amongst the general community. But, you know, they understood, you know, the type of technology that was being brought in, and they welcomed it because the insecticides that they use to curb outbreaks, they're horrible.

I mean, they were fogging one part of the town with the insecticide while I was visiting, and they actually refused to take me there because it's associated with breathing difficulties. So they didn't want me anywhere near the area where they were fogging.

And then this family, two of the children had had hemorrhagic Dengue. You know, and with hemorrhagic Dengue, more people get Dengue hemorrhagic fever than all the other hemorrhagic viruses combined. You know, we're talking Ebola and Marburg. More people get this than all of those.

So they'd had experience with the hemorrhagic form...

FLATOW: And they'd rather do this than try that again.

TRIVEDI: Yes.

(SOUNDBITE OF LAUGHTER)

FLATOW: All right, Bijal, thank you very much. We've run out of time. Bijal Trivedi is a writer and author of the feature on mosquitoes in the current issue of Scientific American. After the break, we're dialing the clock back 100 years, back to those first explorations of Antarctica. That would be going on about right now, 100 years ago. We'll talk about it. Stay with us. We'll be right back after this break.

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