A Biotech Offensive Against Disease-Carrying Mosquitoes

16:54 minutes

Mosquitos flying towards a man mowing a lawn. The man is surrounded by a protective bubble.
Illustration by KL Murphy for Science Friday

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This article is part of The State of Science, a series featuring science stories from public radio stations across the United States. This story, by Cary Barbor, was originally published by WGCU

The Lee County Mosquito Control District released thousands of mosquitoes in Fort Myers to bring down the population.

As we head into the rainy season, you will certainly notice an increase in the number of pesky mosquitoes in your life. What is the Lee County Mosquito Control District doing to bring down their numbers? Believe it or not, last month they released more mosquitoes – 30,000 more, as a matter of fact.

That’s because they are releasing male mosquitos that have been sterilized. As you may know, male mosquitoes don’t bite, females do: They need the blood to fertilize their eggs.

Rachel Morreale runs the lab at the Lee County Mosquito Control District.

“We are able to separate the females from the males in the lab, and then we irradiate the males to sterilize them,” she said. “And then we take those sterilized males to the field and release them.”

The males then go on to mate with female mosquitos. But they will not actually reproduce.

“And then the females will lay eggs that do not hatch,” Morreale continues. “That’s how we have the population declines.”

The program targets the aedes aegypti mosquito, an invasive species that is the vector for such dangerous viruses as dengue fever, Zika, and chikungunya.

The agency used this method successfully a few years ago on Captiva. Last month, they implemented it again in the Edison Park neighborhood of Fort Myers.

The researchers are also looking to measure how far the sterilized males travel, so the insects are covered in a fluorescent powder, then trapped and counted.

The sterile insect technique has been used since the 1950s. The agency hopes to use it throughout Lee County as the rainy season continues here in Southwest Florida.

Read this story on WGCU’s website. 

On This Segment:

Mosquitoes are the primary spreaders of some highly dangerous diseases for people: The insect spreads diseases like yellow fever, dengue fever, malaria, and zika, which kill millions of people globally each year. There’s one species of mosquito that’s invasive to the United States, and whose populations are spreading: Aedes aegypti, which is recognizable by black and white markings on its legs. 

Lee County, Florida is taking aim at this species with biotechnology. Their strategy is to release 30,000 sterilized male mosquitoes into the environment, who will go on to mate with females, who then will release eggs that do not hatch. Male mosquitoes don’t bite, only females do. The goal of this method is to decrease the Aedes aegypti population with every generation.

Biotechnology to combat this mosquito species is nothing new. Ira speaks with reporter Cary Barbor at WGCU in Fort Myers about this strategy in her city. He also speaks with Dr. Omar Akbari, professor of cell and developmental biology at UC San Diego, about his research on using CRISPR to alter Aedes aegypti into harmless insects. 

Segment Transcript

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As the song says, June is busting out all over, but it’s not just the flowers. We’re talking the dreaded mosquito. You’ve got your common ways to fight back, right– repellents, sprays, long-sleeved clothing. But in Southwest Florida, Lee County is using biotechnology to target a specific species of mosquito that can spread yellow fever and other deadly diseases. Their strategy involves releasing even more mosquitoes.

Wow. What’s the story here? Let’s talk about this method with Cary Barbor, reporter for WGCU Public Radio, based in Fort Myers, Florida. Welcome to Science Friday.

CARY BARBOR: Thanks for having me.

IRA FLATOW: More mosquitoes. Tell us about it. How is more better?

CARY BARBOR: I know. It sounds funny. But the Lee County Mosquito Control District actually released 30,000 extra mosquitoes in April of this year. They are male mosquitoes that have been sterilized. So when they mate with the females, the eggs that are laid will not hatch. So that eventually, in a couple of generations, that will bring down the population of the mosquitoes in that area.

IRA FLATOW: And what kind of mosquitoes are we talking about here? Why are they the targets?

CARY BARBOR: They’re called aedes aegypti mosquitoes, which they’re a vector for dangerous diseases, like you said– Zika, dengue fever, chikungunya– they can carry yellow fever. They’re an invasive species. And they’re particularly hard to control for a couple of reasons– they bite in the daytime. Their habitats can be hard to target. And they seem to be becoming resistant to common insecticides.

IRA FLATOW: That is a problem. And I know you went to the lab in Lee County, where they’re working on this sterilization project. Tell me what you saw there.

CARY BARBOR: Well, the lab is run by Rachel Morreale. And she and her colleagues are breeding aedes aegypti in that lab. It’s the only species they work with in that lab. And they are breeding them by the hundreds of thousands, if you want to put that in your nightmare file.

They separate the females from the males in the lab. And they then sterilize the males with radiation– just a regular X-ray like you would get at the doctor’s office. They do it at the pupa stage, which is between larva and adult. And then they dust the males with fluorescent powder so that, after they release them, they can identify which ones came from the lab, and they can see how long they lived and how far they traveled, et cetera.

IRA FLATOW: That is really cool.

CARY BARBOR: It’s really cool. This is Rachel Morreale describing how they dust them with the fluorescent powder.

RACHEL MORREALE: We’re using infant nasal aspirators. These are loaded up with DayGlo ECO, which is a formaldehyde-free pigment, by just gently squeezing. We get this very fine powder mist, and we’re able to very lightly, but effectively, dust the mosquitoes. And that actually will stay with them for the rest of their lives. They can’t really get rid of that marking.

IRA FLATOW: Really interesting. But this isn’t a new technology, right?

CARY BARBOR: It’s not new. It’s been in use since 1951, actually on Sanibel Island, which is also near here. They used it to eliminate the screw-worm fly. It’s been used throughout the years for various insects. Lee County started using it in June 2020.

IRA FLATOW: And how will we know what it’s working or if it’s working? What’s next?

CARY BARBOR: Well, I just talked to them over in the lab, and they said they don’t have any data yet. But what they can do is eventually they will trap the mosquitoes and see how far they traveled, see how long they lived, et cetera. And that will tell them how the population is changing and whether it’s working.

IRA FLATOW: Well, we’ll have you check back with us when we know, Cary, OK?

CARY BARBOR: Sounds great.

IRA FLATOW: Cary Barbor, reporter for WGCU Public Radio, based in Fort Myers, Florida.

Florida isn’t alone in using biotechnology to combat the dangerous aedes aegypti mosquito. Similar strategies have been used in California, South America, and Northeast Africa. There’s another branch of biotechnology, though, that might be weaponized using CRISPR to target the DNA of these disease vectors.

Dr. Omar Akbari is professor of cell and developmental biology at the University of California-San Diego, based in San Diego, California. Welcome to Science Friday.

OMAR AKBARI: Thank you so much. It’s really great to be here.

IRA FLATOW: Oh, it’s our pleasure. OK, so explain to us how you use CRISPR to alter mosquitoes.

OMAR AKBARI: Yeah. So we’re using CRISPR and a number of different technologies that we’re developing. We’re primarily developing genetic biocontrol technologies. And these are essentially technologies where we can use the insect to combat itself. And so in the aedes aegypti, which is the major dengue, chikungunya, yellow fever, Zika vector that’s an invasive species, we have been basically expressing CRISPR machinery in the genome of the mosquito such that we can use this to produce sterilized male mosquitoes at scale.

And we’re looking to use this technology to basically mass produce sterilized male mosquitoes as eggs– embryos– and use different types of release technologies to spray these into the environment such that these male mosquitoes can hatch out of these eggs, they can go find the female mosquitoes, they can mate with them. And the consequence of that is those females won’t produce any viable progeny. And over time, if you do continually release these sterilized males, the population will dwindle and eventually crash. And so you can actually eliminate the mosquitoes in a very species-specific and safe way.

IRA FLATOW: We just heard, in Florida, how they’re releasing sterilized mosquitoes using a little different technique. How is your technique different?

OMAR AKBARI: Yeah. There was a trial this year in Lee County, where they released 30,000 sterilized male mosquitoes. And the technology that they used to sterilize the mosquitoes was an old technology. It’s called X-ray radiation. And what that essentially does is you irradiate the adult male mosquitoes and it breaks apart their DNA such that they become sterilized.

And the problem with that is that reduces their fitness, which is their ability to survive and reproduce or mate in the environment. And so you have to release a lot more of those types of irradiated males. And they also have to release the adults with their approach. So it’s very difficult to scale, but it still will work. It’s still shown to be effective, but it’s more difficult to scale.

IRA FLATOW: Yeah, you’re saying yours is a more efficient method, if I might describe it that way.

OMAR AKBARI: Basically, our technology is more efficient, more scalable. And when you’re trying to suppress populations of billions of mosquitoes, you really want something that is efficient and scalable so you can have a wider impact.

IRA FLATOW: Now, as we say, Florida has tried their method. Your strategy has not been deployed in the wild yet, right? When might we see this happening?

OMAR AKBARI: Yeah. So we’re actively working to transition the technologies we’re developing in our laboratory to field trials. We have launched a company just last year, which we called Sinvect, which we’re working on still fundraising for that company to enable a field trial so we can determine the effectiveness of this approach. And we’re hoping that we can get those underway maybe sometime next year.

And in addition to that, we are transitioning our technology to other mosquito vectors, like anopheles gambiae, which is a major malaria vector in Africa. So we can actually hopefully make an impact there, too.

IRA FLATOW: Yes. And tell me why you’re so passionate about targeting this mosquito.

OMAR AKBARI: Well, this mosquito, aedes aegypti, it’s invasive. And it basically was first found in California in 2011. So it’s a very, very recent invasion in California. I find it in my backyard. It bites my kids. It bites me. It spreads a lot of diseases. It spreads dengue, chikungunya, yellow fever, Zika virus. It puts our entire country at risk. And I think it’s very hard to control. The current technologies for trying to control it using insecticides aren’t working. These mosquitoes are resistant to the insecticide.

So we really need new technologies. And something that is safe for the environment is also needed. And that’s why I’m really passionate about using genetic biocontrol technologies, where you actually use the mosquito to control itself. I think it’s the most powerful way to control these vectors.

IRA FLATOW: Do these mosquitoes look any different than the other mosquitoes?

OMAR AKBARI: They do. They have these black stripes along their legs. So they look kind of like Darth Vader. Yeah, you can identify them just by looking for the stripes.

IRA FLATOW: Wow. Are there ecological risks to getting rid of aedes aegypti mosquitoes altogether? I mean, might there be some unintended consequences?

OMAR AKBARI: Yeah. I think in the United States, or in California, removing a species that just invaded shouldn’t have any long-term ecological consequences. And I think when you talk about removing mosquitoes, there’s a bit of misconception there. Because there’s about 3,500 species of mosquitoes worldwide.


OMAR AKBARI: And there’s only about a handful of them that transmit diseases or pathogens to us. So we’re really only talking about removing maybe 10 to 15 different vectors. And if we did that, we would get rid of 99% of the pathogens they transmit. So we’re not talking about removing all mosquitoes, but just specific ones that are harmful to us. And I think, if you do it that way, then I don’t really believe that there’s going to be any major ecological consequences.

IRA FLATOW: And this mosquito carries a lot of diseases.

OMAR AKBARI: It does. It carries a lot of viruses, aedes aegypti. And so, if you were to remove it, then you could actually stop the transmission of multiple different viruses. And I think that there could be a major impact there.

IRA FLATOW: Very interesting. Do you think it’s possible that our next pandemic comes from a mosquito-borne illness?

OMAR AKBARI: It’s possible. The last epidemic, which was Zika virus, was mosquito-borne– actually was transmitted by aedes aegypti. And that was a major problem back in 2015. I remember when I first opened the doors of my lab at UC-Riverside, on the news, there were pictures of babies that were born with microcephaly, which was caused by Zika virus. And so that was a major problem.

And COVID, fortunately, was not transmissible by mosquito. But what if it was? So in a way, we dodged a pretty big bullet there. It was airborne transmissible, but not mosquito-borne. So the next one could be mosquito-borne, and we need to invest in better tools and technologies to protect us.

IRA FLATOW: So what would make a mosquito-borne pandemic particularly scary? What about the mosquitoes?

OMAR AKBARI: Well, I feel that the Zika virus epidemic was pretty scary. When you have pregnant women worried about traveling or worried about being bitten by a mosquito because their unborn could potentially be born with microcephaly, I thought that was extremely scary actually. And so you could imagine something like that, that may be even more broad-scale, that would be pretty scary.

IRA FLATOW: And because these bugs go everywhere and they bite during the day, this kind of mosquito, easier to spread, right?

OMAR AKBARI: They do bite during the day. They hide inside your closets, in your bathrooms. They come out at night. They’ll feed on you while you’re sleeping. Their egg– this is one interesting fact about aedes aegypti– is that their eggs actually can desiccate. Meaning that they can lay their eggs on a leaf by the water. And then, when it dries out, the egg will survive in this dipod state. And it can survive like that for up to five years.

And so what it will do is it’ll just sit there. And the next time, rain, comes the water will touch the egg, the egg will hatch, out will come your larvae, then it will become your adult. So you have this species that can just sit there in completely dried out areas, and then, when rain comes, it can hatch out. And so this is another reason why it’s very hard to control.

IRA FLATOW: Now you have scared me, describing how perfect– this is like a perfect disease-spreading animal, right?

OMAR AKBARI: It is. And I will add to that. One of the things that we have taken into consideration in our technologies we’re developing is this fact that we can store those eggs. So we’re developing technologies that we can deploy as eggs, which will enable us to build factories where we can produce eggs and then store them. And then we can deploy them and out will come your sterilized males. So we really take advantage of the biology of the insect as well.

IRA FLATOW: This is Science Friday, from WNYC Studios.

Could the mosquito– let’s say you get this to work– could the mosquito evolve to be resistant to your technique?

OMAR AKBARI: We’ve thought of that, too. And so we have technologies where that could be problematic, where a mosquito could evolve or its genome could evolve. And it will evolve. But the technology I’m talking about here, where we produce sterilized males, we’re essentially producing a dead-end product. We have a factory where we produce these eggs. The eggs get deployed. Out come your sterilized males. Sterilized males will find wild females. They’ll mate with them. And they won’t produce any progeny because the male is sterile.

So there really isn’t a mechanism or opportunity for evolution to take place because you’ve created a dead-end product. That’s basically a pesticide.

IRA FLATOW: That is good to hear. And I imagine the rest of the world is waiting to see how you do.

OMAR AKBARI: I think so. I think there’s a lot of people that are looking at the technologies we’re developing. They’re very excited about it. And they’re waiting for us to figure out how to transition it. Which is not an easy task, actually. While most of our work in the lab is small scale. But when you actually want to take something and scale it and transition it to the real world, that’s a pretty big task actually. And so we’re trying to achieve that.

IRA FLATOW: Yeah. Well, what do we do in the meantime? This is mosquito season. What actions can we individually do to try to fight this mosquito in the meantime?

OMAR AKBARI: I think the best approach is to just wear– when you’re out and about– wear long-sleeved clothing or pants to protect your exposed areas. And if you do happen to wear shorts, there are repellents. And the repellents do work. So use the Deet-based repellents, and that will protect you. Make sure you have screens in all your windows so they don’t get inside your house. Keep your doors closed.

These are things that actually do work. You prevent contact at all means with the mosquito. And if you do that, then you’re not going to get diseases.

IRA FLATOW: Well, that’s great news to hear you folks are working on this. I want to thank you for taking time to be with us and telling us about it.

OMAR AKBARI: Thank you so much.

IRA FLATOW: Dr. Omar Akbari, professor of cell and developmental biology, University of California, in San Diego.

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