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PRI's Environmental News Magazine

Engineering a Better Mosquito

Air Date: Week of June 22, 2012

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The Aedes aegypti , the yellow fever mosquito, can also spread dengue fever. (Photo: USDA)

A new strain of mosquito has been engineered to self-destruct within a generation. Key West, Florida is considering unleashing these bugs to keep dengue fever at bay. Michael S. Doyle, Executive Director of the Key West Mosquito Control District tells host Bruce Gellerman that the genetically modified mosquitoes could save money and serious discomfort. Luke Alphey, Scientific Officer at Oxitec, the British company behind the bugs, promises limited risks with genetically engineered mosquitoes.

Transcript

GELLERMAN: Dengue fever is known as break bone fever—that’s because the disease, transmitted by mosquitoes, causes intense joint pain, and suffering. Worldwide it’s estimated as many as 100 million people a year are infected with Dengue…and the rate has increased 30 fold in just 50 years.
There’s no vaccine, and no treatment… we are losing the war against Dengue. But there is a new weapon in the works: it’s a genetically modified mosquito that’s designed to self-destruct within a generation. Officials in Key West are hoping to enlist the new mosquito in their fight against Dengue... but first, they need permission from regulators. Michael Doyle is Executive Director of the Florida Keys Mosquito Control District.

Genetically engineered males will produce larva that die in development. (Photo: Wikimedia/ Brasil Econt)

DOYLE: The last time there was really active transmission in the United States and Florida in particular was the mid 30s. And it was pretty much eradicated through mosquito control and hasn’t been here since. And then in 2009, we started getting confirmed cases of it in Key West proper, which was a surprise in the US for many people.

GELLERMAN: So, the last case of Dengue was a few years back, right?

DOYLE: Yeah, November 2010 was the last official case that we know of. When Dengue arrived, we realized that we had to reduce these mosquito numbers en masse in order to prevent any further transmission and to keep Key West as safe as it is, as it always has been.

Key West, Florida. (Photo: Wikimedia)

And so, we hired about eight full-time people in addition to the two that we had. And those folks have been going door-to-door ever since. Literally- there’s about eight thousand properties in Key West and our inspectors try to get to every one of those once a month to six weeks to dump out containers and treat with low toxicity insecticides.

GELLERMAN: Sounds very expensive.

DOYLE: It is, very. It’s about a million dollars plus. We’re now doing aerial treatments using the same bacterial product- called BTI- and spraying it from a helicopter, over the entirety of Key West, right now once a week. That seems to be effective, but again it’s very expensive.

GELLERMAN: So, now, there’s this company called OxiTech, which is based in England and they have a new technology that uses genes, actually. They treat the male mosquito with a gene and I understand that you’re considering using it.

Spraying for mosquitoes cost Key West $500,000 a year in chemicals alone. (Courtesy of FKMCD)

DOYLE: Yes. Yes. And the solution is based on some really good successes in the agricultural world. There’s been people working on this thing called the sterile insect technique, which essentially means you sterilize males of millions of male insects of whatever species—Mediterranean fruit fly or screwworm or anything else—and you flood the environment with these sterile males. They mate with the wild females and the offspring either don’t happen at all or they die before they become adults and pests.

GELLERMAN: So, you’ve got birth control for male mosquitoes!

DOYLE: That’s exactly right and it’s been amazingly effective.

GELLERMAN: In terms of OxiTech’s technology- this gene technology- how much would that cost you?

DOYLE: The technology that OxiTech is offering, which essentially would be us buying mosquito eggs from them and then we would rear them and release these genetically modified males- we’re told between $200,000 and $255,000 a year. And, if promises are true, then we would have better control for less money.

GELLERMAN: So, who has to approve this new technology- this new gene technology in Florida?

DOYLE: Hence the problem. Mosquitoes are not an agricultural insect; they’re a public health insect. And so the USDA, unfortunately, we got a letter from them saying that it’s not in their jurisdiction. So, we were very disappointed, very, very disappointed that they were not taking this on, and handed us off to either EPA or CDC or FDA. CDC is not a regulatory agency, so they’re not really a possibility- none are required to take it on. It’s not in their jurisdiction, so it’s essentially fallen between the cracks.

GELLERMAN: Well in the absence of a regulator, couldn’t the Florida Keys Mosquito Control District- meaning you and the other people on the board- just decide to… hey- let’s just do this, let’s just use this new technology.

DOYLE: (Laughs.) Well, it’s…technically I guess you could. I mean, if we decided that using high-power squirt guns and squirting the mosquitoes with water would solve our problem, we could go out and do that without a permit and very few people would have a problem with it. But the fact that word genetically modified is connected with the whole process- that conjures up some scenarios in many people’s minds that have serious consequences.

GELLERMAN: Yeah, the imagination doesn’t have to run too far wild- I'm thinking of the movie Mothra, you know…

DOYLE: Or Jurassic Park, which was mentioned in a recent city commission meeting that someone came up and said this could be just like Jurassic Park, you know- mother nature will find a way. What potential impacts could there be on the environment or on human health if one of the mosquitoes bit someone or something of that nature- and those are real questions that need to be answered with real facts, and unfortunately we have no one to look at the facts for us.

GELLERMAN: Well, we’re going to speak to OxiTech’s Chief Scientific Officer, and we’ll put those questions to him.

DOYLE: That would be tremendous.

GELLERMAN: Michael Doyle is the Executive Director of the Mosquito Control District office in Key West, Florida. Well for answers we now turn to Luke Alphey. He’s Chief Scientific Officer with Oxitech- that's the company making the new genetically modified mosquitoes.

ALPHEY: It's very safe. We, of course, have dealt with independent regulatory authorities in a number of different countries, who have been each analyzed our technologies prior to any kind of field use or indeed, in many cases, prior to any laboratory use. And they have concluded that it is as safe as one could reasonably hope for.

GELLERMAN: So, I know that you’ve released these in Brazil and in Cayman, Malaysia, right?

ALPHEY: That’s right.

GELLERMAN: The regulatory agencies there have given their seal of approval there to do field experiments?

ALPHEY: Yes, precisely. Of course each of those trials are with collaborators in those countries- usually with the governments of those countries. In each case, those field experiments were preceded by risk analysis, but also after the fact, they have shown that our mosquitoes did exactly what we anticipated that they would.
In the Cayman Islands, for example, we showed that they would mate wild females- which is what it’s supposed to do- and then when we stopped releasing them it all went away, as expected from the environment. This gene has of course a very strong selective disadvantage- like death or sterility, and it so it disappears from environment very quickly if you stop releasing those mosquitoes.


The Mosquito patrol leaves no stone unturned in their search for stagnant, mosquito-breeding water. (Courtesy of The Florida Keys Mosquito Control District)

GELLERMAN: So, no unexpected accidents? You didn’t have females, for example, pick up this gene and then go out and spread this gene, biting people?

ALPHEY: Right, well nothing picks up a gene. But of course when you’re separating males from females, that is not 100 percent accurate. And so, in practice, we release about one… in the Cayman Islands, experiment… we released about one male for every 3,000 females. So, an extraordinarily low number of females. But both the males and the females are just like regular wild mosquitoes except for having this gene that will kill their offspring.

GELLERMAN: So, in the case of Cayman, you had 3,000 males that were genetically modified to one female… but you release three million mosquitoes… so you had like a thousand genetically modified females. If one of those were to bite me, what would happen?

ALPHEY: You would be bitten by a mosquito. What normally happens when you’re bitten by a mosquito? For many people you wouldn’t notice at all- particularly for this mosquito, which is not a very aggressive biting mosquito. Some people would have a small reaction to mostquito bite and this mosquito is much like any other.


Backyard water features can become breeding grounds for mosquitoes. (Courtesy of FKMCD)

Now, remember, those were released over the period of six months- so the per week, per whatever addition of females is very low. Some of the numbers get a bit intimidating with this kind of approach, when we talk about releasing millions of mosquitoes. But to give you one sort of analogy: We produced the eggs at Oxford for that trial and shipped them out to the Cayman Islands. And we shipped- I don’t remember what it was- 30 million eggs or something like that. And that really sounds like a lot- but it’s probably half a coffee cup of eggs for the entire trial.

GELLERMAN: But the numbers of mosquitoes that you’re releasing- I was reading- at least in Brazil and Malaysia- is a huge number compared to the native population- like ten to one!

ALPHEY: Yeah, we aim to release about ten engineered males for each wild male. So that most of the wild females, most of the time, will see and mate a sterile male instead of a wild male.

GELLERMAN: Now, what happens if you have that rare male mosquito that does get the gene that doesn’t express it the way that you want or hope or want or intend? And, their progeny becomes a superbug and goes on to be immune for later generations to your gene.

ALPHEY: Right. So, what we have put into the mosquito is something that is bad for it. So if our gene was to be less effective or less active, it would just make the mosquito weakened than it otherwise would be. That doesn’t make it stronger than a normal one. So, just to be clear, we don’t put in antibiotic resistant genes or insecticide resistance genes or anything like that that might help a mosquito or anything that comes into contact with it.

GELLERMAN: But, aren’t you putting selective pressure on the population by introducing this gene?


Male (left) and female (centre and right) Aedes aegypti. (Wikimedia)

ALPHEY: Anything you do to the population will put some kind of selective pressure on it. So, if you spray off chemicals, there is some pressure that builds up resistance to those. If you went round and filled all the breeding sites and filled them with concrete, then that would provide some selective pressure for those mosquitoes to use a wider range of breeding sites.
And so, you would get some possibility of resistance through a behavioral change. So, I certainly wouldn't say that there isn’t the possibility of evolving resistance to our approach, or any other approach to controlling the mosquitoes. But, in the 50 year history of sterile insect industry, with billions and billions of irradiated sterile male fruit flies, for example, being released every week- history would suggest that this approach is somewhat less susceptible to resistance than many other approaches.

GELLERMAN: Well, Mr. Alphey, thank you so much.

ALPHEY: Thanks a lot!

GELLERMAN: Luke Alphey is Chief Scientific Officer with Oxitech.

 

Links

The Florida Keys Mosquito Control District

Oxitec uses genetics to eradicate pests

 

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