Controlling Mosquitoes With Bacteria Biologists identified bacteria that shorten the lifespan of disease-carrying mosquitoes. Shorter lives mean less time for the mosquitoes to incubate and transmit diseases like dengue and malaria. Biologist Andrew Read of The Pennsylvania State University explains the findings.
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Controlling Mosquitoes With Bacteria

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Controlling Mosquitoes With Bacteria

Controlling Mosquitoes With Bacteria

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IRA FLATOW, host:

Moving on, changing gears. Talking about mosquitoes. You know, the illnesses carried by mosquitoes infect and kill more than 1 million people worldwide each year and scientists, of course, are always looking for new ways to kill the deadly insects. And they have come up with a new one now. Biologists reporting in the journal Science this week say that they have identified a bacterium that infects disease-carrying mosquitoes. And this bacterium shortens the mosquito's lifespan. And a shorter life could mean less transmission of mosquito-borne illnesses, like dengue and malaria. And here to explain the findings and how they might be applied is Andrew Read. Dr. Read is professor of biology and entomology at the Center for Infectious Disease Dynamics at Penn State University. He is a co-author of a commentary in Science explaining the study. Welcome to Science Friday.

Dr. ANDREW READ (Professor, Biology and Entomology, Center for Infectious Disease Dynamics, Pennsylvania State University): Hello, Ira and Happy New Year.

FLATOW: Happy New Year to you. Why would shortening a mosquito lifespan mean less disease? Does it just mean that he is around fewer years or months or weeks or days to spread things?

Dr. READ: That's mostly it. So, diseases like malaria and dengue, they take some time to develop in the mosquito. So, even after the mosquito has picked up those diseases, they aren't transmitted from the mosquitoes for about two weeks. And so, that means that a mosquito with malaria or dengue is not dangerous until it's at least two weeks old. So, the idea is that if you could kill the older ones, then you'd be taking out the ones which have the infection. So, by taking those guys out, that should help control the disease.

FLATOW: So, only the older ones can transmit the disease?

Dr. READ: That's right. So, it has to be - well, for malaria, it's around two weeks. For dengue, it's two weeks or maybe a bit less than that. It's very environmentally sensitive. But most mosquitoes don't live very long in the field anyway. So, those guys that are two weeks old, those are old mosquitoes. And it's one of the great ironies of diseases like malaria that most mosquitoes don't live long enough to transmit the disease.

FLATOW: They don't?

Dr. READ: No. So, most mosquitoes have a very hard life in the field. They have a hard time from predators - spiders, birds, that sort of thing - as well as very difficult environmental conditions and the risk of taking a blood feed on people, where they get slapped and so forth. So, most mosquitoes actually die pretty fast. They may die - 10 or 20 percent of them are dead every day. And so, you don't get too many mosquitoes that live two weeks or more, enough to transmit diseases like dengue or malaria.

FLATOW: So, if you can get those older ones, you've really cut off a large reservoir?

Dr. READ: That's right. So, the idea is that instead of targeting the mosquitoes themselves, what we can do is target the dangerous mosquitoes, and those are the ones that are two weeks or so old.

FLATOW: Has anybody ever tried this idea out?

Dr. READ: So, there's been no attempt at doing this in the field yet, but there are various techniques being developed in an attempt to take out, disproportionately, the older mosquitoes. But these are so far working in the laboratory.

FLATOW: Mm hmm. And how do you go about infecting a large number of mosquitoes out there in the wild?

Dr. READ: Well, so, what Scott O'Neill's group in Queensland has done is to adapt a bacterial line which will kill old mosquitoes. And they've managed to adapt it to the mosquito which transmits dengue. The way they have envisaged doing this is that one would infect very large numbers of females with the bacteria in the laboratory and then release those females. They would mate with wild-type females and spread the bacteria through the mosquito population.

FLATOW: Mm hmm. And so, how would you disseminate it to begin with?

Dr. READ: Well, that is a bit - that is a technical challenge. No question of that. It would take very good mosquito-rearing facilities. And remember, mosquitoes are only breeding when they are fed blood, so they need a large amount of blood going into an insectary to develop millions of mosquitoes for release. But technically, that is possible and people have achieved numbers certainly in the hundreds of thousands. So, it's feasible to do this.

FLATOW: Mm hmm. And how does the bacteria spread through the population once you release the infected mosquitoes? Is it by mating or…?

Dr. READ: Yeah, that's the really neat thing about this bacteria. So, it isn't like a regular disease like we get, like flu or something. This disease is transmitted from mother to offspring and only from mother to offspring. So, the tricky thing then is how do you get a disease, which is only transmitted to a mother's offspring, to spread through a population? And what this bacteria has done which is really neat is to evolve a trick whereby if infected males mate with uninfected females, those uninfected females don't produce any progeny. So, the infected females always reproduce infected offspring, whereas the infected males stop uninfected females from reproducing at all. And so, that tips the balance in favor of the bacteria. So, the bacteria can spread through the population because of its very bad effects on the uninfected females.

FLATOW: How soon before you can try this out?

Dr. READ: Well, this is going to be an interesting issue, I think. The - there are two sides to this. One is the science, which is the sort of things where we can do more experiments in the laboratory. And I know Scott O'Neill's group in Queensland is doing some of these to try and work out some of the technical problems. And then the other side of it is the regulatory issues. When will it be possible to release mosquitoes infected with the bacteria in the field? And that's going to be much trickier. It would be possible in principle to try this experimentally on contained populations in the wild like, for example, on islands. And there's a lot of talk of that at the moment.

FLATOW: Right.

Dr. READ: Whether it's possible to get these sort of large-scale releases through regulatory agencies, that's going to be an interesting problem.

FLATOW: Hang on there, Dr. Read. Stay with us. We have to take a short break. We'll come back and talk lots more about mosquitoes and controlling them, take your questions. Stay with us. We'll be right back.

(Soundbite of Talk of the Nation theme)

FLATOW: I'm Ira Flatow. This is Science Friday from NPR News.

(Soundbite of music)

FLATOW: I'm Ira Flatow. You're listening to Science Friday from NPR News. We're talking about bacteria that infect mosquitoes and kill the older ones, so that they possibly may not spread any dengue or malaria to people. And with me to talk about that is my guest, who has written a paper in the journal Science this week. He's Dr. Andrew Read. He's professor of biology and entomology at Center for Infectious Disease Dynamics at the Pennsylvania State University. He's actually the co-author of a commentary in Science that explains the study, not the author. Dr. Read, we have some questions. Would you like to take them from our audience? How about that?

Dr. READ: Sure, no problem.

FLATOW: Let's go to the phone to Paul in Fort Wayne, Indiana. Hi, Paul.

PAUL (Caller): Hello.

FLATOW: Hi there.

PAUL: Hi. I have a question and I'll take my answer off the air. I just wanted to know if the effects on the birds or the fish that eat the mosquitoes that have been given the bacterium are known.

FLATOW: Yeah. How do you know what's going to happen to the people - (Laughing) the people - the birds or insects or whatever that eat the...

Dr. READ: As far as I know, that hasn't been directly tested. But I don't think there's any reason for concern there because these bacteria are extremely specific to insects and in fact, have been rather hard to get into these mosquitoes. So, it's very unlikely that they could cause any problems in birds or fish or anything else. It's been quite tricky just to get them into insects.

FLATOW: Do we know how they actually kill the mosquitoes?

Dr. READ: Actually, we don't have a very good understanding of that yet, and there's quite a lot of work going on trying to find out how they do this. Not all species of the - not all strains of this bacteria do kill mosquitoes. This one is rather unusual in doing so. And a lot of work's going into that because if we knew what that mechanism was, we could possibly enhance it, optimize the level of killing.

FLATOW: And the bacterium is called what?

Dr. READ: Wolbachia.

FLATOW: Wolbachia.

Dr. READ: And this particular strain goes by a particularly unexciting name of W-male pop. It used to be called popcorn.

(Soundbite of laughter)

Dr. READ: Which was much sexier.

FLATOW: (Laughing) For obvious reasons. Let's go to Nathan in Dryden, Michigan. Hi, Nathan.

NATHAN (Caller): Hey, Ira. How you doing?

FLATOW: Hi, there.

NATHAN: Thank you.

FLATOW: You're welcome.

NATHAN: I have two questions. One is - is there a possibility this bacterium could species-hop and cause problems for other organisms? And my second question is, if we do - if this does work, will this decimate mosquito populations and cause ecosystem collapses? And I'll take my questions off the air. Thank you.

FLATOW: OK. Yeah, are there unintended consequences?

Dr. READ: OK. Well, on the first issue of the species-hop, it is possible, in principle, that these things could jump into other mosquito species or other insects. They came originally from fruit flies and it is possible, in principle, that they could do that. And historically, I mean in evolutionary time, these Wolbachia have jumped around different insect lineages. They are, nonetheless, very tricky to get into mosquitoes and these jumps to do happen rarely, so it seems to me that's less of an issue.

Now, the question of whether or not they would decimate mosquito populations and lead to ecosystem collapses is a really interesting one. In fact, because they only kill the old mosquitoes, there's going to be a very large number of mosquitoes still around. And so, unlike other ways of controlling mosquitoes, like with insecticides for example, where total decimation happens, killing only the old ones actually will have probably very little impact on mosquito populations and, as a result, won't lead, or it shouldn't lead, to any of the sort of theoretical possibilities that your caller's raising there.

FLATOW: Mm hmm. I mentioned before the break about the possibility of a schedule for testing this out. You talked about the scientific hurdles. But even more problematic, I guess, would be any of the political or cultural hurdles.

Dr. READ: That's right. I think that's true for a very large number of different control measures that people are trying to throw at dengue and malaria now, that using anything which is going to be, you know, rather radical changes to current practice is going to be a difficult issue to get past regulatory authorities. And I think some of the science that can be done can be done to look at reassuring or looking to get the evidence for or against particular risks factors, like the possibility of species jump and so forth. But at the end of the day, it's going to have to be done on some sort of semi-natural population - in cages, large cages outdoors - and then eventually on some restricted islands - populations restricted by - in space, perhaps on islands and so forth.

FLATOW: Michael in Davis, California, hi. Welcome to Science Friday.

MICHAEL (Caller): Hi, Ira. And hi, Andrew. This is Michael Torelli(ph), Andrew.

Dr. READ: Oh, hello, Michael.

MICHAEL: How're you doing?

DR. READ: Good.

FLATOW: Well, that's two out of three of us who know who you are (Laughing).

MICHAEL: Right, sorry. So, this project that Scott O'Neill has made this wonderful progress on is ultimately based on work that I did with a former post-doc, Ari Hoffman(ph), here in California, showing that Wolbachia would spread rapidly through natural populations. We found it first in Southern California and we watched it spread to Canada within 10 years. So, I'm a theoretician working on the O'Neill project and have been doing experimental work on this for 20 years.

FLATOW: And you noticed it killing mosquitoes all this time?

MICHAEL: We studied in drosiphila simulans, a sister species to drosophila melanogaster, the fly that comes to your rotten bananas in your kitchen.

FLATOW: Mm hmm. And it seems to be pretty potent?

MICHAEL: We saw it spread within populations. So, within two years, it would completely take over a population.

FLATOW: Mm hmm. I was talking about - with Dr. Read about the possibility of when this might be tried in public. What are your thoughts on that?

MICHAEL: Well, I know - well, I'm working with Scott, so the cages have just been completed in Cairns, these very large field cages. And those field releases are - the releases into those cages are happening this month.

FLATOW: And where?

MICHAEL: James Cook University, just north of Cairns in Australia, in Queensland.

FLATOW: And why was that site chosen?

MICHAEL: It was chosen because the Australian government is also supporting the project as long - as well the Gates foundation, because dengue is becoming increasingly a problem in Queensland.

FLATOW: Mm hmm.

MICHAEL: So, I was just there a month ago, and the day I arrived to work on the design of the experiment in the cage, a dengue outbreak was declared in Cairns.

FLATOW: Mm hmm. So, they're ready to go ahead with this.

MICHAEL: We are definitely ready to go ahead with this.

FLATOW: And how soon would we - how soon...

MICHAEL: In a cage - in a completely controlled cage situation.

FLATOW: I see. And how soon would we know if this is successful or not?

MICHAEL: We'll know - we're meeting again in May to analyze our first round of cage data. And the critical issues are, as Andrew beautifully described in his Science commentary, we have to know whether the laboratory - how the laboratory effect of lifespan shortening translates to the field conditions.

FLATOW: Well, I wish you both good luck. Thank you, Michael Torelli, for calling.

MICHAEL: Sure.

FLATOW: And happy holiday. Also, Andrew, I guess you'll be watching this carefully - what's going on there in Australia.

Dr. READ: Yeah, indeed. I mean, I think the interesting thing is going to be the step after the cages. Because in that situation, you want to know well, if things are going to spread and if they're killing the old mosquitoes, at one point are they going to have a good impact on the disease? I mean, the question is not can you kill old mosquitoes? It's can you kill enough of the dengue-carrying mosquitoes to have an impact on population health - human population health? And that's going to be tricky to demonstrate, because you need a very widespread release in order to make that happen, so that there's enough people around with dengue to see an impact. That is going to be a big challenge. The next step is - the one after the cages is going to be the real hard one.

FLATOW: Always is, isn't it?

Dr. READ: It is always is. No question of that.

FLATOW: Well, thank you, Dr. Read, for taking time to be with us and have a good holiday.

Dr. READ: Sure. You, too.

FLATOW: Andrew Read is professor of biology and entomology at the Center for Infectious Disease Dynamics at Penn State University.

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