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Can mutant mosquitoes be used to fight Zika and dengue fever?

March 3, 2016 at 8:01 PM EDT
As mosquito-borne diseases such as dengue fever and Zika virus continue to ravage Brazil, scientists are racing to fight back. Their latest tactic: genetically engineered mosquitoes that will pass along fatal mutations to their offspring, destroying mosquito populations from within. But some researchers worry our limited knowledge of Zika could throw a wrench into this plan. Miles O’Brien reports.

JUDY WOODRUFF: With the outbreak of the Zika virus growing across the Americas, scientists are working on new ways to try to stop its spread by targeting the insects that carry the virus, mosquitoes.

One idea centers on altering mosquitoes so they will declare war on other mosquitoes.

Science correspondent Miles O’Brien has our report. It’s part of his series of stories that he’s filed from Brazil on Zika.

MILES O’BRIEN: The most deadly animals on Earth may have finally met their match, and the enemy is them. This is the scene every morning in Piracicaba, Brazil, where the mosquito-borne Zika virus is raging, along with a long-running outbreak of dengue fever.

Scientists hit the road, releasing swarms of genetically modified mosquitoes that carry a DNA time bomb. They are killer mosquitoes.

KARLA TEPEDINO, Oxitec: We are in a colony room. This is where we want to have females happy, healthy, and things like that.

MILES O’BRIEN: These mosquitoes are created by a British company called Oxitec. Karla Tepedino runs the supply line.

KARLA TEPEDINO: This is the biggest mosquito factory in the whole world. We are producing two million male mosquitoes per week.

MILES O’BRIEN: You could say it’s in-gene-ious. Oxitec technicians insert a synthetic gene into mosquito eggs that causes them to create too many proteins. It’s a fatal disease.

While they are still in the lab, they’re given an antidote that keeps the disease at bay. Once they are released, they find a female and breed. But their offspring inherit the gene that causes the fatal disease. With no antidotes in the wild, they die not long after they are hatched, before they can breed.

KARLA TEPEDINO: The beauty this technique is that it can reach the mosquitoes where no other technique can find it. We are using mosquitoes to fight themselves.

MILES O’BRIEN: It appears to be working. And here’s how they know. In addition to the killer gene, they add one that’s a special marker. Only the genetically modified mosquitoes will glow under a special light. This way, they can track the mosquito population. They say 90 percent of the insects in this area now carry the fatal flaw.

KARLA TEPEDINO: As the health secretary of Piracicaba has stated last year they had 133 cases of dengue, this year, only one in the area that we are treating.

MILES O’BRIEN: Mosquitoes killing mosquitoes. It may sound too good to be true, and despite more than a decade of work, it remains unclear if this can have lasting impact on a bigger scale. It’s a high-tech twist in the long, difficult war to stop the spread of diseases carried by the mosquito species called Aedes aegypti.

We have been battling the same enemy for generations.

NARRATOR: Notice the white-tipped palps, the triangular white spots on the abdomen, the white leg bands, and the white flyer shaped design on the thorax. These are characteristic of the adult aegypti mosquito.

MILES O’BRIEN: Aegypti is blamed for spreading Zika virus, as well as dengue, West Nile and yellow fever. Combined, the diseases infect hundreds of millions of people a year, causing a host of maladies and birth defects, killing several million.

But with Zika, there is growing concern here that other species are guilty as well. In this government lab in Recife, Brazil, they are working to develop a test that can tell if a mosquito is carrying Zika virus.

Right now, no one knows for certain how common it is, or in which species.

Marcelo Paiva is a molecular entomologist.

You know, when compare this against dengue or yellow fever, any number of other viruses borne by mosquitoes, we don’t know so much about Zika, do we?

MARCELO PAIVA, Fiocruz/UFPE: We have no idea, actually.

MILES O’BRIEN: Really? Tell me.

MARCELO PAIVA: This is totally new.

MILES O’BRIEN: It’s kind of — well, it’s virgin science.

MARCELO PAIVA: It is, yes. We were in a dark field, now — no light at end of tunnel. Now we’re trying to clarify things.

MILES O’BRIEN: As they try to solve this complex puzzle, his boss, entomologist Constancia Ayres, is trying to prove a theory that would have huge, global implications, that another mosquito species called Culex quinquefasciatus could also be a so-called vector for Zika.

Culex is 20 times more abundant here in Brazil, and is also much more common than Aedis aegypti in North America and Europe.

CONSTANCIA AYRES, Entomologist: In Micronesia, when we had the first outbreak of the Zika in 2007, there is no Aedes aegypti there. So, probably, another vector was transmitting the disease. And Culex also transmitted other arbovirus, such as West Nile virus, Japanese encephalitis, so why not Zika?

MILES O’BRIEN: The two breeds behave very differently. Culex bites at night, while aegypti prefers the day. Culex breeds in dirty water. Aegypti likes her water clean. This would dramatically up the ante for traditional mosquito control techniques.

CONSTANCIA AYRES: So, if both species are involved, you will have to use repellent 24 hours a day, basically.

MILES O’BRIEN: Wow. Yes. So you’re going deet all the time.

CONSTANCIA AYRES: Yes, all the time.

MILES O’BRIEN: That’s not good. That’s an important, a significant thing. It’s a 24-hour fight.

They are infecting Culex mosquitoes with Zika in the lab, then dissecting them to see how they carry and transmit the virus. The jury is still out on what happens in the real world. It could mean there will be demand for another breed of weaponized mosquito.

This not a new battle here in Brazil. As a matter of fact, it’s actually a long war. And they have had some success over the years. In the mid-’50s and the mid-’70s, they very nearly eradicated these mosquitoes using pesticides, many of them DDT.

But even before DDT was banned, though, the mosquitoes developed a resistance to it. So, today, with the population of humans and mosquitoes so much greater than ever, there really is no realistic way to think about eradication.

But scientists all over the world are not ready to surrender. Leslie Vosshall is a professor of neurogenetics at the Rockefeller University in New York.

LESLIE VOSSHALL, The Rockefeller University: So we’re trying to figure out why some people are more attractive than others. The diseases start with a mosquito. The mosquito needs to find someone to bite. The more attractive people are bitten more. We want to understand why that is.

MILES O’BRIEN: She and her team performed what they all the mosquito magnet study. Open the gate, and down the chute they go. Turns out mosquitoes love some of us more than others. So what is the differentiator?

LESLIE VOSSHALL: So, mosquitoes, especially the mosquitoes that are spreading Zika, dengue, chikungunya, they love humans over any other animal. So they’re cuing into our body odor, the carbon dioxide in our breath, our body heat. So, it’s the body odor that I think is what distinguishes us from other non-human animals.

MILES O’BRIEN: Vosshall and her team are creating designer mosquitoes. It’s genetic engineering, but a different version from Oxitec’s self-destructing insects.

Here, they create unique attributes, for example, a bug that can’t detect certain odors, to try and understand what they are hunting.

LESLIE VOSSHALL: Obviously, if we figure out what makes a mosquito magnet attractive, then we have understood a big part of what mosquitoes are hunting. Then we can interrupt their hunting behavior.

MILES O’BRIEN: In the meantime, all we really have are nets and deet. Researchers aren’t even sure how the chemical thwarts mosquitoes.

Can’t science do better?

LESLIE VOSSHALL: Ultimately, how cool would it be to have like a cream that you put on your arm that has a probiotic, right, that makes you demagnetized as a mosquito magnet?

MILES O’BRIEN: But, for now, there is little to stop the global health havoc caused by mosquitoes. Zika and birth defects are just part of the devastation. The most deadly animal on Earth is an easy foe to underestimate and it marches on with impunity.

Miles O’Brien, the “PBS NewsHour,” Recife, Brazil.