No More Mosquitoes?

No More Mosquitoes?

Posted: February 4, 2016

We could quite possibly rid the world of disease-causing mosquitoes in the next few years. But… do we want to?

I’m Anna Rothschild and this is Gross Science.

Ok so, you’ve probably seen on the news that there’s this mosquito-borne virus sweeping through the Americas—particularly in Brazil. It’s called Zika, and in adults it’s usually pretty mild, only causing a rash, red eyes, and some flu-like symptoms. But scientists are starting to see an upsetting relationship between Zika virus and birth defects in babies. If pregnant women get the disease, their babies could be born with something called microcephaly, where their brains and heads are much smaller than normal. And that can lead to various cognitive and physical issues.

We still haven’t totally established a link between Zika and microcephaly, but it’s concerning enough that health officials are warning women in the affected areas not to get pregnant. And those of us living in United States aren’t necessarily home free. The disease is spread by Aedes mosquitoes, which live in many parts of the US, too.

Now, I know this show’s called Gross Science, but let me just be clear that there’s nothing about the Zika outbreak that I find gross. Except maybe that mosquitoes are nasty and they carry a lot of diseases. In fact, it seems like every few years we hear about an emerging mosquito-borne illness. And if you’re like me, you’re asking yourself, “Why can’t we do something to keep mosquitoes from spreading disease?" Or better yet, “Why can’t we get rid of mosquitoes altogether?”

Well, it turns out that maybe we could. You see, there’s this new genetic technology called the CRISPR gene drive that has the potential to do just that—though it raises some ethical issues. With the CRISPR gene drive, we can easily insert genes into organisms, like one that would keep mosquitoes from transmitting a certain disease, or would ensure that all baby mosquitoes are born male, which in time would effectively wipe out the population.

Now, you’re probably saying, we’ve been genetically engineering things for years! What’s the big deal? Well, most of the time, when we insert a gene into a plant or animal, the trait it codes for can get diluted out of the population pretty easily, and this happens for a few reasons. To begin with, when we genetically alter an organism, it often lowers its ability to survive and reproduce, so it tends to have fewer babies. Also, in most species we get one set of chromosomes from our mom and one set from our dad. So, if you mate a modified animal with a wild one, their babies will all have one copy of the modified gene. If all those mate with animals in the wild, half the babies will carry a copy of the gene. By the great-grandchild generation, only a fourth will carry the gene, and so on. You’d have to keep releasing genetically engineered animals to prevent the gene from all but disappearing.

Now, this isn’t a necessarily bad strategy. In fact, to combat Zika, there are plans in Brazil to release genetically modified mosquitoes whose offspring won’t be able to survive. But, the CRISPR gene drive does something different. When you use it to insert a new gene into an organism, you stick in a little extra code for an enzyme that can identify any unmodified copies of the gene, too. So, when a chromosome with the CRISPR gene drive is paired up with one that’s unmodified, the enzyme snips out the unmodified section. Then, the cell repairs the chromosome using the modified gene as a template. Basically, this ensures that every baby of a genetically modified organism will have two copies of the gene, for generations to come.

This is an incredibly powerful tool. It has the ability to rapidly change whole populations of fast-breeding creatures in the wild. And the technology is moving quickly, too. Scientists only got the CRISPR gene drive working in yeast at the end of 2014. But they’ve already created a mosquito that’s unable to transmit malaria. And I spoke with one scientist who said that there’s already a collaboration in the works to target one of the mosquito species that carries Zika, too.

But, no one has released any of these mosquitoes into the wild yet. A tool this powerful bring up a lot of ethical questions. How comfortable are we with changing whole populations of organisms? Or eradicating a species all together? Sure, there are thousands of species of mosquitoes, and the ecological importance of the disease-bearing ones is a little unclear. But, it’s still a big decision. And who gets to make it?

On the other hand, over 3,000 babies in Brazil have brain damage likely due to Zika. And worldwide, about 3.2 billion people are at risk for malaria. There is a strong ethical case to be made for using this technology as quickly as possible, too.

Anyway, this is only an outline on what we know about Zika and CRISPR, but I’m going to include far more info in the description. And, who knows: your community might needs to be dealing with these ethical issues at some point in the future. So, please check out those links and then tell me what you think. I would love to hear your opinions, so please put ‘em in the comments. Alright, see you next week.

Ew.

PRODUCTION CREDITS

Host, Writer, Editor, Animator

Anna Rothschild

Many Thanks to Dr. Kevin Esvelt and Jeffrey Wood

Resume Play

Music Provided by APM

Original Footage

©WGBH Educational Foundation

FOOTAGE AND IMAGES

The Mosquito Killing with Human Blood

Pond5/azuri

Zika virus in blood, illustration

Kateryna Kon/Science Photo Library

Countries and territories with active Zika virus transmission—Map

CDC

File:Zika.Virus.Rash.Arm.2014

Wikimedia Commons/FRED

Baby belly

Wikimedia Commons/David Roseborough from Los Angeles, United States

Baby with Microcephaly

CDC

Distribution of Aedes mosquitoes in the US—Map

CDC

d2623-8 (Aedes aegypti)

Flickr/USDA

Pinky

Pinky and the Brain

File:Anopheles stephensi

Wikimedia Commons/CDC

File: Plasmodium falciparum 02

Wikimedia Commons/Lukas.S

Chikungunya (Chikungunya mosquito)

Flickr/CDC Global

List of mosquito genera

Wikipedia

Malaria Geography—Map

CDC

SFX

Cockroaches

Freesound/StateAardvark­
(used with permission from author)

Squeak Pack/squeak_10

Freesound/Corsica_S

Ding Ding Small Bell

Freesound/Johnsonbrandediting

Poof of Smoke

Freesound/Planman

Scissors

Freesound/Suzzy457

Produced by WGBH for PBS Digital Studios

POSTER IMAGE

Mosquitoes

©WGBH Educational Foundation 2016

Want more info?

The CDC on Zika:
http://www.cdc.gov/zika/

Vox explains Zika virus in 6 charts:
http://bit.ly/1POrNjA

Scientific American on what it would take to establish a causal relationship between Zika and microcephaly:
http://bit.ly/1Q4LPAt

The New York Times on a possible link between Zika and Guillain-Barré:
http://nyti.ms/1POs4Dd

NPR on releasing GM mosquitoes to fight Zika:
http://n.pr/1nxV5WX

NOVA Next piece on the CRISPR gene drive:
http://to.pbs.org/1PK4D7I

MIT Tech Review piece on using CRISPR to create a mosquito that can’t spread malaria:
http://bit.ly/1WVJkWI

Paper explaining the potential applications of gene drives, and also the ethical issues, written by scientists:
http://elifesciences.org/content/3/e03401

Wired on the ethics of CRISPR:
http://bit.ly/23CkEaf

NOVA Next on using CRISPR to edit human embryos:
http://to.pbs.org/1PtVMvl