This Mosquito Likes Us Too Much For Our Own Good

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 (Matthew Twombly for NPR)
(Matthew Twombly for NPR)

Aedes aegypti is the dog of the mosquito world. It acts as if it's man's best friend.

"It's been with us for a long time, probably for at least 5,000 years when we started keeping water next to our homes [ideal for laying eggs] and it's adapted to people," says Marten Edwards, an entomologist at Muhlenberg College in Allentown, Pa. "It loves us. It loves our cities. It loves our blood. It functions very well with us."

There's just one problem. This mosquito makes us sick.

Aedes aegypti is the primary mosquito responsible for spreading the Zika virus that's sweeping through Latin America and the Caribbean. For a long time it was known as the "Yellow Fever" mosquito because it's the primary vector for the virus that causes yellow fever. Aedes aegypti also spreads dengue and chikungunya.

A promotional press release amid the media frenzy over Zika called Aedes aegypti "a heat-driven missile of disease." While the tiny bug might not be able to blow anything up, it is very efficient at delivering viruses from one person to another.

An Aedes aegypti mosquito lands on human skin in a research lab in Cali, Colombia.
An Aedes aegypti mosquito lands on human skin in a research lab in Cali, Colombia.

"It's not like a mosquito can just suck up a virus and immediately inject into somebody else," says Marten. "The biology of the virus is connected to the biology of the mosquito." The stomach of Aedes aegypti is a fertile place for the Zika virus to reproduce. "This doesn't happen in the vast majority of mosquitoes," he says. "So that's what makes the Aedes aegypti unusual."

The mosquito's feeding habits are another boon for virus spreading. In general, female mosquitoes bite people or other warm-blooded creatures because they need the blood to hatch their eggs. Most mosquitoes get some blood in one bite and get on with reproduction. But Aedes aegypti is what's known as a "sip feeder." It takes lots of little sips of blood from lots of people. So once an Aedes aegypti mosquito is infected with a virus, it's able to spread it multiple times in its two- to four-week life.

That's partly why Zika has spread "explosively," as the World Health Organization head Margaret Chan characterized it, in the Americas.

Globally there are thousands of different types of mosquitoes. Aedes aegypti primarily is found in the tropics. Entomologists say its habitat is expanding but currently its range extends from the southern United States to northern Argentina in the Americas. It prospers across sub-Saharan Africa, in India and in warmer, wetter parts of Southeast Asia. Basically Aedes aegypti hangs out in a wide band around the equator.

And it likes cities.

"This is an urban mosquito," says Audrey Lenhart, an entomologist with the Centers for Disease Control and Prevention in Atlanta. "It tends to breed in close proximity to human habitations." Trash is a favorite breeding site. So are abandoned tires because of the water trapped inside.

Other mosquitoes, by contrast, breed in swamps and feed off deer.

Lenhart is now part of the CDC's emergency response to the Zika outbreak. Her earlier work looked at how Aedes aegypti spreads dengue in Latin America and what can be done to control it.

"It's a tricky mosquito to control. It doesn't bite at night like the mosquitoes that transmit malaria, so bed nets are not necessarily useful. They rest both inside and outside houses so there's not an easy way to target the adult mosquito [with pesticide]."

"It's domesticated," says Rebekah Kading, an entomologist at Colorado State University. She reiterates that Aedes aegypti has developed a lot of habits that make it really good at spreading disease.

"It's feeding on people almost exclusively. It doesn't fly very far so it's just circulating virus in an area." Its flight span is about a quarter of a mile, according to one study.

How do we get rid of this unwanted friend?

The researchers interviewed for this story said that people need to make their homes and neighborhoods less friendly to mosquitoes. For example, dump out any containers with even a little standing water in the bottom — Aedes aegypti's larvae can develop in even a bottle cap full of water. And even without water, the eggs can survive for months, until the rains arrive.

As with any complex, long-term relationship, breaking up with Aedes aegypti may be hard for humans to do.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.

Copyright NPR. View this article on npr.org.

Transcript

DAVID GREENE, HOST:

Throughout Central and South America and the Caribbean, fears are growing about the Zika virus. This mosquito-borne virus is believed to cause birth defects in infants. NPR's Jason Beaubien has the story of the culprit, Aedes aegypti.

JASON BEAUBIEN, BYLINE: Aedes aegypti is dangerous to humans, in part, because it thrives among people.

AUDREY LENHART: This is an urban mosquito. It tends to breed in close proximity to human habitations.

BEAUBIEN: That's Audrey Lenhart, an entomologist with the Centers for Disease Control and Prevention in Atlanta. She's now part of the CDC's emergency response to the Zika outbreak. Her earlier work looked at how Aedes aegypti spreads dengue in Latin America and what can be done to control it.

LENHART: It's a tricky mosquito to control. It doesn't bite at night like the mosquitoes that transmit malaria, so bed nets are not necessarily useful in this scenario. They rest both inside and outside houses. There's not an easy way to target the adult mosquito. That is the important one that transmits the disease.

BEAUBIEN: Some other mosquitoes are content to breed in rural swamps and feed off deer. But Aedes aegypti likes human blood and piles of garbage.

MARTEN EDWARDS: We do a good job, as us humans, at providing them with their larval habitat, and they know that.

BEAUBIEN: Marten Edwards, who studies mosquito and tick-borne diseases at Muhlenberg College in Allentown, Pa., says of the hundreds of different kinds of mosquitoes that exist, Aedes aegypti, in particular, love us.

EDWARDS: They thrive on our blood. They like to live in small containers of water, and we're great at providing that in our trash around the house, in our tires, in our bottle caps and so they have adapted to our ways pretty well.

BEAUBIEN: Aedes aegypti has become one of the dominant mosquitoes in the tropics. Entomologists say that its habitat is expanding, but currently, its range extends from the southern United States to northern Argentina in the Americas. It prospers across sub-Saharan Africa, in India and in warmer, wetter parts of Southeast Asia. Basically, Aedes aegypti hangs out in a wide band around the equator.

In general, female mosquitoes bite people or other warm-blooded creatures because they need the blood to hatch their eggs. And while most are content to get some blood and get on with reproduction, Aedes aegypti is what's known as a sip feeder. It takes lots of little sips of blood from lots of people. Rebekah Kading, an entomologist at Colorado State University says Aedes aegypti has developed a lot of habits that make it really good at spreading disease.

REBEKAH KADING: It's domesticated. It's breeding around human habitations. It's feeding on people almost exclusively. It doesn't fly very far (laughter), so it's just, you know, circulating virus in an area.

BEAUBIEN: And Aedes aegypti spreads more than just Zika. It's also commonly known as the yellow fever mosquito because it's involved in those outbreaks. It also is the primary transmitter of dengue and chikungunya.

All of the researchers interviewed for this story said the best way to get rid of Aedes aegypti is to stop making our homes so hospitable to them. Dump out any containers that have even a little standing water in the bottom. But given that Aedes aegypti larvae can blossom in even a few drops of water, making them unwelcome may not be easy.

Jason Beaubien, NPR News. Transcript provided by NPR, Copyright NPR.