Deconstructing Dengue: How Old Is That Mosquito? Dengue fever, a nasty disease caused by a virus, is just beginning to show up in the U.S. It's carried from person to person by mosquitoes, and one researcher studying the spread is looking for clues in the age of the insects. But it's not very easy to tell how old a mosquito is.

Deconstructing Dengue: How Old Is That Mosquito?

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SCOTT SIMON, HOST:

You know, scientists can spend years working on problems that at first may seem to many people kind of pointless. For example, there's a researcher in Arizona who's trying to find a way to measure the age of - ooh, sorry. mosquitoes.

But as NPR's Joe Palca reports, if it's successful, the work will not only be professionally rewarding, it could have major implications for human health.

JOE PALCA, BYLINE: There's a nasty disease called dengue that's just beginning to show up in the United States. It's caused by a virus, and it's transmitted from person to person by a mosquito. A mild case of dengue is no worse than flu. A serious case can mean death.

Michael Riehle is at the University of Arizona in Tucson. He's trying to solve a curious puzzle about dengue - why there have been dozens of cases in nearby Texas and none - or virtually none - in Arizona. Riehle thinks the answer has to do with Arizona's geography.

MICHAEL RIEHLE: It's right on the edge of the range where these dengue mosquitoes are found. It's a fairly harsh environment, and we think that they might not be surviving long enough to efficiently transfer the disease to other people.

PALCA: So to test his hypothesis, Riehle wants to be able to compare the life spans of mosquitoes in Arizona with those in Texas. It's not easy to tell how old a mosquito is. It's not as if they carry around birth certificates or government-issued IDs.

Right now the tools for measuring the age of a mosquito are pretty crude. For example, you can look at a female mosquito's ovaries to see if they've produced any eggs. Riehle says if they have, that means the mosquito is at least five days old, since they can't produce eggs before that.

RIEHLE: But that's all it can tell us, less than 5 days or more than 5 days.

PALCA: So Riehle has a new idea. He wants to see if he can use a mosquito's genes to tell its age. There are ways to tell when a particular gene is switched on or off in a mosquito. Riehle is looking for genes that switch on or off when the mosquito reaches a particular age. He's found one. He needs more in order to make more accurate predictions. To help in his search, Riehle raises mosquitoes in a special climate-controlled room down the hall from his office.

RIEHLE: So this is the basic insectory. This is a level 2 containment facility so the mosquitoes won't get out.

PALCA: The insectory is about the size of a large closet with metal shelves floor to ceiling. This place is a Tupperware salesman's dream. The shelves are stuffed with plastic containers in a variety of convenient sizes. Riehle points to a large-ish container. Inside are what look like tiny wiggling worms swimming around in a couple inches of water.

RIEHLE: There's a whole bunch of pupae in there that you can see. These will all come out in the cage and then after two days of allowing them to hatch in there we'll know the exact age of the mosquito.

PALCA: Knowing its age gives him a precise starting point to see how or if different genes change over time. If he can find genes that change with age in the lab, Riehle can look for the same genes in wild mosquitoes and use them to estimate the wild mosquito's age.

This work has implications for a number of mosquito-borne diseases. Malaria mosquitoes have to live at least two weeks or so before they can transmit the malaria parasite. Knowing more about the age of wild mosquito populations could help prevent, or at least predict, outbreaks of disease.

But the search for age-related genes is going slowly. That's not terribly surprising. In science, you usually have to go down a lot of blind allies before you find what you're looking for, if you ever do. Riehle says it's a lesson students coming into to his lab have to learn.

RIEHLE: You give them a project and they just expect it to work and have no problems and get their results by the end of the semester and they're on their way. And it's always interesting to see them learn that, yeah, a lot of science is failure and building upon what doesn't work.

PALCA: So it's not failure itself that's bad, it's just not learning anything from your failures.

RIEHLE: Exactly. Yeah. Actually, what we call failure a lot of times leads to new lines of discovery.

PALCA: So Riehle will continue to search for genes that will reveal a mosquito's age. And with persistence, and enough failures, he thinks he'll find them.

Joe Palca, NPR News.

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