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ROBERT SIEGEL, host:

This is ALL THINGS CONSIDERED from NPR News. I'm Robert Siegel.

MICHELE NORRIS, host:

And I'm Michele Norris.

Malaria is an enormous health problem around the world. Traditional strategy for controlling the disease is to kill the mosquito that transmits the malaria parasite. Now, scientists have come up with a new idea.

As NPR's Joe Palca reports, instead of killing the mosquito, they found a way to let it live while killing the parasite it carries.

JOE PALCA: There's a kind of fungus that can get under a mosquito's skin, literally.

Dr. RAYMOND ST. LEGER (University of Maryland): The insect literally fills up with fungus.

PALCA: Raymond St. Leger is at the University of Maryland. Ultimately, filling up with a fungus is a bad thing for the mosquito. In fact, eventually it will kill the mosquito. But in the meantime, St. Leger realized that he could use genetic engineering to alter the fungus so it would do useful things inside the mosquito.

Dr. ST. LEGER: The trick we did was to engineer the fungus so that it produces a protein which is anti-malarial, anti- the parasite itself.

PALCA: You don't get malaria by being bitten by any old mosquito. You have to be bitten by a mosquito that is carrying the malaria parasite. What St. Leger's fungus does is rid the mosquito of the malaria parasite.

Dr. ST. LEGER: So the fungus acts like a little hypodermic syringe, and when it's in the blood of the insect, the fungus then produces the anti-malarial protein, and within a couple of days it basically cures the mosquito of malaria.

PALCA: And once it's cured, the mosquito can't spread the disease. These findings appear in the latest issue of the journal´┐ŻScience.

Now, you might wonder why St. Leger doesn't just engineer his fungus to kill the mosquito more quickly. Well, they've done that. But St. Leger says mosquitoes are resourceful. Finding ways to reliably and permanently defend people from mosquitoes is tricky. Insecticides have been used, natural plant toxins have been used.

Dr. ST. LEGER: One by one, all these defenses have fallen, as the mosquitoes have managed to outflank every attempt we've made to control them by some evolutionary trick or other.

PALCA: But because the fungus takes its own sweet time to kill the mosquito, the pressure to use one of those evolutionary tricks to evade the fungus is not as great as it would be with a more lethal insecticide.

Professor ANDREW READ (Center for Infectious Disease Dynamics, Pennsylvania State University): Of course, it does open up the prospect that the malaria could become resistant to whatever you put in the fungus.

PALCA: Andrew Read is a senior scholar at the Center for Infectious Disease Dynamics at Penn State University.

Clearly, the malaria parasite can develop resistance to drugs used to treat it. But Read says it should be possible by modifying the fungus to keep one step ahead of the parasite. Although this new approach has only been tried in the lab, Read says it should be ready for field testing before too long.

Prof. READ: Because it's already approved for agricultural use for locust control.

PALCA: Although that's for a version of the fungus that hasn't been engineered to produce anti-malarial proteins. Getting approval to release a genetically modified fungus into the environment will probably take longer. But Read thinks it will be worth the effort.

Prof. READ: One of the great things about this paper on the genetically modified fungi is it does raise the scientific interest a lot in the fungi.

PALCA: Fungi, or if you prefer, fungi or fungi or funguses, could be used to inject all manner of deadly toxins into disease-carrying mosquitoes.

Joe Palca, NPR News, Washington.

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