Better You Than Me: Scientists Sicken Mosquitoes To Stop Dengue

Aug 25, 2011
Originally published on August 25, 2011 12:27 pm

Scientists in Australia are using a bacterium to try to stop a deadly virus in its tracks.

The dengue virus causes a potentially fatal flu-like illness. The World Health Organization says the number of cases of dengue around the world is skyrocketing, and the disease is endemic in more than 100 countries. It has even shown up in Florida recently. There's no vaccine against the virus yet, so control efforts have focused on the mosquito that transmits the disease.

About six years ago, Scott O'Neill of Monash University had an idea about using bacteria called Wolbachia to prevent dengue's spread. The idea works like this: Use a strain of Wolbachia to shorten the mosquito's life, killing it before it becomes mature enough to transmit the dengue virus. It was a good idea, but it didn't work because the infection didn't spread to enough mosquitoes.

But then O'Neill discovered something surprising. There are many strains of Wolbachia. Some do bad things to mosquitoes, such as shortening their lives, while others give them nothing more than the mosquito equivalent of the sniffles. Mosquitoes infected with any of these strains couldn't spread dengue.

With a mild infection, the mosquitoes would live long enough to spread the Wolbachia around, but not the dengue.

O'Neill infected hundreds of thousands of mosquitoes with a mild strain of Wolbachia in the lab, and released them in two small communities in Northern Queensland near Cairnes, Yorky's Knob and Gordonvale. This time, success: Close to 100 percent of the mosquitoes got infected, which O'Neill says he thinks "greatly reduced ability to transmit dengue between people."

These results appear this week in the journal Nature.

There's very little dengue in Australia, so O'Neill is planning releases in Vietnam, Indonesia and Brazil, countries where the disease is more prevalent.

The bacteria could prevent dengue transmission down the line, and negate the use for dangerous pesticides, but there's always the law of unintended consequences. O'Neill says he thinks there won't be any negative ones, since there are a lot of insect species that are naturally infected with Wolbachia. He says regulatory authorities in Australia are convinced his plans are safe.

It would be a kind of poetic justice if a bacterial infection in mosquitoes could prevent a viral or parasitic disease in people.

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RENEE MONTAGNE, host:

For years, researchers have been looking for a way to block the spread of a disease called dengue. Now, a field test in Australia is showing some promise. It's a potentially fatal, flu-like illness, and the number of dengue cases around the world is skyrocketing. There's no vaccine against the virus, so control efforts have focused on the mosquito that transmits it.

NPR's Joe Palca has this report on a new approach that uses bacteria to block the spread of dengue.

JOE PALCA: The approach uses a bacteria called wolbachia to infect dengue mosquitoes.

Mr. MICHAEL TURELLI (Biologist, University of California Davis): Interest in that started in the late 1990s.

PALCA: Michael Turelli is a biologist at the University of California Davis. Turelli's colleague Scott O'Neill of Monash University in Australia had an idea of how to use wolbachia to prevent dengue's spread. There's a strain of the bacteria that shortens the mosquito's life, killing it before it becomes mature enough to transmit the dengue virus.

O'Neill got money from the Bill and Melinda Gates Foundation to try to infect the dengue mosquitoes with the life-shortening bacteria, and then release them so they'd hook up with wild mosquitoes and infect them. Turelli says it was a good idea, but it didn't work. The wolbachia infection didn't spread to enough mosquitoes.

Mr. TURELLI: Bill and Melinda, we spent your first $7 million. Sorry, the project was a failure.

PALCA: But then, Turelli says O'Neill discovered something surprising about wolbachia. There are many strains of wolbachia. Some do bad things to a mosquito, like shortening their lives. Others give them nothing more than the mosquito equivalent of the sniffles. O'Neill says mosquitoes infected with any of these strains couldn't spread dengue.

Mr. SCOTT O'NEILL (Biologist, Monash University): They just couldn't grow the dengue virus if the wolbachia was present in the body of the mosquito. And if it can't grow in the mosquito, it can be transmitted between people.

PALCA: With a mild infection, the mosquitoes would live long enough to spread the wolbachia around. O'Neill convinced the Gates Foundation to give him some more money. He infected hundreds of thousands of mosquitoes with a mild strain of wolbachia in the lab, and released them in two small communities in Northern Queensland, near Cairns.

Mr. O'NEILL: Yorky's Knob to the north, and Gordonvale to the south.

PALCA: This time, success.

Mr. O'NEILL: Over a very short period of time, the wolbachia was able to invade the wild mosquito population until close to 100 percent of all mosquitoes had the wolbachia infection, and so we presume greatly reduced ability to transmit dengue between people.

PALCA: These results appear in the journal Nature. There's very little dengue in Australia. O'Neill is planning releases in Vietnam, Indonesia and Brazil, countries where the disease is more prevalent. Now, wolbachia doesn't infect humans, but there's always the law of unintended consequences. The bacteria might prevent dengue transmission, but no one knows for sure what else might happen. O'Neill says regulators in Australia are convinced his plans are safe. After all, wolbachia is already out there.

Mr. O'NEILL: If you were to go and look at some overripe bananas just about anywhere, in any kitchen around the world, you'd see those small flies with red eyes hovering around. And just about every one of those would have the strain of wolbachia in them.

PALCA: O'Neill and his colleagues have only been working with wolbachia for five or six years.

Mr. JASON RASGON (Researcher, Johns Hopkins Malaria Research Institute): I'm actually kind of amazed at the rapid pace of progress that this research group has been making.

PALCA: Jason Rasgon is a researcher at the Johns Hopkins Malaria Research Institute. He's hoping to use a similar approach with malaria. He's been able to infect the malaria-carrying anopheles mosquito with several strains of wolbachia.

Mr. RASGON: They all dramatically and significantly reduce malaria parasite infection in anopheles mosquitoes. So these kind of strategies have potential for malaria, as well.

PALCA: It would be a kind of poetic justice if a bacterial infection in mosquitoes could prevent a viral or parasitic disease in people.

Joe Palca, NPR News, Washington. Transcript provided by NPR, Copyright NPR.