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Germ-Infected Mosquitoes Can't Spread Dengue

Release of Bacteria-Carrying Mosquitoes Could Halt Dengue Spread
WebMD Health News
Reviewed by Laura J. Martin, MD

Aug. 24, 2011 -- By releasing 300,000 live mosquitoes, scientists say they've freed a remote region of Australia from the threat of dengue fever.

Before releasing them, the researchers deliberately infected the mosquitoes with a strain of a common insect bacterium, Wolbachia pipientis, that makes them incapable of spreading the dengue virus.

The four types of dengue virus sicken 50 million people each year. Those who get a second infection with a different strain are at risk of life-threatening dengue hemorrhagic fever.

The only way a person can get dengue is via the bite of a dengue-infected mosquito. A. aegypti is the mosquito that spreads the dengue virus. The hope is that this relatively inexpensive strategy can end the pandemic of dengue fever sweeping tropical regions of the world, says study leader Scott O'Neill, PhD, of Monash University in Victoria, Australia.

"It is a very exciting result that this strain of wolbachia really reduces the ability of dengue virus to grow in mosquitoes," O'Neill said at a news conference held to announce the findings. "And if dengue cannot grow in mosquitoes, it cannot infect people."

Wolbachia bacteria are very common. Some 70% of all insect species in the world are naturally infected, says study researcher Scott Ritchie, PhD, of James Cook University in Cairnes, Australia.

"Wolbachia already infects many mosquito species that bite people but don't spread dengue," Ritchie said at the news conference.

There are two reasons why wolbachia infects so many insects: how it spreads and how it affects the insect. The bacterium is spread by an infected female to all of her offspring. And the bacterium kills all the offspring of an uninfected female that mates with an infected male. So as the bacterium spreads in an insect population, infected females have a tremendous evolutionary advantage.

Once a mosquito population has a certain level of wolbachia infection, nearly 100% of that population soon carries the bacteria. In an indoor lab, O'Neill's team showed that this is exactly what happens when mosquitoes carrying the wMel strain of wolbachia are released in a population of uninfected mosquitoes.

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