James Gathany/ASSOCIATED PRESS - Scientists have made a promising advance for controlling dengue fever, a tropical disease spread by mosquito bites. They've rapidly replaced mosquitoes in the wild with skeeters that don't spread the dengue virus.
The war against dengue fever has enlisted a tiny new ally: a cunning bacterium that inoculates mosquitoes against the virus that causes the debilitating disease.
The dengue virus hops from person to person via mosquitoes, so if the insects can’t carry the virus, disease transmission might be slowed or even halted.
That’s the hope of researchers racing to erase dengue, which infects 50 million to 100 million people worldwide each year in 100 mostly tropical countries, causing about 22,000 deaths, according to the World Health Organization. There is no vaccine available, and patients suffering the intense joint and muscle pain that mark a dengue infection have no treatment options other than painkillers. Growing resistance by mosquitoes to pesticides adds urgency to the battle against the virus.
That’s why researchers are hailing a promising field test in Australia reported Wednesday in the journal Nature.
In two isolated neighborhoods near Cairns, Queensland, researchers released batches of female mosquitoes deliberately infected with the protective bacterium, called Wolbachia. The bacterium, passing from mother to offspring, ripped through the mosquito population in the two neighborhoods, flipping entire swarms of the bugs from potential dengue carriers to dengue destroyers.
The test proved that deliberate introduction of Wolbachia can effectively spread the protective bacterium, said Scott O’Neill, the researcher at Monash University in Melbourne who led the project, called the Eliminate Dengue Program. “Wolbachia completely blocks the ability of dengue virus to grow in the mosquito,” he said. “If it can’t grow in the mosquito, it can’t be transmitted to people.”
During this year’s Australian wet season, which began in January, the researchers made 10 weekly releases of the dengue-resistant mosquitoes by driving through neighborhoods in a mosquito-carrying van. They then monitored the proportion of mosquitoes captured in each location that carried Wolbachia .
Even after they stopped releasing mosquitoes, the proportion they captured carrying Wolbachia continued to climb, reaching 100 percent in one location in three months and 90 percent in the other.
“I think it’s a huge deal,” said Jason Rasgon, a Johns Hopkins University researcher developing a similar strategy to battle malaria. “This strain of Wolbachia has the potential to spread worldwide and in theory eliminate dengue transmission.”
That’s because the bacterium is a cunning manipulator of insect reproduction. Somehow — scientists are unsure exactly how — females carrying Wolbachia reproduce more successfully than females that don’t carry it. This evolutionary strategy has been so successful that various strains of Wolbachia infect an estimated 70 percent of all insect species.
Strikingly, though, this evolutionary marvel does not naturally infect the species of mosquito that carries dengue virus, Aedes aegtypti.
So O’Neill and his colleagues set about finding a strain of Wolbachia that could infect Aedes aegypti while simultaneously protecting against dengue virus. They found that strain in their own back yard, inside Australian fruit flies.
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