Scientists have discovered that the Wolbachia bacterium can halt mosquitoes from spreading dengue fever, a deadly virus that threatens about 2.5 billion people a year. “If there is no virus in the mosquito, it can’t spread to people, so disease transmission can be blocked,” says Zhiyong Xi, who has maintained the bacterium in mosquitoes in his lab for nearly six years. (Credit: Muhammad Mahdi Karim/Wikimedia Commons)

MICHIGAN STATE (US)—There is no vaccine or treatment for dengue fever—the deadly virus transmitted by mosquitoes that threatens 2.5 billion people each year—but new research has found that a bacterium can stop dengue viruses from replicating.

“In nature, about 28 percent of mosquito species harbor Wolbachia bacteria, but the mosquitoes that are the primary transmitters of dengue, Aedes aegypti, have no Wolbachia in them,” says Zhiyong Xi, assistant professor of entomology at Michigan State University and author of the study published in the  journal PLoS Pathogens.

While dengue fever is rare in the continental United States, Hawaii was the site of a dengue epidemic in 2001. Overall, about one-third of the world’s population is at risk of contracting dengue fever and up to 100 million people are infected each year.

While most people recover in about two weeks, the infection can turn into dengue hemorrhagic fever, which causes bleeding from the nose and gums and can be fatal.

“We found that Wolbachia is able to stop the dengue virus from replicating. If there is no virus in the mosquito, it can’t spread to people, so disease transmission can be blocked.”

In earlier work, Xi and colleagues introduced the Wolbachia bacterium into Aedes aegypti mosquitoes by injecting embryos with the parasite. They have maintained the bacterium in the mosquitoes in the lab for nearly six years because it is passed from mothers to offspring.

When a Wolbachia-infected male mates with an uninfected female, the bacterium causes a reproductive abnormality that triggers early embryo death.

Wolbachia doesn’t affect embryo development when a female contains the same Wolbachia as a male, so the bacterium can spread quickly, infecting an entire mosquito population.

Wolbachia can’t be passed from mosquitoes to humans.

Another report with similar results was recently published by Australian researchers, though the groups used different strains of the Wolbachia bacterium. “The strain we used has a 100 percent maternal transmission rate and causes the mosquitoes to live slightly longer,” Xi explains.

“The strain the Australian researchers used causes the mosquitoes to die a bit sooner. There are advantages to both. The longer the mosquitoes live, the more likely they are to pass on the Wolbachia infection to their offspring and infect the entire population in a shorter timeframe. But if the mosquitoes die earlier, they can’t bite people and transmit the dengue virus.

“In both instances, the results demonstrate the potential using the Wolbachia bacterium as a control method for dengue virus.”

Xi and colleagues are now working to understand how the Wolbachia bacterium stops the dengue virus from replicating in mosquitoes.

“Only when we know the mechanisms underlying Wolbachia-mediated viral interference, will we will be able to determine why it’s happening and further improve the efficiency of the viral interference,” he says.

The research is funded by the National Institutes of Health. Xi’s research also is supported by the Michigan Agricultural Experiment Station.

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