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Chinese Scientists Cut Local Numbers of Dangerous Mosquito by 94%

WEDNESDAY, July 17, 2019 (HealthDay News) -- Some mosquitoes spread diseases to humans through their bite, passing along harmful pathogens like Zika, dengue fever, West Nile virus and chikungunya.

Now humans are turning the tables, infecting these dangerous mosquitoes with bacteria that sabotage their ability to spawn.

Chinese researchers were able to reduce these mosquito populations by as much as 94% using a bacteria-based strategy that interferes with the insects' reproductive cycle.

"In principle, all the mosquito-borne diseases, including dengue, malaria, West Nile, chikungunya and filariasis, can be controlled using this technology," said senior study author Zhiyong Xi. He is director of the Sun Yat-sen University/Michigan State University Joint Center of Vector Control for Tropical Diseases. "There will be none of those diseases without transmission by mosquitoes."

The mosquito control strategy hinges on bacteria called Wolbachia, which can affect the reproductive biology of mosquitoes, said Peter Armbruster, a professor of biology at Georgetown University, in Washington, D.C.

Essentially, a male mosquito carrying a specific strain of Wolbachia cannot successfully reproduce if the female is infected with a different strain of Wolbachia, explained Armbruster, who wrote an editorial accompanying the report in the July 17 issue of the journal Nature.

The Chinese research team created a lab-based colony of mosquitoes that all carry a newly developed combination of three Wolbachia strains. This hybrid strain doesn't occur in the wild. The colony produced around 10 million male mosquitoes a week, Xi said.

The male mosquitoes were then released into the wild, in areas designated for pest control.

"They mate with wild females and then the wild females produce inviable eggs," Armbruster said. "It's a way of letting the males do the work by finding the females and preventing them from reproducing."

The researchers also treated the mosquitoes with a low dose of radiation, enough to sterilize any accidentally released females carrying the triple bacteria strain but not enough to impair the male mosquitoes' reproductive drive. This helped speed up laboratory production of the mosquitoes, Armbruster explained.

Field trials focused on Aedes albopictus mosquitoes were able to drive populations down by around 83% to 94%, with no wild mosquitoes detected for up to six weeks after release, the researchers reported.

Dr. Amesh Adalja is senior scholar at the Johns Hopkins Center for Health Security in Baltimore. "Mosquitoes have long been a scourge of mankind and their effective control is one of the most daunting tasks in infectious diseases," he said.

"Exploiting the phenomenon of mating incompatibility through male mosquito Wolbachia infections, combined with irradiation, is an elegant solution that this study demonstrates is feasible," Adalja said.

At least one American company, MosquitoMate, is already using a similar bacteria-based approach to control mosquitoes, Armbruster noted. The innovation in the study was the combination of three different Wolbachia strains and the use of radiation to make sorting and releasing mosquitoes an easier process.

You don't want to release both male and female mosquitoes with the triple strain, because they'll be able to successfully mate. Until now, lab technicians have had to run the mosquito swarms through a machine that separated males from females, and then do a second hand-sort to make sure all the females had been removed, Armbruster said.

Because the approach targets specific disease-carrying species of mosquitoes, it will not wipe out other benign mosquito populations that co-exist in the same area, Xi added.

"As mating happens only within the same species, this is a species-specific control tool, without any impact on non-target species," Xi said. "The majority of mosquito species in nature are not disease vectors, and thus will not be targeted by our technique."

These field tests released the lab-infected male mosquitoes on two small islands located on rivers that run through Guangzhou, the city with the highest dengue transmission rate in China, the study authors said.

The goal was to reach a 5-to-1 ratio of infected males versus wild males, to effectively suppress the mosquito populations, Xi said.

Further research will be needed to see if the same laboratory production techniques could be used to battle mosquitoes in large U.S. cities, Armbruster said.

"It's still an open question whether this is scalable to a major metropolitan area," Armbruster said.

More information

The U.S. Centers for Disease Control and Prevention has more about mosquito control.

SOURCES: Zhiyong Xi, Ph.D., professor, microbiology and molecular genetics, and director, Sun Yat-sen University/Michigan State University Joint Center of Vector Control for Tropical Diseases; Peter Armbruster, Ph.D., professor, biology, Georgetown University, Washington, D.C.; Amesh Adalja, M.D., snior scholar, Johns Hopkins Center for Health Security, Baltimore; July 17, 2019, Nature

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