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China's 'mosquito factory' aims to wipe out virus, other diseases

Every week, scientists in southern China release 3 million
bacteria-infected mosquitoes on a 3 km (two-mile) long
island in a bid to wipe out diseases such as dengue,
yellow fever and Zika .

The scientists inject mosquito eggs with wolbachia
bacteria in a laboratory, then release infected male
mosquitoes on the island on the outskirts of the city of
The bacteria, which occurs naturally in about 28 percent
of wild mosquitoes, causes infected males to sterilize the
females they mate with.
"The aim is trying to suppress the mosquito density below
the threshold which can cause disease transmission ," said
Zhiyong Xi, who is director of the Sun Yat-sen University
Centre of Vector Control for Tropical Diseases and
pioneered the idea.
"There are hot spots ," Xi said. " This technology can be
used at the beginning to target the hot spots ... it will
dramatically reduce disease transmission. "
Mosquito-borne diseases are responsible for more than
one million deaths worldwide every year and Zika has
become a concern for athletes at this year's Olympic
Games, which open in Rio de Janeiro on Friday.
Some athletes, including the top four ranked male golfers,
have declined to take part.
An outbreak of the Zika virus in Brazil last year has
spread through the Americas and beyond, with China
confirming its first case in February.
U.S. health officials have concluded that Zika infections in
pregnant women can cause microcephaly, a birth defect
marked by small head size that can lead to severe
developmental problems in babies.
The World Health Organization has said there is strong
scientific consensus that Zika can also cause Guillain-
Barre, a rare neurological syndrome that causes temporary
paralysis in adults.
Sun Yat-sen's Xi said that several countries had expressed
interest in his experiments, especially Brazil and Mexico.
In the laboratory, mosquito eggs are collected from
breeding cages containing 5,000 females and 1,600
males and injected with the wolbachia bacteria. Xi's
facility has the capacity to breed up to five million
mosquitoes a week.
While a female mosquito that acquires wolbachia by
mating is sterile, one that is infected by injection will
produce wolbachia-infected offspring. Dengue, yellow
fever and Zika are also suppressed in wolbachia-injected
females, making it harder for the diseases to be
transmitted to humans.
Xi set up his 3,500 square metre (38,000 sq ft)
"mosquito factory" in 2012 and releases the males into
two residential areas on the outskirts of Guangzhou.
Xi said the mosquito population on the island has been
reduced by more than 90 percent.
One villager on the island, 66 year-old Liang Jintian, who
has lived there for six decades, said the study was so
effective he didn't have to sleep with a mosquito net any
"We used to have a lot of mosquitoes in the past. Back
then some people were worried that if mosquitoes were
released here, we would get even more mosquitoes," he
said. "We have a lot less mosquitoes now compared to
the past."

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