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5-Animals: Scientists create GM mosquitoes to fight malaria and save thousands of lives



------------------------------- GENET-news -------------------------------

TITLE:  Scientists create GM mosquitoes to fight malaria and save
        thousands of lives
SOURCE: The Guardain, UK, by David Adam
        http://www.guardian.co.uk/medicine/story/0,11381,1588607,00.html
DATE:   10 Oct 2005

------------------ archive:  http://www.genet-info.org/ ------------------


Scientists create GM mosquitoes to fight malaria and save thousands of lives

- Plan to breed and sterilise millions of male insects
- Leader says project almost ready for testing in wild

Genetically modified mosquitoes could soon be released into the wild in
an attempt to combat malaria. Scientists at Imperial College London, who
created the GM insects, say they could wipe out natural mosquito
populations and save thousands of lives in malaria-stricken regions.

Led by Andrea Crisanti, the team added a gene that makes the testicles of
the male mosquitoes fluorescent, allowing the scientists to distinguish
and easily separate them from females. The plan is to breed, sterilise
and release millions of these male insects so they mate with wild females
but produce no offspring, eradicating insects in the target region within
weeks.

Professor Crisanti said: "Our mosquitoes are nearly ready for testing in
the wild. This is a technology that works and could make a real
difference. The beauty is that it's very specific. Unlike insecticides,
sterile males target only the species you want to attack."

Mosquitoes that spread malaria have long been a target for sterile male
technology, which has been used to eradicate the screwworm fly from the
US, Mexico and Central America.

The International Atomic Energy Agency has been using its radiation
technology to support health projects, and wants to release sterile
mosquitoes to tackle malaria in northern Sudan and on Reunion island in
the Indian ocean - but they and other groups have been hampered by an
inability to distinguish the males, which do not bite people. Female
mosquitoes transmit malaria, even if sterile, so releasing them alongside
males would make the situation worse.

Prof Crisanti said: "The really challenging problem is to identify the
males. There is no difference between the larvae and as adults they fly,
so the logistics of trying to separate them when they're adults is immense."

To solve the problem, his team altered the DNA of the mosquito species
Anopheles stephensi, the principal carrier of malaria in Asia, so that
the males expressed a fluorescent green protein in their sperm. A sorting
machine based on laser light separated male from female larvae, according
to whether they glowed or not. Writing in Nature Biotechnology today, the
scientists say the machine could sort 180,000 larvae in 10 hours.

The next step is to scale up the technique to provide the millions of GM
insects needed to make a large-scale release effective. The scientists
also need to check the sterile males will be strong enough to compete
with wild rivals when released - the strategy depends on female
mosquitoes, who only mate once in their two-week lifespan, choosing
sterile males.

Prof Crisanti said other mosquito species could be modified in the same
way, including Anopheles gambiae, which is responsible for a large part
of the 2.7m deaths caused by malaria each year. He is talking to
international agencies about setting up a trial. Scientists have
previously considered releasing both male and female mosquitoes that have
been genetically modified in a different way, making them unable to
transmit malaria. The idea is that altered insects would spread the
disruptive genes through natural mosquito populations, but concerns about
whether the inserted genes could transfer to other organisms have so far
scuppered plans to set up large-scale breeding colonies to test it.

Prof Crisanti argued that, because the new GM mosquitoes are sterilised,
releasing them into the environment does not pose significant risks: "It
won't transmit any genes to the environment. This allows us to test the
transgenic technology in a very safe way that overcomes the previous
environmental and safety concerns." Releasing males only would ensure
people were not bitten by GM mosquitoes, he added.

Sue Mayer of Genewatch agreed that the new GM insect did address some of
the previous concerns, but she called for thorough testing of the
mosquitoes before they were considered for release. "Changing one gene
can sometimes affect others, so there are still questions to ask," she said.

There are political barriers too. The London group's insect is best
suited to tackling malaria in impoverished urban areas of south-east Asia
and India, where World Health Organisation trials of sterile male
mosquitoes to fight dengue fever collapsed in the 1970s amid biowarfare
accusations. The males of the mosquito involved in the Delhi trials could
be separated because their pupae were smaller, but they were never
released after newspaper articles claimed the experiment might secretly
be used to gather data on how to spread yellow fever.

Chris Curtis, a malaria expert with the London School of Hygiene and
Tropical Medicine who worked on the WHO project in India, said: "We were
all set to go and there was a huge uproar. You have to handle the public
relations very carefully."

Female mosquitoes can travel several kilometres after mating, he said, so
the sterile male technique is best suited to isolated insect populations,
such as in cities. "If females that have already mated fly in from
outside your release area then they carry on laying fertile eggs. That's
fatal."

Footnotes

Malaria

The world's most common and deadly parasitic disease. It is spread from
person to person when female mosquitoes feed on human blood. Infects up
to 500 million people each year, and kills an estimated 2.7 million people.

Sterile male technology

Male insects can be sterilised using chemicals and radiation. If enough
sterile males can be released to breed with females, the insect
population of a target region can crash within weeks.

Fluorescent green protein

Originally identified in jellyfish that live in the cold waters of the
north Pacific ocean. The protein glows green under ultraviolet light.

Large-scale release

Huge numbers of sterile males would have to be released, possibly several
hundred thousand at different locations throughout a city in several
waves over a month.

Yellow fever

The disease was absent from Asia but appeared on a US list of potential
biowarfare agents. When an Indian journalist discovered the common name
of the insect involved was "yellow fever mosquito" the trials were halted.




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