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The multimillion-dollar effort to eradicate one of the world's deadliest
diseases received a significant but controversial boost yesterday when
scientists announced the creation of genetically modified mosquitoes
that cannot pass on malaria, March 2007 by Ian Sample.

Trials revealed that the GM mosquitoes could quickly establish
themselves in the wild and drive out natural malaria-carrying insects,
thereby breaking the route through which humans are infected.

The strategy is likely to prove contentious as it would require the
unprecedented release of tens of thousands of GM organisms into the
wild. But it has raised hopes among scientists, some of whom believe it
may be powerful enough to finally bring under control a disease which
strikes 300 million people a year and causes more than 1 million deaths,
mostly of children in sub-Saharan Africa.

Plans to combat malaria with disease-resistant mosquitoes have been
hampered in the past by fears that adding crucial resistance genes
weakens the insects, making them too feeble to survive in the wild. For
the idea to work, the malaria-resistant insects must breed and become
dominant, so that the parasite is not picked up from infected animals
and passed on to humans through insect bites.

Researchers led by Marcelo Jacobs-Lorena at the Malaria Research
Institute at Johns Hopkins University in Maryland created genetically
modified mosquitoes by giving them a gene that made it impossible for
them to pass on the plasmodium parasite that causes malaria. Around
1,200 GM mosquitoes were then released into a cage holding
malaria-infected mice and the same number of wild mosquitoes.

Over time, the researchers found that the GM mosquitoes slowly became
the majority, reaching 70% in nine generations. The scientists believe
that even though malaria-resistance weakened the mosquitoes by making
them immune to the parasite, they fared better in the long term than
insects infected with it because they lived longer and laid more eggs.

"This fitness advantage has important implications for devising malaria
control strategies," the team write in the journal Proceedings of the
National Academy of Sciences.

The finding was hailed as welcome proof that GM mosquitoes, made with
cheap laboratory techniques, could ultimately have a greater impact on
malaria than chemical sprays and other treatments.

Andrea Crisanti, who leads a team working on GM mosquitoes at Imperial
College, London, said the latest work raised hopes by showing the
insects would be unlikely to die out if released into the wild.

"This has tremendous potential. You can start with a few mosquitoes and
in future generations, all of them are resistant to the disease. It
should be much cheaper than the controls used now, because you have a
strategy where the mosquito spreads the gene which confers resistance.
You don't need insecticides any more," he said.

In wild populations, only a small fraction of females carry the malaria
parasite, so disease-resistant strains must become well-established to
affect the spread of disease. Scientists are focusing on ways to perfect
how resistance genes are inherited, ensuring they are passed on in every
mosquito egg. Normally, offspring have a 50% chance of inheriting a
specific gene from the mother.

Trials in sub-Saharan Africa, where malaria claims the life of a child
every 30 seconds, could be conducted within five years, but scientists
will first have to prove as far as possible that the resistance genes
will not trigger a more aggressive form of malaria, or spread to other
insects.

At a glance

Malaria kills more than 1 million people a year

90% of malaria deaths occur among young children in sub-Saharan Africa

The disease costs Africa $12bn (?6.2bn) in lost GDP and consumes 40% of
public health spending

60% of malaria deaths strike the poorest 20% of the global population

71% of all deaths from malaria are in the under-fives

Children can die within 48 hours after the first symptoms appear

[www.guardian.co.uk]