- The first step has been taken towards altering mosquitoes
so they cannot pass on malaria. But it is not clear whether genetically
modified mosquitoes could displace natural populations, or if we should
even try to make this happen.
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- For decades, researchers have been trying to enhance
the Anopheles mosquito's resistance to the parasite that causes malaria,
one of the world's most prolific killers. In 2000, a technique for inserting
genes into these mosquitoes was finally developed.
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- Now Marcelo Jacobs-Lorena of Case Western Reserve University
in Ohio and his colleagues have managed to add a gene to Anopheles that
codes for a protein that binds to the walls of their guts and salivary
glands. This makes it difficult for the parasite to pass through. "It's
a watershed," says Fotis Kafatos, whose commentary accompanies the
Nature paper.
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- But it is only the first step on a long road. The modified
mosquitoes have only a fifth as many plasmodium parasites in their saliva,
but that is still enough to pass on the disease. And in the wild, those
parasites that do make it through to the saliva might be selected for,
making the scheme completely useless.
-
- "For this to work, it would have to be 100 per cent,"
says Kafatos, who works at the European Molecular Biology Laboratory in
Heidelberg. The solution may be to add several resistance genes.
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- Wild populations
-
- Finding these genes will be the easy bit. What no one
has worked out is how to get them to spread throughout wild populations
of Anopheles. The altered mosquitoes do not seem to be any fitter than
their wild relatives so they wouldn't naturally replace them. To increase
the chances of the resistance genes being passed on to offspring, researchers
hope to tag them onto a transposon, a piece of DNA that jumps around the
genome.
-
- But no one has yet found a suitable transposon to attach
them to. Even if researchers do find a way to promote the spread of the
resistance genes, modified mosquitoes would still have to be bred and released
on a massive scale after a campaign to decimate the wild population.
-
- "I think there's a less than 50 per cent chance
that this is ever going to happen," says Chris Curtis, who works on
malaria control at the London School of Hygiene and Tropical Medicine.
-
- If and when the perfect mosquito can be developed, it
will still take years to prove that it is safe to release into the environment,
adds Jacobs-Lorena, though scientists cannot think of any reason why these
transgenic mosquitoes should be more dangerous than wild ones. In the meantime,
other less controversial options are being pursued, says Kafatos, such
as developing human vaccines against the parasite.
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- Journal reference: Nature (vol 417, p 452)
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- http://www.newscientist.com/news/news.jsp?id=ns99992314
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