GM-mosquitoes halt malaria transmission
Malaria-proof mosquitoes raise hopes
for disease eradication.
23 May 2002
TOM CLARKE
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| Transgenenic mosquito larvae
(left and right) have an antiparasitic protein
(green) that wild insects (middle) lack. |
| © J. Ito and A. Ghosh |
|
|
One new gene leaves mosquitoes unable to transmit malaria,
new research shows. The preliminary findings are the first to
suggest that genetically engineering mosquitoes to eradicate the
disease is scientifically feasible.
"It's a proof of principle," says geneticist Marcelo
Jacobs-Lorena at Case Western Reserve University in Cleveland,
Ohio, who developed the mosquito.
Mosquitoes ingest the malaria parasite, Plasmodium
when they suck a sufferer's blood. The parasite then moves from
an insect's gut into its saliva, so that when it bites another
person it enters their blood. This way between 300 and 500
million people are infected with malaria each year - one to
three million die from the disease.
Malaria parasites rapidly evolve resistance to drugs and
while vaccines against them are a long way off. Some hope that
if mosquitoes can be genetically altered to prevent them
transmitting the parasite, they could help to stop malaria in
its tracks. Provided that they are safe to release and thrive in
nature, the idea is that engineered mosquitoes would slowly
replace malaria-ridden wild mosquitoes.
Last year, Jacobs-Lorena and his colleagues found a molecule
called SM1 that stops a malaria parasite passing from a
mosquito's gut to it's salivary gland1.
Now they have slotted the gene for SM1 into mosquitoes.2
The gene is incorporated into a molecular mechanism that
manufactures the enzymes mosquitoes need to digest blood. So SM1
is produced as soon as the mosquito feeds.
Modified mosquitoes feeding on malaria-infected mouse blood
are 80% less likely to have malaria in their salivary glands,
shows Jacobs-Lorena's team. What's more the insects are almost
totally unable to pass on malaria to other mice.
"It's good news," says Andrea Crisanti, a geneticist at
Imperial College in London, U.K. It's direct evidence, he says,
that mosquitoes' capability to carry disease can be modified.
But Crisanti, the first scientist to insert a foreign gene into
a mosquito, warns there are some major drawbacks.
Transmission statement
No one knows how SM1 acts. Without understanding the
mechanism it would be impossible to get permission to release
such a mosquito into the environment. "It may cause any number
of unpredicted effects," warns Crisanti.
Moreover a different form of the parasite causes human
malaria than the one that causes mouse malaria. So far there is
no evidence that a mosquito carrying SM1 will stop human forms
of malaria getting into mosquito saliva and possibly evidence to
the contrary.
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| GM mosquitoes (bottom) will
need to be tested in contained field sites. |
| © J. Ito and A. Ghosh |
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|
Jacobs-Lorena is confident that if SM1 doesn't work for human
malaria other very similar molecules that will do the job. But
like Crisanti he is cautious about modified mosquitoes. "We'd
need to do very thorough homework to ensure that they cause no
harm."
GM mosquitoes will need to be tested in contained field sites
to make sure that inserted genes spread through the natural
population and remain active for long periods, without
side-effects. Even then, given the public's negative reactions
to GM foods, this approach to controlling the disease may never
pass popular muster.
Nonetheless this line of research is throwing new light on
how the mosquito and malaria parasite interact that could help
develop drugs or vaccines. For example, drugs containing
molecules like SM1 could prevent Plasmodia from reproducing
within the mosquito. SM1 itself is too unstable to survive in
the human blood stream. |
