NATURE SCIENCE UPDATE WEEKLY HIGHLIGHTS
http://www.nature.com/nsu/
27 May
(c) Nature News Service 2002
GM-MOSQUITOES HALT MALARIA TRANSMISSION
Malaria-proof mosquitoes raise hopes for disease eradication.
http://www.nature.com/nsu/020520/020520-7.html
Malaria-proof mosquitoes raise hopes for disease eradication.
23 May 2002
TOM CLARKE
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.
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.
References
1.Ribolla, P. E. M. & Jacobs-Lorena, M. Targeting
Plasmodium ligands on mosquito salivary glands and
midgut with a phage display peptide library.
Proceedings of the National Academy of
Sciences, 98, 13278 - 13281, (2001).
2.Ito, J., Ghosh, A., Moreira, L. A., Wimmer, E. A. &
Jacobs-Lorena, M. Transgenic anopheline mosquitoes
impaired in transmission of a malaria parasite.
Nature, 417, 452 - 455, (2002).
© Nature News Service / Macmillan Magazines Ltd 2002
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