Posted on 1-6-2002
Gene-Altered
Mosquito Latest Trojan Horse
By Rick Weiss, Washington Post Staff Writer, Thursday, May 23,
2002; Page A03
Scientists in Cleveland for the first time have created genetically
engineered mosquitoes that have a reduced capacity to transmit
malaria. The
feat points to the possibility of disrupting the scourge by
releasing
gene-altered insects in Asia and Africa, where the disease kills
an
estimated 2 million people every year, most of them children
younger than
5. But that prospect has alarmed some scientists and others
who fear that
such a program could trigger ecological disruption and ultimately
increase,
rather than decrease, the global burden of disease.
Experts said the advance has also brought renewed attention
to the fact
that the United States has yet to promulgate regulations limiting
the
environmental release of genetically engineered insects capable
of
transmitting human or animal diseases. The new work, published
in today's
issue of the journal Nature, is the culmination of 15 years
of efforts by
several competing teams trying to gain control over the genetic
machinery
of the mosquito. Although scientists had previously managed
to insert
various genes into the notoriously irritating insects, none
until now had
succeeded in making a mosquito that blocks the development of
the malarial
parasite inside the insect's body.
That parasite, a single-celled creature called Plasmodium, must
pass
through a mosquito's gut and then be reinjected via mosquito
saliva into
humans or other animals to complete its life cycle. Control
of the disease
has been difficult because plasmodium has developed resistance
to
medicines, mosquitoes have become resistant to insecticides,
and efforts to
develop an effective vaccine have so far failed. Taking a novel
tack,
Marcelo Jacobs-Lorena of Case Western Reserve University and
his colleagues
identified a small protein that binds tightly to a mosquito's
gut lining.
The team then engineered mosquitoes with a gene that allows
the insects to
produce that protein after ingestion of a blood meal.
In experiments, most plasmodium cells failed to pass through
the
mosquitoes' gut lining and could not travel to the insects'
salivary
glands. When the team allowed the mosquitoes to feed on malaria-infected
animals and then later bite uninfected ones, disease transmission
was about
80 percent less likely than with normal mosquitoes. Jacobs-Lorena
suggested
that scientists could knock down wild populations of mosquitoes
with
insecticides and then repopulate the area with laboratory-reared
gene-altered ones. But he acknowledged that five to 10 years
of work might
be needed first.
Additional genes that block other aspects of plasmodium's life
cycle in
mosquitoes ought to be added, he said, to reduce transmission
even more.
Moreover, he said, the work so far has been done only with a
variety of
plasmodium that infects rodents, not people. And the team has
yet to make
engineered mosquitoes of the species that spreads human malaria
in Africa,
where most cases occur. The mosquito species used in the experiment
spreads
malaria in India.
In addition to technical challenges, Jacobs-Lorena added, funding
is
sparse. "It's a poor country's disease. If we had a way to prevent
heart
attacks I'm sure there'd be a line of company executives outside
my office
ready to write checks." But others expressed relief that the
work might
progress slowly, saying recent experiences with gene-altered
crops -- many
of which spread their genes through the environment more widely
than had
been anticipated -- teach that extreme caution is warranted.
"We've had
unexpected results in virtually every area of genetically engineered
organisms," said Andrew Kimbrell, executive director of the
International
Center for Technology Assessment, which has filed petitions
with the
federal government seeking to block the release of engineered
insects until
regulations are drawn.
Andrew Spielman, a professor of tropical public health at Harvard
University, echoed those concerns, saying it would be ecologically
unwise
and probably medically useless to release engineered mosquitoes
in malarial
areas. "The lure of this kind of quick fix is so great that
people tend to
be very sloppy in their thinking," Spielman said.
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