Monday, April 9, 2001
Splicing the Sting Out of Bugs
Health: Genetic altering of insects and bacteria could prevent
them from transmitting diseases such as malaria. But ultimate effects
ATLANTA--Charles Beard's recipe
for stopping the kissing bug, a tropical pest that kills 50,000 people
each year, calls for ammonia, ink and guar gum. The result is an odorous
goop that resembles the bug dung that, unpleasant as it may seem, happens
to be a vital meal for young kissing bugs.
But Beard adds something else to his faux
feces that could prove to be even more noxious. It is genetically engineered
bacteria that, once ingested, render the kissing bug unable to pass along
its deadly disease.
Now, a world that is already debating the
safety of gene-spliced foods is about to meet a new class of genetically
engineered organisms: modified bugs. Beard's creation is just one in a
series of plans to turn insects and bacteria into warriors against disease
and crop pests.
This summer, scientists hope to start the
first U.S. field tests on a gene-spliced insect--a version of a moth that
chews through $24 million worth of U.S. cotton plants each year. Researchers
are also trying to create mosquitoes that cannot carry malaria, which
still kills 1 million a year, or West Nile fever, which is spreading across
the United States. On the drawing board are ticks that cannot carry Lyme
disease or Rocky Mountain spotted fever. Although the work is advancing
quickly, questions remain about which U.S. agencies would monitor the
If released in the wild, scientists say,
a properly engineered bug would spread its disease-defusing trait to its
wild cousins, protecting a whole community or region. Public health officials
say the bugs could be a crucial new weapon against often-deadly diseases
such as malaria, which has built resistance to drugs and pesticides and
has reemerged in places where it was once defeated.
"The situation is awfully bleak out there,"
said Barry Beaty, an insect specialist at Colorado State University. "A
lot of people are dying. We need new ways to respond to the problem."
But if much of the world is anxious about
genetically engineered foods, then modified bugs are sure to set off alarms
as well. "Once you release an insect, it flies, and you can't control
its distribution in the environment," cautioned Svata Louda, a University
of Nebraska plant ecologist. "That's just one of the things that makes
ecologists apprehensive about new versions of an insect."
Critics also ask whether an engineered bug
gene might mutate over time into something dangerous, or whether it would
jump to an unintended insect species. Another question: Given that bugs
travel freely, how many people in an area would have to give consent before
gene-spliced bugs were released?
Scientists say they have kept these questions
well in mind over the last decade. But it is only now, thanks to funding
from such heavyweights as the U.S. government and the World Health Organization,
that they have accomplished enough in the lab to start thinking about
conducting field tests that would produce some answers.
In London this June, researchers from around
the world will hash out basic scientific questions about field trials--where
they might be conducted, what data should be collected and how they should
be monitored. The meeting is sponsored by the WHO, the National Institutes
of Health and London's Imperial College.
At the same time, U.S. officials say they
are taking some early, tentative steps to sort out which agency should
make sure that the new bugs pose no harm to people or the environment.
In some cases, jurisdiction seems clear.
In July, for example, scientists from the U.S. Department of Agriculture
and UC Riverside hope to start the first field test of a gene-spliced
insect, the pink bollworm moth, a bane to cotton growers. Because the
Agriculture Department itself has authority over plant pests, it has claimed
jurisdiction over the field trial.
The scientists want to place 2,350 gene-altered
moths in a large mesh cage in an Arizona cotton field. Their long-term
plan is to insert a lethal gene into the moth that would be passed to
their offspring, wiping out the next generation of insects. But in their
first field trial, the scientists will use only a marker gene and watch
how it affects moth behavior.
Robert Rose, a USDA official charged with
assessing the scientists' plan, said he is considering the stability of
the mesh cage and the fitness of altered moths to survive in the wild.
Only sterile moths would be put into the cage, he said, a step that aims
to diminish their effect on the environment if they escape.
Federal jurisdiction is less clear over
other bugs now being developed. A "talking points" document by the NIH
says "there are gaps" in the existing law covering field tests.
An antimalaria mosquito, for example, would
not be considered a plant pest and therefore would probably not fall under
USDA jurisdiction, Rose said. But officials at the Environmental Protection
Agency say it is not clear that they would oversee the mosquitoes, either.
Beard, a parasitic-disease specialist with
the Centers for Disease Control and Prevention, says he consulted the
CDC's own biosafety committee about his plans for the kissing bug. The
bug has infected 14 million people in Central and South America with Chagas
disease, which causes heart and digestive problems that kill 50,000 a
Kissing bugs hide in the thatch huts common
in the developing world, and they feed on the blood of people and animals.
But the bugs cannot live on blood alone. They must also consume bacteria,
Rhodococcus rhodnii, which they pick up from the dung of their parents.
Beard has produced a gene-altered version
of the bacteria and loaded it into his fake dung. Once the bug eats the
dung, the bacteria attack and kill any Chagas disease agent that the bug
is also carrying.
"We've tested this concept in jars. Now
we want to test it in a place that's more like the field," Beard said
recently near his CDC office outside Atlanta.
He swept open the door to a greenhouse to
show his plan. Inside, he had built a protective mesh tent, and then a
second mesh tent inside the first. Within that, he had built a small thatch
hut, the kind that might be found in Honduras or Guatemala.
Within weeks, Beard and his research partner,
Dr. Ravi Durvasula of Yale University, plan to seed the hut with the fake
dung, then release a handful of kissing bugs. They want to study how the
altered bacteria flow through the kissing bug population. Like the moth
researchers, Beard is using bacteria that carry only a marker gene, not
the gene designed to attack Chagas disease. The tents are meant to stop
the kissing bugs from escaping.
Agriculture officials in California also
have high hopes for gene-altered insects, as they continue the battle
against the Mediterranean fruit fly.
State and federal officials control the
crop-eating pest by flooding the environment with sterile males, which
crowd out wild males in the competition for females and yet produce no
offspring. Officials release about 500 million sterile flies each week
in Southern California, at an annual cost of $15.8 million. A similar
program in Florida costs nearly $3 million.
To sterilize the flies, officials use radiation,
which also leaves the insects weak and diminishes their ability to mate
in the wild. Researchers think they would have a more robust fly if they
accomplished the sterilization through a genetic flaw. "If we could release,
say, 75,000 flies per square mile instead of 250,000, that would save
money," said Patrick Minyard, an official with the state Agriculture Department.
Several researchers said bug scientists
should take heed of the past problems with introducing new insects to
A fly released in 1906 and for decades afterward
to control the gypsy moth has also caused damage to 200 other butterflies
and moths in the Northeast, said Jeff Boettner, an insect specialist at
the University of Massachusetts in Amherst. The fly's wide appetite was
known at the time, but researchers believed that was a good trait.
Now, they want to preserve many of the targeted
butterflies. "We change our views over time about what risk is and what
is proper," Boettner said.
Louda, the Nebraska researcher, said weevils
released in the state to control an invasive, foreign thistle plant have
also attacked a native thistle more than expected. This suggests that
the present tools are "not sufficient" for evaluating what effect a new
insect species will have on plants, she said.
But Rebecca Goldburg of Environmental Defense,
which questions the safety of bioengineered foods, suggested that people
might find a certain amount of risk acceptable if it helped stop disease.
"People have been more reluctant to take
on environmental risk when we see the benefit of a product going to big
biotech and chemical companies," she said. "Consumers in general are less
concerned if sick people are getting the benefit."