Stronger Breed of Head Lice Survives
By ADAM GORLICK
The Associated Press
AMHERST, Mass. (AP) - John Clark is trying to solve a
problem that's left hundreds of parents - not to mention their children -
scratching their heads in search of answers.
Over-the-counter shampoos are losing their effectiveness
against head lice, parasites that can plague 12 million schoolchildren each
year. Clark and researchers at the University of California have been trying
to find out why some head lice don't die when doused and scrubbed with
pesticide-based shampoos.
"The lice are becoming resistant and the resistant lice are
taking over," Clark said.
The reason, he said, lies in the shampoos' active ingredient
that attacks the insects' central nervous systems and causes the critters to
suffocate. The poison acts in the same way as DDT, a pesticide that was widely
used to kill lice before it was banned in the United States in 1973.
After three decades of exposure to DDT, lice began
developing a genetic immunity to it. The pesticide-laced shampoos, which were
made available without a prescription in the 1980s, helped the resistant
strain of lice evolve, public health experts said.
"We get calls from child care providers and schools who say
lice are increasingly more difficult to get rid of," said Steven Shuman, the
state Department of Public Health's deputy director for maternal, child and
family health. "When people get lice, they want to get rid of them as fast as
possible. And that leads to a misuse of the products designed to kill them."
In samples of head lice sent to him from school nurses
across the country, Clark said he has no problem finding bugs with the genetic
makeup that makes them stronger than the pesticide.
"We started hearing about resistance in 1994," Clark said.
"I would say that between five and 10 years at the most, they won't be
effective at all."
But studying dead head lice tells only so much. In order to
get a sense of how the parasites behave and exactly how they react to
pesticides, researchers had to design an environment where the louse - which
has only been able to survive on a human scalp - can live.
"Nobody wants these things living on them, so we had to
create an artificial scalp to study them while they're alive," Clark said.
Clark and the other researchers, funded by a $500,000 grant
from the National Institute of Health, have been trying to replicate
conditions of a human scalp where a louse can feed on blood and lay eggs.
In a setup that looks nothing like a human head, the lice
are placed inside tubes with a tuft of human hair. A thin plastic membrane
stretches over the bottom of the tube, fooling the lice into believing it is a
scalp. The tube is then lowered into a container of blood, which a louse can
feed on through the membrane.
"They lay their eggs there, they raise their kids there and
they eat there," Clark said. "They're happy."
Miwa Takano-Lee, a researcher at the University of
California at Riverside who helped design the artificial scalp, said the
device will help scientists study why lice spread so rapidly among people.
"Everybody assumes they're transported from head-to-head
contact," Takano-Lee said. "But they do not jump. We're trying to figure out
what motivates them to disburse. They have everything they need when they're
on a person's scalp, so it doesn't make sense why they would want to leave."
But the research goes beyond the interest of science.
When many students - including some in Massachusetts - are
diagnosed with head lice, some are not allowed to attend class.
In a rush to relieve their children's' itchy scalps and
anxious to save the hours it could take to comb lice out of their hair,
parents often turn to insecticide-based shampoos.
"I speak to so many frustrated parents," said Deborah
Altschuler, president of the National Pediculosis Association, a Needham-based
nonprofit group that advocates against the misuse of pesticidal lice
treatments. "They've spent all this money on products that didn't do anything,
and their kids still have lice."
Altschuler, who said using chemical lice treatments can
cause cancer and other health hazards if used incorrectly, said picking lice
and their eggs off a scalp is the best way to get rid of them.
"We are not entirely anti-pesticide or anti-chemical," she
said. "But we need to reserve those treatments in a way that they'll be safe
and effective."
A convenient solution to lice control might be found in the
development of new products that mix different active ingredients, Clark said.
By mixing compounds that kill lice differently, it would take the insects
longer to develop a resistance than if they were subjected to just a single
poison.
"If we're going to get a handle on control, it's going to
have to be done through very controlled prescription use of pesticides,"
Clark said. "When these things are sold over-the-counter, they're not used
properly. And that leads to the problems we're seeing now."
Copyright 2002 The Associated
Press.
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