The louse is winning.
Long the scourge of scratching schoolchildren, head lice once yielded
to a stiff scrubbing with special insecticidal shampoos. But today,
scientists at the University of Massachusetts and Harvard report, colonies
of lice regularly outwit the strongest treatments, which contain
permethrin, an insecticide derived from chrysanthemums. Studies have found
that anywhere from 50 percent to 98 percent of the parasites survive the
biggest-selling shampoos and sprays.
''Lice,'' said
John Clark, a bug specialist at UMass-Amherst, ''are
true survivors.''
The war on lice has long been hobbled by a basic trait of the insect:
It can't survive once pried from its human host, making it next to
impossible to breed or study lice in the lab.
Now, humans are on the counterattack. For the first time, UMass
researchers succeeded in creating a habitat where lice can thrive -
someplace other than the human head. That discovery, unveiled last month
at the American Chemical Society national conference in Boston, is
expediting research into the habits and biology of the louse and could
eventually lead to new treatments for a pest that ends up banishing
thousands of kids from the classroom each year.
''How wonderful,'' exclaimed Andrew Spielman, the Harvard School of
Public Health scientist credited with being the first to catalog
widespread treatment resistance among lice. ''This is an important social
issue. It's not nice having lice in your child's head; in the average
person's eyes, it just isn't good.''
Americans spend millions of dollars attempting to rid themselves and
their children of the bugs. But for years, parents and nurses noticed the
more they tried to eliminate lice with chemical treatments, the more the
lice stuck around.
And so did the controversy surrounding them. For example, while most
specialists believe head lice don't present a health threat, a small but
persistent coalition argues that head lice possess some of the
disease-propagating potential of their cousins, body lice, long known to
spread typhus.
Similarly, there's disagreement about the extent of resistance:
Companies that make chemical shampoos dispute researchers' estimates,
arguing that misuse of the products leads to unfounded reports of
resistance.
Then there's the whole matter of whether the pesticide-laced shampoos
should be used at all. An advocacy group with headquarters in Needham, the
National Pediculosis Association, is devoted to finding alternative means
of controlling the parasites, recommending specially designed combs to
remove lice, which then meet their ultimate fate in a cup of water or on a
towel.
''We're not really focused on killing lice here,'' said Deborah Z.
Altschuler, president of the Needham association. ''We're just focused on
getting them out of your hair.''
Some school districts enforce a ''no-nits'' policy: Children with any
evidence of the bugs or their eggs (nits) are banned from classrooms.
Boston does not follow such a prohibition. Instead, while the city's
schools do send children with a full-blown case of lice home, they're
allowed back in class after treatment, even if there's residual evidence,
such as louse egg casings.
''Our mission,'' said Debra Fox, assistant director of the school
health department in Boston, ''is to keep children in school as much as
possible, not exclude them.''
But doing that has proven increasingly difficult with the rampant
presence of lice resistant to chemical treatments, a development that has
spurred the quest to better understand the bugs.
To investigate resistance, Harvard's Spielman decided to visit cultures
that don't think lice are so bad. That took him to the island of
Borneo.
''A lousy head is a social head there,'' Spielman said. ''A person who
is not scratching his head is one who probably lives alone and may be
living alone for a reason, I suppose.''
Spielman discovered that lice in Borneo never before exposed to
insecticide shampoos were easily thwarted. That stood in stark contrast
with scientists' experience in the United States.
As researchers began comparing Borneo lice with US lice, they
discovered a prime case of Darwinian survival of the fittest: Over time,
as the lice vulnerable to insecticide succumbed, the ones left behind
possessed a genetic profile that allowed them to withstand treatments, and
those were the bugs that came to dominate the lice world in the United
States.
Studying them, though, proved maddening.
''If you were going to study head lice before, you had to grow them on
yourself or find somebody who would be willing to have head lice grown on
their head,'' Clark said. ''It's pretty obnoxious to have these things
growing on you.''
So, in collaboration with a lab at the University of California at
Davis, researchers in Amherst developed an elaborate system that mimics
the favorite lice habitat, supported by a grant from the National
Institutes of Health.
Human blood, warmed to body temperature, is pumped into a square
plexiglass container - the food bowl for the lice. The bugs reside in
small plastic test tubes dangling in the blood. Higher up in the test tube
is a teepee made of human hair, just the right spot for the lice to hang
out and lay eggs in between meals.
To get to the blood, the bugs use their mouths to slice through a
specially designed membrane separating them from their meal.
''They just puncture the membrane to get at the blood,'' said John
Edman, director of the Center for Vector-Borne Diseases at UC-Davis and
one of Clark's collaborators. ''They're little blood machines.''
The world's first colony of lab-reared lice is allowing UMass
researchers to become better acquainted with the lifestyles, as well as
the genetic characteristics, of the insects. Researchers hope that
knowledge leads to improved treatments.
And while the artificial habitat appears to work well most of the time,
occasionally the lice crave a taste of the real thing, appearing to get an
additional boost in breeding and activity by feeding on actual human
volunteers.
''We have a number of people involved in the project who donate their
effort and time, so to speak. And so do I,'' Clark said. ''You just tape
the lice onto your ankles and let them feed for a couple of hours. All in
the name of science.''
Stephen Smith can be reached at stsmith@globe.com
