'The kid still has lice'
As millions of children return to school this week after the holidays, so will
head lice. It's not a new problem, but studies suggest the insects are
becoming more resistant to treatment
Tuesday, January 07, 2003
Carolyn, a working mother of three, tries not to let the little things faze
her. But when her middle child came home with grayish white lice eggs glued to
her hair, she "freaked."
Researchers in the U.S. found resistance levels of up to 98% against
permethrin, the active ingredient in most
She rushed to the drugstore and bought boxes of insecticide-laced shampoos,
then scrubbed every head in the house, including her own. She bagged the
stuffed toys, washed the sheets, towels, pillowcases and hats, and obsessed
about lice lurking in the mattresses. Morning and night, she picked through
her six-year-old's hair with a nit comb, prying empty lice shells off with her
A week after the first pesticide treatment, she did a second to ensure any
surviving nits were killed after hatching. Two weeks later, as she parted her
daughter's hair after a bath, she watched, horrified, as a wingless bug
casually sauntered across her scalp. Head lice, which will return to schools
across Canada this week along with millions of children back from the
holidays, are growing increasingly immune to the over-the-counter shampoos
used to treat them, studies suggest.
Resistant nits have been reported in Britain, France and Israel. University
of Massachusetts researchers who recently sampled louse specimens from
children in Massachusetts, Florida, California and Texas found bug resistance
to permethrin, the active ingredient in most anti-lice shampoos, ranged from
13% in some communities to as high as 98% in others.
Two years ago, Harvard University researchers found U.S. lice collected
from two sites were strongly resistant to permethrin, regardless of the dose.
By comparison, the compound quickly killed lice collected from children in
Borneo, where permethrin is almost never used as a pediculicide.
"We continue to hear on a daily basis from people who are having
experiences with products that just don't work," says Deborah Altschuler,
president of the U.S.-based National Pediculosis Association, which advocates
non-chemical removal of lice and nits. Dr. Gerry Wright, director of research
and development for Pfizer Consumer Healthcare Group, which markets NIX creme
rinse, the market leader in over-the-counter lice medicines, says the company
has not "heard any direct evidence" of NIX-resistant head lice in Canada. "I
haven't seen any publications, similar to the ones in the U.S., where they've
evaluated Canadian lice," he said.
But if U.S. lice are becoming resistant, there is a good chance Canadian
lice are, too. And the Canadian Paediatric Society warns that, since all
anti-lice insecticides act in similar ways, if resistance develops to one
class of compound, it could very well spread to others, "resulting in
difficulty in quickly controlling head lice infestations."
University of Massachusetts toxicologist John Clark believes overuse of DDT
is partly to blame for the growing resistance problem. DDT was used for
decades for "all sorts" of ecoparasites -- including body lice and crab lice
-- before it was banned in the 1970s. DDT and insecticides in many head lice
treatments act on the nervous system in the same way. They allow the sodium
channel in a parasite's nervous system to remain open too long.
"That causes the nervous system to go crazy, and they die," says Clark.
(Humans metabolize the toxins rapidly, making them safe at the concentrations
used in lice shampoos.) But over the years, mutant lice have emerged that have
an altered sodium channel gene that makes them resistant to this "knock down"
Overuse of lice shampoos is also fuelling the problem. According to an
article on resistant pediculosis in the journal Contemporary Pediatrics
parents have been known to mistake dandruff for lice and give their children
multiple chemical treatments "for supposed louse infestations." Other parents
are dousing their kids with insecticides as soon as they learn of even one
case of head lice in their child's school. Worse still, when treatments fail,
some desperate parents have resorted to using kerosene, gasoline or
Clark predicts that, within five to 10 years, most anti-louse treatments
will no longer be very effective. "We need to look at alternative treatments
and alternative compounds, because we may reach a point at which the
treatments we're using now just won't work at all." But the study of pediculus
humanus capitis has been a long neglected field. Unlike body lice, which can
carry typhus, head lice have not been implicated in the transmission of
disease, so there has never been a high priority in studying them, says Clark.
(His team is, in fact, looking at whether head lice are vectors for disease.)
What's more, there was no way to rear them in the lab: Lice need a constant
blood supply, surviving only six to 26 hours away from their human hosts.
Clark and his research team have resorted to Scotch-Taping feeding cups to
their ankles to allow lice to feed three or four times a day. "It's pretty
nasty. Once you do that, there's a huge interest in trying to find an
artificial way to feed them. And that's what we've done."
Clark and researchers at the University of California have developed an
artificial feeding membrane, a fake scalp that allows for the colonization of
human head lice, "independent of any human involvement." The system consists
of a small plastic container through which human blood is pumped. The lice
live on an artificial membrane in test tubes that dangle in blood, and the
container is kept in an incubator. To further dupe the lice, researchers have
added a few tufts of human hair, which the bugs have taken to like bats to a
According to the Canadian Paediatric Society, 1% to 10% of elementary
school children in Canada are infested with head lice at any given time. Adult
lice are wingless parasites about two to three millimetres long, about the
size of a sesame seed. They have claws for grasping and a pair of "chitinous"
jaws to bite into the scalp. They live for 23 to 30 days, the females
producing up to 140 eggs before they die.
The eggs, or nits, themselves are less than 1 mm in length. They range in
colour from creamy brown to grayish white, and glue themselves to the hair
shaft close to the scalp, most often above and behind the ears and at the nape
of the neck. Lice, which don't hop or fly but crawl from head to head, can
affect anyone regardless of social-economic status or hygiene. In fact, nits
prefer a clean, dry head.
The Canadian Paediatric Society's committee on infectious diseases and
immunization recommends children return to school or daycare after treatment
with a pediculicide and that family members, friends, schoolmates and other
close contacts be examined and treated if necessary. A second application
seven to 10 days after the first is recommended and, if any surviving lice are
spotted 24 to 48 hours after the first treatment, parents should suspect
resistance, or a particularly heavy infestation, and use another insecticide,
or consult their doctor.
Chemical lice treatments available in Canada include permethrin and
pyrethrin-containing products such as NIX, R&C Shampoo and Lice-Enz, as well
as Kwellada, which contains the insecticide lindane. SH-206 is a natural
product that contains acetic acid, citronella oil and camphor and is believed
to work by dissolving the "cement" that protects the nit shells, allowing the
acetic acid to penetrate and kill the developing louse.
Alternative treatments such as mayonnaise, Vaseline and olive oil have not
been rigorously studied, though some parents swear by them.
The National Pediculosis Association says most attempts to use Vaseline to
try to smother lice "are largely unsuccessful," not to mention then having to
remove the Vaseline. Tea tree oil has also been used, but it can be irritating
to the skin and even toxic to the liver in high doses, the NPA warns.
A Yale University pediatrics professor has developed a new shampoo that
causes lice eggs to glow under ultraviolet light, making them easier to spot,
according to the New Scientist. The Hospital for Sick Children in Toronto has
recommended an oil and vinegar treatment that involves mixing equal amounts of
mineral or vegetable oil with white vinegar, soaking the hair with the
solution, then covering with a shower cap or plastic wrap for one to two hours
before rinsing with regular shampoo. Nits should then be removed manually by
stripping the hair using fingernails or a nit comb with teeth spaced less than
0.3 mm apart.
In fact, Altschuler argues that manual removal of head lice and nits is
safer and more effective than chemical lice medicines. She also encourages
regular and routine screening, so that parents can spot an infestation as
quickly as possible.
"We hear all the time from mothers who call and think they've done the
right thing: 'I've washed everything in the house, I've done all the laundry,
I changed the bed every day, I sprayed the dog, I divorced my husband and the
kid still has lice.' " They would be better off saving their energy for
diligently combing their child's head, Altschuler says.
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