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.
By Sharon Kirkey – National Post
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.”
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 fingernails.
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” effect.
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 garden-strength insecticides.
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 barn.
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.