In the war against head lice, we face an enemy that is fast and plentiful, with nimble armies that can evolve and outwit standard weaponry. Will we ever take the lead in this scalp-biting, nit-picking arms race?
Recently, experts from around the world gathered in Buenos Aires, Argentina, to swap battle tactics at the Third International Congress on Phthiraptera, the group of 3,000 species of wingless parasitic insects that includes Pediculus capitis, bane of parents and school nurses across the land.
Researchers reported needed progress in the fight. Some are turning to new classes of insecticides for which head lice haven't developed resistance. Others are eschewing the poison and getting creative: tricking lice into thinking they're drowning; moisturizing the blighters until they leak water; or blasting hot air until the insects are desiccated hulls.
They know that their efforts will not save human lives. Head lice - unlike their close relatives, body lice - don't carry diseases, says Dr. Sydney Spiesel, an associate clinical professor of pediatrics at Yale University.
Every year, 6 million to 12 million Americans are infested with head lice, regardless of socioeconomic status, says Deborah Altschuler, director of the National Pediculosis Association. Annual sales of anti-louse shampoos exceed $160 million, according to some estimates - and for years, the insecticides they contain have been the gold standard for getting rid of head lice.
But recent reports suggest that many lice alive today have inherited mutations rendering them impervious to common treatments such as lindane, a potent DDT-related insecticide (it is banned in California) and permethrin, the active ingredient in Nix.
Some researchers are instead reaching into the barnyard medicine cabinet for a new anti-louse remedy: ivermectin, an insecticide that has been used to treat parasites in horses and sheep for years.
Small preliminary studies suggest that two oral doses of ivermectin can also kill head lice that don't respond to other insecticides.
Neurotoxins aren't the only way to slay a louse. One new treatment already on the market in Europe uses slippery silicone instead. The over-the-counter product, a lotion consisting of a substance called dimeticone, has a polymer base that slides easily across a louse's hide and into its breathing tubes. After the lotion dries, large molecules left behind form a snug coating, blocking those tubes.
"You effectively shrink-wrap the louse," says Ian Burgess, director of the Medical Entomology Centre, a private research organization in Royston, England, that helped develop the new product.
Strangely enough, asphyxiation isn't what kills the louse, Burgess says. Instead, the coating tricks the insect into thinking that it's being engulfed by water. "In response, the louse immediately closes down all the hatches, as if it were a submarine." It switches to a state of suspended animation - but unfortunately for the louse, the shrink-wrapping is there to stay. After a while, the creature exhausts its energy reserves and dies.
In a study published last year, 70 percent of 127 people who used dimeticone lotion - a night application and morning rinse - were free from infestation after two treatments. Negotiations are under way with companies in the United States to license the product, which is known as Hedrin in Britain.
Dieno George, chief executive of the British pharmaceutical company Thornton & Ross, estimates that pharmacies in the United States could carry the lotion as early as summer.
Another potential lice-killer might be waiting in the shower. Many hair conditioners and cream rinses contain compounds - modified vegetable oils, mostly - that attach to hair oil and water. A louse's casing is slightly oily and also semi-porous, and this composition is crucial to the beast for sweating out its extra moisture. Cream rinse, when it mixes with body louse wax, throws off this delicate balance.
"What was once a somewhat-waterproof louse is perhaps not so waterproof anymore," Burgess says. The moisturized louse starts to lose water - and in time, it will dehydrate and die.
In a study of 126 subjects published last year, a combination of conditioner and meticulous removal with a comb - the so-called wet combing method - worked effectively for 57 percent of lice-infested volunteers in England and Scotland.
Quick drying, rather than slow leaking, is the idea behind a new desiccation device that promises to treat an infestation in as little as 30 minutes.
The LouseBuster, a portable hot-air machine with a flexible hose, can expel twice as much air as a hair dryer. Its blast of 140-degree air can suck the moisture out of whatever happens to be in its path - be they adult lice clinging to hair strands or eggs cemented to the strands' base.
"It would be like sticking your head out of a car window at 150 mph," says Dale Clayton, a professor of biology at the University of Utah and co-inventor of the LouseBuster. "That would dry out your eyeballs right away."
By slowly raking a nozzle expelling hot air along the scalp, the LouseBuster killed 80 percent of adult lice and 98 percent of eggs, even when operating at a slightly cooler temperature than a normal hair dryer.
A week after being treated with the new device, all of the infestations had disappeared.
The LouseBuster is being developed by a University of Utah spinoff company called Larada Sciences, for which Clayton is chief scientific officer.
Home hair dryers are no substitute for the new device, he says. It's easy for overzealous parents to burn delicate scalps.
Regina Nuzzo writes for the Los Angeles Times.