At Lab, It’s a Good Day When the Lice Are Biting
Few creatures are more disgusting to parents than head lice--and few creatures demand more of the scientists who study them.
Lice need human blood to live, which means researchers must routinely walk around with little louse-filled tubes strapped to their legs. When the creatures are hungry, they can crawl down and bite the scientists’ legs. (Understandably, louse research isn’t very popular.)
The difficulty in maintaining louse colonies in labs has made it hard for scientists to answer even the most elementary louse questions--such as issues involving insecticide-resistance, or whether kids can get head lice infestations from a few eggs on a hairbrush or need closer contact with an infested playmate.
Lice from “field trips” to schools are too variable.
“If you pull lice off someone’s head, you have no idea how old they are, what stage of their life they’re at, what they’ve been treated with--it’s just not a uniform population,” says louse researcher John Edman, director of the center for vector-borne diseases at UC Davis
Now, at last, comes a breakthrough: Researchers have developed an automated system for the care and keeping of lice that allows them to live without biting the scientists’ legs.
Here’s how it works. The lice are placed in little containers, along with tufts of human hair for that cozy, at-home feel. The containers float on a reservoir of blood--obtained from a blood bank. Floors of the containers consist of thin, artificial membranes--stand-ins for human skin. When the lice get hungry, they puncture the membrane and suck blood.
The automated louse-rearer is helping researchers gather basic information about the louse life cycle, says Miwa Takano Lee, a post-doctoral researcher at UC Davis who helped develop the contraption.
The researchers have also started investigating the critter’s behavior--testing, for instance, how fast a louse can walk from one tube to another, using a bridge of a single strand of hair. Preliminary findings suggest that adult lice are speedy and well-balanced whereas younger lice still in their early “nymph” stages hardly go anywhere.
If these findings hold up, it would suggest that a kid is pretty unlikely to get infested from casual contact with hair containing only nits and nymphs, Edman says. Thus, these kind of studies (besides being morbidly fascinating) could help inform parents and schools.
“Currently, so little is known that many people are overly cautious and paranoid,” Lee says. “By presenting scientific evidence we can try to reduce some hysteria.”
Other collaborators on the team are using the louse-rearing system to nurture mutant lice that are resistant to common louse shampoos. They are doing this for a noble, not nefarious, purpose.
John Clark, professor of environmental toxicology at the University of Massachusetts at Amherst, and his graduate student Kyong Yoon have been trying to learn where and how U.S. lice are becoming resistant to permethrin, an insecticide commonly used in head louse shampoos.
They had some depressing news to report at the annual meeting of the American Chemical Society last week: Tests of samples of lice from different places revealed that resistant rates in some Los Angeles schoolchildren is 50%. In the Texas population, the rate was 75% to 80%, and in one population in Florida, a whopping 98%.
Clark and Yoon have also shown how that resistance is happening. Permethrin and other so-called pyrethroid insecticides work by interfering with a certain protein in the membrane of nerve cells. Resistant lice have alterations in that protein that stop the permethrin from doing its deed.
Such lice exist naturally. But when populations are bombarded with insecticides, they survive to reproduce while others perish.
Yoon and Clark have designed a diagnostic test that makes it easy to determine if a particular louse infestation is resistant--so that other chemicals can be used and pyrethroids avoided altogether.
Once the pyrethroids are gone, the resistant lice should soon die out, says Clark. That’s because, in the absence of permethrin, resistant, mutant lice are less healthy than normal, susceptible lice.
The automated louse-rearer still needs perfecting. (Science fair project, anyone?) Right now, animals can be gently reared from egg to adulthood--but not beyond. The scientists hope that one day the system will maintain whole colonies indefinitely.
For now, Lee occasionally must strap lice to her legs.
“Until I have successfully reared several generations on the apparatus,” she pledges, “I will not stop.”
*
If you have an idea for a Booster Shots topic, write or e-mail Rosie Mestel at the Los Angeles Times, 202 W. 1st. St., Los Angeles, CA 90012, rosie.mestel@latimes.com.
