According to a new study, lice in 30 states are becoming resistant to many common treatments for the parasite, including parasites in Washington.
The research, which as presented at the 250th National Meeting and Exposition of the American Chemical Society, found that lice were developing resistances to pyrethroids, a family of insecticides, including the active ingredient in most lice-control products, called permethrin.
“We are the first group to collect lice samples from a large number of populations across the U.S.,” says Kyong Yoon, Ph.D and lead researcher. “What we found was that 104 out of the 109 lice populations we tested had high levels of gene mutations, which have been linked to resistance to pyrethroids.”
According to Yoon, the resistance has been building for many years, with the first case in Israel in the 1990s. Yoon also reported one of the first cases of pyrethroid-resistant lice in the US in 2000 while a graduate student at the University of Massachusetts in Amherst.
“I was working on insecticide metabolism in a potato beetle when my mentor, John Clark, suggested I look into the resurgence of head lice,” he says. “I asked him in what country and was surprised when he said the U.S.”
After the discovery, Yoon expanded his research and contacted local schools to collect samples. He tested the gathered parasites for genetic mutations know as kdr , or knock-down resistance mutations, which desensitize an insect’s nervous system to pyrethroids.
The most recent study cast an even wider net, asking for lice gathered from more than half of US states, including California, Texas, Florida, Maine and Washington. The most pyrethroid-resistant lice were found in New York, New Jersey, New Mexico and Oregon, and had up to three mutations.
According to Yoon, Lice can still be controlled using medications available only by prescription, but that this solution isn’t the cure.
“If you use a chemical over and over, these little creatures will eventually develop resistance,” Yoon says. “So we have to think before we use a treatment. The good news is head lice don’t carry disease. They’re more a nuisance than anything else.”
