Back-to-School Warning: Head Lice Now Resistant to Treatment in 25 States

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As a new school year starts, the American Chemical Society had some lousy news. Researchers found that lice populations in at least 25 states have developed resistance to over-the-counter treatments still widely recommended by doctors and schools. The researchers presented their findings yesterday at the 250th National Meeting & Exposition of the American Chemical Society (ACS), the world’s largest scientific society.

“We are the first group to collect lice samples from a large number of populations across the U.S.,” says Kyong Yoon, Ph.D at Southern Illinois University, Edwardsville. “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.”

Pyrethroids are a family of insecticides that are commonly used to treat head lice. One of those, permethrin, is the active ingredient in many anti-lice treatments. Yoon became one of the first to highlight the problem in the U.S. back in 2000, but the first report on this development came from Israel in the late 1990s. Yoon has been testing lice for a trio of genetic mutations known collectively as kdr, which stands for “knock-down resistance.”

In Yoon’s most recent report, he collected population samples of lice from 30 states. Twenty-five of those states had all three genetic mutations—meaning they are the most resistant to pyrethroids. In some samples, including ones from California, Florida, Maine and Minnesota, every insect in the sample had resistance genes. “It’s almost saturated with [these genes], which means that people using permethrin and pyrethrin based products will probably have a very hard time controlling the lice,” says Yoon.

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