Genetic Mutation and Insecticide: Lice Resistant to Common OTC Meds

In time for the start of school for many kids, lice in 25 states have developed resistance to common over-the-counter treatments. The situation has been developing for many years, says researcher Kyong Yoon, Ph.D., of Southern Illinois University. The first such case of lice insecticide-resistance was reported in Israel in the late 1990s, for instance. 

Yoon and other researchers recently presented their work on this topic at the 250th National Meeting & Exposition of the American Chemical Society (ACS). Presentations from the conference are available here.

"We are the first group to collect lice samples from a large number of populations across the U.S.," said Yoon in a release. "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."

The latter is a family of insecticides commonly used to defend against mosquitoes and other insects. Pyrethroids include permethrin, which is used in some of the most common drug-store treatments of lice, the release noted.

Yoon's earliest work on lice in the U.S. began when he tested the insects for genetic mutations called kdr, for "knock-down resistance." These mutations, which change an insect's nervous system and make them unflapped by pyrethroids, showed up in many lice that Yoon tested, the release said.

In the most recent study, Yoon gathered lice from 30 states with the help of public health workers. The samples that showed kdr came from California, Texas, Florida, Maine and 21 others. Others--New York, New Jersey, New Mexico and Oregon--had up to three mutations. Michigan was the only state with lice that remain wholly susceptible to the insecticide. Researchers are investigating why this would be the case, Yoon said, according to the release.

The good thing is, lice can still be controlled by some chemicals available by prescription. But: "If you use a chemical over and over, these little creatures will eventually develop resistance," Yoon said in the release. "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."

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