Research shows that, in at least 25 American states, lice have developed resistance to over-the-counter treatments still widely recommended by doctors and schools. Most head lice treatments are available without a prescription, increasing the chances that they will be overused.
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The ability of lice to become more resistant to pyrethroid has only increased over the past many years, said Dr. Yoon.
So what are parents to do?
Lice can be successfully treated with products containing other chemicals, some of which require a prescription. The first such case of lice insecticide-resistance was reported in Israel in the late 1990s, for instance.
The trio of mutations – called kdr, for “knock down resistance” – affects the insect’s nervous system and makes them less sensitive to the insecticide chemicals that are found in lice treatments and also in mosquito repellant or fly spray, for example. The samples from Texas, California, Maine and Florida had the three genetic mutations and thus made them the most resistant states to pyrethroids. Researchers are investigating why these bugs have not developed a resistance.
A warning for parents as kids head back to school. Out of the 109 populations of lice obtained from the samples, 104 were found to have high amounts of gene mutations, which are associated with immunity to pyrethroids.
The study on lice populations across the United States will be presented at a meeting of the American Chemical Society in Boston this week. Since that report came out, Yoon has expanded his survey.
“It’s a really, really serious problem right now in the US”, Yoon says.
To help prevent your child from getting lice, doctors say you should have your daughter wear her hair up and don’t allow your children to share brushes, combs or hats with their friends.
“If they’re using things like headbands or hats, they can spread it from one child to another”, he said.
It doesn’t look promising for the rest of the untested states, based on Yoon’s findings: Michigan is only state so far to have a population of lice that is still largely treatable with common over the counter treatments.
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Dr. Sky Izaddoost, a pediatrician with the Children’s Hospital of San Antonio Physician Group, says even if a portion of the lice in the area are resistant, that can have a big impact.
