Every parent dreads the notice from school announcing that someone’s adorable moppet has lice.
Now, these notices may become a more common occurrence.
Researchers say lice in 25 states have developed gene mutations that indicate they are developing resistance to a common class of chemical treatments.
The researchers are presenting their work today at the 250th American Chemical Society National Meeting & Exposition in Boston.
Lice Developing Gene Mutations
Lead author Kyong Yoon, Ph.D., assistant professor at Southern Illinois University Edwardsville, said his group was the first to collect lice samples from a large number of populations across the country.
They found that 104 out of 109 lice populations had high levels of gene mutations, which have been linked to resistance to pyrethroids.
Pyrethroids are a class of insecticides used widely indoors and outdoors to control mosquitoes and other insects. The group includes permethrin, the active ingredient in some of the most common lice treatments sold at drug stores.
The more resistant lice become, the harder they are to kill.
“You can use more product to kill the insect,” Yoon said in an interview with Healthline. “But the more you use, the more resistant they become.”
Earlier he had tested the pests for a trio of genetic mutations known collectively as kdr, or “knock-down resistance.” These mutations had been found in house flies in the late 1970s after farmers and others had shifted from DDT and other harsh insecticides to pyrethroids.
“We need to learn a lesson from the overuse of over-the-counter products,” Yoon said. “Over 20 years they cause problems. It was a great chemical, but we didn’t learn to use less.”
He said it was similar to what happens when antibiotics are overused, leading to an increase in drug resistance.
“We ignored this with pyrethroids in the 1990s. We think the product is resistant-proof. But it isn’t,” Yoon said.
Looking for Alternative Treatments
Some people have dealt with this problem by turning to plant-based lice solutions.
Susan C. Stevenson, director of the Albany Children’s Center in California, spoke to Healthline about her own observations.
“I have noticed that more and more parents are using healthier options and more natural deterrents for lice such as tea tree oil,” Stevenson said. “Parents use a shampoo or conditioner with this ingredient to repel lice.”
Other ingredients include coconut oil, menthol, eucalyptus oil, lavender oil, and rosemary oil.
Yoon recommends caution when using these products too.
“People think these chemicals are safe because they’re from nature. But they are very potent natural oils,” he said. “These products are easy to access, but there’s a potential problem. They’ll become resistant.”
Yoon added that distraught parents may not read the instructions thoroughly and may misuse or overuse the product.
Resurgence of Head Lice
Yoon was one of the first scientists to report on the issue in 2000, when he was a graduate student at the University of Massachusetts, Amherst.
He had been working on insecticide metabolism in the potato beetle, when John Clark, Ph.D. a professor of veterinary and animal sciences at the University of Massachusetts, suggested he examine the resurgence of head lice.
“I asked him in what country and was surprised when he said the U.S.,” Yoon said in a press release.
The problem was first noticed in Israel in the late 1990s, Clark said. That made sense when you look at the history.
“After World War II, many people were in resettlement camps,” Clark said. “They were dusted with DDT … and that’s probably where they first saw kdr mutations.”
In this most recent study, Yoon cast a wide net, gathering lice from 30 states with the help of a lot of public health workers.
Population samples with all three genetic mutations associated with kdr came from 25 states, including California, Texas, Florida, and Maine. Having all three mutations means these lice populations are the most resistant to pyrethroids.
Samples from New York, New Jersey, New Mexico, and Oregon had one, two, or three mutations. The only state with a population of lice still largely susceptible to the insecticide was Michigan. Why Michigan lice haven't developed resistance is still under investigation, Yoon said.
Using Chemistry to Find a Solution
There’s no quick fix to this problem, but both Yoon and Clark pointed to a new class of chemicals they say is promising.
“Now we have a group of new chemistries and all these active ingredients don’t share the same mode of action,” Clark explained. “For the first time we have at least three new insecticides with different modes of action.”
These are available only by prescription. When chemicals are offered over-the-counter, they are sometimes overused, both scientists said.
Head lice, however, may be getting a bad rap.
“They are more a nuisance than scary,” said Clark.
And there are worse things. Lyme disease and malaria come to mind for Clark.
“But most moms and dads in the United States won’t ever face malaria, but could face lice outbreaks several times in their lifetimes,” he said.