Hard to kill super lice are resistant to many chemicals


They’re the creepy-crawly critters that make every parent squirm. And new research shows that they are becoming increasingly difficult to kill.

The bugs known as super lice have developed genetic mutations that make them resistant to many of the over-the-counter and prescription chemicals that used to kill them.

“You use the product as the manufacturer says, and that product is no longer able to control head lice. And that’s rapidly happening in the United States,” said John Clark, a professor of environmental toxicology and chemistry at the University of Massachusetts Amherst who was part of a new study published last week in the Journal of the Entomological Society of America.

Clark and a team of researchers examined the genes of lice from 32 sites in the U.S. and Canada and found that 99.6% of those tested in 2007-09 were genetically resistant to the pyrethrin- and permethrin-based chemicals most frequently used to treat them; those are the chemicals in such over-the-counter lice products as RID and Nix.

“In the UK and Europe, they don’t even use pyrethroids anymore. Virtually everyone but the United States and Canada has given up using these over-the-counter products,” Clark said.

The U.S. Centers for Disease Control and Prevention does not track lice outbreaks or chemical resistance. That’s because lice are seen as a nuisance rather than a health scourge.

But Dr. Eric Ayers, an assistant professor of internal medicine and pediatrics with the Wayne State University Physicians Group and Children’s Hospital of Michigan, said the problem is growing.

“We have seen an increased number of cases of it in the last six months,” said Ayers, noting that the biggest challenge in fighting the spread of super lice is the misuse of over-the-counter and prescription treatments.

He said that if the instructions aren’t followed exactly, the lice can not only survive, but grow stronger. They’re then able to tolerate that same medication the next time it is applied. Then, those more-resistant bugs can move from the head of one child to another, spreading super lice.

“In irony, that’s probably what we’re seeing here,” he said. “Over a period of time, they’re moving from child to child. The lice become stronger, and now they’re super because someone didn’t treat their kid’s head properly.”

Drug-resistant lice tends to crop up in pockets around the country, said Shirley Gordon, director of the Head Lice Treatment and Prevention Project at Florida Atlantic University. She studies persistent cases of the pests.

“The more a product is used within a community, the more lice in that community become resistant,” she said. “We don’t like to use the term super lice, because it’s sensational and frightening. It’s not a super bug, but a louse that has become resistant.”

Sarah Casello-Rees, who owns Rapunzel’s Lice Boutique with locations in Michigan, said her business is booming, and it’s bolstered by people who say common treatments don’t work.

“People are not coming to us because they want to spend $145 for a treatment. They’re coming to us because they’ve already tried everything else, and they don’t have any other choice,” she said. Her company uses a heated air system to kill lice and their eggs.

Casello-Rees’ experience is supported by a new Harris Poll of 2,000 U.S. mothers ages 25 or older that shows just 32% who used an over-the-counter treatment say the infestation was eliminated with just one application; 68% reported that treatment required two or more applications or that no over-the-counter treatment resolved it, according to the survey funded by Sanofi Pasteur, the maker of the prescription lice treatment Sklice Lotion.

The makers of Nix did not respond to a Detroit Free Press request for comment.

But RID, which is made by Bayer Healthcare, sent this response: “It is important to note that this current study does not address the efficacy of any treatment on resistant head lice. … When used according to directions, RID is effective in killing lice.”

Clark said UMass researchers did test the product, along with Nix and Pronto, and found them ineffective.

“We actually have a study out where we applied exactly those materials and followed manufacturer instructions. … Even with two treatments, at least 25% of the populations survived,” Clark said. “You also can’t ignore what we’re hearing anecdotally from the lice removal companies.”

Clark suggests skipping over-the-counter medications and instead asking doctors for a prescription for a product such as Sklice, Natroba or Ulesfia, all of which use different chemicals that have been shown to be effective at killing even the pyrethroid-resistant lice.

Natasha Buttrey, a technician and dispatcher for the national Lice Doctors removal company, says 20,000 families call its hotline each year from around the country.

“We find people who’ve been dealing with this for days, weeks and sometimes years. Lice are adaptable. We’re treating them with the same chemicals over and over and over, and we’re not expecting them to do what is natural for a parasite, and that’s adapt.”

Treatment tips

If you or a member of your household has lice, here are some practical tips from Dr. Eric Ayers, an assistant professor of internal medicine and pediatrics with the Wayne State University Physicians Group and Children’s Hospital of Michigan.

• Bathe and check your child’s head for lice and nits daily. Many people only know they have lice because of the itching. But, notes Shirley C. Gordon, director of the Head Lice Treatment and Prevention Project at Florida Atlantic University, only 50% of people have an allergy to the saliva of a louse, which means only half of people with lice itch.

• Don’t try to treat it without confirmation. First, visit the doctor to be certain that it’s head lice causing the problem.

• After seeing the doctor, be certain you use the proper medication, following directions exactly, and for the proper time.

• Although the American Academy of Pediatrics said it’s not necessary to comb through the hair and remove the nits after treating with medication, Ayers said it’s not a bad idea to take the time and effort. “As a holistic and naturalistic practice, it’s not going to hurt anybody.”

• Wash anything that has come into contact with the hair and scalp in hot water above 120 degrees, including hats, pillowcases and bedding. Boil all hair brushes and combs before using again to sanitize them. Throw away all grooming products used in the hair.