'Tis the season for back-to-school shopping, and stores are starting to stock their shelves with wigs and hats for Halloween festivities. For many parents of school-aged children, this means it's time to start worrying about head lice outbreaks that will inevitably plague schools across the country.
And now there's a new excuse for parental panic over lice: at least 25 U.S. states harbor lice with genetic mutations associated with resistance to over-the-counter insecticide treatments, according to an ongoing study by Kyong Yoon, PhD, of Southern Illinois University. Yoon and colleagues studied multiple populations of lice collected from professional "nit-pickers" across 30 states. Of the 109 louse populations studied, 104 showed nearly 100% genetic resistance to the most commonly used pyrethroid treatments. They presented their findings at the American Chemical Society meeting this week.
So is it time to ditch the Nix yet? Not quite, said Jason Yaun, MD, assistant professor of pediatrics at the University of Tennessee Health Science Center (UTHSC) in Memphis. Though Yoon's study found high levels of resistance in Tennessee and several surrounding states, Yaun said Nix, an over-the-counter permethrin treatment, still seems to be the safest and most successful solution for lice.
Yoon's population study, which is not yet published or peer-reviewed, may have found so-called "knockdown resistance," or kdr-like genes to be widespread across the nation, but this doesn't necessarily mean that traditional treatments won't work in states where the allegedly resistant populations of lice have been found.
"The relationship between clinical and genetic resistance is still debated," said Rémy Durand, PharmD, PhD, HDR, a researcher in the Department of Parasitology and Mycology at Hôpital Avicenne in Paris, France. While kdr mutations are well known for their effects on insecticide resistance in many insect species, Durand pointed out that some limited studies have actually reported that the presence of these "mutant alleles" in lice did not correlate with clinical failure.
"Although the presence of kdr-type mutations alone may not directly predict clinical failure, their increasing frequency in head louse populations coincides with reports of product failures in controlled studies," Yoon et al wrote in a previous paper on resistance allele frequencies in the U.S. and Canada.
Durand explained that different levels of resistance might also exist, meaning that lice can still die from insecticides even if they have the kdr mutations for resistance. "It is possible that the level of expression of kdr alleles plays a role in the phenotype," he said. So while some genetically resistant lice survive insecticide treatment, partially-resistant lice may just end up suffering a slow and painful death. While the idea of torturing the tiny pests to death might seem appealing to the frustrated, vengeful patient battling an itchy lice infestation, these partially resistant lice do more harm than good.
"If you've got some resistance and they don't die immediately, the population will continue to select for those that have some resistance until the whole population is resistant," said Rosmarie Kelly, PhD, MPH, an entomologist with the Georgia Department of Public Health. "So it just may be that the pyrethroids do work, and we just need to change the protocols for use," which is something that should be investigated, Kelly added.
When the standard over-the-counter treatments don't work immediately, that does not mean that the lice must be resistant. Though it's possible that the lice may have the genes for resistance, often the problem is actually a failure to follow the treatment instructions, according to Lauren Mutrie, MD, assistant professor of pediatrics and global health at UTHSC. Mutrie said that families often come to her clinic after treating their children with an over-the-counter pediculicide and seeing that symptoms persist, "usually because of inadequate treatment."
Parents of louse-infested children might not leave the insecticide treatments on the child's scalp for enough time, or they may not follow directions to repeat treatment as needed, Yaun said. This can lead to recurring infestations. And overusing the chemicals can be hazardous to a child's health, according to the CDC.
The CDC recommends that parents closely follow instructions on the label for over-the-counter treatment, which should still be a first resort. If the lice persist after two or three treatments, then parents should take their kids to a pediatrician to discuss potential resistance and other FDA-approved options for treatment, like Sklice and Spinosad. The American Academy of Pediatrics (AAP) added these two treatments to their guidelines in April. Lindane, another FDA-approved treatment that is not approved by the AAP, remains controversial due to potential side effects ranging from rashes to seizures.
Yoon, on the other hand, disagrees with the CDC's suggestion regarding pyrethroid-based over-the-counter products. He said that patients "need to go talk to a doctor first before running down to the CVS or Walgreens to buy the over-the-counter product and try it. It may or may not work, and because of the availability it's very possible that you're contributing to the resistance problem."
But doctor visits take time and money, and prescription treatments tend to be far more costly than the standard over-the-counter options. Promoting parental awareness of lice in the classroom and resistance in the community could be a more efficient and cost-effective way to deal with the potential for outbreaks or resistance, Kelly said.
While health care providers should dedicate time to teaching parents and their kids how to treat and prevent lice, they should also make sure the family "understands these instructions and also has the means to eradicate lice from the household," such as money for medications and repeat treatment, or access to hot water to wash linens, Mutrie said.
"Kids are bullied and stigmatized for having lice," she added. "School administrators, teachers, parents and students need empowerment through knowledge and accurate information."
Özgür Kurt, MD, PhD, a professor of parasitology at Acibadem University in Istanbul, said that the social stigma surrounding lice infestations has led to some parents regularly using "anti-lice shampoos or even inappropriate agents such as gas oil on their children's hair" to prevent head lice infestations from occurring in the first place. According to a 1998 JAMA study, products including acetone, bleach, vodka, and WD-40 have also been unsuccessfully used to treat lice.
Such treatments are worse for children's health than the lice -- which pose almost no direct health risks. Violently scratching the scalp may lead to a secondary bacterial infection of the skin, but the lice themselves cause no damage and carry no pathogens.
School nurses deal with lice infestations and outbreaks more than any other health care workers, so educating children about lice is largely their responsibility. They should be able to provide accurate information about the treatment and transmission of lice, but they should also try to reduce the social stigma associated with lice, said Nichole Bobo, RN, director of Nursing Education for the National Association of School Nurses (NASN). Bobo said students are bullied at school, and their families often suffer from feelings of anxiety, frustration, and guilt while struggling to get rid of lice.
"These feelings are often related to the myths and misconceptions about head lice that abound such as: only dirty people get head lice, head lice carry diseases, head lice can jump or fly, you can use home remedies to get rid of head lice," she said.
NASN, CDC, and the AAP all agree that classroom screenings and "no-nit" policies should be discouraged. "School policies should be evidence-based," said Bobo. "Abandon no-nit policies, allow the children to remain in class, and notify parent or caregivers by the end of the school day."
"Discouraging close head-to-head contact between students is an evidence-based strategy, based on knowledge about how head lice are transmitted, that can be used to prevent the spread of head lice," Bobo added. "Providing school-wide information periodically to families about the diagnosis, treatment, and prevention of head lice can be considered a prevention measure."
Regardless of whether lice are resistant to standard pyrethroid treatment, a head lice infestation is no cause for panic. Yaun said that head lice are "the second most common school age infection behind the common cold," and misinformation is the main reason that parents either use treatments incorrectly or become overly concerned.
Kyong Yoon's head lice resistance studies have been supported by: Oystershell Laboratories, a pharmaceutical company that manufactures an insecticide-free lice treatment product called Elimax; Sanofi, a pharmaceutical company that owns Sklice (brand name Ivermectin); the National Institutes of Health, and the National Institute of Allergy and Infectious Diseases.