Attention, Head Lice: Resistance Is Futile!

Head lice, pediculus humanis capitis, give us so much to be thankful for.  Purely from a linguistic point of view, they enrich how we describe our human behavior and misadventures. For example, a bad idea is lousy. Being insipid will get you tagged as being a louse, while being absurdly fussy will earn one the mantle of being nitpicky. Conversely, being assiduously thorough, and reviewing a matter with a finetooth comb may be regarded as a virtue.

All that is well and good, but the little suckers-these head lice-continue to be a scourge, and give just about everyone a case of the heebie jeebies. What’s more, head lice are adept at countermeasures, and keep evolving around our attempts to annihilate them.  The stigma that we tend to assign to being infected by lice actually works to their advantage. Families embarrassed or ashamed of finding nits in the hair of their children often keep it secret, and help perpetuate their spread. From folk remedies to off-label uses of pharmaceuticals, head lice challenge us by out-evolving what we humans keep throwing at them (or in most cases, applying to them).  Recently, this epic story of newer and better lice therapies has re-entered the limelight in a couplet of stories that I’ll summarize here.

Like some other famous parasites (see pinworms), humans are the sole host of head lice.  They are a global phenomenon, and affect people of all ages, and of socioeconomic strata, and ethnicity (though they have a harder time with the oval shaped hair shaft of folks of African descent).  In the US alone, some 6-12 million children ages 3-12 years are effected, to the tune of untold lost hours from school, and lost momyears to combing egg casings, called nits, out of hair.  A 2004 estimate placed the direct and indirect cost of head lice infestations at $1 billion.  Scratch, scratch, cha-ching!

Like that famous louse in the Bobbie Burns poem, lice found on the scalp are doing their job: eating, and making babies. Adult head lice are about the size of a grape seed or sesame seed, and move about on their six legs or holding on adroitly to the shafts of hair on our heads.  The head lice found by parents or discovered by school nurses are to be distinguished from other lice species, none of which anyone regards with any fondness. Pubic lice, aka ‘crabs’ live in the coarse hairs of the groin, armpits, or eyebrows. Body lice live on clothing and lay their eggs on what we wear or where we lay, and may in some instances, carry diseases. Chewing lice by distinction, infect animals such as our pets, but can incidentally affect humans.  If you need to take a minute and absently scratch your head here, go right ahead.

Head lice need our warmth to survive. Hence, eggs laid in cases glued to hair called nits, will be found within a millimeter or two of the scalp. Eggs will hatch within a few days, and nits found within a centimeter of the base of a hair shaft suggest an active infection.  Head lice feed on their human host by sucking blood from the skin. For most affected children and adults, they are unaware of being infected. For some, the head lice saliva or feces can cause an itchy, inflammatory reaction we all unconsciously mimic when we talk about the subject.  In the worst cases, some affected children may develop infected sores from scratching so much. Parents may complain more of these kids having trouble sleeping than being aware of the bugs on their children’s heads.

A female louse can lay up to half a dozen eggs a day for her monthlong lifespan.  Contrary to myth, lice cannot jump, fly, pogostick, or jetpack from host to host. Rather, they spread via contact, through direct touch or via shared clothing or bedding. Lice cannot survive off-human for more than a couple of days, then they starve. It is in understanding this life cycle that we have looked historically to treatments, and to stopping these wee beasties in their tracks.

Over the last decade, the standard anti-head lice weapons in the pediatrician’s armamentarium have faltered due to increasing resistance in these hardy parasites. What’s more, lice infections rarely spontaneously resolve—you’ve gotta do something.  Even treated kids can get reinfected by other, undertreated or undiagnosed classmates. Agents such as permethrin that were toxic to lice, with minimal absorption and few side effects in adults and children—had 100% lice-kill in the 1980s.  In some communities now, the resistance to these lotions, creams and rinses approaches 80%, rendering lotions and shampoos less effective. To avoid being just another smelly thing to put on your hair unless these agents must be used more aggressively.

Newer lotions, such as Malathion, have more recently come into use in the US, and have established themselves as a bigger gun, and are a second line of treatment. Even still, in Europe where Malathion has been in use for over a decade, reports of resistance are growing. Consequently, parents are counseled to apply these lice killers more than once, 7-10 days apart.  Round 1 theoretically kills the adult lice with Round 2 finishing off the next generation of hatched young.

How do you know if they are resistant to what you are using? Care providers and parents can bank on this if live lice are seen 2-3 days following a completed round of treatment. For now, the insect permethrins and topical lotions remain the first line of medical treatment.  Nitpicking—while the time honored method of picking nits out of wet hair bit by crunchy bit with the proverbial fine tooth comb—is regarded as a difficult but helpful adjunctive approach. It has not proven effective as the sole means of getting rid of the little buggers.

Historically, a number of anti-head lice remedies have arisen-from the inspired to the clever to the ridiculous-with varied success. While research is limited (especially on children), the effectiveness of herbal shampoos has not been established.  Unfortunately, prolonged water immersion doesn’t do much more than prune the skin, and leaves lice unharmed.  Fads come and go with supposedly newer/better occlusive agents meant to suffocate lice, such as Vaseline, olive oil, butter, or mayonnaise.  These appear to have more of a tendency to make a gooey mess than having a lethal impact on the adult lice or their eggs.  How to make a difficult problem creepier? Investigators have postulated that some lice appear to be killed following application of these household products, only to show their resistance to them via the ‘resurrection effect’; whereby they are crawling about again within minutes to hours. Yikes.

And, these pantry and medicine cabinet approaches seem like a spa appointment compared to other harsher, ill-advised, and potentially hazardous materials, including gasoline, kerosene, and in the polite words of one colleague, ‘dog mess’.  Shaving your head, of course, is the most effective treatment, but in the effete words of one article, it ‘may not have the desired cosmetic consequence.”  Agreed.

Hope springs eternal. One inexpensive option may be the exception. As noted recently in a pithy article in the NYT Well blog, Cetaphil skin cleanser—also marketed as Nuvo—may be a unique exception. The blog cites a compelling 2004 Pediatrics study on some 133 children. The lotion was applied to the hair of head lice infected kids, and blow-dried til it hardened over the hairshafts. After 8 hours and a rinse, the lice do appear to asphyxiate. Pure upside: When repeated weekly for three weeks, the study reported a 95% cure rate, with no apparent side effects. Other authors question if the cure rate is truly that high. Still, the Cetaphil/Nuvo treatment shows promise, and like some of these therapies, it is worth discussing with your children’s care provider.

Newer approaches are coming along. Benzyl alcohol 5% lotion, aka BAL, is another topical lotion recently approved by the FDA. This aromatic stuff works by gumming up the respiratory machinery of the lice. Upside:  BAL can be safely applied to kids over 6 months, and rinsed off in about 10 minutes, to be applied again in a week. Easy! Downside: this lotion can be pricey, it isn’t widely known by all practitioners necessarily, and it may not be covered by insurance. Again, BAL may be a satisfactory second or third line of treatment for the hard to treat cases. Run it by your primary care provider if the lice dare laugh at the first rounds of treatment you try.

Lastly, there is the ‘emerging therapies’ category, and a treatment that may one day join the arrows in our quiver against lice, as a sort of oral nuclear option.  A study of children in the UK, France, and Israel, compared the treatment of topical Malathion lotion to an oral, anti-parasite drug, Ivermectin. Ivermectin won with a 95% vs 85% cure rate for the Malathion. Upside: two oral doses only, taken a week apart. Voila! Downside: Ivermectin is not yet approved in the US for use against lice, and the medication has some significant side effects for some children. So, stay tuned, as other oral agents may come down the pipeline. For kids who’ll take an oral medication, it sure beats sitting for hours, by a sunny window, picking out the nits!

And so, as I write this, someone somewhere is feeling lousy. If we can just sift through the data with a finetooth comb fast enough, maybe we’ll outpace our cleverly evolving head lice ‘friends.’ Perhaps, even, we’ll get a head before they do.

Top photo by Allen Rendell

Middle photo by Paul Pellerito

Cartoon below by me