School time and that means L.I.C.E.

Head lice are not your typical pests.  For one thing, they largely afflict children. For another, they have very short lives off their host, so are not considered structural pests. Yet PMPs and school IPM coordinators are frequently asked questions or asked to help with head louse infestations.  So I think it's important for the pest control community to know something about these insects, and the latest treatment options.

When my daughter was in second grade she came home from school with head lice. My wife was horrified, but I have to admit I was a little excited.  "My chance to get experience killing head lice," I thought.  But after the third shampoo treatment, and head lice still showing up, it wasn't fun anymore. Perseverance, and lots of time with the louse comb finally got rid of the problem; but it left me with a greater respect for the head louse as a worthy opponent.

With the new school year, we expect new cases of head lice. And according to a new paper delivered at the American Chemical Society and reported this week in Smithsonian.com, this year's head lice are running with a tougher crowd. In the paper by Kyong Sup Yoon, Southern Illinois University-Edwardsville, Texas is among 25 states tested so far and shown to have head louse populations that are resistant to the most commonly used over-the-counter (OTC) head louse shampoo treatments: pyrethrins and permethrin.  In fact, most of the samples tested by Yoon and colleagues (104 out of 109 samples) showed resistance to OTC louse treatments.

If you work with school nurses at a school district, or are asked by customers about lice treatment, or are simply a parent yourself, it pays to be familiar with the latest treatment options for head lice.  After all, these aren't your mother's lice.

First, many lice problems can still be handled with OTC products. Keeping IPM in mind, however, multiple methods (insecticide plus mechanical control in this instance) are always better than one. Louse combs are a great second tool in the parents' tool box.  These fine toothed combs allow hair to pass between the tines, but not lice. Combing should always be done in combination with use of a louse shampoo.

In addition, new treatment options for lice are now available through your doctor.  These products include ivermectin (Sklice®), spinosad (Natroba™), and benzyl alcohol (Ulesfia®).  These products will likely be more expensive, you you might want to try the OTC route + combing first.  But it's always good to have options.  A recent review article by Drs. Cynthia Devore and Gordon Schutze in the journal Pediatrics does a nice job of reviewing these as well as other options for treating children for head lice.

Devore and Gordon also address the current recommendations for how schools should handle control including whether children should be screened, how to manage a child on the day lice are detected, and whether children should be restricted from school (they argue no).  This paper could be an especially useful resource pass on to your school nurse if you work for a school district.

To spray or not to spray

So are environmental sprays needed to help control head lice infestations in a school or home?  One can certainly find pesticides labeled for environmental louse control. Most professionals say no, sprays are not necessary.

Transfer of lice on furniture from one person to another can certainly occur.  I remember a day when my daughter had head lice.  She was reading a book in our living room chair when she got up to go outside.  I started to take her place when I noticed a live and hungry-looking head louse on the chair back where her head had been pressed.

Despite the occasional transfer of lice via furniture or bedding in this way, spraying of such items is not recommended.  Head to head contact, sharing of combs, scarves and hats during play, are far more important means of transmission; and spraying will not help stop these activities. Simple washing of hats, pillowcases and clothing is a safer and more effective means of dis-infesting these items than pesticide sprays.

Keep in mind that these tiny insects have a very short life span once they are off the human head. Head lice are highly sensitive to desiccation, and according to the CDC live no more than 1-2 days off of a host. Any head lice lurking on a bean bag chairs or coat rack in a classroom, therefore, will not survive a weekend in an empty classroom.

So let's leave treatment of head lice to doctors and parents. But let's be ready to offer advice and provide resources for customers and colleagues battling these adaptable pests.  For more information on head lice see our Extension publication on head lice.

A lousy problem

Head lice are well adapted to living in human hair, but are
almost never found living off of the head.

One of the most fascinating sibling rivalries in entomology has to be that of the human louse, Pediculus humanus.

The version of this species of louse that most of us are likely to encounter is the head louse Pediculus humanus capitus (the reason for the extra Latin name in the scientific name is that the head louse is a subspecies of the human louse).  The head louse, as most elementary school teachers know, lives exclusively on the human head--and seems to especially relish grade-school children.

The other subspecies of the human louse is the body louse, Pediculus humanus humanus. The body louse is mostly physically identical to the head louse, but has a distinct feeding preference for the body rather than the head.  Body lice do not venture to the heads of their human hosts; but leave the head region to their slightly leaner, head-inhabiting cousins.  It is thought that the two subspecies parted ways some 100K years ago, when humans began to don clothing on a regular basis.  Today, the body louse thrives only on people who change their clothing infrequently.  This because body lice rely on clothing as a hiding place between blood meals, and frequent changing of clothes and showering tend to eliminate infestations.  In the U.S. today, the main group of persons who maintain body lice infestations are in homeless communities of large cities.  The two lice subspecies do not interbreed in the wild, although when forced, they will breed in the laboratory under the prying eyes of entomologists.

The body louse, while less familiar to affluent Americans today, has played a huge role in human history. Body lice transmit  human typhus, one of the major deadly human diseases.  When Napoleon's half million man army attacked and was defeated by Russia in 1812, it's said that more French soldiers died from typhus than were killed by Russians.  In 18th century England, "gaol fever" (another name for typhus) killed more prisoners than all the public executioners in the British realm.

Lucky for us that the head louse does not seem to transmit typhus or any other human disease. It's no wonder, then, that entomologists and physicians have long wondered why the difference between the two lice.

Newly published research by University of Illinois entomologists, summarized in the ESA's Entomology Today may provide some insight into this question.  DNA analysis suggests that it all comes down to seemingly minor differences in the immune responses between the subspecies.  According to one of the authors, Barry Pittendrigh, head lice have a stronger immune response than body lice.

“Our experiments suggest that the head louse immune system is fairly effective in fighting off the bacteria that cause trench fever" (another louse-transmitted disease), Pittendrigh said. “However, the body lice don’t seem to have as good an immune response.”

While reasons for the body louse's weaker immune response is speculative at this time, part of the explanation may have something to do with bacterial ecology inside the bug. Many bacteria live inside insects, some good and some bad for the host.  Body lice appear to get extra vitamins from their bacteria, consequently they tend to be a little larger than head lice, according to the story. So for body lice, a weaker immune system may be beneficial.  Unfortunately, the weaker immune system also allows bacteria that cause typhus and trench fever and the like to survive.  Why head lice seem to follow a different survival strategy is still a puzzle.

I'll admit that all of this is pretty far removed from the very practical vocation of pest control, but ultimately these sorts of biological questions have implications for why pests are pests--and sometimes how they can be controlled. Bed bugs, for example, harbor a bacterium called Wolbachia, which a lot of researchers are interested in at the moment. Some think that the Wolbachia bacteria may help explain temperature sensitivities of bed bugs, and might hold a key to new control strategies. Similarly, studies of termite gut micro-flora may someday point to better baits or wood protectants.

So the next time you encounter a head louse, wonder a little bit at the long path it's taken to become one of the most successful human parasites.  And be thankful it has a strong immune system.