Contributors: C.S. Apperson, Extension Entomology Specialist; J.R. Baker, Extension Entomology Specialist; L. Garcia, Entomologist-Plant Protection Section, NC Department of Agriculture; M.G. Waldvogel, Extension Entomology Specialist.
Order: Anoplura
Family: Pediculidae
Scientific Name: Pediculus humanus humanus (Body Louse), Pediculus
humanus capitis (Head
louse), Pthirus pubis (Crab Louse)
Three species of lice are parasites of people: head lice, body lice, and pubic lice. Outbreaks are most often associated with disasters, or crowded and unsanitary conditions when people cannot bathe or wash their clothing regularly. However, human lice are not restricted to any particular socioeconomic level and may become a problem in seemingly sanitary environments. Each year in North Carolina, county health departments diagnose several thousand cases of human lice (pediculosis), primarily head lice. This estimate probably represents only the tip of the iceberg, since many cases are probably unreported by people consulting private physicians for treatment. Successful control of louse problems requires communication, cooperation, and a control program that employs sanitation, treatment with pediculicides, and delousing of clothing and other personal articles. The most important point to remember is that solving the problem is more important than finding someone to blame for it.
Open and frank discussion, quick action, and sensitivity to the embarrassment experienced by infested persons is needed by everyone involved.
Biology
Lice are small (less than 1/6 inch long) wingless insects with flattened, elongate bodies and somewhat oval heads. They have a three-stage life cycle (egg, nymph and adult), as shown below. The nymphs molt three times before reaching maturity. In order to survive, lice require temperature and humidity conditions similar to those found associated with human bodies. They dry out rapidly if they are away from people for more than 24 to 36 hours.
Head Lice
Head lice live on the skin among the hairs on people's heads. They glue eggs ("nits") to the base of the hair shaft, frequently behind the ears or on the nape of the neck. Nits hatch in 5 to 10 days, and the light-colored nymphs begin feeding immediately. Development takes 18 to 20 days; adults can live for about one month. Head lice can infest clothing and other items that come in contact with the head (e.g., hats, shirt collars, brushes, combs, etc.), but they cannot survive off of a person for more than 24 to 36 hours. Head lice have little real medical impact. Their feeding activity irritates the scalp, causing intense itching. They are not known to transmit any disease organisms, but a secondary infection may result if the skin is broken by repeated scratching. The most notable impact of head lice is the personal embarrassment experienced with being identified publicly as having lice (e.g., in a classroom).
Children, particularly those of elementary school age, are most likely to get head lice because of their close contact and social interactions with each other. Nursing home residents and other people sharing close quarters and bathing and communal facilities are also likely to get lice. Sharing combs and brushes creates opportunities for the spread of lice. Children who become infested in school will carry lice home and may infest family members who unknowingly become a source for recurring louse problems in the home.
Solving the Problem
Solving head lice problems is not difficult if everyone cooperates. In school situations, principals and nurses should be notified immediately if a child is identified as having head lice. If school officials do not take any action because they are unaware of the problem, lice will likely spread to other children in the class. If the problem continues unchecked, eventually even those children who were treated previously become reinfested and they must be subjected to treatment again.
Policy should encourage parents to report lice and problems should be handled to minimize embarrassment. Any particular child is not necessarily the source of the problem. Parents, school administrators, teachers and other school staff should handle these situations discretely, being sensitive to the children's situation which is difficult enough for them without the problem becoming a matter for public discussion. Children exhibiting symptoms of head lice (excessive head scratching and/or abrasions on the scalp) need to be checked for the presence of nits or lice by someone who can positively identify the eggs or the insects. The whitish-to-cream colored eggs are small (about 1 mm) and oval with a distinct cap. To the unaided eye, nits can easily be confused with dandruff, globules of hair oil or even dried flakes of hairspray. Upon closer examination with a magnifying glass, the eggs are more easily recognized. On average, the actual number of head lice found on a person is as low as 5 to 10. Therefore, careful inspection of the head, particularly along the back of the neck and around the ears is important. Another useful way to check for lice is to have the person hold his or her head over a light-colored towel or piece of cardboard, then brush the hair and scalp vigorously towards the towel. Dislodged lice should be visible on the towel.
Once a louse infestation is confirmed, follow these three steps:
Be persistent and thorough. Because the eggs are literally cemented to the hair shaft, they are not easily dislodged. Contrary to popular belief, using vinegar in a shampoo or as a rinse is not effective because it does not dissolve the glue that binds the nits to the hair shaft. There are also special non-insecticidal rinses that dissolve the glue binding the eggs to the hair. Nits are more easily removed after shampooing/rinsing, when the hair is still damp. Several combing sessions may be needed to remove all of the nits.
Spraying furniture, carpeting and bedding with an insecticide serves no real purpose other than providing some margin of psychological comfort. Although such sprays kill an occasional stray louse, family members who are already being treated with insecticidal shampoos would be exposed unnecessarily to additional pesticides. Spraying insecticides is not recommended except under extraordinary circumstances.
The extent of delousing activities in a school depends largely on the age of the students and the layout of the classroom. As in the home, vacuuming carpeting and/or sleeping mats can help. Mats with vinyl or other non-fabric coverings can be cleaned with hot, soapy water. Clothing or personal items that students leave in closets, storage areas or desks should be removed and cleaned. Application of insecticides in the classroom is not necessary.
Body Lice
Body lice and head lice look identical, but their location on people is a reasonably accurate diagnostic clue. Head lice are found almost exclusively on the scalp, whereas body lice may be found either on the body or clothing. Unlike head lice, body lice attach their eggs to the fibers of undergarments, particularly along inside seams and other areas of close body contact. A female body louse usually deposits about 10 eggs per day, and a total of 270 to 300 eggs over her lifetime. The eggs are incubated by the person's body heat and hatch in about one week. Temperatures above 100 degrees F or below 75 degrees F reduce or completely stop egg hatch. Development time (egg to adult) is 3 to 5 weeks.
Body lice are most common during the winter months, when people tend to wear layers of clothing, creating a warm, moist environment that is ideal for louse development. An important point to note is that body lice spend most of their life on clothing and crawl onto the host to feed for short periods.
Although as many as 1,000 body lice have been removed from heavily infested clothing, ten lice per person is probably more typical. Body louse problems are more likely to occur in situations where the same clothing is worn constantly for several days or weeks. Since body lice can survive away from a person for 24 to 48 hours, they can survive in clothing that is removed nightly but worn again the following day.
Although body lice can transmit certain disease organisms, this problem is generally confined to underdeveloped countries where poor sanitation and overcrowding are major contributing factors.
Feeding activity by the lice causes significant skin irritation, swelling and the formation of red welt-like marks. Severe infestations can lead to allergic reactions and skin disorders, such as impetigo and eczema.
Treatment for body lice is virtually identical to the procedures for head lice. First, the infested person must be treated with pediculicides (lotions or shampoos). As in the case of head lice, body lice move rapidly from person to person upon brief contact or when clothing is shared. Other family members (or classmates) with whom the person comes in contact should be checked and treated if necessary. Clothing, bed linen and other personal items that have been used recently must be deloused as outlined in Step 3 for head lice. Vacuuming mattresses, carpets and uphostlery will help remove stray lice.
Pubic Lice
Crab or pubic lice are usually found on the hairs in the pubic areas; however, they can be found among the coarser hairs of the chest, armpits, eyebrows, eyelashes, moustaches and beards. Unlike body lice, crab lice are dark gray-to-brown in color. The name "crab lice" comes from their flattened, oval crab-like shape. Their second and third pairs of legs have thumb-like projections that aid in grasping the host's hair.
Eggs of pubic lice are dark brown and smaller than those of head and body lice. The female lays about 30 eggs during her 3 to 4 week lifespan, usually on the hairs of the pubic region. Crab lice are more sedentary than body and head lice, and usually pass their entire life cycle in the area where the eggs were deposited.
Crab louse bites produce discrete, round slate-gray-to-bluish colored swellings on the skin. Proteins in the louse's saliva may cause an allergic reaction and intense itching. As with head lice, secondary bacterial infections may result from constant scratching and breaking the skin. Lice infesting the eyelids can cause severe inflammation and swelling around the eyes. Crab lice are not known to transmit disease organisms, but one survey found that one-third of the individuals with crab lice also had a sexually transmitted disease.
Crab lice are spread primarily through sexual contact. It is possible, but extremely rare, that they could be acquired through contact with infested toilet seats, clothing or bedding. As with other louse problems, successful treatment is based on a combination of sanitation and pediculicides. Family members who share a bed with the infested person must be examined and treated if necessary. Undergarments and bed linens should be washed in hot water for at least 20 minutes, then dried on a high setting. Louse control products are available either directly at a drugstore or by prescription; however, advice from a physician should be sought before treatment decisions are made. Because crab lice can only survive off of people for about 24 hours, insecticidal treatments in the home, workplace, school or other areas are neither necessary nor recommended.
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