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BIOLOGY AND CONTROL OF HUMAN LICE

By: Michael Waldvogel and Charles Apperson, Extension Entomology
Insect Note - ENT/rsc-7

Introduction
head louseiLice have been associated with people throughout written history. Outbreaks are most often associated with disasters or crowded and unsanitary conditions when people cannot bathe or wash their clothing regularly. However, we also know that human lice are not restricted to any particular socioeconomic level in our communities 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 likely go unreported because people consult their private physician for treatment.

Life Cycle
Lice are small (<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. Our concern is for three species of human lice, whose common names indicate their preferred feeding site.

Head Lice (Pediculus humanus capitis)

Head lice (image at top of page) live on the skin among the hairs on people's head. 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 about 5-10 days and the light-colored nymphs begin feeding immediately. Development takes about 18-20 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 do not survive off of a person for more than about 24 hours.

Head lice are not known to transmit any disease organisms. However, their feeding activity irritates the scalp, causing intense itching, and a secondary infection may result if the skin is broken by repeatedly scratching the area. 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 (e.g., sharing hats, combs and brushes) creates opportunities for the lice to be spread among them. 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. Parents should notify the school principal or nurse immediately if their child is identified as having head lice. Don't be embarrassed by the problem and hesitate about calling the school. Remember two very important points. First, just because your child has head lice does not necessarily mean that he/she is the source of the problem. Second, and most importantly, 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.

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 low: about 5-10. 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 their head over a light-colored towel or piece of cardboard, then brush their hair and scalp vigorously towards the towel. Dislodged lice should be visible on the towel. Once a louse infestation is confirmed, you should take the appropriate control measures.

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 (Pediculus humanus corporis)
Body lice look virtually identical to 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 9-10 eggs per day, and a total of 270-300 eggs over her lifetime. The eggs are incubated by the person's body heat and hatch in about one week. Temperatures above 100oF or below 75o F. reduce or completely stop egg hatch. Development time (egg to adult) is about 3-5 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 24-48 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.

Pubic Lice (Phthirus pubis)
Pubic or crab 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 3-4 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 same 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 1/3 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.

SUMMARY
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.


For additional information, we recommend that you consult the National Pediculosis Association.



References used in preparing this publication:
Goddard, J. 1993. Physicians Guide to Arthropods of Medical Importance. CRC Press, Boca Raton, FL.

Image of louse: Department of Entomology, University of Nebraska

Pest information and control recommendations presented here were developed for North Carolina and may not be appropriate for other states or regions. Any recommendations for the use of chemicals are included solely as a convenience to the reader and do not imply that insecticides are necessarily the sole or most appropriate method of control. Any mention of brand names or listing of commercial products or services in the publication does not imply endorsements by North Carolina Cooperative Extension nor discrimination against similar products or services. All recommendations for pesticide use were legal at the time of publication, but the status of pesticide registrations and use patterns are subject to change by actions of state and federal regulatory agencies. Individuals who use chemicals are responsible for using these products according to the regulations in their state and to the guidelines on the product label. Before applying any chemical, always obtain current information about its use and read the product label carefully. For assistance, contact the Cooperative Extension Center in your county.

Distributed in furtherance of the acts of Congress of May 8 and June 30, 1914. North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, or disability. In addition, the two Universities welcome all persons without regard to sexual orientation. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.




Last updated - May 2003

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