BIOLOGY AND CONTROL OF HUMAN LICE
By: Michael Waldvogel and Charles Apperson, Extension Entomology
|Insect Note - ENT/rsc-7|
Lice have been associated with people throughout written history. Outbreaks are most often associated with disasters or crowded and/or 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 hundred 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.
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 on their host. Head lice can infest clothing and other items that come in contact with the head (e.g., hats, shirt collars, barrettes, 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 and middle 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
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. For that reason, a "no-nit" policy can be unproductive because children may be kept out of school unnecessarily due to misidentification. 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:
Body Lice (Pediculus
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. 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 (Phthirus
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. 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, we strongly recommend that infested persons first seek advice from their personal physician. 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 are they recommended.
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.
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