Lice

Head lice (also called pediculus capitis or pediculosis) and humans have evolved together partly due to the fact that head lice depend totally on humans for their existence and do not occur on any other host species. Preserved head lice have been found in the hair of mummies from Egypt buried 5000 years ago. Head lice are a common problem particularly in environments where people are living in close proximity to each other. Transmission occurs by direct contact with an infested person or indirectly by contact with clothing, personal grooming articles, bedding, or upholstered furniture containing viable nits or lice. Although infection is neither life-threatening nor associated with significant complications, it does cause considerable distress, expense and anxiety to those affected. Head lice infestations affect 6-12 million persons in the United States each year, and this number may be on the increase. In other first world countries the infestation rate is believed to be much the same with 1-2% of the population affected. In second and third world countries the percentage of the population affected may be much higher with some published reports suggesting over 40% of children affected.

Lice are wingless, six-legged insects that cannot jump, fly or swim. The life cycle of the head louse from egg to egg is about 26 days. A mature adult female louse lays four to five eggs a day over her lifetime of 23-30 days (Lane, 1987). The egg case, commonly referred to as a "nit", is firmly attached to the hair shaft with a cement-like biological glue. This provides a protective environment for the developing louse (called a nymph). After a 7-10 day incubation period, the nymph hatches and then develops through three additional nymph stages of 3-4 days each. The adult can start laying eggs from about 2 days after the final moult. Adult females are the largest in size at about 5 mm in length and adult males are about 4 mm in length. The smallest nymph is about 1 mm when it hatches from the egg. Head lice spend most of their life in the hair, not on the scalp, and only come down to the scalp skin to feed. Feeding usually takes about 15 minutes or less and lice feed about three times a day.

Diagnosis is made on the basis of finding nits (i.e., the silvery-white eggs firmly attached to the hair shaft), often concentrated on the crown hair, behind the ears, and at the nape of the neck. Many head lice infections cause no symptoms, and probably less than half cause itch so a lack of itching does not mean there is no lice infestation. Parents of children are recommended to look for nits at regular time intervals even if there is no complaint from the child. The simplest and most effective way to find nits and lice is to apply conditioner (white conditioner is best since the lice and eggs are easier to see) to the hair and then use a fine toothed comb or nit comb. Wipe the conditioner off the fine tooth comb onto a paper tissue and look for lice and eggs. Repeat this exercise several times all over the scalp. The conditioner makes it harder for the lice to hold on to the hair and it makes the hair easier to comb. You might use a normal comb first to remove tangles and then a fine toothed comb or nit comb second.

Social stigma and persistent misconceptions complicate the implementation of appropriate management strategies. Although it is a popular belief, being affected by lice is not an indicator of personal cleanliness. Lice make no significant distinction between dirty and clean hair and can happily live on either. However, the stigma of having lice, or having children with lice, often prevents people from seeking treatment. Failing to inform schools and doctors, and subsequently not receiving treatment, makes the spread of lice and the persistence of an outbreak much more likely. Only with a concerted, joint effort between the affected individuals and their families, and the schools and doctors, can an infestation of lice be successfully stopped. Without a coordinated effort, individuals being treated for lice may become reinfestated from coming into contact with those not being treated.

Lice treatment

Typical commercially available head lice products fall into four groups on the basis of active ingredient: pyrethrins, synthetic pyrethroids (permethrin and bioallethrin), organophosphates (malathion or maldison), and herbal agents. Some studies suggest the head lice in the USA and elsewhere are becoming resistant to some of the medicated shampoos used in treating lice infestations. This makes treatment using medicated shampoos harder as more than one treatment may need to be applied to get rid of the lice. There are few studies that compare the differnt chemical treatment available for effectiveness, but of those published studies malathion containing shampoos were most effective closely followed by pyrethrins.

A complete treatment regime consists of two treatments with a head louse product 7 days apart, the first to kill the adult lice, and the second to kill the juvenile lice hatched from the eggs over the intervening 6 days. No product currently available kills all eggs in one application so retreatment is necessary. Checking for living lice subsequent to treatment is important and if any living lice are observed then it may be the lice are resistant to the treatment originally used. If this is the case treatment with a product containing a different active ingredient is required. In between treatment applications it is a good idea to comb with a louse comb two or three times to keep the number of blood sucking lice to a minimum.

Some reports suggest that the most effective method of removing lice is the nit comb alone. For those who are reluctant to apply chemical insecticide treatments to the skin, or if the lice seem resistant to such chemicals, the nit comb is the only reliable answer. The use of the nit comb every two to three days for several weeks has been found a highly effective, simple, and cheap method of removing infestations.

Lice references

• Canyon DV, Speare R, Muller R. Spatial and kinetic factors for the transfer of head lice (Pediculus capitis) between hairs. J Invest Dermatol. 2002 Sep;119(3):629-31.
• Meinking TL, Serrano L, Hard B, Entzel P, Lemard G, Rivera E, Villar ME. Comparative in vitro pediculicidal efficacy of treatments in a resistant head lice population in the United States. Arch Dermatol. 2002 Feb;138(2):220-4.
• Plastow L, Luthra M, Powell R, Wright J, Russell D, Marshall MN. Head lice infestation: bug busting vs. traditional treatment. J Clin Nurs. 2001 Nov;10(6):775-83.
• Meinking TL, Entzel P, Villar ME, Vicaria M, Lemard GA, Porcelain SL. Comparative efficacy of treatments for pediculosis capitis infestations: update 2000. Arch Dermatol. 2001 Mar;137(3):287-92.
• Hipolito RB, Mallorca FG, Zuniga-Macaraig ZO, Apolinario PC, Wheeler-Sherman J. Head lice infestation: single drug versus combination therapy with one percent permethrin and trimethoprim/sulfamethoxazole. Pediatrics. 2001 Mar;107(3):E30.
• Suleman M, Fatima T. Epidemiology of head lice infestation in school children at Peshawar, Pakistan. J Trop Med Hyg. 1988 Dec;91(6):323-32.
• Bailey AM, Prociv P. Persistent head lice following multiple treatments: evidence for insecticide resistance in Pediculus humanus capitis. Australas J Dermatol. 2000 Nov;41(4):250-4.
• Gratz NG: Human Lice. Their Prevalence, Control and Resistance to Insecticides. A Review 1985-1997. Geneva: World Health Organization, 1997
• Sokoloff F. Identification and management of pediculosis. Nurse Pract. 1994 Aug;19(8):62-4.
• Sexton C, Miller AJ. A comparison of a single occasion treatment of head louse infestation with phenothrin liquid shampoo or a carbaryl lotion. Curr Med Res Opin. 1991;12(7):466-70.
• Awahmukalah DS, Dinga JS, Nchako Njikam J. Pediculosis among urban and rural school children in Kumba, Meme division, south-west Cameroon. Parassitologia. 1988 May-Dec;30(2-3):249-56.
• Lane AT. Scabies and head lice. Pediatr Ann. 1987 Jan;16(1):51-4.
• Brandenburg K, Deinard AS, DiNapoli J, Englender SJ, Orthoefer J, Wagner D. 1% permethrin cream rinse vs 1% lindane shampoo in treating pediculosis capitis. Am J Dis Child. 1986 Sep;140(9):894-6.
• Arene FO, Ukaulor AL. Prevalence of head louse (Pediculus capitis) infestation among inhabitants of the Niger Delta. Trop Med Parasitol. 1985 Sep;36(3):140-2.
• Slonka GF, Fleissner ML, Berlin J, Puleo J, Harrod EK, Schultz MG. An epidemic of pediculosis capitis. J Parasitol. 1977 Apr;63(2):377-83.