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Pediculosis (Lice)

Key Points

  • Pediculosis, or louse infestation, is a common clinical issue that is of limited morbidity but significant public health concern, especially in school-age children.
  • Humans may be parasitized by three louse types: body lice, head lice, and pubic lice.
  • Because lice live on clothing or hair (scalp, genital hair, or eyelashes), the primary therapeutic strategy is to identify the type of lice and to completely remove or treat the existing lice and eggs.

Introduction

Humans may be parasitized by three louse types: body lice, head lice, and pubic lice. Body lice live in the patient’s clothing, not on the body. They are often found along seam lines of clothing apparel and can also be found in bedding. Head and pubic lice are found on the hair of the scalp and genital area, respectively. Pubic lice may also infest the eyelashes. Though not considered a serious threat to human health, louse infestation is contagious and can become a public health concern, especially when infestations affect school-age children, their caretakers, and household members. It is important to note that the patterns of treatment-resistance especially to over-the-counter products have emerged, and thus the therapeutic strategies have shifted in recent years.

There is limited morbidity associated with lice. The primary concern is a hypersensitivity reaction to components of the louse saliva, which results in pruritus 4-6 weeks following the onset of the infestation. Notably, severe pruritus may result in excoriations with secondary skin infections such as impetigo. Human body (but not head) lice are rarely associated with the spread of relapsing fever (Borrelia recurrentis), epidemic typhus (Rickettsia prowazekii), and trench fever (Bartonella quintana).

Initial Evaluation

The lice, eggs, or nits (empty egg casings) are not always obviously visualized. Important clues include excoriated erythematous papules (shown in this image) or maculae ceruleans (slate-blue macules) on areas of skin that come in contact with the hair.

The eggs of head lice are highly monomorphous ovoid structures that are firmly attached to the hair shaft via a white concretion such that they are challenging to remove. These are typically located close to the scalp (within millimeters) and may camouflage into the hair. The incubation time of head louse eggs ranges from 7-12 days, depending on heat exposure and weather. When empty, these egg casings are referred to as nits and are typically lighter in color and easier to visualize. Important diagnostic considerations are hair shaft casts (circumferential keratinous bands that easily slide up and down the hair shaft), seborrheic dermatitis (loose, greasy scale that is very loosely adherent to hair, if at all), and a superficial fungal infection of the hair shaft. It is important to note that the primary mode of transmission of hair lice is through direct contact with the head of an affected individual, though rarely may also occur through fomites such as hats and hair brushes.

Head louse

[Reproduced with the permission of the University of Nebraska-Lincoln Extension. Managing head lice safely (018). UNL Extension-Lancaster County. http://lancaster.unl.edu/pest/lice/headlice018.shtml. Accessed November 2, 2012.]

Pubic lice may also affect the eyelashes

[Pubic lice on eyelashes. Wikipedia.org. http://en.wikipedia.org/wiki/Pubic_lice. Accessed November 2, 2012.]

Differential diagnosis

Scabies

Tick bite

Bullous arthropod

Papular urticaria

Treatment

First-line therapy: The first-line therapy for pediculosis depends on the type of infestation. In general, removal of the lice and nits from the clothing (body lice) or hair (hair or pubic lice) is the priority of treatment.

Body lice

  • All of the patient’s infested clothing and bedding should be disposed of if possible. The remaining bedding and clothes should be washed in very hot water, dried with heat, and the seams ironed. An alternative strategy would be to seal infested clothing and bedding in an airtight plastic bag for a week.
  • The patient must bathe well with soap and water.
  • Topical anti-lice treatment of the patient is usually not required. The presence of nits on the patient’s hair represents a second lice infestation (head or pubic lice).
  • Topical steroids and oral antihistamines may be required for days to weeks to control the pruritus. If extensive excoriation is noted, the patient should be carefully examined or tested for bacterial superinfection and treated with systemic antibiotics if necessary.
  • Body lice typically occur in persons with limited access to hygiene. These persons may also be at risk for nutritional deficiencies and tuberculosis. Their social situation should be investigated.

Head lice

A common first-line treatment for head lice is to utilize over-the-counter permethrin 1% or pyrethrins, applied directly to the hair and scalp. It is important to note that pyrethrin-resistance is developing and if a first attempt at treatment with pyrethrin fails, it would be prudent-if evidence of louse infestation still clearly exists-to repeat treatment with a distinct class of medications.

  • Permethrin is a synthetic pyrethroid that is less allergenic than pyrethrin (made from chrysanthemum extract). It is available over-the-counter and applied to shampooed, non-conditioned, towel dried hair in a 1% lotion formulation (such as Nix) for 10 minutes, then rinsed. This can be repeated daily for 10 days if active infestation persists, as this medication is not ovicidal (does not kill eggs). It is important to note that many conditioners or conditioning shampoos impair the efficacy of topical permethrin.
  • Pyrethrin can be applied to dry hair in a shampoo or mousse formulation for 10 minutes, then rinsed. Because it is not ovicidal, application must be repeated in 9 days in order to kill newly hatched lice.

Alternate/subsequent steps

  • An alternative treatment schedule for topical benzyl alcohol, permethrin and pyrethrin application is on days 0, 7, and 13 to 15 (total 3 applications) given that they are not ovicidal.
  • Malathion 0.5% (Ovide) is a highly efficacious prescribed medication, killing 100% of mites and 98% of ova in 20 minutes. Application in a well-ventilated space is suggested, as it is a highly flammable product (78% isopropyl alcohol). It should be applied onto dry hair and allowed to dry without use of a hair dryer or other heat supply. If live lice persist, it should be reapplied in 9 days; however, malathion is highly effective after a single application.
  • Benzyl alcohol 5% (Ulesfia) may be used in children over the age of 6 months. This prescribed medication is applied for 10 minutes then repeated 7 days later.
  • Sulfamethoxazole/trimethoprim in appropriate dose for body weight for 2 weeks will kill head lice because it eradicates a symbiotic gastrointestinal bacteria that is essential for survival of the louse. (For adults, this is 1 DS tablet twice daily.) This treatment may be effective in situations in which topical applications have failed or where they are not possible or feasible. In patients allergic to sulfa, trimethoprim alone can be used.
  • Ivermectin (Stromectol), an oral anthelminthic agent, may be given in two doses of 200 micrograms each, separated by 10 days. It should only be used in children who weigh more than 15 kg.
  • Shaving the head will cure head lice. This is rarely necessary, and can be considered, but only if acceptable to the child and parent.

Pitfalls

  • It is advisable that a follow-up evaluation by a physician or other health care provider be routinely scheduled at the end of the treatment period in order to assess for evidence of ongoing louse infestation and decision-making of whether additional or alternative treatments are needed.
  • Head lice can be resistant to lindane, permethrin, and pyrethrin-based agents. If two treatments with any agent are ineffective, lice resistance is confirmed and an alternative agent should be used. Recurrence may also stem from ongoing exposure to a contagious individual or fomite.
  • Removing nits by combing does not add to the efficacy of treatment, as nits are merely egg-casings. Nit removal alone is ineffective in curing headlice. “No Nit” policies enforced by some schools, however, require nit removal for children to return to school.
  • Pyrethrins are a potential contact allergen and should be avoided in individuals with strong sesquiterpene lactone allergy (includes chrysanthemum, feverfew, liverwort, lettuce, artichoke, ragweed, endive, echinacea, daisy, dandelion, magnolia families).
  • Lindane 1% (Kwell) is a prescribed shampoo with partial ovicidal activity. It is considered only for use in individuals who have failed first-line treatments, as it has been associated with neurotoxicity and lowered seizure threshold, especially in individuals who weigh less than 50 kg, are HIV-infected, or take other medications that lower seizure threshold. It is no longer recommended by the American Academy of Pediatrics and has been banned in certain American states.

Pubic lice

  • Permethrin 1% cream (Nix) rinse applied to the affected area and washed off after 10 minutes.
  • For eyelash pediculosis, petrolatum is applied 3-5 times a day for 10 days. As many nits and lice are removed mechanically as possible.
  • Examine and treat all infected contacts.
  • Examine the patient for other sexually transmitted infections.
  • Refer children with pubic lice to Child Protective Services.

Alternate steps

  • Pyrethrins (RID, Triple X, A-200) applied to the affected genital area and washed off after 10 minutes.
  • In cases where topical treatment has failed or is not feasible, weight-dosed oral sulfamethoxazole/trimethoprim given daily for 14 days is effective.

Pitfalls

  • The extent of pubic lice infection is the extent that hair extends from the pubic area. In hairy men, infestation may extend down the legs, up onto the chest, and into the axillae. The whole affected area must be treated. Systemic treatment with sulfamethoxazole/trimethoprim may be considered in these cases.

When to refer to a dermatologist

  • When the diagnosis of pediculosis is not clear.
  • When treatment-resistant pediculosis occurs.
  • For the evaluation and management of a superinfection of pediculosis.

Clinical Case

Case 1

  • 15-year-old healthy female high school student
  • No significant past medical history
  • Review of systems is noncontributory
  • Presents for management of 6 weeks’ history of an intensely pruritic eruption on the scalp and neck
  • Recent history of a louse infestation outbreak on school athletic team
  • Denies recent travel, new cosmetics for hair or skin

Initial evaluation

  • Healthy appearing female teenager
  • Scattered erythematous macules and excoriated papules on the neck; several lice and egg casings are noted in the scalp hair
  • No evidence of superinfection is present
  • Complete skin and hair examination does not reveal additional sites of infestation
  • Diagnosis: head lice
  • Recommend permethrin 1% lotion applied on days 0, 7, and 15 for 10 minutes to clean, non-conditioned, towel-dried hair
  • Topical triamcinolone 0.1% lotion applied b.i.d. to the scalp and posterior neck to alleviate pruritus
  • Follow-up in 9 days

Follow-up evaluation

  • Several lice, eggs, and nits noted, raising concern for permethrin-resistance
  • Malathion 0.5% is prescribed (day 0 and repeat application on day 9)
  • Follow-up in 2 weeks (no evidence of lice infestation is found)

References

Frankowski, BL, Bocchini, JA (2010) Clinical report – Head Lice, Pediatrics, 126: 392-403.