Lice primarily attach to clothing and hair shafts, then transfer to the skin for blood feeds. Females lay eggs that hatch 6 to 10 days later, subsequently maturing into adults. The lifespan of these parasites with regular access to a host is 1 to 3 months for head lice and 18 days for body lice vs only 3 to 5 days without a host.28 Transmission of P humanus capitis primarily occurs via direct contact with affected individuals, either head-to-head contact or sharing of items such as brushes and headscarves; P humanus corporis also may be transmitted via direct contact with affected individuals or clothing.
Pediculosis is an important infestation to consider when providing care for refugee populations. Risk factors include lack of access to basic hygiene, including regular bathing or laundering of clothing, and crowded conditions that make direct person-to-person contact with affected individuals more likely.29 Body lice are associated more often with domestic turbulence and displaced populations30 in comparison to head lice, which have broad demographic variables, most often affecting females and children.28 Fatty acids in adult male sebum make the scalp less hospitable to lice.
Presentation—The most common clinical manifestation of pediculosis is pruritus. Cutaneous findings can include papules, wheals, or hemorrhagic puncta secondary to the louse bite. Due to the Tyndall effect of deep hemosiderin pigment, blue-grey macules termed maculae ceruleae (Figure 3) also may be present in chronic infestations of pediculosis pubis, in contrast to pediculosis capitis or corporis.31 Body louse infestation is associated with a general pruritus concentrated on the neck, shoulders, and waist—areas where clothing makes the most direct contact. Lesions may be visible and include eczematous patches with excoriation and possible secondary bacterial infection. Chronic infestation may exhibit lichenification or hyperpigmentation in associated areas. Head lice most often manifest with localized scalp pruritus and associated excoriation and cervical or occipital lymphadenopathy.32
FIGURE 3. Maculae ceruleae—blue-grey macules—may be present on the skin secondary to Pediculosis infestation.
Diagnosis—The diagnosis of pediculosis is clinical, with confirmation requiring direct examination of the insect or nits (the egg case of the parasite)(Figure 4). Body lice and associated nits can be visualized on clothing seams near areas of highest body temperature, particularly the waistband. Head lice may be visualized crawling on hair shafts or on a louse comb. Nits are firmly attached to hair shafts and are visible to the naked eye, whereas pseudonits slide freely along the hair shaft and are not a manifestation of louse infestation (Figure 5).31
FIGURE 4. Pediculosis nits—the egg cases of the parasite—may firmly attach to the hair shaft.
Treatment—Treatment varies by affected area. Pediculosis corporis may be treated with permethrin cream 5% applied to the entire body and left on for 8 to 10 hours, but this may not be necessary if facilities are available to wash and dry clothing.33 The use of oral ivermectin and permethrin-impregnated underwear both have been proposed.34,35 Treatment of pediculosis capitis may be accomplished with a variety of topical pediculicides including permethrin, pyrethrum with piperonyl butoxide, dimethicone, malathion, benzyl alcohol, spinosad, and topical ivermectin.22 Topical corticosteroids or emollients may be employed for residual pruritus.
FIGURE 5. The pseudonit closely mimics pediculosis nits but consists of keratinized cell casts that are freely dislodged.
Equally important is environmental elimination of infestation. Clothing should be discarded if possible or washed and dried using high heat. If neither approach is possible or appropriate, clothing may be sealed in a plastic bag for 2 weeks or treated with a pediculicide. Nit combing is an important adjunct in the treatment of pediculosis capitis.36 It is important to encourage return to work and/or school immediately after treatment. “No nit” policies are more harmful to education than helpful for prevention of investation.37
Pediculosis corporis may transmit infectious agents including Bartonella quintana, (trench fever, endocarditis, bacillary angiomatosis), Borrelia recurrentis (louse-borne relapsing fever), and Rickettsia prowazekii (epidemic typhus).31,38,39 Additionally, severe pediculosis infestations have the potential to cause chronic blood loss in affected populations. In a study of patients with active pediculosis infestation, mean hemoglobin values were found to be 2.5 g/dL lower than a matched population without infestation.40 It is important to consider pediculosis as a risk for iron-deficiency anemia in populations who are known to lack access to regular medical evaluation.41