Pediculosis is a disease caused by lice infestations. The three lice species that are parasitic to humans are Pediculus humanus capitis (head louse), Pediculus humanus corporis (body louse), and Pthirus pubis (crab louse). Louse infestations affect hundreds of millions of people worldwide each year, and are spread most commonly by close person-to-person contact. They have been reported in all countries and all levels of society. While head and pubic lice do not have an association with disease transmission, body lice can transmit typhus and louse-borne relapsing fever.
Life cycle of lice consists of egg, nymph stage, and adult. Eggs, also known as nits, are yellowish and may be cemented to the hair shafts in head louse. The nymph, an immature louse, hatches from the egg in about 8 days, and as the adult form, is an obligate blood feeder. Lice have six legs, are tan to grayish-white, 2.5 to 3.5 cm in length, have no wings, and are flat in shape. Pubic lice are smaller than head or body lice, measuring around 1 to 2 mm in length. They have six legs with two large front legs which resemble the pinchers of a crab. Lice are unable to jump or fly, and transmission is thought to occur by head-to-head contact, sharing of headgear, or other direct contacts with fomites (inanimate objects that harbor the organism such as seats). It is also common for several members of the same household to be affected. Infestations are more common in the warmer months, as well as in areas with higher humidity.
In general, it may take 2 to 6 weeks to develop symptoms after the first exposure, while pruritus can develop after 1 or 2 days after exposure to lice. Head lice occur most frequently in younger children in daycare or elementary school and typically present on the head, eyebrows, and eyelashes. Common symptoms of head lice infestation include a sensation of something moving in the hair, itching, or the visualization of nits or lice. Diagnosis is by identification of nits, nymphs or the adult louse on the scalp or hair. Unlike head and pubic lice, body lice do not live on the skin but rather live and lay their eggs in seams of clothing or bedding. Body lice usually spread by direct contact but can also be transmitted through clothing, bed linens and towels. Patients typically present with itching, leading to scratching that can lead to secondary bacterial infection.Skin lesions may be found in areas covered by clothing such the axilla, trunk, and groin.The diagnosis is made clinically and is confirmed by visualization of at least one louse on visual inspection. Presence of body lice should be considered in patients with pruritis who live in crowded conditions or have evidence of poor hygiene.
The distribution of pubic lice is generally limited to areas where the hair is short, such as pubic hair, but may occasionally be found on eyelashes, eyebrows, and axillary and beard hair. As with head lice, pubic lice have an egg, nymph and adult form. Transmission is usually through sexual contact, so infestations are most frequently found in adults. If pubic lice are found, clinicians should consider evaluating for the presence of other sexually transmitted infections.
When lice are found in one member of a family, all other family members in contact should also be examined for evidence of infestation. Multiple topical pediculicides are considered first-line treatments for lice infestation. These include pyrethroids, malathion, lindane, benzyl alcohol, and ivermectin. It is important to recognize that available treatments kill lice but do not reliably destroy eggs. Repeated treatment 7 to 10 days after the initial treatment is sometimes required for complete eradication. Body lice may also be eradicated through proper hygiene and laundering or application of insecticide to affected clothing. Because lice can be present on inanimate fomites, heating infested clothing and bedding with hot water is necessary to destroy all stages of lice.
References:
Bragg BN, Simon LV. Pediculosis Humanis (Lice, Capitis, Pubis) [updated 31 January 2019]. Treasure Island, FL, StatPearls Publishing; 2019. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470343/.
Burgess IF, Silverston P. Head lice. BMJ Clin Evid. 2015;2015.
Dagrosa AT, Elston DM. What’s eating you? head lice (Pediculus humanus capitis). Cutis. 2017;100(6):389-92.
Steen CJ, Carbonaro PA, Schwartz RA. Arthropods in dermatology. J Am Acad Dermatol. 2004;50(6):819-42, quiz 42-4.
