Integumentary system ORGAN SYSTEMS


Pediculosis is an infestation of lice (blood-feeding ectoparasitic insects of the order Phthiraptera).

Before we begin:

Pediculosis is an infestation of lice (blood-feeding ectoparasitic insects of the order Phthiraptera).


  • Pediculosis capitis (Head lice infestation)
  • Pediculosis corporis (Pediculosis vestimenti, Vagabond’s disease)
  • Pediculosis pubis (Crabs)


Life cycle:

Diagrammatic representation of life cycle of head louse | Dermatology [Bolognia JL, Jorizzo JL, Rapini RP. (editors)], 2nd edition, Meinking TL, Burkhart CN, Burkhart CG, Elgart G, Infestations, page-1295, ©Elsevier (2008)

Pediculosis capitis (Head lice infestation):

Pediculus humanus var capitis AKA head louse | Centers for Disease Control and Prevention’s Public Health Image Library (PHIL) #377 Public Domain,

Pediculosis corporis (Pediculosis vestimenti, Vagabond’s disease):

Image of body lice. CDC image – public domain

Pediculosis pubis (Crabs):

Adult pubic lice are 1.1–1.8 mm in length. Pubic lice typically are found attached to hair in the pubic area but sometimes are found on coarse hair elsewhere on the body (for example, eyebrows, eyelashes, beard, mustache, chest, armpits, etc.). Pubic lice infestations (pthiriasis) are usually spread through sexual contact. Dogs, cats, and other pets do not play a role in the transmission of human lice. | Centers for Disease Control and Prevention:, Public Domain,

Clinical features


Pediculosis in the head of a 6-year-old boy caused by the crab louse, as confirmed by optical (c) and electron microscopy (d) | a. There were some small pieces of erythema (in the circle) and a brown dot-like substance on the scalp (arrow). b. The dermoscopy revealed a brown parasite (0.9 mm in horizontal axes and 1.2 mm in vertical axes) with two crab-like feet adhered to the scalp. c. Under the microscope, the parasite was characterized by a flat body like a crab and three pairs of feet in different sizes. There was an area (red box) full of blood in the middle part of the parasite. A large number of short setae (arrow) were noted at the edge of the parasite abdomen. d. The SEM showed a vivid three-dimensional ultrastructure of the parasite: the whole body was composed of three parts including spherical head, chest, and elliptical abdomen; a pair of feelers was noted on the head; the three pairs of feet were in shaped section and curved serrated claws were noted at the end of foot; short setae in different length were not only at the edge of the abdomen but also on the feet. | Ran Yuping et al. – , CC BY-SA 3.0,

Differential diagnosis:

  • Dandruff (pityriasis sicca)
  • Impetigo
  • Seborrhoeic dermatitis
  • White piedra, black piedra
  • Monilethrix, pseudomonilethrix
  • Pili torti
  • Psocids (book lice)


Non-pharmacological management:

A few historical methods to get rid of lice. (a) Detecting lice or nits by direct visual examination; (b) wooden comb found at Ein Rachel (Negev Desert) (100 BC–200 AD) containing 10 head lice and 5 nits; (c) modern fine plastic comb. | Sangaré, A. K., Doumbo, O. K., & Raoult, D. (2016). Management and Treatment of Human Lice. BioMed Research International, 2016, 8962685.

Pharmacological management (ovicides):

Local treatment suffices for all but exceptional cases of head lice infestation. Many head lice are resistant to pyrethroids. Good results without the development of resistance are achieved with dimethicones.
  • > 95% ovicidal:
    • Long contact (overnight application):
      • Malathion 0.5% lotion
      • Occlusive agents:
        • Crotamiton 10%
        • Dimethicone 4%
    • Short term (10-30 mins):
      • Malathion 0.5% gel
      • Spinosad 0.9% suspension
  • 70% ovicidal:
    • Short contact (10 mins):
      • Permethrin 1% lotion
      • Benzyl alcohol 5%
Treatment for head lice Course over time of therapeutic interventions in the life cycle of the head louse: Unless an ovicide is used, the treatment must be repeated on day 8 (day 1 = first day of treatment) so as to eliminate the nymphs that were protected inside eggs at the time of the first treatment before they are sexually mature and can lay new eggs. Studies have shown that after egg lay some nymphs may hatch later, after 13 days. In the worst case, therefore, nymphs that survived the first repeat treatment undamaged inside the egg may not hatch until the 13th day. The only way to eliminate these would be a third treatment on day 15. Ovicides, on the other hand, only need to be applied once. | Meister, L., & Ochsendorf, F. (2016). Head Lice. Deutsches Arzteblatt International, 113(45), 763–772.

Before we finish:

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