Pediculosis pubis

Pediculosis pubis (pubic lice) on the abdomen

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This page is about clinical aspects of the disease.  For microbiologic aspects of the causative organism(s), see Pediculus pubis.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Kiran Singh, M.D. [2]
Synonyms and keywords: Pubic louse infestation; Phthiriasis pubis

Historical Perspective

• Pediculosis pubis was reported in the literature as early as 1946.
• In 1946, Andrew G. Franks describes the use of DDT in the treatment of pediculosis pubis.

Classification

Infestation with pubic lice may be classified according to the site affected into:

• Phthiriasis pubis: infestation of pubic hair with pubic lice
• Phthiriasis palpebrarum: infestation of eyelashes with pubic lice

Pathophysiology

Transmission

Pubic lice are usually acquired by intimate contact between individuals. Parent-to-child infestations are more likely to occur through routes of shared towels, clothing, beds or closets. Adults are more frequently infested than children. As with most sexually transmitted pathogens, they can only survive a short time away from the warmth and humidity of the human body. Infection in a young child is not necessarily indicative of sexual abuse, although this possibility should be kept in mind.

Life Cycle

Pubic lice (Phthirus pubis) have three stages: egg, nymph and adult. Eggs (nits) are laid on a hair shaft. Females will lay approximately 30 eggs during their 3–4 week life span. Eggs hatch after about a week and become nymphs, which look like smaller versions of the adults. The nymphs undergo three molts before becoming adults. Adults are 1.5–2.0 mm long and flattened. They are much broader in comparison to head and body lice. Adult lice are found only on the human host and require human blood to survive. If adults are forced off the host, they will die within 24–48 hours without a blood feeding. Pubic lice are transmitted from person to person most-commonly via sexual contact, although fomites (bedding, clothing) may play a minor role in their transmission.

Pubic Lice life cycle

Macroscopic Characteristics

Pubic lice have three forms: the egg (also called a nit), the nymph, and the adult.

• Nit: Nits are lice eggs. They can be hard to see and are found firmly attached to the hair shaft. They are oval and usually yellow to white.
• Nymph: The nymph is an immature louse that hatches from the nit (egg). A nymph looks like an adult pubic louse but it is smaller. To live, a nymph must feed on blood. It takes 2–3 weeks after hatching to mature into adults capable of reproducing.
• Adult: The adult pubic louse resembles a miniature crab when viewed through a strong magnifying glass. Pubic lice have six legs; their two front legs are very large and look like the pincher claws of a crab. This is how they got the nickname "crabs." Pubic lice are tan to grayish-white in color. Females lay nits and are usually larger than males. To live, lice must feed on blood. If the louse falls off a person, it dies within 1–2 days.