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Causal Agent:

Phthirus pubis, the pubic or crab louse, is an insect of the order Psocodea and is an ectoparasite whose only host are humans.

Life Cycle:

Pubic lice (Phthirus pubis) have three stages: egg, nymph and adult. Eggs (nits) are laid on a hair shaft The number 1. 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 (The number 2, The number 3, The number 4) before becoming adults The number 5. Adults are 1.5–2.0 mm long and flattened. They are much broader in comparison to head and body lice. Adults 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.

Life cycle image and information courtesy of DPDx.

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  • Page last reviewed: September 2, 2015
  • Page last updated: September 2, 2015 The U.S. Government's Official Web PortalDepartment of Health and Human Services
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