Crab louse

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Pediculus pubis Linnaeus, 1758

Crab lice (also known as "crabs", Phthirus pubis, Pthirus pubis, and "pubic lice"[1]) are parasitic insects notorious for infesting human genitals. The species may also live on other areas with hair, including the eyelashes. They feed exclusively on blood. Humans are the only known hosts of this parasite, although a closely related species, Pthirus gorillae, infects gorilla populations.[2]



Infestation with pubic lice is called phthiriasis pubis, while infestation of eyelashes with pubic lice is called phthiriasis palpebrarum.[3]

Signs and symptoms

The main symptom is itching, usually in the pubic-hair area, resulting from hypersensitivity to louse saliva, which can become stronger over two or more weeks following initial infestation. In some infestations, a characteristic grey-blue or slate coloration appears (maculae caeruleae) at the feeding site, which may last for days.


Pubic lice usually infect a new host only by close contact between individuals, usually through sexual intercourse. 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.

Pubic lice are primarily spread through sweat, body contact or sexual contact. Therefore, all partners with whom the patient has had sexual contact within the previous 30 days should be evaluated and treated, and sexual contact should be avoided until all partners have successfully completed treatment and are thought to be cured. Because of the strong association between the presence of pubic lice and classic sexually transmitted infections (STIs), patients diagnosed with pubic lice should undergo evaluation for other STIs.

Infection in a young child or teenager is not necessarily indicative of sexual abuse, although this possibility should be kept in mind.[4][5]


A pubic louse infestation is usually diagnosed by carefully examining pubic hair for nits, nymphs, and adult lice. Lice and nits can be removed either with forceps or by cutting the infested hair with scissors (with the exception of an infestation of the eye area). A magnifying glass or a stereo-microscope can be used for the exact identification. If lice are detected in one family member, the entire family needs to be checked and only those who are infested with living lice should be treated.

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