The pubic or crab louse (Phthirus pubis) is a parasitic insect which spends its entire life on human hair and feeds exclusively on blood. Humans are the only known host of this parasite. Humans can also be infested with body lice (Pediculus humanus humanus) and with head lice (Pediculus humanus capitis)
Although any part of the body may be colonized, crab lice favor the hairs of the genital and peri-anal region. Especially in male patients, pubic lice and eggs can also be found in hair on the abdomen and under the armpits as well as on the beard and mustache, while in children they are usually found in eye-lashes. Infestation with pubic lice is called Phthiriasis or Pediculosis pubis, while infestation of eye-lashes with pubic lice is called Phthriasis palpebrarum. The main symptom is itching, usually in the pubic hair area. It results from hypersensitivity to louse saliva, and it becomes strong enough 2 or more weeks following initial infestation. In the majority of infestations a characteristic grey-blue or slate coloration appears (maculae caeruleae) at the feeding site, which may last for days and is also characteristic for the infestation. Pubic lice are primarily spread through sweat and body odour 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 diseases (STD), patients diagnosed with pubic lice should undergo evaluation for other STDs. Infection in a young child or teenager may indicate sexual abuse
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