Louse infestation is prevalent throughout the world. Phthirus pubis (crab louse) infects the pubic hair shaft and lays eggs at the base of the hair fibers. The louse takes periodic blood meals by piercing the skin with its anterior body part. Pubic lice are generally spread as a sexually transmitted infection (STI) and an infestation warrants further testing of other possible STIs.

The primary symptom of pubic lice is pruritis (itching) although some individuals may be asymptomatic. Pubic lice are generally visible to the eye. The louse infection may spread to other hair bearing areas of the body such as legs, abdomen, chest, and armpits. Eyelash nits are an infestation of pubic lice, not head lice as commonly thought.

Diagnosis is made by demonstration of adult lice and/or nits in the pubic hair. The presence of bruise-like bites or dark specks of louse dung is also diagnostic. Mature lice are about the size of a sesame seed with 3 pairs of legs, wide, crab-like bodies and claws. The nits are smaller in appearance.

A small blood sample may be taken to evaluate the patient for other sexually transmitted infections including HIV, chlamydia, gonorrhea and syphilis.

While being treated for pubic lice it is important that the patient and his/her close contacts are evaluated and treated appropriately. Metal nit combs are effective at removing the nits that are not susceptible to pediculides, a drug that kills adult lice. Louse infestation can be treated with a pediculicide like malathion, permethrin cream, and pyrethrins in an over the counter or prescription strength.