The most common parasites that infect humans are lice (Pediculus) and mites (Scabies). These are transmitted by personal contact, including sexual contact. Pubic lice (Phthirus pubis, or the crab louse) infestation is most common in adolescents and young adults. It is an infestation of hair-bearing areas, especially the groin. Though it is usually spread by sexual contact, lice can be spread by contact with contaminated items and clothing, such as towels.

An adult louse gets onto the skin and lays eggs. 6 to 10 days later, the eggs hatch releasing baby lice (nymphs) that grow into adults and multiply again (usually within 15 days). Both nymphs and adult lice feed on human blood.

Common Signs & Symptoms
Intense itchiness at the infected area (usually the groin, anus, and abdomen areas) is the most common symptom. Often the itchiness is worse at night. Small red or bluish irritations of the skin are often seen. Crab eggs (nits) attach to hair and appear as tiny white-grey specks. Sometimes the crab louse can be seen moving within the pubic hair. Public lice can also infect other hairy areas (eyelashes, etc). The photograph (below right) shows irritated and inflamed skin caused by crab lice bites. Closer examination would show nits (eggs) on his pubic hair. The other photo shows a crab louse (arrow). Click on the images to see it more clearly.

How’s it Diagnosed?
Diagnosis is made by observing either the characteristic shape of the louse or nits (eggs).

How’s it Treated?
Treatment is with anti-parasite medication (e.g., Lindane or Permethrin). Re-treatment may sometimes be necessary if symptoms continue or recur. It is crucial that all bedding and clothing be decontaminated with hot-water machine washing (or dry cleaning) or else reinfection will occur.

How do I avoid Getting It (Prevention)?
Avoiding contact with infected individuals is how one avoids this uncomfortable infection. Even correct and consistent condom use does not prevent crab infection because infected pubic hair and skin come into contact with one’s partners pubic hair and skin.

Additional Information
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