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Pubic lice (Crabs)

What are pubic lice (Phthirus Pubis)?

Pubic lice, which resemble crabs through a magnifying glass, are an infestation of the louse Phthirus pubis. Adult pubic lice are about 1.5 to 2 millimeters in length, tan to grayish-white in color, and typically found attached to hair in the pubic area. Occasionally, pubic lice may be found on coarse hair elsewhere on the body such as the eyebrows, chest, or armpits. Pubic lice feed on human blood and have a life cycle similar to head lice. They are most commonly spread through sexual contact, though transfer of live lice through contact with the clothing or bedding of a person with an infestation is possible.

Signs and symptoms

  • Itching in the pubic/genital region
  • Adult lice or lice eggs may be visible on pubic hair

Incubation period

There is no incubation period. An infestation begins with the transfer of a louse or several lice to a new human host. 

Contagious period and spread

  • Pubic lice are most commonly transmitted through sexual contact. Rarely, a shed hair with an attached nit can hatch and start an infestation. Live lice or shed hairs may be present on clothing or bedding that has been used by a person who is infested. 
  • Pubic lice can be spread to others as long as nymphs (immature lice) or adult lice are present.

Public health reporting requirements

  • Cases of pubic lice are not reportable to public health.
  • The possibility of sexual abuse must be considered when infestations occur in prepubescent children. These occurrences must be reported to the appropriate authority.

Control of spread

  • People with pubic lice should be examined by a health care provider and treated for lice.
  • They should also be evaluated for other sexually-transmitted infections. 
  • Sexual contacts should be likewise evaluated and treated. 
  • Parental/guardian consent is not required for minors to be examined and treated.
  • People with pubic lice, or who have signs or symptoms of pubic lice, should avoid sexual activity until after treatment. 
  • General education on STI prevention should be provided to people with an infestation.

Environmental control measures:

  • Launder clothing and bedding of people with infestation in hot water (130o F) and dry them on a high heat setting for at least 40 minutes. Alternately, items may be dry cleaned. 
  • Items that cannot be cleaned can be placed in a plastic bag for two weeks.

Treatment

  • Over-the-counter and prescription treatments are available. People with infestation should consult with a health care provider if they have any questions about which treatment to use. 
  • Follow treatment instructions closely. Nits can survive treatment, so depending on the medication, a second treatment may be needed to kill lice that have hatched from those eggs.
  • If pubic lice are present on the eyebrows or eyelashes, special care must be taken. Follow the product directions for applying treatments, or consult with a health care provider for guidance on product use.
  • Use a nit comb or fingernails to remove nits from the hair.

Exclusion

No exclusions are necessary since STIs require close intimate physical contact for transmission, virtually always of a sexual nature.

Role of teachers, caregivers, and family

  • General education about sexual health and STI prevention is recommended.
  • Infections in prepubescent children and other high-risk individuals must be reported to appropriate authorities to address the possibility of sexual abuse.