Pubic Lice (Crabs) Facts on Transmission, Life Span, Infestation

What are Pubic or Crab Lice?

Pubic lice or crab lice infestation  is caused by the insect Phthiriasis pubis which clings to the pubic hairs. Pubic lice infestation is also known as phthiriasis or pediculosis pubis. The common term is crabs. Pubic lice are parasitic insects which differ in appearance from head lice and body lice. It looks like tiny crabs, hence the name “crab lice”.

The lice have 3 pairs of legs, the middle and hind legs are stout, while the front pair is large and looks like the claws of a crab. The claws help the louse to cling onto clothing or to the coarse pubic hairs. While the l usually infest the pubic hair,  it may also be found on the eyebrows, eyelashes, armpits, chest hair, and facial hair. In rare cases, the scalp hair may be involved. While African-Americans are rarely affected by a head lice infestation, they are just as prone as any other race group to pubic lice infesting the scalp hair.

The lice feed on human blood and remain fixed at its feeding sites for long periods. It is not as fast-moving as head lice.

Picture of a crab louse from Wikimedia Commons

Pubic Lice Transmission

Pubic lice are usually sexually transmitted. For this reason, pubic lice on a child may be a sign of sexual abuse. Rarely, it may spread by close personal contact or by sharing of clothes, towels, and other personal effects. Infestation does not occur via toilet seats and condoms cannot protect from pubic lice. Pubic lice are not spread by animals and they are not disease carriers.

Lice Life Span

The life span of pubic lice is about a month. There are 3 stages in their life cycle – eggs (nits), nymphs, and adult lice. Each female louse lays less than 30 eggs, which hatch in about 7 to 8 days to release the nymphs. The nymphs look like adult lice but are smaller in size. It molts over 2 to 3 weeks and after their third molt, it becomes and adult louse.

Symptoms of Pubic Lice

  • Itching in the genital area is one of the more prominent symptoms. It may also extend to the thighs and  area around the anus (perianal) or occur in the armpits and even other areas. The itching seems to be more intense at night (nocturnal).
  • Skin lesions include sores in the genital area and sometimes a bluish-gray bruise-like marks on the body (maculae cerulea) where the lice have fed.
  • Secondary infections, usually bacterial, may develop in the area.
  • There may be signs of other sexually transmitted diseases (STDs).
  • Eyelid infestation may occur, known as Phthiriasis palbebrarum, which may be misdiagnosed as lid eczema and blepharitis (inflammation of the eyelash follicles along the edge of the eyelid).

Treatment of Pubic Lice

Most OTC and prescription medication that are used in the treatment of head lice, may also be used for pubic lice . This includes lotions, creams, mousse or special bath washes containing the following :

  • permethrin
  • pyrethrin
  • malathion
  • lindane
  • benzyl alcohol

Treatment may need to be repeated after 7 to 10 days in persistent cases of pubic lice. Rarely, oral ivermectin may be given. Antihistamines may be prescribed for relief from itching.

Prevention and Conservative Management

  • A person should avoid further sexual contact during treatment.
  • Sexual partners should be treated where necessary.
  • Special care should be taken for treatment of lice and nits on the eyelashes and eyebrows.
  • Evaluation for other STDs.
  • Wash all clothing, bed linen, towels, and other articles with hot water.
  • Store items in tightly sealed plastic bags for 2 weeks can kill the lice.
  • Shaving of pubic hairs or hair on other parts of the body may be advisable.

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