Pubic lice

Organism

The crab louse Phthirus pubis is transmitted by close body contact. The incubation period is usually between five days and six weeks, although some people have a prolonged period of infestation before symptoms appear.

Adult lice infest pubic hairs, body hair in men, and rarely, eyebrows, eyelashes, beards and moustaches. They are not found on head hair. The lice lay eggs (nits) which adhere firmly to the hair shaft. The louse is most commonly found below the waist.

The life cycle of the crab louse is 15 days and the period of infectivity is as long as the lice or eggs remain alive. Contact infectivity is high.

Clinical presentation

Symptoms

There may be no early symptoms, or there may be an itch due to hypersensitivity, producing a macular rash in the hairy areas.

Sometimes fine gritty debris from the lice is seen on the underwear.

Signs

There are signs of pale brown lice and pale small, oval nits adherent to the hairs.

Blue macules (maculae caeruleae) may be visible at the feeding sites.

STI Atlas (external site)

Investigations

This is based on finding lice and/or nits in the hair.

Examination of the nits or lice confirms the diagnosis. Often it is impossible to remove the louse without crushing it, so it is better to cut the hair for examination under the microscope.

A full screen for other STIs should be conducted, as often, other concurrent diseases are present.

Treatment

Lotions: The patient should be advised to wash all over with soap and water in the evening and dry well. Apply the lotion and leave on overnight, and wash off in the morning.
Shampoos: These are usually applied to the hairy areas and left on for 10 minutes before being washed off in the shower.
The application should be reapplied again in a week to kill any newly hatched lice.
Patients should be advised to avoid close body contact until they and their partners have completed treatment and follow-up.
Patients should be advised that dead nits may remain adherent to the hairs and do not imply treatment failure. These may be removed with a fine-toothed comb.
Usually advice is also given to wash all currently used underwear and night clothes.

Standard

Treatment should be repeated after one week.

Permethrin 5 per cent cream – apply and leave on overnight, and wash off in the morning.
Pyrethrin or Permethrin shampoo – apply and wash out after 10 minutes.
Maldison 0.5 per cent lotion – apply and leave on overnight, and wash off in the morning.
Petroleum jelly can be used for eyelash infestation twice daily for seven days. The lice can subsequently be removed from eyelashes and eyebrows with tweezers or forceps.

Allergic

Avoid treatments to which there is a known sensitivity.

Pregnancy

Permethrin (category B2) is safe during pregnancy or breastfeeding.
Avoid maldason in pregnancy.
Australian categorisation system for prescribing medicines in pregnancy (external site).