Pediculosis Pubis

Pediculosis pubis, also known as crabs, pubic lice, or phthiriasis, is an infestation by the pubic louse, Pthirus pubis. This wingless insect feeds on blood and lays its eggs (nits) primarily on pubic hair but can also infest hair near the anus, armpits, beard, eyebrows, moustache, and eyelashes. The condition is usually transmitted during sexual contact but can also spread via bedding, clothing, and towels, particularly in crowded living conditions.

Signs and Symptoms

The primary symptom of pediculosis pubis is an intense itch in the pubic area and groin, especially at night. This itch results from an allergic reaction to the saliva of the feeding lice. About three weeks after the initial infestation, affected individuals may notice grey-blue discolouration at the feeding sites, known as maculae caeruleae. Visible nits and live lice may be seen crawling on the skin, and black powder-like louse droppings may be found in the underwear.

Additional signs include scratch marks, crusting, scarring, and sometimes blood-stained underwear. Secondary bacterial infections, such as impetigo, conjunctivitis, and blepharitis, may occur due to persistent scratching. In some cases, large lymph nodes in the groin and armpits might be felt. Notably, some individuals with pubic lice infestation may remain asymptomatic.

Causes

Pubic lice are primarily spread through vaginal, oral, anal, or manual sexual contact, regardless of condom use. One sexual encounter with an infected person carries a high risk of transmission. Less commonly, lice can spread through close personal contact such as kissing and hugging, or through contaminated bedding, clothing, and towels. In children, infestation of the eyebrows or eyelashes may indicate sexual exposure or abuse.

Diagnosis

Diagnosis of pediculosis pubis involves careful inspection of the pubic hair for nits, young lice, and adult lice. A magnifying glass, dermatoscope, or stereo-microscope can aid identification. Lice and nits can be removed with forceps or by trimming the infested hair, except in cases of eye infestation. Testing for other sexually transmitted infections (STIs) is recommended as there is a strong association between pubic lice and STIs.

Treatment

First Line

Treatment for pubic lice typically involves over-the-counter topical permethrin 1% cream. This is applied to the affected areas and washed off after 10 minutes. Alternative treatments include pyrethrins combined with piperonyl butoxide, and brands like Licide, A-200, Pronto, and RID shampoos. Both treatments may need to be repeated after seven to ten days to kill newly hatched lice.

Other Treatments

In some non-European countries, lindane shampoo is used, although it has been withdrawn by the European Medicines Agency due to safety concerns. Carbaryl, another treatment, has limited use due to its potential carcinogenicity. Sexual partners should be evaluated and treated, and sexual contact should be avoided until all partners are cleared of infestation. For eye infestations, lice can be removed with forceps or by trimming the lashes, and petroleum jelly may be applied to the eyelashes.

Epidemiology

Pediculosis pubis occurs globally across all ethnic groups and social levels. Approximately 2% of the population is affected worldwide. Accurate statistics are challenging to obtain due to the discreet nature of self-treatment and the non-reportable status of the condition in many regions. The trend of pubic hair removal may have reduced the incidence of pubic lice in some areas by eliminating their natural habitat.

Etymology

The term phthiriasis or phthiriasis pubis is used to describe infestation with pubic lice, while phthiriasis palpebrarum refers to infestation of the eyelashes. The pubic louse was first described by Linnaeus in 1758 as Pediculus pubis, with the current name Pthirus pubis officially adopted in 1958.

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Self-assessment MCQs (single best answer)

What is the primary symptom of pediculosis pubis?

What causes the itching associated with pediculosis pubis?

Which of the following is NOT a common site of infestation by pubic lice?

What is the primary mode of transmission for pubic lice?

Which medication is commonly used as a first-line treatment for pubic lice?

What should be done if pubic lice are found on the eyelashes?

What is the scientific name of the pubic louse?

What is the recommended course of action for sexual partners of individuals with pubic lice?

Which of the following is a potential secondary condition resulting from persistent scratching due to pubic lice?

What is the term used to describe infestation with pubic lice on the eyelashes?