Crab lice (Pthirus pubis) (also known as crabs or pubic lice and frequently mis-spelled as Phthirus pubis) are parasitic insects notorious for infesting human pubic hair. The species may also live on other areas with hair, including the eyelashes. They feed exclusively on blood. Humans are the only known hosts of this parasite, although a closely related species, Pthirus gorillae, infects gorilla populations.
Classification
Infestation with pubic lice is called phthiriasis pubis, while infestation of eyelashes with pubic lice is called phthiriasis palpebrarum.
Signs and symptoms
The main symptom is itching, usually in the pubic-hair area, resulting from hypersensitivity to louse saliva, which can become stronger over two or more weeks following initial infestation. In some infestations, a characteristic grey-blue or slate coloration appears (maculae caeruleae) at the feeding site, which may last for days.
Transmission
Pubic lice usually infect a new host only by close contact between individuals, usually through sexual intercourse. Parent-to-child infestations are more likely to occur through routes of shared towels, clothing, beds or closets. Adults are more frequently infested than children. As with most sexually transmitted pathogens, they can only survive a short time away from the warmth and humidity of the human body.
Pubic lice are primarily spread through sweat, body fluids. Therefore, all partners with whom the patient has had sexual contact within the previous 30 days should be evaluated and treated, and sexual contact should be avoided until all partners have successfully completed treatment and are thought to be cured. Because of the strong association between the presence of pubic lice and classic sexually transmitted infections (STIs), patients diagnosed with pubic lice should undergo evaluation for other STIs.
Infection in a young child or teenager is not necessarily indicative of sexual abuse, although this possibility should be kept in mind.
Diagnosis
A pubic louse infestation is usually diagnosed by carefully examining pubic hair for nits, nymphs, and adult lice. Lice and nits can be removed either with forceps or by cutting the infested hair with scissors (with the exception of an infestation of the eye area). A magnifying glass or a stereo-microscope can be used for the exact identification. If lice are detected in one family member, the entire family needs to be checked and only those who are infested with living lice should be treated.
Treatment
Crab lice can be treated with permethrin 1% cream rinse and pyrethrins. They can be used for this purpose and are the drugs of choice for pregnant or lactating women. These agents should be applied to the affected areas and washed off after 10 minutes. Shaving off or grooming any hair in the affected areas with a fine-toothed comb is necessary to ensure full removal of the dead lice and nits. Resistance of pubic lice to pyrethroids must be, if at all, very rare. A second treatment after 10 days is recommended. It is also crucial to make sure that all the bed sheets are changed. The sheets used before the first application of the treatment must be put away in a plastic bag, without air and well shut. They should be left alone for 15 days before washing to avoid the reproduction and survival of lice eggs that may have been left on the sheets and lead to reinfestation.
Pubic lice on the eyelashes can be treated with a permethrin formulation by applying the solution to the infested hair with an applicator.
Lindane shampoo (1%), a pediculicide, although banned in more than 50 countries, is approved by the U.S. Food and Drug Administration (FDA) as safe and effective when used as directed for the second-line treatment of pubic lice ("crabs"). While serious side effects have been reported, they are considered to be rare and have almost always resulted from misuse of medication, such as excessive application and oral ingestion. To minimize this risk, Lindane medications are now dispensed in small single-use bottles. The Centers for Disease Control and Prevention (CDC) notes that Lindane should not be used immediately after a bath or shower, and it should not be used by persons who have extensive dermatitis, women who are pregnant or lactating or children aged under two years. The FDA similarly warns against use in patients with a history of uncontrolled seizure disorders and premature infants, and recommends cautious use in infants, children, the elderly, and individuals with other skin conditions (e.g., atopic dermatitis, psoriasis) and in those who weigh less than 110 lbs (50 kg).
Epidemiology
Current worldwide prevalence has been estimated at 2 percent of two human populations, accurate numbers are difficult to acquire, because pubic lice infestations are not considered a reportable condition by many governments, and many cases are self-treated or treated discreetly by personal physicians.
Although any part of the body may be colonized, crab lice favour the hairs of the genital and peri-anal region. Especially in male patients, pubic lice and eggs can also be found in hair on the abdomen and under the armpits as well as on the beard and mustache, while in children they are usually found in eyelashes.