Crab louse: Wikis


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Classification and external resources
ICD-10 B85.
ICD-9 132
DiseasesDB 10028
MedlinePlus 000841
eMedicine emerg/298
MeSH B01.500.131.617.564.159.730
Pubic lice or (street name) Crabs
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Phthiraptera
Suborder: Anoplura
Family: Phtiridae
Genus: Phtirius
Leach, 1815
Species: P. pubis
Binomial name
Phtirius pubis
(L., 1758, originally Pediculus pubis)
Pubic lice in genital area
Pubic lice in abdomen
Pubic lice on eyelashes

The pubic or crab louse, colloquially termed "crabs" or "fullers" (Phtirius pubis, commonly misspelled Phthirus pubis) is a parasitic insect species notorious for infesting human genitals. The species may also live on other areas with hair, including the eyelashes. They feed exclusively on blood. Humans and gorillas are the only known hosts of this parasite.



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.


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.


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. It is dangerous to remove lice or eggs in the eyelashes by plucking or cutting the hairs.

Lindane shampoo (1%), a pediculicide, although banned in more than 50 countries,[1] 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.[2][3] 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.[4] 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).[2]

Clinical information

Current worldwide prevalence is 2–10 percent of human populations.[5] Although any part of the body may be colonized, crab lice favour the hairs of the genital (Fig. 1) and peri-anal region. Especially in male patients, pubic lice and eggs can also be found in hair on the abdomen (Fig. 2) and under the armpits as well as on the beard and mustache, while in children they are usually found in eyelashes (Fig. 3).

Infestation with pubic lice is called Phtiriasis pubis, while infestation of eyelashes with pubic lice is called Phtiriasis palpebrarum.[6] The main symptom is itching, usually in the pubic-hair area. It results from hypersensitivity to louse saliva, and it becomes strong enough two or more weeks following initial infestation. In the majority of infestations a characteristic grey-blue or slate colouration appears (maculae caeruleae) at the feeding site, which may last for days and is also characteristic for the infestation. Pubic lice are primarily spread through sweat and body contact or sexual contact. 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 may indicate sexual abuse.[7][8]

See also


  1. ^ Commission for Environmental Cooperation. North American Regional Action Plan (NARAP) on lindane and other hexachlorocyclohexane (HCH) isomers. November 30, 2006. North American Commission for Environmental Cooperation
  2. ^ a b Lindane shampoo, USP, 1% prescribing information. Updated March 28, 2003.
  3. ^ (FDA). Lindane Post Marketing Safety Review (PDF). Posted 2003.
  4. ^ U.S. Centers for Disease Control and Prevention (CDC). Ectoparasitic infections. Sexually transmitted diseases treatment guidelines. 2006. MMWR Recomm Rep. 2006, August 10;55 (No. RR-11):79-80.
  5. ^ Anderson AL, Chaney E. Pubic Lice (Phtirius pubis): History, biology and treatment vs. knowledge and beliefs of US College students. Int. J. Envirn.Res.Public Health 2009; 6: 592-600
  6. ^ Manjunatha NP, Jayamanne GR, Desai SP, Moss TR, Lalik J, Woodland A. Pediculosis pubis: presentation to ophthalmologist as pthriasis palpebrarum associated with corneal epithelial keratitis. Int. J. STD AIDS 2006; 17: 424-426
  7. ^ Klaus S, Shvil Y, Mumcuoglu KY. Generalized infestation of a 3 1/2-year-old girl with the pubic louse. Pediatr Dermatol. 1994; 11: 26-28.
  8. ^ Varela JA, Otero L, Espinosa E, Sánchez C, Junquera ML, Vázquez F. Phthirus pubis in a sexually transmitted diseases unit: a study of 14 years. Sex. Transm. Dis. 2003; 30: 292-296.

External links

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