Crab louse

Phthirus Classification and external resources
A magnified crab louse
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
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Insecta Order: Phthiraptera Suborder: Anoplura Family: Pthiridae Genus: Pthirus Leach, 1815 Species: P. pubis
Binomial name
Pthirus pubis (L., 1758, originally Pediculus pubis)

The pubic or crab louse (Phthirus pubis) is a parasitic insect which spends its entire life on human hair and feeds exclusively on blood. Humans are the only known host of this parasite. Humans can also be infested with body lice (Pediculus humanus humanus) and with head lice (Pediculus humanus capitis).

Epidemiology

Pubic lice usually infect a new host only by close contact between individuals, usually through sexual contact. 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 ^[1].

Diagnosis

A pubic louse infestation is usually diagnosed by carefully examining pubic hair for nits, nymphs and adults. Lice and nits could be removed either with forceps or by cutting the infested hair with scissors (with the exception 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.

Clinical Information

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 eye-lashes (Fig. 3). Infestation with pubic lice is called Phthiriasis or Pediculosis pubis, while infestation of eye-lashes with pubic lice is called Phthriasis palpebrarum ^[2]. 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 diseases (STD), patients diagnosed with pubic lice should undergo evaluation for other STDs. Infection in a young child or teenager may indicate sexual abuse.^[3][4]

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, though it does not suffice as treatment on its own. Resistance of pubic lice to pyrethroids must be, if at all, very rare. A second treatment after 10 days is recommended. 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 pediculocide, 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. ^{[5] [6]} 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. ^[7] The FDA similarly warns against use in patients with a history of uncontrolled seizures 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).^[5]

See also

• Lindane
• Head louse
• Body louse

References

External links

• crab louse on the UF / IFAS Featured Creatures Web site
• Edinburgh Royal Infirmary on Pubic Lice
• Medline Plus article
• Lindane Facts
• Guideline on the Management of Phthirus pubis infestation (UK, 2007)
• Genetic Analysis of Lice Supports Direct Contact Between Modern and Archaic Humans