Crab louse
Encyclopedia
Crab lice (also known as crabs or pubic lice and frequently mis-spelled as Phthirus pubis) are parasitic
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...

 insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s notorious for infesting human pubic hair
Pubic hair
Pubic hair is hair in the frontal genital area, the crotch, and sometimes at the top of the inside of the legs; these areas form the pubic region....

. The species may also live on other areas with hair, including the eyelash
Eyelash
An eyelash or simply lash is one of the hairs that grow at the edge of the eyelid. Eyelashes protect the eye from debris and perform some of the same function as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object is near...

es. They feed exclusively on blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

. Human
Human
Humans are the only living species in the Homo genus...

s are the only known hosts of this parasite, although a closely related species, Pthirus gorillae
Pthirus gorillae
Pthirus gorillae or gorilla louse is a species of parasitic sucking louse that afflicts gorillas. It is found in the African continent specifically in Rwanda and Democratic Republic of the Congo...

, infects gorilla
Gorilla
Gorillas are the largest extant species of primates. They are ground-dwelling, predominantly herbivorous apes that inhabit the forests of central Africa. Gorillas are divided into two species and either four or five subspecies...

 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 itch
Itch
Itch is a sensation that causes the desire or reflex to scratch. Itch has resisted many attempts to classify it as any one type of sensory experience. Modern science has shown that itch has many similarities to pain, and while both are unpleasant sensory experiences, their behavioral response...

ing, usually in the pubic-hair area, resulting from hypersensitivity
Hypersensitivity
Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized state of the host. The four-group classification...

 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
Sexual intercourse
Sexual intercourse, also known as copulation or coitus, commonly refers to the act in which a male's penis enters a female's vagina for the purposes of sexual pleasure or reproduction. The entities may be of opposite sexes, or they may be hermaphroditic, as is the case with snails...

. 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 nit
Nit
* The egg of a louse* Head lice * A trivial detail; the object of nitpicking* Nit , a unit of luminance equivalent to one candela per square metre...

s, nymphs
Nymph (biology)
In biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis before reaching its adult stage. Unlike a typical larva, a nymph's overall form already resembles that of the adult. In addition, while a nymph moults it never enters a...

, 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
Permethrin
Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to...

 1% cream rinse and pyrethrin
Pyrethrin
The pyrethrins are a pair of natural organic compounds that have potent insecticidal activity. Pyrethrins are neurotoxins that attack the nervous systems of all insects. When present in amounts not fatal to insects, they still appear to have an insect repellent effect. Pyrethrins are gradually...

s. 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
Lindane
Lindane, also known as gamma-hexachlorocyclohexane, , gammaxene, Gammallin and erroneously known as benzene hexachloride , is an organochlorine chemical variant of hexachlorocyclohexane that has been used both as an agricultural insecticide and as a pharmaceutical treatment for lice and...

 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
Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention are a United States federal agency under the Department of Health and Human Services headquartered in Druid Hills, unincorporated DeKalb County, Georgia, in Greater Atlanta...

 (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
Dermatitis
-Etymology:Dermatitis derives from Greek derma "skin" + -itis "inflammation" and genetic disorder.-Terminology:There are several different types of dermatitis. The different kinds usually have in common an allergic reaction to specific allergens. The term may describe eczema, which is also called...

, 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
Psoriasis
Psoriasis is an autoimmune disease that appears on the skin. It occurs when the immune system mistakes the skin cells as a pathogen, and sends out faulty signals that speed up the growth cycle of skin cells. Psoriasis is not contagious. However, psoriasis has been linked to an increased risk of...

) 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 (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).

See also

  • Body louse
    Body louse
    The body louse is a louse which infests humans. The condition of being infested with head lice, body lice, or pubic lice is known as pediculosis.-Origins:...

  • Head louse
    Head louse
    The head louse is an obligate ectoparasite of humans. Head lice are wingless insects spending their entire life on human scalp and feeding exclusively on human blood...

  • Integrated Taxonomic Information System
    Integrated Taxonomic Information System
    The Integrated Taxonomic Information System is a partnership designed to provide consistent and reliable information on the taxonomy of biological species. ITIS was originally formed in 1996 as an interagency group within the U.S...

  • List of cutaneous conditions
  • List of parasites (human)
  • Pediculosis
    Pediculosis
    Pediculosis is an infestation of lice — blood-feeding ectoparasitic insects of the order Phthiraptera. The condition can occur in almost any species of warm-blooded animal , including humans...


External links

  • crab louse on the UF
    University of Florida
    The University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...

     / IFAS
    Institute of Food and Agricultural Sciences
    The University of Florida’s Institute of Food and Agricultural Sciences is a federal-state-county partnership dedicated to developing knowledge in agriculture, human and natural resources, and the life sciences, and enhancing and sustaining the quality of human life by making that information...

    Featured Creatures Web site
  • Edinburgh Royal Infirmary on Pubic Lice
  • Guideline on the Management of Phthirus pubis infestation (UK, 2007)
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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