The crab louse or pubic louse (''Pthirus pubis'') is an insect that is an

obligate {{wiktionary, obligate As an adjective, obligate means "by necessity" (antonym ''facultative'') and is used mainly in biology in phrases such as: * Obligate aerobe, an organism that cannot survive without oxygen * Obligate anaerobe, an organism that ...

ectoparasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

of humans, feeding exclusively on blood. The crab louse usually is found in the person's

pubic hair Pubic hair is terminal body hair that is found in the genital area of adolescent and adult humans. The hair is located on and around the sex organs and sometimes at the top of the inside of the thighs. In the pubic region around the pubis bon ...

. Although the louse cannot jump, it can also live in other areas of the body that are covered with coarse hair, such as the perianal area, the entire body (in men), and the

eyelash An eyelash (also called lash) (Latin: ''Cilia'') is one of the hairs that grows at the edge of the eyelids. It grows in one layer on the edge of the upper and lower eyelids. Eyelashes protect the eye from debris, dust, and small particles and p ...

es (in children). Humans are the only known hosts of the crab louse, although a closely related species, ''

Pthirus gorillae ''Pthirus gorillae'' or gorilla louse is a species of parasite, parasitic sucking louse that afflicts gorillas. It is found in the African continent, specifically in Rwanda and Democratic Republic of the Congo. ''P. gorillae'' and ''P. pubis'' (t ...

'', infects gorillas. The human parasite is thought to have diverged from ''Pthirus gorillae'' approximately 3.3 million years ago. It is more distantly related to the genus ''Pediculus'', which contains the human

head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may ...

and body lice and lice that affect

chimpanzee The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...

s and

bonobo The bonobo (; ''Pan paniscus''), also historically called the pygmy chimpanzee and less often the dwarf chimpanzee or gracile chimpanzee, is an endangered great ape and one of the two species making up the genus '' Pan,'' the other being the comm ...

Description

An adult crab louse is about 1.3–2 mm long (slightly smaller than the body louse and head louse), and can be distinguished from those other species by its almost round body. Another distinguishing feature is that the second and third pairs of legs of a crab louse are much thicker than the front legs and have large claws.

Life cycle

The eggs of the crab louse are laid usually on the coarse hairs of the genital and

perianal The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...

regions of the human body. The female lays about three eggs a day. The eggs take 6–8 days to hatch, and there are three nymphal stages which together take 10–17 days before the adult develops, making a total life cycle from egg to adult of 16–25 days. Adults live for up to 30 days. Crab lice feed exclusively on blood, and take a blood meal 4–5 times daily. Outside the host they can survive for 24–48 hours. Crab lice are transmitted from person to person most commonly via sexual contact, although fomites (bedding, clothing) may play a minor role in their transmission.

Infestation of humans

Infestation of the eyelashes is referred to as pediculosis ciliaris or phthiriasis palpebrarum. The main symptom of infestation with crab lice 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 several days. Crab egg

Current worldwide prevalence has been estimated at 2% of the human population, but accurate numbers are difficult to gauge because crab louse infestations are not considered a reportable condition by many health authorities, and many cases are self-treated or treated discreetly by physicians. It has been suggested that an increasing percentage of humans removing their

, especially in women, has led to reduced crab louse populations in some parts of the world.Bloomberg
Brazilian bikini waxes make crab lice endangered species
published 13 January 2013, retrieved 14 January 2013 Crab Lice CDC

Crab lice are not known to transmit disease. In infested individuals an average of a dozen lice can be found. Although they are typically found attached to hair in the pubic area, sometimes they are also found on coarse hair elsewhere on the body (for example, eyebrows, eyelashes, beard, moustache, chest,

armpits The axilla (also, armpit, underarm or oxter) is the area on the human body directly under the shoulder joint. It includes the axillary space, an anatomical space within the shoulder girdle between the arm and the thoracic cage, bounded superio ...

, etc.). They do not generally occur on the finer hair of the scalp. Crab lice attach to pubic hair that is thicker than other body hair because their claws are adapted to the specific diameter of pubic hair and other thick hairs of the body. Crab louse infestations ( pthiriasis) are usually spread through

sexual contact Human sexual activity, human sexual practice or human sexual behaviour is the manner in which humans experience and express their Human sexuality, sexuality. People engage in a variety of sexual acts, ranging from activities done alone (e.g. ...

and are most common in adults. The crab louse can travel up to on the body. Crab louse infestation is found worldwide and occurs in all races and ethnic groups and in all socio-economic levels. Occasionally they may be also transmitted by close personal contact or contact with articles such as clothing, bed linen, and towels that have been used by an infested person. Crab lice found on the head or eyelashes of children may be an indication of sexual exposure or abuse. Symptoms of crab louse infestation in the pubic area include itching, redness and inflammation. Crab lice are not known to transmit disease; however, secondary bacterial infection can occur from scratching of the skin. Crab louse infestation can be diagnosed by identifying the presence of active stages of the louse, as well as of eggs (nits) on the pubic hair and other hairs of the body. When infestation is diagnosed, other family members and contact persons should also be examined. A magnifying glass or dermoscope could be used for better identification.

References

External links

* {{DEFAULTSORT:Crab louse Ectoparasites Insects described in 1758 Lice Parasitic arthropods of humans Parasitic infestations, stings, and bites of the skin Pubic hair Sexually transmitted diseases and infections Taxa named by Carl Linnaeus