Crab louse

Crab lice (singular, louse), scientific name Phthirus pubis and commonly called "crabs" due to their resemblance to the crab, are one of three kinds of human lice in the large group of lice families, the others being head lice and body lice, which live in clothing. They are wingless, about 1 to 3 mm long. They attach themselves to hair strands, and hatch out of pods with lids, or "nits". Ones that are too tightly attached to be brushed off must be removed by pulling with the nails or a fine-toothed comb.

General information

The crab louse can live in almost any form of human hair, but is found most commonly in pubic hair, leading to its other common name of pubic louse. Its legs are adapted to climbing along relatively widely spaced hairs, and so can be found in eyelashes, pubic hair, beards, moustaches, and even armpit hairs. The individual louse can survive for about 24 hours apart from its necessary human host, so that crab lice can be passed on in sleeping bags and bedding. The female may lay up to 40 eggs at a time, resulting in a fluctuating but growing population. The louse feeds on blood and can leave irritating spots on the skin, sometimes mistaken for pimples, a condition called Pediculosis pubis.

Pubic lice have legs that are spaced further apart than head lice; this is an adaptation that enables them to move around more easily in their habitat.

The female louse glues her eggs, called nits - nits look like tiny white beads - to hair shafts. Lice bite through the skin to suck blood, and the bite causes itching. Bites can become secondarily infected; scratching may break the skin and help cause this kind of infection. The most common symptom of crab lice is itching of genital area.

Pubic lice are most commonly spread by sexual contact and are considered a sexually transmitted disease, but can also be spread by sharing clothes or bedding. Pubic lice can be spread by sitting on a toilet seat.

Life cycle

There are three stages in the life of a pubic louse: the nit, the nymph, and the adult.

Nit: Nits are pubic lice eggs. They are hard to see and are found firmly attached to the hair shaft. They are oval and usually yellow to white. Nits take about 1 week to hatch.
Nymph: The nit hatches into a baby louse called a nymph. It looks like an adult pubic louse, but is smaller. Nymphs mature into adults about 1 week after hatching. To live, the nymph must feed on blood.
Adult: The adult pubic louse resembles a miniature crab when viewed through a strong magnifying glass. Pubic lice have six legs, but their two front legs are very large and look like the pincher claws of a crab; this is how they got the nickname "crabs." Pubic lice are tan to greyish-white in color. Females lay nits; they are usually larger than males. To live, adult lice need to feed on blood. If the louse falls off a person, it dies within 1-2 days.

Treatment

Pubic lice are easily killed with a 1% permethrin or pyrethrin lice shampoo, but the pubic hair must be shaved or combed with a fine-toothed comb to remove the nits. Lice can survive in bedding and clothing, so these items must be treated, sterilized, or contact with them must be avoided for two weeks, after which time any lice will have died.

Lindane (1%), another pediculocide, is not recommended for pregnant or nursing women or for children less than 2 years old.

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Lice | Parasites | Sexually-transmitted diseases

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General information

Life cycle

Treatment

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