Адам шашындағы бітелер

Insect parasite of humans
the animal

The head louse (Pediculus humanus capitis) is an obligate ectoparasite of humans. Head lice are wingless insects that spend their entire lives on the human scalp and feed exclusively on human blood. Head lice cannot fly, and their short, stumpy legs render them incapable of jumping, or even walking efficiently on flat surfaces. A much more distantly related species of hair clinging louse, the pubic or crab louse (Pthirus pubis), also infests humans. It is morphologically different from the other two species and is much closer in appearance to the lice which infest other primates. Louse infestation of the body is known as pediculosis, pediculosis capitis for head lice, pediculosis corporis for body lice, and phthiriasis for pubic lice.

Like other insects of the suborder Anoplura, adult head lice are small (2.5–3 mm long), dorsoventrally flattened (see anatomical terms of location), and wingless. The thoracic segments are fused, but otherwise distinct from the head and abdomen, the latter being composed of seven visible segments. Head lice are grey in general, but their precise color varies according to the environment in which they were raised.

Head lice, like other insects of the order Phthiraptera, are hemimetabolous. The time required for head lice to complete their nymph development to the imago lasts for 12–15 days. Mating attachment frequently lasts more than an hour.

The number of children per family, the sharing of beds and closets, hair washing habits, local customs and social contacts, healthcare in a particular area (e. g. school), and socioeconomic status were found to be significant factors in head louse infestation. Girls are two to four times more frequently infested than boys. Children between 4 and 14 years of age are the most frequently infested group.

All stages except eggs are blood feeders and bite the skin four to five times daily to feed. They inject saliva which contains an anticoagulant and suck blood. The digested blood is excreted as dark red frass.

Although any part of the scalp may be colonized, lice favor the nape of the neck and the area behind the ears, where the eggs are usually laid. Head lice are repelled by light and move towards shadows or dark coloured objects in their vicinity.

Lice have no wings or powerful legs for jumping, so they move using the claws on their legs to move from hair to hair.

About 6–12 million people, mainly children, are treated annually for head lice in the United States alone. In the UK, it is estimated that two thirds of children will experience at least one case of head lice before leaving primary school. High levels of louse infestations have also been reported from all over the world, including Australia, Denmark, France, Ireland, Israel, and Sweden.

Analysis of the DNA of lice found on Peruvian mummies may indicate that some diseases (such as typhus) may have passed from the New World to the Old World, instead of the other way around.

The sequencing of the genome of the body louse was first proposed in the mid 2000s and the annotated genome was published in 2010. An analysis of the body and head louse transcriptomes revealed these two organisms are extremely similar genetically.

Human lice are divided into three deeply divergent mitochondrial clades known as A, B, and C. Three subclades have been identified, D (a sister clade of A), E (a sister clade of C), and F (a sister clade of B).