Lice

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synonym Lice (pteroptera lice) generally refers to lice (animals)

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Lice are human lice. The back and abdomen of adult human lice are flat and gray white; The head is small and slightly rhombic; Thoracic 3-segment fusion; Abdominal segmentation is obvious. The ventral and posterior ends of female lice are "W" shaped; The ventral and posterior ends of male lice are blunt. The pubic lice are short and wide like crabs; The chest is wide and short, and the abdomen gradually narrows after being wide in the front. The ventral side has a conical protuberance and bristles; The forefoot and paw are thin, while the middle, hind foot and paw are obviously thick.^{[5 ]}

Human head lice parasitize on the hair part of the human head and lay eggs at the root of the hair, especially behind the ears. Human lice mainly live on close fitting clothes and trousers, with many in creases, collars and waists, and lay eggs on the fabric fibers of clothes and trousers. The pubic lice parasitize on the thicker and sparser hair, mainly on the pubic hair and the hair around the anus, and most of the hair in other parts is eyelashes. Under natural conditions, the nymph sucks human blood at least once a day, while the adult sucks several times, usually defecating while sucking blood.^{[5 ]}

Lice can spread epidemic typhus, trench fever and lice borne relapsing fever, which is harmful to human health. Change clothes, sheets and hair frequently to prevent lice.^{[5 ]}

Latin name: louse
circles: Animal kingdom
door: Arthropoda

Outline: Insecta
order: Lice
section: Pediculidae
Chinese scientific name: Lice

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Origin of name

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Licentia, Human Licidae. one kind parasitic Small worms that suck blood and infect diseases on people and animals. The name is related to its characteristics. The "louse" is the same as the "louse". "Xun" means fast, and "kun" means many insects. The insect is quick and agile, and often has a large number, so it is called. Compendium of Materia Medica: "lice are fast and numerous, so they are also commonly known as lice^[2] 。”

classification

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There are three kinds of lice parasitic on human body, namely body louse （Pediculus humanus corporis）、 Head lice (Pediculus humanus capitis) and Pubic lice （Phthirus pubis）。 Body lice and head lice are the varieties of human lice in the genus Pedis, while pubic lice is a separate genus of pubic lice. Of the three species, the body louse is the most important, which is the transmission Epidemic typhus 、 Lice transmitted recurrent fever I.e Trench fever Important media. Among the three species, the body louse is the most important. It is an important vector for the transmission of epidemic typhus and louse transmitted retrogressive fever, namely trench fever^[3] 。

body louse

Lice

The body length is about 3.5mm, which is gray or grayish white. The head is slightly olive shaped, the widest at the antennae, tapering back, and the neck is small and movable.^[4] The antenna is short, divided into five segments, and the terminal segment is longer. The eyes are small and underdeveloped, located on both sides behind the antennae. The mouthpiece is a puncture suction type, which is retracted into a bag below when not in use. Thoracic fusion is indistinguishable, and there is a pair of pores on both sides of the midthorax. The abdomen is long and flat, divided into nine sections, only seven sections can be seen in the appearance, and there is a pair of pores on both sides of each section. There is no dark horny lateral film at the edge of abdomen. It's sturdy, Tarsal ganglion There is only one section with a large, curved claw at the end. Tibia There is a prominent shin finger on the inside of the tip, and there is an obvious thorn on the finger. When the claws and the shin fingers are closed, the hair can be firmly held. male Lice Blunt round at the end of abdomen, often genitals Of Penis reach. The tail of female lice is bifurcated, which looks like a "W" shaped depression.

Head lice

Head lice (shi) The body color is dark and small, about 2.5~3.5mm long. Each segment of antennae is short and thick, the abdominal edge is dark black, and others are similar to body lice.

Pubic lice

Pubic lice (shi) Its color is gray white, its body length is 1.5~2.0mm, and its body width is almost equal to its body length. The abdomen is short, not clearly segmented, with warty projections on both sides, and the last pair is the largest. The front legs are small, and the middle and back legs are thick. There are large and strong claws on the tarsal joint, which are similar to crab shaped. Other structures and body louse 、 Head lice be similar.

Developmental stage

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Lice The development of nymph And adult stage.^[4]

egg

Lice The egg is light yellow, oval, 0.9~1.0mm long, and covered at one end. When laying eggs, female lice use their tails to hold hair or clothing fibers and secrete glue to stick the eggs so that they do not fall off. Head lice and Pubic lice They lay eggs on hair, body louse They lay eggs on the fabric of clothes.

nymph

Lice After 6-8 days of development, the eggs of nymph 。 The nymph's shape is basically similar to that of the adult, only looks slightly lighter in color and smaller in size. Once the nymph is hatched, it can suck blood. After about 9 days, it will become an adult after 3 times of molting.

adult

nymph After three times of peeling, adults are adults. Male and female adults can mate within 10 hours after the last nymph peeling. An adult can mate several times in his life. The female starts to lay eggs 2 days after mating, and can lay 7-8 eggs every day. A female can lay 200-300 eggs in her lifetime. It usually takes 3-4 weeks to develop from eggs to adults. When the temperature is suitable (30~32 ℃) and the blood source is available at any time, it only takes 16 days to complete a passage.

Life habits

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Parasitic condition

Lice Yes, I have completely adapted host Body surface environmental Parasitic insect Its requirements for parasitic environment are relatively constant and specific. as body louse The optimum temperature of is 30~32 ℃, which is the temperature of human body surface. The optimum relative humidity is 10%~60%. Do not like humidity and high temperature. Has a tendency towards darkness. Therefore, when the weather turns warm in spring and the host sweats or heats due to activity, lice are easy to crawl from the body surface to the outside of clothes and spread outward through the contact of the host or clothes.

Vampire habit

Lice Of nymph And adults suck blood, and only suck human blood. The amount of blood sucking can generally reach more than 1/3 of their body weight. (If you find that you are smoking, please do not pull it out with brute force. Wipe the head of the lice with alcohol to make it fall loose)

Cluster parasitic activity

Lice Have the habit of clustering. as body louse Most of them are gathered at the collar, armpit and trouser waist of underwear. Head lice Mainly focus on hair roots. Pubic lice Mainly concentrated in the perineum.

Lice and diseases

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In three Lice Medium, body louse and Head lice It's communication Epidemic typhus 、 Lice transmitted recurrent fever The main communication media of. Body lice can be transmitted Trench fever 。

Biological attributes

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Head lice (head loose) has produced a lot of pesticides Drug resistance And it reappears in many parts of the world, partly because people widely use shampoo containing pesticide ingredients to control head lice. Serious infestation of lice may cause severe skin irritation, and scratching due to itching may cause Secondary infection 。 If it happens to livestock, the leather and wool may be rubbed and damaged, and the production of meat and eggs may decline. The feathers of seriously infected birds may be severely damaged. dog tick One of them is to Tapeworm Infectious to dogs Intermediate host And rat lice are spread among rats Murine typhus （ murine typhus ）。

Lice Sucking lice Item（ Anoplura ）, which is permanent outside the body of birds and mammals Parasitic insect 。 Its development does not leave each stage host 。 The lice are small, wingless, flat in back and abdomen, and have special grasping devices at the end of the foot. There are two kinds of lice parasitic on human body, namely Human lice （ Pediculus humanus ）And shame Pubic lice （ Pthirus pubis ）。 It is generally believed that human lice can be divided into two subspecies, namely human Head lice （ P．h．capitis ）And people body louse （ P．h．corporis ）。

Lice control measures

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Physical lice control

one
Boiling and scalding: Lice Heat resistant, 50 ℃, 30 min can kill lice and eggs. Boil, steam, scald and flow steam.
two
Dry heat: For sweaters, leather clothes, cotton padded clothes, bedding and other items that are afraid of moisture and high heat, dry heat can be used to kill lice. The temperature should be kept at 65~80 ℃ for 30~60min.
three
Freezing: lice have poor tolerance to low temperature, and can be stored at minus 15 ℃ for 7 hours Lice All frozen to death; Not only can lice be frozen to death at minus 20 ℃ for 9 hours, but also can eggs be frozen to death.

Drug lice control

one
Dichlorvos: soak in 0.2% Dichlorvos solution for 30min.
two
Permethrin : 0.01% permethrin lotion, 24h.
three
Chinese herbal medicine:

(1) Vinegar: Heat the vinegar to 27~30 ℃ to wash and rub the hair. It can kill lice eggs and soften the eggs. It is easy to comb them down with a comb.

(2) 10% baibu lijing alcohol extract, can kill Head lice and Pubic lice 。

Common types

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Human lice

Gray white, narrow and long, female up to 4.4mm, male slightly smaller.

head

Slightly rhombic in shape, the antennae are about the same length as the head, divided into 5 segments, extending to both sides of the head. The eye is obvious and located behind the antenna. mouthparts It is a prick suction type. Except that the short and small toothed suction beak protrudes from the head, the main part of the mouthpiece is retracted in the head Oral needle It is usually stored in the mouth needle bag near the abdomen of the pharynx. When sucking blood, fix the skin with a sucking beak, and puncture it through the mouth Esophageal sinus pump The contraction draws blood into the digestive tract.

chest

Three segments are fused, and there is one pair of spiracles on the side of the midthorax, without wings and wing marks. Three pairs of feet are thick and roughly equal in length. Each foot Tibia There is a fingerlike tibial process on the medial side of the distal end, Tarsal ganglion Only one segment has a curved claw at its end. The claw and the tibial process cooperate to form a powerful gripper, so the lice can hold tightly host The hair or underwear fibers will not fall off.

abdomen

The sections are obvious, and 8 sections can be seen in the appearance. Ossified at both sides of the third to eighth segments Lateral dorsal film There are 6 pairs of valves on each plate. The ventral end of female lice is W-shaped, and there is a reproductive abdomen and a pair of reproductive limbs on the ventral surface of the 8th segment. The ventral end of the male lice is V-shaped. There are two small backplates on the back of 3~8 segments, and three on the back Ventral segment It can be seen inside the body External genitalia 。

people Head lice And people body louse There is little morphological difference. Only the human head lice are slightly small, slightly dark, and have short and thick antennae.

Pubic lice

Observation on the fine structure of pubic lice and their eggs

Gray white, wide and short like a crab. The body length of female lice is 1.5~2.0mm, and that of male lice is slightly smaller. The chest is very wide, so the base nodes of the left and right feet are far apart. The front foot and paw are relatively small, the middle and rear foot tibia and paw are obviously thick, and the abdomen is wide and short. Due to the fusion of the front 4 segments, the front 3 pairs of valves are arranged in an oblique line. The lateral edges of section 5-8 are respectively provided with conical protrusions Seta 。

Parasitism habit

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Human lice And shame Pubic lice Are parasitic on the human body. people Head lice It parasitizes on the part of the human head with hair and lays eggs at the hair root, mostly behind the ears. people body louse They mainly live in close fitting clothes and trousers Frill There are many places such as collar and trouser waist, which lay eggs on the fabric fiber of the clothes. The pubic lice parasitize in the thicker and rarer parts of the body hair, mainly on the pubic hair and the hair around the anus. Most of the other parts are eyelashes, which lay eggs at the base of the hair.

Lice are Progressive metamorphosis , egg in life history nymph And adults. Oval, about 0.8 × 0.3mm, white, commonly known as nit 。 The egg adheres to the hair or fiber, and its free end is covered with pores and chambers. The nymph hatches from the egg lid. Its shape is similar to that of the adult, but it is small, especially its abdomen is short, and its reproductive organs are not yet mature. The nymph becomes an adult after three molts.

Human lice can lay 300 eggs Pubic lice About 30. At the optimum temperature (29~32 ℃) and humidity (76%), Human lice It takes 23 to 30 days for eggs to develop into adults, and 34 to 41 days for pubic lice. The life span of female human lice is 30-60 days, and that of pubic lice is less than 30 days; Male lice have a shorter lifespan.

Both nymphs and male and female adults are addicted to human blood. The louse is not resistant to hunger. The nymph needs to suck blood at least once a day, and the adult needs to drink blood several times, often while defecating. The lice are extremely sensitive to temperature and humidity. They are afraid of both heat and humidity and cold. Since the temperature and humidity on the surface of the normal human body are the optimal temperature and humidity for lice, lice generally do not leave the human body. When host When the body temperature rises after illness or strenuous exercise, and the body becomes cold after death, the lice will crawl away from the original host. These habits play an important role in the spread of lice and the spread of diseases.

The spread of human lice is caused by direct and indirect contact between humans. The transmission of pubic lice is mainly through sexual intercourse.

Virus transmission

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The stinging lice can appear at the stinging part after sucking blood papule and ecchymosis , causing severe itching due to scratching Secondary infection 。 Most patients have a history of unclean sexual intercourse, and the first symptom is often the pudenda skin Itch It feels like insects crawling, especially in case of heat. As the lice are closely attached to the skin and hair roots, it is difficult to see with the naked eye, but only erythema, papules, light brown Lichenoid transformation Others, serious cases caused by scratching impetigo Ulcer. Shame parasitic on eyelashes Pubic lice It is mostly found in infants, causing Eyelid Itching, eyelid congestion, etc, Pubic lice disease The diagnosis is based on finding the worm body from the affected part.

The spread of diseases is mainly caused by Human lice , especially people body louse spread Epidemic typhus , Trench fever and Lice transmitted recurrent fever 。 In addition, Endemic typhus After being transmitted from fleas to humans, it can also be transmitted by human lice.

(1) Epidemic typhus: caused by Rickettsia proctor （ Rickettsia prowazecki ）It is an acute infectious disease caused by human lice. The patients were infectious from 1 to 2 days at the end of incubation period to several days after fever abatement, and the infectivity was the strongest in the first week after onset. After sucking the patient's blood Rickettsia Invasion into lice stomach epithelial cells And a large number of proliferation, a few days later, the epithelial cells burst, the pathogen is discharged with lice feces. When the lice suck the blood of others again, the lice feces pollute the skin wound, or Rickettsia invades the body through the wound after the lice body is crushed, Rickettsia proctor It can survive for 66 days in lice feces, so it may also be polluted by breathing or hands conjunctiva And infected.

⑵ Trench fever : Also known as five-day fever, it is caused by Human lice Caused by Rickettsia quinta Acute fever Sexual diseases. Symptoms and Epidemic typhus Similar and mild, but the course of disease is longer. Human infection is also similar to epidemic typhus, except that Rickettsia can only reproduce in the stomach or on the surface of epithelial cells, and does not invade the cells.

⑶ Regression fever : It is an acute febrile infectious disease with periodic onset. Lice transmission Relapsing fever It was originally Obai Shu Spirochete （ Borrelia obermeieri ）。 The pathogen passes through 5 to 6 days after being inhaled by lice along with the patient's blood Gastric wall get into Hemocoelom And reproduce in large numbers. They do not enter the tissues or excrete from the feces. Therefore, the infection is caused by the pathogen in the body fluid after the louse body is crushed and enters the human body through the wound.

Preventive drugs

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1、 sulfur Ointment can only alleviate but not cure. It is easy to stop and repeat. It is generally required to apply it 3-5 times a day for 1-2 months. The effect is poor.

2、 Lindane Cream , same relief Pubic lice Symptoms, toxic, and can not be cured. It is generally required to use it 3-5 times a day for 20-30 days, with poor effect.

3、 Baibu tincture It is configured by the hospital itself. High concentration will hurt the skin, but low concentration will not work. It usually needs to be used continuously for 1-2 months. And guarantee to clean it for half an hour every day.

4. The lice are clear, which can kill the adults and the eggs inside the hair follicle.

Prevention and control principle

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The first is prevention. Pay attention to personal hygiene, such as frequent dressing, bathing and changing Bedclothes Wash hair frequently to prevent lice Pubic lice We should pay more attention to morality and keep clean.

There are many ways to kill lice, which can be divided into physical and medical methods. yes Clothing The simplest method is steaming, dry heating, ironing, etc. The clothes that are not resistant to high temperature can be frozen. Never use pesticides to kill lice to prevent poisoning^[1] 。

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