Head louse

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Head louse
Male human head louse.jpg

Head louse ( Pediculus humanus capitis )

Systematics
Class : Insects (Insecta)
Order : Animal lice (Phthiraptera)
Family : Human lice (Pediculidae)
Genre : Pediculus
Type : Human louse ( Pediculus humanus )
Subspecies : Head louse
Scientific name
Pediculus humanus capitis
De Geer , 1778

The head louse ( Pediculus humanus capitis ) is a wingless insect belonging to the order of the animal lice (Phthiraptera). It belongs to the human lice family (Pediculidae) and the genus Pediculus  - this genus comprises four species , two of which parasitize humans exclusively . The infestation is known as pediculosis . Whether Pediculus humanus and Pediculus capitis are separate or just subspecies of a species is debatable among scientists; if it was a subspecies, the correct name for the body louse would be Pediculus humanus humanus and for the head louse Pediculus humanus capitis .

The term “clothes louse” is misleading insofar as Pediculus humanus uses clothing that is directly attached to the body as a “refuge”, but basically sucks blood everywhere on the body - with the exception of the head . Pubic lice or pubic lice ( Phthirus pubis ) also parasitize only humans, but belong to a different genus ( Phthirus ) and family (Phthiridae).

Biological characteristics

Empty egg shell (= nit), magnification 25 times. The hair root is on the lower right outside of the picture.
Adult male (left) and female head lice between match head and 1 euro cent coin

The natural habitat of the head louse is the human scalp and hair. Head lice absorb blood by scratching the top layer of skin with stiletto-like continuations of their head and sucking up blood from an opened capillary . At the same time, they inject saliva into the microscopic wound to stop the blood from clotting . So far unknown constituents of lice saliva have an immunogenic effect, i.e. are recognized as foreign by the human immune system .

The head louse has pigmented eyes. The abdomen of the head louse is divided into seven sections (segments). In each segment there is a breathing opening (stigma) on each side of the body. Another pair of spiracles is located in the thorax area . The spiracles are less than ten micrometers in diameter and merge into trachea , which branch out and supply the internal organs of the louse with oxygen.

The end links of the legs are shaped into hook-shaped claws . With these claws the head louse can hold on to hair or move along it very well. Typically, a head louse holds on to one hair with some claws and grabs another with the free claws. This way, the parasites can get from one head to another quickly. On the other hand, head lice can only move awkwardly on smooth surfaces.

Head lice only undergo an incomplete metamorphosis ( hemimetabolism ). This means that nymphs hatched from the egg already look like adult lice, but are significantly smaller. Newly hatched nymphs are 1–2 mm long, adult lice approx. 3 mm long. A head louse is sexually mature after about 9–12 days. Only then does she try to get on another person's head. Female head lice can lay fully viable eggs by means of parthenogenesis , i.e. without fertilization by a male.

In the adult and sexually mature animals, the male louse is somewhat smaller and slimmer than the female. They can reach a size of up to 3 mm when fully grown.

The chitinous carapace of the louse can be transparent, whitish-grayish or brownish. In populations with weak skin pigmentation, the chitin shell is usually whitish-grayish, whereas in populations with dark skin it is more brownish. After sucking blood , the louse appears reddish because the digestive tract, which is filled with blood, shimmers through the chitin shell. The different color of the chitin shell is an adaptation that took place in the course of evolution, which makes it difficult for the host to recognize the parasites and makes delousing difficult.

The optimum temperature for the development of the eggs is between 34 ° C and 36 ° C. At this temperature and high humidity (conditions that are characteristic of the scalp), juvenile lice usually hatch from the egg within 7–8 days. If the temperature drops, the embryo takes longer to develop . However, about 30% of all eggs do not contain an embryo or the embryo has not developed into a viable louse.

Development history / history

The ancestors of today's head lice parasitized our hominid ancestors . About 5.6 million years ago, the ancestors of the head louse / clothing louse separated into two species, each specializing in chimpanzees and humans. Pediculus schaeffi still affects chimpanzees and Pediculus humanus still affects humans.

Studies of mitochondrial DNA (mtDNA) have shown that Pediculus humanus divided into three monophyletic groups about two million years ago , each with a characteristic geographic distribution. The monophyletic group A includes head lice and clothes lice and is common worldwide. The monophyletic group B is found exclusively in head louse populations of Europe , America, and Australia . Groups A and B were in North America before the discovery of America and were discovered several times in the hair of Indian mummies . The monophyletic group C has so far only been detected in Nepal and Australia. According to one theory, clothes lice and head lice separated into two types when our ancestors lost their thick coat and began to coat themselves with fur.

A genetic analysis of head lice published in 2004 , presented by a team led by David Reed from the University of Florida , identified two groups of ancestry whose development - estimated using the molecular clock  - had been separate from one another for more than 1.1 million years. Today one population occurs on all continents, the second only in America. Since the separation of the two lice populations roughly coincides with the period in which Homo erectus emigrated from Africa , the researchers suspect that Homo erectus brought the ancestors of one population with them and that they also colonized the Neanderthals that emerged from Homo erectus . When the modern man ( Homo sapiens ), who emerged from Homo erectus in Africa, emigrated from Africa decades later , he brought with him the second population that had in the meantime - like himself - changed genetically in Africa. While there was apparently no intensive contact between Neanderthals and Homo sapiens in Europe , in which the lice living exclusively on the human head could be transmitted, closer contact must have come about - according to David Reed - in Asia : The later from In any case, Asia from groups of Homo sapiens that migrated to America seem to have carried both lice populations with them, their own and those presumably taken over by Homo erectus .

Lice and lice eggs have been identified in 8,000 to 10,000 year old textiles, hair and combs that were found in archaeological excavations e.g. B. in the Aleutian Islands , in the southwest of the United States , in Mexico and Peru . Seven nits were discovered on a Coptic wooden comb from Antinoë in Egypt. Comparable finds are known from the Hellenistic and Roman Palestine .

In the 17th and 18th centuries, head lice infestation was widespread in Europe in all social classes. Head lice were a real nuisance for wig wearers. In the 19th century, head lice infestations were extremely common in the poorer sections of the population in both cities and rural areas. Families where people lived very close together and several people shared a bed were particularly affected. Under these conditions, most people had head and clothing lice at the same time.

Occurrence

In contrast to clothes lice, head lice are common worldwide. However, the frequency varies considerably from population group to population group. As a rule, children are affected more often than adults and girls more often than boys. This is related to the age- and gender-specific behavior that allows head lice to change host more easily, and not to biological characteristics of the host.

In Central and Northern Europe, the incidence of head lice infestation in childhood is between 2 and 20%, in developing countries it is up to 60%. In an urban slum in Brazil , 80% of all girls had head lice.

Head lice infestation typically occurs in the form of small epidemics in supervised facilities, kindergartens or schools. If there are epidemics in kindergartens or school classes, 30% and more of all children can be affected.

For Germany, a frequency of 600 to 1000 new cases per 10,000 children per year was determined. This makes head lice infestation the most common parasitic infection in childhood and the most common infectious disease after the common cold.

The frequency of head lice infestations varies considerably depending on the season. From January to July / August new cases occur constantly, but in a relatively small number. With the beginning of the summer vacation, the number of new cases increases rapidly and reaches a maximum around the 37th calendar week. After that, the number of new cases declines and reaches the "base value" again at the end of the year.

The head louse as a parasite

Transmission route in humans

Video recording of a live head louse on a hairbrush

The typical route of transmission is close head contact with a person infected with head lice. Presumably almost all new diseases develop in this way. Shared pillows, towels or combs can theoretically lead to an infection, but in practice this is the exception, as Australian researchers have shown: Speare and others examined 48 severely infected children. In 1845 they isolated lice from the children's heads, but only found a young head louse on the pillow in two cases. Hats, earmuffs, cuddly toys, etc. are practically irrelevant for the transmission of head lice: Researchers systematically examined 1000 headgear from school children and did not find a single louse - on the other hand, they collected 5500 lice from the heads of the students who had worn these hats. Textile surfaces such as sofa sets, headrests, carpets, etc., but also smooth surfaces such as tables, school desks, and floors are unsuitable for head lice and do not pose an infection risk. In a study by James Cook University in Townsville , Australia, 118 classrooms and those there taught 2,230 children examined for head lice infestations. Not a single head louse was found on the benches, on the tables or on the floor. In contrast, 14,033 lice were collected from the children's heads.

Head lice are similarly common in children who wash their hair regularly and those with little grooming. In contrast to earlier epochs, head lice infestation in Germany is not associated with poverty. A study in Braunschweig showed that head lice infestations were less common in children with a migration background than in children without a migration background. There is also no consistent association between hair characteristics such as color, length, thickness of hair and the presence of head lice.

Parasite-Host Interactions

Head lice feed exclusively on human blood. To survive, they must draw blood every two to four hours. If head lice cannot suck up blood, for example because they fell out of the hair during the night, they usually do not survive longer than a day. Female head lice live for around 20 days and a maximum of 30 days under optimal conditions. A female louse produces 150 to 300 eggs in the course of her life. The eggs are glued to the hair shaft just above the scalp with a secretion. The secretion hardens to a cement-like substance and then has a similar structure to the matrix of the hair. These very resistant egg shells containing chitin are called nits .

The eggs are mainly stuck on where the hair is particularly close together: on the temples, behind the ears and on the neck. Here the temperature remains relatively constant and the humidity is particularly high, so there is less risk that lice that have just hatched will dry out. The nymphs hatch within 7–8 days at an average room temperature. For a long time it was believed that all viable embryos would have left the egg shell (= nit) after 10 days at the latest. However, a new work shows that these can only hatch after 14 days or later.

Immune response and symptoms

The skin's immune system recognizes components of lice saliva as foreign and reacts to them with a delayed-type immune response. This manifests itself in the form of small swellings ( papules ) measuring a few millimeters to one centimeter on the scalp. This swelling is very itchy. The pronounced itching induces scratching. If the inflamed area is scratched intensely, the scalp is destroyed (excoriation). Long-term excoriations can lead to ulcers. Excoriations and ulcers are entry portals for pus pathogens ( streptococci , staphylococci ). If the bacterial infection of the scalp persists and is not treated, the regional lymph nodes swell .

In the case of an initial attack, the symptoms only appear after 3–5 weeks, so that the parasitosis is usually only recognized then. This means that the affected person has been infected for several weeks and may have infected other people. If the scalp is affected again after a healed pediculosis capitis, the symptoms appear after 48 hours. The proportion of symptom-free head louse carriers is unknown.

Transmission of pathogens

While clothes lice have long been known to carry pathogens, the role of head lice in transmitting bacteria has only recently been explored. Studies have shown that head lice can transmit Rickettsia prowazekii (causing typhus ) and Bartonella quintana (causing five-day fever ). These dangerous bacteria are very rare in Europe, but widespread in some developing countries. When the blood is sucked, the bacteria enter the human bloodstream via the saliva of the head louse . Pus pathogens, on the other hand, are carried passively from one infected area of ​​the scalp to other areas via the legs and body of the lice.

diagnosis

The disease is usually discovered when a louse falls off its head while combing, a child scratches itself frequently or a louse is discovered on closer inspection. There are two basic difficulties in detecting head lice infestation:

  • First, in Europe 80% of those affected have fewer than ten lice, while in developing countries there are often a hundred or more; To be sure that a child's head is free from lice, a detailed examination is therefore necessary.
  • Second, head lice - especially the juvenile stages of development - are difficult to spot because they are very small and almost transparent, or roughly the color of hair.

The eggs of the head lice are usually easier to see than the animals themselves, especially under magnification. The former are firmly attached to a hair and are usually limited to five areas: hair on the temples, hair behind the ears and hair on the neck. While the empty egg shells ("nits") can easily be recognized as whitish objects, the viable, grayish-brownish eggs are rather inconspicuous.

It is important to distinguish between the two types of eggs: If there are only whitish egg shells on the hair in the absence of already hatched lice, this does not need to be treated. Greyish-brownish eggs, on the other hand, usually contain a viable louse embryo that hatches out of the egg as a juvenile louse after eight days at the latest. In this case, treatment is necessary.

An indirect method of finding out whether eggs contain viable louse embryos - that is, lice will be found on the scalp in a few days - is the distance between the eggs and the hair roots. Because a child's hair grows about an inch per month, and juvenile lice usually hatch from embryonated eggs within eight days, eggs that are more than an inch from the scalp are usually not at risk. No matter how they are look, they only contain dead louse embryos. However, since it can happen in exceptional cases that juvenile lice only hatch after 14 days or later, this method is not very reliable.

Two methods have proven themselves to detect / exclude a head lice infestation: The so-called "visual inspection" and "wet combing": In the visual inspection, the hair and scalp are systematically examined with a magnifying glass. When combing with a damp hair, the hair is first moistened with a hair conditioner, then put in strands and combed out strand by strand with a lice comb. After each combing out, the comb is spread out on white paper or cloth. If a louse has got stuck between the teeth of the comb, it can be easily recognized on the white background. This diagnostic method also has a therapeutic effect.

The method of choice for detecting lice is by damp combing out. The method has a sensitivity of 91%. If the visual inspection were to be relied on, the frequency of head louse carriers would be underestimated by a factor of three. A visual inspection, on the other hand, is better if you just want to look for eggs. The method sensitivity is 86%.

Head lice cannot be confused with other objects on the scalp. The diagnosis is always clear. However, young lice are so small that it is difficult to see them with the naked eye. Eggs or egg shells are relatively easy to distinguish from scales and dried-on remnants of hair gel, hairspray or hair sleeves (remnants of the inner root sheath). Eggs cling to hair at an acute angle, all have the same oval shape and are difficult to remove, even with a lice comb. Cosmetic residues and flakes, on the other hand, are of irregular shape and can be easily removed.

Treatment and hygienic measures

Hortus sanitatis , Mainz 1491. Fig. For chapter Pediculus - Louse

Contrary to popular opinion, frequent washing of the hair has no effect on the infestation with head lice. Nits cannot be removed by simply washing your hair and cannot be easily stripped off. Likewise, saunas , blow-drying your hair or the use of normal hoods are not pesticides and may even lead to additional scalp damage.

In principle, there are three options for treating head lice infestation:

  • the mechanical removal of head lice with the help of a lice comb,
  • the local application of a head lice remedy to the scalp and
  • the ingestion of substances that head lice ingest while sucking blood and then kill them

Locally effective head lice remedies can be divided into two groups according to their mode of action: products that have a toxic effect on the nervous system of the lice (i.e. have a chemical active principle) and products that have a physical effect. Another distinction is based on the extraction of the ingredients: defined chemical substances or substance combinations or a complex mixture of substances from plant extracts.

In principle, treatment is only given if at least one live head louse has been discovered or eggs with viable louse embryos on the hair can be detected (see section " Diagnosis "). If only nits (egg shells) stick to the hair and if no louse can be detected on the scalp, no treatment is required.

Since head lice are infected for the first time, it usually takes 4–6 weeks before the disease is recognized, so it is very likely that the patient has infected other people in the meantime. The recommendation is derived from this to examine all persons with whom there was head contact in the past 14 days for head lice infestation (see section “ Diagnosis ”) and to treat them if head lice are detected.

Mechanical removal

Lice comb (bug buster) during the combing diagnosis with conditioner

Lice combs have been used for thousands of years; they have been found, for example, as burial objects on Egyptian mummies. The method is reliable when performed consistently. In order to safely remove all head lice - including those that are still hatching from existing eggs - the hair must be combed out twice a week for three to four weeks. There are combs with plastic or steel teeth. It is crucial that the tines are absolutely parallel and that the tine spacing is no more than 0.2 mm. Hair that has been moistened beforehand (see section “ Diagnosis ”) is easier to comb out than dry hair. In a comparative study, the combing method was inferior to treatment with malathion .

Eggs and egg shells can be stripped off more easily if the hair is moistened with vinegar beforehand. Since eggs or egg shells (nits) usually only adhere to a relatively small number of strands of hair, the affected hair can simply be cut off. This is usually not visible to an outsider. A full head shave will safely get rid of all lice and eggs; However, if the reason for the shave is not hidden, those affected - especially if children were affected - may be teased.

The Robert Koch Institute has recommended since 2007: During pregnancy and breastfeeding, with MCS syndrome (multiple hypersensitivity to chemical substances) and chrysanthemum allergy, head lice should be removed purely mechanically by wet combing with a lice comb.

Locally acting substances

These are over-the-counter, pharmacy-only drugs, medical products that are sold in pharmacies or drugstores, or cosmetics that are sold in specialist shops or via the Internet.

Substances with a chemical mechanism of action

Head lice remedies, which have a toxic effect on the nervous system of the louse, are insecticides from the group of carbamates ( carbaryl ), organophosphates (malathion), synthetic pyrethroids such as allethrin , permethrin or deltamethrin or pyrethrum (natural chrysanthemum extract). Some products also contain the substance piperonyl butoxide . Since these substances do not have a safe effect on lice eggs, a second treatment is often necessary after 8-10 days (when all the louse embryos in the eggs have hatched). The only exception are permethrin preparations, for which a single application may be sufficient. Products with a chemical mechanism of action are increasingly being viewed critically by experts since populations of head lice that are resistant to chemically acting substances have developed worldwide. For example, in the UK, permethrin is less than 50% effective. A British study, for example, found resistance in over 80 percent of the cases of 3,000 English students. A study from Israel came to similar results. If head lice are resistant to one substance group, other substances from the same or a different substance group are often no longer effective. It is advisable to check the success of the treatment with a nit comb. Pyrethrum and pyrethroids are considered safe when used as intended. The most common side effect is itching and burning of the scalp. Pyrethroids applied to the scalp penetrate the skin in negligible quantities, their non-toxic metabolites enter the bloodstream and are excreted via the kidneys or intestines with a delay. If the scalp is scratched, the substances penetrate the body more easily. Nausea occurs very rarely. If substances with a chemical mechanism of action are accidentally swallowed, serious neurological complications can occur. A French study suggests that earlier use of chemically acting substances may increase the risk of developing leukemia . Pyrethrum and pyrethroids can trigger an allergy or exacerbate an existing allergy to chrysanthemums .

The following products are on sale in Germany:

According to § 18 IfSG, these three drugs have been tested and approved by the Federal Office for Consumer Protection and Food Safety as disinfestants for combating animal pests. The medicinal products Jacutin-Gel and Quellada H Shampoo with the active ingredient lindane were withdrawn from the market at the end of 2007 when Regulation (EC) No. 850/2004 , which banned the use of this biocide, came into force.

A new therapy consists of the application of a 0.5% ivermectin lotion, which is rubbed once into dry hair, left for ten minutes and then washed out. This lotion was approved in the United States under the trade name Sklice and, in a double-blind, placebo-controlled study in children aged six months and over, along with hygienic environmental measures , showed a louse-free rate of 95% after two days and 74% after fifteen days (placebo: 31% and 18%) with very good tolerability and equally good effectiveness in the case of permethrin and pyrethrin resistance.

Plant-based substances

Plant-based head lice remedies are complex mixtures. They typically consist of essential oils and / or fatty acids. Numerous essential oils / fatty acids have been shown to be effective in laboratory tests. The effectiveness of individual essential oils depends on their concentration and the type of solvent. For most products, the effectiveness has only been proven in laboratory experiments. The product Paranix, a combination of coconut, ylang ylang and anise oil, has been compared with other head lice remedies in human studies. It showed 92% effectiveness in Israel and 82% effectiveness in the UK. How the plant substances work has not been investigated. Some substances clearly have a neurotoxic mechanism of action, for others a physical principle of action is assumed. LICENER shampoo against head lice contains extracts from the de-oiled seeds of the neem tree and is supposed to develop a physical effect by closing the tracheal system of the lice so that they suffocate. If a head lice remedy is made from a plant, it does not automatically mean that it is also safe. Essential oils can cause allergies or irritate the skin. The compatibility of medical products and cosmetics based on plants is poorly documented. In the past, plant-based products had to be taken off the market at the instigation of the health authorities because of possible damage to health.

Physically acting products

A new generation of head lice remedies physically eliminates the parasites. Most products contain dimeticone , a silicone oil . Depending on the length of the molecular chains, silicone oils have excellent creeping and spreading properties, are extremely thin or thick to waxy. Due to its physical properties, Dimeticon can wet surfaces very well. It can penetrate microscopically tiny openings, for example the breathing openings of lice, and also coat finely structured surfaces with an oil film. The effect on head lice occurs within a few minutes. Due to the physical principle of action and the rapid onset of action, it is extremely unlikely that resistant parasites will develop.

Silicone oil accidentally ingested through the mouth is excreted unchanged through the intestine. There is no metabolism . Accordingly, the group of substances is considered non-toxic.

Various head lice remedies containing Dimeticon are on the market in Germany. The products differ in terms of the dimeticone concentration, the exposure time, the composition of dimeticones with different physical properties and the addition of herbal additives, which in turn have an effect on head lice. For the head lice remedies NYDA and EtoPril , published data on the effectiveness in humans are available in scientific journals. NYDA showed an effectiveness of 97% in children from Brazilian slums with a lot of head lice, with EtoPril the effectiveness was between 70 and 97%, depending on the study location and type of study. The effectiveness of the other products has not yet been sufficiently documented. New developments in the Dimeticone area are specifically aimed at reducing the exposure time. So is z. B. with DIMET20 an incubation time of 20 minutes is sufficient, compared to 8 hours with NYDA . Other preparations with Dimeticon are Hedrin and Jacutin Pedicul Fluid .

So far, only laboratory studies have been carried out on the effect of dimethicones on lice eggs. DIMET20 showed very good results in the laboratory . A further investigation shows that the effect strongly depends on the physico-chemical characteristics of the dimethicone used. Two products containing dimethicone showed a very good effect, another product none at all. As long as the effectiveness of products containing dimethicone on eggs has not been confirmed by studies on humans, these products must also be used twice with an interval of 8-10 days. NYDA and Jacutin Pedicul Fluid have been tested and recognized by the BVL for combating animal pests according to Section 18 of the Infection Protection Act (IfSG) .

Dimethicone -containing lice agents are partially resistant. Treated hair should be protected from open flames. A comparison of 12 lice remedies published by Stiftung Warentest in September 2018 showed that only the three tested preparations with the active ingredient Dimeticon received the top rating “suitable”.

Mosquito Lice Shampoo 10 contains mineral oil and is used with a ten-minute exposure time. The mechanism of action is unclear; studies on its effectiveness are not available. The preparation replaces the predecessor product Mosquito Lice Shampoo , which is recognized as a disinfestation agent, with the active ingredient soybean oil, which the manufacturer has taken from the market. EtoPril lice foam contains 1,2-octanediol . A disruption of the water balance through damage to the protective layer on the lice's chitin shell is assumed to be the mechanism of action. A study is available on the effectiveness.

Some of the funds are reimbursed as reimbursable medical products in accordance with the Drugs Directive in Germany by the statutory health insurance companies for children up to the age of 12 if they are prescribed by a doctor.

Comparison of mechanical with chemical removal

The right combing technique and a suitable lice comb with closely spaced tines are prerequisites for successful mechanical removal. In a study in 2005 , Hill and other scientists from the London School of Hygiene and Tropical Medicine compared purely mechanical removal , i.e. combing wet hair (combing method), with chemical removal using the insecticides malathion or permethrin . Result: After 15 days of treatment, 57 percent of the test subjects using the combing method no longer had any head lice or nits, but only 13 percent of the chemically treated subjects were lice-free. In this work, the removal of head lice with a special nit comb and the correct combing technique was more effective than treatment with chemical agents. The researchers explained this result with the increasing resistance of the head lice to the commonly used insecticides. Critics complain that the chemical was applied only once and not twice, as is usual and required. However, other authors found completely contrary results, in their studies the chemical active ingredients were superior to combing. It probably depends on the combing technique and the chemical preparations used on the one hand and the local resistance situation on the other.

Oral treatment with ivermectin

Ivermectin is an anti- roundworm drug that also works on blood-sucking lice and scabies mites. Head lice ingest the substance when they suckle blood. Ivermectin was originally developed for veterinary medicine and is not approved in Germany for the treatment of head lice infestations. As a rule, it is sufficient to take 400 µg per kg of body weight twice, one week apart. In a comparative study with insecticide-refractory head lice infestation, 95% were free from lice after two weeks compared to 85% under treatment with 0.5% malathion.

Other treatments

Head lice can be combated with a single treatment with hot, dry air. According to this, a single thorough treatment with a special hot air device is sufficient to kill 98% of nits and 80% of head lice; the remaining head lice are no longer able to reproduce. The treatment method promises high success with a comparatively simple and short application period without insecticides. The use of conventional hairdryers is not recommended, however, as the air becomes too hot and cannot be directed sufficiently towards the scalp.

6 hot-air methods were tested in, all methods killed 88 to 100% of the eggs and up to 80% of the animals.

The effectiveness of mayonnaise and oil has not been proven.

In Austria, the one hour exposure to a 2.5% vinegar solution is officially recommended.

Hygienic measures

Since head lice can only feed and multiply on the human head, hygienic measures are of secondary importance. As a precaution, combs, hairbrushes, hair clips and hair bands can be cleaned in hot soapy water and pajamas, bed linen and underwear can be changed and headgear and scarves washed. There is no need to clean upholstered furniture, curtains, carpets, mattresses, headrests in cars, etc. Sprays containing insecticides are potentially harmful and should not be used. A preventive effect of the application of fragrances or other herbal products on the hair has not been proven.

In Israel , where it is estimated that one in ten children had previously been infested with head lice, the closings and distance regulations decided in the wake of the COVID-19 pandemic proved successful . By suspending school and kindergarten visits for weeks, Israeli researchers estimated from mid-May 2020 that most of the children affected at the beginning of the measures developed symptoms at home and have since been treated by their parents. Remaining lice will likely make it more difficult in future to switch from child to child due to the distance regulations, so that a significant decline in the head lice population can be expected.

Legal regulations in Germany

If head lice are discovered in a child attending a community facility - e.g. after-school care center, kindergarten or school - the parents must report the head lice infestation to the community facility in accordance with Section 34 (5 ) of the Infection Protection Act (IfSG). According to Section 34 (6) IfSG, managers of communal facilities are obliged to notify the responsible health department of any head lice infestation that has been found. If pediculosis capitis is discovered by chance while visiting a facility, the child does not need to be sent home immediately. The parents must confirm verbally or in writing that appropriate treatment has been carried out using a proven drug or medical device. The child can then visit the community facility again. A doctor's certificate is not required, but the facility may require it if a child has multiple head lice.

Popular belief

Even today, infected people are often still unjustifiably stigmatized, although cleanliness no longer plays a dominant role in transmission in modern industrialized countries. At the moment, the spread of head lice depends much more on whether many people live together in a confined space (kindergarten, school, holiday camp, school camp, etc.), whether they maintain closer or more distant relationships with one another ("cuddle") and, for example, whether they are out false shame to hide a head lice infestation for a long time. In the past, hygiene and cleanliness were often far worse in the lower social classes of today's industrialized countries, especially when larger groups of them lived in a confined space. Primarily in poorer countries, however, these conditions still apply to larger population groups today and thus facilitate the spread of head lice in these regions.

For some ethnic groups, however, lice infestation is a sign of health, as it is erroneously assumed that harmful juices are sucked out by lice.

Sources and further information

literature

  • Heinz Mehlhorn, Werner Peters: Diagnosis of parasites in humans, including the therapy of native and tropical parasitoses. Fischer, Stuttgart 1983, ISBN 3-437-10849-2 .
  • Hermann Feldmeier: Pediculosis capitis - The most important parasitosis of childhood. In: Pediatric and Adolescent Medicine. No. 4, 2006, pp. 249-259. PDF
  • Hermann Feldmeier: Head louse infestations - a compendium. Thieme, Stuttgart 2010, ISBN 978-3-13-153691-4 .

Web links

Commons : Pediculus humanus  - collection of images, videos and audio files

Individual evidence

  1. ↑ eurekalert.org. from April 9, 2012: Head and body lice appear to be the same species, genetic study finds.
    Brett Olds et al. a .: Comparison of the transcriptional profiles of head and body lice. In: Insect Molecular Biology , Volume 21, No. 2, 2012, pp. 257-268, doi: 10.1111 / j.1365-2583.2012.01132.x
  2. ^ A b I. F. Burgess: Head Lice Biology. In: J. Heukelbach (Ed.): Management and Control of Head Lice Infestation. UNI-MED, Bremen 2010.
  3. ↑ JR BUSVINE: Evidence from double infestations for the specific status of human head lice and body lice (Anoplura). In: Syst. Entomol. No. 3, 1978, pp. 1-8.
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