Head-louse infestation
Encyclopedia
Pediculosis capitis is a human medical condition caused by the colonization of the hair and skin by the parasitic
insect Pediculus humanus capitis—the head louse
. Typically, only the head or scalp
of the host
is infested. Head lice feed on human blood (hematophagy
), and itching from lice bites is a common symptom of this condition. Treatment typically includes application of topical
insecticides such as a pyrethrin
or permethrin
, although a variety of herbal remedies are also common.
Lice infestation in general is known as pediculosis
, and occurs in many mammalian and bird species. The term pediculosis capitis, or simply "pediculosis", is sometimes used to refer to the specific human pediculosis due to P. humanus capitis (i.e., head-louse infestation). Humans are hosts for two other lice as well—the body lice and the crab lice.
Head-lice infestation is widely endemic, especially in children. It is a cause of some concern in public health, although, unlike human body lice, head lice are not carriers of other infectious diseases.
The most common symptom of infestation is pruritus (itching) on the head which normally intensifies 3 to 4 weeks after the initial infestation. The bite reaction is very mild and it can be rarely seen between the hairs. Bites can be seen, especially in the neck of long-haired individuals when the hair is pushed aside. In rare cases, the itch scratch cycle can lead to secondary infection with impetigo
and pyoderma
. Swelling of the local lymph nodes and fever are rare. Head lice are not known to transmit any pathogenic microorganisms.
From each egg or "nit" may hatch one nymph that will grow and develop to the adult louse. Full-grown lice are found to be the size of a sesame seed. Lice feed on blood 1-8 times each day by piercing the skin with their tiny needle-like mouthparts. Lice cannot burrow into the skin.
Head lice and body lice (Pediculus humanus
) are similar in appearance, although the head lice is often smaller. Pubic lice (Pthirus pubis), on the other hand, are quite distinctive. They have shorter bodies and pincer-like claws, and are colloquially known as "crabs".
(Rochalimaea quintana) and louse-borne relapsing fever (Borrellia recurrentis).
The condition is diagnosed by the presence of lice or eggs in the hair, which is facilitated by using a magnifying glass or running a comb through the child's hair. In questionable cases, a child can be referred to a health professional. However, the condition is overdiagnosed, with extinct infestations being mistaken for active ones. As a result, lice-killing treatments are more often used on noninfested than infested children. The use of a louse comb is the most effective way to detect living lice. In cases of children with dirty, long and/or curly/frizzy hair, an alternative method of diagnosis is examination by parting the hair at 2 cm intervals to look for moving lice near the scalp. With both methods, special attention should be paid to the area near the ears and the nape of the neck. The examiner should examine the scalp for at least 5 minutes. The use of a magnifying glass to examine the material collected between the teeth of the comb could prevent misdiagnosis.
The presence of nits alone, however, is not an accurate indicator of an active head louse infestation. Children with nits on their hair have a 35-40% chance of also being infested with living lice and eggs. If lice are detected, the entire family needs to be checked (especially children up to the age of 13 years) with a louse comb, and only those who are infested with living lice should be treated.
As long as no living lice are detected, the child should be considered negative for head louse infestation. Accordingly, a child should be treated with a pediculicide ONLY when living lice are detected on his/her hair (not because he/she has louse eggs/nits on the hair and not because the scalp is itchy).
Clothes, towels, bedding, combs and brushes, which came in contact with the infested individual, can be disinfected either by leaving them outside for at least 2 weeks or by washing them at 60°C(140 degrees F) for 30 minutes. This is because adult lice can survive only one to two days without a blood meal, and are highly dependent on human body warmth. An insecticidal treatment of the house and furniture is not necessary.
Lice on the hair and body are usually treated with medicated shampoos or cream rinses. Nit combs can be used to remove lice and nits from the hair. Laundering clothes using high heat can eliminate body lice. Efforts to treat should focus on the hair or body (or clothes), and not on the home environment.
Some lice have become resistant to certain (but not all) insecticides used in commercially available anti-louse products. A physician or pharmacist can prescribe or suggest treatments. Empty eggs of head lice may remain attached to the hair shaft long after the lice have been eliminated, but rarely are adult lice seen even with an active infestation. Since there is no way to determine whether each egg is alive or dead, chemical treatment (which may not kill the eggs) should be considered only when live (crawling) lice are discovered in order to kill the adults. Instead, nitpicking, which is checking each hair strand for eggs and picking off each egg, should be used to prevent the possibility of an egg hatching resulting in reinfestation.
) has increased worldwide since the mid-1960s, reaching hundreds of millions annually.
Despite improvements in medical treatment and prevention of human diseases during the 20th century, head louse infestation remains stubbornly prevalent. In 1997, 80% of American elementary schools reported at least one outbreak of lice. Lice infestation during that same period was more prevalent than chicken pox.
About 6-12 million children between the ages of 3 and 11 are treated annually for head lice in the United States alone. High levels of louse infestations have also been reported from all over the world including Israel, Denmark, Sweden, U.K., France and Australia.
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 2-4 times more frequently infested than boys. Children between 4 and 13 years of age are the most frequently infested group. In the U.S., African-American children have lower rates of infestation.
The United Kingdom's National Health Service and many American health agencies http://www.nyc.gov/html/doh/html/cd/cdped.shtmlhttp://www.nhsdirect.nhs.uk/articles/article.aspx?articleId=186&PrintPage=1http://www.worsleyschool.net/science/files/lice/page.html report that lice "prefer" clean hair because it's easier to attach eggs and to cling to the strands; however, this is often contested.
Head lice (Pediculus humanus capitis) infestation is most frequent on children aged 3–10 and their families. Females get head lice twice more often than males, and infestation in persons of Afro-Caribbean or other black
descent is rare because of hair consistency. But these children may have nits that hatch and the live lice could be transferred by head contact to other children.
, Canada
, and Australia
commonly exclude infested students, and prevent return of those students until all lice, eggs, and nits are removed. This is the basis of the "no-nit policy". Data from a primarily American study during 1998-1999 found that no-nit policies were present at 82% of the schools attended by children suspected of louse infestation. A separate 1998 survey revealed that 60% of American school nurses
felt that "forced absenteeism of any child who has any nits in their hair is a good idea."
School head lice policy involves a number of issues:
All of these policies are controversial. In particular, a number of health researchers and organizations object to the required removal of nits (i.e., the no-nit policy). Opponents to the no-nit policy point out that nits, being empty egg casings, have no clinical importance. Transmission can only occur via live lice or eggs. Time-consuming nit removal, therefore, has no direct effect on transmission. This has led to the perception that the no-nit policy serves only to ease the workload of school nurses and punish the parents of infested children.
Proponents of the no-nit policy counter that only a consistently nit-free child can be reliably shown to be infestation-free. That is, the presence of nits serves as an indirect proxy for infestation status. Proponents argue that such a proxy is necessary because lice screening is prone to false negative conclusions (i.e., failure to find lice present on actively infested children). For example, a 1998 Israeli study found that 76% of live lice infestations were missed by visual inspection (as verified by subsequent combing methods). Although lice cannot fly or jump, they are fast and agile in their native environment (i.e., clinging to hairs near the warmth of the scalp), and will try to avoid the light used during inspection. Lice colonies are also sparse (often fewer than 10 lice), which can contribute to difficulty in finding live specimens. Further, lice populations consist predominantly of immature nymphs, which are even smaller and harder to detect than adult lice.
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
insect Pediculus humanus capitis—the head louse
Head louse
The head louse is an obligate ectoparasite of humans. Head lice are wingless insects spending their entire life on human scalp and feeding exclusively on human blood...
. Typically, only the head or scalp
Scalp
The scalp is the anatomical area bordered by the face anteriorly and the neck to the sides and posteriorly.-Layers:It is usually described as having five layers, which can conveniently be remembered as a mnemonic:...
of the host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
is infested. Head lice feed on human blood (hematophagy
Hematophagy
Hematophagy is the practice of certain animals of feeding on blood...
), and itching from lice bites is a common symptom of this condition. Treatment typically includes application of topical
Topical
In medicine, a topical medication is applied to body surfaces such as the skin or mucous membranes such as the vagina, anus, throat, eyes and ears.Many topical medications are epicutaneous, meaning that they are applied directly to the skin...
insecticides such as a pyrethrin
Pyrethrin
The pyrethrins are a pair of natural organic compounds that have potent insecticidal activity. Pyrethrins are neurotoxins that attack the nervous systems of all insects. When present in amounts not fatal to insects, they still appear to have an insect repellent effect. Pyrethrins are gradually...
or permethrin
Permethrin
Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to...
, although a variety of herbal remedies are also common.
Lice infestation in general is known as pediculosis
Pediculosis
Pediculosis is an infestation of lice — blood-feeding ectoparasitic insects of the order Phthiraptera. The condition can occur in almost any species of warm-blooded animal , including humans...
, and occurs in many mammalian and bird species. The term pediculosis capitis, or simply "pediculosis", is sometimes used to refer to the specific human pediculosis due to P. humanus capitis (i.e., head-louse infestation). Humans are hosts for two other lice as well—the body lice and the crab lice.
Head-lice infestation is widely endemic, especially in children. It is a cause of some concern in public health, although, unlike human body lice, head lice are not carriers of other infectious diseases.
Signs and symptoms
Impetigo
Impetigo is a highly contagious bacterial skin infection most common among pre-school children. People who play close contact sports such as rugby, American football and wrestling are also susceptible, regardless of age. Impetigo is not as common in adults. The name derives from the Latin impetere...
and pyoderma
Pyoderma
Pyoderma means any skin disease that is pyogenic. These include superficial bacterial infections such as impetigo, impetigo contagiosa, ecthyma, folliculitis, Bockhart impetigo, furuncle, carbuncle, tropical ulcer, etc. Autoimmune conditions include pyoderma gangrenosum...
. Swelling of the local lymph nodes and fever are rare. Head lice are not known to transmit any pathogenic microorganisms.
Cause
Head lice are generally spread through direct head-to-head contact with an infested person; transmission by sharing bedding or clothing such as headwear is much less common. Body lice are spread through direct contact with the body, clothing or other personal items of a person already carrying lice. Pubic lice are most often spread by intimate contact with an infested person. Head lice occur on the head hair, body lice on the clothing, and pubic lice mainly on the hair near the groin. Human lice do not occur on pets or other animals. Lice do not have wings and cannot jump.From each egg or "nit" may hatch one nymph that will grow and develop to the adult louse. Full-grown lice are found to be the size of a sesame seed. Lice feed on blood 1-8 times each day by piercing the skin with their tiny needle-like mouthparts. Lice cannot burrow into the skin.
Head lice and body lice (Pediculus humanus
Pediculus humanus
Pediculus humanus is a species of lice that infects humans. It comprises two subspecies:*Pediculus humanus humanus Linnaeus, 1758 – the body louse*Pediculus humanus capitis De Geer, 1767 – the head louse...
) are similar in appearance, although the head lice is often smaller. Pubic lice (Pthirus pubis), on the other hand, are quite distinctive. They have shorter bodies and pincer-like claws, and are colloquially known as "crabs".
Vectorial capacity
Head lice (Pediculus humanus capitis) are not known to be vectors of diseases, unlike body lice (Pediculus humanus humanus), which are known vectors of epidemic or louse-borne typhus (Rickettsia prowazeki), trench feverTrench fever
Trench fever is a moderately serious disease transmitted by body lice. It infected armies in Flanders, France, Poland, Galicia, Italy, Salonika, Macedonia, Mesopotamia, and Egypt in World War I Trench fever (also known as "Five day fever", "Quintan fever" (febris Quintana in Latin), "Urban trench...
(Rochalimaea quintana) and louse-borne relapsing fever (Borrellia recurrentis).
Diagnosis
The presence of nits alone, however, is not an accurate indicator of an active head louse infestation. Children with nits on their hair have a 35-40% chance of also being infested with living lice and eggs. If lice are detected, the entire family needs to be checked (especially children up to the age of 13 years) with a louse comb, and only those who are infested with living lice should be treated.
As long as no living lice are detected, the child should be considered negative for head louse infestation. Accordingly, a child should be treated with a pediculicide ONLY when living lice are detected on his/her hair (not because he/she has louse eggs/nits on the hair and not because the scalp is itchy).
Prevention
Examination of the child’s head at regular intervals using a louse comb allows the diagnosis of louse infestation at an early stage. Early diagnosis makes treatment easier and reduces the possibility of infesting others. In times and areas when louse infestations are common, weekly examinations of children, especially those 4–15 yrs old, carried out by their parents will aid control. Additional examinations are necessary if the child came in contact with infested individuals, if the child frequently scratches his/her head, or if nits suddenly appear on the child’s hair. Keeping long hair tidy could be helpful in the prevention of infestations with head lice.Clothes, towels, bedding, combs and brushes, which came in contact with the infested individual, can be disinfected either by leaving them outside for at least 2 weeks or by washing them at 60°C(140 degrees F) for 30 minutes. This is because adult lice can survive only one to two days without a blood meal, and are highly dependent on human body warmth. An insecticidal treatment of the house and furniture is not necessary.
Treatment
There is no product or method which assures 100% destruction of the eggs and hatched lice after a single treatment. However, there are a number of treatment modalities that can be employed with varying degrees of success. These methods include chemical treatments, natural products, combs, shaving, hot air, and silicone-based lotions however all effective treatments require a two-fold process of killing both the adult lice and the eggs. Generally the eggs (nits) need to be manually picked off one by one in order to ensure all live eggs are removed.Lice on the hair and body are usually treated with medicated shampoos or cream rinses. Nit combs can be used to remove lice and nits from the hair. Laundering clothes using high heat can eliminate body lice. Efforts to treat should focus on the hair or body (or clothes), and not on the home environment.
Some lice have become resistant to certain (but not all) insecticides used in commercially available anti-louse products. A physician or pharmacist can prescribe or suggest treatments. Empty eggs of head lice may remain attached to the hair shaft long after the lice have been eliminated, but rarely are adult lice seen even with an active infestation. Since there is no way to determine whether each egg is alive or dead, chemical treatment (which may not kill the eggs) should be considered only when live (crawling) lice are discovered in order to kill the adults. Instead, nitpicking, which is checking each hair strand for eggs and picking off each egg, should be used to prevent the possibility of an egg hatching resulting in reinfestation.
Epidemiology
The number of cases of human louse infestations (or pediculosisPediculosis
Pediculosis is an infestation of lice — blood-feeding ectoparasitic insects of the order Phthiraptera. The condition can occur in almost any species of warm-blooded animal , including humans...
) has increased worldwide since the mid-1960s, reaching hundreds of millions annually.
Despite improvements in medical treatment and prevention of human diseases during the 20th century, head louse infestation remains stubbornly prevalent. In 1997, 80% of American elementary schools reported at least one outbreak of lice. Lice infestation during that same period was more prevalent than chicken pox.
About 6-12 million children between the ages of 3 and 11 are treated annually for head lice in the United States alone. High levels of louse infestations have also been reported from all over the world including Israel, Denmark, Sweden, U.K., France and Australia.
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 2-4 times more frequently infested than boys. Children between 4 and 13 years of age are the most frequently infested group. In the U.S., African-American children have lower rates of infestation.
The United Kingdom's National Health Service and many American health agencies http://www.nyc.gov/html/doh/html/cd/cdped.shtmlhttp://www.nhsdirect.nhs.uk/articles/article.aspx?articleId=186&PrintPage=1http://www.worsleyschool.net/science/files/lice/page.html report that lice "prefer" clean hair because it's easier to attach eggs and to cling to the strands; however, this is often contested.
Head lice (Pediculus humanus capitis) infestation is most frequent on children aged 3–10 and their families. Females get head lice twice more often than males, and infestation in persons of Afro-Caribbean or other black
Black people
The term black people is used in systems of racial classification for humans of a dark skinned phenotype, relative to other racial groups.Different societies apply different criteria regarding who is classified as "black", and often social variables such as class, socio-economic status also plays a...
descent is rare because of hair consistency. But these children may have nits that hatch and the live lice could be transferred by head contact to other children.
History
School policy
Because head louse infestation occurs primarily in children, much of the effort to prevent head lice transmission has focused on school and day care settings—places where large numbers of children come into close contact. Schools in the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, and Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
commonly exclude infested students, and prevent return of those students until all lice, eggs, and nits are removed. This is the basis of the "no-nit policy". Data from a primarily American study during 1998-1999 found that no-nit policies were present at 82% of the schools attended by children suspected of louse infestation. A separate 1998 survey revealed that 60% of American school nurses
School nursing
School nursing is a specialized practice of professional nursing that advances the well being, academic success, and lifelong achievement of students...
felt that "forced absenteeism of any child who has any nits in their hair is a good idea."
- Establishing criteria to infer infestation
- Screening asymptomatic children for evidence of infestation
- Establishing the circumstances under which children will be inspected
- Immediate exclusion of infested children
- Establishing criteria to permit previously infested children to return to school (e.g., the no-nit policy)
All of these policies are controversial. In particular, a number of health researchers and organizations object to the required removal of nits (i.e., the no-nit policy). Opponents to the no-nit policy point out that nits, being empty egg casings, have no clinical importance. Transmission can only occur via live lice or eggs. Time-consuming nit removal, therefore, has no direct effect on transmission. This has led to the perception that the no-nit policy serves only to ease the workload of school nurses and punish the parents of infested children.
Proponents of the no-nit policy counter that only a consistently nit-free child can be reliably shown to be infestation-free. That is, the presence of nits serves as an indirect proxy for infestation status. Proponents argue that such a proxy is necessary because lice screening is prone to false negative conclusions (i.e., failure to find lice present on actively infested children). For example, a 1998 Israeli study found that 76% of live lice infestations were missed by visual inspection (as verified by subsequent combing methods). Although lice cannot fly or jump, they are fast and agile in their native environment (i.e., clinging to hairs near the warmth of the scalp), and will try to avoid the light used during inspection. Lice colonies are also sparse (often fewer than 10 lice), which can contribute to difficulty in finding live specimens. Further, lice populations consist predominantly of immature nymphs, which are even smaller and harder to detect than adult lice.