Head lice infestation

Head lice infestation (pediculosis capitis)
Classification and external resources
Head lice bites on the nape of the neck
ICD-10	B85.0
DiseasesDB	9725
MedlinePlus	000840
eMedicine	med/1769
MeSH	D010373

Head lice infestation^[1] (also known as pediculosis capitis, or as "having nits" or "having cooties")^[1] the colonization of the hair by the head louse (Pediculus humanus capitis), typically only involves the head or scalp of the human host. Head lice feed on human blood; itching from lice bites is a common symptom of this condition.^[2] Treatment includes application of topical insecticides such as a pyrethrin or permethrin, although a variety of herbal remedies are also common.^[3]

Lice infestation in general is known as pediculosis, and occurs in many mammalian and bird species.^[4] 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)^{[citation needed]}. Humans are hosts for two other lice as well — the body louse and the crab louse.

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. It has been suggested that in the past, head lice infection has been a mutualistic beneficial condition which helps to defend against the far more dangerous disease-carrying body louse.^[5]

Signs and symptoms

Adult male (left) and female (right) head lice

The most common symptom of infestation is pruritus (itching) on the head which normally intensifies 3 to 4 weeks after the initial infestation^{[citation needed]}. 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^{[citation needed]}. 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.^[6] 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^{[citation needed]}. Lice do not have wings and cannot jump^{[citation needed]}.

From each egg or "nit" may hatch one nymph that will grow and develop to the adult louse^{[citation needed]}. 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^{[citation needed]}. Lice cannot burrow into the skin.

Head lice and body lice (Pediculus humanus) are similar in appearance, although the head lice is often smaller.^[7] 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"^{[citation needed]}. Head lice are not known to be transmitters of diseases, unlike body lice.

Diagnosis

Lice comb (Bug Buster) wet combing with conditioner for diagnosis and treatment. Head lice can be seen in foam.

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.^[8] The use of a louse comb is the most effective way to detect living lice.^[9] 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^{[citation needed]}. 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^{[citation needed]}. 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.^[9][10] 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).^[11]

Prevention

World War II-era American poster, created to prevent outbreaks of pediculosis among servicemen.

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.^[12] This is because adult lice can survive only one to two days without a blood meal, and are highly dependent on human body warmth.^[13] An insecticidal treatment of the house and furniture is not necessary.

Treatment

Except for recent studies on neem seed extract,^[14] 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,^[15] and silicone-based lotions^[16] 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^{[citation needed]}.

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^{[citation needed]}, 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.

Tea Tree Oil is one of the few natural ingredients that have been proven to be effective in laboratory tests.^[17] Other home remedies such as putting vinegar, isopropyl alcohol, olive oil, mayonnaise, or melted butter under a shower cap have been disproven.^[18] Similarly, the CDC claims that swimming has no effect on treating lice, and can in fact harm the treatment by commercial products.^[19]

Epidemiology

The number of cases of human louse infestations (or pediculosis) has increased worldwide since the mid-1960s, reaching hundreds of millions annually.^[21]

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.^[22] Lice infestation during that same period was more prevalent than chicken pox.^[22]

About 6-12 million children between the ages of 3 and 11 are treated annually for head lice in the United States alone.^[6] High levels of louse infestations have also been reported from all over the world including Israel, Denmark, Sweden, U.K., France and Australia.^[11][23]

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^{[citation needed]}. Girls are 2-4 times more frequently infested than boys^{[citation needed]}. Children between 4 and 13 years of age are the most frequently infested group.^[24] In the U.S., African-American children have lower rates of infestation.^[6]

The United Kingdom's National Health Service^{[citation needed]} and many American health agencies 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.^[25] Females get head lice twice as often as males,^[25] and infestation in persons of Afro-Caribbean or other black descent is rare because of hair consistency.^[25] But these children may have nits that hatch and the live lice could be transferred by head contact to other children.^[26]

See also

• Pediculosis
• List of cutaneous conditions
• Head louse
• To a Louse (on a lady's bonnet). Perhaps the most widely known cultural reference to pediculosis capitis, occurring in a noted poem by Robert Burns.

References

External links

• Use of Cetaphil skin cleanser to treat head lice -- New York Times
• Original study in using nontoxic DSP lotion to treat head lice. A Simple Treatment for Head Lice: Dry-On, Suffocation-Based Pediculicide -- Pediatrics
• In-depth information about Pediculosis capitis and how to treat it