Pediculosis

Head lice in humans
Classification and external resources
Pediculus humanus capitis (♀)
ICD-10	B85.0
ICD-9	132.0
DiseasesDB	9725
MedlinePlus	000840
eMedicine	med/1769
MeSH	D010373

Pediculosis is an infestation of lice -- blood-feeding ectoparasitic insects of the order Phthiraptera.^[1][2] The condition can occur in almost any species of warm-blooded animal (i.e., mammals and birds), including humans.^[1][2] Although "pediculosis" in humans may properly refer to lice infestation of any part of the body, the term is sometimes used loosely to refer to pediculosis capitis, the infestation of the human head with the specific head louse.

Classification

Pediculosis may be divided into the following types:^[3]:446-8

• Pediculosis capitis
• Pediculosis corporis (Pediculosis vestimenti, Vagabond's disease)
• Pediculosis pubis (Crabs)

Pediculosis due to human head lice

Presentation

Head-louse infestation is most frequent on children aged 3–10 and their families. Approximately 3% of school children in the United States contract head lice.^[4]

Females get head lice more often than males, and infestation in the black ethinicity is rare.^[5]

Head lice are spread through direct head-to-head contact with an infested person. From each egg or "nit" may hatch one nymph that will grow and develop to the adult louse.

Lice feed on blood once or more often each day by piercing the skin with their tiny needle-like mouthparts. While feeding they excrete saliva, which irritates the skin and causes itching.^[4]

Lice cannot burrow into the skin.

Diagnosis and symptoms

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

To diagnose infestation, the entire scalp should be combed thoroughly with a louse comb and the teeth of the comb should be examined for the presence of living lice after each time the comb passes through the hair. The use of a louse comb is the most effective way to detect living lice.^[6]

The most characteristic 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.

The most common symptom of lice infestation is itching. Excessive scratching of the infested areas can cause sores, which may become infected. In addition, body lice can be a vector for louse-borne typhus, louse-borne relapsing fever or trench fever.

Treatment and prevention

The number of diagnosed cases of human louse infestations (or pediculosis) has increased worldwide since the mid-1960s, reaching hundreds of millions annually.^[7] 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.

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 4–13 yrs old, carried out by their parents will aid control.

Epidemiology and (lack of) disease vectors

About 6-12 million people, mainly children, 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 Denmark, Sweden, U.K., France and Australia.^[8][9] Normally head lice infest a new host only by close contact between individuals, making social contacts among children and parent child interactions more likely routes of infestation than shared combs, brushes, towels, clothing, beds or closets. Head-to-head contact is by far the most common route of lice transmission.

The United Kingdom's National Health Service, and many American health agencies[1][2][3], report that lice "prefer" clean hair, because it's easier to attach eggs and to cling to the strands.

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 fever (Rochalimaea quintana) and louse-borne relapsing fever (Borrellia recurrentis).

Pediculosis due to human body lice

This condition, is caused by body louse (Pediculus humanus humanus, sometimes called Pediculus humanus corporis^[10]) is a louse which infests humans and is adapted to lay eggs in clothing, rather than at the base of hairs, and is thus of recent evolutionary origin. Pediculosis is a more serious threat due to possible contagion of diseases such as typhus. Epidemiology and treatment of human body lice is described in the article on body lice.

Pediculosis due to pubic or "crab" lice

The pubic or crab louse (Pthirus pubis) is a parasitic insect which spends its entire life on human hair and feeds exclusively on blood. Humans are the only known host of this parasite, although it is more closely related to the louse parasites in other primate species, than are human head or body lice which probably evolved from it as the "original" louse infestation of humans. Epidemiology and treatment of pubic lice is discussed in the article on pubic lice.

Bovine Pediculosis

Pediculosis is more common in cattle than any other type of domesticated animal.^[11] This is a significant problem, as it can cause weight loss of 55 to 75 pounds per animal.^[11] Some species of lice infesting cattle include the cattle biting louse[Damalinia (Bovicola) bovis], the shortnosed cattle louse (Haematopinus eurysternus), the longnosed cattle louse (Linognathus vituli), and the little blue cattle louse (Solenopotes capillatus).^[1]

Treatment

Cattle infested with bovine pediculosis are generally treated chemically, by drugs like ivermectin and cypermethrin.

See also

• Head louse
• Body louse
• Crab louse
• Treatment of human head lice
• Nitpicking

References

External links

• Head Lice Information, Harvard School of Public Health
• National Pediculosis Association
• Barbara L. Frankowski, Leonard B. Weiner (1 September 2002). "Head Lice". Pediatrics 110 (3): 638–43. PMID 12205271. http://aappolicy.aappublications.org/cgi/content/full/pediatrics;110/3/638. 
• Morewitz H (2005). "A Brief History of Head Lice.". http://nuvoforheadlice.com/history.htm. 
• Speare R (2007). "Head Lice Information Sheet". James Cook University, N. Queensland, Australia. http://www.jcu.edu.au/school/phtm/PHTM/hlice/hlinfo1.htm. 
• Pediculus humanus facts, life cycle and head lice treatment overview at MetaPathogen