AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Background

Pediculosis (ie, louse infestation) dates back to prehistory. The oldest known fossils of louse eggs (ie, nits) are approximately 10,000 years old.¹ Lice are so ubiquitous that terms and phrases such as "lousy," "nit-picking," and "going over things with a fine-tooth comb" are part of everyday vocabulary.

Over the last 3 decades, the incidence of pediculosis has risen steadily, making the diagnosis and treatment of louse infestation one of the most common tasks in general medical practice. This article focuses on the pathophysiology and life cycle of 3 prevalent human ectoparasites: (1) Pediculus humanus capitis (ie, head louse), (2) Pediculus humanus corporis (ie, body louse), and (3) Phthirus pubis (ie, pubic louse). The clinical aspects of presentation, diagnosis, and treatment of these ancient and common human pests are also discussed.

Pathophysiology

Human lice (P humanus and P pubis) are found in all countries and climates. They belong to the phylum Arthropoda, the class Insecta, the order Phthiraptera, and the suborder Anoplura (known as the sucking lice). Mammals are the hosts for all Anoplura, and, although lice prefer human hosts, P humanus is also known to live and reproduce on pigs.

The Anoplura are wingless and have 3 pairs of legs, each ending with a clawlike talus for grasping. The size and shape of the claws are adapted to the texture and shape of the hairs and/or clothing fibers they grasp. Their bodies are flat and covered with tough chitin. Human lice have small anterior mouthparts with 6 hooklets that aid their attachment to human skin during feeding. The sucking mouthparts retract into the head when the lice are not feeding. In general, lice feed approximately 5 times per day for approximately 35-45 minutes each time.

In each species, the female louse is slightly larger than her male counterpart. The life cycle of lice is 30-35 days from egg to adult. Early death is common, resulting from gut rupture during feeding or cementing of the female to the hair shaft during ovipositioning.

P humanus capitis

The average length of the head louse is 1-2 mm. The louse is wingless and white to gray and has a long, dorsoventrally flattened, segmented abdomen. It has 3 pairs of clawed legs. Its average life span is 30 days. After incubation of the ova (8-10 d), the nymph molts 3 times before reaching its adult form (8-10 d later).

The female head louse lays as many as 10 eggs per 24 hours, usually at night. She positions her ova at the base of the hair shaft, within 1-2 mm of the scalp, with a predilection for the posterior hairline and postauricular areas. Egg and glue extrusion onto the hair shaft takes 16 seconds.

The female louse cannot survive for more than 3 days off the human head. Head lice can travel up to 23 cm/min. The head louse is unable to move on smooth surfaces (eg, glass, plastic). Lice can be dislodged by combs, towels, and air movement (including hair dryers in either low or high setting).² Hair combing and sweater removal may eject adult lice more than 1 meter from infested scalps. Lice lay eggs on most fabric, often within 5 minutes of contact, and more than 50% of the eggs typically hatch.

P humanus corporis (also known as Pediculus humanus humanus)

The body louse is larger than the head louse. Body lice range in size from 2-4 mm; the female lice are larger than the male lice. The body louse is also flat and white to gray with a segmented abdomen. Unlike the head louse and the pubic louse, the body louse does not live on the human body. P humanus corporis lives in human clothing, crawling onto the body only to feed, predominantly at night. P humanus corporis prefers cooler temperatures, living and laying its 10-15 eggs per day some distance from the human body on the fibers of clothing, mainly close to the seams. The adult female body louse, unlike the head louse, can survive as long as 10 days away from the human body without a blood meal. The life cycle from nit to death is approximately 35 days, with 3 episodes of molting before maturity. On average, 20 adult female lice can be found on a person with an infestation.

P pubis

The pubic louse gets the nickname of "crab" from its shorter, broader body (0.8-1.2 mm) and large front claws, which give it a crablike appearance. The pubic louse is white to gray and oval and has a smaller abdomen than both P humanus capitis and P humanus corporis. The average life cycle of P pubis is also 35 days, although the period from ova to adult (15 d) is slightly longer than that of the other 2 forms. The average female pubic louse lays only 1-2 eggs per day. Their large claws enable pubic lice to grasp the coarser pubic hairs in the groin, perianal, and axillary areas. Heavy infestation with P pubis can also involve the eyelashes, eyebrows, facial hair, and, occasionally, the periphery of the scalp. These insects are less mobile than P humanus and P corporis, mainly resting while attached to human hairs. They cannot survive off the human host for more than 1 day.

Nits

The average nit (ie, ovum) of the 3 types of lice is 0.8 mm long. The nit attaches to the base of the hair shaft or to fibers of clothing with a strong, highly insoluble cement. The nit is topped with a tough but porous cap known as the operculum. This porous sheath allows for gas exchange while the nymph develops in the casing. The ova require optimum conditions of 30°C and 70% humidity to hatch within the average time frame of 8-10 days; the incubation period is longer at lower temperatures. Ova do not hatch at temperatures lower than 22°C but can remain alive for as long as 1 month away from the body (ie, on fomites, clothing, brushes).

Frequency

United States

Pediculosis is extremely common; more than 12 million Americans are infested each year. Head lice infestation is more common in the warmer months, while pubic lice infestation is more common in the cooler months.³

International

Hundreds of millions of cases of louse infestation are reported annually worldwide, with an apparent increase over the past few decades. In a study of 6,169 Belgian school children aged 2.5-12 years, the prevalence of head lice was 8.9%.⁴ The prevalence in 1,569 school children in Izmir, Turkey, was 16.6%.⁵ In 2005, the incidence of pediculosis doubled in the Czech Republic.⁶ Live lice were detected in 14.1% and dead nits in another 9.8% of 531 children aged 6-15 years in 16 schools.⁶

Mortality/Morbidity

• Mortality with pediculosis occurs from the 3 infectious vector-borne diseases (ie, typhus, relapsing fever, trench fever) that are caused by P corporis. For more details, see Other Problems to be Considered.
• The morbidity associated with pediculosis no doubt relates to the social stigma attached to each of the 3 types of infestation. Pruritus, bite reactions, and secondary skin infections can also cause significant morbidity.

Race

• In North America, black persons are less commonly affected by head louse infestation than persons from any other racial group. This is probably due in part to the use of pomades and in part because the claw size of the head louse is more adapted to the round shape of the hair shaft found in white persons and Asian persons.

Sex

• Girls are at higher risk of head louse infestation than boys because of social behavior (eg, social acceptance of close physical contact; sharing of hats, combs, hair ties).
• No sexual predilection exists in body or pubic louse infestation; males and females are equally likely to become infested.

Age

• Children aged 3-11 years are most likely to become infested with head lice because of close contact in classrooms and daycare facilities.
• Age is not a significant risk factor in body louse infestation.
• P pubis infestation is more common in people aged 14-40 years who are sexually active.

CLINICAL

Section 3 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

History

Infestations are underreported because of the social stigma attached, namely the preconceived notion that lice of any kind are related to dirt and poor personal hygiene.

• P humanus capitis
• • Parents of school-aged children often seek an assessment after an outbreak of head louse infestations at school is reported.
  • Pruritus is the major symptom, and parents may note the lice and nits in the hair of the child.
  • The duration of the problem is often valuable information because most children are infested with head lice for as long as 2 months before their discovery.
  • Areas affected in head louse infestation include the scalp, the back of the neck, and postauricular areas.
• P humanus corporis
• • Patients infested with P corporis (generally people of low socioeconomic status) experience nocturnal pruritus, particularly in the axillary, truncal, and groin regions. The lice move from the clothing to the body at nighttime to feed, causing intense pruritus.
  • The investigating physician should inquire about the patient's socioeconomic status and living conditions.
• P pubis
• • Involvement with pruritus of the groin, axillae, and eyelashes or eyebrows can help to differentiate P pubis infestation from head or body louse infestation.
  • Adults infested with P pubis are usually sexually active and have groin and body hair involvement.
  • Children have eyelash and eyebrow involvement. Parents of children infested with P pubis should be questioned about being infested because the parents are usually the source of infestation.

Patients may describe associated features such as papules or wheals, indicating bite reactions. Patients may have a history of secondary infection after excoriation, which may help to confirm the presence of an infestation.

A diagnosis of any type of pediculosis requires the finding of live specimens of lice and/or a viable nit (ie, one located at the base of the hair shaft <2 mm from the scalp). The practitioner should assess the patient's risk factors for infestation (eg, age, sex, race, social and/or economic status, living environment).

Physical

• P humanus capitis
• • Patients infested with head lice generally present with an itchy scalp. The back of the neck and postauricular areas are commonly involved.
  • If excoriations are present, secondary infection, (ie, impetigo) should be excluded and treated, if present.
  • In patients infested with head lice, lymphadenopathy in the posterior auricular and cervical nodes is not uncommon.
  • Bite reactions manifested as pruritic papules and/or wheals may be present, depending on the length of time since the blood meal. Healed bites may reappear when new bites occur in other areas.
  • Close inspection of the scalp in affected patients may reveal the nits, live lice, and small dark specks of insect feces. True nits can be differentiated from dried hairspray and hair casts by attempting to separate the nit from the hair; the hair casts and dried hairspray separate easily, while nits remain securely attached. If the physician remains unsure, a Wood lamp examination reveals yellow and/or green fluorescence of the lice and their nits.
  • Uncommonly, the hair of patients who are heavily infested and untreated is tangled with exudates, predisposing the area to fungal infection. This results in a malodorous mass known as a plica polonica. Numerous lice and nits are found under the matted hair mass.
• P humanus corporis
• • Physical examination findings in body louse infestation include multiple erythematous papules (bites) located anywhere on the body but concentrated in the axillae, groin, and trunk (ie, areas most often covered by clothing). Thus, the face, feet, and arms are not commonly affected.
  • Maculae cerulea may be present as blue-gray macules, which are actually a discoloration of the skin due to the insect's bite. Enzymes in the louse saliva are believed to cause the breakdown of human bilirubin to biliverdin, causing the change in skin color associated with maculae cerulea. The finding of maculae cerulea is believed to be pathognomonic for infestation with lice.
  • The development of secondary infections due to excoriations is also possible. The diagnosis of body lice depends on the close examination of the patient's clothing for lice, nits, and insect feces. The seams of clothing worn on the axillae and groin regions are common sites of residence. The number of body lice per host is usually approximately 10, although as many as 1000 lice can be present.
  • Body louse infestation is also known as vagabond disease, and patients who have an infestation for many years can develop a condition termed vagabond skin. The skin becomes thickened and darkened after years of bites and subsequent rubbing and excoriations.
  • Individuals with P corporis infestation should also be examined for the presence of pubic and head lice. Examining the individual for systemic illness that may be related to one of the vector-borne diseases associated with P corporis is also important (see Other Problems to be Considered).
• P pubis
• • The primary symptom in patients with pubic lice is pruritus in the affected areas. Another clinical feature of pubic louse infestation is the presence of pathognomonic maculae cerulea.
  • The groin, axillae, eyebrows, eyelashes and, rarely, facial hair may be sites of infestation. Scalp involvement is rare and is usually confined to the marginal areas. In adults, eyelash involvement in the absence of genital involvement is rare.
  • Excoriations are common.
  • Because of the less-mobile nature of pubic lice, they are more likely to be found on affected areas clasping onto the hairs near the skin's surface.
  • Inguinal lymphadenopathy and axillary lymphadenopathy have also been reported with pubic louse infestation.

Causes

Causative organisms include P humanus capitis (head louse), P humanus corporis (body louse), and P pubis (pubic louse)

• Risk factors for infestation with P humanus capitis
• • Factors that predispose to head louse infestation include young age (see Age), close crowded living conditions, sex (see Sex), race (see Race), and warm weather. The risk of nosocomial transmission is low, unless close patient-to-patient contact (eg, playrooms, institutions) is present.
  • Based on an 11-year study of the Israel Defense Force, the head lice infestation rate is highest during the warmer summer months.
• Risk factors for infestation with P humanus corporis
• • The risk factors for body louse infestation include the presence of close, crowded living situations (eg, crowded buses and trains).
  • Social circumstances in which the washing and/or changing of clothing is not possible are also significant risk factors for body lice.
  • P corporis can also be acquired via bedding or clothing recently used by an individual infested with lice; thus, individuals who are homeless, who are impoverished, or who are living in refugee camps are at high risk for infestation.
• Risk factors for infestation with P pubis
• • Risk factors for infestation of the pubic louse also include crowded living conditions.
  • Intimate or sexual contact with an individual who is infested is another common risk factor.
  • Because these organisms are most often spread through close or intimate contact, P pubis infestation is classified as a sexually transmitted disease (STD). Condom use does not prevent transmission of P pubis. Upon diagnosis of pubic lice, concern should be raised about the possibility of concomitant STDs.
  • In children, infestation is usually contracted from a parent who is infested (sexual transmission to children is rare). In most cases of infestations in children, transmission is due to shared bed linens and close nonsexual contact.

DIFFERENTIALS

Section 4 of 11  

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• Differentials
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Other Problems to be Considered

P humanus capitis

Dried hairspray/gel
Hair cast (ie, pseudocyst)
Seborrheic dermatitis
Dermatophyte infection
Black piedra and white piedra, caused by Piedraia hortae and Trichosporon beigelii
Psocids
Hair shaft abnormalities (ie, Monilethrix, trichorrhexis nodosa)

P humanus corporis

Folliculitis
Insect Bites
Acne
Delusions of parasitosis
Xerosis with excoriations
Impetigo
Postinflammatory hyperpigmentation

P pubis

Dermatophyte infection
Folliculitis
Delusions of parasitosis
Contact dermatitis
Conjunctivitis (if eyelash involvement)

Lice may carry Staphylococcus aureus and group A Streptococcus pyogenes on their surface and transmit these coagulase-positive pathogens to others.

The body louse, P humanus corporis, is a known vector of 3 major bacterial diseases, all of which have caused epidemics.

• Typhus: The intracellular pathogen Rickettsia prowazekii causes typhus. Typhus fever epidemics have consistently been related to times when overcrowded conditions and body louse infestations were prevalent. For example, mass migration, refugee camps, and times of war have been linked to body louse infestations and secondary epidemics of typhus. The illness begins with a high fever and progresses over hours to days with malaise, backache, headache, and myalgia. A petechial rash appears approximately on day 4, beginning in the flank and axillary regions and quickly spreading to the trunk and extremities. By the second week, the fever begins to wane, profuse sweating occurs, and convalescence ensues. CNS involvement during this period places the patient at high risk of mortality.
• Trench fever: The extracellular pathogen Bartonella quintana causes trench fever. Although rarely fatal, this disease has been the cause of many epidemics and is believed to be related to bacterial infective endocarditis. Infection in humans results from autoinoculation of louse feces into abraded or scratched skin. The infection has a 10- to 30-day latency period and results in a fever similar to that of typhus, with headache, myalgia, and pain in the back and the legs.
• Relapsing fever: The spirochete Borrelia recurrentis causes relapsing fever. This disease is highly fatal in malnourished persons. Although not common in North America, epidemics have been described during the last few decades in Asia, South America, Africa, and Europe. Human infection with this spirochete occurs only when a crushed louse comes into contact with an abrasion. The bacteria replicate in the louse hemolymph, not in the gut; therefore, no transmission occurs through the salivary glands or via the feces. The bacteria infection causes a high fever, headache, dizziness, and myalgia. Rash and sweating also appear and wane approximately on day 5. As the name indicates, this fever often returns several times.

No evidence indicates that any species of louse has the ability to transmit HIV.

WORKUP

Section 5 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Lab Studies

• A Wood lamp examination of the area considered to be infested shows yellow-green fluorescence of lice and nits.
• Because the diagnosis of infestation requires identification of a live louse and/or a viable nit, examining suggestive particles under the microscope confirms the diagnosis.
• A fine-tooth "bug-busting" comb is useful to dislodge eggs and to remove live lice/nymphs. Cellulose tape can be applied over an infested area to pick up lice and place them on a microscopic slide to be examined.
• Dermoscopy can be used to reliably differentiate nymph-containing eggs from empty cases or pseudonits.⁷
• Scrapings for a fungal culture can be collected if dermatophyte infection is in the differential diagnoses. This is useful when the diagnosis is unclear, ie, no nits or lice have been identified.
• In P pubis infestation, blood tests and a thorough examination for concomitant STDs, including HIV infection, are appropriate if the physician considers the individual to be at risk for these conditions.

Histologic Findings

Histology is rarely required for diagnosis. Examination of a bite shows intradermal hemorrhage and a deep, wedge-shaped infiltrate with many eosinophils and lymphocytes.

TREATMENT

Section 6 of 11  

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Medical Care

• P humanus corporis
• • Treatment of P humanus corporis infestation with any pediculicide is usually unnecessary because the louse lives on the clothing.
  • Treatment of clothing and bed linens includes washing them in hot water and drying them with high heat. Dry cleaning is also effective for killing lice and their nits on clothing.
  • Education about hygiene and accessibility to laundering facilities are important in preventing the spread of body lice and reinfestation.⁸
  • In cases of heavy pediculosis, treatment of the body with a pediculicide shampoo or lotion may be beneficial, especially if the patient also has confirmed or suspected concomitant head or pubic louse infestation. Oral ivermectin 12 mg given as 3 doses 7 days apart has also been shown to be efficacious in a cohort of homeless men.⁹
• P humanus capitis and P pubis
• • Pediculicides: These include permethrin, lindane, malathion, or mercuric oxide ointment.
  • • The pyrethroids are neurotoxic to lice; however, they are not very effective against developing nits, although they do have a residual effect. Lotions appear to be more efficacious than shampoos because of their increased contact time with the skin and hair of affected areas. Permethrin is available as a 1% solution (Nix) and as a 5% solution (Elimite), and a formulation of pyrethrin and piperonyl butoxide (Rid) is available. A-200 shampoo also contains benzyl alcohol. Permethrins are usually the first line of treatment, although resistance to permethrin is an increasingly important problem.
    • Lindane (hexachlorocyclohexane, a chlorinated hydrocarbon) is in the same pharmacologic class as dichlorodiphenyl trichloroethane (DDT). The use of lindane is controversial because of its known CNS toxicity.¹⁰ The compound is extremely lipid-soluble and is therefore highly permeable to the CNS. Acute lindane poisoning has been reported after ingestion of amounts as small as 5 mL or 50 mg. Kwell (lindane shampoo) has been removed from the Canadian market because of the availability of safer alternatives.
    • Malathion (Ovide) is an irreversible acetylcholinesterase inhibitor that is specific for insects. The US Food and Drug Administration (FDA) recently approved malathion for use against head lice in the United States. Malathion is available as a 0.5% and a 1% solution.
    • A study in children showed that treatment with Chick-Chack, a natural remedy that contains coconut oil, anise oil, and ylang ylang oil, had greater than 90% efficacy.¹¹
    • Mercuric oxide ointment is useful in the treatment of eyelash infestation with P pubis.
  • Asphyxiants: Petrolatum (twice daily for 7-10 days) is often used, with good results, for eyelash infestation. The petrolatum covers the lice and their nits, preventing respiration. The dead lice are removed mechanically, usually with tweezers.
  • Specific oral antibiotics: Oral antihelminthics, including ivermectin, levamisole, and albendazole,¹² have been found to be effective against head louse infestation. Administration should be repeated in 7-10 days to kill lice emerging from nits that may have survived the first treatment. Co-trimoxazole (ie, trimethoprim and sulfamethoxazole) was initially reported to be efficacious; however, controlled studies have shown only minimal eradication.
  • Mechanical removal and shaving
  • • Solvents are available to help dissolve the cement away from the nit and to aid in mechanical removal of nits with fine-tooth combs (eg, LiceMeister). Formic acid and plain white vinegar have been shown to be effective solvents.
    • Most studies have shown that mechanical removal alone (ie, wet-combing every 2-3 d for a minimum of 2 wk) is not as effective as when this technique is combined with a pediculicide.¹³
    • Shaving is effective but is usually not necessary or socially acceptable. However, in resistant disease, it may be a consideration.

MEDICATION

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The goals of pharmacotherapy are to eradicate the infestation, to prevent complications, and to reduce morbidity.

Drug Category: Pediculicides

In cases of heavy pediculosis, treatment of the body with a pediculicide shampoo or lotion may be beneficial, especially if the patient also has confirmed or suspected concomitant head or pubic louse infestation.

Drug Name	Pyrethrins (RID Mousse, RID Shampoo, R&C, A200)
Description	Treatment of P humanus infestations. Stimulates nervous system of parasite, causing seizures and death. First-line treatment in head, pubic, and severe body louse infestation.
Adult Dose	Apply shampoo to dry hair and allow to set for 10 min before rinsing; repeat in 1 wk prn
Pediatric Dose	Apply as in adults
Contraindications	Documented hypersensitivity
Interactions	None reported
Pregnancy	X - Contraindicated; benefit does not outweigh risk
Precautions	Do not apply to eyes, face, or mucous membranes; discontinue use if irritation occurs

Drug Name	Lindane (Kwell, Scabene)
Description	Stimulates nervous system of parasite, causing seizures and death. Chlorinated insecticide available as 1% lotion, cream, and shampoo. Second-line treatment if other agents fail or are not tolerated. Not very safe in children because of transcutaneous absorption that leads to neurotoxicity. Overall, permethrin is a safer choice.
Adult Dose	Shampoo: Apply to dry head or pubic hair and surrounding areas; allow to set for 4 min, then lather for 4 min and rinse; repeat in 7 d prn Lotion: Apply to affected skin/hair; put on clean clothing; rinse off in 8-12 h
Pediatric Dose	Infants and children: Apply thin film topically over entire body, including hairline, neck, scalp, temple, and forehead; leave on 6-8 h before washing off with water; may repeat in 1 wk if necessary; not to exceed 30 g/application
Contraindications	Documented hypersensitivity; neonates; acutely swollen skin or Norwegian scabies
Interactions	Oil-based hairdressings may increase toxicity of lindane
Pregnancy	B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions	Caution if history of seizures; do not apply to eyes, face, or mucous membranes; caution in pregnancy; adverse reactions have been reported (eg, DIC, aplastic anemia)

Drug Name	Malathion (Ovide)
Description	Recently approved (1999) by US FDA to treat head lice. Irreversible cholinesterase inhibitor that is hydrolyzed and therefore detoxified rapidly by mammals but not by insects; ovicidal and pediculicidal. Binds to hair and provides some residual protection after therapy. Available as 0.5% and 1% aqueous-based lotions.
Adult Dose	Apply lotion to dry hair; leave on 8-12 h, rinse; repeat in 7 d prn
Pediatric Dose	<2 years: Not recommended >2 years: Apply as in adults
Contraindications	Documented hypersensitivity
Interactions	None reported; however, potential for interaction with aminoglycosides and antimyasthenics
Pregnancy	B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions	Contains flammable alcohol; do not expose lotion or wet hair to open flame or electric heat (eg, hair dryers); allow hair to dry naturally and uncovered following application; avoid contact with eyes; flush eyes immediately with water if contact occurs

Drug Name	Mercuric oxide
Description	Ointment (1%) is treatment of choice for Phthirus palpebrarum. For louse infestation of eyelashes, inspect eyelids and remove nits mechanically.
Adult Dose	Apply to eyelashes qid for 14 d
Pediatric Dose	Apply as in adults
Contraindications	Documented hypersensitivity
Interactions	Not to be used with topical sulfur or iodine compounds
Pregnancy	C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions	Avoid direct contact with eyes; adverse effects include sensitization, contact dermatitis, and mercury poisoning (eg, nausea, headache, dizziness, gingivitis); discontinue use if persistent erythema, pain, or edema occurs

Drug Name	Isopropyl myristate (Resultz)
Description	Not available in the United States (currently in phase III clinical trials). Available in Canada and Europe. Noninsecticide-based drug containing isopropyl myristate, an ingredient commonly used in cosmetics. Mode of action is a mechanical process that weakens the waxy shell of lice, resulting in internal fluid loss and dehydration.
Adult Dose	Apply to dry hair and massage into hair until the scalp and back and sides of neck are thoroughly wet; leave on for 10 min, then rinse with warm water; repeat in 7 days to kill any eggs that might have hatched Protect eyes with towel or washcloth during application
Pediatric Dose	<4 years: Not established >4 years: Administer as in adults
Contraindications	Documented hypersensitivity
Interactions	None reported
Pregnancy	C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions	For external use only; do not use near eyes; if contact with eyes, immediately flush with water; soak all combs and brushes in hot water for 10 min; carefully inspect family members daily between treatments and for at least 2 wk after treatment; stop use if skin irritation or infection occurs, or infestation of eyebrows or eye lashes occurs

Drug Category: Anti-infectives

Therapy must be comprehensive and cover all likely pathogens in the context of this clinical setting.

Drug Name	Ivermectin (Mectizan)
Description	Binds selectively with glutamate-gated chloride ion channels in invertebrate nerve and muscle cells, causing cell death. Half-life is 16 h; metabolized in liver. DOC for onchocerciasis and strongyloidiasis. Recently shown to be effective against pediculosis but not yet approved by FDA. Not effective against nits.
Adult Dose	12 mg PO as single dose; may repeat in 1 wk prn
Pediatric Dose	<5 years: Not recommended >5 years: 0.2 mg/kg PO as single dose
Contraindications	Documented hypersensitivity; meningitis
Interactions	May interact with other ligand-gated chloride channels, such as those gated by GABA; should not be used with drugs that have similar effects (eg, benzodiazepines, barbiturates, valproic acid)
Pregnancy	C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions	Adverse effects include nausea, vomiting, and, uncommonly, ophthalmologic reactions (eg, corneal opacity, uveitis, conjunctivitis, optic neuritis)

Drug Name	Fluorescein dye strips (SoftGlo strips)
Description	Used with white petrolatum. This is an off-label use of dye strips used in the diagnosis of corneal abrasion.
Adult Dose	Apply to eyelashes nightly for 3 nights
Pediatric Dose	Apply as in adults
Contraindications	Documented hypersensitivity
Interactions	None reported
Pregnancy	C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions	Vision may become blurred with use of white petrolatum

FOLLOW-UP

Section 8 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Deterrence/Prevention

• Environmental eradication
• • Fomites (eg, pillow cases, linens, towels, toys, hats) should be washed in hot water and dried. They should be exposed to temperatures greater than 50-55°C for at least 5 minutes. Any object that the infested child or parent has come into contact with should be washed thoroughly in hot water.
  • Another way to administer environmental control is to seal potential fomites in plastic bags for at least 2 weeks so that all the nits hatch and die without a blood meal.
  • Providing education to children about the sharing of hats, combs, and hair-ties is also a good idea.
  • Giving children separate areas to store their belongings in the classroom may help prevent the spread of lice.
• Treatment of contacts
• • The treatment of family members, friends, and/or other close contacts is important in helping to prevent further spread of lice and in preventing reinfestation.
  • Patient education regarding treatment of contacts is essential.
  • Parents with children who are infested should be advised to treat the entire family with a pediculicide and to provide environmental fomite control.
• Education about hygiene and accessibility to laundering facilities are important in preventing the spread of body lice and reinfestation.⁸

Prognosis

• Causes of therapeutic failure
• • Misdiagnosis
  • Inappropriate treatment
  • Noncompliance
  • Insufficient application of pediculicide (ie, amount, duration)
  • Lack of ovicidal activity of pediculicide and failure to retreat in 7-10 days
  • Lack of removal of live nits
  • Lack of environmental eradication
  • Reinfestation
  • Resistance to pediculicide

Patient Education

• Education is important with respect to the proper use of the chosen pediculicide, nit removal, and environmental control.
• In cases of school-wide head louse infestations, all children and their family members should be examined for infestation. The preconceived notion that head lice are related to dirt and poor personal hygiene should be dispelled.
• For excellent patient education resources, visit eMedicine's Parasites and Worms Center. Also, see eMedicine's patient education articles Lice and Crabs.

MISCELLANEOUS

Section 9 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Medical/Legal Pitfalls

• In March 2003, the FDA issued a public health advisory warning of an increased adverse effects risk of lindane treatment in persons who are young, small, or elderly. Heightened caution should be exercised if lindane is used in these populations.
• Human lice can be used as a forensic tool. A mixed DNA profile of 2 hosts can be detectable in bloodmeals of body lice that have had close contact between an assailant and a victim.¹⁴

Special Concerns

• P corporis may be the vector for typhus, trench fever, and relapsing fever.
• P pubis infestation may be associated with other sexually transmitted infections. In children, infestation is usually acquired from an infested parent and is rarely the consequence of sexual abuse; however, P pubis infestation maybe acquired secondary to sexual abuse, and the child should be examined for signs of abuse.
• Resistance
• • Over the last few decades, the incidence of pediculosis has risen, as has the problem of increasing resistance of the lice to permethrin, which is the first-line treatment of choice in Europe and North America.
  • In England, head lice have been reported as resistant to permethrin and malathion, creating great difficulty in eradicating the pests.
  • Speculation exists that the insects have become resistant through several mechanisms, including mutating their target enzymes (eg, acetylcholinesterase) so that they no longer bind the organophosphate permethrin with the same affinity and increasing the metabolism of the insecticides, turning them into harmless compounds before they can damage the insects.
  • Emerging resistance will make the treatment of pediculosis more challenging in the future. As the insects avoid our battery of insults with treatments such as permethrin and malathion, alternating between these trusted pediculicides and the new oral antibiotics that have been shown to be effective will be necessary.
  • As more studies provide more information on the safety and efficacy of these compounds in the treatment of head lice, combination therapy may become the mode of treatment for this millennium. One thing is certain—these tough little critters will remain a problem; they have been causing infestations for 10,000 years and counting.

MULTIMEDIA

Section 10 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Media file 1:  Nit on a hair. Note the thin, translucent cement surrounding the hair shaft. Photo courtesy of David Shum, MD, Division of Dermatology, University of Western Ontario.
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Media file 2:  Nit from Pediculus humanus capitis on a hair.
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Media file 3:  Two empty nits from Pediculus humanus capitis. Note the open shells still attached to the hairs and the porous operculi through which the lice have hatched. Photo courtesy of David G. Schaus.
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Media file 4:  Three specimens of Pediculus humanus capitis.
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Media file 5:  Pediculus humanus corporis.
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Media file 6:  Phthirus pubis. Note the clawlike talus.
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REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

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Article Last Updated: Nov 1, 2007