Basics
Description
Infestation of the head, body, or anogenital region by parasitic, wingless insects that feed exclusively on human blood
Epidemiology
- Head lice
- Spread by head-to-head contact
- Most common among children 3 " 12 years old
- Associated with female gender, warmer weather, crowded living conditions
- Less common among African Americans
- Point prevalence estimates range from <1% in some places to >90% in others.
- Body lice
- Spread by close physical contact with infested persons, clothing, or bedding
- Associated with poor sanitation, cool climates, homelessness, war, disasters, refugee camps
- No racial or gender differences
- Pubic lice
- Usually sexually transmitted
- Can also spread through contact with clothing or bedding recently used by infested person
- Most common among young adults
Incidence
- Varies widely with location and living conditions.
- Estimated 6 " 12 million cases per year in the United States
General Prevention
Humans are the only host for all three types of lice. Recurrences are common and may be prevented by examining and treating close contacts, especially bedmates.
- Head lice
- Avoid head-to-head contact with infested persons; don 't share brushes, hats, or hair ties. Avoid lying on pillows, furniture, or stuffed toys used by infested person within last 2 days.
- Wash clothing and bedding used by infested person with hot water ( ≥130 °F) and set dryer to highest heat setting. Items may also be dry-cleaned or sealed in a plastic bag for 2 weeks. Vacuum furniture and carpet.
- Environmental insecticide is not helpful.
- Treatment of pets is not necessary.
- "No-nit " school policies do not control head lice transmission and are not recommended.
- Body lice
- Regularly wash clothes.
- Avoid using clothing or bedding used by infested person.
- Pubic lice
- Avoid close body contact or sharing clothes with infested person.
- Not prevented by condom use
Pathophysiology
- Bites of louse are painless.
- To facilitate blood meal, lice inject enzymes, anticoagulant, and vasodilators. These provoke host inflammatory response causing pruritus.
- Bites characterized by intradermal hemorrhage and infiltrates of eosinophils and lymphocytes
- Excoriation can introduce secondary infections.
- Vector-borne pathogens (body lice only) can cause chronic bacteremia, angiomatosis, or endocarditis.
Etiology
- Head lice (Pediculus humanus capitis)
- Adults white-to-gray; 2 " 4-mm long; 6 legs; no wings. Crawl quickly away from threat or bright light. Cannot jump or fly. If removed from host, will die within 2 days
- Females lay up to 10 eggs per day over 2 " 3-week lifespan, attaching egg to base of hair shaft with adhesive.
- Eggs are very temperature sensitive; hatch in 7 " 12 days; empty white egg casing remains on hair.
- Emerging nymphs (instars) die without blood meal within a few hours. Molt 3 times over 9 " 11 days to become egg-laying adults.
- Typical infestation includes lice in all stages of development; effect of treatment depends on stage of life cycle.
- Body lice (P. humanus corporis)
- Morphology and life cycle similar to head lice, but adults are slightly larger
- Live and lay eggs on clothing and only come to the skin to feed 4 " 5 times per day
- Able to live longer off host than head lice
- Eggs hatch in 6 " 10 days.
- Pubic lice (Phthirus pubis)
- Crab-like appearance, with larger talus adapted to coarser hair; predilection for pubic hair
- May also infest axillary hair, perianal area, eyelashes, beard, and rarely scalp
Commonly Associated Conditions
- Body lice
- May act as a vector for epidemic typhus (Rickettsia prowazekii), relapsing fever (Borrelia recurrentis), and trench fever (Bartonella quintana) or plague (Yersinia pestis)
- Pubic lice
- Commonly occurs with other sexually transmitted infections
- Although pubic lice on children 's eyelashes usually result from close contact with infested parent, must also consider sexual abuse
Diagnosis
History
- Chief complaint is usually pruritus; however, patients may be asymptomatic.
- May complain of disrupted sleep
- Ask about exposure to others with similar symptoms, crowded living conditions, and previous similar episodes.
- Review details of previous treatments to differentiate improper or incomplete treatment, reinfestation, and resistance to pediculicide.
Physical Exam
- General points
- Definitive diagnosis requires visualization of live lice.
- Bright light and magnification are helpful.
- Head lice
- Wet combing slows the movement of lice.
- Use comb to lift and separate hair to visualize scalp and base of hair shafts.
- Lice and nits (eggs or empty egg casings) most commonly found behind ears, on back of head, and nape of neck
- Typical case involves 5 " 10 live lice.
- Nits are firmly affixed at a characteristic angle to the hair shaft (vs. dandruff). Nits within 1 cm of scalp suggest active infestation. Nits >1 cm from scalp are likely empty egg cases.
- May see excoriation, oozing, matted hair, or lymphadenopathy with secondary infection
- Body lice
- Skin exam may reveal erythematous macules and papules from bites; rarely lice
- Lice and nits may be found along seams on inside of clothing, especially near axillae, inguinal areas, waistband, or collar.
- In long-standing infestations, may find epidermal thickening, hyperpigmentation, or scaly plaques
- With secondary infection, may find adenopathy, fever, and malaise
- Pubic lice
- Small, crab-shaped lice and nits in pubic hair or perianal region; be sure to also check axillae, beard, and eyelashes.
- May find brownish clumps of louse fecal matter
- With heavy infestation, may find maculae cerulea: 0.5 " 1-mm bluish macules on the lower abdomen, thighs, or buttocks
- Eyelash infestation may cause blepharitis or conjunctivitis.
Diagnostic Tests & Interpretation
Diagnostic Procedures/Other
Diagnosis is made by direct visualization of lice or under magnification. Lice will stick to cellulose tape applied to infested area, and tape can then be affixed to glass slide for microscopy. Lice and nits fluoresce yellow green under Wood lamp.
Differential Diagnosis
- Seborrheic, contact, or atopic dermatitis
- Impetigo
- Scabies
- Xerosis with excoriation
- Hair casts, hair spray or other debris, other insects
Treatment
Medication
Head lice
- General issues:
- Because of different mechanisms of action, effects on different stages of louse life cycle, and potential adverse effects, careful adherence to manufacturers ' instructions regarding pediculicide use is essential (preparation of hair, length of application, posttreatment rinsing, combing, and reapplication).
- Conditioner or excess water on hair can interfere with efficacy.
- Use enough product to coat all hair and scalp, especially areas behind ears and along hairline at back of neck. After treatment, use fine-toothed comb to remove visible lice and nits.
- Recheck head daily for lice and nits for 2 " 3 weeks.
- Pediculicides irritate mucous membranes; may be toxic if taken internally
- Permethrin lotion 1% (OTC); 5% (Rx)
- Initial drug of choice; resistance increasing
- Minimum age: 2 months
- 10-minute application to damp hair. Reapply 7 " 10 days later if live lice persist.
- Pediculicidal with some ovicidal activity (acts on insect nervous system)
- Residue on hair kills newly hatching nymphs as they emerge for up to 2 weeks.
- Pyrethrin 1% with piperonyl butoxide (OTC)
- Resistance varies by geographic location.
- Minimum age: 2 years
- 10-minute application to dry hair. Reapply 7 " 10 days later.
- Pediculicidal with low ovicidal activity
- Contraindication: allergy to chrysanthemums or ragweed
- Malathion lotion 0.5% (Rx):
- Resistance common in United Kingdom but not in the United States where product contains terpineol.
- Minimum age: 6 years
- 8 " 12-hour application to dry hair. Leave uncovered. Reapply 7 " 10 days later if live lice persist.
- Pediculicidal and highly ovicidal (organophosphate; cholinesterase inhibitor)
- Highly flammable: Avoid hair dryers, smoking, and irons during treatment.
- Benzyl alcohol lotion 5% (Rx)
- Minimum age: 6 months; potential toxicity in younger infants, especially if taken internally
- 10-minute application to dry hair. Reapply after 7 days.
- Pediculicidal but not ovicidal (interferes with action of respiratory spiracles)
- Spinosad topical suspension 0.9% (Rx):
- Minimum age: 4 years
- 10-minute application to dry hair. Repeat in 7 days if live lice present.
- Does not require combing for nit removal
- Pediculicidal and ovicidal (neurotoxic to insects; also contains benzyl alcohol; combination prevents resistance)
- Ivermectin lotion, 0.5% (Rx)
- Minimum age: 6 months
- 10-minute application to dry hair. Single treatment; do not reapply.
- Pediculocidal; not ovicidal but few nymphs survive more than 2 days (acts on ion channels in invertebrate nerve and muscle cells)
- Wet combing alone to remove nits and lice may be helpful when medication is ineffective or as an alternative to pediculicide use.
- Controversial and untested treatments:
- Occlusion: olive oil, mayonnaise, and petroleum jelly do not asphyxiate lice but may slow their movement and facilitate removal with nit comb
- Shaving: can be effective but not necessary and may not be cosmetically acceptable
- Trimethoprim-sulfamethoxazole (oral 10-day course): may enhance cure rate of topical permethrin; not FDA-approved for this use
- Essential oils (e.g., tea tree oil): may have some activity against lice and eggs but are unregulated and may be toxic
- Hot air: Several mechanical devices deliver hot air to the scalp to desiccate lice and nits, but efficacy is questionable.
- Lindane shampoo 1%: no longer recommended due to neurotoxicity and increased resistance
Body lice
- Pediculicides are usually not needed if infested clothing and other fomites are appropriately laundered, treated with pediculicide, or destroyed. Oral ivermectin has been used effectively during epidemics.
Pubic lice
- The same OTC pediculicides are used for head lice and pubic lice; resistance less common
- It is important to treat all infested areas and sexual contacts.
- For eyelash infestation, apply petroleum jelly twice daily for 10 days. Remove nits with tweezers.
Alert
Pediculicides are oculotoxic. Do not use on eyelashes or eyebrows. If pediculicide gets in eyes, immediately flush with water. Pregnancy risk category varies for pediculicides. Check package insert.
Ongoing Care
Complications
- Head lice
- Intense pruritus can disrupt sleep.
- Stigma associated with infestation can lead to social isolation, teasing, or bullying.
- Days lost from school or work due to "no-nit " policies impact academic performance and worker productivity.
- Secondary bacterial infections can result in pyoderma and lymphadenopathy.
Additional Reading
- Centers for Disease Control and Prevention. Lice. http://www.cdc.gov/parasites/lice. Accessed February 14, 2015.
- Frankowski BL, Bocchini JA, Council on School Health and Committee on Infectious Diseases. Head lice. Pediatrics. 2010;126(2):392 " 403. [View Abstract]
- Lebwohl M, Clark L, Levitt J. Therapy for head lice based on life cycle, resistance and safety considerations. Pediatrics. 2007;119(5):965 " 974. [View Abstract]
- Meinking TL. Clinical update on resistance and treatment of Pediculosis capitis. Am J Manag Care. 2004;10(Suppl 9):S264 " S268. [View Abstract]
- Tebruegge M, Runnades J. Is wet combing effective in children with pediculosis capitis infestation? Arch Dis Child. 2007;92(9):818 " 820. [View Abstract]
Codes
ICD09
- 132.9 Pediculosis, unspecified
- 132.0 Pediculus capitis [head louse]
- 132.1 Pediculus corporis [body louse]
- 132.2 Phthirus pubis [pubic louse]
- 373.6 Parasitic infestation of eyelid
- 132.3 Mixed pediculosis infestation
ICD10
- B85.2 Pediculosis, unspecified
- B85.0 Pediculosis due to Pediculus humanus capitis
- B85.1 Pediculosis due to Pediculus humanus corporis
- B85.3 Phthiriasis
- B85.4 Mixed pediculosis and phthiriasis
SNOMED
- 20848007 Infestation by Pediculus (disorder)
- 81000006 Pediculosis capitis (disorder)
- 25188002 Pediculosis corporis (disorder)
- 91566005 Mixed pediculosis
- 71011005 Infestation by Phthirus pubis (disorder)
- 187211004 Mixed pediculus infestation
FAQ
- Q: Are people with long hair more likely to get head lice?
- A: No. Longer hair is not associated with greater likelihood of getting head lice. However, removing lice and nits is easier when hair is shorter.
- Q: How long should children with head lice be excluded from school?
- A: The risk of transmission decreases enough to allow children to return to school once they have been treated with a single pediculicide application.
- Q: Given the increase in resistance, should we stop using OTC treatments and use prescription products instead?
- A: Resistance of head lice varies widely by community. Currently, permethrin 1% remains the initial treatment of choice. Prescription products are more expensive and have greater potential for toxicity. Careful adherence to manufacturers ' directions and simultaneous treatment of close contacts (especially bedmates) decreases the likelihood of treatment failure and reinfestation.
- Q: How can health professionals allay anxiety and decrease the social stigma of head lice?
- A: Emphasize that head lice infestation is not a sign of poor housekeeping or hygiene. Point out that the benefits of close friendships outweigh the minimal health risks related to head lice. Encourage open communication to facilitate treatment of close contacts.