Pediculosis

(Redirected from Lice)

Background

Drawing of a louse clinging to a human hair.
  • Caused by lice/louse: small wingless insects, dorsoventrally flattened, with reduced or no eyes and enlarged tarsal claws for clinging[1]

Taxonomy of Human Lice

  • Pediculus humanus
    • Head louse (capitus)^
    • Body louse (coporis)
  • Pthirus pubis
    • Pubic louse

Transmission

  • Pediculus humanus capitis^
    • Affects millions of school-age children all over the world
    • Transmission is by close head-to-head contact and rarely through fomites such as hats, clothes, or pillowcases
  • Pediculus humanus corporis
    • Propagated when clothes are not washed or changed regularly
    • Usually affect homeless people, displaced persons, or prisoners in poor conditions
    • Vector for:
  • Pthirus pubis
    • Infests pubic hair and occasionally other hairy areas, such as eye lashes
    • Usually transmitted during intimate body contact, such as during sexual intercourse. Treatment must therefore include the patient's partner.

^Most common[2]

Clinical Features

Heavily infested hair with pediculus humanus capitis (arrow).
Massive infestation of pediculus humanus corporis of: (A) head (B) beard and (C, D) pubis.

Pediculus humanus capitis

  • May see live mites or nits (egg sacks) on hair shaft close to scalp
  • May be asymptomatic or pruritic

Pediculus humanus corporis

Pthirus pubis

Differential Diagnosis

Domestic U.S. Ectoparasites

See also travel-related skin conditions

Evaluation

  • Generally a clinical diagnosis

Management

Over the Counter (OTC)

  • Permethrin 1% lotion shampoo (if >2 months old)[3]
    • Wash hair with non-conditioned shampoo
    • Apply Permethrin for 10 min and rinse
    • Repeat on day 9
  • Pyrethrin lotion
    • Apply to affected areas and wash off after 10 min
    • Repeat in 7 days

Prescription

Reserved for failed OTC treatment

  • Spinosad 0.9% topical suspension (if >6 months old)
    • Apply to scalp and air and wash off after 10 min.
    • Repeat in 10 days
  • Malathion 0.5% lotion (if >6 years old)
    • Applied to affected areas and wash after 8 hrs
    • Repeat in 7 days
  • Benzyl Alcohol 5% lotion (> 6 months old)
    • Apply to dry hair and wash off after 10 min
    • Repeat in 7 days
  • Ivermectin 400mcg/kg PO
    • Once on day 1 THEN once in 7 days
    • Reserved for patients failing topical treatment
  • Lindane therapy
    • Only consider if patient has failed two prior prescription treatments
    • Avoid in children <50 kg due to seizure association

Eyelash Infestation

  • Apply ophthalmic petroleum jelly q12hrs x 10 days

Pediatrics <2yo

  • Wet combing is an alternative to medical therapy
    • Usually transmitted during intimate body contact, such as during sexual intercourse. Treatment must therefore include the patient's partner.

Disposition

  • Discharge
    • Children can return to school after first topical treatment has been applied
    • Instruct parents and all close contacts to wash clothing and bedding in hot soapy water to avoid disease spread

See Also

References

Authors:

Ross Donaldson