PEDICULOSIS (LICE)

PEDICULOSIS (LICE) - George E.Kikano, MD
BASICS
DESCRIPTION
• Pediculosis is an infestation by lice.
• Characteristics of lice
- Feed solely on human blood, by piercing the skin, injecting saliva, and then sucking blood
- Move quickly
- A mature adult female lays 3-6 eggs (nits) a day. Nits are 0.8 mm long, white, and appear cemented to the base of the hair.
- Nits may survive 3 weeks when removed from host.
• 2 species of lice infest humans
- Pediculus humanus has two subspecies, the head louse (capitis) and the body louse (corporis). Both species are smaller than 2 mm, flat, wingless, and have 3 pairs of legs that attach closely behind the head.
- Phthirus pubis (pubic or crab louse): Resembles a sea crab and has widespread claws on the 2nd and 3rd legs.
• System(s) Affected: Skin/Exocrine
• Synonym(s): Lice; Crabs
GENERAL PREVENTION
• Proper hygiene
• Careful follow-up in schools by public health nurses may help prevent recurrence and spread of head lice.
• Washing combs, brushes, hats, coats, collars, sheets, pillow cases, etc., will help to prevent reinfestation by head lice.
• Safe sex (pubic lice)
EPIDEMIOLOGY
• Predominant age
- Pubic lice: Most common in adults
- Head lice: Most common in children 3-10 years old
• Predominant sex: Female > Male
Incidence
In the US: 6-12 million new cases per year
RISK FACTORS
• Overcrowded sleeping quarters (Pediculosis capitus and corporis)
• Sexual contact (Phthirus pubis)
• Immunosuppression
• Sharing combs, hats, clothing, and bed linen
• Close personal contact
• Poor personal hygiene (not a risk factor for P. capitus)
Genetics
No genetic pattern
ETIOLOGY
Infestation by lice
ASSOCIATED CONDITIONS
• Pubic lice are readily transmitted by sexual contact, with a 90% transmission rate. Up to 1/3 of patients have at least 1 concomitant sexually transmitted disease (STD).
• Eyelash infestation on a child may be a sign of sexual abuse.


DIAGNOSIS
SIGNS AND SYMPTOMS
• Pediculosis capitis (head lice)
- Found most often on the back of the head and neck and behind the ears (warmer areas of the hair)
- Nits are white spheres found on the hair shaft. They cannot be moved.
- Pruritis common, mostly at night
- Scratching can cause inflammation and secondary bacterial infection.
- Eyelashes may be involved.
- Lymphadenopathy in severe infestation
• P. corporis (body louse)
- Poor hygiene
- Adult lice and nits in the seams of clothing
- Pruritus
- Secondary infection
- Uninfected bites present as red papules, 2-4 mm in diameter, with an erythematous base.
• P. pubis (pubic louse)
- Anogenital pruritus
- May have no symptoms during 30-day incubation period
- Nits are present at the base of hair shafts.
- Delay in treatment may lead to development of groin infection and regional adenopathy.
- Pubic hair most common site
- Lice may spread to hair around anus, abdomen, axillae, chest, beard, eyebrows, and eyelashes.
- Infested adult patients may spread lice to eyelashes of children. This may induce blepharitis.
TESTS
Lab
Special tests
• Careful examination of hair shafts under the microscope
• Lice and nits can easily be seen under a microscope. Nits cannot be moved from hair shaft.
• On Wood's lamp exam, live nits fluoresce white, empty nits fluoresce gray.
• Examination of the seams of clothing reveals body lice and their eggs.
Diagnostic Procedures/Surgery
• History and physical exam
• Microscopic exam
DIFFERENTIAL DIAGNOSIS
• Scabies and other mite species that can cause cutaneous reactions in humans
• Dandruff can sometimes look like head lice.
TREATMENT
GENERAL MEASURES
Nit removal
• After treatment with shampoo or lotion, nits remain in scalp or pubic hair.
• Nits are best removed with a very fine comb (nit comb). Removal may be made easier by soaking the hair in a solution of equal parts water and white vinegar and wrapping wet scalp in a towel for at least 15 minutes.
• Repeat treatment periodically as needed for stubborn nits.
• All family contacts possibly infested with head lice should be treated concomitantly.
• Discard the clothes or wash them in hot water.
• Evaluate for other STD (if diagnosed with pubic lice).
Diet
No special diet
Activity
No restrictions
MEDICATION (DRUGS)
First Line
• Head lice: Many topical preparations are effective (1% lindane may be used but may have to be repeated in 1 week; 1% permethrin or pyrethrin is effective). They should be applied and washed off after 10 minutes.
• Pubic lice: Treatments available include synergized pyrethrins, or permethrin. These can be used either as the shampoo left on for 10 minutes or the lotion, which can be left on for several hours for best results.
• Body lice: Best treated with synergized pyrethrins lotion applied once and left on for several hours
• Eyelash infestation: Treated by careful manual removal of lice and nits, or by application of petroleum jelly t.i.d.-q.i.d. for 5 days
• In rare cases, oral trimethoprim/sulfamethoxazole can be used.
• Contraindications: Avoid lindane in premature infants, infants, and pregnant women
• Precautions
- Pediculicides should never be used to treat eyelash infections.
- Accidental ingestion and gross overuse of lindane may be associated with central nervous system toxicity. Use carefully in immunocompromised patients.
- Lindane: Use properly to avoid neurotoxicity.
Second Line
For resistant head lice, shaving the head or oral antibiotics may be indicated.
FOLLOW-UP
PROGNOSIS
• With appropriate treatment, >90% cure rate
• Recurrence common, mainly from reinfection, failure to comply with treatment
COMPLICATIONS
• Persistent itching may be caused by too-frequent use of the pediculicide.
• Secondary bacterial infections
PATIENT MONITORING
As needed
REFERENCES
1. Habif T. Clinical Dermatology. 4th ed. St. Louis, MO: Mosby; 2004.
MISCELLANEOUS
• See also: HIV Infection and AIDS; Typhus Fevers
• Other notes: Typhus, relapsing fever, and trench fever are spread by body lice during wartime and in underdeveloped countries.