Pediculosis (Lice)
BASICS
- Definition: Contagious parasitic infection by ectoparasitic blood-feeding insects (lice)
- Species:
- Pediculus humanus: head louse (var. capitis), body louse (var. corporis)
- Pthirus pubis (pubic/crab louse)
EPIDEMIOLOGY
- Incidence: 6–12 million new US cases/year
- Prevalence: 1–3% in industrialized countries (head lice)
- Demographics: Head lice most common in children (ages 3–11, girls > boys); pubic lice more common in adults
ETIOLOGY & PATHOPHYSIOLOGY
- Transmission: Direct human-to-human contact (head-to-head, sexual, shared clothing/linens)
- Life cycle:
- Eggs (nits) cemented to hair shafts close to scalp, hatch in ~10 days
- Nymphs mature in 7–10 days
- Itching: delayed hypersensitivity to louse saliva
- Body lice: Linked to poor hygiene, clothing/bedding vectors
- Pubic lice: Typically sexually transmitted
RISK FACTORS
- Head lice: School-aged children, girls, shared combs/hats, close contact
- Body lice: Poor hygiene, homelessness
- Pubic lice: Promiscuity, sexual contact
GENERAL PREVENTION
- Wash/dry-clean/vacuum items in contact with infested person
- Screen/treat contacts
- Good hygiene
- Avoid sharing personal items (combs, hats)
- Limit sexual partners (pubic lice)
COMMONLY ASSOCIATED CONDITIONS
- Up to 30% with pubic lice have ≥1 concomitant STI
- Body lice can transmit Bartonella quintana, Borrelia recurrentis, Rickettsia prowazekii
DIAGNOSIS
History
- Symptoms: Pruritus (worse at night), often school outbreaks
- Assess for contact/exposure
Physical Exam
- Head lice: Nits near scalp (esp. nape, behind ears), excoriations, secondary infection, live lice visible on combing
- Body lice: Lice/nits in clothing seams, trunk/groin involvement, pyoderma
- Pubic lice: Pubic/anogenital hair, blue macules, may spread to other hairy areas
Differential Diagnosis
- Scabies, dandruff, other debris (nits tightly adherent vs. dandruff easily removed)
Tests
- Diagnosis: Visualization of live lice/nits (wet combing improves detection)
- Wood lamp: Live nits fluoresce white, empty nits gray
- STI screening: For pubic lice
TREATMENT
General Measures
- Wash all potentially contaminated items in hot water (>60°C)
- Vacuum furniture/carpets, bag unwashable items for ≥2 weeks
- Mechanical nit removal with fine-toothed comb
Medications
First Line
- Permethrin 1% (Nix), pyrethrins with piperonyl butoxide (Rid, Pronto)
- Apply for 10 min, rinse; repeat on day 9 if live lice remain
- Avoid pyrethrins in ragweed allergy
- Body lice: Synergized pyrethrin lotion to clothing/body
- Eyelashes: Petroleum jelly BID x10 days
Second Line
- Malathion 0.5% lotion: Apply 8–12h, rinse; repeat as needed (flammable)
- Spinosad 0.9% lotion, benzyl alcohol 5% lotion, ivermectin 0.5% lotion
- Oral ivermectin (off-label): For difficult/resistant cases (avoid in children <15kg)
- Lindane: No longer recommended (neurotoxicity risk)
Pediatric/Pregnancy Considerations
- Avoid: Permethrin/pyrethrin <2mo, ivermectin/spinosad <6mo, malathion <2yrs, lindane in all ages
- Pregnancy: Permethrin, pyrethrin, malathion, spinosad, benzyl alcohol = Category B
ADDITIONAL & ALTERNATIVE THERAPIES
- Wet combing every 3–4 days x2 weeks
- Cetaphil lotion, dimethicone: Off-label, not FDA approved
- No evidence for: Vinegar, oils, mayo, petroleum jelly, herbal shampoos
ONGOING CARE
- Return to school: After completing topical treatment, nits may remain (no-nit policies not necessary)
- Monitor: Suspect resistance if no dead lice 8–12h after treatment
PATIENT EDUCATION
PROGNOSIS
-
90% cure with proper treatment; recurrence common due to reinfection/nonadherence or resistance
COMPLICATIONS
- Sleep disturbance, social stigma, secondary infection, body lice—epidemic typhus/trench fever
ICD-10 Codes
- B85.0 Pediculosis due to Pediculus humanus capitis
- B85.1 Pediculosis due to Pediculus humanus corporis
- B85.3 Phthiriasis (pubic lice)
CLINICAL PEARLS
- Diagnosis requires finding live lice; empty nits may persist for months
- Improper application is a common cause of treatment failure
- Routine retreatment (day 9) recommended for non-ovicidal products
- Resistance is rising: if no dead lice after treatment, change agent
- School "no-nit" policies are not necessary