Pediculosis

Infestation of hair-bearing areas of the body by lice, which are obligate ectoparasites that feed on human blood.

Aetiology

• Pediculosis capitis – Head lice
Causative agent: Pediculus humanus capitis

• Pediculosis corporis – Body lice
Causative agent: Pediculus humanus corporis

• Pediculosis pubis (Crab louse) – Pubic lice
Causative agent: Pthirus pubis

• Direct head-to-head or skin contact

• Sharing of combs, brushes, hats, scarves

• Sexual contact (especially pubic lice)

• Clothing, bedding, towels (especially body lice)

Pathophysiology

1. Lice attach to hair or clothing fibers.

2. They feed on blood several times a day.

3. Saliva injected during feeding → allergic reaction → intense pruritus

4. Scratching leads to excoriation, secondary infection.

Clinical presentation

• Severe itching, often worse at night

• Nits attached firmly to hair shaft (close to scalp in head lice)

• Excoriation marks, papules

• Adenopathy can occur in chronic cases

• Specific distribution:
• Head lice: occipital and post-auricular scalp
• Body lice: areas where clothing touches skin (trunk)
• Pubic lice: pubic area, may involve axillae, chest hair, eyebrows, eyelashes

• Visible crawling lice

• Pubic lice → Maculae ceruleae/sky blue dot due to hemosiderin deposition

Investigations

• Clinical observation of lice and nits

• Fine-tooth combing improves detection

• Wood lamp can make nits fluoresce pale blue

Management

Pediculosis capitis (Head lice)

• Permethrin 1% lotion/shampoo — first-line
Apply to damp hair, leave for 10 minutes, rinse; repeat in 7–10 days

• Alternative treatments
• Malathion 0.5% lotion
• Ivermectin oral/topical
• Dimeticone lotion
• Wet-combing ("nit comb") method

Pediculosis corporis (Body lice)

• Improve hygiene

• Wash clothing and bedding with hot water

• Topical pediculicides if needed

Pediculosis pubis

• Permethrin 1% cream or lotion

• Treat sexual partners

• Screen for other STIs

• For eyelashes: petrolatum ointment applied twice daily for 8–10 days