Scabies and pediculosis

Overview

Scabies and lice are ectoparasite infestations. Both are common in Pakistan, especially in crowded homes, hostels, madrassas, prisons and care settings. Both cause itch, spread by close contact, and need the whole household treated together.

The PGET stem usually gives night-time itching in several family members, or nits in a schoolchild's hair.

Scabies

Cause and spread

• Caused by the "itch mite" Sarcoptes scabiei var. hominis, a tiny eight-legged mite.
• The fertilised female burrows into the stratum corneum and lays eggs as she goes.
• Spread by close or prolonged skin contact (sharing a bed, caring for children, sexual contact). Spread from clothing and bedding is less important but possible.
• Affects any age, race or social class; most common in children and young adults and in poor, overcrowded settings.

Why it itches

The itch is a hypersensitivity reaction to the mite and its products. It therefore starts only some weeks after a first infestation (much sooner on reinfestation), and it continues for weeks after cure.

Clinical features

• Intense itch, worse at night, often in several members of the same household.
• Small red papules, vesicles and occasional pustules, with excoriations and an eczema-like rash.
• Burrows: short, fine, wavy grey lines a few millimetres long, with the mite at one end. These are diagnostic but not always seen.
• Typical sites: finger webs, sides of fingers, flexor wrists, elbows, axillary folds, belt line, buttocks, male genitals (itchy nodules on the penis and scrotum are almost diagnostic), around the nipples and the umbilicus.
• Face and scalp are spared in adults but may be involved in infants, who also get lesions on the palms and soles.

Complications

• Secondary bacterial infection (impetigo) with Staph. aureus or Strep. pyogenes.
• After streptococcal infection: post-streptococcal glomerulonephritis and, in some settings, rheumatic fever.
• Persistent scabies nodules in children.
• Eczematisation from scratching and irritant treatments.

Crusted (Norwegian) scabies

Diagnosis

• Mostly clinical: history of night itch in contacts plus typical distribution.
• Dermoscopy can show the mite at the end of a burrow.
• Skin scraping from the end of a burrow, mounted in potassium hydroxide or oil, shows the mite, eggs or faecal pellets.

Management

First-line: 5% permethrin cream.

How to use any scabicide correctly:

1. Apply to all skin from the neck down, including palms, soles, genitals, between fingers and toes and under nails.
2. In infants and young children (up to about 2 years) and the elderly, also treat the scalp, face and neck (avoid eyes and mouth).
3. Leave on overnight, then wash off.
4. If hands are washed before the cream is due off, put more on the hands.
5. Repeat after 1 week to kill mites that hatch from eggs.
6. Treat everyone in the household and other close contacts on the same day, whether or not they itch.
7. Wash clothes, towels and bedding used in the last few days in hot water (about 60°C) or seal them in a bag for several days.

Alternatives:

• Oral ivermectin, two doses about 2 weeks apart: useful for crusted scabies, institutional outbreaks and when topical treatment is impractical.
• Malathion lotion if permethrin is not available.
• Benzyl benzoate: irritant; avoid in children.
• Sulphur ointment: an older, cheap option still used in community programmes.

For the itch: antihistamines at night, menthol cooling creams, and a mild topical steroid after the scabicide course.

Pediculosis (lice)

Lice are wingless, six-legged, blood-sucking insects about 2–4 mm long. They are seen with the naked eye.

Head lice

• Spread: direct head-to-head contact; sharing combs and hats is less important.
• Symptoms: itchy scalp, excoriations and papules at the nape and behind the ears; sometimes secondary impetigo and enlarged neck nodes.
• Diagnosis: finding a live louse by wet combing with a fine-toothed comb is the best proof. Nits are egg cases glued firmly to the hair shaft (unlike dandruff, which brushes off). Nits far from the scalp are usually empty and show past infestation.
• Treatment:
  • Physical agents: dimeticone lotion or isopropyl myristate coat and suffocate lice; no resistance develops.
  • Insecticides: permethrin, malathion, phenothrin or carbaryl; resistance is common.
  • Wet combing with conditioner every few days for about 2 weeks.
  • Repeat any lotion after 7 days to catch newly hatched lice.
  • Check and treat affected family members on the same day.

Body lice

• Lice and eggs are found in the seams of clothing, not usually on the skin.
• Itchy papules and excoriations on the trunk; chronic cases get thickened, darkened skin ("vagabond's disease").
• Treatment: mainly hygiene: hot washing and drying of clothes and bedding, bathing; permethrin or malathion to the skin if needed.

Pubic lice

• Spread by close body contact, usually sexual.
• Itch in the pubic area, often worse at night; lice look like small crabs near the base of hairs, with nits further up the shaft.
• Eyelash involvement in a child should raise concern about sexual abuse.
• Treatment: as for head lice (permethrin or malathion to the whole body), repeated after a week; for eyelashes use a bland ointment such as petroleum jelly.
• Treat sexual partners and screen for other STIs.

Scabies versus lice versus other itchy rashes

Quick revision

• Scabies: Sarcoptes scabiei; itch is allergic and worse at night.
• Burrows in finger webs and wrists; genital nodules in men; face spared except infants.
• 5% permethrin, neck down (whole body in infants), overnight, repeat after 1 week.
• Treat all contacts together; wash bedding hot.
• Itch may last a few weeks after cure.
• Crusted scabies: immunosuppressed, many mites, little itch, oral ivermectin, barrier nursing.
• Head lice: wet combing, dimeticone, repeat after 7 days.
• Body louse: clothing seams; spreads epidemic typhus, trench fever, relapsing fever.
• Pubic lice: Phthirus pubis; treat partners; screen for STIs.

Written by The House Job from standard references (Kumar and Clark's Clinical Medicine; Levinson's Review of Medical Microbiology and Immunology).

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