Scabies

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Introduction

Scabies is an intensely pruritic infestation caused by human mite called Sarcoptes scabiei.

It is contracted by close contact and rarely via fomites. Occurs commonly in children and inmates of overcrowded institutions such as prisons and boarding Houses.

Infection of households is common
Sexual intercourse is also another possible method of spread among adults.

Sharing a bed or using the same underwear will also suffice to contact the disease.

Symptoms and clinical features of scabies

  1. Severe pruritus worse at night is characteristic
  2. The typical lesion is the burrow – It is hardly seen because of the marked excoriation and
    secondary infection on the skin
  3. Papulo-pustular eruptions with excoriation and impetiginized.
  4. Characteristic sites of predilection:
    • Interdigital spaces of the fingers
    • Flexural surfaces of the wrist
    • Extensor surfaces of the elbows and knees
    • Anterior axilliary area
    • Nipples
    • The phallus (especially in adults)
  5. General immune status and experience with S. scabiei play a role
  6. In a normal host, the initial infection is asymptomatic for about 3-6 weeks during which time the individual is capable of transmitting the disease
  7. All family or living unit members must therefore be treated, not just the itching ones.
  8. After a reinfestation, symptoms appear within 24 hours.

Crusted scabies (Norwegian scabies)

  • Crusted scabiesis an uncommon variant of scabies.
  • Patient fails to mount a resistance and the mites proliferate dramatically
  • It may be found among HIV/AIDS patients, institutionalized inmates like prisoners, refugees, and psychiatric patients.

Differential diagnoses

  • Infantile acropustulosis
  • Papular acral dermatitis of childhood.
  • Dermatitis herpetiformis
  • Atopic dermatitis

Complications of scabies

  1. Secondary bacterial infection leading to acute glomerulonephritis

Investigations

  • Burrow scraping on to a glass slide for microscopy
  • Video dermatoscopy

Treatment for scabies

Treatment objectives

  1. Treat the infestation
  2. Treat secondary bacterial infection
  3. Relieve pruritus

Drug treatment

1. Scabicides:

Permethrin 5% cream

  • Adult: apply over the whole body and wash off after 8-12 hours
  • Child: supervision required with application and rinsing

Or:

Benzyl benzoate 25% in emulsion

  • Adult: apply over the whole body; repeat without bathing next day and wash off 24 hours later. If necessary apply a third time
  • Child: Benzyl benzoate is an irritant and should be avoided in children

Or:

Precipitated sulfur 5-10% in petroleum jelly

  • Adult and child: apply over all the body daily for 7-10 days

2. Antihelminthic:

Ivermectin

  • Adult: Single 200 microgram/kg oral dose for crusted scabies
  • Child: over 5 years: 200 micrograms/kg daily for 2 days

Antihistamine:

3. Chlorphenamine

Adult: 4 mg orally every 4-6 hours; maximum 24 mg a day

Child:

  • 1 month – 2 years 1mg orally every 12 hours;
  • 2-5 years: 1 mg every 4-6 hours;
  • 6-12 years: 2 mg every 4-6 hours

4. Topical antipruritic:

Crotamiton cream (for residual itching)

  • Adult: apply every 8-12 hours
  • Child: less than 3 years: apply once daily only

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