Scabies

Overview – Scabies

Scabies is a highly contagious parasitic skin infestation caused by the mite Sarcoptes scabiei. It is a significant cause of dermatological morbidity worldwide, particularly in tropical and resource-limited communities. The condition is characterised by intense nocturnal itching and a widespread, excoriated rash. Scabies does not resolve without treatment, making early recognition and simultaneous treatment of contacts essential for effective control, especially in community settings.

Definition

Scabies is a cutaneous infestation caused by the human-specific mite Sarcoptes scabiei, which burrows into the stratum corneum of the skin and causes a pruritic rash through mechanical disruption and immune response to mite products.

Aetiology

• Causative agent: Sarcoptes scabiei (scabies mite)
• Zoonotic infestations from pigs, horses, and dogs → mild and self-limiting
• Human-to-human infestations → persist without treatment

Pathophysiology

• Mites inhabit the stratum corneum (outermost layer of epidermis)
• Feed on keratinocytes and form burrows via digestion
• Mating occurs on the skin surface; fertilised females burrow into skin to lay eggs
• Salivary proteolytic enzymes digest keratin for nutrition
• No systemic invasion – remains superficial

Transmission

• Direct prolonged skin-to-skin contact is the primary route
• High prevalence in:
  • Children (≈50%)
  • Adults (≈25%)
  • Remote tropical communities (esp. Indigenous populations)

Clinical Features

• Intense pruritus, worsened at night and after hot showers
• Excoriated rash often affecting the:
  • Trunk
  • Wrists and interdigital spaces (scaly burrows)
  • Palms, soles, and sometimes the scalp (especially in infants)
• Burrows may appear as fine, serpiginous lines with a grey centre
• Secondary bacterial infection may develop due to scratching

Diagnosis

Clinical Diagnosis

• Chronic, symmetrical pruritus
• Presence of burrows or a typical rash distribution

Skin Scraping (under microscopy)

• Mite evidence includes:
  • Intact larvae, nymphs, or adults
  • Hatched/unhatched eggs
  • Mite faeces or moulted skin fragments

Management

Pharmacological

• Topical Permethrin 5% cream (first-line)
• Oral Ivermectin (non-PBS listed, expensive; reserved for crusted scabies or failed topical therapy)

Environmental Measures

• Wash bedding, clothing, and towels
• Sun-dry or use heat exposure
• Clean household surfaces (vacuum, insecticides)
• Crucial for managing crusted scabies due to environmental contamination

Public Health Measures

• Treat all close contacts simultaneously
• Community-wide treatment in outbreak settings (e.g. remote Indigenous communities)
• Repeat treatment after 7 days to target newly hatched mites

Summary – Scabies

Scabies is a contagious skin infestation caused by the mite Sarcoptes scabiei, which triggers intense pruritus and a characteristic rash through superficial burrowing in the stratum corneum. Transmission occurs via close contact, and without appropriate treatment of both the patient and their close contacts, recurrence is common. For a broader context, see our Microbiology & Public Health Overview page.