Epidemiology

Etiology

• Highly contagious
• Transmission is via direct person-to-person contact

Pathophysiology

• The fertilized, female mite tunnels into the superficial skin layer (stratum corneum), forming burrows in which she lays her eggs and deposits feces (scybala).
• After 2 months, the female parasite dies on site.
• Following a period of 3 weeks, the larvae mature into adult mites, maintaining the infestation cycle.
• The excretions of the mites and their decomposing bodies contain antigens which cause an immunological response (see type IV hypersensitivity reaction), presenting as severe pruritus and excoriations.

Clinical features

• Intense pruritus that increases at night
  • The name "scabies" comes from "scratch"
  • The warmth of the skin, especially under blankets and pajamas, can stimulate mite movement and activity, increasing pruritus.
• Skin lesions
  • Burrows of 2–10 mm in length
• Predilection sites
  • Wrists (flexor surface)
  • Medial aspect of fingers
  • Interdigital folds (hands and feet)
  • Male genitalia (e.g., scrotum, penis)
  • All other intertriginous areas of the skin (anterior axillary fold, buttocks)

Diagnostics

• Detection of mites, larvae, ova, or mite feces
  • Revealed in dermoscopy
  • Microscopic examination of the skin
  • Skin scraping and histology

Treatment

• Drug of choice: permethrin 5% lotion
• Alternatives
  • Oral ivermectin: especially indicated in large outbreaks or severe forms of scabies