• Clinical science

Scabies

Summary

Scabies is a parasitic skin infestation caused by the Sarcoptes scabiei var. hominis (S. scabiei) mite, which is primarily transmitted via direct human-to-human contact. The female scabies mite burrows into the superficial skin layer, causing severe pruritus, particularly at night. Primary lesions commonly include erythematous papules, vesicles, or burrows. Treatment involves topical medical therapy (e.g., permethrin) and decontamination of all clothing and textiles.

Etiology

  • Pathogen: Sarcoptes scabiei var. hominis
  • Transmission
    • Highly contagious
    • Typically via direct physical contact
  • Risk factors: crowded living conditions (e.g., institutions such as nursing homes, child care facilities, and prisons)

References:[1][2][3][4]

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.

References:[5][6]

Clinical features

  • Incubation period: approximately 3–6 weeks following infestation.
  • Intense pruritus at night
  • Burning sensation
  • Skin lesions
  • 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)
    • Periumbilical area or waist
    • Additionally in children, elderly persons, and immunosuppressed patients: scalp, face, neck, under the nail, palms of hands, and soles of feet

References:[3][5][7][8]

Diagnostics

  • Typical history and skin lesions on clinical examination (see “Symptoms/clinical findings” above)
  • Environmental diagnosis (direct contact with infected persons)
  • Detection of mites, larvae, ova, or mite feces
    • Revealed in dermoscopy
    • Microscopic examination of the skin
    • Skin scraping and histology

Scabies may be mistaken for eczema, especially as the topical use of glucocorticoids initially alleviates symptoms!

References:[5]

Treatment

  • Medical therapy: topical application of a scabicidal agent
    • Drug of choice: permethrin 5% lotion
      • Mechanism of action: inhibition of voltage-gated sodium channels in the mite → delayed repolarization of neurons → paralysis and death of the mite
    • Alternatives
      • Lindane 1% lotion: in the case of treatment failure or side effects
        • Mechanism of action: blocks GABA channels → neurotoxicity in the mite
      • Oral ivermectin: especially indicated in large outbreaks or severe forms of scabies
    • Symptomatic treatment of pruritus
  • General measures
    • Wash all textiles (e.g., clothing and bedding)

References:[9]

Complications

  • Bacterial superinfection

References:[3]

We list the most important complications. The selection is not exhaustive.