Scabies

Scabies, Krätze.

Highly contagious parasitic skin disease caused by Sarcoptes scabiei var. hominis, characterized by intense pruritus, particularly at night. Transmission occurs through close skin-to-skin contact.

• Global burden: 200–400 million cases annually
• Switzerland: not a notifiable disease, but increasing cases in nursing homes, asylum centres, schools
• Frequent outbreaks in institutional settings, especially among migrants and homeless populations
• More prevalent during autumn and winter months

• Classic scabies
• Crusted scabies (Norwegian scabies)
• Nodular scabies
• Infantile scabies
• Occult scabies (e.g. in immunosuppressed individuals)

The female mite burrows into the epidermis to lay eggs. Clinical manifestations are due to an immune response to antigens from mite saliva, feces, and decaying mite material. Transmission typically requires prolonged direct skin contact (>5–10 minutes); indirect transmission via textiles is rare.

Incubation period:

• Primary infection: 3–6 weeks
• Reinfection: 1–4 days

• Intense nocturnal pruritus
• Erythematous papules, pustules, vesicles, and serpiginous burrows (typically interdigital)
• Predilection sites: interdigital spaces, wrists, axillae, areolar and genital regions
• Head and back usually spared (except in infants and crusted scabies)
• Nodular scabies presents with persistent nodules (especially genital area)
• Crusted scabies: hyperkeratotic plaques, minimal pruritus, very high mite burden

• Clinical diagnosis based on characteristic distribution, nocturnal itch, and exposure history
• Dermoscopy: visible burrows with “delta-wing” sign
• Microscopy after skin scraping (KOH or methylene blue): mites, eggs, or fecal pellets
• Ink test: lightly apply a drop of alcohol-diluted ink to the affected area, then dab with absorbent paper; the ink is preferentially retained in the scabies burrows, revealing them as dark, thread-like lines against the surrounding skin.
• PCR may assist in atypical cases
• Biopsy reserved for unclear cases (e.g., crusted scabies vs. psoriasis)

• Interdigital spaces, wrists, elbows, axillae, periumbilical region, areolae, buttocks, genitals
• Infants: also scalp, face, palms, and soles
• Crusted scabies: generalized involvement including scalp and nails

• Severe nocturnal itch
• Recent close contact with affected individuals (family, school, institutions)
• Eczema refractory to standard treatment
• Simultaneous pruritus in close contacts

• Spongiosis and acanthosis
• Perivascular lymphocytic infiltrates with eosinophils
• Mite components visible in the stratum corneum

• Secondary bacterial infection (notably Staphylococcus aureus or Streptococcus pyogenes)
• Post-scabetic eczema
• Persistent post-scabetic papules (may last weeks to months)
• Sepsis in crusted scabies (rare but potentially fatal)
• Psychosocial distress and stigmatization

Favourable if appropriately treated. Recurrence is common with reinfection or incomplete treatment of close contacts. Chronic cases may result from misdiagnosis or inadequate therapy.

• Early detection, especially in institutional settings
• Simultaneous treatment of all close contacts
• Hygiene measures: wash clothing and linens ≥ 60 °C or seal in plastic bags for ≥ 72 hours
• Isolation for crusted scabies until effectively treated

General measures

• Wash clothing, bedding, and towels at ≥ 60 °C or seal in plastic bags for 3 days
• Keep fingernails short and clean
• Treat all close contacts at the same time
• Repeat application after 7–14 days to target newly hatched mites
   

Topical therapy

• Permethrin 5% cream: standard first-line treatment in Switzerland
  • Apply to entire body (including genitals, palms, soles, under nails)
  • Infants: also apply to scalp and face
  • Leave on for 8–12 hours
  • Repeat after 7–14 days
• Alternatives: Benzyl benzoate 10–25% (irritating), Crotamiton 10% (less effective)

Systemic therapy

• Ivermectin 200 μg/kg orally, repeat after 7–14 days
  • Available in Switzerland as Subvectin® (3 mg tablets, special use authorization)
  • Indicated for: crusted scabies, treatment failure, large outbreaks, cognitive impairment
  • Contraindicated in children <15 kg and during pregnancy (topical treatment preferred)
• Combination therapy (topical + systemic) recommended in crusted scabies

1. Engelhardt B, et al. Management of scabies outbreaks in Switzerland. Swiss Medical Forum, 2023.
2. WHO. Ending the neglect to attain the Sustainable Development Goals: A road map for neglected tropical diseases 2021–2030.
3. Thomas J, et al. Interventions for treating scabies: Cochrane Review. Cochrane Database Syst Rev, 2021.
4. Dupuy A, et al. Accuracy of dermoscopy in diagnosing scabies. J Am Acad Dermatol, 2021.
5. Currie BJ, et al. Scabies: a global disease needing new therapies. Lancet Infect Dis, 2022.
6. Federal Office of Public Health (FOPH). Scabies – professional guidance. Updated 2024.
7. Swissmedic. Ivermectin: status in Switzerland. Updated 2023.
8. Davis JS, et al. Review: scabies diagnosis and management. BMJ, 2022.
9. Romani L, et al. Scabies control: challenges and perspectives. Curr Opin Infect Dis, 2024.
10. Mounsey KE, et al. Tolerance of Sarcoptes scabiei to ivermectin. Clin Microbiol Rev, 2023.