Scabies is a contagious skin infestation caused by the microscopic mite Sarcoptes scabiei var. humans, which burrows into the superficial layers of the epidermis. The condition affects humans worldwide and is particularly common in crowded living conditions and among individuals with limited access to hygiene facilities.
Etiology and Transmission
- The disease is caused exclusively by the female mite of the Sarcoptes scabiei species.
- Transmission occurs primarily through prolonged skin-to-skin contact; brief contacts are generally insufficient for transmission.
- Indirect transmission via contaminated bedding, clothing, or towels is possible but less common.
Pathophysiology
- After a mite penetrates the stratum corneum, it creates a tunnel in which it lays eggs.
- The immune response to mite proteins, feces, and eggs produces intense pruritus, especially at night.
Clinical Presentation
- The hallmark symptom is intense itching that worsens at night.
- Typical lesions include erythematous papules, vesicles, and linear burrows (often 1–10 mm) visible on the skin surface.
- Common sites: interdigital spaces of the fingers, wrists, elbows, axillae, waistline, genitalia, and feet.
- In infants and immunocompromised patients, the presentation may be more widespread and include crusted (Norwegian) scabies, characterized by hyperkeratotic plaques with high mite burden.
Diagnosis
- Clinical diagnosis is based on characteristic distribution of lesions and pruritus.
- Confirmatory methods: skin scraping examined under microscopy to identify mites, eggs, or fecal pellets.
- Dermoscopy can aid visualization of the “delta wing” sign (the mite’s head and legs).
Treatment
- First-line topical therapy: 5% permethrin cream applied overnight to the entire body (from neck down) and repeated after 8–14 days.
- Alternative topical agents: 10% sulfur ointment (particularly in infants) and benzyl benzoate.
- Oral ivermectin (200 µg/kg) is used for crusted scabies or when topical therapy is impractical; a second dose is given 1–2 weeks later.
- All close contacts and household members should receive simultaneous treatment, even if asymptomatic, to prevent reinfestation.
Prevention and Control
- Regular laundering of clothing, bedding, and towels in hot water (≥50 °C) and drying on high heat.
- Isolation of affected individuals and treatment of contacts during outbreaks in institutions (e.g., nursing homes, prisons).
Epidemiology
- Scabies affects an estimated 200 million people globally at any time.
- Prevalence is higher in tropical regions, low- and middle-income countries, and among populations with overcrowding.
Complications
- Secondary bacterial infection (e.g., Staphylococcus aureus or Streptococcus pyogenes) may result from scratching, leading to impetigo, cellulitis, or post‑streptococcal glomerulonephritis.
- Crusted scabies, a severe form, can cause extensive skin breakdown and systemic illness.
Historical Notes
- Descriptions of scabies date back to ancient Greek and Roman medical texts.
- The causal mite was identified in 1687 by Italian physician Giovanni Cosimo Bonomo and his collaborator, physician Giovanni Battista Morgagni.
Public Health Impact
- Scabies contributes to morbidity through itch, sleep disturbance, and secondary infections.
- WHO lists scabies as a neglected tropical disease, highlighting the need for improved surveillance and treatment access.
References
(References are omitted in this summary but are available from peer‑reviewed dermatology and infectious disease literature.)
