What is it?

Scabies represents a highly contagious skin infestation caused by the microscopic mite Sarcoptes scabiei var. hominis, which burrows into the upper layer of human skin (stratum corneum). The condition is characterized by intense nocturnal pruritus (nighttime itching) and distinctive skin lesions including burrows, papules (small raised bumps), and secondary inflammatory changes. The female mites create superficial tunnels in the skin where they deposit eggs, leading to an inflammatory reaction that produces the characteristic symptoms of this parasitic infection.

Who is affected?

Scabies is a widespread condition worldwide:

Prevalence: Affects approximately 200 million people worldwide, with frequent spread in nursing homes, schools, prisons, military units, and other crowded facilities
Age: Higher prevalence in children, adolescents, and elderly populations, though all age groups can be affected
Socioeconomic factors: Disproportionately affects low-income communities, overcrowded environments, and underserved areas. Increased risk in immunocompromised individuals, those with limited hygiene access, and healthcare workers
Geography: More prevalent in tropical and subtropical regions, with increasing incidence in temperate climates

What causes it?

Scabies is transmitted directly, person to person:

Parasite: Sarcoptes scabiei var. hominis, a host-specific human parasite measuring 0.3-0.4mm
Transmission mechanism: Direct skin-to-skin contact (minimum 15-20 minutes for transmission), rarely through contaminated objects (bedding, clothing)
Mite lifecycle: Female mites burrow 0.5-5mm daily, laying 2-3 eggs per day over a 4-8 week lifespan
Development: The cycle from egg to adult mite takes approximately 2-3 weeks
Contagiousness: The patient is contagious until the first complete application of scabicidal treatment

What are the clinical features?

Scabies presents with characteristic signs and symptoms that develop following mite infestation:

Signs:

Pathognomonic burrows (fine, serpentine lines, 5-15mm in length, representing mite tunnels)
Erythematous papules (small red bumps distributed in characteristic locations)
Secondary lesions (excoriations from scratching, pustules from bacterial superinfection)
Typical distribution: Interdigital web spaces, wrists, elbows, axillae, nipples, periumbilical area, genitalia, and buttocks
Nodular lesions (persistent inflammatory nodules, particularly in genital areas and axillae)
Crusted lesions (in immunocompromised patients with hyperkeratotic "Norwegian scabies")

Symptoms:

Intense nocturnal pruritus (severe itching that worsens at night, affecting both infested and non-infested areas due to hypersensitivity reaction)
Secondary bacterial infection symptoms (worsening pain, local warmth, purulent discharge)
Sleep disruption (due to intense nighttime itching)
Social distress (embarrassment and anxiety related to contagious nature)

Disease progression:

After initial infestation, symptoms do not appear immediately — it takes several weeks for the host to become sensitized to the mite. Once established, pruritus worsens rapidly without treatment. With re-infestation, symptoms appear within 24-48 hours, as the body is already sensitized.

How is it diagnosed?

Diagnosis combines clinical assessment with confirmatory testing when possible:

Clinical diagnosis: Based on characteristic distribution pattern, intense nocturnal pruritus, and household contacts with similar symptoms
Dermoscopic examination: Visualization of burrows, mites, and eggs using dermatoscope
Microscopic confirmation: Skin scraping allows identification of mites, eggs, or parasitic waste (positive in only 50% of cases)
Response to treatment: Therapeutic trial with scabicide often used as diagnostic tool
Differential diagnosis: Distinction from atopic dermatitis, contact dermatitis, drug eruptions, and other pruritic conditions

What treatment options are available?

Treatment includes scabicidal therapy and hygiene measures:

First-line topical therapy:
- Permethrin 5% cream (first-choice treatment, applied whole-body for 8-14 hours)
- Treatment repeated in 7 days to eliminate recently hatched larvae
Topical alternatives:
- Benzyl benzoate 25% lotion (less expensive option in underserved areas)
- Precipitated sulfur 5-10% in petrolatum (safe for infants under 2 months)
Systemic therapy:
- Oral ivermectin 200μg/kg (equally effective as topical permethrin, preferred for outbreaks in communal settings)
- Repeat dose in 7-14 days
- Contraindicated in pregnancy and children <15kg
Adjuvant treatment:
- Antihistamines for symptomatic pruritus relief
- Topical corticosteroids for inflammatory reactions
- Antibiotics for secondary bacterial infections
Hygiene and decontamination measures:
- Machine wash bedding and clothing in hot water (≥60°C)
- Dry on hot cycle for 40 minutes
- Vacuum furniture and carpets
- Store non-washable items in sealed bags for 72 hours

Key points for patients

Scabies is highly contagious requiring treatment of all household members and close contacts simultaneously
Treatment must be followed through completely, even though itching may persist for 2-4 weeks after effective therapy
Post-scabies syndrome (persistent itching without active infestation) is common and does not indicate treatment failure
Secondary bacterial infections may develop and require antibiotic treatment
Laundering bedding and clothing and cleaning the living space is essential to prevent re-infestation
Return to work/school is typically permitted after the first treatment application
Follow-up examination recommended if symptoms persist beyond 4 weeks post-treatment