Scabies: Disease Overview and Treatment
What is Scabies?
Scabies is a highly contagious skin infestation caused by the parasitic mite Sarcoptes scabiei var. hominis, characterized by intense pruritus (especially nocturnal) and a distinctive papular rash with burrows. 1, 2
- The predominant symptom is pruritus, which develops several weeks after initial sensitization to the mite, but may occur within 24 hours after subsequent reinfestations. 1
- Classic lesions include serpiginous burrows, erythematous papules, and secondary excoriations from scratching. 3
- Predilection sites include finger webs, wrists, axillary folds, waist, abdomen, buttocks, genitals, and inframammary folds. 3
- Scabies affects over 200 million individuals worldwide and is recognized by the WHO as a neglected tropical disease. 2
First-Line Treatment
Permethrin 5% cream is the recommended first-line treatment for scabies across all age groups. 1, 4, 5
Application Protocol:
- Apply to all areas of the body from the neck down and wash off after 8-14 hours (typically overnight application). 1, 5
- A single application is generally curative for uncomplicated scabies. 4, 5
- Permethrin is effective, safe, and has minimal toxicity compared to alternatives. 1
Alternative Treatment: Oral Ivermectin
Oral ivermectin 200 μg/kg is an effective alternative, with a repeat dose required after 2 weeks. 4, 5
Critical Administration Details:
- Must be taken with food to ensure adequate bioavailability and epidermal penetration. 4, 5
- The two-dose schedule addresses ivermectin's limited ovicidal activity. 4
- Particularly useful in institutional outbreaks or when topical application is impractical. 4
Contraindications:
- Contraindicated in children weighing < 15 kg or younger than 10 years due to potential blood-brain barrier penetration and neurotoxicity. 4, 6
- Should be avoided in pregnant or lactating women due to insufficient safety data. 4, 5
Age-Specific Application Guidelines
Infants and Young Children (≤ 2 years):
- Apply permethrin to the entire body, including scalp, hairline, forehead, temples, and neck—not just neck-down as in adults. 4
- Permethrin is the only recommended agent for this age group. 4
Children ≥ 10 years (or ≥ 15 kg):
- May apply permethrin from neck down only, unless immunocompromised. 4
- Oral ivermectin becomes an option at this weight threshold. 4
Special Populations
Pregnant or Lactating Women:
- Permethrin 5% cream is the only recommended treatment. 1, 4, 5
- Ivermectin lacks sufficient safety data in pregnancy. 4
Crusted (Norwegian) Scabies:
This severe variant requires aggressive combination therapy and specialist consultation. 4, 5
- Topical permethrin 5% cream applied daily for 7 days, then twice weekly until cure. 4, 5
- Plus oral ivermectin 200 μg/kg on days 1,2,8,9, and 15. 4, 5
- Single-agent therapy will fail due to massive mite burden (thousands to millions of mites). 4
- Occurs primarily in immunocompromised, debilitated, or malnourished individuals. 4
Alternative Topical Agents (When Permethrin Unavailable or Fails)
Sulfur 6% Ointment:
- Apply nightly for 3 consecutive nights; wash off previous application before reapplying. 1
- Thoroughly wash off 24 hours after the last application. 1
Lindane 1%:
- Apply thinly from neck down and wash off after 8 hours. 1
- Critical contraindications and warnings:
- Never use in children < 10 years, pregnant/lactating women, or persons with extensive dermatitis. 1, 4, 5
- Never apply after bathing—increases systemic absorption and risk of seizures. 1, 5
- Seizures and aplastic anemia have been reported with improper use. 1
- Resistance has been documented in some geographic areas. 1
Contact and Environmental Management
Simultaneous treatment of all contacts is mandatory to prevent reinfection—this is the most common cause of treatment failure. 4, 5, 6
Who to Treat:
- All household members, close personal contacts, and sexual partners within the preceding month must be treated simultaneously, even if asymptomatic. 1, 4, 5
Environmental Decontamination:
- Machine-wash and dry all bedding, clothing, and towels on hot cycles, or dry-clean. 1, 4, 5
- Alternatively, isolate items from skin contact for ≥ 72 hours—mites cannot survive off-host longer than this. 1, 4
- Fumigation of living areas is not required. 1, 4, 5
Post-Treatment Course and Retreatment Criteria
Pruritus and rash may persist for up to 2 weeks after successful therapy due to allergic dermatitis—this does NOT indicate treatment failure. 4, 5, 6
When to Retreat:
- Retreatment is indicated only after 2 weeks if:
- Use an alternative regimen (switch between permethrin and ivermectin) if retreatment is needed. 4, 5
Common Pitfall:
- Avoid premature retreatment within the first 2 weeks based solely on persistent itching. 4
Institutional Outbreak Management
During outbreaks in nursing homes, hospitals, or residential facilities, treat the entire at-risk population concurrently. 1, 4
- Mass oral ivermectin is recommended for ease of administration. 4
- Outbreak response should involve specialist consultation to coordinate treatment and control measures. 1, 4
Critical Treatment Pitfalls to Avoid
- Failure to treat asymptomatic contacts simultaneously is the leading cause of reinfection and treatment failure. 4, 6
- Not repeating ivermectin dose at 2 weeks allows mite eggs to hatch and reinfestation to occur. 6
- Applying lindane after bathing dramatically increases systemic absorption and neurotoxicity risk. 1, 5
- Using lindane in contraindicated populations (children < 10 years, pregnant women, extensive dermatitis) risks seizures and aplastic anemia. 1, 4, 5
- Inadequate topical application—must cover all body surfaces from neck down, including under nails and body folds. 4
- Expecting immediate symptom resolution—post-treatment pruritus lasting up to 2 weeks is normal. 4, 5
Adjunctive Symptomatic Management
Topical corticosteroids (e.g., triamcinolone) should only be considered if pruritus persists beyond 2 weeks AND after confirming no live mites are present. 5