Scabies: Mite Infestation – Diagnosis, Treatment & Prevention

Etiology

Sarcoptes scabiei var. hominis – obligate human ectoparasite. Female burrows into stratum corneum, lays eggs → larvae → nymphs → adults (10–14 day cycle).

Transmission

• Prolonged skin-to-skin contact (sexual, household, caregiving).
• Fomites (bedding, clothing) – minor role; mites survive 48–72h off host.
• Crusted (Norwegian) scabies: hyperinfestation → highly contagious via brief contact/fomites.

Clinical Features

• Intense nocturnal pruritus (type IV hypersensitivity to mite products).
• Burrows: Thin, grayish, serpiginous lines (finger webs, wrists, elbows, axillae, genitalia, buttocks).
• Papules, vesicles, nodules (scrotum, axillae).
• Secondary infection: Impetigo, cellulitis (S. aureus, Strep).

Diagnosis

• Clinical (burrows + distribution + history + contact).
• Dermoscopy: "Delta wing" / "jet with contrail" sign.
• Skin scraping + KOH / mineral oil → microscope: mite, eggs, feces (scybala).

Treatment

Agent	Regimen	Notes
Permethrin 5% Cream	Neck-to-toes, 8–14h, repeat Day 7	First-line; safe >2 mo, pregnancy
Ivermectin PO	200 mcg/kg Day 1 & Day 8	Alternative; >15 kg; not in pregnancy
Benzyl Benzoate 25%	Daily × 3 days	Irritating; used in resource-limited settings
Sulfur 6–10% in Petrolatum	Nightly × 3 nights	Safe in infants, pregnancy

Environmental Measures

• Wash bedding/clothing >60°C; dry hot cycle.
• Seal non-washables in plastic bag × 72h.
• Treat all household/close contacts simultaneously.

Crusted Scabies

• Immunocompromised, elderly, institutionalized.
• Requires combination: permethrin daily × 7 days + ivermectin Days 1,2,8,9,15 ± keratolytics.
• Infection control: isolation, PPE.

Scabies is curable; treatment failure usually due to inadequate application, missed contacts, or reinfestation.