Scabies

Scabies is a highly contagious skin infestation caused by the mite Sarcoptes scabiei var. hominis, which burrows into the epidermis to lay eggs.

• Transmission occurs primarily via prolonged skin-to-skin contact, and less commonly via contaminated bedding or clothing.

• Crowded living conditions, poor hygiene, and close contact (households, dormitories, refugee camps) increase the risk.

• The incubation period for a first infestation is usually 2–6 weeks, whereas reinfestation may cause symptoms within 1–4 days due to prior sensitization.

Epidemiology:

• Scabies affects all age groups but is most common in children and young adults.

• Immunocompromised individuals are at higher risk of developing severe forms, including crusted (Norwegian) scabies.

Signs & Symptoms

Classic Scabies:

• Intense pruritus, often worse at night

• Papules, vesicles, and nodules, especially in interdigital spaces, wrists, elbows, axillae, waist, genitalia, and buttocks

• Burrows: short, elevated, serpiginous tracks in the superficial epidermis

• Excoriation and secondary bacterial infections due to scratching

Crusted (Norwegian) Scabies:

• Thick, hyperkeratotic crusts resembling psoriasis

• Extensive scaling over palms, soles, elbows, knees, and scalp

• Often mild pruritus despite heavy infestation

• More common in immunocompromised or debilitated patients

Complications:

• Secondary bacterial infections (Staphylococcus aureus, Streptococcus pyogenes)

• Impetiginization, cellulitis, or post-streptococcal glomerulonephritis

• Spread to close contacts if untreated

Diagnostic Criteria

Clinical diagnosis is generally sufficient:

• Intense nocturnal itching

• Papules, vesicles, nodules in characteristic locations

• Burrows (short elevated S-shaped tracks)

• Crusted lesions in Norwegian scabies

• Household contacts often symptomatic

Laboratory confirmation (rarely needed):

• Skin scraping: Mites, eggs, or fecal pellets observed under microscopy

• Dermoscopy: Visualize burrows or mites

• Ink test: Ink applied to suspected burrow shows linear patterns

Investigation

• Microscopic examination of skin scrapings for mites, eggs, or feces

• Dermatoscopy to visualize burrows in atypical cases

• Assessment of secondary bacterial infection via swab if necessary

• Evaluation of household contacts

Treatment

Non-Pharmacological Treatment

• Treat all household contacts simultaneously, regardless of symptoms, to prevent reinfestation

• Clean environment: Wash clothing, bedding, and towels in hot water and dry thoroughly

• Avoid skin-to-skin contact until treatment is completed

• Advise short-term isolation in institutional settings during treatment

Pharmacological Treatment

Topical therapy (first-line):

• Benzyl benzoate emulsion (BBE) (25% for adults, 12.5% for children):

  • Adults and children over 2 years: Apply with fingers from the neck down to cover the whole body surface, paying attention to all skin folds. Leave in place for 6–8 hours overnight. Repeat the application after 7 days.

OR

• Lindane lotion 1%: Apply as for BBE above (do not use in children less than 1 year).

AND

• Betamethasone valerate cream (topical): Apply every 12 hours for itching.

AND

• Cetirizine (PO) 10 mg: Every 12 hours for 3–4 weeks.

OR

Systemic therapy (for extensive/Norwegian scabies):

• Ivermectin (PO) 200 micrograms/kg: Stat dose, then repeat after 1 week.

Adjunctive measures:

• Antihistamines for symptomatic relief of pruritus

• Topical antibiotics for secondary bacterial infections

Special considerations:

• Norwegian scabies requires combination therapy: systemic ivermectin + topical permethrin, repeated as necessary

• Immunocompromised patients may need prolonged therapy and close follow-up

Prevention

• Avoid prolonged skin-to-skin contact with infected individuals

• Immediate treatment of affected contacts

• Environmental decontamination: Wash bedding and clothing in hot water; dry in sunlight or hot dryer

• Education on early recognition and seeking prompt treatment

• Regular screening in institutional settings