Genital Scabies

Genital scabies is infestation of the genital skin by the mite Sarcoptes scabiei var. hominis, causing intense itch and characteristic nodules of the penis and scrotum. It is acquired by prolonged skin to skin contact, including sexual contact, and is considered an STI in adults.

• Common in crowded settings, informal settlements, institutions, and among people with HIV.
• Crusted (Norwegian) scabies occurs in immunosuppression, causing very high mite burden and outbreaks.

Severe itch, worse at night, with erythematous papules on the penis, scrotum, labia, buttocks, and groin; firm, red brown pruritic nodules on the glans and scrotum are pathognomonic.

• Burrows in the finger webs, wrists, axillae, waist and breast areolae; spares the face in adults.
• Differential diagnosis: eczema, contact dermatitis, pubic lice, herpes simplex, syphilis, molluscum contagiosum, folliculitis, lichen planus, balanitis, papular urticaria, prurigo nodularis.
• Complications: secondary bacterial infection (impetigo, cellulitis, glomerulonephritis, rheumatic fever), persistent nodules for months, sleep loss, crusted scabies, institutional outbreaks.

Clinical, with dermoscopy or skin scraping.

• Dermoscopy shows delta wing jet sign; skin scraping with KOH to see mites, eggs or scybala under the microscope; burrow ink test.
• Swab for infected lesions; screen for HIV, syphilis, gonorrhoea, chlamydia.
• Biopsy for atypical nodules.

Treat the patient, sexual partners and household together.

• Supportive: wash bedding, towels and clothes at 60 degrees Celsius and dry on high heat, or seal in plastic bags for 72 hours, vacuum soft furnishings, avoid skin contact until treated, avoid sex until 24 hours after treatment, treat partners and household members simultaneously, including those without symptoms.
• Pharmacological: permethrin 5 percent cream applied from neck to toes (including genitals, under nails, skin folds) and left for 8 to 14 hours, then washed off, repeated after 7 days; or ivermectin 200 micrograms/kg orally on day 1 and day 8 with food (not for children under 15 kg or pregnancy); benzyl benzoate 25 percent lotion applied for 24 hours on two consecutive nights, repeated after 7 days (dilute 1 in 2 for children, 1 in 3 for infants); sulfur 5 to 10 percent in petrolatum on three consecutive nights for infants and pregnancy. Itch: cetirizine 10 mg at night; persistent nodules: clobetasol 0.05 percent ointment twice daily for 2 to 4 weeks or intralesional triamcinolone acetonide 10 mg/mL. Secondary infection: flucloxacillin 500 mg four times daily for 7 days. Crusted scabies: ivermectin 200 micrograms/kg on days 1, 2, 8, 9 and 15 with daily permethrin and keratolytic.
• Procedures: none.
• Special groups: pregnancy, permethrin or sulfur; infants, permethrin 5 percent (excluding face) or sulfur; HIV and crusted scabies, isolation and repeated treatment; elderly institutionalised, treat all residents and staff.
• Red flags: crusted lesions, widespread infection, fever with cellulitis, nodules not clearing, no response after two treatments.
• Follow-up: review at 2 and 4 weeks; itch can continue for 2 to 4 weeks after cure; retreat if new burrows; sexual health screen.