Scabies

Synonyms

Sarcoptic itch; Seven-year itch.

Epidemiology

Approximately 300 million individuals are affected worldwide each year. Overcrowding promotes the spread of the disease. Refugee camps are hotspots. Residential homes.

Definition

Intensely pruritic infestation caused by the mite Sarcoptes scabiei var. hominis.

Aetiology & Pathogenesis

Sarcoptes scabiei var. hominis is a human ectoparasite with marked host specificity. Human-to-human transmission occurs with close personal contact, sometimes via clothing or bedding. Female mites (0.3-0.5 mm) dig a burrow in the stratum corneum of the epidermis to lay their eggs; sexually mature mites develop in 3 weeks. Immunologic reaction to mite antigens causes inflammation and pruritus.

Signs & Symptoms

Marked pruritus, especially at night. Initially the mites burrow and develop elongated inflamed papules; in infants there can be evidence of vesicles. An exanthem with tiny papules and fine crusts may be found symmetrically over the flanks and proximal extremities, indicating a cellular immunologic reaction against scabies antigens. Face and interscapular regions are spared.

Localisation

The predilection sites for burrows: interdigital, anterior axillary folds, nipples, umbilicus, groin, penis, wrists and dorsal aspects of the feet. In children the face, scalp, palms, and soles can be affected. Exanthem -> see Symptoms.

Classification

Special form: Crusted (“Norwegian")scabies: massive infestation in immunosuppressed individuals, clinically presents as hyperkeratotic papules/plaques with thick scales.

Laboratory & other workups

Identification of the mite, its eggs, or scybala (feces) under the dermatoscope or microscope.

Dermatopathology

Usually not necessary, however, consider a biopsy in cases of persisting lesions causing pseudolymphomatous papules or small nodules.

Course

Can be chronic. Recurrences may occur.

Complications

Complications include impetiginisation, post scabetic papules (nodular scabies) and persistent inflammatory reaction without presence of mites. Itching often persists after successful eradication of the mites (post scabies dermatitis).

Diagnosis

Characteristic clinical features, including severe pruritus, worsening at night; a history of contact with a person with pruritus. Microscopic identification of mites, their eggs or scybala (feces) from specimen obtained by skin scraping or de-roofing burrow with scalpel blade.

Differential diagnosis

Pruritic dermatoses, prurigo, dermatitis herpetiformis, urticaria, psoriasis (in crusted scabies).

Prevention & Therapy

The treatment of choice is topical permethrin cream (5%) applied from top to toe once for 8-12 hours. Repeat the second course after 7 days. If there are still signs of active scabies after 14 days, repeat treatment with an alternative drug. Second line treatments include benzyl benzoate used on 3 consecutive days or crotamiton. Ivermectin orally for crusted scabies or if topical treatment is difficult.

Prevention of reinfection: Change clothing, bedding and wash everything. All non-washable items should be aired for 4 days (mites can live for 2-3 days at room temperature). Identify and treat in parallel contact persons (family, kindergarden, sexual partner).

Special

None.

2.4.2 Scabies