Scabies

Scabies

Introduction

• Scabies is an intensely pruritic skin infestation
• A source of human infestation for thousands of yrs (2500 yrs, Roman times)
• The term scabies is derived from Latin word scabere (to scratch).
• Prevalence rates are higher in children and sexually active individuals than in other persons.
• Caused by the host-specific mite, Sarcoptes scabiei var hominis. Is an obligate human parasite

Scabies mite

Pathophysiology

• Transmission is via direct and prolonged contact with an infected individual (not via inanimate objects)
• The entire life cycle of the mite lasts 30 days and is spent within the human epidermis.

Pathophysiology

• After copulation, the male mite dies and the female mite burrows into the superficial skin layers
• Once on the skin, fertilized female mites burrow through the stratum corneum at the rate of about 2 mm per day, and produce two or three oval eggs each day (total of 60-90 eggs).
• The ova require 10 days to 3 weeks to become mature adult mites

• Mites move through the top layers of skin by secreting proteases that degrade the stratum corneum.

• They feed on dissolved tissue

• Scybala (feces) are left behind as they travel through the epidermis, creating linear lesions clinically recognized as burrows.

• Upon initial infestation, a delayed type IV hypersensitivity reaction to the mites, eggs, or scybala develops over 4-6 weeks.

• The hypersensitivity reaction is responsible for the intense pruritus that is the clinical hallmark of the disease.

Clinical features

Distribution of the lesion differs in adults and children. Adults • Lesions manifest primarily on the flexure aspects of the wrists, the interdigital web spaces of the hands, and genitalia.

Infants and children

• Lesions can appear any where and any site may be involved.
• The diagnosis of scabies is considered in any patient presenting with a recent onset of intense itching that is accentuated at night.
• Similar symptoms in close contacts should immediately rank scabies at the top of the clinical differential diagnosis.

General Presentation

Clinical Types

• Classical
• Crusted

Crusted scabies (immunocompromised)

– Syn: Norwegian, scabies (so named because the first description was from Norway in the mid-1800s) – Is a highly contagious form of the disease. – Hundreds to millions of mites infest the host individual, – Usually immunocompromised, elderly.

Management

• Treatment includes administration of :

  • Scabicidal agents
  • Antipruritic agent (e.g.sedating antihistamine)
  • Antimicrobial agent if secondarily infected

• All family members and close contacts must be evaluated and treated,

• All clothing, bed linens, and towels used within the last week to be launder in hot water the day after treatment and again in 1 week.

• Application of topical antiscabietic agents, with repeat application in 7 days. These include:

  • Permethrin 5% cream is the drug of choice, especially for infants >2 mo and small children
  • Lindane1% lotion or cream
  • Sulfur 6% in petrolatum
  • Crotamiton (Eurax)10% cream or lotion for treatment of scabies

• An oral agent, ivermectin is proved to be effective

• Dose of 200-250 mcg/kg given at diagnosis and repeated in 7-14 days.