DESCRIPTION

• Scabies is a parasitic infection caused by the mite Sarcoptes scabiei, which infects the stratum corneum of the skin and results in an intense pruritic rash.
• Crusted scabies is a subtype categorized by a more intense pruritus and rash with a heavier burden of mites.
  • Previously called “Norwegian scabies”
  • More common in immunocompromised (i.e., HIV, long-term corticosteroid use) and debilitated patients with sensory neuropathies and paralysis
• Nodular scabies is a rare clinical subtype presenting with red to brown nodules secondary to hypersensitivity reaction to mites and their by-products.

EPIDEMIOLOGY

• Results from close personal and prolonged contact with another human infected with mites
• Occurs worldwide and is endemic in many countries
• Scabies affects all people from different ethnicities, socioeconomic levels, and gender.
• Incidence varies worldwide, with cyclical fluctuations for new cases; estimates are 1 to 15 new cases per 1,000 people per year.
• Estimated 300 million cases worldwide; estimated 5–10% in children in developing countries

ETIOLOGY

S. scabiei var. hominis adult female mite is about 0.3- mm long with eight legs. It is barely visible with the naked eye.

PATHOPHYSIOLOGY

• The mite of scabies is a parasite that burrows into the skin and lays eggs. They travel anywhere between 0.5 and 5 mm a day. The larvae hatch from the eggs in 2 to 3 days and become adults and then the cycle repeats.
• Papules are not due to the mite itself but due to a hypersensitivity reaction (immune-mediated response) to the mites’ saliva, eggs, and feces.
• If the individual has never been exposed, there is an incubation period that can be between 4 and 6 weeks before symptoms manifest.
• Those with prior exposure and thus sensitized can have milder symptoms that occur within 1 to 4 days.
• Crusted scabies subtype has thousands to millions more mites, making infectivity easier even at less contact. The mite is the same as with classic scabies.