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 steroid 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, social economic levels, and gender.

General Prevention

• Avoid direct skin-to-skin contact with a person who has scabies and with the clothing/bedding used by a person who has scabies.
• Ensure that any close contacts that have been exposed are treated even if asymptomatic because symptoms can take up to 30 days to develop.
• Everyone in the household should be treated at the same time.
• All bedding and clothing used in the prior 3 days by a person with scabies needs to be washed with hot water and dried in a hot dryer for at least 10 minutes or should be dry-cleaned.
• Furniture and carpets in the household of an infected person should be vacuumed.
• Anything that cannot be washed should be isolated from humans for at least 2 days or, more conservatively, for up to 3 weeks.

Pathophysiology

• The mite of scabies is a parasite that burrows into the skin and lays eggs. They travel anywhere between 0.5 and 5.0 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 which 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.

Etiology

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