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Scabies

Scabies is a highly contagious mite infestation of the epidermis that causes an incredibly itch rash. It's usually transmitted through close skin contact, such as holding hands for a prolonged time or sex.


N.B. Spread via fomites (clothing, towels, etc.) is very uncommon as the mite perishes within hours of leaving the host.


N.B. It can’t be caught from animals as the organism causing it is different.


Presentation

  • Itchy rash that is symmetrical, and mainly affects the hands, wrists, axillae, thighs, buttocks, waist, and soles of the feet. The head and neck are usually spared.

    • The Itch occurs 4-6 weeks after the initial infection (host is still infectious), is worse at night, and may persist for several weeks after treatment

  • Burrows (pathognomonic feature) - Thread-like tracks typically found in the web spaces of the fingers/toes.

Day 6 of scabies on right hand, wrist, and arm. Many itchy red spots are visible. (https://commons.wikimedia.org/wiki/File:ScabiesD06.jpg)

Investigations

Always think scabies in a patient with a new widespread itchy rash, especially if they report close contacts with similar symptoms. The diagnosis is typically clinical and most easily confirmed using dermoscopy.


Investigations include:

  • Dermoscopy

  • Skin scrapings

  • Burrow ink test - shows a classical zig-zag line where the ink has tracked into a burrow

  • Ectoparasite preparation


Crusted Scabies

This is an extremely contagious and serious version of scabies in the immunocompromised. Compared to normal scabies:

  • Rather than individual spots and burrows, these patients have patches of red skin that turn into scaly plaques due to dense hyperkeratosis (often misdiagnosed as psoriasis)

  • Patients don’t present with an itch as they can’t form an immune response to the infestation

  • Transmitted a lot more easily e.g. brief handshake/hug

  • Can be spread via fomites e.g. clothing, towels, etc.


Management

1st line - Permethrin cream

  • This is applied to the whole body, and left on for 8-12 hours before washing it off. It should be repeated a week later to kill all the eggs that survived the first round of treatment.

  • Oral Ivermectin is 2nd line here if difficult to treat or crusted scabies


It's also important to advise patients that:

  • All household and close contacts should also be treated, even if asymptomatic

  • All clothes, bedclothes, towels and other materials in contact with scabies need to be washed at very high heat

  • Thoroughly hoover carpets and furniture



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