Scabies

• Scabies:

  • Highly contagious skin infestation caused by a mite
  • Spread by close contact and is more common among disadvantaged populations
  • Highest risk - children, the elderly, and people in long term care facilities
• Aetiology:

  • Parasitic mite - Sarcoptes scabiei var. hominis
  • Transmitted through direct skin-to-skin contact
  • Less commonly transmitted indirectly via formites
  • Clinical features of scabies primarily result from local allergic reaction to the presence of the scabies mite, rather than being directly caused by the mite itself
• Risk factors:

  • Direct contact with infected person
  • Formites - indirect contact through bedding, clothes, or towels
  • Living conditions - poverty and overcrowding
  • Environment - transmission more common in warm, tropical, humid environments
  • Immunosuppression
• History:

  • In first infection may be asymptomatic for up to 6 weeks, but in and subsequent infections this period will shorted
  • Once symptomatic - severe pruritus, worse at night, can cause sleep disturbance
  • May have other close contacts with similar symptoms
  • Important to take detailed social history - poor living conditions, overcrowding
• Clinical exam:

  • Typically found in the webbing and sides of fingers, wrists, elbows, axillae, feet and genitals
  • Rash is due to local hypersensivity reaction to mite
  • Rash appearance is quite variable but can include - erythematous papules or vesicles, and surrounding dermatitis
  • Burrows are characteristic - small irregular tracks (around 1cm), classically found in the webbed spaces between the fingers.
  • On dermatoscopy - mites or mites eggs/faeces may be visible in burrows = delta sign
• Crusted/Norwegian scabies:

  • Severe variant of scabies
  • Infected with thousands/millions of mites (5-20 in typical infection)
  • Very contagious
  • Causes crusted, scaly, keratotic rash
  • Rash typically in the finger webs, wrists, and elbows
  • Itch may be less prominent, or even absent
• Investigations:

  • Usually diagnosed clinically, but investigations can assist with diagnosis
  • Dermatoscopy - can see burrows better
  • Skin scraping and biopsy - of the burrow
• General advice:

  • Scabies is difficult to eradicate as it is highly contagious and has a long incubation period
  • Good hygiene
  • Wash all bed linen, clothes, toys
  • Close contacts of a person with scabies will need to be examined and treated
• Topical therapies:

  • 1st line = permethrin 5% cream
  • Pyrethoid family of medications - disrupts neurons of lice and scabies mites
  • Applied to entire body (excluding face) and left on for 8 hours. Repeat treatment in 7 days
  • 2nd line = Benzyl benzoate 25% emulsion
  • Itch can continue up for 4 weeks after treatment - crotamiton cream and chlorphenamine at night
• Systemic therapies:

  • Ivermectin = oral scabicide
  • Mainstay of systemic treatment for difficult to treat or crusted scabies. also good for outbreaks e.g. in care home
• Complications:

  • Secondary bacterial infection is common - Group A strep or Staph aureus
  • Treat secondary infections with antibiotics due to risk of sequelae from GAS - glomerulonephritis and rheumatic fever
  • Many patients who at risk of scabies are also at risk of these significant post-infectious sequelae