Scabies, Lice and Infestations

Insect bites

Presentation

  • Variable presentation depending on the insect, location etc and can vary from small papulo-urticaria to larger bullae.  Most are itchy and some may be painful.
  • May appear in a linear/regional distribution (linear- e.g. bed bugs; exposed regions- e.g. outdoor insects e.g. midges) where the insect has had access
  • At the extreme end, bites can induce an allergic reaction and/or can become infected

bites

A quick note about tick bites: see also Lyme Disease

Management

  • Try and identify the source and avoid that if possible.  Alternatively, use repelling creams/sprays.  Make sure household pets are treated, and that bed linen is clean.
  • Topical steroids and antihistamines may be used short term for symptomatic relief.

Scabies (Sarcoptes Scabiei)

Pathophysiology

  • Note that the symptoms of scabies is actually most likely an allergic reaction (mostly type IV, some type I) to saliva, mites, eggs, faeces.
    • As a result, most patients are asymptomatic for the first 6 weeks of infestation
  • Most infestations only composed of 10-12 mites in a patient who maintains hygiene (can be 100s if neglected)
  • The female mites burrow through the keratin layer at around 2mm/day, laying eggs as they go.
  • Scabies is highly contagious (skin-skin), so it is not uncommon for an entire household to get it

Presentation

  • Generalised itching (particularly when hot/warm)
  • Widespread eruption of inflammatory papules
    • Burrows may also be visible and tracks may also be seen
      • These are often fine, wavy, grey, dark or silvery lines with a minute speck (mite) at the end
    • Scabetic nodules may develop on the elbows, nipples, web spaces, wrists, axillae, penis or scrotum.  They are firm, dull red/brown, intensely itchy and may persist after treatment (they are not a sign of active infestation but the delayed reaction to an infestation)
    • Note that an eczematous reaction may also occur which can confuse the clinical picture with eczema.  Fissures/infection risk is also a possibility.
  • May have a contact history with someone with scabies

Investigations

  • Skin scraping with a blunt scalpel or needle.  KOH staining usually confirms whether a mite (which should adhere to the implement) is present
  • NB Scrapings are not very sensitive- the diagnosis will always be clinical based on history and examination.

Management

  • Permathrin cream top to toe for 8 hours (30g will cover average adult); twice, one week apart
  • Treat all in household and close contacts at the same time if possible (just once- the first treatment)
  • Prescribe mild-moderate topical steroid for secondary eczema/itch (may take a while to resolve)
  • Wash all clothes and linen at 50°C at first treatment
  • If permathrin is not appropriate (some patients may be allergic), then malathion aqueous liquid

Headlice (pediculosis capitis)

  • Infestation with pediculus capitis– which lives on the scalp of humans (cannot survive more than 3 days off the head.  Female may lay up to 10 eggs/day onto the hair shaft.

Pediculus_humanus_development

  • More common in girls aged 4-11 (i.e. primary school age) with longer hair
  • Symptoms (itchy scalp) may not develop til 2 weeks after initial infestation
  • Diagnosing lice can be done simply by fine combing the scalp (wet or dry).  If it is diagnosed in one member of the family, the rest of the family should be checked.

Management

  • If an infestation is confirmed, it can be eradicated with a combination of
    • Dimeticone 4% lotion or Malathion 0.5% aqueous liquid.  (both applied twice with a week between applications)
    • Active combing (Bugbuster comb)
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