Scabies

Scabies

Cover image: Scabies is an infestation of the skin by the Sarcoptes scabiei mite. It causes generalized intractable pruritus with a characteristic distribution pattern. Risk factors include immunosuppression and crowded living conditions. Scabies is easily transmitted through skin to skin contact. Animal and fomite transmission may also occur. | Medcomic/Jorge Muniz

Scabies, previously known as the seven-year itch, is a contagious skin infestation by the mite Sarcoptes scabiei.


Aetiology

Scabies is essentially a disease of children

Risk factors

  • Lower socioeconomic status
  • Crowding
  • Poor hygiene
  • Immunosuppression
    • Norweigean scabies

Pathophysiology

  • TRANSMISSION:
    • Intimate prolonged contact (eg. household)
    • Fomite transmission (clothing & bedding)
    • Sexual transmission
scabies1
The Calgary Guide | http://calgaryguide.ucalgary.ca/

Clinical features

  • Asymptomatic
    • First 4 weeks
  • Severe itching, worse at night
  • Family members also infected

Morphology

  • PRIMARY LESIONS
    • Burrows (pathognomic)
      • Serpentine, thread-like, greyish or darker lines ranging from a few mm to few cm
    • Papules & papulovesicle
      • Due to hypersensitivity to mite
  • SECONDARY LESIONS
    • Pustules due to 2° infection
    • Eczematoid lesion
    • Nodular lesion
      • On scrotal & penile skin

Sites of predilection:

  • ADULTS
    • Flexor aspects of wrists
    • Ulnar aspect of forearm
    • Ant. axillary fold
    • Umbilicus & periumbilical region
    • Genitalia & upper thighs
    • Lower part of buttock and nasal clefts
    • Nipples & areolae in women
    • Sites spared: Scalp, face, palm, soles
  • INFANTS
    • Scalp, face, palm, soles
afp20120915p535-f3
Characteristic distribution of lesions in adults with classic scabies. Burrows are more common on hands and wrists, whereas papular or nodular lesions generally are present elsewhere. | Flinders DC, De Schweinitz P. Pediculosis and scabies. Am Fam Physician. 2004;69(2):345.

Variants

  • Norwegian scabies/Crusted scabies
    • Seen in,
      • Immunocompromised patients
      • Lymphoreticular & other malignancies
      • HIV patients
      • Immunosuppressive therapy
    • C/F:
      • Widespread, crusted & hyperkeratotic lesions teeming innumerable mites
640px-norwegian_scabies_in_homeless_aids_patient
Photo of AIDS Patient with crusted Scabies. Patient reported it took 6 months for this to develop after an initial “itch” | By Ukster1 at English Wikipedia(Original text: Andrew G) – Own work (Original text: self-made), Public Domain, https://commons.wikimedia.org/w/index.php?curid=3821727

Complications

  • SECONDARY INFECTIONS:
    • S. aureus, S. pyogenes
    • Acute post-streptococcal GN following streptococcal pyoderma in scabies (10%)
    • Eczematisation, impetigo, secondary lymphadednitis

Management

All members of the household to be treated irrespective of infection status

Supportive management

  • Pruritus
    • Promethazine (Phenergan) + Zn-ointment
  • Secondary infection
    • Antibiotics (Erythromycin)

Medical management

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  • Permethrin 5% (Scabicide of choice)
    • 1 application/day
      1. Whole body below chin application
      2. Allowed to dry for 8-12 hours
      3. Bath
  • Benzyl benzoate 25%
    • 3 applications/12-hr
  • γ-BHC (γ-Benzene hexachloride) 1%
    • Avoided in infants
  • Crotamiton 10%
    • 2 applications daily X 14 days
  • Sulphur ointment 10%
    • 2 applications daily X 14 days
  • Ivermectin 
    • Norwegian scabies
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