Sarcoptes scabiei: Difference between revisions

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Sarcoptes scabiei
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==Background==
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* A mite that causes '''scabies'''
  
   
  +
*A mite that causes '''scabies'''
−
== Microbiology ==
  
   
  +
===Microbiology===
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* Eight-legged mite
  
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* Lives on human skin, but can survive 24 hours on clothes and linens
  
   
  +
*Eight-legged mite (arachnid)
−
== Epidemiology ==
  
  +
*Lives on human skin, but can survive 24 hours on clothes and linens
   
  +
===Epidemiology===
−
* Transmitted by direct contact
  
−
* In the case of crusted scabies, may also have transmission via fomites
  
   
  +
*Transmitted by person-to-person direct contact
−
== Management ==
  
  +
**They don't jump
  +
**Transmission via unwashed bed sheets or heavily contaminated clothing
  +
**Animal scabies ([[mange]]) can transiently infect humans
  +
*Common worldwide
  +
*More common in:
  +
**Crowded conditions
  +
**Institutional setting
  +
**Children less than 2 years of age
  +
***School transmission unlikely given contact is not typically close enough
  +
**Winter time in Northern hemisphere
  +
**Periods of civil unrest
  +
*In the case of crusted scabies, may also have transmission via fomites
   
  +
=== Pathophysiology ===
−
* 5% permethrin applied from hairline of neck down entire body, left for 12 hours, then washed off
  
−
** Must be reapplied on any areas (like hands) that are washed during the 12 hours
  
−
* All clothes/beddings must either be washed in 50+ ºC water, or placed in a sealed plastic bag for 3 to 7 days
  
−
* Household contacts should be treated as well
  
   
  +
* Male and female crawl around on the skin and mate either on the skin or in a burrow
  +
* Female, once fertiziled, burrows into epidermis and lays 2-3 eggs daily along the path of the burrow
  +
** Lays up to 20-25 eggs before she dies
  +
** Moults about every 5 days
  +
* Eggs hatch into larvae in 3 to 4 days
  +
* Mites can live off of human host for 24 to 36 hours (longer if cold)
  +
  +
== Clinical Manifestations ==
  +
  +
=== Classical Scabies ===
  +
  +
* Low burden (5 to 15 mites)
  +
* Only symptom is intense pruritis, which is caused by delayed type IV hypersensitivity reaction
  +
** Usually appears after after 4 to 6 weeks on first infection, but within 24 to 48 hours on repeat infestation
  +
** Often worse at night
  +
* Can see burrows, but not always
  +
** Classically in webs of fingers
  +
** They can be subtle and atypical
  +
  +
=== Crusted Scabies ===
  +
  +
* Sometimes called Norwegian scabies
  +
* Seen in cellular immunocompromise, including advanced [[HIV]], [[leprosy]], [[lymphoma]], and the elderly
  +
* Starts as areas of erythema anywhere on the body (most commonly scalp, hands, and feet)
  +
* Develops into crusted or scaly areas
  +
* No or minimal itching, due to lack of cell-mediated hypersensitivity
  +
* Heavy mite burden, with thousands
  +
  +
=== Atypical Scabies ===
  +
  +
* Scalp, seen in infants and young children
  +
* More generalized lesions, in infants and children
  +
* Nodular scabies (violacenous, pruritic nodules)
  +
** Typically on scrotum or genetalia, or breasts
  +
  +
== Differential Diagnosis ==
  +
  +
* [[Eczema]]
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* [[Tinea]]
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* [[Atopic dermatitis]] or [[contact dermatitis]]
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* [[Papular urticaria]]
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* [[Seborrheic dermatitis]]
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* [[Bullous pemphigoid]]
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  +
== Diagnosis ==
  +
  +
* Usually made clinically
  +
* If sending a skin scraping, use the leading edge of the burrow
  +
  +
==Management==
  +
  +
*5% [[Is treated by::permethrin]] applied from hairline of neck down entire body, left for 12 hours, then washed off
  +
**Must be reapplied on any areas (like hands) that are washed during the 12 hours
  +
*For clinical failure or more extensive infestations, [[Is treated by::ivermectin]] 200 μg/kg, repeated once at day 14
  +
**Treatments are not ovacidal
  +
*For crusted scabies, consider combination topical plus oral
  +
**[[Permethrin]] applied daily for 7 days, repeated weekly for 2 weeks
  +
**[[Ivermectin]] 200 μg/kg p.o. on day 1, 2, 8, 9, and 15; can be extended to include days 22 and 29 for severe cases
  +
*Alternatives include lindane 1% lotion, benzyl benzoate 10-25%, and others
  +
*Household management
  +
**All clothes/beddings must either be washed in 50+ ºC water, ironed, dry-cleaned, or placed in a sealed plastic bag for 3 to 7 days
  +
**Household contacts should be treated as well
  +
*Itching may continue for 4 to 6 weeks due to the cell-mediated hypersensitivity reaction to dead mites and eggs
  +
  +
== Prevention ==
  +
  +
=== Infection Prevention and Control ===
  +
  +
* For crusted scabies, strict contact precautions
  +
* Contacts should be treated empirically, including family, patient care staff, etc.
 
{{DISPLAYTITLE:''Sarcoptes scabiei''}}
  
{{DISPLAYTITLE:''Sarcoptes scabiei''}}
 
[[Category:Ectoparasites]]
  
[[Category:Ectoparasites]]

Latest revision as of 11:27, 15 May 2023

Background

  • A mite that causes scabies

Microbiology

  • Eight-legged mite (arachnid)
  • Lives on human skin, but can survive 24 hours on clothes and linens

Epidemiology

  • Transmitted by person-to-person direct contact
    • They don't jump
    • Transmission via unwashed bed sheets or heavily contaminated clothing
    • Animal scabies (mange) can transiently infect humans
  • Common worldwide
  • More common in:
    • Crowded conditions
    • Institutional setting
    • Children less than 2 years of age
      • School transmission unlikely given contact is not typically close enough
    • Winter time in Northern hemisphere
    • Periods of civil unrest
  • In the case of crusted scabies, may also have transmission via fomites

Pathophysiology

  • Male and female crawl around on the skin and mate either on the skin or in a burrow
  • Female, once fertiziled, burrows into epidermis and lays 2-3 eggs daily along the path of the burrow
    • Lays up to 20-25 eggs before she dies
    • Moults about every 5 days
  • Eggs hatch into larvae in 3 to 4 days
  • Mites can live off of human host for 24 to 36 hours (longer if cold)

Clinical Manifestations

Classical Scabies

  • Low burden (5 to 15 mites)
  • Only symptom is intense pruritis, which is caused by delayed type IV hypersensitivity reaction
    • Usually appears after after 4 to 6 weeks on first infection, but within 24 to 48 hours on repeat infestation
    • Often worse at night
  • Can see burrows, but not always
    • Classically in webs of fingers
    • They can be subtle and atypical

Crusted Scabies

  • Sometimes called Norwegian scabies
  • Seen in cellular immunocompromise, including advanced HIV, leprosy, lymphoma, and the elderly
  • Starts as areas of erythema anywhere on the body (most commonly scalp, hands, and feet)
  • Develops into crusted or scaly areas
  • No or minimal itching, due to lack of cell-mediated hypersensitivity
  • Heavy mite burden, with thousands

Atypical Scabies

  • Scalp, seen in infants and young children
  • More generalized lesions, in infants and children
  • Nodular scabies (violacenous, pruritic nodules)
    • Typically on scrotum or genetalia, or breasts

Differential Diagnosis

Diagnosis

  • Usually made clinically
  • If sending a skin scraping, use the leading edge of the burrow

Management

  • 5% permethrin applied from hairline of neck down entire body, left for 12 hours, then washed off
    • Must be reapplied on any areas (like hands) that are washed during the 12 hours
  • For clinical failure or more extensive infestations, ivermectin 200 μg/kg, repeated once at day 14
    • Treatments are not ovacidal
  • For crusted scabies, consider combination topical plus oral
    • Permethrin applied daily for 7 days, repeated weekly for 2 weeks
    • Ivermectin 200 μg/kg p.o. on day 1, 2, 8, 9, and 15; can be extended to include days 22 and 29 for severe cases
  • Alternatives include lindane 1% lotion, benzyl benzoate 10-25%, and others
  • Household management
    • All clothes/beddings must either be washed in 50+ ºC water, ironed, dry-cleaned, or placed in a sealed plastic bag for 3 to 7 days
    • Household contacts should be treated as well
  • Itching may continue for 4 to 6 weeks due to the cell-mediated hypersensitivity reaction to dead mites and eggs

Prevention

Infection Prevention and Control

  • For crusted scabies, strict contact precautions
  • Contacts should be treated empirically, including family, patient care staff, etc.
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