Sarcoptes scabiei: Difference between revisions

Latest revision as of 15:27, 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.

@@ Line 1: / Line 1: @@
+==Background==
-* A mite that causes '''scabies'''
+*A mite that causes '''scabies'''
-== Microbiology ==
+===Microbiology===
-* Eight-legged mite
-* 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
+* Male and female crawl around on the skin and mate either on the skin or in a burrow
-* All clothes/beddings must either be washed in 50+ ºC water, or placed in a sealed plastic bag for 3 to 7 days
+* Female, once fertiziled, burrows into epidermis and lays 2-3 eggs daily along the path of the burrow
-* Household contacts should be treated as well
+** 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]]
+* [[Tinea]]
+* [[Atopic dermatitis]] or [[contact dermatitis]]
+* [[Papular urticaria]]
+* [[Seborrheic dermatitis]]
+* [[Bullous pemphigoid]]
+== 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''}}
+[[Category:Ectoparasites]]