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Scabies Flashcards

1
Q

What causes scabies?

A

Human itch mite Sarcoptes scabiei var hominis

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2
Q

What is the lifecycle of the sarcoptes?

A

4-6 weeks

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3
Q

Describe the lifecycle of the sarcoptes

A

Mite burrows into human skin
Lays their eggs
Eggs develop, hatch and grow into adults after moulting - approx 10-15 days
Female lays 25 eggs and dies

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4
Q

How long does it take for egg to grow into adult sarcoptes?

A

10-15 days

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5
Q

What proportion of sarcoptes eggs develop into adults?

A

10%

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6
Q

What is the average number of mites in an initial infestation of scabies?

A

10-15

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7
Q

How many mites are implicated in subsequent infestation of scabies?

A

approx half of initial infestation eg 5-10

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8
Q

How does transmission of scabies occur?

A

Close skin contact with other person; unlikely through hand shake

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9
Q

How long can scabies mite live off a host?

A

24-36 hours

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10
Q

When might fomites transmission occur in scabies?

A

Uncommon
Wearing heavily contaminated clothing
Using a bed recently occupied by infested person

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11
Q

What characteristic of scabies infestation may make fomites transmission more likely?

A

‘Crusted scabies’ (greater number of mites and increased survival)

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12
Q

What is the main clinical feature of scabies?

A

Intense generalised pruritus, worse at night

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13
Q

What is the pruritus in scabies infestation due to?

A

Delayed type 4 hypersensitivity reaction to mite and mite products (faeces and eggs)

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14
Q

When do symptoms typically occur in INITIAL scabies infestation?

A

3- 6 weeks

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15
Q

In recurrent infestation of scabies, when do symptoms occur? Why?

A

1-3 days after re-infestation

due to prior sensitisation to the mite and products

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16
Q

Do you need pruritus to confirm scabies?

A

NO

Can occur without itch

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17
Q

What are the most common lesions in scabies?

A

Erythematous papules
often EXCORIATED
characteristic distribution

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18
Q

What is the characteristic distribution of scabies?

A 
interdigital webspaces
sides of fingers
under finger nails
flexor aspects wrist
extensor aspect elbow
anterior and posterior axillary folds
Nipples in women
Penis and scrotum in men
umbilicus
upper medial aspect thighs
buttocks
sides and back of feet
19
Q

What part of the body is typically spared in scabies?

20
Q

What is the pathognomonic lesion in scabies?

A

BURROW
linear intra-epidermal tunnel produced by moving mite
short wavy greyish/white threadlike elevation 2-10mm long

21
Q

What makes burrows difficult to identify in scabies?

A

excoriation

eczematisation

22
Q

Where might nodular lesions occur in scabies?

A

Penis and scrotum
Buttock
Groin
Axillary regions

23
Q

Nodular lesions are intensely pruritic and can persist after treatment, why?

A

hypersensitivity reaction to mite

24
Q

What is crusted scabies?

A

Caused by scabies crustosa/Norwegian scabies

25
Who are crusted scabies more common in?
immunocompromised states - AIDS - leprosy - lymphoma - those receiving systemic or potent topical steroids - organ transplant recipients - elderly - physically disability - Down syndrome
26
How is crusted scabies characterised?
``` erythematous scaly crusted lesions malodorous Fissures Any part of body including FACE and SCALP Itch may be mild or absent ```
27
What complication can occur from crusted scabies?
Sepsis due to fissures providing point of entry for bacteria
28
Which animals can scabies rarely be contracted from?
Dogs - Sarcoptes scabiei var Canis | Cats - Notoedres cati
29
What is the difference in animal scabies vs classical scabies?
shorter incubation period lesions confined to point of contact self-limitig as mites do not reproduce in human hosts Human to human transmission does not occur
30
What is scabies incognito?
Widespread atypical papular lesions that mimic generalised forms of eczema due to use of topical steroids which masks symptoms Still INFECTIOUS
31
How to make definitive diagnosis of scabies?
Skin scraping of burrow Glass slide + 10% potassium hydroxide Microscopy to visualise mite, eggs, faeces
32
Why is 10% potassium hydroxide used when preparing slide for microscopy in scabies?
Dissolves excess keratin for better visualisation of mite
33
Scabies - differential diagnosis?
``` Scabies requires HIGH CLINICAL suspicion Impetigo Folliculitis Papular urticaria Atopic dermatitis Contact dermatitis Dermatitis herpetiformis Psoriasis Seborrhoeic dermatitis Pityriasis rosea Secondary syphilis Lymphoma Pseudolymphoma ```
34
What organisms are implicated in secondary bacterial infection in scabies?
Staphylococcus aureus Group A B-haemolytic streptococci Peptostreptococci
35
How does secondary eczematisation occur in scabies?
constant scratching | irritant effects of topical medication
36
What is the general advice for scabies infestation?
``` WASH Bedding, clothing, towels used in previous FOUR days - 60 deg wash Alternative - dry in hot dryer - dry-clean - seal in plastic bag for 72 hours ```
37
What topical options are available for scabies treatment?
Permethrin % - wash off 12 hours, reapply 1 week later | Malathion 0.5% - wash off 24 hours, reapply 1 week later
38
When might permethrin be contraindicated?
Allergy/sensitivity in past or to CHRYSANTHEMUMS
39
What treatment regimen might people with crusted scabies require?
COMBINATION Permethrin cream daily for 1 week then twice weekly until cure AND oral ivermectin days 1, 2, 8, 9 and 15 but may require longer
40
What other precaution should happen for a person with crusted scabies?
Isolate them Barrier nurse Thorough clean room after treatment All household members/contacts should be treated
41
How long might itch continue for following treatment for scabies?
Up to 2 weeks
42
When should treatment failure be suspected in scabies?
New burrows appear | Itch longer than 4 weeks
43
What might improve/reduce the post scabetic itch?
Sedative antihistamine at night Crotamiton 10% cream topical hydrocortisone - if mite definitely eradicated Emollients for dry skin eczema

DipGUM (39 decks)

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