Scabies Flashcards
What causes scabies?
Human itch mite Sarcoptes scabiei var hominis
What is the lifecycle of the sarcoptes?
4-6 weeks
Describe the lifecycle of the sarcoptes
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
How long does it take for egg to grow into adult sarcoptes?
10-15 days
What proportion of sarcoptes eggs develop into adults?
10%
What is the average number of mites in an initial infestation of scabies?
10-15
How many mites are implicated in subsequent infestation of scabies?
approx half of initial infestation eg 5-10
How does transmission of scabies occur?
Close skin contact with other person; unlikely through hand shake
How long can scabies mite live off a host?
24-36 hours
When might fomites transmission occur in scabies?
Uncommon
Wearing heavily contaminated clothing
Using a bed recently occupied by infested person
What characteristic of scabies infestation may make fomites transmission more likely?
‘Crusted scabies’ (greater number of mites and increased survival)
What is the main clinical feature of scabies?
Intense generalised pruritus, worse at night
What is the pruritus in scabies infestation due to?
Delayed type 4 hypersensitivity reaction to mite and mite products (faeces and eggs)
When do symptoms typically occur in INITIAL scabies infestation?
3- 6 weeks
In recurrent infestation of scabies, when do symptoms occur? Why?
1-3 days after re-infestation
due to prior sensitisation to the mite and products
Do you need pruritus to confirm scabies?
NO
Can occur without itch
What are the most common lesions in scabies?
Erythematous papules
often EXCORIATED
characteristic distribution
What is the characteristic distribution of scabies?
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
What part of the body is typically spared in scabies?
BACK
HEAD
What is the pathognomonic lesion in scabies?
BURROW
linear intra-epidermal tunnel produced by moving mite
short wavy greyish/white threadlike elevation 2-10mm long
What makes burrows difficult to identify in scabies?
excoriation
eczematisation
Where might nodular lesions occur in scabies?
Penis and scrotum
Buttock
Groin
Axillary regions
Nodular lesions are intensely pruritic and can persist after treatment, why?
hypersensitivity reaction to mite
What is crusted scabies?
Caused by scabies crustosa/Norwegian scabies
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
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
What complication can occur from crusted scabies?
Sepsis due to fissures providing point of entry for bacteria
Which animals can scabies rarely be contracted from?
Dogs - Sarcoptes scabiei var Canis
Cats - Notoedres cati
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
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
How to make definitive diagnosis of scabies?
Skin scraping of burrow
Glass slide + 10% potassium hydroxide
Microscopy to visualise mite, eggs, faeces
Why is 10% potassium hydroxide used when preparing slide for microscopy in scabies?
Dissolves excess keratin for better visualisation of mite
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
What organisms are implicated in secondary bacterial infection in scabies?
Staphylococcus aureus
Group A B-haemolytic streptococci
Peptostreptococci
How does secondary eczematisation occur in scabies?
constant scratching
irritant effects of topical medication
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
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
When might permethrin be contraindicated?
Allergy/sensitivity in past or to CHRYSANTHEMUMS
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
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
How long might itch continue for following treatment for scabies?
Up to 2 weeks
When should treatment failure be suspected in scabies?
New burrows appear
Itch longer than 4 weeks
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
