[7] Scabies Flashcards
What is scabies?
An itchy rash caused by the parasitic mite Sarcoptes scabiei
How do scabies mites colonise the skin?
They mate on the skin surface, the male dies and the female tunnels into the epidermis and deposits eggs along the burrow
How long does it take for scabies mite eggs to develop from eggs to adult mites?
10-15 days
What happens once scabies mites develop into adults?
They return to the surface and mate again
What is the life-span of scabies mites?
4-6 weeks
How are scabies mites classically transmitted?
Via direct skin contact
How can crusted scabies be transmitted?
Via bedding, towels, clothes and furniture
What causes the symptoms of scabies?
Allergic reaction to the host’s body to mite proteins
What are the risk factors for scabies?
- Overcrowding
- Poverty and poor nutritional status
- Homelessness
- Poor hygiene
- Dementia
- Sexual contact
- Immunosuppression
What is the first period of scabies infection?
Asymptomatic infection
After what period do scabies symptoms develop in primary infection?
3-4 weeks
What are the characteristic features of scabies?
- Intense itching
- Superficial burrows
When is the itching due to scabies worst?
At night and when the person is warm
How do the burrows of scabies mites often appear?
As linear lesions with rows of erythematous papular or vesicular lesions
What additional skin lesions can be seen in scabies?
- Widespread, symmetrical, itchy, papular eruptions around axillae, peri-areolar, abdomen, buttocks and thighs
- Excoriation marks
What is crusted scabies also known as?
Norwegian scabies
What is crusted scabies?
A hyper-infestation of mites which presents as exfoliating scales
Who is most at risk of crusted scabies?
- Elderly
- Immunocompromised
- Decreased peripheral sensation
How does crusted scabies appear?
Hyperkeratotic lesions affecting the hands, feet, nails, scalp and ear
What secondary symptoms may be associated with crusted scabies?
- Lymphadenopathy
- Eosinophilia
- Secondarily infected lesions
Why is crusted scabies more concerning than classical scabies?
- Very contagious
- More difficult to eradicate
How is scabies diagnosed?
Clinically
What additional techniques may help identify scabies?
- Magnifying lens of burrows
- Ink burrow test
How can diagnosis of scabies be confirmed?
Take skin scraping form the affected areas
What are the differentials for scabies?
- Seborrhoeic dermatitis
- Dermatitis herpetiformis
- Pediculosis
- Atopic dermatitis
What is the primary method of scabies treatment?
Topical application of parasiticidal preparation overnight on the whole body (including between fingers, toes and under nails)
When should parasiticidal preparation be re-applied for scabies?
A week after first application
What is the first-line parasiticidal preparation for scabies?
Permethrin 5% dermal cream
How does permethrin treatment differ for crusted scabies?
May require 2 or 3 applications on consecutive days to penetrate hyperkeratotic areas
What further steps should be taken to eradicate scabies?
Wash towels, clothes and bed-linen
Who else should be treated for scabies in addition to the index patient?
- Household members
- Close contacts
- Sexual contacts
When should contacts of the index patient be treated for scabies?
Simultaneously to reduce risk of re-infestation
When should treatment failure for scabies be assumed?
If symptoms persist beyond 6 weeks from first applications
What are the potential complications of scabies?
- Flaring or reactivation of eczema or psoriasis
- Secondary bacterial infection
- Social stigma and psychological harm
