Scabies Flashcards
What is the name of the mite that causes scabies infestation
a) Sarcoptes scabiei var hominis
b) sarcoptes scabiei var canis
c) sarcoptes scabiei notoedres cati
a) sarcoptes scabiei var hominis
How is scabies transmitted?
Scabies is transmitted by close skin to skin contact or through sexual transmission especially in young adults
Rarely fomite transmission can occur if a person heavily contaminated with scabies sleeps in a bed and then someone else uses it.
Spread through a handshake is very rare.
hHow long can scabies mites live of the host for ?
24-36 hours
how long can scabies mites associated with crusted scabies or Norwegian scabies live for?
up to 7 days
Describe the life cycle of the scabies mite and how it causes infestation in the host
Scabies mite burrows into the skin (usually between fingers or toes; in the webbed spaces) –> it then lays it eggs –> the eggs hatch to become ADULTS (after moulting for a period of 10-15 days) –> mites can survive for 24 -36 hours before dying –> half the eggs die and
A typical female mite will lay 25 eggs.
what is the average number of mites in humans infected with scabies
10-15 mites
What are the symptoms typical of scabies infestation
Pruritus (intense itch) usually worse at night,
Generalised erythematous papules
what causes the classical itch in scabies?
Delayed type IV hypersensitivity reaction to the scabies mite and the mite products (faeces and egg)
What are the clinical signs you might expect to find suggestive of Scabies
- Burrows - in the interdigital webbed spaces (fingers and toes) - linear line can be white/grey colour
- Erythematous papules - usually on the side of the fingers, under finger nails, flexor aspect of the wrists, extensors at the elbows, axillae, nipples in women, scrotum and penis in men, abdomen and up to the umbilicus. The back and head/scalp is usually spared. Head and scalp are affected in babies and young children
- palms and soles are affected in elderly, infants and young children
- excoriation marks
What type of scabies can affect patients with immunocompromised co-morbidities
Crusted scabies/Norweigan scabies/ Scabies Crustosa
How does Crusted or Norwegian scabies present clinically
Usually in patients with immunocompromised states e.g. AIDS, leprosy, on long term potent steroids, organ transplant recipients but up to 40% patients have no predisposing risk factors.
- erythematous scaly crusted lesions that can be offensive smelling and associated with fissures that can affect any part of the body including the fact and scalp.
- itching can be mild or absent
What are the potential complications of crusted scabies?
Sepsis - due to fissures in the skin provide an entry point for bacteria specifically staphylococcus aureus, group A beta haemolytic streptococci, or peptostreptococci.
Secondary eczematisation due to constant scratching
Glomerulonephritis
Leucocytoclastic vasculitis
Why is itch less of a symptom in crusted scabies compared to classical scabies
Potentially due to the immunocompromised state in the host causes an impaired immune response.
Can humans catch animal scabies from dogs or cats? Do they require treatment
Very rarely humans may catch animal scabies. However because the scabies mites can’t survive of the human host they die very quickly. Only the animals require treatment.
What type of scabies may a patient present with following the use of longterm topical potent steroids
Scabies incognito
What diagnostic methods can we use to confirm the diagnose scabies?
Scabies is most often a clinical diagnosis
Definite diagnosis relies on microscopic identification of the mites, eggs or faecal pellets (scybala) - using a scalpel blade scrape the skin burrows and place the specimen on a slide with 10% potassium hydroxide. Then examine under the microscope
- Add a drop of mineral oil to the lesion or on the scalpel blade, the entire lesion is scraped away with the scalpel blade. The oil and skin scrapings are then transferred to the microscopic slide and examined under the microscope.
- Burrow ink test (BIT) : apply black or blue ink to the suspected papule then wipe off with alcohol to remove the ink from the surface. A positive BIT occurs when a characteristic dark zigzagged line running across and away from the lesion due to the ink tacking down the mite burrow.
What are the four scabicides that have been used in the treatment of scabies
- Permethrin 5% cream
- Malathion aqueous 0.5% liquid
- Benzyl benzoate 25% emulsion
- Oral Ivermectin (topical not available in the UK)
What is the first line treatment used in the treatment of scabies (assuming it is not crusted scabies)
first line: permethrin 5% cream
How would you explain to a patient how to use permethrin cream
Apply to the whole body (notemanufacturers state not to include above chin but BNF states to include!) paying special attention to interdigital spaces, hands and under the finger nails. leave on for 8-12 hours
make sure you apply it to cool and dry skin
if you wash your hands during this time will need to reapply
after 8-12 hours then wash off, and repeat in 1 weeks time
ensure you clean any bedding/clothes/towels that have been used in the last 4 days by the person infected with scabies and close contacts/household members. wash at 60 degrees and then dry in dry cleaner, dryer or seal in a bag for up to 72 hours.
when might you consider using malathion 0.5% aqueous lotion instead of permethrin for treatment of scabies
allergy to chrysanthemums
if permethrin caused topical reaction or didn’t work
note there are no clinical trials evaluating malathion as a treatment
What instructions do you need to tell a patient before using malathion 0.5% aqueous lotion
apply to cool, dry skin allover the body (manufacturers state chin down but BNF state everywhere including scalp/ face and head).
once applied leave to dry before putting on clean clothes
pay special attention to interdigital webs, under the nails and the hands
leave on for 24 hours
if you wash your hands in this time re-apply
wash off after 24 hours and repeat in 1 weeks time
Out of the four scabicides which one is no longer recommended for treatment of scabies and why?
a)malathion 0.5%
b) permethrin 5%
c) benzyl benzoate
d) ivermeticin PO
Benzyl benzoate - no longer recommended as not as effective as permethrin or malathion and may cause skin irritation
What dose of oral Ivermeticin do you use in the treatment of scabies
Oral Ivermeticin 200mcg/kg (200 micrograms per kg) in those weighing > 15kg repeat the dose at 2 weeks.
when is ivermeticin typically used for the treatment of scabies
Typically in crusted scabies, or in scabies resistant to topical treatments
