Scabies

Question 1

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

Answer 1

a) sarcoptes scabiei var hominis

Question 2

How is scabies transmitted?

Answer 2

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.

Question 3

hHow long can scabies mites live of the host for ?

Answer 3

24-36 hours

Question 4

how long can scabies mites associated with crusted scabies or Norwegian scabies live for?

Answer 4

up to 7 days

Question 5

Describe the life cycle of the scabies mite and how it causes infestation in the host

Answer 5

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.

Question 6

what is the average number of mites in humans infected with scabies

Answer 6

10-15 mites

Question 7

What are the symptoms typical of scabies infestation

Answer 7

Pruritus (intense itch) usually worse at night,

Generalised erythematous papules

Question 8

what causes the classical itch in scabies?

Answer 8

Delayed type IV hypersensitivity reaction to the scabies mite and the mite products (faeces and egg)

Question 9

What are the clinical signs you might expect to find suggestive of Scabies

Answer 9

1. Burrows - in the interdigital webbed spaces (fingers and toes) - linear line can be white/grey colour
2. 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
3. palms and soles are affected in elderly, infants and young children
4. excoriation marks

Question 10

What type of scabies can affect patients with immunocompromised co-morbidities

Answer 10

Crusted scabies/Norweigan scabies/ Scabies Crustosa

Question 11

How does Crusted or Norwegian scabies present clinically

Answer 11

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

Question 12

What are the potential complications of crusted scabies?

Answer 12

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

Question 13

Why is itch less of a symptom in crusted scabies compared to classical scabies

Answer 13

Potentially due to the immunocompromised state in the host causes an impaired immune response.

Question 14

Can humans catch animal scabies from dogs or cats? Do they require treatment

Answer 14

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.

Question 15

What type of scabies may a patient present with following the use of longterm topical potent steroids

Answer 15

Scabies incognito

Question 16

What diagnostic methods can we use to confirm the diagnose scabies?

Answer 16

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

2. 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.
3. 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.

Question 17

What are the four scabicides that have been used in the treatment of scabies

Answer 17

1. Permethrin 5% cream
2. Malathion aqueous 0.5% liquid
3. Benzyl benzoate 25% emulsion
4. Oral Ivermectin (topical not available in the UK)

Question 18

What is the first line treatment used in the treatment of scabies (assuming it is not crusted scabies)

Answer 18

first line: permethrin 5% cream

Question 19

How would you explain to a patient how to use permethrin cream

Answer 19

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.

Question 20

when might you consider using malathion 0.5% aqueous lotion instead of permethrin for treatment of scabies

Answer 20

allergy to chrysanthemums
if permethrin caused topical reaction or didn’t work

note there are no clinical trials evaluating malathion as a treatment

Question 21

What instructions do you need to tell a patient before using malathion 0.5% aqueous lotion

Answer 21

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

Question 22

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

Answer 22

Benzyl benzoate - no longer recommended as not as effective as permethrin or malathion and may cause skin irritation

Question 23

What dose of oral Ivermeticin do you use in the treatment of scabies

Answer 23

Oral Ivermeticin 200mcg/kg (200 micrograms per kg) in those weighing > 15kg repeat the dose at 2 weeks.

Question 24

when is ivermeticin typically used for the treatment of scabies

Answer 24

Typically in crusted scabies, or in scabies resistant to topical treatments

Question 25

What are the side effects associated with Oral Ivermeticin

Answer 25

Vomiting, abdominal pain and rashes

Question 26

What is the general advice needed to give to patients when treating scabies infestation

Answer 26

advice them to wash clothes/towels/bedding that has been used during the past 4 days at a high heat - 60degrees

Then dry in a dry cleaner, dryer or seal in a plastic bag for up to 72 hours (as mite can’t live longer than 72 hours without the human host)

Question 27

What treatment would you advise in crusted scabies

Answer 27

Topical treatment with permethrin 5% cream once daily for 7 days, then twice weekly until cure plus oral Ivermeticin on days 1,2, 8, 9, and 15

Patients with crusted scabies should be isolated immediately with barrier nursing

All household members or anybody exposed should be treated at the same time as the infested person.

Question 28

How long can the post scabetic itch last?

Answer 28

Up to 2 weeks following successful treatment for scabies

if it persists for longer consider the need for re-treatment in the case of treatment failure or re-infection.

Question 29

How would you treat post scabetic itch

Answer 29

Crotamiton 10% cream (2-3 times daily) this kills the mites

or if you are sure the scabies has been succesfully treated can use 1% hydrocortisone to help with the itch cycle,

Question 30

what treatments are suitable in pregnant or breastfeeding mothers

Answer 30

Topical treatments with - permethrin 5% cream or malathion 0.5% aqueous lotion are suitable. Just ensure BF mothers wash off before feeding over the nipples and then re-apply.

Question 31

How would you manage sexual partners and household members of people diagnosed with scabies

Answer 31

Examine and treat sexual partners and close family household members even if asymptomatic

Question 32

What is the look back period for scabies for partner notification

Answer 32

4 weeks