1. Scabies is caused by the mite Sarcoptes scabei var hominis, which burrows under the skin and lays eggs, causing intense itching.
2. It spreads through direct, prolonged skin-to-skin contact and can affect people of any age.
3. Treatment involves applying topical scabicides like permethrin or oral ivermectin to kill the mites and eggs, with multiple applications required to fully clear the infection.
2. Scabies
Sarcoptes scabei var hominis: specific for humans
Sarcoptes scabei var canis: animal mite, rarely causes infection in
humans
Tramsmission
1. Acquired through direct, prolonged, skin-to-skin contact with an
infected person(i.e., same household).
2. Sexual contact.
3. ?Fomite ( infected clothing, bedding)
3. Female lifespan 46 weeks; lays 4050 eggs.
Lays 3 eggs per day in tunnels; eggs hatchin 4 days. Burrow 23 mm
daily, usually at night, and lay eggs during the day.
Hatched larvae migrate to skin surface and mature into adults.
Males and females copulate. Gravid female burrows back under
stratum corneum; male falls off skin.
4. Epidemiology
Estimated at 300 million cases/year worldwide.
Epidemics ocured in 15 year cycles, latest 1960
Children (often 5 years). Nodular scabies
more common in children.
Young adults (body contact).
Elderly and bedridden patients
5. Pathogenesis
Hypersensitivity of both immediate and delayed types occurs in the
development of lesions other than burrows.
First infestation: For pruritus to occur, sensitization to S. scabiei must
take place -takes several weeks to develop if 1st infestation.
Reinfestation: After reinfestation, pruritus may occur within 24 h
6. Clinical features
Pruritic papular lesions- Intense, widespread, usually sparing head and
neck.
Lesions at Site of Infestation
Intraepidermal Burrows-grey, slightly elevated
Scabietic (Scabious) Nodule
Hyperkeratosis/Crusting Psoriasiform
Hypersensitivity lesion:
Small erythematous papules / papulovesicles
Persistent nodular lesions (penis)
Secondary changes
Pustules: due to secondary infection
Eczematised : common infants, children
7. Sites
Burrows finger webs, sides of finger, flexural aspects of wrists, feet, male genitalia
Hypersensitivity
Excoriated papules,
papulovesicles
Infants: scalp, face,
palms, soles
Line Of Hebra
8. R.H., a 26 year old woman comes to see you with a seven week history
of a rash which is worse on her hands. It is extremely itchy, particularly at
night. She is worried that she could give this itching to her 4 year old
son
10. Diagnosis of scabies is made by looking at the burrows or rash.
Confirmation of diagnosis
Skin scraping papule/ pustule microscopy : mites, eggs, or feces
11. Treatment
TOPICAL
5% permethrin : apply for 8 hours on days 1 & 8
1% GBHC: apply for 8 hours on days 1 & 8
25% Benzyl benzoate: 3 application for 12 hourly
10% Crotamiton: apply for 8 hours on days 1,2,3 & 8
10% Precipated Sulphur: twice daily for 14 days; DOC in pregnancy
1% Lindane Solution-Apply only once. Wash off in 8 to 12 hours.
ORAL
Ivermectin 200亮g/kg body weight on day 1, 8 and 15
12. General principles
1. Apply to whole body below jaw line including genitals, soles, under
free edge of nails
2. Treat all family members simultaneously
3. Ordinary laundering of linen
4. Antihistamines: for 4-6 weeks
5. Persistent nodular lesion topical steroid may be required
13. Norwegian scabies or crusted scabies
Immunocomprised patients
Mentally challenged
The number of infesting mites may be >1 million.
C/F: widespread crusted, hyperkeratotic lesion
Innumerable mites (hundreds)
Very contagious
Treatment - Topical 5% permethrin or
topical 5% benzoyl benzoate
applied daily for seven days, then twice weekly until cure
Keratolytic creams on alternate days to scabicide
Oral ivermectin on days 1, 2, 8, 9, and 15
(add days 22, 29 if infestation is severe).
14. Animal scabies
Mite - Sarcoptes Scabiei var Canis
Transmission - Infected animal to human;
human to human transmission does not occur
Source horses, cattle, dogs, cats; (this infection in animals is called
Mange)
C/F small, pruritic papules temprorary
no burrows
site - front of trunk,
medial aspect of upper extremities
Treatment antihistamines
specific antiscabetic not required