Scabies is a superficial epidermal infestation by the mite Sarcoptes scabiei var. hominis.
Etiologic Agent:
S. scabiei var. hominis. Thrive and multiply only on human skin, i.e., obligate human parasite.
Transmission
Skin-to-skin contact
Fomites: Mites can remain alive for >2 days on clothing or in bedding; hence, scabies can be acquired without skin-to-skin contact.
intimate personal contact, such as having sexual intercourse
Scabietic (Scabious) Nodule:Inflammatory papule or nodule ;burrow sometimes seen on the surface of a very early lesion.• Distribution : Areola, axillae, scrotum, penis.
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Scabies
Scabies is a superficial epidermal infestation
by the mite Sarcoptes scabiei var. hominis.
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Etiology
• Etiologic Agent:
S. scabiei var. hominis. Thrive and multiply
only on human skin, i.e., obligate human
parasite.
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Epidemiology
• Age of Onset :
Children (often ≤5 years). Nodular
scabies more common in children.
Young adults (usually acquired by body
contact).
Elderly and bedridden patients; may be
health care-associated in hospitals,
chronic care facilities, nursing homes.
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Transmission
1) Skin-to-skin contact
2) Fomites: Mites can remain alive for >2
days on clothing or in bedding; hence,
scabies can be acquired without skin-to-
skin contact.
3) intimate personal contact, such as having
sexual intercourse
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Risk Factors
risk factors include age of institution
(>30 years), size of institution (>120
beds), ratio of beds to health care
workers (>10:1).
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Pathogenesis
1) Hypersensitivity of both immediate and
delayed types occurs in the development
of lesions other than burrows. Infestation
is usually by only approximately 10 mites.
2) First infestation: For pruritus to occur,
sensitization to S. scabiei must take
place.
3) Reinfestation: After reinfestation, pruritus
may occur within 24 h.
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Clinical Manifestation
Incubation Period: Onset of pruritus
varies with immunity to the mite:
• First infestation, about 21 days
• Reinfestation, immediate, i.e., 1–3 days.
Duration : Weeks to months unless
treated. Crusted scabies may be present
for years.
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Clinical Manifestation
Skin Symptoms :
Pruritus
Rash
Some individuals experience pruritus for
many months with no rash.
Tenderness of lesions suggests
secondary bacterial infection.
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Lesions at Site of Infestation
1. Intraepidermal Burrows :
Gray or skin-colored ridges, 0.5–1 cm in
length
• Distribution :
Areas with few or no hair follicles, usually where
stratum corneum is thin and soft, i.e., interdigital
webs of hands > wrists > shaft of penis > elbows >
feet > genitalia > buttocks > axillae > elsewhere In
infants, infestation may occur on head and neck.
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2. Scabietic (Scabious) Nodule:
Inflammatory papule or nodule ;burrow
sometimes seen on the surface of a very early
lesion.
• Distribution : Areola, axillae, scrotum,
penis.
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Laboratory Examination
2. Dermatopathology:
3. Hematology:
Eosinophilia in crusted scabies.
4. Cultures : S. aureus and GAS cause
secondary infection.
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Topical agents are more effective after
hydration of the skin, i.e., after bathing.
Application should be to all skin sites,
especially the groin, around nails, behind
ears, including face and scalp.
Sexual partners and close personal or
household contacts within last month
should be examined and treated
prophylactically.
Management
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Scabicides :
1. Permethrin:
is effective and safe but costs more than
lindane.
2. Lindane
3. Clean clothing should be put on afterwards.
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Recommended Regimens :
1)Permethrin 5% Cream : Applied to all
areas of the body from the neck down.
2)Lindane (γ-Benzene Hexachloride) 1% Lotion
or Cream : Applied thinly to all areas of the body
from the neck down; wash off thoroughly after 8
h.
Note : Lindane should not be used after a bath or
shower, and it should not be used by persons
with: extensive dermatitis, pregnant or lactating
women, and children younger than 2 years.
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Alternative Regimens:
1.Crotamiton 10% Cream
2.Sulfur 2–10% in Petrolatum Applied to skin
for 2–3 days.
3.Benzyl Benzoate 10% and 25% Lotions
4.Sulfiram 25% Lotion
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Systemic Ivermectin :
Ivermectin: 200 μg/kg PO; single dose
reported to be very effective for common as
well as crusted scabies in 15–30 days.
Secondary Bacterial Infection:
Treat with mupirocin ointment or systemic
antimicrobial agent.
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• SOURCE: From FITZPATRICK’S COLOR ATLAS
AND SYNOPSIS OF CLINICAL DERMATOLOGY
SIXTH EDITION