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

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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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Scabies: Predilection sites

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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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Scabies Papules and burrows on
the lateral hand

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3. Hyperkeratosis/Crusting
Psoriasiform :
In areas of heavily infested crusted scabies,
well-demarcated plaques covered by a very
thick crust or scale .

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3. Hyperkeratosis/Crusting
Psoriasiform :
In areas of heavily infested crusted scabies,
well-demarcated plaques covered by a very
thick crust or scale .

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Lesions Secondary to Chronic Rubbing
and Scratching:
1) Excoriation, lichen simplex chronicus,
prurigo nodules.
2) Generalized eczematous dermatitis.
3) Psoriasiform lesions. Erythroderma.

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Laboratory Examination
1. Microscopy : Finding the Mite
 Burrow with Sarcoptes scabiei (female),
eggs, and feces

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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

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