SCABIES
DEFINITION:
A parasitic
infection of the skin resulting in intensely pruritic
eruptions of the skin consisting of wheals, papules,
vesicles, and thread-like burrows.
EPIDEMIOLOGY:
- incidence:
common
- age of
onset:
- risk
factors:
- Indian
and Inuit communities
- crowded
housing, schools, and day-care centres
- shared
beds
PATHOGENESIS:
- direct
contact with a person infected with the mite
Sarcoptes scabiei
- mating of
adult female with male -> gravid female burrows
into the stratum corneum where she deposits 1-3
oval eggs daily and brown fecal pellets (scybala)
over a period of 4-5 weeks then dies -> eggs hatch
in 3-5 days releasing larvae which grow and molt
into nymphs and achieve maturity in about 2-3
weeks -> hypersensitivity reaction usually between
2-4 weeks after infection
CLINICAL
FEATURES:
- wheals,
papules, vesicles, and thread-like burrows in
children (burrows can also be hockey stick
shaped)
- bullae
and pustules with absence of burrows in infants
- may be
a superimposed eczematous dermatitis due to a
hypersensitivity reaction to the mite
-
intensely pruritic especially at night ->
eczematization, excoriation with secondary
infection
2.
Distribution
- limbs
- interdigital spaces, wrists, elbows, ankles
- trunk
- areola, axillae, umbilicus, groin,
genitalia, buttocks
- areas
spared - head, neck, palms, soles
2.
Infants
- same
as in older children but with scalp, face,
palms, and soles often affected
-
reddish-brown nodules in the axillae, groin,
and on the genitalia sometimes seen
INVESTIGATIONS:
- for
diagnosis
- drop of
mineral oil on a lesion with vigorous scraping of
the entire burrow with a #15 blade -> transfer to
a glass slide and look for movement of a mite,
ova, and/or scybala
- best
yield when scrape from the interdigital web
spaces, genitalia, breasts, soles and palms
MANAGEMENT:
-
prophylactic scabicidal therapy for all household
members and close contacts
-
prophylactic scabicidal therapy for the whole
community for widespread scabies epidemics
- all bed
linen and clothing worn next to the skin should be
laundered in a hot cycle wash and hot drying cycle
(if hot water not available, place linen and
clothes into plastic bags and store away from the
family for 5-7 days)
- return
child to day-care or school after the treatment
has been completed
2.
Scabicidal Therapy
- drug of
choice with single application usually curative
- apply
according to age from head to the soles of the
feet
- leave
on skin for 8-14 hours then remove by shower or
bath
- may
reapply in 1 week if symptoms persist
-
advantages:
-
90-98% cure rate
- only
one application usually needed
- skin
absorption minimal (<2%)
- no
neurotoxicity and minimal irritant dermatitis
-
disadvantages:
- not
recommended under 2 months of age
-
expensive: $20 for one 30 g tube
2.
Lindane (Kwellada)
- use
when permethrin not available
- apply
according to age from head to the soles of the
feet
- leave
on skin for 8-12 hours then remove by shower or
bath and repeat application in 24 hours
-
disadvantages:
-
65-95% cure rare
- two
applications necessary
- skin
absorption may be significant
-
associated with neurotoxicity (CNS excitation,
sei-zures) and mild irritant dermatitis
- not
recommended under 12 months of age
-
resistance to treatment has been reported
3. 7%
Precipitated Sulphur in Vasoline
- use in
infants under 2 months of age
- apply 3
separate applications on consecutive days and
leave on for 24 hours before washing off
3.
Complications
- use
benadryl, hydroxyzine HCl (Atarax), or topical
steroids (1% hydrocortisone)
2.
Infections
-
cloxacillin po 25 mg/kg/day
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