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Scabies: the Insanely Itchy Ectoparasite

moon
GENERAL
highly contagious ectoparasitic skin infection
mite: Sarcoptes scabii
makes superficial burrows in epidermis entering via hair follicles, lays eggs, has babies
worse in immunocompromised, malnourished, elderly or institutionalized individuals
Wikipedia says the Norwegian strain is worst (???)
no vaccine available

INCIDENCE AND DISTRIBUTION
worldwide, all climates
more often seen in crowded and unhygienic living conditions
epidemics may occur among any population
estimate: 300 million cases/year world wide
1 million/year in US

TRANSMISSION
skin to skin contact
fomites
I got it from sitting in an airline seat across the Atlantic ocean
by the transfer of ovigerous females during personal contact
mites hang out esp between the fingers and on the wrists
mites hold onto the skin using suckers on most anterior pairs of legs

SX
insane itch when mites are moving in skin
intense pruritus and excoriations due to scratching, can't sleep
burrow may be visible through skin surface as S-shaped track
prefers soft skin of torso and genitalia, and crevices like armpits & butt cracks
likes the webs between fingers and toes
bites may look like pimples
atopic dermatitis
possible secondary infection: impetigo, cellulitis
infants: acropustulosis: blisters and pustules on the palms and soles of the feet

INCUBATION
onset of sx 2-6 weeks after 1st exposure
previously exposed individuals may react within 4 days of exposure

DIAGNOSIS
generally clinical, by appearance and chance of exposure
apply black liquid ink to skin and wipe off surface
burrows will show where the ink has penetrated
microscopy of skin scrapings in glycerol or mineral oil
positive dx: mite, ova, or fecal pellets present in scraping not easy to find
(no KOH as it will dissolve fecal pellets)
sometimes mite is visible as a pinpoint of white

DDX
atopic dermatitis (Rhus toxicodendron)
syphilis
allergic reactions
lice
fleas

PE
full skin exam
with bright, preferably natural light, and microscope

TREATMENT

PHARMACOLOGICAL TREATMENT

IVERMECTIN
single oral dose in combo with topical is one person's idea of treatment of choice
single dose of Ivermectin reduces the load of scabies, 2nd dose in 2 wks for eradication
1999 small scale test compared lindane topical to oral ivermectin and found no sig difference
compliance is better with oral than with full body topical
used in eradication programs of many parasites of humans and animals
sarcoptic mange in dogs-->scratching, scabs, weight loss
dosing is very important, too much will kill your cat
SE: mild abdominal pain, N/V, myalgia and/or arthralgia
considered safe for use in children over five months of age

ELIMINATE MITES FROM CLOTHING, BEDDING, FURNITURE
treat entire household simultaneously
clean everything continuously for a week
clean everywhere that you have skin contact including cars
vaccuum repeatedly
wash clothing in very hot water and dry on high heat
ironing also kills the mite
toxic: permethrin sprays for items that cannot be laundered
are there nontoxic options for furniture???

TOXIC TOPICALS

DO NOT USE TOPICAL STEROIDS

PERMETHRIN
permethrin 5% is allopathic topical medication of choice (wik)
known insecticide
is toxic, and may cause a reaction of its own
may make patient feel lousy
apply after shower and before bedtime on entire skin surface except face
one application may be sufficient however I was instructed to do it 3 nights in a row

MALATHION
leave on skin for 24 hours
kills both adults and eggs
best topical treatment (USC)
1% malathion or benzene hexachloride (crotamiton for infants)

LINDANE LOTION
approved in the U.S.
second-line treatment where first-line medications like permethrin have either failed
not well tolerated
illegal in 17 other countries, and 33 more countries have restricted its use
rare, serious side effects from product misuse, 3 deaths some dt ingestion
I think this is the one I was prescribed in Vienna, Austria in the 1970's
it made me feel sick, very tired

NONTOXIC TREATMENTS

BATHING TREATMENT
bar soap with sulpur in 1-10%, 6% more most effective
wash whole body daily x4days

SULFUR OINTMENT
10% sulfur ointment in petroleum jelly
some evidence it works
cheap and OTC
OK for pregnant women, infants, children

NEEM OIL
very effective in preliminary tests
for those who are sensitive to permethrin

TEA TREE OIL
5% solution not very effective
effectiveness at higher concentrations not known

TREATMENTS FOR ITCH
antihistamines: chlorpheniramine
prescription: Hydroxyzine (Atarax)
herbal treatments
scalding hot shower finishing with ice cold rinse, chill skin then don't touch

IN DOGS
Sarcoptes scabiei var. canis
sarcoptic mange

LIFE CYCLE
four stages: egg, larva, nymph and adult
females deposit eggs at 2 to 3 day intervals as they burrow through the skin
eggs are oval and 0.1 to 0.15 mm in length
incubation time is 3 to 8 days
after the eggs hatch: larvae migrate to surface
larvae burrow into intact stratum corneum-->make almost invisible "molting pouches"
larval stage has only 3 pairs of legs, lasts 2 to 3 days
molting-->nymphs have 4 pairs of legs, look like small adults-->larger nymphs-->adults
larvae and nymphs mb found in molting pouches & hair follicles
adults are round, sac-like eyeless mites
females are 0.3 to 0.4 mm long and 0.25 to 0.35 mm wide
males are slightly more than half that size, rarely seen
mating occurs after the nomadic male penetrates the molting pouch of adult female
male makes a temporary mating gallery in skin
impregnated females extend their molting pouches-->characteristic serpentine burrows
laying eggs while burrowing
females spend the remaining 2 months of their lives in tunnels

HISTORY
reference to scabies in the Bible (Leviticus, the third book of Moses) ca. 1200 BC
Greek philosopher Aristotle may have reported about them in 4th century BC
Roman physician Celsus named and described “scabies”
Latin for "scratch" = scabere
Italian physician Giovanni Cosimo Bonomo (1663-1699 AD) documented the parasite

SOURCES
http://en.wikipedia.org/wiki/Scabies
http://pathmicro.med.sc.edu/parasitology/arthropods.htm
and my brain

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