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SCABIES

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INTRODUCTION

Sarcoptes scabiei

Sarcoptes scabiei, otherwise known as scabies, is a highly contagious infestation of microscopic

mites that affect humans and animals alike. Contracting scabies is more common then one may

think, and occurs worldwide. No one is safe from an infestation of scabies because it can affect

any race or social class. Scabies can also spread at a rapid pace, and this usually occurs in

crowded areas where there is a chance of prolonged contact. (Bandyopadhyay).

History of Scabies

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o Scabies dates back about 2500 years ago (Scabies Homepage),

and was documented all over Europe; however, it wasn’t known

as scabies to those who experienced it. In these eras it was

known as the “itch”. (Ramos).

o In earlier times scabies was commonly found among the poor

who exhibited bad hygiene, but some of the wealthiest people

also experienced encounters. In fact, Napoleon I was said to have suffered from the “itch”

his whole life. (Ramos).

o In 1687 an Italian man named Giovanni Cosimo Bonomo had finally discovered the mite

responsible for the inflictions. He came across a person who was itching a lot and broke

open one of the pustules. He then took the remnants of what was inside the pustule and

examined it under a microscope. He did this numerous times to different people, of

different ages, and different times of the year getting the

same result each time. (Ramos).

o Bonomo studied his findings until he was satisfied and

then wrote a letter to Francesco Redi who later published

in a book the discovery of scabies. (Ramos).

o Until Bonomo’s remarkable discovery of this flesh eating

mite, people suffered uncontrollable itching and much

distress.

o The treatment Bonomo found effective was a local therapy, sulphur, which was used up

until now. He also realized that the local treatment had to be applied for up to two or

three days after the itching subsided because un-hatched eggs could hatch and restart the

cycle. (Ramos).

Different Types of Scabies

o Clean Man’s Scabies: This is seen in individuals who bathe regularly, and keep very

clean. In this case, the lesions are minimal and hard to see. Itching tends to be not as

intense. (Babu, 2006).

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o Infant Scabies: This occurs in babies and young children, and is often misdiagnosed or

mistreated. Scabies will affect the whole body of the child, and there will be a large

amount of pustules. (Babu, 2006).

o Scabies Incognito: Normally, if a strong type of treatment, such as steroids, are applied

then the scabies are masked and the lesions are suppressed. (Babu, 2006).

o Norwegian Scabies: This is an intense case of crusted scabies. In this case, there can be

up to hundreds or thousands of mites within the lesions. This occurs commonly in

autoimmune deficient individuals, or people who are mentally challenged. (Babu, 2006).

o Animal Scabies: Animals are susceptible to scabies too. Domestic pets that contract

scabies are liable to pass it on to the other members of the household as well. (Babu,

2006).

Physical Features

o Scabies are a certain type of mite. Mites are related to the arachnid family the same as

ticks and spiders.

(Drisdelle).

o Scabies

are creamy white

with brown legs and

mouthparts. “Sarcoptes scabiei type hominis”, 2008.

o The adult female is about 0.4 mm long and 0.3 mm wide. The adult male

is smaller in both dimensions by one third. Also need a microscope to

actually see the mite itself. “Sarcoptes scabiei type hominis”, 2008.

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o They have no armor, no trachea, and no eyes. (Speare, 2008).

o Scabies mites have no respiratory system. They breathe through the skin. (Drisdelle).

o They can be very mobile when not inside a host. (Speare, 2008).

o They have 8 legs with the two in the front as walking legs. (Speare, 2008).

o Scabies have “suckers” that allow them to attach to surfaces to walk upwards. (Speare,

2008).

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Reproduction

o The female mite finds a host and burrows down into his or her skin.

o As the female is burrowing through the host’s skin she leaves a trail of eggs. She can

leave two to three eggs a day for up to two months. (Gould, 2009).

o The eggs will then hatch about four days after they are laid. The new larvae grow and

shed their outer coat about two times and then become adults. (Gould, 2009).

o After fully grown the adult mites burrow through the skin to the surface to find a mate.

(Gould, 2009).

o Males do not dig burrows. Instead, they stay on the skin’s surface waiting for females to

mate with. (Gould, 2009).

o After the females mate they return inside the skin where they continue to burrow and lay

eggs. Then the process starts all over again. (Drisdelle, 2007).

o The entire life cycle of the mites are 10-14 days, and usually

they live for about 30 days. (Gould, 2009).

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Transmission

Scabies can be picked up by several different ways.

o Most commonly is direct prolonged body-to-body contact. This occurs in homes between

family members. Even more commonly between people who share beds or are sexual

partners. “Scabies Frequently Asked Questions”, 2010.

o Sharing clothing or bedding is another form of transmission, but not as common. (Gould,

2009).

o An individual who has scabies, but isn't exhibiting symptoms can still spread them

without knowing. “Scabies Frequently Asked Questions”, 2010.

o Most common place to contract scabies is:

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Signs and Symptoms

o Most common symptom is severe itching also known as pruritus. The itching tends to get

worse at night or after hot showers. “Sarcoptes scabiei type hominis”, 2008.

o May have a pimple-like rash that can affect most of the body or be limited to common

sites such as:

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o The head, face, neck, palms, and soles are

common sites for infants that contract

scabies. “Scabies Frequently Asked

Questions”, 2010.

o Symptoms don’t usually show up until two to

six weeks after contracted; however, if

someone has been re-infested then symptoms

can show up in a week. (Gould, 2009).

o In individuals with weakened immune

systems mites tend to be present in large

amounts, which is commonly known as

Norwegian Scabies. “Scabies Frequently

Asked Questions”, 2010.

Pathogenesis

o F (within 20 min) burrows into the stratum corneum (traverses at a rate of 0.5 - 5

mm/day)

o avoid areas with a high density of pilosebaceous follicles

o Mating takes place once, and the female is fertile for the rest of her life (1 mo),

o Copulation in a small burrow---------the male, falls off the skin & perishes---------

Fertilized female enlarges the burrow using proteolytic enzymes to dissolve the stratum

corneum of the epidermis ----- begins egg laying (3 eggs a day each)

o Six-legged larvae emerge from the eggs after 3-4 days

o 90% of the hatched mites die

o Escape from the burrow by cutting through its roof------then dig short burrows called

moulting pouches & transform into nymphs-------------After further moult into larger

nymphs , adult males and females develop(in 2-3 weeks)

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Clinical features

o IP- 2-6 weeks

o immediate symptoms –in re infection

o Triad`s

o Pruritic papular lesions,

o Excoriations, and

o Burrows

o Site- The circle of Hebra ~ an imaginary circle intersecting the main sites of involvement

- axillae, elbow flexures, wrists & hands, & crotch

Pruritis

o accentuate at night & exacerbated by a hot bath or shower

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Primary lesions of scabies

o burrows, papules, pustules, nodules, occasionally urticarial papules and plaques

interdigital webbing of the hands,

flexural aspect of the wrists, behind the ears, axilla, waist, ankles, feet, buttocks & belt

area

penile & scrotal in men, areola, nipples & genital area in women

In very young children, infants, elderly and immunocompromised hosts, a widespread

eczematous eruption primarily on the trunk is common , scalp & face can also be

affected.

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The burrow

pathognomonic sign and represent the

intraepidermal tunnel created by the

moving female mite.

a 1-10 mm tunnel

serpiginous, greyish-white

thread-like elevations

At the end of it a vesicle/pustule containing

the mite may be noted, especially in infants & children

at entry, slight scale

In infants, commonly located on

the palms & soles : F

To identify burrows quickly:

apply a drop of India ink or

gentian violet to the infested area,

remove it with alcohol

Thin threadlike burrows retain

the ink

Erythematous Papules & Vesicles (filled with serous fluid) rarely contain mites and most likely

are due to a hypersensitivity reaction

Papules= on the shaft of the penis & scrotum in men

& on nipples in women

Vesicles= on the palms & soles

Animal Scabies: Zoonotic scabies

o affect humans who come in close contact with the animal

o incubation period is shorter, the symptoms are transient

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o usually manifests with vesicles & papules with atypical distribution

o Burrows are usually absent

o runs a self-limited course, require no treatment

o Mites from animals are not a source of human infestation, but they can

produce bite reactions

Asymptomatic infestation

o not uncommon

o considered ‘carriers’

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Complications

o Secondary impetiginization

o Lymphangitis & septicemia ~ particularly in crusted scabies

o Post-streptococcal glomerulonephritis

o 'post-scabietic pruritus‘

a. represent the body's response to dead mites that are eventually sloughed off

(within 4 wks) along with natural epidermal exfoliation

b. Tx- antihistamines or a short course of topical or oral corticosteroids

Diagnosis

o Mainly clinical

a. Pruritus with typical lesions & distribution

b. Contact Hx

o Microscope

a. Skin scrapings obtained from the finger webs, wrists, or ankles is most likely to

be positive

b. In Norwegian scabies, scraping of the thick scales will often yield several viable

mites(100)

c. Excoriated lesions are often negative

Dermoscopy

PCR

Biopsy

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H/p

A patchy to diffuse infiltrate with eosinophils is noted in the reticular dermis

On transection, a scabies mite may occasionally be seen within the epidermis

o fragments of the adult mite exoskeleton

o serve as a clue to the Dx when mites, scybala or eggs are not identified

Treatment

Age

cost

severity

previous treatment status

In infants with extensive involvement, several re treatments a week apart occasionally

be required

second application of topical medication.......

Treat simultaneously all household contacts (even with no symptoms)

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