Scabies

On This Page

Introduction
Agent

Synonyms

History of Discovery

Clinical Presentation in Humans

Transmission

Reservoir

Vector

Incubation Period

Morphology

Life Cycle

Diagnostic Tests

Management and Therapy

Epidemiology

Country Information

Public Health and Prevention Strategies


 


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Scabies in the News

Recent Scientific Publication Abstracts

References

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from http://www.tdh.state.tx.us/lab/images/scabies.jpg

Introduction:

Scabies is a prevalent skin condition that effects people of all classes and ethnicities all over the world.  Scabies is an ancient affliction, estimated to have infected humans for the last 2,500 years.  The WHO considers scabies to be a water-related disease because of the connection between bathing and personal hygiene to prevention or control of its spread.  The tick that causes scabies, however, is not dependent on water for transmission or for any part of its life cycle.

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Agent:

Scientific Name: Sarcoptes scabiei (var hominis)

        

Classification:   Kingdom- Animalia

                            Phylum- Arthropoda

                            Class- Arachnida

                            Order- Acarina

                            Family- Sarcoptidae

 

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Synonyms: scabies, itch mite

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History of Discovery:

Based on archeological evidence including Egyptian drawings depicting people afflicted with symptoms of scabies, scabies is estimated to have been infecting humans for at least 2,500 years.  There are many controversial accounts of the history of discovery of the infectious agent.  Prior to the 17th Century, the condition of scabies was known by many names and widely believed to be a humoral disease, possibly associated with a mite.

Earliest known drawings of scabies were made by Giovan Cosimo Bonomo in 1687, who collaborated with Diacinto Cestoni and is disputably the discoverer of the scabies mite. 

In Australian literature, the scabies mite S. scabiei was first collected from a wombat in Tasmania in 1804, but not described as a separate species until eighty years later. 

See http://www.dermato.med.br/hds/bibliography/1998giovan-cosimo-bonomo.htm for a more detailed account of the controversial history of the discovery of scabies

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Clinical Presentation in Humans:

Signs include a vesicular rash, visible burrows in the skin, intense itching of infected areas—caused by allergic reaction to activities and secretions of the mites.  Intense itching may result in disturbed sleep; bleeding and scab formation from scratching can allow for secondary bacterial infection.  Itching may be especially bad at night.  Preferred areas of the body: interdigital and popliteal folds (between the fingers and behind the knee), the groin, inframammary folds. (see picture below)  Immunocompromised individuals may experience Norwegian scabies, which involves extensive scaling and crusting.

from www.dermatologist.co.uk/ skinrash.html

from www.dermnetnz.org/.../ gplect5/page1.html

 

From http://internalmed.wustl.edu/divisions/dermsub/caseofmonth/PageMill_Images/10-97eNorwegian-Scabies.jpg

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Transmission:

Transmission is mostly through prolonged close contact with other people that are infected with the mite; quick contact (as in a hug or a handshake) is unlikely to spread the mite.  Scabies is sometimes classified as a sexually transmitted disease, but it is only sexually transmitted insomuch as sexual contact involves prolonged close contact of exposed skin.  Scabies can also be transmitted through contact with the bedding or clothing of infected persons—mites can survive up to 24 hours outside the skin.

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Reservoir:

Domesticated animals, but usually different strains have distinct host preferences so infections that are contracted from animals may cause irritation and itching, but are usually short-lived.

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Vector:  None

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Incubation period:

Usually between 2 to 6 weeks; can be as little as 1 to 4 days in people that have been sensitized by prior exposure.

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Morphology:

Like other aranchnids, the scabies mite is an eight-legged arthropod with round body.  It is barely visible to the human eye, and females (larger than males) are less than 0.5 mm in length.

from www.onedreamdesign.com/ canine/smite.shtml

A stylized, artist's interpretation of the scabies mite created for a text book. 

 

from http://www.safe2use.com/pests/scabies/gifs/INFEC010.jpg

 

 

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Life Cycle:

Adult mites burrow into the upper layer of the epidermis.  Females lay eggs in the burrows. 

  Scabies mite and eggs. 

 From The Hong Kong Practitioner: http://www.hkcfp.org.hk/article/2003/05/page214-221ua.html

Eggs hatch after 3-4 days into larvae, which dig new burrows closer to the skin surface.  There, the larvae mature into adult mites in about 4 days.  The adults can then either stay in that host or be scratched off and transmitted to a new host.  Adult females can live in the host for up to a month.

Click here for the CDC Diagram

 

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Diagnostic Tests:

Skin scrapings after application of mineral oil to look for eggs under the microscope.

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Management and Therapy:

Skin condition may sometimes spontaneously resolve, but threatment options include:

For noncrusted scabies: 5% pyrethrin or permethrin cream (Elimite)

OR gamma benzene hexachloride (lindane), but may be neurotoxic and not suggested for pregnant or lactating women

OR 10% crotamiton, N-ethyl-o-crotonotoluidide (Eurax) for infants under 2 months

Applied to all skin surfaces in infants, children, and the elderly.

Scabicide should be applied for 8 to 12 hours and then washed off.

Repeat application in 1 week if live mites or eggs are still present.

 

For crusted scabies: Permethrin 5%

May be combined with ivermectin in immunocompromised patients.

Oral dosages of ivermectin may also be effective in treating infection.

 

Eliminate fomites by washing bedding and clothing and heat drying (over 50ºC) or by storing in closed plastic containers for 7 days.

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Epidemiology:

Scabies can strike and age or race, regardless of personal hygiene, though personal hygiene can play a role in prevention.  It is more often seen in crowded living conditions.  There are an estimated 300 million cases a year, with immunocompromised people more likely to develop Norwegian (crusted) scabies.

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Country Information:

Found worldwide and affects people of all socioeconomic statuses.  Epidemics can arise in areas of poverty, poor sanitation, poor water-supply, or overcrowding.

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Public Health and Prevention Strategies:

Access to water effects bathing—improved personal hygiene may prevent or control the spread of scabies.  Since oral ivermectin may be useful in treatment, mass distribution programs of ivermectin to target onchocerciasis may also control scabies.

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