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eMedicine Journal > Emergency Medicine > Infectious Diseases
Scabies

Synonyms, Key Words, and Related Terms: Sarcoptes scabiei var hominis, Norwegian scabies, canine scabies, mange, intense pruritus, nocturnal pruritus, itch mite, 7-year itch, 7 year itch, seven year itch, seven-year itch, mite infestation, skin infestation
Author Information | Introduction | Clinical | Differentials | Workup | Treatment | Medication | Follow-up | Miscellaneous | Test Questions | Pictures | Bibliography

AUTHOR INFORMATION Section 1 of 12    Click here to go to the top of this page Click here to go to the next section in this topic

Authored by William D Binder, MD, Clinical Instructor in Emergency Medicine, Brown University Medical School; Consulting Staff, Instructor, Department of Emergency Medicine, Massachusetts General Hospital

Coauthored by Joseph Sciammarella, MD, FACP, FACEP, FAAMA Major, MC, USAR, Attending Physician, Department of Emergency Medicine, Mercy Medical Center, Rockville Centre, New York

Edited by Joseph A Salomone III, MD, Associate Professor, Department of Emergency Medicine, Truman Medical Center, University of Missouri at Kansas City School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Jeter (Jay) Pritchard Taylor III, MD, Compliance Officer, Attending Physician Emergency Medicine Residency, Department of Emergency Medicine, Palmetto Richland Memorial Hospital, University of South Carolina; John Halamka, MD, Chief Information Officer, CareGroup Healthcare System, Assistant Professor of Medicine, Department of Emergency Medicine, Beth Israel Deaconess Medical Center; Assistant Professor of Medicine, Harvard Medical School; and Robert E O'Connor, MD, MPH, Director of Education and Research, Department of Emergency Medicine, Christiana Care Health System; Professor of Emergency Medicine, Thomas Jefferson University

Author's Email:William D Binder, MDClick here to view conflict-of-interest information on the author of this topic
Editor's Email:Joseph A Salomone III, MD 

eMedicine Journal, June 19 2006, VOLUME 7, Number 6
INTRODUCTION Section 2 of 12   Click here to go to the next section in this topic Click here to go to the top of this page Click here to go to the next section in this topic

Background: Scabies is a common parasitic infection of global proportion. Worldwide, an estimated 300 million cases occur annually. The arthropod Sarcoptes scabiei var hominis causes an intensely pruritic and highly contagious skin infestation, which affects males and females of all socioeconomic stratas and all ethnic groups.

Scabies has been reported for more than 2500 years. Aristotle discussed “lice in the flesh,” which resulted in vesicles, and Celsus recommended sulfur mixed with liquid pitch as a remedy for the disease. However, the disease was first ascribed to the mite by Giovan Cosimo Bonomo in 1687. It was the first human disease recognized to be caused by a specific pathogen.

Pathophysiology:

The scabies mite is an obligate parasite and completes its entire life cycle on humans. Other variants of the scabies mite can cause infestation in other mammals such as dogs, cats, pigs, ferrets, and horses, and these variants can infest human skin as well. However, they are unable to reproduce in humans and only cause a transient dermatitis.

The S scabiei var hominis mite that infects humans is female and can just be seen with the naked eye (0.3-0.4 mm long). The male is about one half this size. The male fertilizes the female on human skin and then dies. Newly mated females burrow into human skin, using proteolytic enzymes to dissolve the stratum corneum of the epidermis. The mite has 4 pairs of legs and tracheal breaths and thus does not penetrate deeper than the outer layer of the epidermis.

The female deposits eggs in the burrows, and then the eggs incubate and hatch after 3-5 days (range up to 8 d). About 90% of the hatched mites die, but those that survive go through various molting stages and reach maturity after a little more than 2 weeks. The female adults, who never leave their burrows, die after 1-2 months.

In a classic scabies infection, anywhere from 5-15 mites (range, 3-50) live on the host. Little evidence of infection exists during the first month (range, 2-6 wk), but after 4 weeks and with subsequent infections, a delayed-type IV hypersensitivity reaction to the mites, eggs, and scybala (packet of feces) occurs. The time required to induce immunity in primary infestations probably accounts for the latent period of 4 weeks of asymptomatic infection. In reinfestation, the sensitized individual may develop a reaction rapidly (within hours). The resultant skin eruption, and its associated intense pruritus, is the hallmark of classic scabies.

Crusted, or Norwegian scabies (so named because the first description was from Norway in the mid 1800s), is a distinctive and highly contagious form of scabies. In this variant, hundreds to millions of mites infest the host individual, who is usually immunocompromised, elderly, or physically and/or mentally disabled and impaired. Extensive, widespread, crusted lesions appear with thick, hyperkeratotic scales over the elbows, knees, palms, and soles. Serum immunoglobulin E (IgE) and immunoglobulin G (IgG) levels are extremely high in these patients, yet the immune reaction does not seem to be protective. Cell-mediated immunity in classic scabies demonstrates a predominantly CD4 T-cell infiltrate in the skin, while one study suggests a CD8 predominance in crusted scabies.

Atypical infestations may also befall the very young (neonates).

Frequency and epidemiology

While many accounts of the epidemiology of scabies suggest that epidemics or pandemics occur in 30-year cycles, this may be an oversimplification of its incidence. These accounts coincided with the major wars of the 20th century. Because it is not a reportable disease, and data are based on variable notification, the incidence of scabies is difficult to ascertain. Indeed, while epidemics have been reported (1919-1925, 1936-1949, 1964-1979), it is clearly an endemic disease in many tropical and subtropical regions. Prevalence rates are extremely high in aboriginal tribes in Australia, in Africa, in South America, and in other developing regions of the world. Incidence in parts of Central America and South America and in one Indian village approach 100%. In parts of Bangladesh, the number of children with “the itch” exceeds the number with diarrheal and respiratory diseases combined.

Worldwide, the prevalence of scabies has been estimated at 300 million cases annually, although this figure may be an overestimate. In the United States and in other developed regions around the world, scabies occurs in epidemics in nursing homes, hospitals, long-term care facilities, and other institutions. It is seen frequently in the homeless populations but occurs episodically in other populations as well. No recent published data are available on its incidence in the United States. In one epidemiologic study in the United Kingdom, scabies was shown to have a higher frequency of occurrence in winter months than in summer months, and it more commonly affected women and children. In this study, the disease was found to be more prevalent in urban regions.

While scabies appears to be more common in the younger population, it certainly occurs in all ages, all ethnic groups, all socioeconomic levels, and in both sexes. It is not directly related to hygiene, but it is associated with poverty and crowding.

Mode of transmission

Mites are unable to fly or jump. They crawl at a rate of 2.5 cm/min. While the mite’s life cycle occurs completely on its host, they are able to live on bedding, clothes, or other surfaces at room temperature for about 48 hours while remaining capable of infestation and burrowing. At temperatures below 20°C S scabiei are immobile, although they can survive such temperatures for extended periods.

Transmission is predominantly through direct skin-to-skin contact, and for this reason, scabies has been considered a sexually transmitted disease. Indirect contact through fomites such as infested bedding or clothing is possible, although not usual. However, the greater the number of parasites on a person, as in crusted scabies, the more likely that indirect contact will abet transmission of the disease.

Mortality/Morbidity:

Classic scabies is primarily a nuisance. However, it can indirectly lead to long-term morbidity. Scabies and other parasitic skin diseases can lead to long-term colonization of skin lesions by group A streptococci. Several studies have demonstrated a correlation between poststreptococcal glomerulonephritis (PSGN) and scabies. Conversely, in one World Health Organization sponsored study in the Solomon Islands, an intervention of mass chemotherapy lead to a decrease of scabies by 96% and a parallel drop in an indicator of renal disease. In remote Aboriginal communities in Australia where scabies is endemic, the repeated infestations appear to be related to the extremely high levels of renal failure and rheumatic heart disease observed in the communities.

While the microbiology of secondary bacterial infection in scabies lesions probably changes based on geographic location, one study demonstrated that the predominant aerobic and facultative bacteria recovered from lesions were Staphylococcus aureus, group A streptococci, and Pseudomonas aeruginosa. Multiple anaerobes were recovered as well, suggesting polymicrobial colonization of lesions.

Other complications of scabies include impetigo, furunculosis, and cellulites. The staphylococci and/or streptococci in the lesions can lead to pyelonephritis, abscesses, pyogenic pneumonia, sepsis, and death.
CLINICAL Section 3 of 12   Click here to go to the next section in this topic Click here to go to the top of this page Click here to go to the next section in this topic

History:

Physical:

Causes:

DIFFERENTIALS Section 4 of 12   Click here to go to the next section in this topic Click here to go to the top of this page Click here to go to the next section in this topic

Bites, Insects
Dermatitis, Atopic
Dermatitis, Contact
Psoriasis
Urticaria


Other Problems to be Considered:


Classic scabies

Insect bites
Atopic dermatitis
Contact dermatitis
Psoriasis
Fiberglass exposure
Lichen planus
Dermatitis herpetiformis
Bullous pemphigoid
Urticaria
Chronic lymphocytic leukemia
Necrotizing vasculitis
B-cell lymphoma with monoclonal infiltrate

Crusted scabies

Eczema
Psoriasis
Ichthyosis
Adverse drug reactions
Seborrheic dermatitis
Erythroderma
Langerhans cell histiocytosis

WORKUP Section 5 of 12   Click here to go to the next section in this topic Click here to go to the top of this page Click here to go to the next section in this topic

Lab Studies:

TREATMENT Section 6 of 12   Click here to go to the next section in this topic Click here to go to the top of this page Click here to go to the next section in this topic

Emergency Department Care:

Consultations: Dermatology or infectious disease consultation may be required for severe refractory scabies or for disseminated scabies in patients with immunocompromise. Caution must be exercised when treating pregnant patients.
MEDICATION Section 7 of 12   Click here to go to the next section in this topic Click here to go to the top of this page Click here to go to the next section in this topic

Scabicides should be prescribed for patients, household members, and close personal contacts. Symptomatic treatment may require antihistamines. More severe symptoms may require a short course of topical or oral steroids. Secondary infections may require antibiotics.

Drug Category: Scabicides -- Treatment options include either topical or oral medication. Topical options include permethrin cream, lindane, benzyl benzoate, crotamiton lotion and cream, sulfur, Tea tree oil, oil of the leaves of Lippia multiflora Moldenke, a shrub found growing in West Africa Savannah. Oral options include ivermectin.

Permethrin is the drug of choice in the United States and the United Kingdom, but it is not available in France. In some studies, it has been shown to be more effective than a single dose of oral ivermectin, although it has equivalent efficacy when 2 doses of ivermectin are used at time zero and 2 weeks later.
Drug Name
Permethrin cream 5% (Elimite) -- DOC, especially for infants > 2 mo and small children. More effective than crotamiton in treating symptoms and reducing chances of a secondary bacterial infection. Even after successful treatment, postscabietic nodules and pruritus may persist for months. Recommended by CDC as first-line therapy. In vitro resistance has been documented and treatment failures have been documented.
Adult DoseApply from chin to toes and shower off 10-12 h later; repeat in 1 wk
Pediatric DoseAdminister as in adults; can apply to head and neck in children <5 y; not recommended for children <2 mo
ContraindicationsDocumented hypersensitivity
Interactions None reported
Pregnancy C - Safety for use during pregnancy has not been established.
PrecautionsMay exacerbate redness, swelling, and itching at least temporarily
Drug Name
Lindane (Kwell) -- Stimulates nervous system of parasite, causing seizures and death. Previous standard treatment for scabies but is now considered second-line treatment if other agents fail or are not tolerated. Not very safe in children due to transcutaneous absorption leading to neurotoxicity. Overall, permethrin is a safer choice.
Adult DoseApply thin layer from chin to toes; use on dry skin and shower off 10 h later; repeat in 1 wk
Pediatric DoseInfants and children: Apply thin film topically over entire body including hairline, neck, scalp, temple, and forehead, leave on 6-8 h before washing off with water; may repeat in 1 wk if necessary; not to exceed 30 g/application
ContraindicationsDocumented hypersensitivity; neonates; acutely swollen skin or Norwegian scabies
InteractionsOil-based hairdressings may increase toxicity
Pregnancy B - Usually safe but benefits must outweigh the risks.
PrecautionsCaution if history of seizures; do not apply to eyes, face, or mucous membranes; caution if history of keratinization/ichthyosis disorders
Drug Name
Sulfur in petrolatum (2 -10%, with 6% preferred) -- One of few effective scabicidal treatments that may be used safely without fear of toxicity in very small children and in pregnant women. Sulfur is messy, malodorous, and stains clothes, and requires repeat applications, thus reducing compliance. It can cause a dermatitis in hot and humid climates.
Adult DoseApply to entire body below head on 3 successive nights and bathe 24 h after each application
Pediatric DoseAdminister as in adults
ContraindicationsDocumented hypersensitivity
InteractionsNone reported
Pregnancy C - Safety for use during pregnancy has not been established.
PrecautionsResuscitative equipment should be immediately available when administering medication
Drug Name
Crotamiton (Eurax) -- For the treatment of scabies. Mechanism of action is unknown.
Adult DoseApply thin layer onto skin of entire body from neck to toes; repeat in 24 h; take a cleansing bath 48 h after last application
Pediatric DoseAdminister as in adults
ContraindicationsDocumented hypersensitivity; can cause seizures
InteractionsNone reported
Pregnancy C - Safety for use during pregnancy has not been established.
PrecautionsDo not apply to face, urethral meatus, eyes, mucous membranes, or swollen skin; can cause seizures
Drug Name
Benzyl benzoate -- Ester of benzoic acid and benzyl alcohol. Neurotoxic to mites. Not available in the US but first line in France.
Adult DoseUse 25% emulsion; apply below neck 3 times within 24 h without an intervening bath
Pediatric DoseMay reduce adult dose to 12.5% or less due to stinging
ContraindicationsDocumented hypersensitivity; breastfeeding women; infants and children <2 y
InteractionsNone reported
Pregnancy X - Contraindicated in pregnancy
PrecautionsMay cause stinging
Drug Name
Ivermectin (Mectizan, Stromectol) -- Binds selectively with glutamate-gated chloride ion channels in invertebrate nerve and muscle cells, causing cell death. Half-life is 16 h; metabolized in liver. First-line therapy.
Adult Dose150-200 mcg/kg/d PO as single dose
Pediatric Dose <5 years: Not established
>5 years: Administer as in adults
ContraindicationsDocumented hypersensitivity
InteractionsMay interact with other ligand-gated chloride channels, such as those gated by GABA
Pregnancy C - Safety for use during pregnancy has not been established.
PrecautionsTreat mothers who intend to breastfeed only when risk of delayed treatment outweighs possible risks to the newborn caused by ivermectin excretion in milk
Repeat courses of therapy may be required in immunocompromised patients
May cause nausea, vomiting, and mild CNS depression; may cause drowsiness
FOLLOW-UP Section 8 of 12   Click here to go to the next section in this topic Click here to go to the top of this page Click here to go to the next section in this topic

Deterrence/Prevention:

Complications:

Patient Education:

MISCELLANEOUS Section 9 of 12   Click here to go to the next section in this topic Click here to go to the top of this page Click here to go to the next section in this topic

Medical/Legal Pitfalls:

Special Concerns:

TEST QUESTIONS Section 10 of 12   Click here to go to the next section in this topic Click here to go to the top of this page Click here to go to the next section in this topic

CME Question 1: What is the pathognomonic lesion of scabies?


A: Linear vesicles
B: Wavy linear burrows
C: Nodules
D: Hyperkeratotic plaques
E: None of the above

The correct answer is B: The linear wavy burrow is the pathognomonic lesion of scabies.

CME Question 2: What is the drug of choice for the treatment of scabies?


A: Permethrin 5% (Elimite) lotion
B: Lindane 1% (Kwell) lotion
C: Crotamiton 10% (Eurax) lotion
D: Sulfur 10% in petrolatum
E: Oral mebendazole (Vermox) tablets

The correct answer is A: Permethrin is safe and effective, even in areas where scabies has been refractory to lindane. One application is highly effective in eradicating scabies. Because of its relative safety, many clinicians now consider it the drug of choice for treating scabies.

Pearl Question 1 (T/F): The symptoms of scabies are the result of a type I hypersensitivity reaction.

The correct answer is False: A delayed-type IV hypersensitivity reaction to the mites, their eggs, or scybala (packets of feces) occurs. This reaction is responsible for the intense pruritus that is the hallmark of the disease.

Pearl Question 2 (T/F): The manifestations of scabies can occur within hours of exposure.

The correct answer is True: The hypersensitivity reaction to the mites and their waste products occurs approximately 30 days after infestation. However, individuals who are already sensitized from a prior infestation can develop symptoms within hours.

Pearl Question 3 (T/F): Scabies is most prevalent among patients in nursing homes.

The correct answer is False: Children younger than 15 years have the highest prevalence of scabies. Other populations at risk include individuals who are sexually active, debilitated, or immunocompromised.

Pearl Question 4 (T/F): Crusted scabies may have millions of mites on the host.

The correct answer is True: In crusted scabies, millions of mites may be infesting the host. In classic scabies, usually 5-15 mites infest the host.
PICTURES Section 11 of 12   Click here to go to the next section in this topic Click here to go to the top of this page Click here to go to the next section in this topic

Caption: Picture 1. Scabies mite. Courtesy of William D. James, MD.
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Caption: Picture 2. Scabies mite scraped from a burrow (original magnification 400X). Courtesy of Audra Malerba, DO.
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Caption: Picture 3. Scabies. Courtesy of William D. James, MD.
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Caption: Picture 4. In crusted scabies, sections show multiple mites (arrows) within the hyperkeratotic stratum corneum (H&E, original magnification 100X). The epidermis is spongiotic. Courtesy of Audra Malerba, DO.
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Caption: Picture 5. In routine scabies, a single mite is seen. Eosinophilic spongiosis may be present (H&E, original magnification 400X). Courtesy of Audra Malerba, DO.
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Caption: Picture 6. Norwegian scabies. Courtesy of William D. James, MD.
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Caption: Picture 7. Scabies on leg. Courtesy of William D. James, MD.
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Caption: Picture 8. Erythematous vesicles and papules are present on torso extremities, some with adjacent linear excoriations. Courtesy of Audra Malerba, DO.
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Caption: Picture 9. Scabies on buttocks. Courtesy of William D. James, MD.
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Caption: Picture 10. Scabies on hand. Courtesy of William D. James, MD.
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Caption: Picture 11. Scabies on penis. Courtesy of William D. James, MD.
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Caption: Picture 12. Scabies on penis. Courtesy of Hon Pak, MD.
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BIBLIOGRAPHY Section 12 of 12   Click here to go to the next section in this topic Click here to go to the top of this page

NOTE:
Medicine is a constantly changing science and not all therapies are clearly established. New research changes drug and treatment therapies daily. The authors, editors, and publisher of this journal have used their best efforts to provide information that is up-to-date and accurate and is generally accepted within medical standards at the time of publication. However, as medical science is constantly changing and human error is always possible, the authors, editors, and publisher or any other party involved with the publication of this article do not warrant the information in this article is accurate or complete, nor are they responsible for omissions or errors in the article or for the results of using this information. The reader should confirm the information in this article from other sources prior to use. In particular, all drug doses, indications, and contraindications should be confirmed in the package insert. FULL DISCLAIMER
eMedicine Journal, June 19 2006, VOLUME 7, Number 6
© Copyright 2001, eMedicine.com, Inc.

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