Basics
Description
- Scabies is a parasitic infection caused by the mite Sarcoptes scabiei, which infects the stratum corneum of the skin and results in an intense pruritic rash.
- Crusted scabies is a subtype categorized by a more intense pruritus and rash with a heavier burden of mites.
- Previously called "Norwegian scabies "
- More common in immunocompromised (i.e., HIV, long-term steroid use) and debilitated patients with sensory neuropathies and paralysis
- Nodular scabies is a rare clinical subtype presenting with red to brown nodules secondary to hypersensitivity reaction to mites and their by-products.
Epidemiology
- Results from close personal and prolonged contact with another human infected with mites
- Occurs worldwide and is endemic in many countries
- Scabies affects all people from different ethnicities, social economic levels, and gender.
Incidence
Varies worldwide, with cyclical fluctuations for new cases; estimates are 1 " 15 new cases per 1,000 people per year.
Prevalence
Estimated 300 million cases worldwide
General Prevention
- Avoid direct skin-to-skin contact with a person who has scabies and with the clothing/bedding used by a person who has scabies.
- Ensure that any close contacts that have been exposed are treated even if asymptomatic because symptoms can take up to 30 days to develop.
- Everyone in the household should be treated at the same time.
- All bedding and clothing used in the prior 3 days by a person with scabies needs to be washed with hot water and dried in a hot dryer for at least 10 minutes or should be dry-cleaned.
- Furniture and carpets in the household of an infected person should be vacuumed.
- Anything that cannot be washed should be isolated from humans for at least 2 days or, more conservatively, for up to 3 weeks.
Pathophysiology
- The mite of scabies is a parasite that burrows into the skin and lays eggs. They travel anywhere between 0.5 and 5.0 mm a day. The larvae hatch from the eggs in 2 " 3 days and become adults and then the cycle repeats.
- Papules are not due to the mite itself but due to a hypersensitivity reaction to the mites ' saliva, eggs, and feces.
- If the individual has never been exposed, there is an incubation period which can be between 4 and 6 weeks before symptoms manifest.
- Those with prior exposure and thus sensitized can have milder symptoms that occur within 1 " 4 days.
- Crusted scabies subtype has thousands to millions more mites, making infectivity easier even at less contact. The mite is the same as with classic scabies.
Etiology
S. scabiei var hominis adult female mite is about 0.3-mm long with eight legs and barely visible with the naked eye.
Diagnosis
History
- Patients usually present with a history of rash that is intensely pruritic and worse at night because mite activity increases at night based on temperature of the human body.
- Rash present on hands and wrist and may also be in genital area.
- Children younger than 2 years of age may present with a vesicular rash on face and other regions of body not typical in older children and adults.
- Other family members or household contacts with a similar rash given contact with infected person is needed for transmission.
Physical Exam
- Usually presents with a papular erythematous rash
- One pathognomonic sign is the burrow line, a linear, wavy, S-shaped mark which occurs as the mite burrows into the skin; can be difficult to see because scratching can obliterate the burrow, but it helps with diagnosis if visualized
- To better identify burrows, can use a washable marker on the skin, then remove markings with water or alcohol. The ink will remain within the burrow, making it easier to see.
- Common sites of rash are interdigital web spaces of hands and feet. Papules can be present in flexor region of wrist, extensor region of elbows, axillary folds, genital region, and periareolar regions of breast.
- Presentation differs in young children versus older children and adults.
- Children younger than 2 years of age usually have a more widespread distribution that also includes face, neck, palms, and soles.
- Rash in young children also can be more vesicular.
Diagnostic Tests & Interpretation
Lab
- Direct visualization
- Potassium hydroxide preparation of a skin scraping
- Use a blade to scrape skin, isolate the mite from scrapings, and view scrapings under microscopy.
- Look for mites and mite fecal matter.
- Visualization of the burrows can be made easier using the "burrow ink test. "
- Use ink to mark areas where scabies are suspected, then wipe away the surface ink with alcohol pad.
- If ink tracks into the mite burrow, making a grossly visible zigzagged line, the test is positive.
- In atypical cases, skin biopsy can be formed.
- Other more specialized tests are under development such as antigen detection, PCR of skin scrapings, or intradermal tests.
Differential Diagnosis
- Contact dermatitis
- Atopic dermatitis
- Insect bites
- Drug rash
- Infantile acropustulosis
- Impetigo
- Papular urticaria
- Viral exanthem
Treatment
Medication
- Permethrin 5% cream
- Drug of choice for children and infants >2 months of age
- Is neurotoxic to the mite
- The cream is applied from neck to toe, paying special attention to interdigital regions; skinfolds of wrist, elbow, and inguinal creases; and under nails.
- In young children, include the entire head and neck as well because these aren 't spared in this age group.
- Rinse cream off the body 8 " 14 hours after application.
- Often, one retreatment 1 week after initial treatment is needed. Some recommend retreating once 4 days later (instead of waiting 7 days).
- Crotamiton 10% cream
- Not commonly used
- Not approved in children
- Apply from chin to toe and reapply 24 hours later. Then remove by a cleansing bath 48 hours after the last application.
- Sulfur 5 " 10% cream
- Can be used for infants younger than 2 months and pregnant lactating woman
- Must be reapplied daily for 3 days
- Ivermectin
- Oral antiparasitic agent
- Not recommend for women who are pregnant or lactating
- Safety profile for children is unknown.
- Not FDA approved for treatment of scabies
- Mild to moderate topical steroids
- Note, topical steroids have no efficacy in treating the mite infection but can be helpful for the intense pruritus during and just after the scabies infection.
- Lindane 1%
- Not commonly used due to concern for systemic toxicity
- American Academy of Pediatrics (AAP) Redbook (2012) states that "because of safety concerns and availability of other treatments, lindane should not be used for treatment of scabies. "
- Side effects can include seizures, headache, and vertigo.
Ongoing Care
Follow-up Recommendations
Patient Monitoring
- Treatment failure occurs but is usually due to incomplete treatment of all contacts at the same time.
- Recommend follow-up 2 weeks after treatment to ensure no new burrows, new papules, or new vesicles have developed, which would most likely indicate inadequate application of treatment.
Prognosis
Prognosis is great with early identification and treatment.
Complications
- Secondary bacterial skin infection
- Post scabies pruritus: Pruritus that occurs for weeks after treatment should not be confused with treatment failure.
Additional Reading
- American Academy of Pediatrics. Scabies. In: Pickering LK, Baker CJ, Kimberlin DW, et al, eds. Red Book: 2012 Report of the Committee on Infectious Diseases. 29th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2012.
- Chosidow O. Clinical practice: scabies. N Engl J Med. 2006;354(16);1718 " 1727. [View Abstract]
- Golant AK, Levitt JO. Scabies: a review of diagnosis and management based on mite biology. Pediatr Rev. 2012;33(1):e1 " e12. [View Abstract]
- Heukelbach J, Feldmeier H. Scabies. Lancet. 2006;367(9524):1767 " 1774. [View Abstract]
- Leone P. Scabies and pediculosis pubis: an update of treatment regimens and general review. Clin Infect Dis. 2007;44(Suppl 3):S153 " S159. [View Abstract]
- Mounsey KE, McCarthy JS. Treatment and control of scabies. Curr Opin Infect Dis. 2013;26(2):133 " 139. [View Abstract]
- Strong M, Johnstone P. Interventions for treating scabies. Cochrane Database Syst Rev. 2007;(3):CD000320. [View Abstract]
Codes
ICD09
ICD10
SNOMED
- 128869009 Infestation by Sarcoptes scabiei var hominis (disorder)
- 128870005 Crusted scabies (disorder)
FAQ
- Q: What do I do with the clothes or cloth items that cannot be washed at this time?
- A: Store them in a plastic bag and put them away for 3 days because the mite cannot live more than 3 days without a human host. Couches and carpet should be vacuumed.
- Q: When will my child no longer be contagious?
- A: If treated properly, children are no longer contagious after one treatment. Although your child may still have pruritus, he or she is no longer considered contagious and can return to school.
- Q: When will the rash resolve?
- A: The rash may take 3 " 4 weeks to resolve after treatment and should not be considered a treatment failure unless a new rash develops.