Management of Scabies

Gentiane Monsel, MD¹ and Olivier Chosidow, MD, PhD²

¹Department of Dermatology, Saint Louis Hospital, Paris, France
²Université Paris-Est Créteil Val de Marne and Assistance Publique-Hôpitaux de Paris,
Department of Dermatology, Henri Mondor Hospital, Créteil, France

ABSTRACT
Scabies is a common contagious parasitic dermatosis. Transmission of the mite Sarcoptes scabiei var hominis generally occurs by skin-to-skin contact, but with crusted scabies it may also occur through fomites, such as infected clothing or bedding. Diagnosis is usually clinical. A 2010 updated Cochrane review concluded that management of scabies is based on topical scabicides, mainly 5% permethrin. However, oral ivermectin, although not licensed in many countries, may be useful, particularly for patients who cannot tolerate or comply with topical therapy and in institutional scabies epidemics. Patients should also receive detailed information about the infestation to limit further spreading. Cases resulting from close physical or sexual contact, even without symptoms, should be systematically treated. Hygienic measures should be taken after treatment is completed. Patients should be followed to confirm cure, including resolution of itching, which may take up to 4 weeks or longer.

Key Words:
benzyl benzoate, ivermectin, permethrin, scabicides, scabies

Scabies is a common parasitic infection caused by the mite Sarcoptes scabiei var hominis, arthropod of the order Acarina. The worldwide prevalence has been estimated at about 300 million cases annually, although this may be an overestimate.¹ In general, transmission occurs by direct skin-to-skin contact. In crusted scabies, transmission may also occur through infected clothing or bedding. Skin eruption with classical scabies is attributable to both the infestation and a hypersensitivity reaction to the mite. Moreover, because the eruption is usually itchy, prurigo and superinfection are common.

The main symptom is pruritus that typically worsens at night, and it is often associated with itching experienced by other family members in the household or amongst people in close physical contact with an infested individual. The lesions are commonly located in the finger webs, on the flexor surfaces of the wrists, on the elbows, in the axillae, and on the buttocks and genitalia. The elementary lesions are papules, burrows, and nodules. In crusted scabies, clinical signs include hyperkeratotic plaques, papules and nodules, particularly on the palms of the hands and the soles of the feet, although areas such as the axillae, buttocks, scalp, and genitalia in men, and breasts in women may also be affected.¹

The definitive diagnosis relies on the identification of mites. Multiple superficial skin samples should be obtained from characteristic lesions by scraping with a scalpel. The specimens are examined under a microscope, looking for mites, eggs, empty eggs, and scybala. Failure to find a mite is common and does not rule out scabies.¹ New methods such as dermoscopy or adhesive tape test may increase the sensitivity of skin scraping tests and limit false-negative results.^2,3 However, comparing the accuracy of different tests for diagnosing scabies remains elusive without a criterion standard.⁴

Scabies may be endemic in indigenous communities with a high rate of superinfection, which implies the need for specific management. Here, we describe the management of scabies in Western countries.

Indication for Therapy

People with scabies and their close physical contacts, even without symptoms, should receive treatment at the same time. Prescriptions must be provided for all household members and sexual partners.

Patient Education

Patients should receive detailed verbal and written information about scabies infestation.⁵ Infested individuals should be advised to avoid close physical contact until they and their sexual partners have completed treatment.

Treatment Options

Topical and oral products are available, although rigorous studies to guide their use are lacking. Whether oral or topical treatment is more advantageous for improved efficacy, tolerance or convenience remains unknown.^6-9 Table 1 summarizes the doses and side effects of common agents used in scabies management. Topical treatment includes permethrin, lindane, benzyl benzoate, esdépallétrine (bioallethrin), crotamiton, and precipitated sulfur. Topical scabicides have neurotoxic effects on mites and larvae. Despite the varied methodological quality of trials, a recent meta-analysis suggested that topical permethrin is the most effective.⁶ Oral ivermectin interrupts the gamma-aminobutyric acid-induced neurotransmission of many parasites (including mites). However, oral ivermectin is not licensed in most countries. It must be given at 200 µg/kg as a single dose in patients >2 years of age and >15 kg. A second dose is necessary 2 weeks later due to the lack of ovicidal action of the drug.^1,10 Because ingestion of food increases the bioavailability of ivermectin by a factor of 2,¹¹ taking it with food might enhance the penetration of the drug into the epidermis. Finally, topical permethrin is reasonable as first-line therapy. If permethrin is not available (e.g., in France), benzyl benzoate may be used. Oral ivermectin is a good but more expensive alternative; however, this agent may be preferred for patients who cannot tolerate topical therapy or are unlikely to adhere to such a therapeutic regimen.^1,10 In classical scabies, the combination of topical therapy and oral ivermectin has never been compared with either treatment alone. Table 2 presents strategies of treatment according to the clinical picture.

Additional Measures

Scabies is considered to be a sexually transmitted disease, therefore, patients should undergo routine examination for sexually transmitted infection.¹²

Patients must receive detailed information about scabies infestation and therapeutic options, including the amount of drug to be used and proper administration. Topical treatment must be applied to the entire skin surface, including the scalp, all folds, groin, navel, and external genitalia, as well as the skin under the nails. In adults with classical scabies, treating the face is controversial, but in babies, the face must be treated, because transmission may occur by breastfeeding. Hands should not be washed during therapy, otherwise the treatment should be reapplied. If the treatment is applied by someone without scabies, this person should wear medical gloves during administration.

After the completion of treatment, patients should use fresh, clean bedding and clothing. If possible, potentially contaminated clothes and bedding should be washed at high temperature (>50°C) or kept in a plastic bag for up to 72 hours, because mites that are separated from the human host will die within this time period. The use of insecticidal powder or aerosol products should be reserved for materials or objects that cannot be washed.¹³

With classical scabies, the time course for the eradication of parasites after treatment is not known, but there is some concern that patients receiving oral ivermectin may remain contagious longer than those receiving topical therapies.^1,10

Special Treatment Considerations (Table 2)

Impetigo

Scabies complicated by impetigo requires combined antiseptic and antibiotic therapy against Streptococcus pyogenes and Staphylococcus aureus. Oral ivermectin is preferred if skin is damaged.

Crusted Scabies

Management of crusted scabies generally necessitates admission to the hospital and isolation of the patient because of the risk of transmission to people in physical contact. Active epidemiological measures to ensure treatment of all individuals in contact are necessary. Hyperkeratosis is treated with a keratolytic agent. The nails are cut short and brushed with a scabicidal agent.¹³ The combination of topical and oral therapy is advised,¹⁴ although evidence is lacking regarding efficacy. Topical treatment may be repeated. Dosing and frequency of administration is based on the severity of infection. The required number of doses of ivermectin remains uncertain, but depending on infection severity, 3 to 7 doses have been proposed.¹⁰ A test of cure may be performed for crusted scabies.

Pregnancy or Breastfeeding

Permethrin, benzyl benzoate, and sulphur appear to be safe, although evidence is limited.¹⁵ Oral ivermectin is contraindicated.

Children

Permethrin may be used in infants. Benzyl benzoate and esdépallétrine are safe in children <2 years of age, but duration of use should be limited to 12 hours. Ivermectin is not approved for children <15 kg.

Institutional Outbreaks

Management of institutional outbreaks has never been evaluated. The control of institutional outbreaks relies on prompt recognition of the index case, formation of an outbreak management team, determining the extent of the outbreak and risk factors for transmission, immediate implementation of infection control practices, adequate education of all involved individuals, simultaneous treatment of cases and all exposed people, and concomitant environmental disinfection.¹⁶

Follow-up

Patients should understand that after treatment is completed, itching may persist for several weeks, especially in atopic individuals. If itching continues after 4 weeks, the cause should be reinvestigated (Table 3). Symptomatic relief may be achieved with an emollient. A test of cure is not usually required with classical scabies.

Conclusion

Scabies is a frequent, contagious dermatosis. Its management is sometimes complex and updated treatment guidelines are useful.^12,17 Patients and people in close physical contact with infested individuals should receive detailed information from healthcare providers, because treatment failure is often attributable to poor compliance or incorrectly carrying out instructions of prescribed therapy. Decision-making for topical or oral treatment may vary by situation. Randomized controlled trials comparing topical treatment to oral ivermectin demonstrating a high level of evidence are needed.

References

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