Approach Considerations
Scabies treatment includes administration of a scabicidal agent (eg, permethrin, lindane, or ivermectin), as well as an appropriate antimicrobial agent if a secondary infection has developed. [47, 48] A 2019 meta-analysis reports that no single agent ranked most effective with respect to cure and control of adverse effects from the scabies infection. Permethrin, oral ivermectin, and synergized pyrethrins were deemed most effective for cure and symptomatic relief. [49] A small segment of the population is at increased risk for ivermectin toxicity based on genetic predisposition. [50] Close contacts should be treated, and, during epidemics, large numbers may need to be treated. [51, 52, 53, 54]
In a World Health Organization (WHO)–sponsored study in the Solomon Islands, an intervention of mass treatment with ivermectin or permethrin led to a decrease in prevalence of scabies from 25% to less than 1%, as well as a decrease in the prevalence of pyoderma (secondary infection) from 40% to 21%. There was also a decline in hematuria, which was a sign of renal damage by group A Streptococcus secondary infection in children. [55] Treatment also decreased occurrence of streptococcal skin disease. Similar successes have been reported in other populations. [56]
Treatment failures are uncommon but do occur. The most common causes of treatment failure include the following [57] :
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Improper application
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Inadequate application
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Reinfestation - Recurrence of the eruption usually means reinfection has occurred, underscoring the importance of treating all members of the household
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Resistance - Resistance to lindane has been widely reported; less frequently, cases of resistance to permethrin have been noted; resistance to ivermectin is still rare but has been reported in patients who received multiple doses of the drug over several years [57]
Neonates and pregnant women should be treated for scabies only if the benefit exceeds the risk and if the diagnosis is confirmed by a positive skin scraping or biopsy result.
Crusted scabies may require several treatments with scabicides and sometimes several different medications used sequentially. [27] Scabetic nodules may require intranodular steroid injection.
Activity
Individuals affected by scabies should avoid skin-to-skin contact with others. Patients with typical scabies may return to school or work 24 hours after the first treatment. [58]
Consultations
Consultation with a dermatologist or an infectious disease specialist may be required for severe, refractory scabies or for disseminated scabies in patients who are immunocompromised.
Pharmacologic Therapy
A scabicidal agent, such as permethrin, lindane, or ivermectin, is administered to destroy S scabiei mites, with an appropriate antimicrobial agent used as well if a secondary infection has developed. Moxidectin and afoxolaner are emerging as promising new agents. Botanical oils have also been used, but they present a risk of allergic contact dermatitis. Despite the development of resistance, permethrin retains good efficacy. [59, 60, 61, 62]
Itching may persist for up to a month, even following successful treatment. Pruritus may be partially alleviated with an oral antihistamine, such as hydroxyzine hydrochloride (Atarax), diphenhydramine hydrochloride (Benadryl), or cyproheptadine hydrochloride (Periactin). Rarely, individuals with a history of atopy may require a tapered dose of prednisone for the treatment of severe pruritus. Intranodular injection of dilute corticosteroids may be necessary in cases of nodular scabies.
If available, videodermatoscopy can be used to enhance the monitoring of clinical response to scabies treatment and allows for optimal timing of drug application. [63] This may minimize the risk of overtreatment, reduce the potential for side effects, and enhance patient compliance. This is not a widespread technique. With videodermoscopy, a handheld device is used to illuminate, magnify, and record video of the skin.
Crusted scabies
Patients with crusted scabies or their caregivers should be instructed to remove excess scale in order to allow penetration of the topical scabicidal agent and decrease the burden of infestation. This can be achieved with warm water soaks followed by application of a keratolytic agent, such as 5% salicylic acid in petrolatum or Lac-Hydrin cream. (Salicylic acid should be avoided if large body surface areas are involved because of the potential risk of salicylate poisoning.) The scales are then mechanically debrided with a tongue depressor or similar unsharp device.
Because of their heavy mite burden, patients with crusted scabies may require repeated applications of topical scabicides or treatment that simultaneously uses oral ivermectin and a topical agent, such as permethrin
Follow-up
Patients with scabies may need to be reexamined at 2 weeks and again at 1 month after treatment. If a patient has persistent lesions at the 1-month check-up, reinfection or persistent infection should be suspected. In this case, treatment should be reinitiated. The patient’s family or any close contacts should also be examined to check for a source of reinfection. Patients with crusted scabies, especially, should be followed after treatment and may require repeated courses of treatment.
Prevention
All household members and close personal contacts older than 2 months and not pregnant should be treated for scabies, even if they have no symptoms or signs of infestation. (Pets do not require treatment.) Detailed directions regarding treatment and environmental control measures should be provided verbally and in writing. [57]
Instruct patients to launder clothing, bed linens, and towels used within the last week in hot water (60°C or higher) and to machine dry them, the day after treatment is initiated and again in 1 week. Items that cannot be washed may be professionally dry cleaned or sealed in plastic bags for 1 week. All carpets and upholstered furniture should be vacuumed and the vacuum bags immediately discarded.
Mass screening and treatment of all affected individuals give the greatest reductions in scabies prevalence, [22] but once these efforts end, prevalence rates quickly escalate. One approach to this problem is to provide more frequent treatment to a predetermined, randomly chosen number of affected individuals. Sometimes, as a result of nonlinearity, treatment densities do not have to be impractically high to produce significant reductions in scabies burden. Single-dose oral treatment may be effective in mass infestations. [64]
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Scabies mite scraped from a burrow (original magnification, 400X).
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A typical linear burrow on the flexor forearm. Courtesy of Kenneth E. Greer, MD.
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A subtle linear burrow accompanied by erythematous papules on the sole of the foot in a child with scabies. Courtesy of Kenneth E. Greer, MD.
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Erythematous papules and papulovesicles on the flexor wrist. Courtesy of Kenneth E. Greer, MD.
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Scabies on the penile shaft and glans. Courtesy of William D. James, MD.
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Scabietic papules on the penile shaft and scrotum. Courtesy of Kenneth E. Greer, MD.
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Widespread eruption on the back of an infant with scabies. Courtesy of Kenneth E. Greer, MD.
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Nodular scabies in an infant. Courtesy of Kenneth E. Greer, MD.
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Nodular scabies. Courtesy of Kenneth E. Greer, MD.
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Crusted scabies. Courtesy of William D. James, MD.
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Crusted scabies. Courtesy of Kenneth E. Greer, MD.
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Scabies preparation demonstrating a mite and ova. Courtesy of William D. James, MD.
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Scabies. Erythematous vesicles and papules are present on torso extremities, some with adjacent linear excoriations.
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In routine scabies, a single mite is seen. Eosinophilic spongiosis may be present (hematoxylin and eosin; original magnification, 400X).
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Scabies mite in the stratum corneum. Courtesy of William D. James, MD.
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In crusted scabies, sections show multiple mites (arrows) within the hyperkeratotic stratum corneum. The epidermis is spongiotic (hematoxylin and eosin; original magnification, 100X).
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Scabies. Courtesy of William D. James, MD.
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Scabies in the interdigital web spaces. Courtesy of William D. James, MD.
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Papulovesicles and nodules on the palm in a patient with scabies. Courtesy of Kenneth E. Greer, MD.
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Scabies on buttocks. Courtesy of William D. James, MD.
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Scabies on penis. Courtesy of Hon Pak, MD.
