Review Article Journal of Cutaneous Medicine and Surgery 00(0) 1–7 © The Author(s) 2020 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/1203475420960446 journals.sagepub.com/home/cms
Scabies: Diagnostic and Therapeutic Update Robert N. Richards1
Abstract Background: Scabies is globally ubiquitous and is a significant health issue for institutions, the economically disenfranchised, resource-poor areas, and for those with weakened immune systems. Topicals are usually effective, but are cumbersome and expensive to use in large populations and for those nonadherent to topicals. Oral ivermectin became available in Canada for the off-label treatment of scabies in the fall 2018. Objectives: To review the diagnosis and management of scabies. Dose schedules and concomitant management measures are outlined for scabies simplex and for crusted scabies. Ivermectin use is outlined. Methods: Medline, colleague discussions, practice review, and experience from managing scabies in institutions. Results: Oral ivermectin is safe, easier to use, cheaper, more effective, and more economical than topicals in widespread institutional scabies, for those nonadherent to topicals, and in crusted scabies. Conclusions: Oral ivermectin is the treatment of choice in large populations, the nonadherent, and for crusted scabies. Oral ivermectin is produced by Merck Canada as Stromectol 3 mg. The treatment dose for noncrusted scabies is 200 µg/kg, taken in a single dose with food. For example, 15 mg (5 tablets) for a 70 kg person. Retreat in 10-14 days to enhance effectiveness, and perhaps to reduce scabicide resistance. Keywords scabies, crusted scabies, institutional scabies, ivermectin, permethrin, population outbreaks
Scabies occurs globally, and is caused by the species-specific ectoparasitic mite: Sarcoptes scabiei (var. hominis).1-5 In the fall of 2018, oral ivermectin became available in Canada for the off-label treatment of scabies. The use of ivermectin in other jurisdictions has been a huge therapeutic advance for mass populations, institutional outbreaks, crusted scabies, resistant scabies, and those nonadherent to topicals.6,7 Common scabies (scabies simplex) and crusted scabies differ in their morphology, degree of contagion, severity, complications, and treatment. Sarcoptes scabiei (var. hominis) measures about 0.35 mm and lives in linear burrows dug in the stratum corneum. It can be visible to the naked eye as a speck, and may be visible to expert dermoscopists.8 Female mites burrow into the skin and lay eggs, which take 10-14 days to produce new mites. Adult males live on the skin and may enter the burrows for food and mating.1-5 The average scabies simplex case carries about 10-20 mites, but infants and the elderly may harbor between 50 and 250 mites.2 Patients with crusted scabies carry thousands to millions of mites.1–5 Transmission of scabies simplex is most frequently by skin-to-skin contact, usually prolonged skin contact. Some individuals are more susceptible.1-5,9 Those affected can be of any age or social strata, and good personal hygiene does
not always prevent infestation. Large outbreaks are more common in institutions, the economically disadvantaged, crowded tropical areas, and in crowded resource-poor areas such as those found in some indigenous areas in Northern Canada and Australia. Transmission is facilitated by skin-to- skin contact, sleeping with or sex with an infested person, the sharing of living quarters, and close continuous contact. Transfer by casual contact such as shaking hands is rare. The risk of transmission by fomites is negligible except in severe crusted scabies.1-3 Mites cannot jump or fly and die outside their human host within 24-48 (72 maximum) hours.5,9 An infested person is contagious, even when symptom free, but there is no risk of spread in scabies simplex after appropriate treatment. Healthcare workers may find gloves reassuring, but scabies simplex is often present but undiagnosed before gloves are considered, and statistics regarding their
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Departments of Medicine, North York General Hospital and Baycrest Health Sciences, Courtesy Staff Dermatology, Toronto, ON, Canada Corresponding Author: Robert N. Richards, Suite 507, 3018 Yonge Street, Toronto, ON M4N0A2, Canada. Email: revrichards@hotmail.com
2 effectiveness are not available. Hand washing after examinations is logically recommended but there is no factual evidence of its effectiveness. Animals carry mite-specific species such as Sarcoptes canis in dogs, which may produce a temporary eruption in humans, but not scabies, because canine mites do not survive on humans.4
Epidemiology Scabies is a global disease and there is great variation in its prevalence and health burden. The scabies burden is greatest in tropical regions, in areas of overcrowding, in times of war and social disruption, and in economically disadvantaged populations such as indigenous Australians.10 The most commonly affected age groups are children, adolescents, and elderly people. In some areas over 50% of the population is affected and scabies continues to be a significant health problem. Worldwide estimates of current cases vary from 200 to 300 million.5,9 Hay et al noted that scabies is endemic in tropical areas and estimated an average prevalence of 5%-10% in children, commonly with total family involvement.11 In low-frequency countries such as North America and Europe, the occurrence of scabies is more evenly distributed among all age groups. Institutional outbreaks are always of concern.12 Except for institutional outbreaks, scabies is not a reportable disease in western countries; therefore, its epidemiology and true prevalence remain unknown.6 Studies are not available. We know that scabies is ubiquitous and every family doctor, dermatologist, and institution with whom I have spoken has seen cases in the past year. Scabicide sales are not helpful in establishing scabies incidence because these products are used widely for lice, and commonly for trial treatments or misdiagnoses. The occurrence of scabies is cyclical and it is more easily transmitted in some years or decades than others. This periodicity is often less obvious in poor communities. There is always an increase during times of war and social disruption.11,13 There are no North American data but all colleagues with whom I consulted have anecdotally noticed a cyclical pattern in the frequency of scabies.
Clinical presentation of scabies simplex Itch and/or rash begin 4-6 weeks after contact, but a person experiencing scabies reinfestation within 6 months of this initial infection will develop itch in hours to days.5 Scabies itch results from the mechanical effect of mite burrowing, and from an allergic reaction to the mite and its products.1,3,5 In severe cases we see disseminated erythematous papules, excoriations, hemorrhagic crusts, linear scratch marks, eczema (dermatitis), vesicles (even bullae), often pustules and impetigo from secondary bacterial infection, and, if intact, the mites’ linear burrows, which appear as 3-10 mm linear lines, most easily seen around the hands and wrists.
Journal of Cutaneous Medicine and Surgery 00(0) Scabetic nodules may result from an exaggerated hypersensitivity reaction and from rubbing and scratching, and may be skin-colored, red-brown, or violaceous. Bruising, secondary to rubbing and scratching, is not uncommon. Itch occurs all over (below the neck), not just at rash sites, and is usually nocturnal. Severity of itch and the number of lesions vary from person to person, and asymptomatic carriers are not rare.3 Elderly patients may have less itch and fewer typical lesions.1-5 The use of topical steroids reduces visible inflammatory reactions, but may permit the mites to flourish.
Scabies Simplex Distribution Lesions are usually symmetrical, and are seen on the finger webs, anterior wrists, palms, thenar eminences, elbows, anterior axillae, lower buttocks, inner thighs, waist, umbilicus, knees, margins and soles of the feet, and vulva; and almost diagnostically the female areola, breasts, glans penis, shaft, and scrotum. The neck and above are usually spared, except in infants, the elderly, the immunocompromised, and in crusted scabies. Infants are often affected on the face, scalp, palms, and soles. Symptoms and morphology can vary greatly, and most experienced clinicians (author included) have missed the diagnosis.1-5
Diagnosis of Scabies Simplex Classic morphology is diagnostic, but there is often confusing secondary eczema (dermatitis) produced by scratching and/or by excessive washing. Normal soap washing may alter scabies morphology by reducing the number of active lesions. I have, not infrequently, seen patients itch all over, whose only visible lesions were on the genitals or female areolae. A history of itchy family, friends, or intimate contacts is helpful. A definitive office diagnosis is made by retrieving (by needle or scrapings) the mite, its eggs, or its fecal pellets (scybala),1-5,9 but this requires a microscope, time, and skill, so its office use is limited. The mite is located at the end of the burrow and may attach to a carefully inserted pin or needle. Scrapings obtained by a scalpel or similar instrument may be placed on a glass slide, covered with clear tape and examined under a microscope. An alternative is to send a sample to the laboratory, by placing scrapings on black laboratory paper but the yield is less with these methods. Skin biopsy (also time consuming and expensive) is helpful if taken from a burrow showing the mite or its products, but if the burrow is missed, the report will return showing dermatitis.14 Inks or oils may help outline burrows, as does good lighting and magnification. Diagnosis, however, is often established by a positive response to empiric treatment. Clinical and epidemiological scabies research has been limited by a lack of diagnostic standardization. International groups have tried to establish diagnostic criteria that can be implemented in a variety of settings and they note that Level
Richards A evidence requires direct visualization of the mite or its products.15,16 Dermoscopy is heavily operator dependent, but in expert hands can identify the mite but not its eggs or fecal pellets. Mite identification is more difficult in darker skin types and in hairy areas. The expense of dermatoscopes and the requirements for training limit its widespread use.16 An Italian group has recommended the use of a low-cost video dermoscopy but more studies are required.17 There are no blood tests to diagnose scabies or vaccines to prevent scabies.1
Complications of Scabies Simplex In resource- rich areas, mild impetigo, not infrequently, develops from scratching, as it does in eczema and similar conditions, but precise data about its incidence are not available. It is usually mild and easily controlled with topical or oral antibiotics. However, in tropical resource-poor areas (and in crusted scabies), significant impetigo, secondary staphylococcal or streptococcal bacteraemias, and toxin- mediated diseases such as scarlet fever, streptococcal toxic shock syndrome, rheumatic fever, and glomerulonephritis are major health issues.1,5,7,10 The common organisms are Streptococcus pyogenes and Staphylococcus aureus.5 The “SHIFT” trial studied the effects of mass drug administration for scabies control in a Fijian population with endemic disease. On 1 island the incidence of scabies was 32.1% and that of impetigo was 24.6%. Oral ivermectin treatment reduced the incidence of scabies to 1.9% and of impetigo to 8%.18 Similar results were obtained in the “AIM” study in which over 26 000 Solomon Islanders were treated with a combination of ivermectin and azithromycin. Scabies prevalence was reduced from 19.5% to 1.3% and that of impetigo from 22.4% to 5.1%.19 Fortunately, scabies is not a known vector for other diseases.3
Treatment of Scabies Simplex Underclothes and linen should be changed and hot washed at degrees 50 °C or 122 °F, but sterilization is not required.1,4 Alternatively, linens, clothing, and similar items may be sealed in a plastic bag for 72 hours.5 All persons living in the household, and all intimate or prolonged contacts, must be treated simultaneously, even if they do not have symptoms. If not treated, they may be a source of reinfestation for others. Matthewman et al20 compared the effectiveness of individual versus household treatment for scabies. Participants in the household treatment group had about twice the odds of being cured. In resource-rich areas, most patients use 5% permethrin cream or lotion, which kills both mites and eggs. Both are effective and pleasant to use, and most insurers pay for prescribed permethrin. Permethrin produces neurotoxicity by inhibiting sodium channels, which culminates in paralysis
3 and death of the mite.21 Permethrin is available without prescription in Canada, Great Britain, and Europe, but requires a prescription in the United States. Permethrin is applied overnight to ALL the skin from the neck down. No area of skin can be missed so application may require assistance. One night’s application is theoretically adequate, but the vagaries of human behavior and compliance dictate that an important standard of practice is to repeat the treatment in 7-10 days as this is more effective. Additionally, the second treatment will kill newly hatched mites as the initial treatment may not always be ovicidal to all eggs.1-5,9,22 Most authors consider permethrin to be safe for pregnant or lactating women,1,4,5 and for children over 2 months of age.1,4,5,9 The usual amount of product required for a single night’s treatment for persons over 12 is approximately one 30 g tube or 1 container of 100 mL of lotion. For children 5-12 years of age, the usual amount is ½ of the above, and ¼ for children 2-4 years. Prices vary from vendor to vendor. Average prices in Toronto in August 2020 for 1 night’s treatment for 1 adult were $25 for Nix dermal cream (30 g) and $80 for Kwellada-P lotion (100 mL). Presently, neither Nix lotion nor generic permetherin lotions are available in Canada. For infants under 2 months, the American Center for Disease Control and Prevention recommends 5%-10% sulfur ointment (sulfur in vaseline) applied all over for 3 days.4,5 Sulfur ointment is messy and has an unpleasant smell, but is effective and safe.1,4 Ointment-induced secondary irritation is managed by topical steroids and soap avoidance. Infants, and occasionally the elderly and infirm, may require topical applications to the face and scalp.5,9 We have observed that many patients (and their contacts) require reassurance that their acquisition of scabies does not necessarily reflect issues of hygiene or sexual behavior, as this concern is often paramount for them. Pets do not require treatment.3 Other topical applications are used in permethrin- resistant cases, and in countries where economics dictate the use of cheaper 25% benzoyl benzoate, which is effective but irritating. Lindane lotion (1% gamma benzene hexachloride) is applied in the same manner as permethrin, and can be used for treatment failures. It is safe if used properly for a short period.7 Lindane is available in Canada and most states, but is banned in California and many countries because of overuse and accidental swallowing, which can produce nervous system damage. Although used for decades, it is no longer considered safe for children under 10 years, pregnant or nursing women, or those under 110 lb. Topical 0.5% malathion aqueous lotion and ivermectin 1% lotion are used in some countries.4 Ivermectin is not ovicidal so it is important to retreat in 1 week. Sulfur 5%-10% cream, ointment, or lotion is effective when used for 3 consecutive days and is considered safe in pregnancy and infants.5 Post scabetic itch may persist for days/weeks. Treatment is midstrength to strong cortisone creams and soap avoidance. Soaps dry the skin and should be used only for
4 essential areas such as underarms, genitals, hands, and face. First- and second- generation antihistamines assist some patients, but must be used with caution in the elderly. Post scabetic localized nodules respond to intralesional triamcinalone acetonide suspension at 2.5-5 mg/cc., but clinicians must be certain they are not missing persistent infestation.23 Oral ivermectin is indicated for topical failures, those nonadherent to topicals, those unable to apply topicals (physically or mentally disabled, refugees, the homeless), widespread institutional outbreaks, mass populations, and crusted scabies.1,5 Oral ivermectin was introduced in 1981 and has been used extensively to treat strongyloides, onchocerciasis, trichuriasis, and scabies. Veterinarians and farmers use it for heartworm and other helminths in pets and farm animals. Ivermectin was approved in France for the treatment of institutional scabies in 2001.1 In the fall of 2018, Health Canada approved ivermectin for oral use in strongyloides, onchocecriasis, and lymphatic filariasis suspected to be caused by Wucheria bancrofti.24,25 Previously, the drug could be obtained by special access from Health Canada, but this was prohibitively onerous. Similar approval was given by the Food and Drug Administration in the United States in 1997. The decades delay in Canadian availability is presumed to be due to our small market and regulatory issues. Another factor, perhaps, was the 1997 Lancet report of an increased death rate among elderly patients treated with ivermectin for scabies in an Ontario nursing home,26 but this has never been confirmed by any other study, and is no longer considered relevant.3,6,27 The World Health Organization lists ivermectin as one of the most effective and safe medicines needed in a health system.28 Ivermectin is marketed by Merck Canada as Stromectol 3 mg tablets25 and is readily available for off- label use. Ivermectin is not ovicidal so a second dose is given 2 weeks after the initial dose3 to ensure that the newly hatched mites are killed,1,7 even though some studies found single dosing effective.5,7 The oral dose, taken with food at one time, is 200 µg/kg. The dosage per kg weight is (1) 15-24 kg—1 tablet, (2) 25-35 kg—2 tablets, (3) 36-60 kg—3 tablets, (4) 51-65 kg—4 tablets, (5) 66-79 kg—5 tablets, (6) >80 kg—200 mcg/kg.24 The usual adult dose range is 9-15 mg. Some studies combined oral ivermectin with topical scabicides, but this has no consensus, other than in the treatment of crusted scabies.5,7 Ivermectin is remarkably safe and dosing can err above the exact body weight without concern. Side effects in these doses are uncommon and difficult to distinguish from the disease and anxiety, but can include headache, nausea, dizziness, and gastrointestinal upset. Many side effects are thought to result from mite deaths rather than from the drug itself.6,7 There were no side effect withdrawals in the Cochrane review of 15 studies with 1896 participants.6 Significant drug interactions have not been a problem.6,7 Currie7 noted that by
Journal of Cutaneous Medicine and Surgery 00(0) 2010, over 400 million doses of ivermectin have been given in Africa for the treatment of onchocerciasis with minimal adverse events. Ivermectin is not approved for use in pregnancy or nursing, or for children weighing less than 33 lb (15 kg)4 but the drug has been used in these groups without reports of adverse outcomes.1,7 The product monograph notes that less than 2% of the standard dose appears in the breast milk, but safety in newborns has not been established.25 The product monograph suggests taking it on an empty stomach, but many scabies experts believe it is more effective if taken with food, and Currie7 noted that food increases the viability of ivermectin by a factor of 2.29 There is no parenteral ivermectin available for human administration but subcutaneous ivermectin is used regularly in veterinary medicine and has been used in a case of human strongyloidiasis.30 Ivermectin cost per tablet ranges from $20 to $9 depending on the number purchased. Therefore, it is cheaper to use than topical therapies for widespread outbreaks and institutional outbreaks. Institutional scabies7,31,32 can occur in crowded living conditions such as hospitals, nursing homes, residential schools, college dormitories, camps, custodial facilities, and the military. Hard data are not available on transmission rates as they vary hugely from institution to institution. I have seen scabies involve most residents of a nursing home, as well as staff members, visitors, and visitors’ families. But in another facility, I observed single resident involvement with no spread to others. There are clearly unknown factors that influence the spread of scabies. In extensive outbreaks, it is usually cheaper and easier to administer oral ivermectin than topical therapies. Adherence to a single drug protocol is not essential, and some persons, such as pregnant women, may prefer topicals. Depending on the circumstances, infestation control measures must include residents, staff, visitors, and their family contacts. Treatment must be coordinated. Severe outbreaks may require short-term isolation, gowns, contact tracing, and public health assistance. Institutional scabies is a reportable disease in many North American jurisdictions. A dermatologist may be required to assist with diagnosis. Bedding, linens, and clothing should be hot water laundered but sterilization is not required. General cleaning and thorough vacuuming is recommended, including soft and upholstered furniture, but there is no need for fumigation or special treatment of wood furniture, mattresses, or rugs. A scabies outbreak produces anxiety. Residents, staff, their families, and visitors require reassurance and open communication. Educational materials are important. Pregnant women must be reassured that scabies does not affect unborn children. Most institutions already have established protocols to deal with individuals who refuse necessary treatment,such as those that exist now for vaccinations, flu shots, head lice, and similar problems.33
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Mass populations Oral ivermectin, where available, is often cheaper than topicals and easier to administer;therefore, it is useful in large populations.4–7,18,31 A Cochrane review6 considered 15 papers from South Asia and North Africa, which studied 1896 participants. They compared topical permethrin, topical ivermectin, and oral ivermectin. Many studies were incomplete, but nevertheless they concluded: “For the most part, there was no difference in the efficacy of permethrin compared to systemic or topical ivermectin.” However, other authors18 have found oral ivermectin to be more effective. Mass treatment of the population (infants to elderly) was used in Fiji island communities who had an incidence of scabies over 20%.6,7 There were 3 treatment groups: (1) Topical permethrin to scabies patients and contacts. (2) Mass population administration of topical permethrin. (3) Mass population administration of oral ivermectin. A single dose was given to all participants but patients with scabies received a second dose 7 days later. After 2 years the prevalence of scabies in group A was 15.2%, group B was 13.5% and the ivermectin group C 3.6% Nearly all studies, regardless of their protocol, repeated the treatment in 7-14 days and emphasized the importance of follow- up and surveillance. Emerging drug resistance to scabicides is of concern1,4,7 and it is theoretically possible that repeat treatment may assist in preventing drug resistance. New drugs, topical and oral, are under study.5 Crusted scabies previously called Norwegian scabies4,7,10 can occur in those with a weakened immune system as found in immune diseases, AIDS, malignancy, lymphoreticular diseases, those on immunosuppressant drugs, the elderly, the immunocompromised, those with Down’s syndrome, and so on.1-5,14 It also occurs in indigenous Australians,10 even in those without immune defects. It is uncommon in the general community, and experienced dermatologists working outside a hospital or institution may never see a case. Patients with crusted scabies may have millions of mites, which induce an inflammatory and hyperkeratotic reaction, which in many patients is not itchy. Patients may present with thick crusted, often fissured, hyperkeratotic plaques, which typically involve the palms and soles, and may be scattered on the trunk, limbs, and scalp. The trunk is often very xerotic. Fingernails and toenails may be thick and dystrophic and have subungual involvement. The presentation can be confused with psoriasis or eczema and especially so by nondermatologists.1-5,7,10,14 The highly contagious crusts are loaded with mites and eggs. Severe cases may have lymphadenopathy, odiferous secondary infection, and eosinophilia.34 Precise figures on mortality are yet to be elucidated but the most common cause of death is staphylococcal bacteremia, with estimates in indigenous Australians suggesting that 1%-2% of cases end in death from this cause.35 In North America and Europe, the contribution of crusted scabies to mortality will remain obscure because nearly all patients
with crusted scabies have serious comorbidities and problems with immunity. Nevertheless, crusted scabies is a risk factor for sepsis.1,5,10 Grading scales for crusted scabies have been developed based on body surface areas, depth of skin crusting, previous episodes, hospitalizations, degree of skin cracking, and pyoderma. Each domain is scored between a mild 1 and a severe 3 and combined to produce an overall score: grade 1 (4-6), grade 2 (7-9), grade 3 (10-12).1,10 There are no specific studies, but examination gloves are logically important, because crusted scabies can carry millions of mites.7,10 Crusted scabies can be very contagious. Some of my unprotected dermatological colleagues in Toronto acquired scabies when they examined a patient with crusted scabies.
Management of Crusted Scabies The physical and social circumstances that predisposed the patient to crusted scabies require identification and correction. Social workers and public health may assist in monitoring and contact tracing.1,10 Many studies on crusted scabies emanate from Australia as this problem occurs in indigenous Australians.7,10 A topical scabicide is applied daily for 1 week and then 2 times weekly until cured. Keratolytic creams such as urea 10% plus lactic acid 5% or 5%-10% salicylic acid ointments assist in removing scale and facilitate scabicide penetration. Oral ivermectin at 200 µg/kg is given with the treatment duration depending on the severity: Grade 1: days 1, 2, 7. Grade 2: days 1, 2, 7, 8, 14. Grade 3: days 1, 2, 7, 8, 14, 21, 28.10 Antibiotics are often required for secondary bacterial sepsis and some clinicians use them routinely in severe cases, which may not have clinically evident infection, but are often infected with S. pyogenes and S. aureus. Severe cases may require hospitalization with single room isolation and contact precautions. It is recommended that attending staff be protected by protective garments such as gloves, gowns, and shoe covers. After patient discharge, the room needs to be thoroughly cleaned and vacuumed. The patient’s household members and other close contacts require simultaneous topical treatment. The patient’s house requires a thorough cleaning as rugs, furniture, and other fomites may be contaminated with mites shed from skin scales and crusts. Bedding, clothing, and similar items require hot laundering or storage in plastic sealed bags for 10 days. In scabies simplex, mites can live up to 3 days after separation from their host, but in crusted scabies, mites may survive for up to 7 days by feeding on sloughed skin.3
Conclusions Scabies continues to occur globally and has done so far as long as recorded history. We are fortunate that new treatment modalities such as ivermectin enable us to treat problem cases and large populations more satisfactorily.
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Acknowledgments Thank you to Drs Yuanshen Huang, Mary McKenzie, and pharmacist Dr Nina Lathia for manuscript review.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
ORCID iD Robert N. Richards
https://orcid.org/0000-0003-3830-8978
References 1. Chandler DJ, Fuller LC. A review of scabies: an infestation more than skin deep. Dermatology. 2019;235(2):79-90. doi:10. 1159/000495290 2. Wheat CM, Burkhart CN, Burkhart CG, et al. Scabies, other mites, and pediculosis. In: Goldsmith LA, Katz SI, Gilchrest BA, eds. Fitzpatrick’s Dermatology in General Medicine. 8th ed; 2015. 3. Burkhart CN, Buckhart CG, Morrell D. Infestations. In: Bologna JL, Schaffer JV, Cerroni L, eds. Dermatology. vol 2. 4th ed; 2017:1503-1506. 4. Salavastru CM, Chosidow O, Boffa MJ, Janier M, Tiplica GS. European guideline for the management of scabies. J Eur Acad Dermatol Venereol. 2017;31(8):1248-1253. doi:10.1111/jdv. 14351 5. Thomas C, Coates SJ, Engelman D, Chosidow O, ChangAY. Ectoparasites: scabies. J Am Acad Dermatol. 2020;82(3):533-548. doi:10.1016/j.jaad.2019.05.109 6. Rosumeck S, Nast A, Dressler C. Ivermectin and permethrin for treating scabies. Cochrane Database Syst Rev. 2018;4(4):CD012994. doi:10.1002/14651858.CD012994 7. Currie BJ, McCarthy JS. Permethrin and ivermectin for scabies. N Engl J Med. 2010;362(8):717-725. doi:10.1056/NEJMct09 10329 8. Dupuy A, Dehen L, Bourrat E, et al. Accuracy of standard dermoscopy for diagnosing scabies. J Am Acad Dermatol. 2007;56(1):53-62. doi:10.1016/j.jaad.2006.07.025 9. Banerji A, Society CP. First nations, Inuit and Metis health Committee scabies position statement. Pediatr Child Health. 2015;20(7):395-398. 10. Currie B, Davis J. Crusted scabies grading scale and treatment plan. Department of health and families Northern Territory government (Australia). Am J Trop Med Hyg. 2005;3(5):911-914. 11. Hay RJ, Steer AC, Engelman D, Walton S. Scabies in the developing world―its prevalence, complications, and management. Clin Microbiol Infect. 2012;18(4):313-323. doi:10.1111/j. 1469-0691.2012.03798.x 12. Karimkhani C, Colombara DV, Drucker AM, et al. The global burden of scabies: a cross-sectional analysis from the global burden
of disease study 2015. Lancet Infect Dis. 2017;17(12):1247-1254. doi:10.1016/S1473-3099(17)30483-8 13. Mbuagbaw J, Bisseck C, Ozoh G, Etienne M, et al. The epidemic of scabies in Yaounde. The Internet Journal of Dermatology. 2005;4(2) doi:10.5580/aa2 14. Tolkachjov SN, Davis MDP, Yiannias JA. Crusted (Norwegian) scabies: nine-month course with iatrogenic immunosuppression. J Drugs Dermatol. 2018;17(10):1131-1132. 15. Engelman D, Fuller LC, Steer AC; International Alliance for the Control of Scabies Delphi panel. Consensus criteria for the diagnosis of scabies: a Delphi study of international experts. PLoS Negl Trop Dis. 2018;12(5):e0006549. doi:10.1371/journal.pntd.0006549 16. Engelman D, Yoshizumi J, Hay RJ, et al. The 2020 international alliance for the control of scabies consensus criteria for the diagnosis of scabies. Br J Dermatol. 2020 [published online ahead of print February 08, 2020]. 17. Micali G, Lacarrubba F, Verzì AE, Nasca MR. Low- cost equipment for diagnosis and management of endemic scabies outbreaks in underserved populations. Clin Infect Dis. 2015;60(2):327-329. doi:10.1093/cid/ciu826 18. Romani L, Whitfeld MJ, Koroivueta J, et al. Mass drug administration for scabies—2 years of follow-up. N Engl J Med Overseas Ed. 2019;381(2):186-187. d oi:10.1056/NEJMc1808439 19. Romani L, Marks M, Sokana O, et al. Efficacy of mass drug administration with ivermectin for control of scabies and impetigo, with coadministration of azithromycin: a single-arm community intervention trial. Lancet Infect Dis. 2019;19(5):510-518. doi:10.1016/S1473-3099(18)30790-4 20. Matthewman J, Manego RZ, Dimessa Mbadinga LB, et al. A randomized controlled trial comparing the effectiveness of individual versus household treatment for scabies in Lambaréné, Gabon. PLoS Negl Trop Dis. 2020;14(6):e0008423. doi:10.1371/journal.pntd.0008423 21. Facts P. Reregistration Eligibility Decision (RED) Fact Sheet. U.S. Environmental Protection Agency, Office of Prevention, Pesticide and Toxic Substances, Office of Pesticide Programs, U.S, Government Printing Office; 2007. 22. Nolan K, Kamrath J, Levitt J, toxicity L. Lindane toxicity: a comprehensive review of the medical literature. Pediatr Dermatol. 2012;29(2):141-146. doi:10.1111/j.1525-1470.2011.01519.x 23. Richards RN. Update on intralesional steroid: focus on dermatoses. J Cutan Med Surg. 2010;14(1):19-23. doi:10.2310/7750.2009. 08082 24. Regulatory Decision Summary- Stromectol-Health Canada. Accessed September 05, 2018. https:// hpr. hres. ca>reg-content> regulatory-decision-summary-detail 25. Merck Canada Inc. Product Monograph. Including patient Medication Information. Stromectol (ivermectin tablet, USP 3 mg); 2018. 26. Barkwell R, Shields S. Deaths associated with ivermectin treatment of scabies. Lancet. 1997;349(9059):1144-1145. doi:10. 1016/S0140-6736(05)63020-6 27. Middleton J, Walker SL, House T, Head MG, Cassel JA. Ivermectin for the control of scabies outbreaks in the UK.
Richards Lancet. 2019;394(10214):2068-2069. doi:10.1016/S0140-6736( 19)32619-4 28. World Health Organization (WHO). WHO model list of essential medicines (19th list). http://www.who.int/medicines/publications/essentialmedicines 29. CDC. Scabies - Institutional Settings - Control CDC. Accessed November 2, 2010. www.cdc.gov › parasites › scabies › health_professionals 30. Turner SA, Maclean JD, Fleckenstein L, Greenaway C. Parenteral administration of ivermectin in a patient with disseminated strongyloidiasis. Am J Trop Med Hyg. 2005;73(5):911-914. doi:10.4269/ajtmh.2005.73.911
7 3 1. Lim D. Institutional scabies. DermNet NZ. 2010 32. Chong YO, Vasanwala FF. Infected with scabies again? focus in management in long-term care facilities. Diseases. 2019;7(1):3. 33. Mounsey KE, Murray HC, King M, Oprescu F. Retrospective analysis of institutional scabies outbreaks from 1984 to 2013: lessons learned and moving forward. Epidemiol Infect. 2016;144(11):2462-2471. doi:10.1017/S0950268816000443 34. Chosidow O. Scabies and pediculosis. Lancet. 2000;355(9206): 819-826. doi:10.1016/S0140-6736(99)09458-1 35. Lynar S, Currie BJ, Baird R. Scabies and mortality. Lancet Infect Dis. 2017;17(12):1234. doi:10.1016/S1473-3099(17)30636-9
Scabies: Diagnostic and Therapeutic Update Robert N. Richards1
Abstract Background: Scabies is globally ubiquitous and is a significant health issue for institutions, the economically disenfranchised, resource-poor areas, and for those with weakened immune systems. Topicals are usually effective, but are cumbersome and expensive to use in large populations and for those nonadherent to topicals. Oral ivermectin became available in Canada for the off-label treatment of scabies in the fall 2018. Objectives: To review the diagnosis and management of scabies. Dose schedules and concomitant management measures are outlined for scabies simplex and for crusted scabies. Ivermectin use is outlined. Methods: Medline, colleague discussions, practice review, and experience from managing scabies in institutions. Results: Oral ivermectin is safe, easier to use, cheaper, more effective, and more economical than topicals in widespread institutional scabies, for those nonadherent to topicals, and in crusted scabies. Conclusions: Oral ivermectin is the treatment of choice in large populations, the nonadherent, and for crusted scabies. Oral ivermectin is produced by Merck Canada as Stromectol 3 mg. The treatment dose for noncrusted scabies is 200 µg/kg, taken in a single dose with food. For example, 15 mg (5 tablets) for a 70 kg person. Retreat in 10-14 days to enhance effectiveness, and perhaps to reduce scabicide resistance. Keywords scabies, crusted scabies, institutional scabies, ivermectin, permethrin, population outbreaks
Scabies occurs globally, and is caused by the species-specific ectoparasitic mite: Sarcoptes scabiei (var. hominis).1-5 In the fall of 2018, oral ivermectin became available in Canada for the off-label treatment of scabies. The use of ivermectin in other jurisdictions has been a huge therapeutic advance for mass populations, institutional outbreaks, crusted scabies, resistant scabies, and those nonadherent to topicals.6,7 Common scabies (scabies simplex) and crusted scabies differ in their morphology, degree of contagion, severity, complications, and treatment. Sarcoptes scabiei (var. hominis) measures about 0.35 mm and lives in linear burrows dug in the stratum corneum. It can be visible to the naked eye as a speck, and may be visible to expert dermoscopists.8 Female mites burrow into the skin and lay eggs, which take 10-14 days to produce new mites. Adult males live on the skin and may enter the burrows for food and mating.1-5 The average scabies simplex case carries about 10-20 mites, but infants and the elderly may harbor between 50 and 250 mites.2 Patients with crusted scabies carry thousands to millions of mites.1–5 Transmission of scabies simplex is most frequently by skin-to-skin contact, usually prolonged skin contact. Some individuals are more susceptible.1-5,9 Those affected can be of any age or social strata, and good personal hygiene does
not always prevent infestation. Large outbreaks are more common in institutions, the economically disadvantaged, crowded tropical areas, and in crowded resource-poor areas such as those found in some indigenous areas in Northern Canada and Australia. Transmission is facilitated by skin-to- skin contact, sleeping with or sex with an infested person, the sharing of living quarters, and close continuous contact. Transfer by casual contact such as shaking hands is rare. The risk of transmission by fomites is negligible except in severe crusted scabies.1-3 Mites cannot jump or fly and die outside their human host within 24-48 (72 maximum) hours.5,9 An infested person is contagious, even when symptom free, but there is no risk of spread in scabies simplex after appropriate treatment. Healthcare workers may find gloves reassuring, but scabies simplex is often present but undiagnosed before gloves are considered, and statistics regarding their
1
Departments of Medicine, North York General Hospital and Baycrest Health Sciences, Courtesy Staff Dermatology, Toronto, ON, Canada Corresponding Author: Robert N. Richards, Suite 507, 3018 Yonge Street, Toronto, ON M4N0A2, Canada. Email: revrichards@hotmail.com
2 effectiveness are not available. Hand washing after examinations is logically recommended but there is no factual evidence of its effectiveness. Animals carry mite-specific species such as Sarcoptes canis in dogs, which may produce a temporary eruption in humans, but not scabies, because canine mites do not survive on humans.4
Epidemiology Scabies is a global disease and there is great variation in its prevalence and health burden. The scabies burden is greatest in tropical regions, in areas of overcrowding, in times of war and social disruption, and in economically disadvantaged populations such as indigenous Australians.10 The most commonly affected age groups are children, adolescents, and elderly people. In some areas over 50% of the population is affected and scabies continues to be a significant health problem. Worldwide estimates of current cases vary from 200 to 300 million.5,9 Hay et al noted that scabies is endemic in tropical areas and estimated an average prevalence of 5%-10% in children, commonly with total family involvement.11 In low-frequency countries such as North America and Europe, the occurrence of scabies is more evenly distributed among all age groups. Institutional outbreaks are always of concern.12 Except for institutional outbreaks, scabies is not a reportable disease in western countries; therefore, its epidemiology and true prevalence remain unknown.6 Studies are not available. We know that scabies is ubiquitous and every family doctor, dermatologist, and institution with whom I have spoken has seen cases in the past year. Scabicide sales are not helpful in establishing scabies incidence because these products are used widely for lice, and commonly for trial treatments or misdiagnoses. The occurrence of scabies is cyclical and it is more easily transmitted in some years or decades than others. This periodicity is often less obvious in poor communities. There is always an increase during times of war and social disruption.11,13 There are no North American data but all colleagues with whom I consulted have anecdotally noticed a cyclical pattern in the frequency of scabies.
Clinical presentation of scabies simplex Itch and/or rash begin 4-6 weeks after contact, but a person experiencing scabies reinfestation within 6 months of this initial infection will develop itch in hours to days.5 Scabies itch results from the mechanical effect of mite burrowing, and from an allergic reaction to the mite and its products.1,3,5 In severe cases we see disseminated erythematous papules, excoriations, hemorrhagic crusts, linear scratch marks, eczema (dermatitis), vesicles (even bullae), often pustules and impetigo from secondary bacterial infection, and, if intact, the mites’ linear burrows, which appear as 3-10 mm linear lines, most easily seen around the hands and wrists.
Journal of Cutaneous Medicine and Surgery 00(0) Scabetic nodules may result from an exaggerated hypersensitivity reaction and from rubbing and scratching, and may be skin-colored, red-brown, or violaceous. Bruising, secondary to rubbing and scratching, is not uncommon. Itch occurs all over (below the neck), not just at rash sites, and is usually nocturnal. Severity of itch and the number of lesions vary from person to person, and asymptomatic carriers are not rare.3 Elderly patients may have less itch and fewer typical lesions.1-5 The use of topical steroids reduces visible inflammatory reactions, but may permit the mites to flourish.
Scabies Simplex Distribution Lesions are usually symmetrical, and are seen on the finger webs, anterior wrists, palms, thenar eminences, elbows, anterior axillae, lower buttocks, inner thighs, waist, umbilicus, knees, margins and soles of the feet, and vulva; and almost diagnostically the female areola, breasts, glans penis, shaft, and scrotum. The neck and above are usually spared, except in infants, the elderly, the immunocompromised, and in crusted scabies. Infants are often affected on the face, scalp, palms, and soles. Symptoms and morphology can vary greatly, and most experienced clinicians (author included) have missed the diagnosis.1-5
Diagnosis of Scabies Simplex Classic morphology is diagnostic, but there is often confusing secondary eczema (dermatitis) produced by scratching and/or by excessive washing. Normal soap washing may alter scabies morphology by reducing the number of active lesions. I have, not infrequently, seen patients itch all over, whose only visible lesions were on the genitals or female areolae. A history of itchy family, friends, or intimate contacts is helpful. A definitive office diagnosis is made by retrieving (by needle or scrapings) the mite, its eggs, or its fecal pellets (scybala),1-5,9 but this requires a microscope, time, and skill, so its office use is limited. The mite is located at the end of the burrow and may attach to a carefully inserted pin or needle. Scrapings obtained by a scalpel or similar instrument may be placed on a glass slide, covered with clear tape and examined under a microscope. An alternative is to send a sample to the laboratory, by placing scrapings on black laboratory paper but the yield is less with these methods. Skin biopsy (also time consuming and expensive) is helpful if taken from a burrow showing the mite or its products, but if the burrow is missed, the report will return showing dermatitis.14 Inks or oils may help outline burrows, as does good lighting and magnification. Diagnosis, however, is often established by a positive response to empiric treatment. Clinical and epidemiological scabies research has been limited by a lack of diagnostic standardization. International groups have tried to establish diagnostic criteria that can be implemented in a variety of settings and they note that Level
Richards A evidence requires direct visualization of the mite or its products.15,16 Dermoscopy is heavily operator dependent, but in expert hands can identify the mite but not its eggs or fecal pellets. Mite identification is more difficult in darker skin types and in hairy areas. The expense of dermatoscopes and the requirements for training limit its widespread use.16 An Italian group has recommended the use of a low-cost video dermoscopy but more studies are required.17 There are no blood tests to diagnose scabies or vaccines to prevent scabies.1
Complications of Scabies Simplex In resource- rich areas, mild impetigo, not infrequently, develops from scratching, as it does in eczema and similar conditions, but precise data about its incidence are not available. It is usually mild and easily controlled with topical or oral antibiotics. However, in tropical resource-poor areas (and in crusted scabies), significant impetigo, secondary staphylococcal or streptococcal bacteraemias, and toxin- mediated diseases such as scarlet fever, streptococcal toxic shock syndrome, rheumatic fever, and glomerulonephritis are major health issues.1,5,7,10 The common organisms are Streptococcus pyogenes and Staphylococcus aureus.5 The “SHIFT” trial studied the effects of mass drug administration for scabies control in a Fijian population with endemic disease. On 1 island the incidence of scabies was 32.1% and that of impetigo was 24.6%. Oral ivermectin treatment reduced the incidence of scabies to 1.9% and of impetigo to 8%.18 Similar results were obtained in the “AIM” study in which over 26 000 Solomon Islanders were treated with a combination of ivermectin and azithromycin. Scabies prevalence was reduced from 19.5% to 1.3% and that of impetigo from 22.4% to 5.1%.19 Fortunately, scabies is not a known vector for other diseases.3
Treatment of Scabies Simplex Underclothes and linen should be changed and hot washed at degrees 50 °C or 122 °F, but sterilization is not required.1,4 Alternatively, linens, clothing, and similar items may be sealed in a plastic bag for 72 hours.5 All persons living in the household, and all intimate or prolonged contacts, must be treated simultaneously, even if they do not have symptoms. If not treated, they may be a source of reinfestation for others. Matthewman et al20 compared the effectiveness of individual versus household treatment for scabies. Participants in the household treatment group had about twice the odds of being cured. In resource-rich areas, most patients use 5% permethrin cream or lotion, which kills both mites and eggs. Both are effective and pleasant to use, and most insurers pay for prescribed permethrin. Permethrin produces neurotoxicity by inhibiting sodium channels, which culminates in paralysis
3 and death of the mite.21 Permethrin is available without prescription in Canada, Great Britain, and Europe, but requires a prescription in the United States. Permethrin is applied overnight to ALL the skin from the neck down. No area of skin can be missed so application may require assistance. One night’s application is theoretically adequate, but the vagaries of human behavior and compliance dictate that an important standard of practice is to repeat the treatment in 7-10 days as this is more effective. Additionally, the second treatment will kill newly hatched mites as the initial treatment may not always be ovicidal to all eggs.1-5,9,22 Most authors consider permethrin to be safe for pregnant or lactating women,1,4,5 and for children over 2 months of age.1,4,5,9 The usual amount of product required for a single night’s treatment for persons over 12 is approximately one 30 g tube or 1 container of 100 mL of lotion. For children 5-12 years of age, the usual amount is ½ of the above, and ¼ for children 2-4 years. Prices vary from vendor to vendor. Average prices in Toronto in August 2020 for 1 night’s treatment for 1 adult were $25 for Nix dermal cream (30 g) and $80 for Kwellada-P lotion (100 mL). Presently, neither Nix lotion nor generic permetherin lotions are available in Canada. For infants under 2 months, the American Center for Disease Control and Prevention recommends 5%-10% sulfur ointment (sulfur in vaseline) applied all over for 3 days.4,5 Sulfur ointment is messy and has an unpleasant smell, but is effective and safe.1,4 Ointment-induced secondary irritation is managed by topical steroids and soap avoidance. Infants, and occasionally the elderly and infirm, may require topical applications to the face and scalp.5,9 We have observed that many patients (and their contacts) require reassurance that their acquisition of scabies does not necessarily reflect issues of hygiene or sexual behavior, as this concern is often paramount for them. Pets do not require treatment.3 Other topical applications are used in permethrin- resistant cases, and in countries where economics dictate the use of cheaper 25% benzoyl benzoate, which is effective but irritating. Lindane lotion (1% gamma benzene hexachloride) is applied in the same manner as permethrin, and can be used for treatment failures. It is safe if used properly for a short period.7 Lindane is available in Canada and most states, but is banned in California and many countries because of overuse and accidental swallowing, which can produce nervous system damage. Although used for decades, it is no longer considered safe for children under 10 years, pregnant or nursing women, or those under 110 lb. Topical 0.5% malathion aqueous lotion and ivermectin 1% lotion are used in some countries.4 Ivermectin is not ovicidal so it is important to retreat in 1 week. Sulfur 5%-10% cream, ointment, or lotion is effective when used for 3 consecutive days and is considered safe in pregnancy and infants.5 Post scabetic itch may persist for days/weeks. Treatment is midstrength to strong cortisone creams and soap avoidance. Soaps dry the skin and should be used only for
4 essential areas such as underarms, genitals, hands, and face. First- and second- generation antihistamines assist some patients, but must be used with caution in the elderly. Post scabetic localized nodules respond to intralesional triamcinalone acetonide suspension at 2.5-5 mg/cc., but clinicians must be certain they are not missing persistent infestation.23 Oral ivermectin is indicated for topical failures, those nonadherent to topicals, those unable to apply topicals (physically or mentally disabled, refugees, the homeless), widespread institutional outbreaks, mass populations, and crusted scabies.1,5 Oral ivermectin was introduced in 1981 and has been used extensively to treat strongyloides, onchocerciasis, trichuriasis, and scabies. Veterinarians and farmers use it for heartworm and other helminths in pets and farm animals. Ivermectin was approved in France for the treatment of institutional scabies in 2001.1 In the fall of 2018, Health Canada approved ivermectin for oral use in strongyloides, onchocecriasis, and lymphatic filariasis suspected to be caused by Wucheria bancrofti.24,25 Previously, the drug could be obtained by special access from Health Canada, but this was prohibitively onerous. Similar approval was given by the Food and Drug Administration in the United States in 1997. The decades delay in Canadian availability is presumed to be due to our small market and regulatory issues. Another factor, perhaps, was the 1997 Lancet report of an increased death rate among elderly patients treated with ivermectin for scabies in an Ontario nursing home,26 but this has never been confirmed by any other study, and is no longer considered relevant.3,6,27 The World Health Organization lists ivermectin as one of the most effective and safe medicines needed in a health system.28 Ivermectin is marketed by Merck Canada as Stromectol 3 mg tablets25 and is readily available for off- label use. Ivermectin is not ovicidal so a second dose is given 2 weeks after the initial dose3 to ensure that the newly hatched mites are killed,1,7 even though some studies found single dosing effective.5,7 The oral dose, taken with food at one time, is 200 µg/kg. The dosage per kg weight is (1) 15-24 kg—1 tablet, (2) 25-35 kg—2 tablets, (3) 36-60 kg—3 tablets, (4) 51-65 kg—4 tablets, (5) 66-79 kg—5 tablets, (6) >80 kg—200 mcg/kg.24 The usual adult dose range is 9-15 mg. Some studies combined oral ivermectin with topical scabicides, but this has no consensus, other than in the treatment of crusted scabies.5,7 Ivermectin is remarkably safe and dosing can err above the exact body weight without concern. Side effects in these doses are uncommon and difficult to distinguish from the disease and anxiety, but can include headache, nausea, dizziness, and gastrointestinal upset. Many side effects are thought to result from mite deaths rather than from the drug itself.6,7 There were no side effect withdrawals in the Cochrane review of 15 studies with 1896 participants.6 Significant drug interactions have not been a problem.6,7 Currie7 noted that by
Journal of Cutaneous Medicine and Surgery 00(0) 2010, over 400 million doses of ivermectin have been given in Africa for the treatment of onchocerciasis with minimal adverse events. Ivermectin is not approved for use in pregnancy or nursing, or for children weighing less than 33 lb (15 kg)4 but the drug has been used in these groups without reports of adverse outcomes.1,7 The product monograph notes that less than 2% of the standard dose appears in the breast milk, but safety in newborns has not been established.25 The product monograph suggests taking it on an empty stomach, but many scabies experts believe it is more effective if taken with food, and Currie7 noted that food increases the viability of ivermectin by a factor of 2.29 There is no parenteral ivermectin available for human administration but subcutaneous ivermectin is used regularly in veterinary medicine and has been used in a case of human strongyloidiasis.30 Ivermectin cost per tablet ranges from $20 to $9 depending on the number purchased. Therefore, it is cheaper to use than topical therapies for widespread outbreaks and institutional outbreaks. Institutional scabies7,31,32 can occur in crowded living conditions such as hospitals, nursing homes, residential schools, college dormitories, camps, custodial facilities, and the military. Hard data are not available on transmission rates as they vary hugely from institution to institution. I have seen scabies involve most residents of a nursing home, as well as staff members, visitors, and visitors’ families. But in another facility, I observed single resident involvement with no spread to others. There are clearly unknown factors that influence the spread of scabies. In extensive outbreaks, it is usually cheaper and easier to administer oral ivermectin than topical therapies. Adherence to a single drug protocol is not essential, and some persons, such as pregnant women, may prefer topicals. Depending on the circumstances, infestation control measures must include residents, staff, visitors, and their family contacts. Treatment must be coordinated. Severe outbreaks may require short-term isolation, gowns, contact tracing, and public health assistance. Institutional scabies is a reportable disease in many North American jurisdictions. A dermatologist may be required to assist with diagnosis. Bedding, linens, and clothing should be hot water laundered but sterilization is not required. General cleaning and thorough vacuuming is recommended, including soft and upholstered furniture, but there is no need for fumigation or special treatment of wood furniture, mattresses, or rugs. A scabies outbreak produces anxiety. Residents, staff, their families, and visitors require reassurance and open communication. Educational materials are important. Pregnant women must be reassured that scabies does not affect unborn children. Most institutions already have established protocols to deal with individuals who refuse necessary treatment,such as those that exist now for vaccinations, flu shots, head lice, and similar problems.33
5
Richards
Mass populations Oral ivermectin, where available, is often cheaper than topicals and easier to administer;therefore, it is useful in large populations.4–7,18,31 A Cochrane review6 considered 15 papers from South Asia and North Africa, which studied 1896 participants. They compared topical permethrin, topical ivermectin, and oral ivermectin. Many studies were incomplete, but nevertheless they concluded: “For the most part, there was no difference in the efficacy of permethrin compared to systemic or topical ivermectin.” However, other authors18 have found oral ivermectin to be more effective. Mass treatment of the population (infants to elderly) was used in Fiji island communities who had an incidence of scabies over 20%.6,7 There were 3 treatment groups: (1) Topical permethrin to scabies patients and contacts. (2) Mass population administration of topical permethrin. (3) Mass population administration of oral ivermectin. A single dose was given to all participants but patients with scabies received a second dose 7 days later. After 2 years the prevalence of scabies in group A was 15.2%, group B was 13.5% and the ivermectin group C 3.6% Nearly all studies, regardless of their protocol, repeated the treatment in 7-14 days and emphasized the importance of follow- up and surveillance. Emerging drug resistance to scabicides is of concern1,4,7 and it is theoretically possible that repeat treatment may assist in preventing drug resistance. New drugs, topical and oral, are under study.5 Crusted scabies previously called Norwegian scabies4,7,10 can occur in those with a weakened immune system as found in immune diseases, AIDS, malignancy, lymphoreticular diseases, those on immunosuppressant drugs, the elderly, the immunocompromised, those with Down’s syndrome, and so on.1-5,14 It also occurs in indigenous Australians,10 even in those without immune defects. It is uncommon in the general community, and experienced dermatologists working outside a hospital or institution may never see a case. Patients with crusted scabies may have millions of mites, which induce an inflammatory and hyperkeratotic reaction, which in many patients is not itchy. Patients may present with thick crusted, often fissured, hyperkeratotic plaques, which typically involve the palms and soles, and may be scattered on the trunk, limbs, and scalp. The trunk is often very xerotic. Fingernails and toenails may be thick and dystrophic and have subungual involvement. The presentation can be confused with psoriasis or eczema and especially so by nondermatologists.1-5,7,10,14 The highly contagious crusts are loaded with mites and eggs. Severe cases may have lymphadenopathy, odiferous secondary infection, and eosinophilia.34 Precise figures on mortality are yet to be elucidated but the most common cause of death is staphylococcal bacteremia, with estimates in indigenous Australians suggesting that 1%-2% of cases end in death from this cause.35 In North America and Europe, the contribution of crusted scabies to mortality will remain obscure because nearly all patients
with crusted scabies have serious comorbidities and problems with immunity. Nevertheless, crusted scabies is a risk factor for sepsis.1,5,10 Grading scales for crusted scabies have been developed based on body surface areas, depth of skin crusting, previous episodes, hospitalizations, degree of skin cracking, and pyoderma. Each domain is scored between a mild 1 and a severe 3 and combined to produce an overall score: grade 1 (4-6), grade 2 (7-9), grade 3 (10-12).1,10 There are no specific studies, but examination gloves are logically important, because crusted scabies can carry millions of mites.7,10 Crusted scabies can be very contagious. Some of my unprotected dermatological colleagues in Toronto acquired scabies when they examined a patient with crusted scabies.
Management of Crusted Scabies The physical and social circumstances that predisposed the patient to crusted scabies require identification and correction. Social workers and public health may assist in monitoring and contact tracing.1,10 Many studies on crusted scabies emanate from Australia as this problem occurs in indigenous Australians.7,10 A topical scabicide is applied daily for 1 week and then 2 times weekly until cured. Keratolytic creams such as urea 10% plus lactic acid 5% or 5%-10% salicylic acid ointments assist in removing scale and facilitate scabicide penetration. Oral ivermectin at 200 µg/kg is given with the treatment duration depending on the severity: Grade 1: days 1, 2, 7. Grade 2: days 1, 2, 7, 8, 14. Grade 3: days 1, 2, 7, 8, 14, 21, 28.10 Antibiotics are often required for secondary bacterial sepsis and some clinicians use them routinely in severe cases, which may not have clinically evident infection, but are often infected with S. pyogenes and S. aureus. Severe cases may require hospitalization with single room isolation and contact precautions. It is recommended that attending staff be protected by protective garments such as gloves, gowns, and shoe covers. After patient discharge, the room needs to be thoroughly cleaned and vacuumed. The patient’s household members and other close contacts require simultaneous topical treatment. The patient’s house requires a thorough cleaning as rugs, furniture, and other fomites may be contaminated with mites shed from skin scales and crusts. Bedding, clothing, and similar items require hot laundering or storage in plastic sealed bags for 10 days. In scabies simplex, mites can live up to 3 days after separation from their host, but in crusted scabies, mites may survive for up to 7 days by feeding on sloughed skin.3
Conclusions Scabies continues to occur globally and has done so far as long as recorded history. We are fortunate that new treatment modalities such as ivermectin enable us to treat problem cases and large populations more satisfactorily.
6
Journal of Cutaneous Medicine and Surgery 00(0)
Acknowledgments Thank you to Drs Yuanshen Huang, Mary McKenzie, and pharmacist Dr Nina Lathia for manuscript review.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
ORCID iD Robert N. Richards
https://orcid.org/0000-0003-3830-8978
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