Dermatology & Family Medicine & Infectiology
Gale | Clinique Omicron Québec
Scabies is a highly contagious cutaneous ectoparasitosis caused by the mite Sarcoptes scabiei variety hominis - an obligate parasite of humans, which burrows into the horny layer of the epidermis to lay its eggs. Its main manifestation is intense pruritus, typically nocturnal, secondary to a delayed-type hypersensitivity reaction (type IV) to the parasite's proteins and feces. Scabies affects all social strata and all ages without distinction, with a global prevalence estimated at 200 million active cases according to the WHO - which in 2017 classified it as a priority neglected tropical disease. In Quebec, scabies is a frequent cause of dermatological and family medicine consultations, particularly in communities (CHSLDs, residences, daycare centers, barracks, summer camps). Its management requires simultaneous treatment of the patient and his or her close contacts, decontamination of the environment, and monitoring for relapses or reinfestations - without which cycles of transmission in the community are almost inevitable.
Parasite biology, transmission and pathophysiology
- Biology of Sarcoptes scabiei and parasite cycle : microscopic mite (0.3-0.5 mm) invisible to the naked eye - belongs to the order Acariens + family Sarcoptidae - obligate parasite: survives no more than 48-72 hours outside the human host at room temperature (sensitive to dehydration + heat) - more resistant in Norwegian mange (squamous keratosis ++ - millions of mites - prolonged survival on scales); life cycle: total duration 10-17 days - fertilized adult female → digs a furrow in stratum corneum at a rate of 2-3 mm/d → lays 2-3 eggs/d for 4-6 weeks → 6-legged larvae hatch in 3-4 days → 8-legged nymphs → adults in 10-14 days → fertilization on skin surface → new female digs a new furrow - usual parasite load: 5-15 adult mites only in common scabies (contrast with Norwegian scabies: millions of mites); transmission: direct, prolonged skin contact: main route - hand-to-hand (prolonged handshake), sexual intercourse (scabies = SSTI - STI not notifiable but should be screened in this context), intimate contact (mother-infant), occupational contact (CHSLD caregivers) - indirect transmission (bedding, clothing): possible, especially in Norwegian scabies (high parasite load) → low in common scabies (few mites in the environment) - incubation period: primary infection: 3-6 weeks (time required for immunological sensitization → pruritus initially absent) - reinfection: 1-4 days (immune memory → pruritus almost immediate)
- Clinical presentation and special forms : pruritus: cardinal symptom - intense + predominantly nocturnal (bed warmth increases mite activity) + aggravated by heat + diffuse then localized to predilection areas - can seriously disrupt sleep - caution: pruritus is absent or very attenuated in Norwegian scabies (immunocompromised); specific lesions (pathognomonic): scabious furrows (burrows) : slightly elevated sinuous course of 5-15 mm - grayish or pearly - terminated by a pearly vesicle (head of the furrow - shelter of the female) - preferential localizations: interdigital spaces of hands (+++), anterior surface of wrists, edges of feet, penis (in men - pathognomonic penile-scrotal scabious furrow and nodule) + pearly vesicles : small, translucent 1-2 mm vesicles on a non-inflammatory background + scabious nodules: persistent reddish-brown papules or nodules (granulomatous reaction to parasite antigens) - especially on penis + scrotum + axillae + may persist weeks to months after treatment (not to be confused with a relapse); non-specific lesions (secondary to scratching): excoriations + erythematous papules + crusts - may mask specific lesions; topography of lesions according to age: adult and child >2 years: hands (interdigital spaces) + wrists + forearms + elbows + armpits + perimamellar + umbilicus + buttocks + penis + scrotum + lateral edges of feet - face and scalp spared in immunocompetent adults + infants and young children (<2 years): vesicular or pustular lesions on palms and soles (specificity in children) + face + scalp + neck + back → different distribution from adults → diagnosis sometimes difficult; special clinical forms: Norwegian scabies (crusty) : immunocompromised (low CD4 HIV + transplant patients + long-term corticosteroid therapy + bedridden elderly + HTLV-1) + millions of mites → hyperkeratotic keratoderma + thick scales + crusts + little or no pruritus (immune anergy) → extremely contagious → transmission possible by simple contact with the environment (scales) → reporting and outbreak control measures mandatory in CHSLD → hospitalization recommended + infant scabies: palmoplantar vesicular lesions + involvement of face and scalp + nocturnal agitation ++ + scabies of clean people (discreet scabies): people who wash frequently → few lesions + moderate pruritus → diagnosis often delayed → very few furrows + iatrogenic scabies with corticoids (incognito scabies): local application of dermocorticoids → attenuation of inflammation + multiplication of mites → atypical lesions + highly contagious
- Complications of untreated scabies : Bacterial superinfection (impetiginization): scratching → excoriations → → entry point Staphylococcus aureus + Streptococcus pyogenes (GASBH) → impetigo + boils + abscesses + cellulitis - risk of invasive streptococcal disease + post-streptococcal glomerulonephritis (serious complication of cutaneous streptococcal superinfection in tropical countries - rare in Quebec) + contact dermatitis (post-scabial eczema) : persistent inflammatory reaction to treatment or parasite antigens - pruritus and rash may persist 2-6 weeks after effective treatment → not to be confused with treatment failure + persistent scabious nodules: reactional granulomas may persist months after healing → treatment with potent dermocorticoids (clobetasol)
Diagnosis, processing and management of contacts
| Clinical situation | Diagnosis | Treatment and associated measures |
|---|---|---|
| Diagnosis of scabies Clinical - dermoscopy - scraping |
Diagnosis of scabies is above all clinical - parasitological confirmation is useful in cases of doubt, but not always feasible; clinical diagnosis: association of intense nocturnal pruritus + typical lesions (furrows + pearly vesicles) + characteristic topography (hands + wrists + penis) + notion of contact (pruriginous entourage) → high diagnostic sensitivity in an epidemic context - classic diagnostic triad: nocturnal pruritus + involvement of close contacts + lesions in the interdigital spaces of the hands; dermoscopy (dermatoscope): non-invasive examination - simple, rapid in-office technique - the scabious furrow appears as a linear or sinuous path with the mite body at its tip («airplane jet» or «winged triangle» image - delta wing sign) - sensitivity 83-91 % + specificity 86-90 % - superior to clinical examination alone for identifying inconspicuous furrows → useful especially in clean people's scabies and infant scabies; skin scraping and direct microscopic examination: scraping of the pearly vesicle or furrow with a curette or the tip of a vaccinostyle → deposition on slide + KOH 10-20 % (to dissolve keratinocytes) → microscopy: adult mite (8 legs) + eggs + faeces (scybales - brownish oval faecal granules) - sensitivity 46-90 % (variable according to operator's experience and location of lesion scratched) - scratch as a priority: intact beaded vesicle + recent furrow on interdigital space or wrist; skin biopsy: rarely necessary - useful in atypical forms (Norwegian scab + persistent nodules + bullous lesions) → histology: presence of mite + eggs + feces in stratum corneum + dermal inflammatory infiltrate (eosinophils ++); indirect biological diagnosis: blood eosinophilia: present in 50 % of cases - mild (500-1,500/µL) - non-specific - total IgE: often elevated - no diagnostic value in current practice; differential diagnosis: atopic dermatitis (child - family history + atypical topography for scabies + no contagiousness) + lichen planus (purplish polygonal papules - Wickham's network) + urticaria + pruritus medicamentosa + pediculosis corporis (furrows absent - lice visible) + prurigo + palmar psoriasis + dyshidrosis + dermatophytosis. | Principle of treatment - simultaneous treatment mandatory: scabies treatment can only be effective if the patient AND all close contacts are treated simultaneously on the same day - otherwise: cycle of reinfestation inevitable - close contacts to be treated: persons sharing the same bed + sexual partners + household members (even if asymptomatic - incubation period 3-6 weeks → can be infested without pruritus) + infants carried in the arms + caregivers who have had prolonged unprotected skin contact in CHSLDs or in cases of Norwegian scabies; decontamination of the environment (essential measures on the same day as treatment): clothing + bedding + towels: machine wash at 60°C (minimum) or put in airtight plastic bag × 72 hours (mites die without host in 48-72h) - mattresses + sofas + carpets: careful vacuuming + acaricide spray (type A-Par spray) on non-washable textiles → leave on for 3h then air out; permethrin cream 5 % (reference treatment - 1st line): apply to the whole body (neck + arms + trunk + legs + feet + hands - including under nails and navel + perineum + inguinal folds) → leave in contact for 8-14 hours (overnight) → rinse off the next morning - in infants and children <2 years: also apply to face + scalp (avoid eye and mouth contours) - efficacy: 89-97 % cure after 1 application → 2nd application at 7-14 days systematically recommended (to eliminate mites from eggs not destroyed by 1st application - eggs are resistant to permethrin) - side effects: slight skin irritation + transient burning sensation - available in Canada: Kwellada-P (5 %) - by prescription or over-the-counter depending on province |
| Treatment of common scabies in adults and children Permethrin - ivermectin - precise instructions |
The effectiveness of the treatment depends as much on the molecule as on the rigorous application of the instructions - imperfect technique is the most frequent cause of apparent failure; permethrin 5 % cream (Kwellada-P - 1st line - topical treatment): apply to clean, dry skin - preferably in the evening after bathing/showering - cover the entire body surface from neck to toes in adults (including interdigital spaces of hands and feet + under nails + folds) → in children 2 months); ivermectin PO (Stromectol - systemic treatment - 2nd line or mass treatment in communities): dosage: 200 µg/kg single dose PO → repeated at D8-J14 (same rationale as 2nd application of permethrin - resistant eggs) - efficacy comparable to permethrin in common scabies (meta-analyses: similar cure rates at 4 weeks) → advantages of ivermectin: ease of application (tablet vs. topical application all over the body) + mass treatment possible in CHSLD (outbreaks) + treatment of uncooperative subjects (bedridden elderly) + availability ivermectin in Canada: available by prescription (Stromectol) - may be occasionally out of stock → check pharmacy availability - not systematically reimbursed by RAMQ → check eligibility + ivermectin precautions: pregnancy (CI - category C) → permethrin preferred + breastfeeding (CI - excreted in milk) + child <15 kg or <5 years (insufficient data - use topical permethrin) + immature blood-brain barrier (infant) → theoretical risk of neurological toxicity | Alternative topical treatments (if permethrin not available or intolerance): benzyl benzoate (lotion 25 % in adults - 12.5 % in children): application all over the body × 2 consecutive applications 24 hours apart → effective but irritating (burning sensation ++) + sulfur precipitated in petroleum jelly (5-10 %): historical treatment - effective - very well tolerated - used during pregnancy and in infants - unpleasant odor + application 3 consecutive evenings → less practical + lindane (Hexit - gamma-hexachlorocyclohexane): not recommended (neurotoxic + risk of resistance + banned in several countries) - no longer to be used; treatment of residual post-scabious pruritus (after parasitological cure): pruritus and rash may persist 2-6 weeks after effective treatment (hypersensitivity reaction to parasite debris) → do not retreat for 4 weeks unless evidence of reinfestation - symptomatic treatment: oral antihistamines (cetirizine 10 mg/d + loratadine 10 mg/d + hydroxyzine 25 mg in the evening if severe nocturnal pruritus) + medium-class dermocorticoids (betamethasone 0.1 % cream × 2/d × 1-2 weeks): rapid relief of pruritus and rash - do not use powerful corticosteroids before parasitological cure (risk of cortisonated scabies - masking + proliferation of mites) → persistent scabious nodules: powerful dermocorticoids (clobetasol 0.05 % cream under occlusion) + intralesional injection of triamcinolone (very resistant nodules); post-treatment follow-up: consult at 4 weeks - if pruritus persists + new typical lesions → retreat (same protocol) - if pruritus improved + no new lesions → post-scabious reaction → symptomatic treatment only |
| Norwegian scabies (crusty) Immunosuppressed - millions of mites - outbreak |
Norwegian scabies is a severe, highly contagious clinical form occurring in patients who are immunocompromised or unable to scratch (sensory disorders, advanced dementia) - it constitutes a public health emergency in institutional settings; clinical presentation of Norwegian scabies : diffuse hyperkeratotic keratosis (thick scales + adherent yellowish crusts) on hands + feet + elbows + knees + scalp + face + trunk - thickened dystrophic nails (onychoscabies) → pruritus often absent or minimal (immune deficiency → insufficient inflammatory response) - parasite load: thousands to millions of mites (vs. 5-15 in common scabies) → transmission possible by simple contact with scales or environment (bedding + clothing + surfaces) → extremely contagious; contexts at risk of Norwegian scabies: HIV with CD4 <200 + solid organ transplantation (immunosuppressants) + haematological malignancies + long-term systemic corticosteroid therapy + HTLV-1 (retrovirus - higher prevalence in certain aboriginal communities and Caribbean immigrants + Africa) + bedridden elderly (atonic scratching) + Down syndrome (trisomy 21) + leprosy + dermatomyositis; reporting and management of outbreaks in institutional settings: in Quebec: scabies in a CHSLD or care setting must be reported to the regional Public Health Department (DSP) → outbreak management protocol triggered (MSSS + INSPQ) → all cases + contacts identified → simultaneous collective treatment of all exposed residents and staff → contact isolation of the source patient → intensive decontamination of the environment (contagious scales in the scales) | Treatment of Norwegian scabies (combined protocol): combined treatment (topical + systemic) recommended due to massive parasite load: ivermectin PO: 200 µg/kg on D1 + D2 + D8 + D9 (± D15 depending on response) - some experts recommend up to 5-7 doses spaced 7 days apart for very severe forms + permethrin 5 % cream: daily application × 7 days then twice/week × 4 weeks → objective: reduce parasite load rapidly - prior stripping of crusts (keratolytics: petroleum jelly + salicylic acid 5-10 % or urea 20 % cream) → improve penetration of permethrin under crusts + nail treatment: cut nails short + apply permethrin under nails + benzyl benzoate; contact isolation: individual room + contact precautions (gloves + overblouse + mask in case of facial or scalp scabies) → maintained until complete resolution of scabs and negative parasitological confirmation + intensive decontamination of environment: bedding + clothing washed daily at 60°C + acaricide spray on mattresses + furniture + carpets + reinforced vacuuming - room to be decontaminated daily; treatment of all contacts (residents + staff): ivermectin PO × 2 doses (D1 + D8) + permethrin × 2 applications (D1 + D8) → mass treatment coordinated with DSP → follow-up at 4 weeks to confirm cure + source patient's immune workup (if not already done): HIV + HTLV-1 + immunosuppression workup |
| Scabies in pregnant women and infants Permethrin - sulfur - precautions |
Scabies during pregnancy and in infants requires special attention due to therapeutic constraints linked to the safety of available molecules; scabies during pregnancy: clinical diagnosis is identical to the general population - lesions may be more diffuse and pruritic due to the immune changes of pregnancy - risks: bacterial superinfection + major discomfort + impact on sleep → rapid treatment recommended - acceptable molecules during pregnancy: permethrin 5 %: category B (FDA) - no signal of teratogenicity in animal studies + reassuring human data → 1st-line treatment in all trimesters → same protocol as general population + precipitated sulfur 5-10 % in vaseline: historical treatment - no evidence of fetal toxicity - can be used in all trimesters → alternative to permethrin if unavailable → unpleasant odor + 3 consecutive applications + ivermectin: CI during pregnancy (category C - placental passage + insufficient human data) → do not prescribe + lindane: absolutely CI during pregnancy (neurotoxic); scabies in infants (<2 years): specific presentation (palmoplantar lesions + face + scalp) → make diagnosis in the face of any unexplained nocturnal agitation + palmoplantar vesicles in infants - permethrin 5 %: approved from 2 months (adequate safety data) → application to whole body including face and scalp (avoid eyes + mouth) → apply by parent (no self-application) → same duration (8-14h) → rinse off with bath the next day + precipitated sulfur 6 % in vaseline: alternative if permethrin not available or <2 months → 3 consecutive evenings → less well tolerated (odor) + ivermectin: not recommended <5 years or <15 kg (insufficient data + theoretical risk of neurological toxicity) | Practical precautions and advice to the patient for the treatment of scabies: preparation before application (on the evening of treatment): warm bath or shower + careful drying + cut nails short (mites under the nails) + permethrin application must be done on clean, dry skin (not on wet skin - risk of reduced absorption) → apply in a thin but even layer all over the body from neck to toes (adult) → insist on areas of predilection: interdigital spaces of hands and feet + wrists + elbows + armpits + umbilicus + perineum + buttocks + under fingernails + on the evening of treatment: put on clean pyjamas and bedding → leave on overnight (8-14h minimum) → the next morning: rinse thoroughly in the shower → put on clean clothes → wash bedding used the night of treatment at 60°C → D8-J14: 2nd identical application + 2nd washing of bedding; reporting to close contacts: inform all household members + recent sexual partners + ask the community concerned (daycare + camp + CHSLD) to implement collective treatment → without simultaneous treatment of contacts → reinfestation almost certain in the following weeks; reporting: scabies in institutional settings (CHSLD + day-care centers + care facilities) must be reported to the regional Direction de la santé publique (DSP) in Quebec → coordination of collective treatment + outbreak control measures |
| Scabies in the community - outbreak management CHSLD - daycares - mass treatment - DSP |
Scabies outbreaks in the community (CHSLDs, intermediate residences, daycare centers, prisons, camps) represent a major public health challenge in Quebec - their management requires rigorous coordination; definition of a scabies outbreak in an institutional setting (MSSS + INSPQ Quebec criteria): ≥2 confirmed or probable cases of scabies in the same institutional setting within a timeframe compatible with common transmission → immediate triggering of the outbreak protocol; epidemiological investigation: identification of the index case (first case - often retrospective) + mapping of cases (residents + staff) + identification of close contacts (rooms + dining rooms + common activities + caregivers) + analysis of case chronology → verification of concordance with incubation times (3-6 weeks for primary infections); role of the DSP: coordinating the response + supporting the institutional environment + communicating to families and staff + deciding on the perimeter of collective treatment + monitoring the evolution of the outbreak → declared end if no new cases for 6 weeks after the last collective treatment; diagnosis in communities (scabies in CHSLDs): clinical diagnosis often difficult in the elderly (atypical pruritus + lesions masked by malnutrition + xerosis + skin history) → systematic dermoscopy + scraping if lesion suspected → low threshold to initiate collective treatment if well-founded suspicion + identification of Norwegian scab forms (main source of massive contamination) → immediate isolation + combined treatment | Collective treatment in an institutional setting: treatment perimeter: all residents in the same corridor or unit + all staff members who have had unprotected direct contact + frequent visitors (close family) → simultaneous treatment on the same date - the same day for all → permethrin 5 % × 2 applications (D1 + D8): reference topical treatment for autonomous and semi-autonomous residents → for bedridden or uncooperative people: ivermectin PO × 2 doses (D1 + D8) (or D1 + D2 + D8 if Norwegian scabies confirmed) → nursing staff: permethrin 5 % × 2 applications (D1 + D8) at home (treatment to be done in the evening after work); coordinated institutional decontamination: bedding + clothing washed at 60°C on day of treatment → mattresses + wheelchairs + upholstered surfaces → acaricide spray (A-Par) → airing 3h → vacuuming carpets + rugs - repeat decontamination on D8 in parallel with 2nd application; communication to families and staff: clear information letter + detailed instructions on application technique + list of symptoms to monitor + care management contact number → transparency essential to obtain adherence to collective treatment; post-treatment monitoring: new case 4-6 weeks after treatment → reinvestigation + new round of treatment if necessary → end of outbreak: absence of new documented case × 6 weeks after last treatment + Quebec resources: Protocoles de gestion des éclosions de gale - MSSS Quebec + INSPQ → available on INSPQ website + support from regional DSP (ex. DSP Montérégie + CIUSSS) |
ℹ️
Process all contacts on the same day - no exceptions: The golden rule of scabies treatment is to treat the patient and all close contacts - household members, sexual partners, people sharing the same bedding - on the same day, whether or not they have symptoms. A single untreated contact is enough to reinfect the treated patient a few weeks later. Pruritus persisting for up to 4 to 6 weeks after a correctly performed treatment is a hypersensitivity reaction to parasite debris - it is not a sign of treatment failure. Withdraw before 4 weeks only if new typical lesions appear.
Situations requiring urgent medical assessment
Diffuse pruritus + hyperkeratotic keratoderma + thick scabs in an immunocompromised patient (HIV, transplant, long-term corticosteroid therapy) → Norwegian scabies → immediate contact isolation + combined treatment (ivermectin PO + daily topical permethrin) + report to DSP if institutional setting.
Outbreak of ≥2 cases of nocturnal pruritus with suggestive lesions in a CHSLD, daycare center or camp → immediate reporting to the regional DSP + implementation of the MSSS/INSPQ outbreak protocol + simultaneous coordinated collective treatment.
Scabies + high fever + superinfected wounds + skin cellulitis → bacterial superinfection (staphylococcus or streptococcus) → antibiotic therapy (cefazolin IV or amoxicillin-clavulanate PO depending on severity) + concomitant scabicide treatment.
Scabies diagnosed in an adolescent or young adult with a history of unprotected sex → scabies = potential ITSS → full screening for other ITSS (HIV + syphilis + gonorrhea + chlamydia) + referral to an ITSS clinic or SPOT Montréal.
Consult at Clinique Omicron
Clinique Omicron's doctors diagnose and treat scabies in patients of all ages - prescribing permethrin or ivermectin, giving detailed instructions on home decontamination, treating contacts at the same time, and providing post-treatment follow-up. Scabies in the context of STBBI is fully screened. Telemedicine is available for initial consultations when the clinical picture is suggestive. For care available at several points of service in Quebec, visit cliniqueomicron.ca.
The contents of this page are provided for information purposes only and do not replace the advice of a doctor or dermatologist. Scabies is a treatable condition - prompt diagnosis and treatment can prevent it spreading to others.
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