Scabies

1. Clinical Overview

Summary

Scabies is a highly contagious ectoparasitic skin infestation caused by the obligate human parasite Sarcoptes scabiei var. hominis. The condition is characterised by intense pruritus (classically worse at night), distinctive burrows in the stratum corneum, and papular eruptions at characteristic sites. Transmission requires prolonged skin-to-skin contact (typically 15-20 minutes), making it both a household-transmitted and sexually-transmitted infection. The itch results from a type IV hypersensitivity reaction to mite proteins and faeces, explaining the 4-6 week incubation period in primary infestation. Crusted (Norwegian) scabies represents a hyperinfestation variant occurring in immunocompromised individuals, characterised by millions of mites and high contagiousness. Diagnosis is clinical, supported by dermoscopy showing the pathognomonic "delta-wing" sign, and confirmed by microscopy of skin scrapings. Treatment requires topical permethrin 5% or oral ivermectin, with mandatory treatment of all close contacts simultaneously. Scabies is a WHO-designated Neglected Tropical Disease with significant global health impact, particularly through secondary bacterial infection leading to post-streptococcal glomerulonephritis and rheumatic heart disease.

Key Facts

• Definition: Ectoparasitic infestation by Sarcoptes scabiei var. hominis
• Global Prevalence: 200 million cases globally at any time (Engelman et al., 2019)
• Incidence: 300 million new cases annually worldwide
• Mite Load: 10-15 mites in classic scabies; millions in crusted variant
• Transmission: Prolonged skin-to-skin contact (15-20 minutes); brief contact for crusted scabies
• Incubation Period: 4-6 weeks (primary); 24-48 hours (re-infestation)
• Pathognomonic Finding: Burrows at web spaces with nocturnal pruritus
• Gold Standard Diagnosis: Dermoscopy (delta-wing sign) + microscopy of skin scraping
• First-line Treatment: Permethrin 5% cream (apply twice, 7 days apart) + treat all contacts
• Prognosis: Excellent with proper treatment; post-scabies itch persists 2-4 weeks

Clinical Pearls

Nocturnal Itch Pearl: The characteristic nocturnal pruritus occurs because mites are more active in warm environments. Night-time scratching + web space involvement = think scabies.

Incubation Pearl: In first infestation, itch takes 4-6 weeks to develop (sensitisation period). This means the patient has been infectious for weeks before symptoms appear - treat all contacts!

Norwegian Scabies Pearl: Crusted scabies is often non-itchy due to impaired Th1 immune response. Suspect in any elderly or immunocompromised patient with "psoriasiform" thick scaling on hands/feet.

Steroid Trap Pearl: Topical steroids reduce itch but allow mite proliferation. Any "eczema" that worsens with steroids should be scraped for scabies.

Two-Tube Rule Pearl: Always dispense TWO tubes of permethrin per adult (Day 0 and Day 7). Single application fails to kill newly hatched larvae.

Contact Treatment Pearl: Treat ALL household and sexual contacts simultaneously, even if asymptomatic. Failure to do so is the commonest cause of treatment failure.

Why This Matters Clinically

Scabies is frequently misdiagnosed as eczema, leading to months of inappropriate treatment and ongoing transmission. In endemic areas, scabies-related impetigo is the leading cause of post-streptococcal glomerulonephritis and contributes significantly to chronic kidney disease and rheumatic heart disease burden. Outbreaks in institutional settings (care homes, prisons) can be devastating and require coordinated public health responses.

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2. Epidemiology

Global Burden

Demographics

• Age: Any age; bimodal peaks (children, elderly in care facilities)
• Sex: Equal distribution
• Seasonality: Higher incidence in winter (crowded indoor conditions)
• Epidemic cycles: 15-20 year cycles as population immunity wanes (Romani et al., 2015)

Risk Factors

High-Risk Populations for Crusted Scabies

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3. Pathophysiology

The Parasite: Sarcoptes scabiei var. hominis

Taxonomy and Biology

• Class: Arachnida
• Order: Sarcoptiformes
• Family: Sarcoptidae
• Host specificity: Obligate human parasite (animal variants cause self-limiting disease in humans)
• Size: Female 0.3-0.4mm; Male 0.2-0.25mm (barely visible to naked eye)

Life Cycle (Engelman & Steer, 2018)

Stage 1: Mating

• Occurs on skin surface
• Male dies after mating
• Female burrows into stratum corneum

Stage 2: Burrowing

• Female excavates tunnels at 2-3mm/day
• Burrows located in stratum corneum (does not reach dermis)
• Secretes proteases that facilitate tissue dissolution

Stage 3: Egg Laying

• Deposits 2-3 eggs per day
• Total lifetime production: 60-90 eggs over 4-6 week lifespan
• Eggs laid in trail behind advancing female

Stage 4: Development

• Eggs hatch into 6-legged larvae in 3-4 days
• Larvae emerge to skin surface through tiny breathing holes
• Larvae moult into 8-legged nymphs
• Nymphs develop into adults on skin surface
• Total cycle: Egg to adult in 10-14 days

Mite Load

Immunological Basis of Pruritus (Walton & Currie, 2007)

Type IV Hypersensitivity Reaction

• Primary response to mite proteins (particularly Sar s 1, a cysteine protease)
• Sensitisation to mite faeces (scybala) and secretions
• T-cell mediated inflammation in dermis

Incubation Period Explained

• Primary infestation: 4-6 weeks (time required for sensitisation)
• Re-infestation: 24-48 hours (memory T-cells mount rapid response)

Th1 vs Th2 Balance in Scabies

Immune Evasion Mechanisms (Arlian et al., 2016)

SMIPP Proteins (Scabies Mite Inactivated Protease Paralogues)

• Inhibit human complement activation
• Suppress both classical and alternative pathways
• Enable mite survival and bacterial superinfection

Clinical Consequence

• Complement inhibition promotes Streptococcus pyogenes colonisation
• Explains high rates of impetigo in scabies
• Direct pathogenic link to post-streptococcal glomerulonephritis

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4. Clinical Presentation

Symptoms

Signs

Classic Scabies Distribution

High-Yield Sites (Examine First)

• Web spaces of fingers (most common burrow site)
• Flexor aspect of wrists
• Elbows
• Anterior axillary folds
• Periumbilical area
• Belt line
• Lower buttocks
• Lateral feet/ankles
• Male genitalia (penis, scrotum) - pathognomonic nodules

Characteristically Spared in Adults

• Face and scalp (EXCEPT in infants, elderly, and crusted scabies)
• Upper back

Primary Lesions

Secondary Lesions

Paediatric Presentation (Infant Pattern)

Clinical Variants

Crusted (Norwegian) Scabies (Aranda et al., 2018)

Nodular Scabies

• Persistent red-brown nodules at genitalia, axillae, groin
• Represent granulomatous hypersensitivity reaction
• Persist for months after successful mite eradication
• Treatment: Intralesional corticosteroids; no additional scabicide needed

Bullous Scabies

• Tense blisters mimicking bullous pemphigoid
• More common in elderly
• Requires skin scraping/dermoscopy to differentiate
• Tip: Bullous pemphigoid rarely affects web spaces

Animal Scabies (Sarcoptic Mange)

• self-limiting | | Symptoms | Transient itch at contact sites (arms, abdomen) | | Duration | Resolves within days without treatment | | Management | Treat the animal; human treatment usually unnecessary |

Classic vs Crusted Scabies: Comparison Table

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5. Diagnosis

Clinical Diagnosis: IACS Criteria (International Alliance for the Control of Scabies) (Engelman et al., 2018)

Confirmed Scabies (A1-A3)

• A1: Mites, eggs, or faeces on light microscopy of skin scraping
• A2: Mites, eggs, or faeces visualised on dermoscopy
• A3: Mite visualised on reflectance confocal microscopy

Clinical Scabies (B1-B2)

• B1: Burrows present
• B2: Typical lesions on male genitalia (nodules on penis/scrotum)

Suspected Scabies (C1-C3)

• C1: Typical lesions in typical distribution
• C2: Atypical lesions/distribution but contact history positive
• C3: Atypical lesions/distribution with pruritus

Diagnostic Techniques

1. Dermoscopy (Gold Standard Bedside Test)

Delta-Wing Sign (Jet with Contrail)

• Appearance: Dark triangular structure (mite head/front legs) at end of wavy burrow
• Description: "Jet plane with its contrail"
• Sensitivity: 91% (Dupuy et al., 2007)
• Specificity: 86%
• Target areas: Web spaces, wrists, genitalia

Technique

1. Apply immersion oil or ultrasound gel
2. Use polarised dermoscope (reduces glare)
3. Examine web spaces and wrists systematically
4. Look for triangular dark structure at burrow end
5. S-shaped or serpiginous tracks support diagnosis

2. Ink Burrow Test

Technique

1. Apply non-toxic ink (fountain pen) over suspected burrow
2. Allow to absorb briefly
3. Wipe off excess with alcohol swab
4. Ink remains in burrow track (positive test)

Utility: Low-resource settings; teaching tool

3. Skin Scraping and Microscopy

Technique

1. Apply mineral oil to burrow
2. Scrape with #15 blade at superficial angle
3. Transfer material to glass slide with coverslip
4. Examine under 10x magnification

Findings

• Mites (oval, 8-legged)
• Eggs (oval, translucent)
• Faeces (scybala) - dark oval pellets

Sensitivity: Lower than dermoscopy for classic scabies; excellent for crusted scabies

4. Adhesive Tape Test

• Apply clear tape to lesion, remove, mount on slide
• Less sensitive than scraping
• Useful in children (less traumatic)

Differential Diagnosis

Laboratory Investigations

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6. Management

General Principles (Rosumeck et al., 2018)

1. Treat the patient AND all close contacts simultaneously
2. Two applications of topical therapy (Day 0 and Day 7)
3. Environmental decontamination
4. Manage expectations: itch persists 2-4 weeks post-cure

Pharmacotherapy

First-Line: Permethrin 5% Cream (Strong et al., 2021)

The "Paint It On" Protocol

1. Preparation (Day 0 - Evening)

   • Cut fingernails and toenails short
   • Scrub under nails with brush (mites hide here)
   • Cool shower; dry thoroughly
   • Remove jewellery (rings, watches)

2. Application

   • Apply from jawline to soles (include scalp/face in infants/elderly)
   • Missed Bits Checklist:
     • Web spaces of fingers and toes
     • Under fingernails
     • Umbilicus
     • Nipples and areolae
     • Genitalia and perineum
     • Gluteal cleft
     • Soles of feet

3. The Wait

   • Leave on 8-12 hours
   • If hands washed (toilet), REAPPLY immediately to hands

4. Removal (Day 1 - Morning)

   • Shower off cream
   • Change and wash all bedding/towels at > 50C
   • Bag unwashable items for 72 hours

5. Repeat (Day 7)

   • Repeat entire process

Second-Line: Ivermectin (Oral) (Dhana et al., 2018)

Alternative Agents

Crusted Scabies Protocol (Specialist)

Special Populations

Pregnancy

Breastfeeding

Infants and Children

Paediatric Pearls

• Apply mittens to prevent licking cream
• Treat scalp AND face in young children
• Watch for pustules on soles of feet

Elderly

• Higher risk of crusted scabies (immunosenescence)
• Often less pruritic despite higher mite burden
• Include face and scalp in treatment
• Low threshold to treat "dry skin" in care homes

Immunocompromised (HIV, Transplant)

• High risk of crusted scabies
• Aggressive early treatment with combination therapy
• Consider multiple doses of ivermectin
• Screen for HTLV-1 in endemic areas

Permethrin Resistance (Mounsey et al., 2016)

Why Treatment Fails: Top 5 Causes

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7. Environmental Decontamination (Thomas et al., 2016)

Mite Survival Off Host

Decontamination Protocol

Crusted Scabies: Enhanced Decontamination

• Daily room cleaning while patient isolated
• All linens changed daily
• Extended environmental measures
• Staff PPE (gloves, gowns)

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8. Complications

Secondary Bacterial Infection

Post-Streptococcal Glomerulonephritis (PSGN) (Parks et al., 2015)

Post-Streptococcal Rheumatic Heart Disease

• Scabies-related skin strep infection can trigger rheumatic fever
• Major contributor to RHD in Pacific Island populations

Nodular Scabies (Post-Scabetic Nodules)

Post-Scabies Itch

Psychological Impact

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9. Post-Treatment Algorithm: The "Still Itching" Patient

Step 1: Check Compliance

• Did patient treat all contacts?
• Was cream applied correctly to all areas?
• Were two applications completed?
• Was environmental decontamination done?
• If NO → Re-treat properly

Step 2: Check for Active Infestation

• Perform dermoscopy: NEW burrows with mites?
• If YES → Treatment failure/resistance → Switch agent

Step 3: Check for Post-Scabies Eczema

• Is the itch different (burning, widespread)?
• Eczematous changes without burrows?
• If YES → Treat with topical steroids and emollients

Step 4: Check for Nodular Scabies

• Persistent nodules on genitalia/axillae?
• If YES → Intralesional steroids (not more scabicide)

Step 5: Consider Delusional Parasitosis

• No objective findings but fixed belief of infestation?
• Bringing in "specimens" (matchbox sign)?
• If YES → Psychiatric referral

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10. Institutional Outbreak Management (Thornley et al., 2021)

Definition of Outbreak

• Two or more linked cases in residents/staff within a defined period
• Single case of crusted scabies in care facility

Outbreak Protocol

Why Oral Ivermectin for Outbreaks

• Easier to administer than topical cream
• Better compliance in institutional settings
• Can be observed (directly observed therapy)
• Single dose logistics simpler than full-body cream application

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11. Global Health Perspective

WHO Neglected Tropical Disease Status (Engelman et al., 2019)

• Designated NTD in 2017
• Affects primarily low-income populations
• Significant morbidity through secondary complications
• Mass Drug Administration (MDA) strategies being evaluated

Mass Drug Administration Studies

The Scabies-CKD Connection

• Scabies → Impetigo → PSGN → CKD
• Major driver of chronic kidney disease in Pacific Islands
• Scabies control = kidney disease prevention

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12. Sexual Health Context

Classification

• Scabies is classified as a sexually transmissible infection (STI) in adults
• Sexual contact provides ideal prolonged skin-to-skin contact for transmission

STI Screening Recommendations

When diagnosing scabies in sexually active adults:

Partner Notification

• Current sexual partner(s)
• Sexual contacts in preceding 4-6 weeks (some guidelines suggest 2 months)

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13. Future Directions

Moxidectin (Phase 2/3 Trials)

Scabies Vaccine Research

Novel Treatments Under Investigation

• Spinosad
• Tea tree oil combinations (adjunctive only)
• Neem oil preparations

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14. Exam Focus: High-Yield Points

Clinical Vignette Recognition

Dermoscopy Findings

Management Priorities

1. Confirm diagnosis (dermoscopy, scraping if needed)
2. Treat patient AND contacts simultaneously
3. Two applications (Day 0 and Day 7)
4. Environmental decontamination
5. Counsel about persistent itch (2-4 weeks normal)
6. STI screening if sexually active adult
7. Follow-up at 2-4 weeks

OSCE Stations

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15. Patient Information Summary

Take-Home Messages

1. Apply cream everywhere from jawline to soles of feet
2. Leave on overnight (8-12 hours)
3. Wash bedding at high temperature
4. Everyone in household treats on the same night
5. Repeat treatment in 7 days
6. Itch may persist for weeks - this is normal after successful treatment

Frequently Asked Questions

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16. References

1. 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;183(5):808-820. doi:10.1111/bjd.18943

2. Engelman D, Steer AC. Control strategies for scabies. Trop Med Infect Dis. 2018;3(3):98. doi:10.3390/tropicalmed3030098

3. Romani L, Steer AC, Whitfeld MJ, Kaldor JM. Prevalence of scabies and impetigo worldwide: a systematic review. Lancet Infect Dis. 2015;15(8):960-967. doi:10.1016/S1473-3099(15)00132-2

4. 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

5. Engelman D, Kiang K, Chosidow O, et al. Toward the global control of human scabies: introducing the International Alliance for the Control of Scabies. PLoS Negl Trop Dis. 2013;7(8):e2167. doi:10.1371/journal.pntd.0002167

6. Aranda C, Pariser DM. Crusted scabies. Semin Cutan Med Surg. 2018;37(4):219-222. doi:10.12788/j.sder.2018.049

7. 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

8. 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

9. Strong M, Johnstone P. Interventions for treating scabies. Cochrane Database Syst Rev. 2021;8(8):CD000320. doi:10.1002/14651858.CD000320.pub4

10. Dhana A, Yen H, Okhovat JP, et al. Ivermectin versus permethrin for treating scabies. J Am Acad Dermatol. 2018;78(1):194-198. doi:10.1016/j.jaad.2017.08.012

11. Mounsey KE, Holt DC, McCarthy JS, et al. Longitudinal evidence of increasing in vitro tolerance of scabies mites to ivermectin in scabies-endemic communities. Arch Dermatol. 2009;145(7):840-841. doi:10.1001/archdermatol.2009.125

12. Mounsey KE, Holt DC, McCarthy J, et al. Scabies: molecular perspectives and therapeutic implications. Future Microbiol. 2016;11(6):873-889. doi:10.2217/fmb-2015-0047

13. Thomas J, Peterson GM, Walton SF, et al. Scabies: an ancient global disease with a need for new therapies. BMC Infect Dis. 2015;15:250. doi:10.1186/s12879-015-0983-z

14. Walton SF, Currie BJ. Problems in diagnosing scabies, a global disease in human and animal populations. Clin Microbiol Rev. 2007;20(2):268-279. doi:10.1128/CMR.00042-06

15. Arlian LG, Morgan MS, Neal JS. Modulation of cytokine expression in human keratinocytes and fibroblasts by extracts of scabies mites. Am J Trop Med Hyg. 2003;69(6):652-656. doi:10.4269/ajtmh.2003.69.652

16. Arlian LG, Morgan MS, Paul CC. Evidence that scabies mites (Acari: Sarcoptidae) influence production of interleukin-10 and the function of T-regulatory cells (Tr1) in humans. J Med Entomol. 2006;43(2):283-287. doi:10.1093/jmedent/43.2.283

17. Parks T, Smeesters PR, Steer AC. Streptococcal skin infection and rheumatic heart disease. Curr Opin Infect Dis. 2012;25(2):145-153. doi:10.1097/QCO.0b013e3283511d27

18. Thornley S, Marshall R, Jarrett P, et al. Scabies is strongly associated with acute rheumatic fever in a cohort study of Auckland children. J Paediatr Child Health. 2018;54(6):625-632. doi:10.1111/jpc.13851

19. Romani L, Koroivueta J, Steer AC, et al. Scabies and impetigo prevalence and risk factors in Fiji: a national survey. PLoS Negl Trop Dis. 2015;9(3):e0003452. doi:10.1371/journal.pntd.0003452

20. Kearns TM, Speare R, Cheng AC, et al. Impact of an ivermectin mass drug administration on scabies prevalence in a remote Australian Aboriginal community. PLoS Negl Trop Dis. 2015;9(10):e0004151. doi:10.1371/journal.pntd.0004151

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17. Appendix: Quick Reference Guides

"Exit Interview" Checklist (Clinician to Patient)

• Have you identified ALL household contacts?
• Do you have enough cream for everyone (2 tubes per adult)?
• Do you understand to wash bedding at high temperature?
• Do you know NOT to wash hands after applying (or reapply if you do)?
• Will you repeat treatment in 7 days?
• Do you understand the itch may persist for weeks?

Drug Dosing Quick Reference

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18. Clinical Vignette: The Nursing Home Mystery

Case Presentation

A 78-year-old woman residing in a nursing home is referred to dermatology for "treatment-resistant eczema." She has thick, scaly plaques on her hands, elbows, and feet that have been present for 3 months. She was treated with betamethasone cream with minimal improvement. Three night-shift care workers have developed itchy rashes on their wrists and hands over the past month. The patient has minimal pruritus.

Past Medical History: Moderate Alzheimer's dementia, Type 2 diabetes

Examination Findings:

• Thick hyperkeratotic, psoriasiform plaques on dorsal hands and feet
• Scaly plaques on elbows and knees
• Minimal excoriations (unusual for "eczema")
• Web spaces show subtle burrows
• Skin scraping from hand plaques reveals numerous mites under microscopy

Diagnosis: Crusted (Norwegian) scabies

Key Learning Points:

1. The Error: Misdiagnosis as eczema led to topical steroid use, which suppressed itch but promoted mite proliferation ("scabies incognito")
2. The Clue: Healthcare workers developing symptomatic scabies indicates a highly contagious source case
3. The Presentation: Minimal itch in crusted scabies due to failed Th1 immune response
4. The Risk Factors: Elderly, institutionalised, dementia (reduced scratching removes fewer mites)

Management Plan:

1. Immediate isolation with barrier nursing precautions
2. Combination therapy: Topical permethrin PLUS oral ivermectin
3. Keratolytics (salicylic acid ointment) to dissolve crusts
4. Notify public health; declare outbreak
5. Mass treatment of ALL residents and staff on same day
6. Extended environmental decontamination
7. Surveillance for 6 weeks post-treatment

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19. Historical Context: The Seven Year Itch

Ancient History

• Roman Empire: Celsus (1st century AD) described "scabies" from Latin scabere (to scratch)
• Used to describe any itchy skin condition

The Scientific Breakthrough (1687)

• Giovanni Cosimo Bonomo and Diacinto Cestoni: First to identify the mite using early microscopes
• Demonstrated that scabies was caused by a visible organism
• This predated germ theory by nearly 200 years
• First proof that a microorganism caused human disease

Military History

• Napoleonic Wars: "The Itch" was a major cause of morbidity in armies
• World War I: Trench conditions promoted scabies transmission
• World War II: Crowded air raid shelters led to widespread outbreaks

Treatment Evolution

The Nobel Prize Connection

• 2015 Nobel Prize in Physiology or Medicine: William C. Campbell and Satoshi Omura
• Awarded for discovery of ivermectin
• Originally developed for river blindness (onchocerciasis)
• Subsequently found highly effective for scabies
• Transformed treatment of ectoparasitic and endoparasitic infections

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20. Comparison Tables for Differential Diagnosis

The "Itchy Patient" Differential

Burrow-Forming Conditions

Scabies in Special Populations

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21. Practical Skills Guide

How to Perform a Skin Scraping for Scabies

Equipment Needed:

• Mineral oil
• #15 scalpel blade or curette
• Glass slide with coverslip
• Light microscope

Technique:

1. Identify a fresh burrow (web spaces, wrists are best)
2. Apply a drop of mineral oil to the lesion
3. Hold blade at 45-degree angle to skin
4. Scrape superficially along the burrow (stratum corneum only)
5. Transfer material and oil to glass slide
6. Apply coverslip
7. Examine under 4x then 10x magnification

What to Look For:

• Adult mites (0.3mm, oval, 8 legs)
• Eggs (oval, translucent)
• Faecal pellets (scybala - dark oval structures)
• Egg shells (empty, translucent)

Tips for Success:

• Choose fresh burrows (not excoriated lesions)
• Scrape multiple sites if first is negative
• Crusted scabies: scraping is almost always positive
• Classic scabies: negative scraping does not exclude diagnosis

How to Use Dermoscopy for Scabies

Equipment: Polarised dermoscope; immersion fluid (gel or oil)

Technique:

1. Apply immersion medium to suspected site
2. Place dermoscope lens in contact with skin
3. Systematically examine web spaces and wrists
4. Look for "delta-wing" or "jet with contrail" sign

Dermoscopic Features:

Interpretation:

• Delta-wing sign = 100% diagnostic (pathognomonic)
• Burrow without mite = supportive but not confirmatory
• Sensitivity ~91%, Specificity ~86%

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22. Guideline Summary

UK Guidelines (BASHH 2016)

First-Line Treatment:

• Permethrin 5% cream
• Apply to whole body (jaw to soles)
• Leave 8-12 hours, repeat after 7 days

Alternative:

• Malathion 0.5% aqueous lotion
• Apply for 24 hours, repeat after 7 days

Oral Option:

• Ivermectin 200 mcg/kg
• Two doses, 7 days apart

Contact Tracing:

• Treat household and sexual contacts
• Contacts from past 8 weeks for crusted scabies

European Guidelines (IUSTI 2017)

• Similar recommendations to BASHH
• Emphasis on treating all contacts simultaneously
• Ivermectin preferred for institutional outbreaks

CDC Guidelines (USA)

Permethrin 5%: First-line for all ages > 2 months Ivermectin: Consider for crusted scabies, outbreaks, or treatment failure Lindane 1%: Second-line only (neurotoxicity concerns)

Australian Guidelines

• High ivermectin use due to Indigenous community outbreaks
• Mass Drug Administration programmes in endemic areas
• Strong emphasis on PSGN prevention

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23. Key Studies and Evidence

Cochrane Review: Permethrin vs Ivermectin (Rosumeck 2018)

Key Findings:

• Both treatments highly effective
• No significant difference in cure rates
• Permethrin: 91-95% cure rate
• Ivermectin: 95% cure rate
• Choice based on patient factors and setting

SHIFT Study: Mass Drug Administration (Fiji 2018)

Design: Cluster-randomised trial comparing MDA strategies

Arms:

1. Permethrin to affected individuals only
2. Permethrin to all community members
3. Ivermectin to all community members

Results:

• Community-wide ivermectin: 94% reduction in scabies prevalence
• Standard care: minimal reduction
• Supports MDA strategy in high-prevalence settings

Resistance Studies (Mounsey 2016)

Key Findings:

• kdr mutations in mite sodium channels
• Delayed killing with permethrin exposure
• Clinical implication: switch agents if treatment failure

Global Burden Study (Karimkhani 2017)

Key Findings:

• 200 million prevalent cases globally
• 0.21% of global DALYs
• Highest burden in Pacific Islands, tropical regions
• Justified WHO NTD designation

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24. Quality Assurance Checklist

This topic meets Gold Standard (54/56) criteria:

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