Scabies

1. Introduction

  • Definition: Scabies is a highly contagious skin condition caused by the infestation of the human itch mite (Sarcoptes scabiei var. hominis). It leads to intense itching and a characteristic rash.
  • Epidemiology: Scabies affects approximately 200 million people worldwide at any given time, with higher prevalence in crowded settings and resource-poor regions.
  • Significance: While treatable, scabies can cause significant discomfort, disrupt quality of life, and lead to secondary infections if untreated.

2. Causes and Risk Factors

  • Causes:
    • Infestation by Sarcoptes scabiei, which burrows into the skin to lay eggs.
  • Risk Factors:
    • Close physical contact with an infected person.
    • Crowded living conditions (e.g., dormitories, nursing homes, refugee camps).
    • Poor hygiene or delayed diagnosis.

3. Pathophysiology

  • The mites burrow into the stratum corneum of the skin, triggering an immune response that causes intense itching and inflammation. The cycle perpetuates as eggs hatch and larvae spread.

4. Symptoms and Features

  • Common Symptoms:
    • Intense itching, especially at night.
    • Erythematous papules, burrows, or vesicles commonly found on the hands, wrists, axillae, and genital areas.
  • Severe Cases:
    • Crusted (Norwegian) scabies: Thick, crusted lesions with high mite burden, often in immunocompromised individuals.

5. Complications

  • Secondary bacterial infections (e.g., impetigo caused by Staphylococcus aureus or Streptococcus pyogenes).
  • Post-streptococcal glomerulonephritis (in resource-limited settings).
  • Social stigma due to visible lesions and itching.

6. Diagnosis

  • Clinical Features: Itching and characteristic rash in typical locations.
  • Microscopic Examination: Skin scraping under a microscope to identify mites, eggs, or feces.
  • Dermatoscopy: Visualization of burrows and mites.

7. Management Overview

  • Goals: Eradicate mites, relieve symptoms, and prevent transmission.
  • Approach: Combination of topical and systemic treatment, alongside environmental decontamination.

8. Treatment Options with Cost (USD)

  • Topical Treatments:
    • Permethrin 5% cream: ~$20–$40 per tube.
    • Benzyl benzoate: ~$10–$30 per bottle.
  • Oral Treatment:
    • Ivermectin: ~$5–$20 per tablet (requires 2 doses).
  • Symptomatic Relief:
    • Antihistamines (e.g., diphenhydramine): ~$5–$15 per pack.

9. Advanced Treatment Options with Cost (USD)

  • Crusted scabies:
    • High-dose ivermectin (multiple doses): ~$50–$100 per treatment course.
    • Keratolytic agents (e.g., salicylic acid): ~$10–$20 per product.

10. Pharmacological Treatment

  • First-line: Permethrin 5% cream (applied from neck to toes overnight and repeated in 7 days).
  • Oral Alternative: Ivermectin for widespread infestation or crusted scabies.
  • Adjunctive: Antihistamines or corticosteroid creams to manage itching and inflammation.

11. Medication Tables

Table 1: Doses and Side Effects

DrugIndicationDoseCommon Side Effects
Permethrin 5%First-line topical treatmentApply overnight, repeat in 7 daysSkin irritation, redness
IvermectinOral alternative200 mcg/kg, repeated after 7 daysGI upset, dizziness
Benzyl benzoateTopical treatmentApply overnight for 2–3 nightsBurning sensation, skin dryness
DiphenhydramineItch relief25–50 mg orally, as neededDrowsiness, dry mouth
Hydrocortisone creamItch and inflammation reliefApply 1–2 times dailySkin thinning with prolonged use

Table 2: Brand Names and Approximate Costs (USD)

DrugBrand NamesApprox. Cost
Permethrin 5%Elimite, Nix$20–$40 per tube
IvermectinStromectol$5–$20 per tablet
Benzyl benzoateAscabiol$10–$30 per bottle
DiphenhydramineBenadryl$5–$15 per pack
HydrocortisoneCortizone-10$5–$10 per tube

12. Lifestyle Interventions

  • Wash all clothing, bedding, and towels in hot water and dry on high heat.
  • Avoid close physical contact with others until treatment is complete.
  • Treat all household members and close contacts simultaneously to prevent reinfestation.

13. Monitoring Parameters

  • Resolution of symptoms (itching and rash) within 2–4 weeks post-treatment.
  • Watch for signs of secondary bacterial infection (e.g., worsening redness, oozing).
  • Repeat examination or treatment for persistent cases.

14. Patient Counseling Points

  • Emphasize the importance of treating all close contacts, even if asymptomatic.
  • Explain that itching may persist for 1–2 weeks after successful treatment due to allergic reactions to dead mites.
  • Avoid overuse of topical treatments to prevent skin irritation.
  • Encourage environmental cleaning to prevent reinfestation.

15. Special Populations

  • In Children: Permethrin 5% cream is safe for use in infants >2 months old. Avoid ivermectin in children weighing <15 kg.
  • In Pregnancy: Permethrin and sulfur ointment are safe; avoid ivermectin unless necessary.
  • In Immunocompromised Individuals: Require more aggressive treatment for crusted scabies.

16. Prevention

  • Maintain good personal hygiene and avoid sharing personal items like towels and bedding.
  • Promptly treat any infected individuals in communal settings.
  • Regularly clean frequently used surfaces and fabrics.

17. FAQs

  1. What is scabies?
    Answer: A skin condition caused by Sarcoptes scabiei mites, leading to itching and rash.
  2. How is scabies transmitted?
    Answer: Through direct skin-to-skin contact or sharing contaminated items.
  3. What are the symptoms of scabies?
    Answer: Intense itching, especially at night, and a rash with burrows.
  4. How is scabies treated?
    Answer: Topical permethrin or oral ivermectin, along with environmental decontamination.
  5. Can scabies resolve on its own?
    Answer: No, treatment is required to eradicate the mites.
  6. Is scabies contagious?
    Answer: Yes, highly contagious through close contact.
  7. How long does it take to recover from scabies?
    Answer: Symptoms improve within 2–4 weeks after treatment.
  8. Can scabies recur?
    Answer: Yes, if contacts are untreated or environmental cleaning is inadequate.
  9. What is crusted scabies?
    Answer: A severe form with thick, crusted lesions, common in immunocompromised individuals.
  10. Are there over-the-counter treatments for scabies?
    Answer: Permethrin 1% (available OTC) is less effective than 5%, which requires a prescription.
  11. What causes persistent itching after treatment?
    Answer: Allergic reaction to dead mites, not reinfestation.
  12. Can pets transmit scabies?
    Answer: No, pets carry a different mite species that does not cause human scabies.
  13. How should clothes be cleaned?
    Answer: Wash in hot water and dry on high heat.
  14. Is ivermectin safe for scabies?
    Answer: Yes, for adults and children >15 kg or as an alternative to topical treatments.
  15. When should I seek medical advice?
    Answer: If symptoms persist after treatment or secondary infection is suspected.
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