16- Skin and eye infections for canvas 24S

INFECTIOUS DISEASES OF THE SKIN & EYES

Chapter 16 Overview

OBJECTIVES

  • Anatomy of Skin

    • Describe the important anatomical features of the skin.

  • Skin Microbiota

    • List characteristics of the skin’s normal microbiota.

  • Skin Defense Mechanisms

    • List the natural defenses present in the skin.

INTRODUCTION

Skin Structure

  • Each layer has specific functions:

    • Epidermal dendritic (Langerhans) cells: Act as antigen-presenting cells.

    • Mast cells and Macrophages: Play a role in immune response.

    • Sebaceous glands: Contribute to skin defense.

  • Source: American Skin Association.

NORMAL MICROBIOTA

  • Variation by Site:

    • Different microbial communities found across various skin regions.

    • Corynebacterium: Non-spore forming GPR.

    • Cutibacterium (Propionibacterium).

    • Staphylococcus: e.g., S. epidermidis.

  • Skin Regions Classification:

    • Sebaceous sites: High microbial diversity.

    • Moist sites: Significant diversity.

    • Dry sites: Least diversity.

DEFENSES OF THE SKIN

Antimicrobial Peptides

  • Mechanism: Disrupt negatively charged membranes of bacteria.

    • Help maintain low microbial count.

Sebum

  • Nature: Oily substance produced by sebaceous glands.

  • Properties:

    • Low pH, high lipid concentration, toxic by-products inhibiting non-adaptive microorganisms.

Sweat

  • Inhibition: Due to low pH and high salt concentration.

Lysozyme

  • Function: Found in sweat, tears, saliva; breaks down peptidoglycan in bacterial cell walls.

SUMMARY

Skin Defenses and Microbiota

  • Summary of Defenses:

    • Keratinized surface, low pH, high salt concentration, presence of antimicrobial peptides, and lysozyme.

  • Microbiota Presence: Includes Streptococcus, Staphylococcus, Corynebacterium, Lactobacillus, and yeasts like Candida.

OBJECTIVES: SKIN INFECTIONS

  • Highlight Disease: Staphylococcus aureus skin infections.

  • Key Areas to Study:

    • Epidemiology, virulence, disease presentations (Carbuncle, Impetigo, Cellulitis, Scalded Skin Syndrome, Toxic Shock Syndrome, MRSA).

    • Diagnosis, treatment, and prevention of each infection.

    • Differentiate between Carbuncle, Impetigo, and Cellulitis.

MACULOPAPULAR RASH DISEASES

Overview

  • Definition: Skin eruptions caused by various microbes (flat to slightly raised colored bumps).

  • Diseases:

    • Measles, Rubella, Fifth Disease, Roseola.

MEASLES

  • Characteristics: Also known as rubeola; significant mortality among children despite vaccination.

  • Symptoms: Sore throat, dry cough, Koplik's spots, maculopapular exanthem.

  • Pathogenesis: Virus affects respiratory mucosa.

  • Transmission: Highly contagious via respiratory droplets; humans are the only reservoir.

RUBELLA

  • Characteristics: Minor rash disease; serious fetal effects if contracted during pregnancy.

  • Symptoms: Pink macules and papules; joint inflammation in adults.

  • Pathogenesis: Rubivirus induces apoptosis, affecting the fetus.

FIFTH DISEASE

  • Known As: Erythema infectiosum.

  • Symptoms: "Slapped cheek" appearance, mild disease mostly in children.

  • Causative Agent: Parvovirus B19.

ROSEOLA

  • Description: Common in young children; characterized by high fever followed by a rash.

  • Causative Agent: Human herpesvirus 6 (HHV-6).

IMPETIGO

Characteristics

  • Superficial bacterial infection; may involve S. aureus and S. pyogenes.

  • Signs: Peeling skin, honey-colored crusts, lesions around mouth, face, extremities.

Treatment

  • Topical mupirocin or retapamulin; oral antibiotics if severe.

CELLULITIS

  • Causes: Fast-spreading infection of the dermis and subcutaneous tissues.

  • Symptoms: Pain, warmth, swelling, lymphangitis, fever.

  • Causative Agents: S. pyogenes, S. aureus, and others.

  • Treatment: Oral antibiotics for mild cases; IV antibiotics for severe.

VESICULAR OR PUSTULAR RASH DISEASES

Chickenpox

  • Rapid progression from macules to vesicles; centripetal lesion distribution.

  • Risk of complications includes encephalopathy.

Smallpox

  • Unique rash progression and severe symptoms requiring emergency response for any cases.

  • Causative Agent: Variola virus.

CUTANEOUS AND SUPERFICIAL MYCOSES

Ringworm

  • Caused by dermatophytes (e.g., Trichophyton).

  • Transmission via direct contact; diagnosed with culture or microscopic exam.

Superficial Mycosis

  • Caused by Malassezia species; usually cosmetic infections.

CONJUNCTIVITIS

Symptoms

  • Milky discharge in bacterial; clear in viral infections.

Causative Agents

  • Neonatal infections by N. gonorrhoeae or C. trachomatis.

  • Common in bacterial cases for various species including S. pneumoniae and H. influenzae.

Treatment

  • Antibiotic eye drops for bacterial cases; supportive care for viral.

KERATITIS

Overview

  • Can lead to severe complications including blindness, especially due to HSV-1.

  • Transmission: Often associated with contact lens use or herpes reactivation.

Final Summary

Key Infectious Agents and Treatments

  • Various Skin Conditions: List key organisms, modes of transmission, and recommended treatments as summarized in detailed disease tables throughout the chapter.