Chapter 19 Microbiology

Anatomy of the Skin

  • Skin is the largest organ in the human body and serves as a barrier and part of the innate immune system.
      - Structure includes two main layers:
        - Epidermis
        - Dermis

  • Langerhans cells are specialized dendritic cells found under the skin, crucial for immune response.
      - Important for protection against microbes that breach the skin barrier.
      - Skin can be compromised by:
        - Cuts
        - Scrapes
        - Rashes

Types of Rashes

  • Rashes are significant indicators of skin infections and present in various forms:
      - Rash Definition: Any change in skin color or texture.
      - Exanthems: Rashes with systemic symptoms (fever, headache, muscle aches).
      - Enanthems: Rashes on mucous membranes, less common.

Categories of Rashes:

  1. Macular Rashes: Flat, red, and under 1 cm in size.

  2. Papular Rashes: Small, solid, elevated, and non-reddened (not to confuse with maculopapular).

  3. Maculopapular Rashes: Small elevations with redness present.

  4. Pustular Rashes: Filled with pus, indicative of infection.

  5. Vesicular Rashes: Fluid-filled blisters.

Mucous Membranes

  • Epithelial in nature, lining body cavities and openings.

  • Continuous with skin; less protective due to permeability.

Infections of the Eye

  • Focus on conjunctiva and conjunctivitis (pink eye).
      - Common and highly transmissible, affecting individuals of all ages.

Types of Eye Infections:

  1. Conjunctivitis: Inflammation of the conjunctiva.

  2. Keratitis: Inflammation of the cornea.

  3. Endophthalmitis: Infection affecting the inner Eye structures.

Viral Infections of the Skin

  • Measles:
      - Killed over 140,000 children under 15 in 2018.
      - Transmitted via respiratory droplets and direct contact.
      - Incubation: Up to 10 days.
      - Prodromal phase symptoms:
        - Flu-like symptoms (fatigue, fever around 104°F, loss of appetite).
      - Pathognomonic Signs: Koplik spots in the mouth, significant for diagnosis.
      - Rash starts at hairline after Koplik spots, resolves in 4 days.
      - Complications include ADEM and SSPE affecting the CNS.
      - Diagnosis through clinical presentation & antibody detection.
      - Supportive treatment; vaccination is key for prevention.

  • German Measles (Rubella):
      - Transmitted through airborne droplets, incubates 12-23 days.
      - Symptoms include low-grade fever, pinpoint maculopapular rash.
        - Concerns include congenital rubella syndrome in pregnant women.
      - Diagnosis through clinical presentation; supportive treatment.

  • Fifth Disease (Erythema Infectiosum):
      - Caused by human parvovirus; Transmitted via respiratory secretions.
      - Symptoms begin with flu-like symptoms followed by a "slapped cheek" rash.
      - Diagnosis through PCR and antibody detection; supportive treatment.

  • Chickenpox:
      - Varicella zoster virus transmission occurs via skin lesions.
      - No prodromal phase; can lead to severe complications in immunocompromised individuals.
      - Diagnosis is often clinical, supportive treatments include antihistamines and acetaminophen, but never aspirin.

  • Shingles:
      - Reactivation of varicella zoster virus from latency; typically affects older individuals.
      - Travels along sensory nerves resulting in localized rashes.
      - Diagnosis via clinical presentation; zoster vaccine available for prevention.

Bacterial Infections of the Skin

  • Staphylococcal Infections:
      - Staphylococcus aureus: coagulase positive, known for abscesses and multiple toxins damaging skin.
      - Common infections:
        - Folliculitis
        - Boils (furuncle)
        - Carbuncles (multiple boils)
      - Impetigo is a common infection, presenting honey crusted lesions or blistering.
      - MRSA is a concern due to antibiotic resistance; community-acquired MRSA is rising.

  • Streptococcal Infections:
      - Streptococcus pyogenes: gram-positive cocci causing skin infections and necrotizing fasciitis.
      - Characterized by rapid tissue destruction; often requires surgical intervention.

Specialized Conditions

  1. Acne Vulgaris:
       - Caused by Cutibacterium acnes; inflammatory response leads to lesions.
       - Treatment may include antibiotics, depending on etiology.

  2. Gangrene:
       - Localized necrosis with wet or dry forms:
          - Dry: due to non-microbial causes (frostbite, diabetes).
          - Wet: due to microbial infection, especially from clostridium species.
          - Treatment often involves surgery and antibiotics.

Conclusion:

  • Quick summary of conditions affecting skin and eyes along with their causes and implications.