Ch21 Skin and Eye Infections

Key Concepts of Skin and Eye Infections

Anatomy of the Skin
  • Epidermis: Outermost layer of skin.
  • Dermis: Second layer containing connective tissue, blood vessels, and nerves.
  • Hypodermis: Layer beneath the dermis composed of fat and connective tissue, providing insulation and cushioning.
Normal Microbiota of the Skin
  • The skin hosts diverse microbial flora varying by region (moist vs dry areas).
  • Normal flora such as Propionibacterium acnes can become pathogenic under certain conditions (e.g., clogged pores).
Common Skin Infections
  • Folliculitis: Inflammation of hair follicles; can lead to acne, characterized by clogged follicles with sebum and bacteria.
  • Abscess: Localized collection of pus usually due to infection.
  • Furuncles (boils): Pus-filled lesions due to infected hair follicles.
  • Carbuncles: Deep abscesses formed from multiple furuncles.
  • Impetigo: Sores caused by bacteria causing vesicles and crusts, highly contagious.
Key Skin Infection Terms
  • Macules: Smooth skin discolorations.
  • Papules: Small raised bumps.
  • Pustules: Fluid-filled bumps, often seen in infections.
  • Ulcer: Open sore or lesion on the skin.
Bacterial Pathogens
  • Staphylococcus aureus: Frequently causes purulent infections (e.g., folliculitis, carbuncles). Notable for MRSA strains resistant to antibiotics.
  • Streptococcus pyogenes: Responsible for conditions like cellulitis and necrotizing fasciitis.
  • Pseudomonas aeruginosa: Common cause of hot tub rash and otitis externa.
Eye Infections
  • Conjunctivitis: Inflammation of conjunctiva; can be bacterial (e.g., Haemophilus influenzae) or viral.
  • Keratitis: Inflammation of the cornea that can lead to blindness, often caused by Staphylococcus or Pseudomonas.
  • Trachoma: Serious conjunctivitis caused by Chlamydia trachomatis.
Viral Skin Infections
  • Herpes Simplex Virus (HSV-1): Causes oral herpes, can affect eyes.
  • Fifth Disease: Caused by Parvovirus B19; symptomatic with a distinct “slapped cheek” rash.
  • Roseola: Common viral infection in children characterized by a pink rash after high fever.
Fungal Infections (Mycoses)
  • Tinea: Commonly known as ringworm, caused by dermatophytes like Trichophyton. Varies by body part (e.g., tinea pedis for feet).
  • Candidiasis: Caused by Candida albicans, leads to rashes and infections in moist areas.
Parasitic Infections
  • Acanthamoeba keratitis: Infection from contaminated water leading to eye inflammation and pain.
  • Loiasis (African eye worm): Caused by the worm Loa loa, transmitted by deerflies, involves migration under the skin.
Transmission and Treatment
  • Bacterial infections often arise from breaches in the skin, leading to localized skin infections. Treatment includes antibiotics based on the specific pathogen.
  • Viral infections typically don't have specific antiviral treatments except for severe cases (e.g., herpes), where acyclovir may be used.
  • Fungal infections may require topical or systemic antifungals depending on the severity.
  • Parasites may be treated with drugs such as diethylcarbamazine for Loa loa.
Prevention
  • Proper hygiene and wound care to prevent bacteria from entering the skin.
  • Regular cleaning and care for contact lenses to avoid amoebic infections.
  • Avoiding exposure to contaminated water where possible to prevent parasitic infections.
Conclusion
  • Understanding the anatomy, microbiota, common pathogens, and infections of the skin and eyes is essential for diagnosis and treatment of various conditions. Close attention to symptoms and timely medical intervention can mitigate serious health risks.