Ch+19.+Microbial+Diseases+of+the+Skin+and+Wounds

Chapter 19: Microbial Diseases of the Skin and Wounds

Structure of the Skin

  • Functions of the skin:

    • Prevents excessive water loss

    • Regulates temperature

    • Assists in vitamin D formation

    • Involved in sensory phenomena

    • Acts as a barrier against microbial invaders

  • Layers of the skin:

    • Dermis

    • Epidermis

Wounds and Microbial Infections

  • Wounds:

    • Trauma allows microbes to infect deeper tissues (e.g., cuts, scrapes, bug bites).

    • Skin shedding contributes to microbial load in the environment.

  • Skin Microbiome:

    • Composed of normal, harmless microbes (Staphylococcus epidermidis, Malassezia).

    • Waste products can cause body odor.

    • Normal microbiome competes with pathogens, thus beneficial.

Bacterial Diseases of the Skin and Wounds

  • Folliculitis:

    • Infection of hair follicles leading to furuncles (boils) and carbuncles.

    • Caused primarily by Staphylococcus:

      • S. epidermidis (usually non-pathogenic)

      • S. aureus (can cause serious infections)

    • Spread via direct contact or fomites.

  • Staphylococcal Scalded Skin Syndrome (SSSS):

    • Caused by strains of S. aureus.

    • Symptoms include redness, wrinkling, and blistering of skin.

    • Diagnosed by distinctive skin peeling.

  • Impetigo and Cellulitis:

    • Impetigo presents with red patches evolving into pus-filled vesicles.

    • Cellulitis is a deeper infection that can become systemic.

    • Mostly caused by S. aureus and Streptococcus pyogenes.

Other Bacterial and Viral Infections

  • Necrotizing Fasciitis:

    • Caused by S. pyogenes.

    • Rapid tissue destruction and systemic symptoms may occur.

  • Viral Diseases:

    • Poxviruses: Smallpox eradicated through vaccination.

    • Herpes: Herpes virus types 1 and 2 cause skin lesions and are common in adults.

    • Warts: Caused by papillomaviruses; some strains linked to cancer.

Mycoses of the Hair, Nails, and Skin

  • Superficial Mycoses:

    • Common fungal infections caused by Malassezia.

    • Signs include hypo- or hyperpigmented skin patches.

  • Cutaneous Mycoses:

    • Caused by dermatophytes leading to conditions like athlete's foot and ringworm.

Parasitic Infestations

  • Leishmaniasis:

    • Caused by Leishmania from sand fly bites, leading to skin lesions.

  • Scabies:

    • Caused by Sarcoptes scabiei, producing intense itching and rash.

    • Transmitted through prolonged body contact and poor hygiene.