Microbial Diseases Summary

Microbial Diseases Overview

  • Summary of chapters 21-26, covering typical microbial diseases in different human organ systems.
  • Links to NIH and CDC websites for further information on diseases and vaccines.

Microbial Diseases of the Skin

  • Definitions:
    • Vesicles: Small fluid-filled lesions.
    • Bulla/Bullae: Vesicles larger than 1 cm in diameter.
    • Macules: Flat lesions.
    • Pustule/Papule: Raised lesions.
    • Exanthem: Skin rash arising from a disease (e.g., measles).
    • Enanthem: Rash occurring on mucous membranes.

Staphylococcus Skin Infections

  • Coagulase activity test: Differentiates pathogenic from non-pathogenic Staphylococcus.
    • Coagulase: Enzyme that clots fibrin in the blood.
    • Procedure: Suspend isolated culture in plasma; check for clot formation.
    • Positive result: Gel-like substance forms (pathogenic strain).
    • Negative result: Remains liquid (non-pathogenic strain).
    • Example: Staphylococcus aureus is coagulase-positive, while Staphylococcus epidermidis is coagulase-negative.
  • Staphylococcus epidermidis: Normal skin flora but also a healthcare-associated (nosocomial) pathogen (opportunistic).
  • Folliculitis: Infection of hair follicles.
  • Stye: Infection of an eyelash follicle.
  • Furuncle: Boil with abscess surrounded by inflamed tissue.
  • Carbuncle: Spreading furuncle deeper into the tissue.
  • Impetigo: Crusty sores spread by autoinoculation (touching and spreading to other areas).
  • Scaled Skin Syndrome: Staphylococcus infection resembling burns, caused by a toxin (exfoliation).
  • Bullous Impetigo: Caused by toxins that exfoliate the skin.
  • Pemphigus Neonatorum: Impetigo in newborns.
  • Toxic Shock Syndrome (TSS): Caused by Staphylococcus using superantigen Toxic Shock Syndrome Toxin-1 (TSST-1).
    • Often seen in women using tampons or intravaginal contraceptives; can also occur post-surgery due to poor hygiene.

Streptococci

  • Virulence factors: Lyse red blood cells (beta-hemolytic).
  • Capsules: Present, especially in pathogenic forms.
  • Antigenic carbohydrates: A through T, used for classification.
  • Group A Streptococci (GAS): Streptococcus pyogenes.
    • Produces streptolysin (beta-hemolytic toxin).
    • Hyaluronidase: Dissolves connective tissue.
    • Proteins: Adherence and penetration.
  • Diseases caused by Group A Streptococci:
    • Erysipelas: Infection of the dermal layer causing tissue destruction and potential sepsis.
    • Necrotizing Fasciitis (Flesh-eating disease): Produces superantigen exotoxin A, leading to immune overreaction and tissue degradation.
    • Streptococcal Toxic Shock Syndrome: Similar to staphylococcal TSS.

Pseudomonas Aeruginosa

  • Gram-negative bacillus; produces blue-green pigment (pyocyanin).
  • Pus from infected wounds appears bluish-green.
  • Endotoxin in outer membrane; produces exotoxins.
  • Grows as biofilms.
  • Causes:
    • Self-limiting rash (Pseudomonas dermatitis) in poorly chlorinated pools.
    • Swimmer's ear (otitis externa).
    • Opportunistic infections in burn patients (nosocomial).
    • Resistant to many antibiotics.

Acne

  • Common skin disease caused by blocked sebum production.
  • Comedonal acne: Mild, treated with topical benzoyl peroxide.
  • Inflamed acne: Propionibacterium acnes; treated with benzoyl peroxide.
  • Nodular cystic acne: Severe inflammation and pus deep in the skin.

Viral Diseases of the Skin

  • Often transmitted via the respiratory route.

Warts (Papillomas)

  • Small skin growths transmitted by contact and respiratory route, caused by human papillomavirus (HPV).
  • Over 50 types; lower numbers = lower cancer risk; higher numbers = greater cancer risk (skin or cervical).
  • Treatment: Cryotherapy (freezing).
  • Vaccine: Gardasil, protective in males and females against cancer.

Smallpox

  • Only disease eradicated from the human population due to vaccination (orthopoxvirus).
  • Variola major (higher mortality) and minor.
  • Transmitted via respiratory route.
  • Potential bioterrorism agent; Defense personnel are still vaccinated.

Monkeypox

  • Related to smallpox; jumps from animals to humans.
  • Smallpox vaccine provides cross-protection.

Chickenpox (Varicella) and Shingles (Herpes Zoster)

  • Caused by human herpesvirus 3; transmitted through respiratory route.
  • Causes pus-filled vesicles; Reye's syndrome (neurodegeneration).
  • Aspirin use increases the risk of Reye's syndrome during chickenpox.
  • Virus becomes latent in central nerve ganglia; reactivation = shingles/herpes zoster.
  • Live attenuated vaccine available.
  • Shingles vaccine recommended for those over 50 who have had chickenpox.
  • Triggers for reactivation: Immunosuppression, stress, certain medications.
  • Reactivation follows nerve paths (dermatomal distribution).
  • Postherpetic neuralgia: Severe pain after shingles.

Herpes Simplex Virus (HSV)

  • HSV-1: Oral/respiratory transmission; causes cold sores/fever blisters.
  • HSV-2: Sexual contact; causes genital herpes.
  • HSV-1: Latent in trigeminal nerve ganglia; reactivation = cold sores.
  • HSV-2: Latent in sacral nerve ganglia; reactivation = vesicles on skin, fingers, or brain.
  • Herpes Simplex Gladiatorum: Reactivation of HSV on the skin, seen in wrestlers and gladiators.
  • Whitlow: Vesicles on fingers.
  • Encephalitis: Spread to the brain.
  • Treatment: Acyclovir (antiviral).

Measles (Rubeola)

  • Transmitted by respiratory route.
  • Causes macular rash.
  • Koplik's spots: Red spots on oral mucosa (diagnostic).
  • Potential complication: Subacute sclerosing panencephalitis (SSPE).
  • MMR vaccine: Very protective.
  • Infants under one year cannot receive the vaccine, making herd immunity critical.

German Measles (Rubella)

  • Part of MMR vaccine (rubella virus).
  • Congenital Rubella Syndrome: Fetal damage, heart defects, mental retardation, mortality.
  • Not recommended for pregnant women; vaccination should occur before pregnancy planning.

Other Viral Rashes

  • Fifth disease (Erythema Infectiosum): Caused by parvovirus; facial rash (