Infections of the Heart

Rheumatic Heart Disease and Related Conditions

• Rheumatic heart disease results from immune damage due to untreated Streptococcus pyogenes pharyngitis.
• Myocarditis can be caused by Coxsackie B virus and circulating diphtheria toxin.
• Acute benign pericarditis is often viral, while bacterial pericarditis presents a greater risk.
• Vascular inflammation from infections contributes to plaque formation and is significant in atherosclerosis.

Infective Endocarditis (IE)

• Endocarditis is inflammation of the heart endothelium, often affecting heart valves.
• It can be infectious or autoimmune. Fever occurs in 90% of patients; ~85% exhibit heart murmurs.
• Diagnosis follows Duke Criteria, which involve identifying microbes through blood cultures.

Key Microorganisms for Blood Cultures in IE

• Typical microorganisms include:
  • Viridans streptococci
  • Streptococcus bovis
  • HACEK group
  • Staphylococcus aureus
• Persistent positives are defined as:
  • At least two positive cultures drawn 12 hours apart.
  • Majority of four cultures positive, with the first and last drawn at least one hour apart.

Source of Causative Agents

• Causative agents are mostly normal flora but can also be pathogens or contaminants.
• Key risk factors include oral healthcare procedures, dental work, and poor hygiene.
• Staphylococcus aureus, a coagulase-positive organism, is often linked to infections.

Virulence of Staphylococcus aureus

• Clumping factor aids attachment to fibrinogen on endothelial surfaces.
• Coagulase converts fibrinogen to fibrin, shielding bacteria from phagocytosis.
• Alpha toxin creates pores in cell membranes, causing cell leakage and contributing to infection.
• Produces various enzymes and toxins, enhancing virulence and tissue injury.

Medically Important Staphylococci

• Staphylococcus aureus:
  • Coagulase-positive and beta-hemolytic.
  • Associated with conditions like abscesses, endocarditis, toxic shock syndrome, and osteomyelitis.

Antibiotic Classes and Their Mechanisms

• Penicillins (e.g., Ampicillin, Nafcillin):

  • Mechanism: Cell wall synthesis inhibition.
  • Side effects: Hypersensitivity reactions.

• Cephalosporins:

  • Mechanism: Similar to penicillin with enhanced efficacy against Staph.

• Vancomycin:

  • Mechanism: Cell wall elongation inhibition.
  • Side effects: Nephrotoxicity, ototoxicity.

• Daptomycin:

  • Mechanism: Depolarizes cell membranes.
  • Side effects: Muscle aches.

• Aminoglycosides:

  • Mechanism: 30S ribosomal inhibition for protein synthesis.
  • Side effects: Nephrotoxicity, ototoxicity.

• Rifampin:

  • Mechanism: RNA polymerase inhibition.
  • Side effects: Hepatotoxicity.

• Fluoroquinolones:

  • Mechanism: Topoisomerase inhibition.
  • Side effects: Tendon-related issues.

Lyme Disease Management

• Infection prevention involves proper clothing, repellents, and regular tick inspections.
• Early Lyme disease is treated with oral doxycycline; severe cases require systemic treatment.
• Reinfection is possible if treatment occurs before immunity develops.

Relapsing Fever

• Characterized by recurring febrile episodes, often with headaches and muscle aches.
• Antigenic variation leads to relapses.

Types of Relapsing Fever

• Tick-borne Relapsing Fever (TBRF):

  • Caused by Borrelia species transmitted via infected ticks.
  • More prevalent in summer; ~25 cases reported annually in the U.S.

• Louse-borne Relapsing Fever (LBRF):

  • Caused by Borrelia recurrentis, transmitted human-to-human via body lice.
  • Associated with high mortality rates in outbreaks, especially in Africa.

• Typical TBRF experience involves 1-4 fever episodes before resolution.

This quiz covers various cardiovascular diseases including Rheumatic heart disease, Myocarditis, and Pericarditis, highlighting their causes and implications. It also touches on Infective Endocarditis and its effects on the heart. Test your understanding of these critical conditions and their infectious origins.