Study Notes on Microbial Diseases of the Cardiovascular and Lymphatic Systems

MICROBIAL DISEASES OF THE CARDIOVASCULAR AND LYMPHATIC SYSTEMS

Overview of Blood and Lymphatic Systems

  • Human Microbiome Project Findings

    • Recent data suggests that blood is not sterile.

    • The blood can tolerate or resist moderate numbers of pathogens without harm.

    • Blood is low in iron; bacterial growth requires iron.

    • Hemolysis liberates iron, increasing pathogen growth.

  • Defensive Mechanisms

    • Blood contains numerous defensive phagocytic cells.

    • Lymph vessels are very permeable, picking up microbes and their products and returning them to the blood.

    • In hospitals, invasive procedures (needles, catheters, tubes) can lead to frequent contamination.

Bacteremia, Septicemia, and Toxemia

  • Definitions

    • Bacteremia: Presence of bacteria within the bloodstream; a transient condition.

    • Can be introduced by flossing, catheter insertion, injection, etc.

    • Generally clears within days and is not considered a blood infection.

    • Septicemia (Sepsis): Uncontrolled proliferation of bacteria in the bloodstream.

    • Can be fatal.

    • Toxemia: Presence of toxins in blood, for example, tetanospasmin.

    • May arise from a focal infection of bacteria, spreading toxins through blood or lymph.

Signs and Symptoms of Sepsis

  • General Response

    • The inflammatory response to infectious agents in the blood typically results in the release of cytokines, leading to:

    • Fever, chills.

    • Vessels leaking fluid, resulting in decreased blood pressure (BP).

    • Increased heart rate (HR) and respiratory rates.

    • Severe Sepsis: Sepsis resulting in a drop in BP and dysfunction of at least one organ.

    • Septic Shock: Blood infection resulting in pathological low blood pressure, decreased blood flow to organs, leading to coma or death.

  • Lymphangitis: Inflammation of lymph vessels, often visible as red streaks under the skin running from the site of infection to the lymph node, where it often stops. Tender to touch.

Anthrax

  • Etiology: Caused by Bacillus anthracis, a Gram-positive, aerobic, endospore-forming bacterium.

    • Infects primarily grazing animals; humans can be infected through animal products.

  • Transmission: Endospores ingested with grass cause fatal animal sepsis.

  • Types of Anthrax:

    1. Cutaneous Anthrax:

    • Accounts for 90% of cases; mortality rate of 10-20% if untreated.

    • Pathogenesis: Endospores enter through cuts, leading to exotoxin damage and ulceration.

      • Symptoms include a painless black eschar, low-grade fever, malaise.

      • Risk of developing septic shock if bacteria enter the blood from eschar area.

    1. Inhalational Anthrax:

    • Can lead to severe illness or death within one day.

    • Symptoms initially may appear as mild pneumonia; untreated can lead to high fever, hemorrhagic lung complications, septicemia, and death within 1-3 days.

      • Identification (ID50): 2-9 spores.

    1. Gastrointestinal and CNS Anthrax: Less common.

  • Virulence Factors:

    • Exotoxin (A-B type toxins) comprising edema toxin (causes local edema) and lethal toxin (kills host cells and impairs immune response).

    • Capsule made of amino acids that evade immune recognition.

Gangrene

  • Definition: Condition caused by loss of blood supply to a tissue, resulting in localized soft tissue necrosis.

  • Types of Gangrene:

    1. Dry Gangrene: Caused by insufficient blood flow (e.g., atherosclerosis).

      • Symptoms: Tissue drying up, shriveling, blackening.

    2. Wet Gangrene: Results from insufficient blood flow combined with bacterial infection (e.g., burns, frostbite).

      • Symptoms: Tissue appearing bruised, swollen, and decomposing.

    3. Gas Gangrene: Caused by Clostridium perfringens

      • Combination of ischemia and anaerobic bacterial infection leading to extensive tissue damage and gas formation.

      • Symptoms include swelling, discoloration, severe pain, and the presence of gas-filled vesicles.

      • Treatment includes debridement, antibiotics, and in severe cases, amputation.

Plague

Overview

  • Etiology: Caused by Yersinia pestis, a Gram-negative rod.

  • Reservoirs and Vectors:

    • Commonly endemic in wild rodents (rats, squirrels).

    • Transmitted primarily by fleas (e.g., Xenopsylla cheopis).

  • Transmission:

    • Zoonotic transmission through flea bites, contact with infected fluids, and respiratory droplets from infected hosts.

Forms of Plague

  1. Bubonic Plague:

    • Initial infection from flea to lymph nodes leading to buboes (painful, swollen lymph nodes).

    • Symptoms: High fever, buboes, and possible necrosis.

  2. Septicemic Plague:

    • Occurs if bubonic plague is untreated, leading to bacteria in the blood, resulting in shock.

    • Symptoms include black spots on the skin, high fever, and shock.

  3. Pneumonic Plague:

    • Develops from the septicemic form or direct airborne transmission.

    • Highly contagious with symptoms appearing 2 days post-inhalation; high mortality rate without treatment.

  • Control: Rapid recognition and treatment are crucial; vaccine development ongoing.

Lyme Disease

  • Etiology: Caused by Borrelia burgdorferi, a spirochete.

  • Vector: Transmitted primarily through the bite of black-legged ticks (Ixodes scapularis).

  • Transmission: Requires tick attachment for 24-48 hours before bacteria transfer occurs, making only 1% of bites lead to infection.

  • Symptoms:

    • Phase 1: Bull’s-eye rash at the bite site, flu-like symptoms.

    • Phase 2: Dissemination causing chronic complications like arthritis, cardiac irregularities, neurological issues.

    • Phase 3: Possible long-term neurological manifestations unrelated to persistent infection.

  • Prevalence: Approximately 30,000 cases annually in the U.S.

Filariasis and Elephantiasis

  • Etiology: Caused by Wuchereria bancrofti, a nematode.

  • Vector: Transmitted via mosquitoes, primarily in Africa and Asia.

  • Pathogenesis: Nematode larvae injected into the lymphatic system, leading to blockage and resulting in gross limb or scrotal swelling.

Septicemic Meningococcemia

  • Etiology: Caused by Neisseria meningitidis, which can lead to meningitis or septicemia.

  • Pathogenesis: Release of endotoxins promotes a severe inflammatory response, leading to vascular collapse and septic shock.

  • Symptoms: Sudden onset of high fever, petechial rash, rapid progression to shock and potential gangrene.

Ebola Virus Disease

  • Etiology: Caused by the Ebola virus, with zoonotic transmission from various animal reservoirs.

  • Transmission: Direct contact with infected blood or body fluids; not airborne.

  • Symptoms and Pathogenesis:

    1. Incubation period of 3-21 days, initially presenting as severe weakness, fever, and digestive tract symptoms.

    2. Hemorrhaging may occur, with the potential for multi-organ failure and shock.

Endotoxin Effects in Gram-Negative Sepsis

  • Mechanism: Gram-negative bacterial cell walls release the endotoxin Lipid A, triggering the immune response.

  • Cytokine Release: Endotoxin stimulates macrophages to release cytokines like TNF and IL-1, leading to vascular damage and septic shock.

Conclusion

  • Understanding these various microbial diseases affecting the cardiovascular and lymphatic systems is crucial for effective prevention, diagnosis, and treatment.