Diseases of the Cardiovascular and Lymphatic Systems – Comprehensive Study Notes

Learning Objective

• Identify microbes associated with systemic infections of the cardiovascular and lymphatic systems.

Key Definitions

• Bacteremia – bacteria present in blood.
• Fungemia – fungi present in blood.
• Viremia – viruses present in blood.
• Parasitemia – parasites present in blood.
• Toxemia – microbial toxins circulating in blood.

Clinical Consequences of Bloodstream Infection

• Sepsis – systemic inflammatory response to circulating microbes or their toxins.
• Septic shock – life-threatening hypotension caused by endotoxins (disseminated intravascular clotting) or exotoxins; vessels collapse.
• Septicemia – rapid multiplication of pathogens in blood.
  • Progresses from bacteremia, fungemia, viremia.
  • Frequency: Gram + common, Gram - common, fungi rare, viruses rare.
  • Host response: fever, chills, bradycardia.
  • Often lethal.

Intravascular Infections

• Endocarditis – infection of heart endocardium/valves.
• Thrombophlebitis – infection of veins.
• Endoarteritis – infection of arteries.

Infectious Endocarditis (Bacterial)

• Typically forms on damaged valves/septa/shunts.
• Circulating pathogens adhere to fibrin & platelets on damaged endothelium (e.g., atherosclerosis).
• Altered blood flow → part of Virchow’s Triangle (endothelial injury, stasis/turbulence, hyper-coagulability).

Overview of Major Bacterial Circulatory Infections

• Plague (bubonic, septicemic, pneumonic)
• Tularemia
• Brucellosis
• Lyme disease
• Relapsing fever

Plague – Yersinia pestis

• Most virulent bacterial infection recorded historically.
• Spreads: lymph nodes → blood → lungs.

Bubonic Plague

• Vector: rat flea Xenopsylla cheopis.
• Reservoirs: rats, prairie dogs.
• Pathogenesis
  • Incubation 2!–!7 days.
  • Flea ingests bacteria, organisms block foregut, are regurgitated during next bite.
  • Bacteria multiply in lymph nodes → buboes.
  • Symptoms: fever, painful lymphadenopathy; person-to-person spread rare.
  • Septic shock can cause death within one week.

Septicemic Plague

• Occurs when organisms overwhelm lymph nodes and enter systemic circulation.
• S/S: hypotension, fever, hepatomegaly, delirium, seizures; may be fatal before classic signs appear.

Pneumonic Plague (“Black Death”)

• Most deadly form; mortality within 24!–!48 h.
• Transmission: inhalation of respiratory droplets.
• Cultural reference: nursery rhyme “Ring around the Rosy.”

Tularemia – Francisella tularensis (“Rabbit Fever”)

• Worldwide across Northern Hemisphere; wild animals asymptomatic.
• Transmission: tick bite, ingestion (meat/water), direct contact through skin breaks, inhalation.
• Incubation 2!–!5 days.
• Local ulcer → deeper granulomas.
• Clinical forms
  • Ulceroglandular – ulcerated necrotic lesion + regional lymphadenopathy.
  • Oculoglandular – purulent conjunctivitis.
  • Typhoidal – ingestion of large inoculum; malaise, bradycardia, rash (typhoid-like).
• Can form abscesses in multiple organs.

Brucellosis – Brucella spp.

• Zoonosis of cattle reproductive tract.
• Transmission: occupational exposure, unpasteurized dairy/meat, inhalation, mucous-membrane or skin contact.
• Incubation 1!–!3 weeks.
• Symptoms
  • Undulating (“drenching”) night sweats, fever up to (40^{\circ}C),
  • Headache, myalgia, weight loss, splenomegaly, hepatomegaly, lymphadenopathy.
• Chronic course: weeks → years.

Lyme Disease – Borrelia burgdorferi

• Vector: deer tick Ixodes dammini; reservoir: white-footed mice; deer support adult feeding/mating.

Two-Year Tick Life Cycle

1. Spring Year 1 – eggs hatch to 6-legged larvae.
2. Summer – larvae feed on small mammals, may acquire infection.
3. Larvae dormant over winter → 8-legged nymphs.
4. Spring Year 2 – nymphs quest & feed (most human transmission).
5. Summer – nymphs develop to adults.
6. Fall/Winter – adults feed/mate on deer; females lay eggs.

Acute Lyme Disease

• Incubation: days–weeks.
• S/S: fever, migratory bull’s-eye rash (erythema migrans), myalgia, arthralgia, meningeal irritation.
• Primary skin lesion resolves but other symptoms may persist.

Chronic / Secondary Stage

• Begins days → months later.
• Meningitis, facial nerve palsy, peripheral neuropathy, myocarditis, cardiomegaly.

Late Stage

• CNS sequelae: memory, mood, sleep disorders.
• Disabling arthritis (esp. knee) with bone erosion may appear weeks → years post-infection.
• Highly variable; called “The Great Imitator.” Rarely fatal but a source of chronic illness if untreated.

Relapsing Fever – Borrelia spp.

• Vectors: soft ticks or body lice.

Tick-Borne Form

• Usually 2!–!3 relapses; fatalities rare.

Louse-Borne Form

• 10+ relapses; mortality \approx 40\% if untreated.
• Death from myocarditis, cerebral hemorrhage, or hepatic failure.

Pathogenesis (Both Forms)

• Primary attack: fever, myalgia, weakness; resolves ~7 days.
• Relapses correspond to waves of spirochetemia; during remission organisms sequester in organs.

Rickettsial Infections (Obligate Intracellular Coccobacilli)

• General features: fever, rash, myalgia; potential vascular collapse.
• Transmitted by arthropod vectors.

Rocky Mountain Spotted Fever (RMSF) – Rickettsia rickettsii

• Most prevalent rickettsiosis in U.S.; vector: various hard ticks.
• Incubation 2!–!6 days.
• Rash: starts on soles, palms, wrists, ankles → spreads toward trunk (appears day 3). Children often misdiagnosed as measles.
• Other S/S: fever, headache, muscle pain, mental confusion.

Typhus Group

Endemic (Murine) Typhus – R. typhi

• Vector: rat flea Xenopsylla cheopis; reservoir: rats.
• Within 2 weeks: fever, headache, myalgia, truncal rash spreading outward. Low mortality.

Epidemic Typhus – R. prowazekii

• Vector: human body louse Pediculus corporis; flourishes in crowded unhygienic settings.
• Infection via louse feces contaminating eye, respiratory tract, or skin.
• Incubation ≈ 2 weeks → fever, headache, rash trunk → extremities.
• Complications: myocarditis, neurologic dysfunction.

Viral Blood Infections

Epstein–Barr Virus (EBV, HHV-4)

• Affinity for B lymphocytes.
• Causes infectious mononucleosis and Burkitt’s lymphoma.
• Not highly contagious; requires repeated intimate contact (“kissing disease”).
• S/S: fever, malaise, pharyngitis, tender lymph nodes, splenomegaly; lasts weeks–months.
• Complications in 1!–!5\%: laryngeal obstruction, meningitis, encephalitis, hemolytic anemia, thrombocytopenia, splenic rupture.
• Chronic infection associated with oral hairy leukoplakia in immunosuppressed.

Arboviruses (Mosquito-Borne)

Yellow Fever (Flavivirus)

• Target organ: liver; also kidneys, brain, heart.
• Hepatocyte necrosis → jaundice.
• Abrupt onset: fever, chills, headache, bradycardia, hemorrhage, shock.

Dengue Fever (“Breakbone Fever”)

• Endemic Puerto Rico, Caribbean, Hawai‘i; vector: Aedes aegypti.
• S/S: fever, maculopapular rash, severe musculoskeletal pain.
• Severe dengue: shock, pleural effusion, hemorrhage, death.

Filovirus Fevers – Ebola & Marburg

Ebola Virus

• Person-to-person transmissible; exact vector & reservoir unknown.
• Mortality (80!–!90\%); more lethal than Marburg.
• Incubation 4!–!6 days.
• Massive hemorrhage from skin, mucosa, liver, lymphoid tissue, kidneys, gonads.
• Likely infects vascular endothelial cells → vascular leakage & shock.

Parasitic Blood Infections

Trypanosomiasis (Hemoflagellates)

Chagas’ Disease – Trypanosoma cruzi

• Vector: reduviid “kissing” bug; parasites in bug feces inoculated near bite (often lips/eyes).
• Acute febrile illness; disseminates to heart, skeletal muscle, glia.
• Duration up to 3 months; children most affected.
• Epidemiology: 16!–!18 million infected/year; \approx 50{,}000 deaths; leading cause of infectious cardiomyopathy; accounts for 25\% of deaths in untreated 25–44 y/o adults.

African Sleeping Sickness – Trypanosoma brucei

• Vector: tsetse fly.
• Chronic (T. b. gambiense) – \approx 95\% of cases; narcolepsy-like signs; targets CSF & meninges.
• Acute (T. b. rhodiense) – reservoir in wild ungulates; coma, convulsions, death within 4 months; target organ = brain.

Filariasis – Wuchereria bancrofti & Brugia malayi

• Threadlike nematodes inhabit lymphatics for decades.
• Females release millions of microfilariae → lymphatic blockage.
• Pathogenesis driven by molting/dying worms →
  • Lymphatic dilation & endothelial hyperplasia.
  • Granulomatous inflammation, fibrosis, permanent obstruction.
  • Fluid accumulation in skin/subcutis → elephantiasis of limbs & genitalia.
  • Prone to secondary bacterial superinfection.

Ethical / Practical Connections & Exam Tips

• Many pathogens exploit arthropod vectors; control of vectors (ticks, fleas, mosquitoes, lice) remains cornerstone of prevention.
• Climate change & human encroachment influence vector range (e.g., dengue in subtropics).
• Zoonotic transmission highlights importance of food safety (pasteurization, meat inspection) & occupational health.
• Diseases with overlapping, non-specific presentations (Lyme, RMSF, EBV) demand careful differential diagnosis.
• High-mortality infections (plague, Ebola, septic shock) illustrate urgency of rapid identification, isolation, and supportive care.
• Chronic sequelae (Chagas’ cardiomyopathy, filarial elephantiasis, Lyme arthritis) emphasize that “survival” ≠ “recovery.”
• Remember classic rash patterns:
  • RMSF: extremities → trunk.
  • Typhus: trunk → extremities.
• Know incubation periods and vector/reservoir pairs—they are frequent exam questions.