Microbial Cardiovascular and Systemic Diseases: Study Notes

Microbial Cardiovascular and Systemic Diseases

Structures of the Cardiovascular System

The cardiovascular system is essential for transporting blood, nutrients, and immune cells throughout the body. It consists of the heart, blood, and blood vessels, which include arteries, veins, and capillaries.

• Heart: Pumps blood into arteries, which are connected to veins via capillaries.

• Arteries: Carry blood away from the heart.

• Veins: Return blood to the heart.

• Blood composition: Includes serum (liquid part) and formed elements (erythrocytes, leukocytes, and platelets).

Bacterial Diseases of the Cardiovascular System

Septicemia, Bacteremia, and Toxemia

These conditions involve the presence and effects of microbes or their toxins in the blood, leading to systemic symptoms and potentially life-threatening complications.

• Bacteremia: Bacteria circulating and/or growing in the blood.

• Septicemia: Any microbial infection of the blood that produces illness, often with systemic symptoms and possible spread to other organs.

• Toxemia: Release of bacterial toxins into the blood.

• Lymphangitis: Infection and inflammation of lymphatic vessels, often a sign of septicemia.

Signs and Symptoms

• Fever, chills, nausea, vomiting, diarrhea, malaise

• Septic shock can develop rapidly

• Petechiae (small hemorrhagic lesions) suggest bacteremia

• Osteomyelitis may occur if bacteria invade bones

• Toxemia symptoms depend on the toxin: exotoxins (from living bacteria) and endotoxins (from Gram-negative bacteria)

Pathogenesis and Virulence Factors

• Septicemia and toxemia can be caused by various bacteria, more often Gram-negative.

• Opportunistic or healthcare-associated infections are common sources.

• Endotoxin release triggers severe symptoms.

• Bacterial capsules resist phagocytosis; siderophores acquire iron from blood.

Pathogenesis and Epidemiology

• Direct inoculation of bacteria into blood causes septicemia.

• Immunocompetent individuals rarely develop septicemia; infections are usually self-limited.

• Gram-negative bacteria often cause severe septicemia due to endotoxin release, activating defensive reactions in the body.

Endocarditis

Endocarditis is the inflammation of the endocardium, often involving the heart valves. It can lead to the formation of vegetations (masses of platelets and microbes) on valves, impairing heart function.

• Signs and symptoms: Fever, fatigue, malaise, difficulty breathing, tachycardia, and heart valve vegetations.

• Pathogens: Usually caused by normal microbiota, such as Staphylococcus epidermidis (subacute) and viridans streptococci (often from the mouth).

• Pathogenesis: Patients often have an obvious source of infection or abnormal heart valves. Emboli can block blood vessels in other organs.

• Diagnosis: Based on symptoms and echocardiogram visualization of vegetations.

• Treatment: Intravenous antibacterial drugs; prophylactic antibiotics for high-risk patients.

Brucellosis

Brucellosis is a zoonotic infection caused by Brucella melitensis, often acquired from contaminated dairy products or contact with infected animals.

• Signs and symptoms: Fluctuating fever that spikes every afternoon.

• Pathogenesis: Endotoxin contributes to symptoms; transmission via dairy or animal contact.

• Diagnosis: Serological tests and fever pattern.

• Treatment: Usually not required; animal vaccine available.

Tularemia (“Rabbit Fever”)

Tularemia is caused by Francisella tularensis, a highly infectious bacterium with a wide host range. It can survive inside host cells and is transmitted by ticks or contact with infected animals.

• Signs and symptoms: Skin lesions, swollen lymph nodes, ascending lymphangitis; can be fatal but responds to aminoglycosides.

• Pathogenesis: Entry through skin or tick bite; highly infectious (low ID50); highest risk for those handling dead animals.

• Diagnosis: Difficult; requires serological confirmation.

• Treatment: Antimicrobials; vaccine for at-risk individuals.

The Plague

The plague, caused by Yersinia pestis, is one of history’s most devastating diseases. It has multiple virulence factors and can present as bubonic or pneumonic plague.

• Bubonic plague: Enlarged lymph nodes (buboes).

• Pneumonic plague: Infection spreads to lungs, causing severe respiratory symptoms.

• Transmission: Contact with infected animals or flea feces; pneumonic form can be transmitted via aerosols.

• Mortality: Bubonic (50% untreated), pneumonic (100% untreated).

• Prevention: Rodent and flea control, hygiene.

Transmission Cycles

• Sylvatic plague: Maintained in wild rodents, transmitted by fleas.

• Urban plague: Epidemics occur when pneumonic form spreads among humans.

Lyme Disease

Lyme disease is a tick-borne illness caused by the spirochete Borrelia burgdorferi. It evades the immune system by altering membrane proteins and using manganese instead of iron.

• Vector: Deer ticks (Ixodes species).

• Signs and symptoms: Three phases—bull’s-eye rash, neurological symptoms, severe arthritis.

• Epidemiology: Most reported vector-borne disease in the US; increased due to human encroachment, deer protection, and changes in predator populations.

• Diagnosis: Based on symptoms; bacterium rarely detected in blood.

• Treatment: Early—doxycycline, amoxicillin; late—ceftriaxone, penicillin.

• Prevention: Tick repellents, protective clothing.

Ehrlichiosis and Anaplasmosis

These emerging tick-borne diseases are caused by Ehrlichia chaffeensis and Anaplasma phagocytophilum, respectively. Both bacteria live inside host cells and are transmitted by ticks.

• Signs and symptoms: Flu-like illness, leukopenia, thrombocytopenia.

• Diagnosis: Difficult due to non-specific symptoms; antimicrobials are effective.

• Prevention: Avoid tick-infested areas, use repellents and protective clothing.

Viral Cardiovascular and Systemic Diseases

Yellow Fever

Yellow fever is a mosquito-borne viral disease caused by the yellow fever virus and transmitted by Aedes aegypti mosquitoes.

• Signs and symptoms: Three stages—initial fever, remission, then severe symptoms (delirium, hemorrhaging).

• Pathogenesis: Virus replicates in the liver; endemic in South America and Africa.

• Diagnosis: Detection of viral antigens in blood.

• Treatment: Supportive; vaccine provides lifetime protection.

Infectious Mononucleosis (“Kissing Disease”)

Caused by Epstein-Barr virus (EBV/HHV-4), which establishes latent infection in B cells and is transmitted via saliva.

• Signs and symptoms: Severe sore throat, fever, swollen lymph nodes, tonsils, fatigue, appetite loss, rash, leukocytosis.

• Pathogenesis: Infects B lymphocytes; long incubation (30–50 days); asymptomatic in many adults.

• Diagnosis: Large, lobed B lymphocytes and neutropenia.

• Treatment: Symptom relief; no vaccine available.

Cytomegalovirus Disease

Cytomegalovirus (CMV) infection is common and usually asymptomatic, but can cause severe complications in fetuses, newborns, and immunodeficient individuals.

• Transmission: Direct contact with bodily fluids or transplacentally.

• Diagnosis: Enlarged cells with inclusions.

• Treatment: Fomivirsen for eye infections; no vaccine.

Dengue Fever and Dengue Hemorrhagic Fever

Dengue viruses (four strains) are transmitted by Aedes mosquitoes. Dengue fever is usually mild, but dengue hemorrhagic fever can be fatal.

• Signs and symptoms: Fever, edema, muscle/joint pain, rash; severe cases involve internal bleeding and shock.

• Diagnosis: Based on symptoms and travel history.

• Treatment: Supportive; prevention focuses on mosquito control.

African Viral Hemorrhagic Fever

Caused by Ebolavirus or Marburgvirus, these diseases are characterized by fever, fatigue, and severe internal hemorrhaging due to malfunctioning blood clotting.

• Transmission: Contact with bodily fluids of infected individuals.

• Diagnosis: Symptoms and virus detection in blood.

• Treatment: Fluid and electrolyte replacement; vaccines under study.

Protozoan and Helminthic Cardiovascular and Systemic Diseases

Malaria

Malaria is caused by Plasmodium species and transmitted by female Anopheles mosquitoes. Disease severity depends on the species, with P. falciparum being the most severe.

• Signs and symptoms: Fever, chills, diarrhea, headache, anemia, weakness, fatigue.

• Virulence factors: Immune evasion, toxin secretion, adhesins, and altered body chemistry to attract mosquitoes.

• Diagnosis: Identification of Plasmodium in blood.

• Treatment: Various antimalarial drugs; some resistance exists.

• Prevention: Mosquito control and use of bed nets.

Toxoplasmosis

Toxoplasmosis is caused by Toxoplasma gondii, with cats as the definitive host. Most cases are asymptomatic, but immunocompromised individuals and fetuses are at risk for severe disease.

• Transmission: Undercooked meat, contact with cat feces, or transplacental.

• Diagnosis: Detection of organisms in tissues.

• Treatment: Needed for AIDS patients, pregnant women, and newborns.

Chagas’ Disease (American Trypanosomiasis)

Chagas’ disease is caused by Trypanosoma cruzi and is endemic in Central and South America. It is transmitted by Triatoma bugs or blood transfusion.

• Signs and symptoms: Swelling at infection site, chronic symptoms years later.

• Diagnosis: Microscopic identification or xenodiagnosis.

• Treatment: Late stages cannot be treated; prevention involves avoiding Triatoma bugs.

Schistosomiasis (Blood Fluke)

Schistosomiasis is caused by Schistosoma species, with mammals as the definitive host. It is not found in the United States.

• Signs and symptoms: Swimmer’s itch at infection site; eggs cause systemic symptoms.

• Diagnosis: Identification of eggs in stool or urine.

• Treatment: Praziquantel; prevention by avoiding contaminated water.