Diseases of the Cardiovascular and Lymphatic Systems

Overview of the Cardiovascular and Lymphatic Systems

The cardiovascular system consists of the heart, blood, and blood vessels, responsible for transporting nutrients, gases, and waste products throughout the body. The lymphatic system is a network of vessels and nodes that returns interstitial fluid (lymph) to the bloodstream and plays a critical role in immune defense by filtering pathogens and housing immune cells.

• Plasma leaves blood capillaries to become interstitial fluid, which bathes tissues.

• Lymph capillaries collect interstitial fluid and transport it through lymphatic vessels and nodes back to the blood.

• Lymph nodes contain fixed macrophages, B cells, and T cells, which are essential for immune responses.

• Buboes are swollen lymph nodes, often a sign of infection.

Sepsis and Septic Shock

Sepsis is a systemic inflammatory response to infection, often caused by the spread of bacteria or their toxins in the blood. It can progress to severe sepsis and septic shock, which are life-threatening conditions.

• Septicemia: Persistent pathogens or toxins in the blood.

• Sepsis: Systemic inflammatory response syndrome (SIRS) due to infection.

• Severe sepsis: Sepsis with decreased blood pressure and organ dysfunction.

• Septic shock: Sepsis with uncontrollable low blood pressure, often due to massive endotoxin release.

• Lymphangitis: Inflammation of lymph vessels, often seen as red streaks under the skin, indicating septicemia.

Gram-Negative and Gram-Positive Sepsis

Sepsis can be caused by both gram-negative and gram-positive bacteria, each with distinct mechanisms and clinical implications.

• Gram-negative sepsis: Caused by endotoxins from bacteria such as Klebsiella spp., Escherichia coli, and Pseudomonas aeruginosa. Endotoxins trigger a drop in blood pressure and can worsen with antibiotic treatment due to toxin release.

• Gram-positive sepsis: Often associated with nosocomial infections and invasive procedures. Common agents include Group B Streptococcus (neonatal sepsis), Enterococcus faecium, and E. faecalis. Exotoxins may cause toxic shock syndrome.

Puerperal Sepsis (Childbirth Fever)

Puerperal sepsis is an infection of the uterus following childbirth, typically caused by Streptococcus pyogenes. It can spread to the abdominal cavity and is treated with antibiotics.

Bacterial Infections of the Heart

Bacterial infections can affect the heart, leading to inflammation and damage of cardiac tissues.

• Endocarditis: Inflammation of the endocardium, often caused by alpha-hemolytic streptococci (subacute) or Staphylococcus aureus (acute).

• Pericarditis: Inflammation of the pericardium, commonly due to streptococci.

Rheumatic Fever

Rheumatic fever is an autoimmune complication following Streptococcus pyogenes infection (e.g., strep throat). It primarily affects children and young adults, causing arthritis, fever, and inflammation of heart valves, which may lead to permanent damage.

• Symptoms include joint nodules, fever, and possible involuntary movements (Sydenham’s chorea).

• Treatment involves antibiotics and bed rest.

Tularemia

Tularemia is a zoonotic disease caused by Francisella tularensis, a gram-negative rod. It is transmitted from rabbits, ticks, and deer flies, and can infect humans through skin contact, inhalation, or ingestion.

• Symptoms include an ulcer at the entry site and swollen lymph nodes.

• Treatment: Streptomycin or tetracyclines for 10–21 days.

Brucellosis (Undulant Fever)

Brucellosis is caused by Brucella spp., gram-negative rods that grow in phagocytes. It is transmitted via unpasteurized milk or contact with infected animals.

• Symptoms: Undulating fever, night sweats, malaise, muscle aches, and weakness.

• Chronic infection can last for years but is rarely fatal.

Anthrax

Anthrax is caused by Bacillus anthracis, a gram-positive, endospore-forming rod found in soil. It produces two exotoxins (edema and lethal) and can infect humans via cutaneous, gastrointestinal, or inhalational routes.

• Cutaneous anthrax: Endospores enter through a cut (20% mortality).

• Gastrointestinal anthrax: Ingestion of contaminated food (40–50% mortality).

• Inhalational anthrax: Inhalation of endospores (>85% mortality).

• Treatment: Ciprofloxacin or doxycycline.

Gangrene

Gangrene is the death of soft tissue due to loss of blood supply (ischemia) and subsequent infection, most commonly by Clostridium perfringens, a gram-positive, endospore-forming anaerobic rod.

• Gas gangrene: Characterized by tissue swelling, necrosis, and gas production due to bacterial fermentation.

• Treatment: Surgical removal of necrotic tissue (debridement or amputation) and hyperbaric oxygen therapy.

Systemic Diseases Caused by Bites and Scratches

Bites and scratches from animals can introduce pathogens into the body, leading to local or systemic infections.

• Pasteurella multocida: Causes local infection, swelling, pneumonia, and sepsis.

• Bartonella henselae: Causes cat-scratch disease, characterized by papules and swollen lymph nodes.

Vector-Transmitted Bacterial Diseases

Plague

Plague is caused by Yersinia pestis, a gram-negative rod, and is transmitted by fleas (vector: Xenopsylla cheopis) from rodents to humans.

• Bubonic plague: Bacterial growth in blood and lymph, causing buboes.

• Septicemic plague: Bacteria spread to the bloodstream, causing septic shock.

• Pneumonic plague: Bacteria infect the lungs, transmitted by aerosol droplets.

• Treatment: Streptomycin and doxycycline; vaccine available.

Relapsing Fever

Caused by Borrelia spp. (spirochetes), transmitted by soft ticks from rodents. Characterized by recurring fever due to antigenic variation.

• Diagnosis: Bacteria in blood sample.

• Treatment: Tetracycline.

Lyme Disease

Lyme disease is caused by Borreliella burgdorferi and transmitted by deer ticks (Ixodes spp.).

• Reservoirs: Deer (adults), field mice (nymphs).

• Symptoms: Bull’s-eye rash, flu-like symptoms, irregular heartbeat, neurological symptoms, and arthritis.

• Treatment: Antibiotics (early stage).

Typhus and Rocky Mountain Spotted Fever

Caused by Rickettsia spp., obligate intracellular parasites transmitted by arthropod vectors.

• Epidemic typhus: R. prowazekii, transmitted by lice.

• Endemic murine typhus: R. typhi, transmitted by fleas.

• Rocky Mountain spotted fever: R. rickettsii, transmitted by ticks, causes a rash on palms and soles, fever, and headache.

• Treatment: Tetracycline and chloramphenicol.

Viral Diseases of the Cardiovascular and Lymphatic Systems

Infectious Mononucleosis

Caused by the Epstein-Barr virus (HHV-4), infectious mononucleosis is characterized by fever, sore throat, swollen lymph nodes, and fatigue. The virus infects B lymphocytes and is transmitted via saliva.

• Most adults carry antibodies; infection is usually mild or asymptomatic in children.

• Associated with certain cancers (e.g., Burkitt’s lymphoma, nasopharyngeal carcinoma).

Cytomegalovirus Infections

Caused by cytomegalovirus (HHV-5), which can cause asymptomatic or mild disease but may lead to severe complications in newborns and immunocompromised individuals.

• Transmitted via bodily fluids, blood, or transplanted tissue.

• Diagnosis: "Owl eyes" inclusion bodies in infected cells.

Viral Hemorrhagic Fevers

• Yellow fever: Arbovirus transmitted by Aedes aegyptii mosquitoes; causes fever, jaundice, and hemorrhage.

• Dengue: Also transmitted by Aedes mosquitoes; causes severe muscle and joint pain, rash, and sometimes hemorrhagic manifestations.

• Ebola, Lassa, Argentine, Bolivian fevers, Hantavirus: Various transmission routes, often involving rodents or mosquitoes, and can cause severe hemorrhagic symptoms.

Protozoan Diseases

Chagas’ Disease (American Trypanosomiasis)

Caused by Trypanosoma cruzi, transmitted by reduviid bugs. Reservoirs include rodents, opossums, and armadillos.

Toxoplasmosis

Caused by Toxoplasma gondii, transmitted by ingesting undercooked meat or contact with cat feces. Congenital infection can cause severe fetal damage.

Malaria

Caused by Plasmodium spp., transmitted by female Anopheles mosquitoes. Characterized by cycles of chills, fever, and anemia due to destruction of red blood cells.

• Diagnosis: Blood smear to identify Plasmodium in RBCs.

• Treatment: Artemisinin-based combination therapies; prevention includes bed nets and prophylactic drugs.

Helminthic Diseases

Schistosomiasis

Caused by Schistosoma spp., this disease results from tissue damage (granulomas) in response to eggs lodging in tissues. It is not common in North America due to lack of suitable reservoirs.