Infectious Diseases Affecting the Cardiovascular and Lymphatic Systems

CHAPTER 18: Cardiovascular and Lymphatic Systems: Structure and Function

Overview of the Cardiovascular System

The cardiovascular system is a closed circuit composed of the heart and blood vessels, responsible for transporting blood throughout the body. It delivers oxygen and nutrients to tissues and removes carbon dioxide and waste products.

• Heart: The muscular organ that pumps blood. It is covered by the pericardium (a fibrous sac) and lined internally by the endocardium, which can be sites of microbial infection.

• Blood Vessels: Arteries, veins, and capillaries that carry blood to and from all regions of the body.

The Lymphatic System

The lymphatic system is closely related to the cardiovascular system but is a separate network. It is a major source of immune cells and fluids, consisting of lymphatic vessels, lymph nodes, spleen, thymus, tonsils, and gut-associated lymphoid tissue (GALT).

• Function: Screens body compartments for pathogens and supports immune responses.

• Flow: Lymphatic vessels transport lymph in one direction, eventually draining into veins near the heart.

Terminology and Pathological Conditions

Key Terms

• Viremia: Presence of viruses in the blood.

• Fungemia: Presence of fungi in the blood.

• Bacteremia: Presence of bacteria in the blood, which can occur transiently during daily activities (e.g., brushing teeth).

• Septicemia (Sepsis): Bacteria growing and flourishing in the blood, leading to systemic inflammation and potentially septic shock (dangerous drop in blood pressure due to immune response).

Defenses and Normal Biota of the Cardiovascular and Lymphatic Systems

Both systems are normally sterile and have robust immune defenses.

System	Defenses	Normal Biota
Cardiovascular System	Blood-borne components of nonspecific and specific immunity—including phagocytosis, specific immunity	None
Lymphatic System	Numerous immune defenses reside here	None

Major Infectious Diseases of the Cardiovascular and Lymphatic Systems

Malaria

Malaria is a protozoan disease caused by Plasmodium species (e.g., P. malariae, P. vivax, P. falciparum, P. ovale). It is transmitted primarily by the bite of infected female Anopheles mosquitoes.

• Symptoms: Cyclic chills, fever, and sweating (every 48–72 hours), anemia, and organ enlargement (liver, spleen).

• Life Cycle: Involves asexual reproduction in humans (liver and red blood cells) and sexual reproduction in mosquitoes.

• Prevention: Mosquito control, bed nets, chemoprophylaxis, and vaccine development.

• Treatment: Antimalarial drugs such as quinine, chloroquine, or mefloquine.

HIV Infection and AIDS

Human Immunodeficiency Virus (HIV) is a retrovirus that infects cells displaying the CD4 marker and CCR-5 coreceptor. It is primarily transmitted through sexual contact, blood, and from mother to child.

• Symptoms: Initial flu-like illness, followed by a long asymptomatic period, then progression to AIDS (opportunistic infections, cancers, neurological symptoms).

• Pathogenesis: HIV destroys CD4+ T cells, leading to immune deficiency. AIDS is diagnosed when CD4+ T cell count falls below 200 cells/μl.

• Prevention: Safe sex, avoiding needle sharing, screening blood products.

• Treatment: No cure; managed with Highly Active Antiretroviral Therapy (HAART).

Plague

Plague is caused by Yersinia pestis, a gram-negative rod. It has three main forms: bubonic, pneumonic, and septicemic.

• Bubonic Plague: Infection of lymph nodes (buboes), fever, chills, and high mortality if untreated.

• Pneumonic Plague: Respiratory infection, highly contagious.

• Septicemic Plague: Bacteria in the blood, leading to hemorrhage, necrosis, and "black death." Mortality is nearly 100% without treatment.

• Transmission: Flea bites from infected rodents; rare human-to-human transmission.

Lyme Disease

Lyme disease is caused by the spirochete Borrelia burgdorferi and transmitted by deer ticks (Ixodes species).

• Symptoms: Early: erythema migrans (bull's-eye rash), fever, headache. Later: cardiac, neurological, and arthritic symptoms.

• Prevention: Protective clothing, tick checks, insect repellents.

• Treatment: Early, prolonged antibiotics (doxycycline, amoxicillin).

Infectious Mononucleosis

Often called "mono" or "the kissing disease," it is primarily caused by Epstein-Barr virus (EBV), a herpesvirus.

• Symptoms: Sore throat, fever, lymphadenopathy, fatigue, enlarged spleen/liver.

• Transmission: Direct oral contact, saliva, blood transfusions, organ transplants.

• Complications: Associated with Burkitt's lymphoma in immunosuppressed individuals.

Hemorrhagic Fever Diseases

These are viral diseases causing high fever and internal hemorrhaging, often with high mortality rates.

• Examples: Yellow fever (Aedes mosquito), Dengue (Aedes mosquito), Ebola and Marburg (bats), Lassa fever (rats).

• Pathology: Capillary fragility, disruption of blood clotting, bleeding from orifices.

Nonhemorrhagic Fever Diseases

• Cat-Scratch Disease: Caused by Bartonella henslae, transmitted by cat scratches or bites. Presents with papules and lymphadenopathy. Treated with antibiotics.

• Rocky Mountain Spotted Fever (RMSF): Caused by Rickettsia rickettsii, transmitted by hard ticks. Symptoms include fever, rash, and potentially fatal cardiovascular and CNS complications. Treated with antibiotics.

Anthrax

Caused by Bacillus anthracis, a gram-positive, endospore-forming rod. It can infect the skin, lungs, GI tract, or CNS.

• Symptoms: Vary by site; all forms can lead to septicemia and death if untreated.

• Transmission: Contact with contaminated animal products or soil.

• Prevention: Vaccination for high-risk individuals, antibiotic prophylaxis after exposure.

Septicemia

Septicemia is a systemic infection where organisms multiply in the blood, causing fever, altered mental state, low blood pressure (endotoxic shock), and high mortality.

• Causes: Many bacteria and viruses; often introduced via IV lines, surgery, or secondary to other infections.

• Treatment: Immediate antibiotic therapy.