Systemic Microbial Infections: Cardiovascular and Lymphatic Diseases

Systemic Microbial Infections: Cardiovascular and Lymphatic Diseases

Overview of the Cardiovascular and Lymphatic Systems in Infection

The cardiovascular and lymphatic systems are essential for both the dissemination and elimination of infectious agents in the body. These systems transport cells, nutrients, and immune factors, but can also serve as routes for pathogen spread.

• Cardiovascular system: Delivers substances to and removes substances from cells, including pathogens and immune cells.

• Lymphatic system: Lymph capillaries collect interstitial fluid (lymph) and transport it through lymph vessels and nodes, where microorganisms and infectious agents are filtered and targeted by immune responses.

• Buboes: Swollen lymph nodes, often associated with certain infections (e.g., plague).

Sepsis and Related Conditions

Sepsis and its related conditions are systemic responses to infection, often involving the bloodstream and immune system.

• Septicemia: Acute illness caused by the presence of pathogens or their toxins in the blood.

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

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

• Severe sepsis: Sepsis with decreased blood pressure and dysfunction of at least one organ.

• Septic shock: Sepsis with uncontrollable decreased blood pressure, leading to organ failure and high mortality.

Bacterial Infections of the Heart

Various bacteria can infect the heart and its surrounding tissues, leading to serious complications.

• Endocarditis: Inflammation of the endocardium (innermost heart layer).

• Subacute bacterial endocarditis: Impairs heart valve function; often caused by alpha-hemolytic streptococci from oral or tonsil infections.

• Acute bacterial endocarditis: Rapidly progressive; caused by Staphylococcus aureus.

• Pericarditis: Inflammation of the sac around the heart, commonly due to streptococci.

Condition	Causative Agent
Subacute bacterial endocarditis	Alpha-hemolytic streptococci
Acute bacterial endocarditis	Staphylococcus aureus
Pericarditis	Streptococci

Puerperal Fever

• Causative agent: Streptococcus pyogenes

Tularemia

• Causative agent: Francisella tularensis (gram-negative rod)

• Main sources: Rabbits, ticks, and deer flies

Zoonotic Diseases

• Definition: Infections transmitted from animals to humans, caused by bacteria, viruses, parasites, or fungi.

Anthrax

• Causative agent: Bacillus anthracis (gram-positive, endospore-forming aerobic rod)

• Virulence factors:

  • Protective antigen: Binds toxins to target cells, allowing entry.

  • Edema toxin: Causes local swelling and interferes with phagocytosis.

  • Lethal toxin: Kills macrophages.

  • Amino acid capsule: Prevents immune response.

• Types of anthrax:

  • Cutaneous: Endospores enter through a cut; ~20% mortality without treatment.

  • Gastrointestinal: Ingestion of contaminated food; >50% mortality.

  • Inhalational (pulmonary): Inhalation of endospores; nearly 100% mortality (highest).

Systemic Diseases from Bites and Scratches

• Common organisms: Pasteurella multocida, Staphylococcus, Streptococcus, Corynebacterium

Plague

• Causative agent: Yersinia pestis (gram-negative rod)

• Vector: Rat flea (Xenopsylla cheopis)

• Types of plague:

  • Bubonic: Bacterial growth in blood and lymph; 50–75% mortality.

  • Septicemic: Septic shock from bacteria in blood.

  • Pneumonic: Bacteria in lungs; airborne transmission; nearly 100% mortality (highest).

Relapsing Fever and Lyme Disease

• Relapsing fever: Caused by Borrelia spp. (spirochetes)

• Lyme disease: Caused by Borrelia burgdorferi; transmitted by Ixodes ticks; most common tickborne disease in the US.

• Phases of Lyme disease:

  1. First phase: Bull’s-eye rash, flulike symptoms.

  2. Second phase: Irregular heartbeat, encephalitis, facial paralysis, memory loss.

  3. Third phase: Arthritis due to immune response.

• Treatment: Antibiotics must be administered before later stages for effectiveness.

Rocky Mountain Spotted Fever

• Causative agent: Rickettsia rickettsii

• Vectors: Wood ticks (Dermacentor andersoni) and dog ticks (Dermacentor variabilis)

Viral Systemic Diseases

• Infectious mononucleosis: Caused by Epstein-Barr virus (EBV); associated with multiple sclerosis, Hodgkin’s lymphoma, and nasopharyngeal cancer.

• Common antibodies: EBV and herpesvirus antibodies are found in most humans.

Vector-Borne Viral Diseases

• Yellow fever: Fever, chills, headache, nausea, vomiting; transmitted by Aedes aegypti.

• Dengue: Milder than yellow fever, often asymptomatic; severe dengue can cause bleeding and organ impairment.

• Antibody enhancement: Antibodies from previous dengue infections can facilitate new infections, leading to severe dengue.

Emerging Hemorrhagic Fevers

• Ebola Virus Disease (EVD): Animal reservoir believed to be cave-dwelling fruit bats near the Ebola River in Africa.

• Sin Nombre Virus (hantavirus): Transmitted by inhalation of dried urine and feces from infected rodents.

Malaria

• Causative agents: Plasmodium species:

  • P. vivax: Mild, most prevalent; dormant in liver.

  • P. ovale and P. malariae: Benign, geographically restricted.

  • P. falciparum: Most deadly; severe anemia, capillary blockage, affects kidneys, liver, brain.

• Vector: Anopheles mosquitoes

• Life cycle forms:

  • Sporozoite: Injected by mosquito into human; infects liver cells.

  • Merozoite: Released from liver, infects RBCs, causes paroxysms of chills and fever.

  • Gametocyte: Taken up by mosquito, undergoes sexual reproduction in mosquito.

Leishmaniasis

Type	Causative Agent	Clinical Features
Visceral	Leishmania donovani	Invades internal organs
Cutaneous (most common)	Leishmania tropica	Papule ulcerates, leaves scar
Mucocutaneous	Leishmania braziliensis	Affects mucous membranes

Schistosomiasis

• Causative agents:

  • Schistosoma haematobium: Urinary schistosomiasis (Africa, Middle East)

  • Schistosoma japonicum: Intestinal inflammation (Asia)

  • Schistosoma mansoni: Intestinal inflammation (Africa, Middle East, South America, Caribbean)

• Pathogenic mechanism: Eggs released by the parasite cause host tissue damage.

• Life cycle: Requires freshwater snail as intermediate host; cercariae are the infective form for humans.

Impact of Climate Change on Disease Transmission

• Climate change can expand the habitat of insect vectors, increasing the range and incidence of vector-borne diseases.

Additional info: This summary integrates definitions, causative agents, vectors, and clinical features of major systemic infections affecting the cardiovascular and lymphatic systems, as well as the impact of environmental changes on disease transmission.