Chapter 23: Diseases of the Cardiovascular & Lymphatic Systems

Because these systems are usually sterile, any microbial invasion can lead to rapid and life-threatening illness. The chapter begins by outlining sepsis, a systemic inflammatory response caused by infection. Severe cases can lead to septic shock, characterized by dangerously low blood pressure and organ failure. The chapter details the difference between gram-negative sepsis—which involves endotoxins and is often harder to treat—and gram-positive sepsis, now a more frequent cause due to exotoxins from Staphylococcus and Streptococcus species. It also highlights puerperal sepsis, historically caused by Streptococcus pyogenes during childbirth. Bacterial infections of the heart include subacute and acute bacterial endocarditis, often from oral streptococci or Staphylococcus aureus, especially in individuals with damaged or prosthetic heart valves. Pericarditis, inflammation of the heart’s outer layer, is also covered. Rheumatic fever, a post-streptococcal autoimmune complication, is explained in the context of molecular mimicry and valve damage. The chapter then examines zoonotic infections affecting the cardiovascular system. These include brucellosis (Brucella spp.), which causes undulant fever; anthrax (Bacillus anthracis), with cutaneous, gastrointestinal, and inhalational forms; and gas gangrene, caused by Clostridium perfringens producing tissue-destroying toxins. Other infections include plague (Yersinia pestis), relapsing fever, Lyme disease (Borrelia burgdorferi), epidemic typhus, Rocky Mountain spotted fever, and cat-scratch disease caused by Bartonella henselae. The viral section discusses Epstein-Barr virus (EBV) as the cause of infectious mononucleosis and its link to Burkitt’s lymphoma and nasopharyngeal carcinoma. The chapter also covers cytomegalovirus (CMV), yellow fever, dengue, Ebola, and Hantavirus—all of which have cardiovascular implications ranging from mild to hemorrhagic fevers. Finally, the chapter introduces protozoan infections of the blood such as Chagas disease (Trypanosoma cruzi), toxoplasmosis (Toxoplasma gondii), malaria (Plasmodium spp.), and leishmaniasis, as well as helminthic diseases like schistosomiasis. These parasites often cause chronic cardiovascular or systemic damage. By highlighting the microbial threats to these critical systems, this chapter reinforces the importance of early detection, vector control, vaccination, and proper hygiene in managing infectious disease.