Chapter 18: Infections of the Cardiovascular and Circulatory System

The circulatory system serves dual roles in delivering nutrients while simultaneously providing routes for pathogen dissemination, making infections in this domain particularly dangerous. The chapter distinguishes between microbemia, bacteremia, and septicemia, explaining how bacterial presence in the bloodstream can escalate from asymptomatic colonization to life-threatening septic shock when microbial toxins overwhelm immune defenses. Inflammatory infections target specific cardiac structures: endocarditis affects the heart's inner lining and often requires surgical intervention when prosthetic valves are involved, myocarditis typically results from viral or parasitic invasion of heart muscle, and pericarditis involves inflammation of the protective membrane surrounding the heart. The chapter addresses major bacterial conditions including rheumatic fever as an inflammatory aftermath of Group A streptococcal infection and gangrene, where tissue death from reduced blood flow creates environments favoring anaerobic bacterial proliferation. Zoonotic diseases transmitted from animals to humans receive substantial coverage, including brucellosis, tularemia, and cat scratch disease caused by Bartonella species. Vector-borne infections transmitted through arthropods constitute a major disease category, encompassing plague, Rocky Mountain spotted fever with its characteristic rash presentation, Lyme disease transmitted by ticks, and ehrlichiosis. Viral infections discussed include Epstein-Barr virus causing infectious mononucleosis, cytomegalovirus particularly threatening immunocompromised individuals, and viral hemorrhagic fevers characterized by severe vascular damage. The chapter concludes with fungal systemic mycoses and protozoan infections including malaria affecting red blood cells, babesiosis, toxoplasmosis, Chagas disease transmitted by insect vectors, and leishmaniasis spread through sandfly bites, collectively representing the diversity of circulatory pathogens affecting human health.