Cardiovascular and Lymphatic Infections

The cardiovascular system is a closed loop under normal circumstances. Blood flows from the heart through the arteries to the capillaries before returning to the heart via the veins. In healthy people the blood is sterile, or free of microorganisms. As the cardiovascular system is a closed loop, there are no natural portals of entry to the bloodstream. If microbes gain access to the circulatory system through a break in the skin or through capillaries from another organ system, they can spread to potentially infect any other tissue in the body. Bacteremia refers to the presence of bacteria in the blood. Viremia refers to the presence of viruses in the blood. An infection that spans multiple tissue types is called a systemic infection, which is extremely dangerous and must be treated immediately. Microbes that reach the bloodstream are also able to infect elements of the cardiovascular system itself. Endocarditis is inflammation of the inner lining of the heart chambers and valves (the endocardium), which can disrupt the heart's rhythm and lead to death. While the lymphatic system is not a closed loop, it also has no normal microorganisms. Recall that the lymphatic system is the site of lymphocyte production and maturation. Lymphocytes' purpose is to identify and destroy foreign material inside the body. The presence of pathogens is often first detected in the lymphatic system due to its role in immunity.

A causative agent is a biological pathogen or chemical toxin that causes a disease. The causative agents of infectious diseases that affect the cardiovascular and lymphatic system can be bacterial, viral, protozoan, or fungal. Some common diseases of the cardiovascular and lymphatic systems include bubonic and/or pneumonic plague, tularemia, Lyme disease, anthrax, infectious mononucleosis, Chagas disease, and malaria.

Sepsis is a condition in which an infection results in a system-wide inflammatory response, which causes severe damage to the tissues and can result in death if not treated immediately. According to the Centers for Disease Control and Prevention, more than 1.5 million people in the United States develop sepsis yearly, and about 250,000 of them die as a result. Typically, sepsis is caused by bacterial infections, though any pathogen is capable of generating the inflammatory response that causes it. The primary infection occurs in a single location but is able to migrate into the bloodstream, where it prompts a severe inflammatory response throughout the entire body. Originally, gram-positive bacteria were the most common cause of sepsis, which was a frequent cause of death on the battlefield. The discovery of antibiotics reduced the prevalence of cases, and sepsis caused by gram-negative bacteria rose to dominance. However, increased resistance to antibiotics is changing this dynamic.

Septic shock (also referred to as endotoxic shock) is a severe inflammatory response due to a specific type of sepsis that is stimulated by lipopolysaccharide (LPS), a component that is unique to the cell walls of gram-negative bacteria. This immune response can result in damage to the patient's tissues and organs, leading to shock and death. This condition is commonly associated with surgical procedures and is therefore monitored for after surgery. Symptoms of sepsis include high or low temperature, increased heart rate, increased breathing rate or difficulty breathing, and confusion. If sepsis is suspected, treatment with the antibiotics ceftriaxone or azithromycin should begin promptly. The longer treatment is delayed, the higher the likelihood death will occur.