Summary

20.1  Anatomy of the Circulatory and Lymphatic Systems

• The circulatory system moves blood throughout the body and has no normal microbiota.
• The lymphatic system moves fluids from the interstitial spaces of tissues toward the circulatory system and filters the lymph. It also has no normal microbiota.
• The circulatory and lymphatic systems are home to many components of the host immune defenses.
• Infections of the circulatory system may occur after a break in the skin barrier or they may enter the bloodstream at the site of a localized infection. Pathogens or toxins in the bloodstream can spread rapidly throughout the body and can provoke systemic and sometimes fatal inflammatory responses such as SIRS, sepsis, and endocarditis.
• Infections of the lymphatic system can cause lymphangitis and lymphadenitis.

20.2  Bacterial Infections of the Circulatory and Lymphatic Systems

• Bacterial infections of the circulatory system are almost universally serious. Left untreated, most have high mortality rates.
• Bacterial pathogens usually require a breach in the immune defenses to colonize the circulatory system. Most often, this involves a wound or the bite of an arthropod vector, but it can also occur in hospital settings and result in nosocomial infections.
• Sepsis from both gram-negative and gram-positive bacteria are typically a result of injury or introduction of bacteria by medical or surgical intervention.
• Lyme disease is transmitted by arthropod vectors.
• Because their symptoms are so similar to those of other diseases, many bacterial infections of the circulatory system are difficult to diagnose.
• Standard antibiotic therapies are effective for the treatment of most bacterial infections of the circulatory system, unless the bacterium is resistant, in which case synergistic treatment may be required.
• The systemic immune response to a bacteremia, which involves the release of excessive amounts of cytokines, can sometimes be more damaging to the host than the infection itself.