Microbiology, 2021

1088 25 • Summary
SUMMARY
25.1 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.
25.2 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 grampositive
bacteria, puerperal fever, rheumatic
fever, endocarditis, gas gangrene,
osteomyelitis, and toxic shock syndrome are
typically a result of injury or introduction of
bacteria by medical or surgical intervention.
• Tularemia, brucellosis, cat-scratch fever, ratbite
fever, and bubonic plague are zoonotic
diseases transmitted by biological vectors
• Ehrlichiosis, anaplasmosis, endemic and
murine typhus, Rocky Mountain spotted fever,
Lyme disease, relapsing fever, and trench
fever are 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.
25.3 Viral Infections of the
Circulatory and Lymphatic Systems
• Human herpesviruses such Epstein-Barr virus
(HHV-4) and cytomegalovirus (HHV-5) are
widely distributed. The former is associated
with infectious mononucleosis and Burkitt
lymphoma, and the latter can cause serious
congenital infections as well as serious disease
in immunocompromised adults.
• Arboviral diseases such as yellow fever, dengue
fever, and chikungunya fever are characterized
by high fevers and vascular damage that can
often be fatal. Ebola virus disease is a highly
contagious and often fatal infection spread
through contact with bodily fluids.
• Although there is a vaccine available for yellow
fever, treatments for patients with yellow fever,
dengue, chikungunya fever, and Ebola virus
disease are limited to supportive therapies.
• Patients infected with human
immunodeficiency virus (HIV) progress
through three stages of disease, culminating in
AIDS. Antiretroviral therapy (ART) uses
various combinations of drugs to suppress viral
loads, extending the period of latency and
reducing the likelihood of transmission.
• Vector control and animal reservoir control
remain the best defenses against most viruses
that cause diseases of the circulatory system.
25.4 Parasitic Infections of the
Circulatory and Lymphatic Systems
• Malaria is a protozoan parasite that remains an
important cause of death primarily in the
tropics. Several species in the genus
Plasmodium are responsible for malaria and all
are transmitted by Anopheles mosquitoes.
Plasmodium infects and destroys human red
blood cells, leading to organ damage, anemia,
blood vessel necrosis, and death. Malaria can be
treated with various antimalarial drugs and
prevented through vector control.
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