Encyclopedia of Health and Medicine

B
babesiosis An illness that results from INFECTION
with the parasitic protozoan Babesia microti. Most
people who have babesiosis do not have symptoms;
the infection causes illness primarily in people
who are IMMUNOCOMPROMISED or who have had
SPLENECTOMY (surgical removal of the SPLEEN). The
bite of the Ixodes tick, found in the northeastern
United States, is the mode of transmission.
Babesiosis is rare in other parts of the United
States.
B. microti infects the erythrocytes (red BLOOD
cells), causing alterations in their cell membranes
that affect their ability to carry oxygen. Hemolytic
ANEMIA is a key consequence of babesiosis. Symptoms
may include FEVER, COUGH, and shortness of
breath (DYSPNEA). The doctor uses blood tests to
diagnose babesiosis. The tests show the damage to
the erythrocytes and the presence of antibodies.
Treatment with ANTIBIOTIC MEDICATIONS cures the
infection. Rarely, a person may develop the lifethreatening
complication ACUTE RESPIRATORY DIS-
TRESS SYNDROME (ARDS).
bacteria Single-cell microorganisms (microbes).
Bacteria are the most ancient and primitive life
forms known, with fossils dating back more than 3
billion years. A bacterium’s structure is very simple,
consisting of a rigid cell wall that supports and
contains the cytoplasm, fragments of RNA, and a
single strand of DNA within a nonencapsulated
(unbordered) nucleus. Though bacteria are capable
of independent existence, most require a symbiotic
relationship with a host organism. The bacteria
provide needed functions for the host in
exchange for NUTRIENTS and safe haven.
Many types of bacteria exist in and on the body
in just such a symbiotic partnership; these are part
of the body’s NORMAL FLORA. Bacteria in the gastrointestinal
tract digest food, for example. Bifidobacterium
bifidum, Lactobacillus acidophilus, and
Saccaromyces boulardii are some of the more abundant
bacterial families that reside in the small
intestine. However, when normal flora bacteria
are able to establish themselves in tissues other
than their natural habitat or their numbers
become abundant, they cause INFECTION. Escherichia
coli, for example, are abundant normal flora in the
COLON, where they work to prepare the residue of
digestion for elimination from the body. E. coli also
synthesize VITAMIN K, which is essential for COAGU-
LATION (BLOOD clotting). When E. coli escape from
their habitat, however, they cause infections such
as VAGINITIS or URINARY TRACT INFECTION (UTI).
ANTIBIOTIC MEDICATIONS TO TREAT BABESIOSIS
atovaquone
azithromycin
clindamycin
quinine sulfate
See also ANTIBODY; ERYTHROCYTE; GIARDIASIS; LYME
DISEASE; PROTOZOA.
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THE “BAD” E. COLI: O157:H7
The bacterial family Escherichia coli is extensive
and ubiquitous—its many strains live in the gastrointestinal
systems of nearly all animals. E. coli
O157:H7, NORMAL FLORA in cattle, is a family
member of great notoriety for the potential of
severe illness it presents in people. The toxin this
strain releases can destroy red BLOOD cells in
such volume that the KIDNEYS fail, a condition
called HEMOLYTIC UREMIC SYNDROME. E. coli
O157:H7 enters the human food chain as a
foodborne illness.
Bacteria that cause infection are pathogens.
Most pathogenic bacteria exist in the natural envi-