Encyclopedia of Health and Medicine

324 Infectious Diseases
cell lymphocytes containing the latent Epstein-
Barr virus from endlessly proliferating. As a result
of this balance, in most people the virus never
regains enough presence to again cause illness.
Circumstances that challenge the immune system
allow the Epstein-Barr virus to reactivate. The
most notable of these circumstances are HIV/AIDS
and IMMUNOSUPPRESSIVE THERAPY after ORGAN TRANS-
PLANTATION. The reactivated Epstein-Barr virus may
cause symptoms similar to infectious mononucleosis
(chronic infectious mononucleosis) during
which the person may spread the virus to others. It
may also cause lymphoproliferative disorders:
abnormal growth (tumors) of lymphatic structures
such as lymph nodes and MUCOSA-ASSOCIATED LYM-
PHOID TISSUE (MALT). Though research is under way
to develop a VACCINE to prevent infection with
Epstein-Barr virus, at present there are no effective
measures to prevent infection with the virus and
no treatments to eradicate the virus once it establishes
infection.
DISEASES ASSOCIATED WITH EPSTEIN-BARR VIRUS
acute infectious AIDS-associated lymphoma
mononucleosis Burkitt’s lymphoma
chronic infectious generalized lymphoproliferative
mononucleosis disease
nasopharyngeal post-transplant lymphoproliferative
CARCINOMA
disorder (PTLD)
See also B-CELL LYMPHOCYTE; CELL STRUCTURE AND
FUNCTION; HERPES SIMPLEX; HERPES ZOSTER; KAPOSI’S
SARCOMA; LYMPH NODE; LYMPHOCYTE; MONONUCLEOSIS,
INFECTIOUS; OPPORTUNISTIC INFECTION; T-CELL LYMPHO-
CYTE.
Escherichia coli infection Illness that results
from INFECTION with any of the numerous strains
of Escherichia coli BACTERIA, some of which are NOR-
MAL FLORA in the human gastrointestinal tract and
others that are normal flora in the gastrointestinal
tracts of animals consumed as food (such as cattle
and poultry). Most strains of E. coli cause mild to
moderate illness. Illness from E. coli infection
results from the toxins the E. coli release through
their normal metabolic functions. The strain E. coli
O157:H7, found in beef contaminated with fecal
matter, can cause particularly severe illness.
Symptoms and Diagnostic Path
The symptoms of common E. coli infection are
generally mild to moderate in severity and include
• abdominal cramping
• DIARRHEA
• occasionally NAUSEA and VOMITING
The symptoms of E. coli O157:H7 infection are
often more severe and include ABDOMINAL PAIN
with profuse, sometimes bloody diarrhea. Though
most people recover fully after the illness runs its
course in 5 to 10 days, in some people the toxins
the E. coli O157:H7 release cause the massive
destruction of red BLOOD cells (erythrocytes), a
process called HEMOLYSIS. The enormous volume of
dead erythrocytes creates proteins in the blood
that are damaging to the KIDNEYS, resulting in
RENAL FAILURE. The combination of these circumstances
is HEMOLYTIC UREMIC SYNDROME (HUS),
which occurs as a complication of E. coli O157:H7
infection in about 5 percent of people (mostly
children under age 5). HUS nearly always results
in END-STAGE RENAL DISEASE (ESRD), requiring dialysis
or KIDNEY TRANSPLANTATION.
The diagnostic path for E. coli infection may
include culture of stool samples to determine the
causative PATHOGEN, though most often doctors do
this only when the illness continues beyond about
two weeks or has severe symptoms. The doctor
must specifically request culture for E. coli
O157:H7 as most laboratories do not routinely
include this in their testing.
Treatment Options and Outlook
E. coli diarrheal illnesses are very common and
nearly all people who acquire them fully recover
in three to five days without treatment, except
fluid replacement to prevent DEHYDRATION. ANTIBI-
OTIC MEDICATIONS are seldom appropriate because
the cause of symptoms is the toxins the E. coli bacteria
release, and killing the bacteria causes them
to release even more toxins. It is sometimes helpful
to avoid dairy products until bowel activity
returns to normal. People who become seriously
ill with E. coli O157:H7 may require care in the
hospital. Though E. coli O157:H7 infection has
gained substantial notoriety, more than 95 percent