may sustain itself in a dormant stage for weeks to
months outside a host (organism that provides
NUTRIENTSfor a parasite). Once within the SMALL
INTESTINEthe cyst ruptures and the ameba emerges
to enter its active stage. In this active stage the
ameba, called a trophozoite, travels to the COLON
(large intestine) where it feeds on intestinal BACTE-
RIA. As the population of trophozoites increases,
they burrow into the intestinal mucosa (mucous
lining of the colon). Substances trophozoites
secrete to digest the substances they consume
cause ulcerations (sores) that produce symptoms.
Symptoms and Diagnostic PathThe symptoms of amebiasis, also called amebic
dysentery, begin two weeks to four months after
ingesting the contaminated food or water. They
include
- abdominal cramping or ABDOMINAL PAIN
- frequent bowel movements or DIARRHEA(which
may be bloody) - FEVER
The diagnostic path includes microscopic exam-
ination of stool samples to detect the presence of
either cysts or trophozoites. The doctor may also
conduct sigmoidoscopy to examine the colon for
the characteristic ulcerations and to rule out other
causes of the symptoms.
Occasionally trophozoites penetrate far enough
into the intestinal mucosa to enter the BLOODcir-
culation, which transports them to other organs
and extends the infection. The LIVERis the most
common site for distant infection, where it pres-
ents as aHEPATIC ABSCESS, though the LUNGSand the
BRAIN may also become involved. In locations
other than the colon the trophozoites can cause
abscesses, resulting in serious or life-threatening
illness. Symptoms of systemic infection depend on
the affected area.
Treatment Options and Outlook
Treatment for enteric or systemic infection is a
combination of ANTIBIOTIC MEDICATIONS. Appropriate
treatment cures the infection; inadequately
treated or untreated amebiasis becomes chronic
with cycles of alternating RECURRENCEand REMIS-
SIONof symptoms. Until recently doctors believed
it was possible to have an E. histolyticainfection
without symptoms. However, although it is possi-
ble to have an E. histolytica infection with very
mild symptoms, infectious disease specialists have
determined a closely related and nearly identical
ameba, E. dispar, is the cause of infection when no
symptoms are present. E. disparis benign and does
not require treatment.ANTIBIOTIC MEDICATIONS TO TREAT AMEBIASIS
diloxanide furoate iodoquinol
metronidazole paromomycin
tinidazoleRisk Factors and Preventive Measures
Amebiasis is most common in countries where
community sanitation is poor. People who travel
in such countries or are immigrants to the United
States from such countries, are at highest risk for
amebiasis. The infection spreads through direct
contact with fecal contamination, such as by eat-
ing vegetables from contaminated soil or drinking
contaminated water. People who have amebiasis
can spread the infection to other people. Diligent
HAND WASHINGand safe food preparation are effec-
tive measures for preventing the spread of amebi-
asis. Travelers to countries where sanitation is
substandard should follow precautions that
include eating only foods that are thoroughly
cooked and drinking only bottled or canned bev-
erages (without ice) or water boiled for a mini-
mum of one minute.
See also BOWEL MOVEMENT; DRINKING WATER STAN-
DARDS; FOODBORNE ILLNESSES; FOOD SAFETY; GASTROEN-
TERITIS; PERSONAL HYGIENE; PROTOZOA; WATERBORNE
ILLNESSES.antibiotic medications Drugs that kill BACTERIA
and certain other microorganisms. Antibiotic med-
ications are the mainstay of treatment for bacterial
INFECTION. Broad-spectrum antibiotics are capable
of killing numerous types of bacteria; narrow-
spectrum antibiotics kill specific types or strains of
bacteria. There are seven primary classifications of
antibiotic medications—aminoglycosides, cephalo-
sporins, macrolides, quinolones (fluorquinolones),
penicillins, sulfonamides, and tetracyclines—that
contain over 100 different drugs.antibiotic medications 307