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Back to Infectious Diseases
Amoebiasis
Amebiasis is an infection with the intestinal protozoan Entamoeba histolytica.
About 90% of infections are asymptomatic, and the remaining 10% produce
a spectrum of clinical syndromes ranging from dysentery to abscesses of
the liver or other organs.
E. histolytica is acquired by ingestion of viable cysts from fecally
contaminated water, food, or hands. Motile trophozoites are released from
cysts in the small intestine and, in most patients, remain as harmless commensals
in the large bowel. After encystation, infectious cysts are shed in the
stool and can survive for several weeks in a moist environment. In some
patients, the trophozoites invade either the bowel mucosa, causing symptomatic
colitis, or the bloodstream, causing distant abscesses of the liver, lungs,
or brain.
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What are the symptoms?
Symptomatic amebic colitis develops 2 to 6 weeks after the ingestion
of infectious cysts. Lower abdominal pain and mild
diarrhea develop gradually
and are followed by malaise, weight loss, and diffuse lower abdominal or
back pain. Cecal involvement may mimic acute appendicitis. Patients with
full-blown dysentery may pass 10 to 12 stools per day. The stools contain
little fecal material and consist mainly of blood and mucus. In contrast
to those with bacterial
diarrhea, fewer than 40% of patients with amebic
dysentery are febrile. Virtually all patients have heme-positive stools.
Most patients with liver abscess are febrile and have right-upper-quadrant
pain, which may be dull or pleuritic in nature and radiate to the shoulder.
Point tenderness over the liver and right-sided pleural effusion are common.
Jaundice is rare. Although the initial site of infection is the colon, fewer
than one-third of patients with an amebic abscess have active
diarrhea.
Pleuropulmonary involvement, which is reported in 20 to 30% of patients,
is the most frequent complication of amebic liver abscess. Manifestations
include sterile effusions, contiguous spread from the liver, and rupture
into the pleural space.
Diagnosis
Patients have cysts in faeces, serodiagnosis are the
mainstay of daignosis. Radiographic diagnosis confirms the presence of liver
abscess.
Treatment
luminal agents are used for eradication of cysts in patients with colitis
or a liver abscess and treatment of asymptomatic carriers. Only two luminal
drugs are available in the United States: iodoquinol and paromomycin.
The development of nitroimidazole compounds, especially metronidazole,
was a major advance in the treatment of invasive amebiasis. Patients with
amebic colitis should be treated with intravenous or oral metronidazole
(750 mg three times daily for 5 to 10 days).
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