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Parasitic Infections
Figure 1: Gross Pathology of Intestinal Amebiasis
Hematogenous Spread of Amebiasis
Pleuropulmonary amebiasis is most commonly the result of
contiguous spread from a liver abscess rupturing through the right
hemidiaphragm. However, we have reported a case of amebic lung
abscess acquired through hematogenous spread.
26
Amebic abscesses
resulting from hematogenous spread have occasionally been described in
the brain and skin.
Laboratory Diagnosis of Intestinal Amebiasis
In cases of amebiasis, stool samples are always heme-positive.
27
Examination of a fresh stool smear for trophozoites containing ingested
red blood cells is a rather insensitive method. Routine microscopy cannot
Courtesy of Centers for Disease Control and Prevention (CDC) Public Health Image Library. distinguish the E. dispar and E. moshkovskii non-pathogenic amebae
Table 1: Therapeutic Regimens for the Treatment of Amebiasis
from E. histolytica.
1
An enzyme immunoassay kit designed specifically to
detect E. histolytica in fresh stool specimens is commercially available.
Asymptomatic intestinal colonization PCR-based diagnostic tests have been developed, but are not widely
• Diloxanide furoate 500mg TID for 10 days
available.
28
Field studies that directly compared PCR with stool culture or
• Paromomycin 30mg/kg/day in three divided doses for 5–10 days
antigen-detection tests for the diagnosis of E. histolytica infection
• Tetracycline 250mg QID for 10 days, then iodoquinol 650mg TID for 20 days
suggest that these three methods are comparable.
5,29
Serum antibodies
Amebic colitis
against amebae are present in 70–90% of patients with symptomatic
• Metronidazole 750mg TID for 5–10 days, or 2.4g QID for two to three days, or 50mg/kg
E. histolytica infection.
22
However, serological tests do not distinguish
1 dose plus diloxanide furoate or paromomycin
• Tinidazole 2mg daily for three days plus diloxanide furoate or paromomycin
new from past infection since seropositivity persists for years after an
• Tetracycline 250mg QID for 15 days plus chloroquine (base), 600mg, 300mg, then
acute infection.
150mg TID for 14 days
• Dehydroemetine 1–1.5mg/kg/day IM or SC (max. 90mg) for up to five days, plus
Colonoscopy and biopsy, or scraping at the margin of a colonic mucosal
diloxanide furoate or paromomycin ulcer, provide valuable materials for diagnostic information (see Figure 1).
Amebic liver abscess The mucosal lining between ulcers appears normal at colonoscopy.
• Metronidazole 750mg TID for 5–10 days or 2.4g QID for one to two days plus
Histopathological findings include non-specific mucosal thickening and
diloxanide furoate or paromomycin
focal ulcerations with or without amebae in a diffusely inflamed mucosal
• Tinidazole 2mg daily three to five days plus diloxanide furoate or paromomycin
layer. Classic flask-shaped ulcers may be seen with ulceration extending
• Dehydroemetine 1–1.5mg/kg/day IM or SC (max. 90mg) for up to five days plus
through the mucosa and muscularis mucosa into the submucosa.
diloxanide furoate or paromomycin
Staining with periodic acid-Schiff or immunoperoxidase and antilectin
TID = three times a day; QID = four times a day; IM = intramuscular; SC = subcutaneous.
antibodies aids in the visualization of amebae.
30
Adapted from Ravdin and Stauffer, 2005.
12
Approximately 80% of patients with amebic liver abscess present within two Laboratory Diagnosis of Amebic Liver Abscess
to four weeks of infection. In a sonographic evaluation of 212 patients, 34 Laboratory findings include leukocytosis without eosinophilia in 80% of
(16%) had multiple abscesses, 75 (35%) had an abscess in the left lobe, and cases, mild anemia in more than half, elevated alkaline phosphatase
the remaining 103 (49%) had a solitary abscess in the right lobe.
24
levels in 80%, elevated transaminase levels in more aggressive disease,
mild elevation of serum bilirubin level, and a high erythrocyte
Clinical manifestations include fever and a constant, dull upper right sedimentation rate.
21,23,31
Abdominal ultrasonography, computed
abdominal or epigastrium pain.
25
Involvement of the diaphragmatic tomography (CT), and magnetic resonance imaging (MRI) are all excellent
surface of the liver may lead to right-sided pleural pain or referred for detecting liver abscesses, but cannot distinguish amebic from
shoulder pain. Associated gastrointestinal symptoms occur in 10–35% of pyogenic abscesses.
patients and include nausea, vomiting, abdominal distention, diarrhea,
and constipation. There is hepatomegaly with tenderness below the ribs Anti-amebic antibodies are present in up to 99% of patients who have
or in the intercostal spaces. Liver function tests may be normal or slightly been symptomatic for over a week.
21,23
Serological examination should be
abnormal, with jaundice being very rare.
21,23
repeated a week later in those with negative test on presentation. The
galactose lectin antigen is present in the serum of 75% of subjects with
Complications of amebic liver abscess may arise from rupture of amebic liver abscess, and may be particularly useful in patients
the abscess with extension into the peritoneum, pleural cavity, presenting acutely, before an IgG serum anti-amebic antibody response
or pericardium. The differential diagnosis of an amebic liver abscess should occurs.
32,33
Aspiration of the abscess is occasionally required to rule out a
include pyogenic liver abscess, necrotic hepatoma, and echinococcal cyst. pyogenic abscess. Aspiration of amebic liver abscess yields an anchovy-
The likelihood of a liver abscess being amebic rather than pyogenic is paste-like material that lacks white blood cells (WBCs) due to lysis by the
increased by the history of residence in, or recent travel to, endemic areas, parasite. Amebae are visible in the abscess fluid in a minority of patients
male sex, age <50 years, presence of a single lesion in the right lobe of the with amebic liver abscess. Fewer than half of patients with amebic liver
liver, and the absence of jaundice, biliary disease, or diabetes mellitus. abscess have parasites detected in their stool by antigen detection.
60 US INFECTIOUS DISEASE
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