Amebiasis in Ethiopia: Problems in diagnosis and determination of prevalence of infection
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Date
2005-02
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Addis Ababa University
Abstract
Although in Ethiopia intestinal amebiasis is believed to be associated with many cases of
diarrhea, diagnosis is based on examination of fresh stool samples by microscopy, a method
that cannot discriminate the potential invasive Entamoeba histolytica from the commensal
Entamoeba dispar. The annual reports from Wonji Hospital and the Ethio-Netherlands AIDS
Research Project indicate intestinal amebiasis to be a common infection with the highest
prevalence compared to other parasites. Despite a considerably high reporting of intestinal
amebiasis, a twenty-year hospital records among 117080 admitted patients showed only 47
suspected liver abscess cases, suggesting overdiagnosis. Though the prevalence of E.
histolytica/E. dispar by microscopy was 24.9 % in Wonji and Akaki, the specific PCR did not
confirm the presence of any E. histolytica infection. Even after careful microscopic analysis,
by using quality control measures on 246 patients with diarrhea, microscopy demonstrated 40
% positivity of Entamoeba infection. However, application of PCR, a molecular diagnostic
method that can distinguish E. histolytica from E. dispar did not confirm any E. histolytica,
only 9% harboured E.dispar. Coproantigen detection ELISA in the same patients showed
clear lack of sensitivity and specificity whereby only 11.4 % specimens in the genus
Entamoeba specific ELISA were in agreement with the PCR, and none of the eight E.
histolytica antigen positive was confirmed. The absence of E. histolytica infection in Wonji
and Akaki was better justified with lower seropositivity (3 %) finding, using recombinant
surface antigen of E. histolytica. Further study among healthy primary-school students and
prisoners emphasize the high occurrence of E. dispar infection. Each of these samples was
checked for Entamoeba infection, by careful microscopy with ocular measurement, of
formol–ether concentrates. DNA was then extracted from the 213 samples (27.6%) found
Entamoeba-positive, and run in a real-time PCR with primers, based on the SSU-rRNA gene
sequences of E. histolytica and E. dispar, that allow DNA from the two species to be
distinguished. Although E. dispar DNA was identified in 195 (91.5%), no E. histolytica DNA
was detected. This finding is consistent with the previous investigation that many amebic
infections in Ethiopia are incorrectly attributed to E. histolytica and then treated unnecessarly.
In order to further confirm the actual occurrence of E. histolytica, 110 suspected
haematophagous trophozoites were collected from different hospitals and health centers. Only
three (2.7 %) E. histolytica cases were detected by real-time PCR, while 71.3 % were E.
dispar. The finding was similar among HIV/AIDS patients with diarrhea where microscopy
revealed 12 % E. histolytica/E. dispar, but none with E. histolytica. The tradition of
microscopy in a routine diagnostic set-up appears unsatisfactory to reliably differentiate RBCengulfing
ameba from non-invasive ameba. The public health implication of this study is that
patient management and validity of epidemiological surveys are questionable as long as
microscopy is the only diagnostic tool. There is also a need to continue work to establish the
aetiology of diarrhea wrongly associated with amebae and explain the enigma of patients
recovering following “anti-amebic” treatment. The commonly reported complaints of bloody
mucoid diarrhea and association of low CD4 with E. dispar infection among AIDS patients
require alternative explanation. Training in microscopy needs improvement, if not to diagnose the infection accurately, at least to minimize the over-reporting. This work emphasizes the necessity of capacity building for important diarrheal pathogens with molecular diagnostics at referral level
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