Amebiasis in Ethiopia: Problems in diagnosis and determination of prevalence of infection

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