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Journal of Clinical Microbiology, August 2004, p. 3909-3910, Vol. 42, No. 8
0095-1137/04/$08.00+0     DOI: 10.1128/JCM.42.8.3909-3910.2004

LETTER TO THE EDITOR

Etiology of Acute Diarrhea in Adults in Southwestern Nigeria

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Okeke et al. (5) recently reported that Entameoba histolytica was by far the most frequently encountered pathogen found in association with bloody diarrhea. The method used to come to that conclusion consisted of microscopic examination of a simple wet smear, which is nonspecific in the diagnosis of amebiasis. Moreover, multiple infections with other enteric bacteria were very common, which might further confound the conclusion. It is in fact common knowledge that E. histolytica is not commonly seen with acute diarrhea; it is rather chronic in nature most of the time.

As of 1997 it was officially accepted by the World Health Organization (WHO) (7) that E. histolytica sensu lato is composed of two morphologically identical species: the pathogenic E. histolytica and the nonpathogenic, but very common, Entamoeba dispar. These two parasites cannot be correctly distinguished by microscopy alone unless the trophozoites in question are seen engulfing red blood cells. In that case microscopy could be diagnostic, but even the correct diagnosis appears difficult (2).

Finding of entamoeba trophozoites or cysts in bloody diarrhea is not enough to draw conclusions on causality. Our extensive experience with the diagnosis and epidemiology of amebiasis in Ethiopia revealed that, in contrast with the general belief, E. histolytica is quite rare (2-4). Not only in asymptomatic cases, but even in patients with bloody diarrhea, the great majority of trophozoites and cysts found appeared to belong to either E. dispar or altogether different intestinal amoeba (2). Similar results were reported from Cote d'Ivoire (1) and Ghana (6). Unless powerful species-specific diagnostic tests are used, we have to believe that most of these reported cases of "E. histolytica" are in fact cases of E. dispar or altogether different amoeba. We would like to point out that it is incorrect to report E. histolytica using conventional microscopy alone to come to such a sweeping conclusion. Important conclusions, both at the individual level and at the population level, require inclusion of species-specific tests like PCR.

Top Letter References Letter  References

 

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1. Heckendorn, R., E. K. N’Goran, I. Felger, P. Vounatsou, A. Yapi, A. Oettli, H. P. Marti, M. Dobler, M. Traore, K. L. Lohourignon, and C. Lengeler. 2002. Species-specific field tests of Entamoeba spp. in an area of high endemicity. Trans. R. Soc. Trop. Med. Hyg. 97:305-307.
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2. Kebede, A., J. J. Verweij, B. Petros, and T. Polderman. 2004. Misleading microscopy in amoebiasis. Trop. Med. Int. Health. 9:651-652.[Medline]
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3. Kebede, A., J. J. Verweij, T. Endeshaw, T. Messele, G. Tasew, B. Petros, and A. M. Poldreman. 2004. The use of real-time PCR to identify Entamoeba histolytica and E. dispar infections in prisoners and primary-school children in Ethiopia. Ann. Trop. Med. Parasitol. 98:43-48.[CrossRef][Medline]
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4. Kebede, A., J. J. Verweij, W. Dorigo-Zetsma, E. Sanders, T. Messele, L. Lisehout, B. Petros, and T. Polderman. 2004. Overdiagnosis of amoebiasis in the absence of Entamoeba histolytica among patients presenting with diarrhoea in Wonji and Akaki, Ethiopia. Trans. R. Soc. Trop. Med. Hyg. 97:305-307.
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5. Okeke, I. N., O. Ojo, A. Lamikanra, and J. B. Kaper. 2003. Etiology of acute diarrhea in adults in Southwestern Nigeria. J. Clin. Microbiol. 41:4525-4530.[Abstract/Free Full Text]
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6. Verweij, J. J., F. Oostvogel, E. A. Brienen, A. Nang-Beifubah, J. Ziem, and A. Polderman. 2004. Prevalence of Entamoeba histolytica and Entamoeba dispar in northern Ghana. Trop. Med. Int. Health. 8:1153-1156.
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7. World Health Organization. 1997. Amoebiasis. Wkly. Epidemiol. Rec. 72:97-100.[Medline]

						Amha Kebede* Ethiopian Health & Nutrition Research  Institute/Ethio-Netherlands AIDS  Research Project, P.O. Box 1242 Addis Ababa, Ethiopia Anton M. Polderman Department of Parasitology Leiden University Medical Center Wassenaarseweg 62, Postbus 9605 2300RC Leiden, The Netherlands
						* Phone: 251-1-751522 E-mail: amha{at}enarp.com

Authors' Reply

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While our study, published in 2003 (2), was focused on diarrheagenic Escherichia coli, we felt that it was necessary to report other presumptive pathogens that we encountered. Criteria that were used to define Entamoeba histolytica were morphological features, the presence of engulfed red cells, and motility. Since these criteria are more discriminatory than the use of morphology alone (5, 7), it is unlikely that similar but unrelated amoebae would be mistaken for the E. histolytica complex. However, as Kebede and Polderman observe, our wet-mount methodology could fail to delineate pathogenic E. histolytica from morphologically identical, but nonpathogenic, Entamoeba dispar. Following the reclassification of E. histolytica into pathogenic E. histolytica sensu stricto and E. dispar Brumpt, recent and in-press papers (including those cited above) have detailed more-discriminatory molecular methods. As stated by Kebede and Polderman, these methods, in the main published after our study was conducted, are required for precise delineation of these strains in epidemiological studies. They have been used in some, but not all, recent studies and are predicted to completely replace microscopy in the near future.

We are in agreement with Kebede and Polderman on the methodological limitations of that part of our study, but we find insufficient basis to speculate that most of the amoeba reported were nonpathogenic. The epidemiology of E. histolytica and other intestinal pathogens is known to vary geographically (1, 3, 4), and the conclusions drawn from comparisons with data from considerably dissimilar studies are not in any way supported by our findings. Recovery of Entamoeba was very strongly associated with diarrhea in our study (P < 0.0002), and the E. histolytica complex was the most common agent detected in bloody diarrhea specimens in which only one agent was found. Therefore, our data do suggest an association of the E. histolytica complex with diarrheal disease, even if the specific contribution of E. histolytica sensu stricto cannot be assessed. The claim that E. histolytica is unusual in acute infection is not supported by our data or by other published literature, including recent studies employing discriminatory tests. For example, Haque et al. recently demonstrated that E. histolytica is an important cause of acute and bloody childhood diarrhea (1). Thus, we feel that these should be areas of future investigation, rather than speculation, and prefer to restate that there was an association of the E. histolytica complex (E. histolytica and E. dispar) with disease.

WHO issued a statement a few months before our study was conducted on the potential significance of nondelineation of E. histolytica from E. dispar and recommended the development of suitable methodology (6). Notably, the most recent version of the WHO Manual of Basic Techniques for a Health Laboratory, published 6 years later (7), describes only wet-mount microscopy even though it mentions the problems with specificity. This practical consideration arises from the undeniable fact that stool microscopy continues to be the only technology available to many laboratories in areas of endemicity (5). Immunological tests offer greater portability but are often too expensive to be employed routinely in developing countries. They also require cold-chain transportation that may be unavailable and, in the case of antibody tests, fail to distinguish between current and past infections (4, 5). Molecular epidemiology studies conducted in Africa, including our study and the work cited by Kebede and Polderman, have invariably involved partnerships with industrialized countries. This approach, while useful for small research studies, is inadequate and unsustainable for much-needed larger studies or for clinical diagnostics. Thus, as in our paper, Kebede and Polderman emphasize the necessity for capacity building for molecular diagnostics in sub-Saharan Africa. Definitive identification of important diarrheal pathogens—E. histolytica as well as diarrheagenic E. coli, the central focus of our study—cannot be conducted without it.

Top Letter References Letter  References

 

1
1. Haque, R., D. Mondal, B. D. Kirkpatrick, S. Akther, B. M. Farr, R. B. Sack, and W. A. Petri, Jr. 2003. Epidemiologic and clinical characteristics of acute diarrhea with emphasis on Entamoeba histolytica infections in preschool children in an urban slum of Dhaka, Bangladesh. Am. J. Trop. Med. Hyg. 69:398-405.[Abstract/Free Full Text]
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2. Okeke, I. N., O. Ojo, A. Lamikanra, and J. B. Kaper. 2003. Etiology of acute diarrhea in adults in Southwestern Nigeria. J. Clin. Microbiol. 41:4525-4530.
3
3. Roche, J., and A. Benito. 1999. Prevalence of intestinal parasite infections with special reference to Entamoeba histolytica on the island of Bioko (Equatorial Guinea). Am. J. Trop. Med. Hyg. 60:257-262.[Abstract]
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4. Stanley, S. L., Jr. 2003. Amoebiasis. Lancet 361:1025-1034.[CrossRef][Medline]
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5. Tanyuksel, M., and W. A. Petri, Jr. 2003. Laboratory diagnosis of amebiasis. Clin. Microbiol. Rev. 16:713-729.[Abstract/Free Full Text]
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6. World Health Organization. 1997. Amebiasis. Wkly. Epidemiol. Rec. 72:97-99.
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7. World Health Organization. 2003. Manual of basic techniques for a health laboratory. World Health Organization, Geneva, Switzerland.

						Iruka N. Okeke* Department of Biology Haverford College 370 Lancaster Ave. Haverford, PA 19041 Oladipupo Ojo Novartis PharmaServices Lagos, Nigeria Adebayo Lamikanra Faculty of Pharmacy Obafemi Awolowo University Ile-Ife, Nigeria James B. Kaper Department of Microbiology and Immunology University of Maryland Medical School Baltimore, Maryland
						* Phone: (610) 896-1470 Fax: (610) 896-4963 E-mail: iokeke{at}haverford.edu

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Journal of Clinical Microbiology, August 2004, p. 3909-3910, Vol. 42, No. 8
0095-1137/04/$08.00+0     DOI: 10.1128/JCM.42.8.3909-3910.2004

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Kebede, A. Articles by Kaper, J. B. Search for Related Content PubMed PubMed Citation Articles by Kebede, A. Articles by Kaper, J. B.