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Revisiting amebiasis
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in the developed world2,3. We reported 72 patients infected with E. histolytica/ E. dispar in a single travel clinic in Toronto, of whom 69 were infected with the non-pathogen, E. dispar, thereby highlighting the importance of distinguishing pathogen from nonpathogen in the clinic2. Second, in developing countries such as Bangladesh, others have argued that E. histolytica is not associated significantly with diarrhea and dysentery, whereas rotavirus, Campylobacter jejuni, enterotoxigenic Escherichia coli, Shigella spp and Vibrio cholerae O1 are major contributors4. Third, while stool antigen ELISA is an important diagnostic tool, studies on the diagnostic efficacy of these kits are confounded by the absence of a gold standard. Many studies use culture and isoenzyme electrophoresis as a reference standard; however, others have reported low success rates of obtaining positive cultures, even in the presence of trophozoites as evidenced by microscopy5. Hence, the sensitivity and specificity values for stool antigen assays might be somewhat skewed by selecting for stool that are culture positive. In spite of these caveats, the dissemination of an accurate stool antigen kit clearly has the potential to improve our understanding of the epidemiology of E. histolytica and E. dispar. Dylan R. Pillai Institute of Medical Science, 7318, 1 King´s College Circle, University of Toronto, Toronto, Ontario, Canada M5S 1A8. e-mail: [email protected] References 1 Petri, W.A., Jr et al. (2000) Estimating the impact of amebiasis on health. Parasitol. Today 16, 320–321 2 Weinke, T. et al. (1990) Prevalence and clinical importance of Entamoeba histolytica in two highrisk groups: travelers returning from the tropics and male homosexuals. J. Infect. Dis. 161, 1029–1031 3 Pillai, D.R. et al. (1999) Entamoeba histolytica and Entamoeba dispar: epidemiology and comparison of diagnostic methods in a setting of nonendemicity. Clin. Infect. Dis. 29, 1315–1318
TRENDS in Parasitology Vol.17 No.2 February 2001
4 Albert, M.J. et al. (1999) Case-control study of enteropathogens associated with childhood diarrhea in Dhaka, Bangladesh. J. Clin. Microbiol. 37, 3458–3464 5 Strachan, W.D. et al. (1988) Immunological differentiation of pathogenic and non-pathogenic isolates of Entamoeba histolytica. Lancet 1, 561–563
Revisiting amebiasis Response from Petri et al.
We thank Pillai for emphasizing that amebiasis is not exclusively a disease of the developing world. In the developed world, amebiasis disproportionately afflicts immigrants from and travelers to developing countries, residents of institutions for the mentally retarded and homosexuals1–3. The work of Pillai and colleagues has underscored the inadequacy of current diagnostic techniques in North American community labs, where the stool ova and parasite test is <10% sensitive1! Clearly, better diagnostic approaches are needed, especially tests that are sensitive, simple to use and able to differentiate Entamoeba histolytica from the more prevalent, but non-pathogenic parasite Entamoeba dispar. Since our Comment was published4, we have reported the examination of >1000 children in Dhaka for amebiasis using the TechLab E. histolytica II stool antigen detection test. All samples were tested by both culture and antigen detection, with discrepant results resolved by PCR. The stool antigen
65
test was 100% sensitive and 99% specific (Table 1)5. It is time to re-examine studies such as that by Albert et al.6 using accurate diagnostic techniques. William A. Petri, Jr* Division of Infectious Diseases, University of Virginia, Charlottesville VA 22908-1340, USA. Rashidul Haque ICDDRB, Center for Health and Population Research, GPO Box 128, Dhaka, Bangladesh. David Lyerly Richard R. Vines TechLab, Inc.,1861 Pratt Drive, Suite 1030, Blacksburg, VA 24060-6364, USA. *e-mail: [email protected] References 1 Pillai, D.R. et al. (1999) Entamoeba histolytica and Entamoeba dispar: epidemiology and comparison of diagnostic methods in a setting of nonendemicity. Clin. Infect. Dis. 29, 1315–1318 2 Tachibana, H. et al. (2000) Asymptomatic cyst passers of Entamoeba histolytica but not Entamoeba dispar in institutions for the mentally retarded in Japan. Parasitol. Int. 49, 31–35 3 Seeto, R.K. and Rockey, D.C. (1999) Amebic liver abscess: epidemiology, clinical features, and outcome. West. J. Med. 170, 104–109 4 Petri, W.A., Jr et al. (2000) Estimating the impact of amebiasis on health. Parasitol. Today 16, 320–321 5 Haque, R. et al. (2000) Diagnosis of amebic liver abscess and intestinal infection with the Techlab Entamoeba histolytica II antigen detection and antibody tests. J. Clin. Microbiol. 38, 3235–3239 6 Albert, M.J. et al. (1999) Case control study of enteropathogens associated with childhood diarrhea in Dhaka, Bangladesh. J. Clin. Microbiol. 37, 3458–3464
Table 1. Detection of Entamoeba histolytica by culture and E. histolytica II test in stool specimens of 1164 preschool children, Dhaka, Bangladesh Positive
E. histolytica II testb Positive Negative Total
Culture for Entamoeba histolyticaa Negative
16 0 16
34 1114 1148
Total
50 1114 1164
aEntamoeba histolytica was detected by PCR in 79% (27/34) of discrepant [E. histolytica II test (positive) and culture (negative)] stool specimens. Reprinted, with permission, from Ref. 5.
Letters to the Editor Trends in Parasitology welcomes Letters to the Editor on any subject of interest to parasitologists. If stimulated by an article published in this journal, the original author will be given the opportunity to reply. Please mark clearly whether or not your letter is intended for publication, and address it to: The Editor, Trends in Parasitology, Elsevier Science London, 84 Theobald’s Road, London, UK WC1X 8RR.
http://parasites.trends.com 1471-4922/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.
in the developed world2,3. We reported 72 patients infected with E. histolytica/ E. dispar in a single travel clinic in Toronto, of whom 69 were infected with the non-pathogen, E. dispar, thereby highlighting the importance of distinguishing pathogen from nonpathogen in the clinic2. Second, in developing countries such as Bangladesh, others have argued that E. histolytica is not associated significantly with diarrhea and dysentery, whereas rotavirus, Campylobacter jejuni, enterotoxigenic Escherichia coli, Shigella spp and Vibrio cholerae O1 are major contributors4. Third, while stool antigen ELISA is an important diagnostic tool, studies on the diagnostic efficacy of these kits are confounded by the absence of a gold standard. Many studies use culture and isoenzyme electrophoresis as a reference standard; however, others have reported low success rates of obtaining positive cultures, even in the presence of trophozoites as evidenced by microscopy5. Hence, the sensitivity and specificity values for stool antigen assays might be somewhat skewed by selecting for stool that are culture positive. In spite of these caveats, the dissemination of an accurate stool antigen kit clearly has the potential to improve our understanding of the epidemiology of E. histolytica and E. dispar. Dylan R. Pillai Institute of Medical Science, 7318, 1 King´s College Circle, University of Toronto, Toronto, Ontario, Canada M5S 1A8. e-mail: [email protected] References 1 Petri, W.A., Jr et al. (2000) Estimating the impact of amebiasis on health. Parasitol. Today 16, 320–321 2 Weinke, T. et al. (1990) Prevalence and clinical importance of Entamoeba histolytica in two highrisk groups: travelers returning from the tropics and male homosexuals. J. Infect. Dis. 161, 1029–1031 3 Pillai, D.R. et al. (1999) Entamoeba histolytica and Entamoeba dispar: epidemiology and comparison of diagnostic methods in a setting of nonendemicity. Clin. Infect. Dis. 29, 1315–1318
TRENDS in Parasitology Vol.17 No.2 February 2001
4 Albert, M.J. et al. (1999) Case-control study of enteropathogens associated with childhood diarrhea in Dhaka, Bangladesh. J. Clin. Microbiol. 37, 3458–3464 5 Strachan, W.D. et al. (1988) Immunological differentiation of pathogenic and non-pathogenic isolates of Entamoeba histolytica. Lancet 1, 561–563
Revisiting amebiasis Response from Petri et al.
We thank Pillai for emphasizing that amebiasis is not exclusively a disease of the developing world. In the developed world, amebiasis disproportionately afflicts immigrants from and travelers to developing countries, residents of institutions for the mentally retarded and homosexuals1–3. The work of Pillai and colleagues has underscored the inadequacy of current diagnostic techniques in North American community labs, where the stool ova and parasite test is <10% sensitive1! Clearly, better diagnostic approaches are needed, especially tests that are sensitive, simple to use and able to differentiate Entamoeba histolytica from the more prevalent, but non-pathogenic parasite Entamoeba dispar. Since our Comment was published4, we have reported the examination of >1000 children in Dhaka for amebiasis using the TechLab E. histolytica II stool antigen detection test. All samples were tested by both culture and antigen detection, with discrepant results resolved by PCR. The stool antigen
65
test was 100% sensitive and 99% specific (Table 1)5. It is time to re-examine studies such as that by Albert et al.6 using accurate diagnostic techniques. William A. Petri, Jr* Division of Infectious Diseases, University of Virginia, Charlottesville VA 22908-1340, USA. Rashidul Haque ICDDRB, Center for Health and Population Research, GPO Box 128, Dhaka, Bangladesh. David Lyerly Richard R. Vines TechLab, Inc.,1861 Pratt Drive, Suite 1030, Blacksburg, VA 24060-6364, USA. *e-mail: [email protected] References 1 Pillai, D.R. et al. (1999) Entamoeba histolytica and Entamoeba dispar: epidemiology and comparison of diagnostic methods in a setting of nonendemicity. Clin. Infect. Dis. 29, 1315–1318 2 Tachibana, H. et al. (2000) Asymptomatic cyst passers of Entamoeba histolytica but not Entamoeba dispar in institutions for the mentally retarded in Japan. Parasitol. Int. 49, 31–35 3 Seeto, R.K. and Rockey, D.C. (1999) Amebic liver abscess: epidemiology, clinical features, and outcome. West. J. Med. 170, 104–109 4 Petri, W.A., Jr et al. (2000) Estimating the impact of amebiasis on health. Parasitol. Today 16, 320–321 5 Haque, R. et al. (2000) Diagnosis of amebic liver abscess and intestinal infection with the Techlab Entamoeba histolytica II antigen detection and antibody tests. J. Clin. Microbiol. 38, 3235–3239 6 Albert, M.J. et al. (1999) Case control study of enteropathogens associated with childhood diarrhea in Dhaka, Bangladesh. J. Clin. Microbiol. 37, 3458–3464
Table 1. Detection of Entamoeba histolytica by culture and E. histolytica II test in stool specimens of 1164 preschool children, Dhaka, Bangladesh Positive
E. histolytica II testb Positive Negative Total
Culture for Entamoeba histolyticaa Negative
16 0 16
34 1114 1148
Total
50 1114 1164
aEntamoeba histolytica was detected by PCR in 79% (27/34) of discrepant [E. histolytica II test (positive) and culture (negative)] stool specimens. Reprinted, with permission, from Ref. 5.
Letters to the Editor Trends in Parasitology welcomes Letters to the Editor on any subject of interest to parasitologists. If stimulated by an article published in this journal, the original author will be given the opportunity to reply. Please mark clearly whether or not your letter is intended for publication, and address it to: The Editor, Trends in Parasitology, Elsevier Science London, 84 Theobald’s Road, London, UK WC1X 8RR.
http://parasites.trends.com 1471-4922/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.