HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Notice of Inadvertent Duplicate Publication Alert me when this article is cited Alert me if a correction is posted Citation Map Services Related articles in AJTMH Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (9) Citing Articles via Google Scholar Google Scholar Articles by MORÁN, P. Articles by XIMÉNEZ, C. Search for Related Content PubMed PubMed Citation Articles by MORÁN, P. Articles by XIMÉNEZ, C. Related Collections AIDS Amebiasis

INFECTION BY HUMAN IMMUNODEFICIENCY VIRUS-1 IS NOT A RISK FACTOR FOR AMEBIASIS

ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The purpose of this study was to determine whether HIV-1 infected patients in our community were more susceptible to Entamoeba histolytica and Entamoeba dispar infection than non-HIV-infected individuals. The prevalence and frequency of invasive amebiasis was determined in 203 HIV⁺/AIDS subjects and 140 close relatives or sexual partners, all of whom were HIV^–. Anti–E. histolytica antibodies (IgG, IgA) were assessed as indicators of E. histolytica invasive infection. Polymerase chain reaction (PCR) was used for the characterization of the Entamoeba species. The prevalence estimated with PCR data showed that E. histolytica infection was more common in the HIV⁺/AIDS group (25.32%), than in HIV^– contacts (18.46%). E. histolytica + E. dispar infection was more frequent in HIV⁺/AIDS patients (13.3%), than in HIV^– contacts (0.7%). E. histolytica and/or E. dispar infection was highly prevalent in HIV⁺/AIDS patients (34.1%) without evidence of recent or current invasive disease. Contacts of HIV⁺/AIDS patients who were infected with E. histolytica were asymptomatic cyst passers. Our results suggest that E. histolytica strains prevalent in the studied community appear to be of low pathogenic potential.

INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Intestinal parasites are among some of the most important causal etiologic agents of diarrhea in patients with the acquired immunodeficiency syndrome (AIDS), both in developed and underdeveloped countries.^1,2 The most frequent opportunistic parasites in HIV-infected individuals are intracellular protozoa (Isospora belli, Cryptosporidium parvum, Cyclospora).³ However, infection with other extracellular parasites considered nonopportunistic, but otherwise pathogenic for humans, are also related to diarrheal disease in AIDS patients. Among these parasites are Entamoeba histolytica, Giardia lamblia, Strongyloides stercoralis, and Ascaris lumbricoides.^4,5 Parasites can cause diarrhea in HIV-infected patients and can play a role in the progression of HIV infection in AIDS patients, as well as in asymptomatic HIV-infected individuals. Several studies report stimulation of the HIV replication process when host resistance mechanisms against HIV are impaired.^6–8

The adaptive cellular immune response, which is seriously damaged in AIDS patients, is a central mechanism of resistance against the parasite.⁹ However, the effect of HIV infection on susceptibility for amebic infection or invasive amebic disease is unknown. There are reports concerning the occurrence of invasive amebiasis in endemic areas.^4,10,11 In the developing world, including Mexico, parasite prevalence is particularly high, and many cases coincide with the HIV epidemic.^4,12 The anti–E. histolytica antibody seroprevalence in Mexico is 8.41%,¹³ and intestinal infection with E. histolytica/ Entamoeba dispar is 5–7% in urban communities and up to 30% in rural populations.¹² These numbers highlight the high exposure to these protozoa in Mexico. Previous data showed a prevalence of 30% for E. histolytica/E. dispar infection in homosexual men; however, invasive amebic disease appeared to be uncommon.¹⁴

To determine whether HIV-1 infected (HIV⁺) patients in Mexico City are more susceptible to E. histolytica or E. dispar infection than non-HIV-infected individuals (HIV^–), we studied the prevalence and frequency of amebic invasive disease in groups of HIV⁺ patients who met the Centers for Disease Control and Prevention Surveillance Criteria for AIDS.¹⁵ These individuals comprised patients seen at the AIDS Clinic at the Hospital Regional 1^ero. de Octubre, ISSSTE, in Mexico City from April 1999 to April 2000. Simultaneously, HIV^–close relatives or sexual partners of AIDS patients were included as second population. We also studied the anti–E. histolytica antibody response in both serum (IgG) and saliva (IgA) samples and characterized Entamoeba found in fecal specimens using polymerase chain reaction (PCR).

MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Subjects. This study was previously assessed and approved by the Ethics Committee at the Hospital Regional 1^ero. de Octubre, ISSSTE, in Mexico City, in accordance with the Mexican General Health Law for research in humans, which is based on the Declaration of Helsinki.¹⁶ Three hundred forty-three subjects were included in the study after signing a written informed consent (203 HIV⁺/AIDS and 140 HIV^–contacts). The HIV⁺/AIDS patients were on a triple antiviral medication scheme. For the purpose of comparing two groups of individuals exposed to the same E. histolytica/E. dispar infectious sources, we included 203 HIV⁺/AIDS patients in the experimental group and 140 healthy, non-HIV-infected close relatives or sexual partners of HIV⁺/AIDS patients.

Consecutive HIV⁺/AIDS patients were enrolled in the 12-month period from January 2000 to February 2001 and clinically examined. Laboratory tests included microscopic examination of three consecutive stool samples, CD4⁺ lymphocyte T-cell counts, measuring of viral load, and PCR characterization of E. histolytica and E. dispar species. Anti-amoeba antibody response was also assessed both in saliva and in serum samples.

Detection of parasites. Detection of parasites was performed both through microscopic examination of fresh stool samples previously stained with iodine solution (4%) at 40x and afterwards using the flotation technique in a zinc-sulfate gradient (d = 1.192° Bulk).¹⁷

DNA extraction and PCR. DNA was extracted from cysts present in stool samples placed in the zinc-sulfate gradient.¹⁸ Cysts were transferred to 2-mL microcentrifuge tubes, washed four times with 0.15 M NaCl, and suspended in 300 µL of lysis buffer (100 mM EDTA, SDS 0.25%, pH 8).

The tubes were frozen three times in ethanol-dry ice and thawed in a 37°C water bath. Finally, 3 µL of 20 mg/mL proteinase K (Sigma Chemical Co., St. Louis, MO) was added, and the sample was incubated for 1 hour at 55°C. After digestion with proteinase K, lysates were adjusted to 0.7 M NaCl and 1% CTAB (Sigma Chemical Co.). The mixture was incubated at 65°C for 20 minutes. DNA was extracted with chloroform and phenol/chloroform, followed by precipitation with ethanol. Precipitated DNA was suspended in water and placed in a Sephadex G-25 spin column (Pharmacia-Biotech, Uppsala, Sweden).

The DNA extracted was submitted to PCR amplification assay under standard conditions (AmpliTaq Kit, Perkin Elmer Applied Biosystems, Foster City, CA) for 35 one-minute cycles at 94°C, for 1.5 minutes at 55°C, and 2 minutes at 72°C in a DNA thermocycler (Perkin Elmer Applied Bio-systems). For characterization of E. histolytica or E. dispar species, species-specific DNA sequences of rRNA genes for small ribosomal subunits were amplified using Psp5'-3' primer for E. histolytica and NPsp 5'-3' for E. dispar detection. Both amplification products were 876 bp in size.¹⁹ These products were visualized in 1.2% agarose gels in TBE buffer. Gels were stained with ethidium bromide and photographed for later analysis.

CD4⁺ lymphocyte T-cell counts. Quantification of CD4⁺ T-cell lymphocytes was performed through cytofluorometry using T-cell monoclonal antibodies.²⁰ Patients were grouped according to preestablished CD4⁺ T-cell lymphocyte count ranges based on the stage of HIV infection.¹⁵ In some cases, viral loads were measured at different periods throughout follow-up.

Anti-amebic antibody detection. Anti-amebic antibody detection was performed in both saliva and serum samples following the ELISA technique as previously described.²¹

For the detection of anti-amebic IgA, saliva samples were initially titrated for total IgA quantification and then all samples were adjusted to 50 µg/mL. Serum samples were diluted 1:1,000 for anti-amebic IgG detection.

The antigen used in ELISA was a membrane-enriched extract (1 µg/well) obtained from axenically cultured E. histolytica HM1:IMSS as previously described.²¹ Afterwards, 50 µL/well of serum or saliva dilution was added to each micro-titer plate, blocking previously the free antigen spaces with 3% PBS-BSA and subsequently incubated for 2 hours at room temperature. Plates were then washed once with PBS-BSA, added to 0.5% Tween-20 (Sigma Chemical Co.) (PBS-BSA-Tw), and twice with PBS-Tw. Anti-human IgA or IgG heavy chain-specific antibodies coupled with peroxidase (Zymed Laboratories, San Francisco, CA) were used for the detection of the antigen-antibody reaction (50 µL/well of 1: 1,000 dilution). The antibodies were incubated overnight at 4°C and mildly shaken. After three consecutive washes (3 minutes each) with PBS-BSA-Tw, 50 µL/well of substrate solution was added [0.1 M citrate buffer pH 4.5 (10 mL) added with 10 mg o-phenylenediamine and 4 µL of 30% H₂O₂ solution] and allowed to react for 3 minutes; then, the reaction was stopped with 1 M H₂S0₄ (200 µL/well). Plates were read at 490 nm in a Micro-ELISA reader. An ELISA test for the presence of anti-amebic antibodies was considered positive when the O.D. value was above the cutoff point defined as the mean of the respective O.D. values obtained from nonparasitized control individuals (HIV^–) plus two standard deviations (IgG = 0.29 and IgA = 0.53).

Statistical analysis. The statistical analysis was performed using SPSS 10.0 version software (SPSS, Chicago, IL). A descriptive exploratory analysis of the data was performed to assess the distribution of variables (age, gender, marital status, and sexual preferences) in HIV⁺/AIDS (experimental) and HIV^– (control) groups. ² and/or ² for linear trend testing were used to determine the level of association of E. histolytica infection to the HIV⁺/AIDS condition and study group’s immune status. Fisher’s exact test was used to evaluate the association between anti–E. histolytica antibodies and E. histolytica infection in both groups.²²

RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Characteristics of the study populations. Three hundred forty-three individuals were studied: 203 were HIV⁺/AIDS patients, and 140 were HIV^– contacts. In the HIV⁺/AIDS group the mean age was 42.3 ± 10.2 years, and 184 (91%) were males. The HIV^– contacts included 59 males (42%) and 81 females with an overall mean age of 33.0 ± 21.3 years. This group was recruited from close relatives or sexual partners of HIV⁺/AIDS patients. Only 12 (9%) contacts were active homosexuals compared with 137 (67%) in the HIV⁺/AIDS cohort.

Clinical categories of HIV⁺/AIDS patients were based on peripheral T-CD4⁺ lymphocyte cell counts and clinical manifestations (Centers for Disease Control and Prevention [CDC], Atlanta, GA). Thirty-three percent of the HIV⁺/ AIDS patients were classified as stage A, 41.9% were stage B, and 25.1% were stage C. Eighty percent of the patients were diagnosed as HIV⁺ and/or AIDS 5 years prior to their participation in the current study.

Prevalence of parasites infection. Table 1 shows the prevalence of different intestinal parasites was determined by microscopic examination of stool samples. The most common parasites were protozoa, some of them potential pathogens for humans (e.g., G. lamblia and E. histolytica/E. dispar). Thirty-five (17.2%) HIV⁺/AIDS patients excreted at least one intestinal parasite compared with 37 (26.4%) HIV^– contacts. (P = 0.04). With exception of Endolimax nana, which was more common in HIV^– contacts, the frequency of other protozoa was similar in both studied groups (Table 1). The E. histolytica/E. dispar complex was detected in 5.9% of HIV⁺/ AIDS patients and in 2.9% of contacts. Although not statistically significant, there was a twofold increase in frequency of E. histolytica/E. dispar in HIV⁺/AIDS patients.

Specific salivary IgA was found in 39.5% (15 of 38) of E. histolytica–colonized HIV⁺/AIDS patients versus 40.2% (43 of 107) of non-E. histolytica–parasitized patients. In HIV^–contacts, the occurrence of secretory IgA was essentially the same in E. histolytica–colonized (2 of 4 [50%]) and non-E. histolytica–colonized (17 of 33 [51.5%]) individuals. None of the associations between the presence of specific antibody and E. histolytica colonizations was statistically significant.

DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The aim of the current study was to determine the prevalence of enteric protozoa E. histolytica and E. dispar in HIV⁺/ AIDS patients and their contacts in Mexico City. Further, the immunologic status and clinical stages of HIV infection were examined for a potential association with E. histolytica and/or E. dispar intestinal colonization. Intestinal parasites have been identified as causal agents of diarrhea in HIV⁺/AIDS patients in the industrialized world, an occurrence that is even more likely in the developing world where intestinal parasites (protozoa or helminthes) are highly endemic. Indeed, increased prevalence of intestinal parasitic diseases have been documented in HIV-infected individuals and in some cases are related to the progression of HIV infection.^5–8 Mexico is considered highly endemic for E. histolytica infection, including some geographic regions where the infection is especially prevalent.^12,13

The current study describes two closely related populations, HIV⁺/AIDS patients and their HIV^– contacts, and show that both groups were equally likely to have intestinal parasitic infections. Opportunistic parasite infections (Blastocystis hominis, Isospora belli) were detected in only 5 HIV⁺/AIDS patients. We also observed an equally high frequency of multiparasitism in both groups (Table 1). These two observations are consistent with previous studies conducted in other developing countries.^23–26

We speculated that both groups would be equally exposed to E. histolytica and/or E. dispar infection given their close physical contact and similar environments but might differ in their susceptibility to infection. There are previous reports where the apparent association between HIV infection and E. histolytica/E. dispar protozoa is unlikely to be the result of sociodemographic characteristics.^5,27,28 Studies conducting multivariate analysis while controlling for different variables including sexual behavior, showed that E. histolytica/E. dispar infection was more frequently diagnosed in men who have sex with men, than in persons with exposure to other parasites.^29,30 In our study, the prevalence of E. histolytica and/or E. dispar colonization was significantly greater in HIV⁺/AIDS patients than in non-HIV infected contacts (P = 0.019); however, this difference was a consequence of higher prevalence of E. dispar infection in the HIV⁺/AIDS group (22%) versus (3.8%) in non-HIV-infected contacts (P = 0.001) (Table 2).

On the other hand, E. histolytica and/or E. dispar infection were not significantly related to HIV status, sexual behavior, or gender (Table 3). However, there was a trend toward a higher percent of infected individuals as the HIV infection progressed.

Previous studies show that the role of sexual behavior in the higher frequency of E. histolytica/E. dispar infection in homosexual communities is controversial.⁵ Increased fecal-oral contact may place these individuals at higher risk for HIV as well as amebic infection. However, the association between HIV and amebic infection may be more relevant in communities with low-background transmission of E. histolytica, such as homosexual communities in industrialized countries. In underdeveloped countries, like Mexico, with a high prevalence for amebic infection, the observed association may be related to the high exposure to the parasite. In our study, we explored the association of amebic infection in two different populations (HIV⁺/AIDS and HIV^– individuals) exposed to the same environment and parasitic infectious sources. When the Entamoeba species was characterized through PCR assays, HIV⁺/AIDS patients and HIV^– contacts showed a similar prevalence for the E. histolytica species both as a single species or detected together with the E. dispar species (P = 0.16) (Table 2). However, as we previously mention, prevalence of E. histolytica and/or E. dispar was greater in HIV⁺/AIDS group than in HIV contacts (P = 0.019).

We further examined the susceptibility of HIV⁺/AIDS patients to E. histolytica and/or E. dispar infection as related to the immune status. In our study, no significant association was found between infection with E. histolytica and/or E. dispar, and the stage of the HIV infection, including T-CD4⁺ lymphocyte cell counts (Table 3). However, our results can be potentially biased due to the limited number of individuals in the study, and the effect of this circumstance on the statistical analysis. Additional studies may reveal significance in cases where trends or no differences were seen. Interestingly, none of the individuals infected with the E. histolytica (whether HIV⁺ or HIV^–) had diarrhea or invasive amebiasis within 12 months before the study. Further, the presence of secretory or systemic anti-amebic antibody response was not associated with E. histolytica invasive infection in either study population. These results agree with other reports where the seropositivity of the population exposed to E. histolytica does not correlate with the presence of intestinal colonization.³¹ In Japan, nearly all showed high levels of serum anti-amebic antibodies in a population where intestinal and/or amebic liver abscesses were present in 14 of 30 individuals infected with the E. histolytica species.³²

These data confirm the high prevalence of E. histolytica strains in Mexico, particularly in Mexico City. However, during the 12 months of the study, no one developed a clinical event attributable to E. histolytica infection. This suggests that the study populations were colonized with E. histolytica strains of low pathogenic potential. Recently, the polymorphic structure of E. histolytica has been described.^32–35 Polymorphic DNA loci have been characterized both in protein-coding^36,37 and noncoding^33,35,38 sequences. These polymorphic loci are potentially useful in the molecular epidemiology of amebiasis.^35,39 Preliminary data concerning the polymorphism of serine-rich protein and chitinase loci of E. histolytica and E. dispar in isolates obtained from patients with invasive amoebiasis and from asymptomatic cyst passers from different geographic areas in Mexico suggested a complex geographic distribution of different strains of both Entamoeba species.⁴⁰ However, no correlation was found between a particular polymorphic pattern of a given E. histolytica isolate and the invasive or commensal behavior within the human host.

Received October 14, 2003. Accepted for publication February 8, 2005.

Acknowledgments: The authors would like to especially thank Mrs. María Elena Ortiz and Mr. Marco Gudiño for their secretarial and computer assistance. We would also like to thank María del Carmen García de León and José J. Castillo for their technical assistance. This work includes a part of the doctoral dissertation in Biological Sciences, UAM-X/I, by Miss Patricia Morán.

Financial support: This work was supported by DGAPA IN219599, DGAPA IN234202-2, and 2001 UC MEXUS-CONACYT collaborative grant.

^* Address correspondence to Dr. Cecilia Ximénez, Depto. De Medicina Experimental, Facultad de Medicina, UNAM, Dr. Balmis 148, Col. Doctores, C.P. 06726, México. E-mail: cximenez{at}servidor.unam.mx

Authors’ addresses: Patricia Morán, Fernando Ramos, Alicia Valadez, Emma I. Melendro, Enrique González, and Cecilia Ximénez, Depto. de Medicina Experimental, Facultad de Medicina UNAM, Dr. Balmis 148, Col. Doctores, C.P. 06726, México D.F., México. Alejandro Gómez, Coordinación de Investigación en Salud, IMSS, Centro Médico Siglo XXI, Ave. Cuauhtémoc 330, Col. Doctores, C.P. 03020, México D.F., México. Octavio Curiel, Hospital Regional 1^ero. de Octubre ISSSTE, Ave. Instituto Politécnico Nacional 1669, Col. Magdalena de las Salinas, C.P. 07300, México D.F., México.

Reprint requests: Dr. Cecilia Ximénez, Depto. de Medicina Experimental, Facultad de Medicina, UNAM, Dr. Balmis 148, Col. Doctores, C.P. 06726, México D.F., México. Telephone: +5255-56-23-26-66, Fax: +5255-56-23-26-79, E-mail: cximenez{at}servidor.unam.mx.

REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

1. Smith PD, Lane HC, Gill VJ, Manischewitz JF, Quinnan GN, Fauci AS, Masur H, 1988. Intestinal infections in patients with acquired immunodeficiency syndrome (AIDS). Ann Intern Med 108: 328–333.
2. Loughton BE, Druckman DA, Vernon A, Quinn TC, Polk BP, 1988. Prevalence of enteric pathogens in homosexual men with and without acquired immunodeficiency syndrome. Gastroenterology 94: 948–993.[ISI][Medline]
3. Dupont HL, Marshall GD, 1995. HIV-associated diarrhea and wasting. Lancet ii: 352–356.
4. Hung CC, Chen PS, Hsieh SM, Wong JM, Fang CT, Chang SC, Chen MY, 1999. Invasive amoebiasis: an emerging parasitic disease in patients infected with HIV in an area endemic for amoebic infection. AIDS 13: 2421–2428.[ISI][Medline]
5. Fontanet AL, Sahlu T, Rinkedewit T, Messele T, Masho W, Woldemichael T, Yeneneh H, Coutinho RA, 2000. Epidemiology of infections with intestinal parasites and human immunodeficiency virus (HIV) among Sugar-State residents in Ethiopia. Ann Trop Med Parasitol 94: 269–278.[ISI][Medline]
6. Actor JK, Shirai M, Kullberg MC, Buller RM, Sher A, Berzofsky JA, 1993. Helminth infection results in decreased virus-specific CD8+ cytotoxic T-cells and Th1 cytokine responses as well as delayed virus clearance. Proc Natl Acad Sci USA 90: 948–952.[Abstract/Free Full Text]
7. Bentwich Z, Kalinkovich A, Weisman Z, 1995. Immune activation in a dominant factor in the pathogenesis of African AIDS. Immunol Today 16: 187–191.[ISI][Medline]
8. Rizzardini G, Piconi S, Ruzzante S, Fusi ML, Lukwiya M, Declich S, Tamburini M, Villa ML, Fabiani M, Milazzo F, Clerici M, 1996. Immunological activation marker in the serum of African and European HIV-seropositive and seronegative individuals. AIDS 10: 1535–1542.[ISI][Medline]
9. Salata RA, Ravdin JL, 1986. Review of human immune mechanisms directed against Entamoeba histolytica. Rev Infect Dis 8: 261–272.[ISI][Medline]
10. Takeuchi T, Miyahira Y, Kobayashi S, Nozaki T, Mottha S, Matsuda J, 1990. High seropositivity for Entamoeba histolytica in Japanese homosexual men: further evidence for the occurrence of pathogenic strains. Am J Trop Med Hyg 84: 250–251.
11. Reed SL, Wessed DW, David CE, 1991. Entamoeba histolytica infection and AIDS. Am J Med 90: 269–271.[ISI][Medline]
12. Ramos F, Valdez E, Morán P, González E, Padilla G, Gómez A, Ramiro M, Melendro EI, Muñoz O, Clark G, Ximénez C, 2000. Prevalence of Entamoeba histolytica and Entamoeba dispar in highly endemic rural population. Arch Med Res 31: 34–35.
13. Caballero A, Viveros RM, Salvatierra B, Tapia CR, Sepúlveda J, Gutiérrez G, Ortíz OL, 1994. Seroepidemiology of amebiasis in Mexico. Am J Trop Med Hyg 50: 412–419.
14. Quinn TC, Stamm WE, Goodell SE, 1983. The polymicrobial origin of intestinal infection in homosexual men. N Engl J Med 309: 576–582.[Abstract]
15. Bartlett JG, 1999. The Johns Hopkins Hospital 1998–1999 Guide to Medical Care of Patients with HIV Infection. Baltimore, MD: Williams and Wilkins.
16. Investigación en humanos, 2003. Ley General de Salud. Gobierno Federal de los Estados Unidos Mexicanos. SISTA editor, Mexico D.F. pp. 32–34.
17. Ash RL, Orihel TC, 1987. Collection and preservation of faeces. American Society of Clinical Pathologists, eds. Parasites: A Guide to Laboratory Procedures and Identification. Chicago, IL: ASCP Press, 5–14.
18. Acuña-Soto R, Samuelson J, De Girolami P, Zárate L, Millan-Velasco F, Schoolmick G, Wirth D, 1993. Application of the polymerase chain reaction to the epidemiology of pathogenic and non-pathogenic Entamoeba histolytica. Am J Trop Med Hyg 48: 58–70.
19. Clark GC, Diamond LS, 1992. Differentiation of pathogenic Entamoeba histolytica from other intestinal protozoa by riboprinting. Arch Med Res 23: 15–18.[Medline]
20. Strauss K, Hannet I, Engels S, 1996. Performance evaluation of the FACS Court System: a dedicated system for clinical cellular analysis. Cytometry 26: 52–59.[ISI][Medline]
21. Valenzuela O, Ramos F, Morán P, González E, Valadez A, Gómez A, Melendro EI, Ramiro M, Muñoz O, Ximénez C, 2001. Persistence of secretory antiamoebic antibodies in patients with invasive intestinal or hepatic amoebiasis. Parasitol Res 87: 849–852.[ISI][Medline]
22. Kleinbaum DG, Kupper LL, Morgenster H, 1982. Measures of potential impact and summary of the measures. Kleinbaun DG, ed. Epidemiological Research. Principles and Quantitative Methods. New York: Van Nostrand Reinhold, 159–180.
23. Germani Y, Minssart P, Vohito M, Yassibanda S, Gaziou P, Hocquet D, Berthélémy P, Morvan J, 1998. Etiologies of acute, persistent, and dysenteric diarrheas in adults in Bangui, Central African Republic, in relation to human immunodeficiency virus serostatus. Am J Trop Med Hyg 59: 1008–1014.[Abstract]
24. Waywa D, Kongkriengdaj S, Chaidatch S, Tiengrim S, Kowadisaiburana B, Chaikachonpat S, Suwanagool S, Chaiprasert A, Curry A, Bailey W, Suputtamongkol Y, Beeching NJ, 2001. Protozoan enteric infection in AIDS related diarrhea in Thailand. South East Asian. J Trop Med Public Health 32: 151–155.
25. Olmos M, Molina C, Piskorz E, Tawil J, Magnanini F, Casiro A, Cahn P, Concetti H, Janeiro M, Guelfand L, Kaufman S, 1996. Diahrrea and AIDS: more complex diagnostic techniques; better therapeutic results. Acta Gastroenterol Latinoam 26: 91–100.[Medline]
26. Joshi M, Chowdhary AS, Dalal PJ, Manar JK, 2002. Parasitic diarrhoea in patients with AIDS. Nat Med J India 15: 72–74.
27. Borgdorff M, 1994. Epidemiology of HIV-1 infection in Mwanza region, Tanzania. Thesis, Royal Tropical Institute, Amsterdam, The Netherlands.
28. Smith PD, Lane HC, Gill VJ, Manischewitz JF, Quinnan GV, Fauci AS, Masur H, 1998. Intestinal infections in patients with the acquired immunodeficiency syndrome (AIDS). Ann Int Med 108: 328–333.
29. Lowther SA, Dworkin MS, Hanson DL, 2000. Entamoeba histolytica/Entamoeba dispar infections in human immunodeficiency virus infected patients in the United States. Clin Infect Dis 30: 955–959.[ISI][Medline]
30. Esfandiari A, Jordan WC, Brown CP, 1995. Prevalence of enteric parasitic infection among HIV-infected attendees of an inner city AIDS clinic. Cell Mol Biol 41: 519–523.
31. Braga LL, Mendonca Y, Paiva CA, Sales A, Cavalcante ALM, Mann BJ, 1998. Seropositivity for intestinal colonization with Entamoeba histolytica and Entamoeba dispar in individuals in Northeastern Brazil. J Clin Microbiol 36: 3044–3045.[Abstract/Free Full Text]
32. Haghighi A, Kobayashi S, Takeuchi T, Masuda G, Nosaki T, 2002. Remarkable genetic polymorphism among Entamoeba histolytica isolates from a limited geographic area. J Clin Microbiol 40: 4081–4090.[Abstract/Free Full Text]
33. Bhattacharya S, Bhattacharya A, Diamond LS, 1992. Entamoeba histolytica extrachromosomal circular ribosomal DNA: analysis of clonal variation in a hypervariable region. Exp Parasitol 74: 200–204.[ISI][Medline]
34. Clark CG, Diamond LS, 1993. Entamoeba histolytica: a method for isolated identification. Exp Parasitol 77: 450–455.[ISI][Medline]
35. Zabi J, Clark CG, 2001. Isolation and characterization of polymorphic DNA from Entamoeba histolytica. J Clin Microbiol 39: 897–905.[Abstract/Free Full Text]
36. Li E, Kunz-Jenkins C, Stanley SL, 1992. Isolation and characterization of genomic clones encoding a serine-rich Entamoeba histolytica protein. Mol Biochem Parasitol 50: 355–357.[ISI][Medline]
37. Kholer S, Tannich E, 1993. A family of transcripts (K2) of Entamoeba histolytica polymorphic repetitive regions with highly conserved elements. Mol Biochem Parasitol 59: 49–58.[ISI][Medline]
38. Burch DJ, Li E, Reed S, Jackson TF, Stanley SL, 1991. Isolation of a strain specific Entamoeba histolytica cDNA clone. J Clin Microbiol 29: 696–701.[Abstract/Free Full Text]
39. Ghosh S, Frisardi M, Ramírez L, Descateaux S, Sturm K, Newton OA, Dantos JI, Ganguly CH, Lohia A, Reed S, Samuelson J, 2000. Molecular epidemiology of Entamoeba spp.: evidence of a bottleneck (demographic sweep) and transcontinental spread of diploid parasites. J Clin Microbiol 38: 3815–3821.[Abstract/Free Full Text]
40. Ramiro M, Morán P, García G, Ramos F, Valadez A, González E, Melendro EI, Ximénez C, 2003. Coinfección por diferentes clonas de amiba, pertenecientes a la misma especie, en el humano. Medicina Interna de Mexico 19: (S-1) 40.

Related articles in AJTMH:

Notice of Inadvertent Duplicate Publication

AJTMH 2006 75: 1023. [Full Text]  

This article has been cited by other articles:

				Y. Chen, Y. Zhang, B. Yang, T. Qi, H. Lu, X. Cheng, and H. Tachibana Seroprevalence of Entamoeba histolytica Infection in HIV-Infected Patients in China Am J Trop Med Hyg, November 1, 2007; 77(5): 825 - 828. [Abstract] [Full Text] [PDF]

				R. Fotedar, D. Stark, N. Beebe, D. Marriott, J. Ellis, and J. Harkness Laboratory Diagnostic Techniques for Entamoeba Species Clin. Microbiol. Rev., July 1, 2007; 20(3): 511 - 532. [Abstract] [Full Text] [PDF]

				C.-C. Hung, H.-Y. Sun, and S.-C. Chang LETTERS TO THE EDITOR Am J Trop Med Hyg, November 1, 2006; 75(5): 775 - 775. [Full Text] [PDF]

				C. Ximenez LETTERS TO THE EDITOR Am J Trop Med Hyg, November 1, 2006; 75(5): 775 - 776. [Full Text] [PDF]

				J.-J. TSAI, H.-Y. SUN, L.-Y. KE, K.-S. TSAI, S.-Y. CHANG, S.-M. HSIEH, C.-F. HSIAO, J.-H. YEN, C.-C. HUNG, and S.-C. CHANG HIGHER SEROPREVALENCE OF ENTAMOEBA HISTOLYTICA INFECTION IS ASSOCIATED WITH HUMAN IMMUNODEFICIENCY VIRUS TYPE 1 INFECTION IN TAIWAN Am J Trop Med Hyg, June 1, 2006; 74(6): 1016 - 1019. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Notice of Inadvertent Duplicate Publication Alert me when this article is cited Alert me if a correction is posted Citation Map Services Related articles in AJTMH Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (9) Citing Articles via Google Scholar Google Scholar Articles by MORÁN, P. Articles by XIMÉNEZ, C. Search for Related Content PubMed PubMed Citation Articles by MORÁN, P. Articles by XIMÉNEZ, C. Related Collections AIDS Amebiasis