Entamoeba moshkovskii infections in children, Bangladesh

Entamoeba moshkovskii cysts are morphologically indistinguishable from those of the disease-causing species E. histolytica and the nonpathogenic E. dispar. Although sporadic cases of human infection with E. moshkovskii have been reported, the organism is considered primarily a free-living amoeba. No simple molecular detection tool is available for diagnosing E. moshkovskii infections. We used polymerase chain reaction (PCR) to detect E. moshkovskii directly in stool. We tested 109 stool specimens from preschool children in Bangladesh by PCR; 17 were positive for E. histolytica (15.6%) and 39 were positive for E. dispar (35.8%). In addition, we found that 23 (21.1%) were positive for E. moshkovskii infection, and 17 (73.9%) of these also carried E. histolytica or E. dispar. The high association of E. moshkovskii with E. histolytica and E. dispar may have obscured its identification in previous studies. The high prevalence found in this study suggests that humans may be a true host for this amoeba.

Effectiveness of peptone-yeast extract (P-Y) medium in the cultivation and isolation of Entamoeba histolytica/Entamoeba dispar in Turkish patients

Amebiasis is a common protozoan infection worldwide, causing serious health problems in both children and adults. Today, almost 10% of the world population is infected with Entamoeba histolytica/Entamoeba dispar. The aims of this study were both the comparison of the reproduction rates and densities of E. histolytica/E. dispar in Robinson, Dobell-Laidlaw and P-Y culture media and isolation of E. histolytica/E. dispar from stool samples in Peptone-Yeast (P-Y) medium. Trophozoites and cysts of E. histolytica/E. dispar, maintained in Robinson medium, and stool samples of patients with amebiasis were inoculated into P-Y, Robinson and Dobell-Laidlaw culture media. Reproduction rates reached their peak levels 48 h after the inoculation in all culture media. Reproduction rates in P-Y and Robinson media were found similar; however, they were higher than the reproduction rate in Dobell-Laidlaw medium (p < 0.01); there was no statistically significant difference between the reproduction rates of P-Y and Robinson media (p > 0.05). Twelve isolates from 12 patients were cultivated in P-Y medium and checked for reproduction everyday for 7 days. Twelve of the 12 (100%) isolates were cultivated in P-Y medium, indicating that the P-Y was an effective medium for the isolation of E. histolytica/E. dispar in stool samples. According to these results, P-Y medium could be preferred in immunologic, serologic and molecular studies and, thus the definitive diagnosis of amebiasis due to its low cost and simple formula.

Real-time PCR for detection and differentiation of Entamoeba histolytica and Entamoeba dispar in fecal samples

A closed-tube, real-time PCR assay was developed for sensitive and specific detection and differentiation of the two closely related intestinal protozoan parasites Entamoeba histolytica and Entamoeba dispar directly from human feces. The assay is performed with the LightCycler system using fluorescence-labeled detection probes and primers amplifying a 310-bp fragment from the high-copy-number, ribosomal DNA-containing ameba episome. The assay was able to detect as little as 0.1 parasite per g of feces. The two pairs of primers used were specific for the respective ameba species, and results were not influenced by the presence of other Entamoeba species even when present in exceeding amounts. PCR was evaluated using several hundred stool samples from areas of amebiasis endemicity in Vietnam and South Africa, and results were compared with those of microscopy and ameba culture. PCR was found to be significantly more sensitive than microscopy or culture, as all samples positive by microscopy and 22 out of 25 (88%) samples positive by culture were also positive by PCR, but PCR revealed a considerable number of additional E. histolytica- or E. dispar-positive samples. Compared to culture and subsequent ameba differentiation by isoenzyme analysis, PCR was 100% specific for each of the two Entamoeba species. Interestingly, the comparison with PCR revealed that culture, in particular, underestimates E. histolytica infections. Given the high sensitivity and specificity of the developed PCR assay, the inability of microscopy to distinguish between the two ameba species, and the time it takes to culture and subsequently differentiate entamoebae by isoenzyme analysis, this assay is more suitable than microscopy or culture to correctly diagnose intestinal E. histolytica or E. dispar infection.

[Usefulness of multiplex-PCR for identification of Entamoeba histolytica and Entamoeba dispar]

We evaluated the usefulness of a multiplex-PCR method for differentiation of Entamoeba histolytica and Entamoeba dispar, which are morphologically indistinguishable species. Cultured trophozoites of E. histolytica HM-1: IMSS and E. dispar SAW were used as the positive control. Seven human fecal samples, from which E. histolytica-like cysts were detected by microscopic examination, and three intestinal protozoan parasites, Cryptosporidium parvum HNJ-1, Giardia intestinalis Portland-1, and Blastocytis hominis Nand II, were used for the evaluation of sensitivity and specificity of the PCR method. The other PCR method, which has been used for the diagnosis of amebic infections in Japan, was also performed by using the same samples for the evaluation. In comparison with the conventional PCR method, the multiplex-PCR showed 1) higher sensitivity, 2) the size of diagnostic fragments of PCR products was clearly different in both Entamoeba species, 3) it was possible to perform PCR using a single tube per sample, and then to save the amount of DNA polymerase, 4) no diagnostic amplification products were found in other intestinal protozoan parasites, and 5) E. histolytica specific fragment was amplified in all clinical samples examined. In conclusion, it is considered that the multiplex-PCR method is a useful tool for detection of both Entamoeba species DNA from fecal samples and for the distinction between E. histolytica and E. dispar.

Entamoeba dispar in a terminal case of acquired immune deficiency syndrome compared with Brumpt's (1925) original cat material

A rectal biopsy from a terminal case of acquired immune deficiency syndrome is compared with a similar biopsy taken by Brumpt in 1925 from a cat which he had infected with what he named Entamoeba dispar.

Dilated cardiomyopathy and amebic gastritis in a giant anteater (Myrmecophaga tridactyla)

An approximately 11-mo-old female giant anteater (Myrmecophaga tridactyla) exhibited anorexia, lethargy, hypothermia, depression, and minimal response to external stimuli. Radiography and ultrasonography revealed an enlarged heart, with free gas and fluid in the abdomen. Abdominocentesis produced a clear brown fluid with an acute to subacute septic suppurative exudate. Cardiac ultrasonography revealed a dilated, thin-walled left ventricle with a comparatively low fractional shortening. Despite intensive supportive care, the anteater died. Postmortem findings included gastric ulceration with perforation near the pylorus. Entameba spp. and Acanthamoeba spp. were both identified in large numbers at the site of the gastric ulceration and perforation.

Amebic infections due to the Entamoeba histolytica-Entamoeba dispar complex: a study of the incidence in a remote rural area of Ecuador

An epidemiologic field study was conducted in the village of Borbòn in Esmeraldas province in northern Ecuador to compare different parasitologic methods in the diagnosis of infection with the Entamoeba histolytica/Entamoeba dispar complex. The results of two stool antigen detection assays (the Prospect Entamoeba histolytica microplate assay and the E. histolytica II assay) were compared with isoenzyme characterization of the amebic isolates. Nearly all (176 of 178, 98.9%) subjects were positive for intestinal parasites on direct microscopic examination, and cysts and/or vegetative forms morphologically consistent with the E. histolytica/E. dispar complex were recorded in 48 of 178 cases (27%). Culture in Robinson's medium was positive for amebic stocks in 89 (50%) of the 178 samples tested. Of the 37 isolates successfully stabilized, cloned, and characterized by zymodeme analysis, seven (18.9%) showed isoenzyme patterns of E. histolytica, whereas 26 (70.3%) showed patterns of E. dispar. The remaining four strains were identified as Entamoeba coli (three isolates; 8.1%) and Dientamoeba fragilis (one strain; 2.7%).The immunochromatographic tests showed different degrees of sensitivity and specificity when compared with isoenzyme characterization as the reference technique. The microplate assay, which does not discriminate between E. histolytica and E.dispar, showed a sensitivity of 54.5% and a specificity of 94% for both these amebic species. In contrast, the second-generation E. histolytica II test had a sensitivity of 14.3% and a specificity of 98.4% for E. histolytica sensu stricto. Our survey clearly demonstrated that more specific and sensitive diagnostic tests, such as stool antigen detection assays and isoenzyme analysis, are needed to establish the actual worldwide distribution of E. histolytica and E. dispar.

Epidemiology of amebiasis in a region of high incidence of amebic liver abscess in central Vietnam

The recent identification of Entamoeba dispar as a separate species, which is nonpathogenic for humans but morphologically indistinguishable from Entamoeba histolytica, has prompted the World Health Organization to recommend reinforced efforts for reassessment of the epidemiology of amebiasis and, in particular, of E. histolytica. In this regard, the distribution of amebic liver abscess (ALA) cases were analyzed in the province of Thua Thien Hué (TT Hué) in central Vietnam, a region known for its high incidence of invasive amebiasis. In addition, in a particular area of Hué City, a parasitologic and seroepidemiologic survey was performed to identify possible risk factors for transmission of E. histolytica. Based on the analysis of hospital charts from April 1990 to April 1998, 2,031 cases of ALA were identified, indicating an ALA incidence of at least 21 per 100,000 inhabitants per year. Incidence varied substantially between the various districts of TT Hué and directly correlated with population density. The risk for ALA was significantly higher in summer and was age and sex dependent because 95% of the cases were adults, of which more than 80% were males. There was no clustering of cases within households and recurrent cases of ALA occured more frequently than predicted in the study population. Despite the higher incidence of ALA in males, the parasitologic and seroepidemiologic survey revealed a significant higher infection rate for intestinal protozoon parasites, including E. histolytica in females. Besides level of education and access to a toilet or tapwater, use of river water was identified as an important risk factor for E. histolytica infection.

Biological aspects of a Brazilian strain of Entamoeba dispar

A strain of Entamoeba dispar was characterized by clinical diagnosis, serological and electrophoretical isoenzyme analysis and by the polymorphism of a 482 bp genomic fragment analysis. The pathogenesis and virulence of this strain was investigated considering the experimental infection in hamster livers in association with the original intestinal microbiota. Liver lesions were observed in hamsters experimentally infected with trophozoites from xenic cultures, but not from the monoxenic cultures. Moreover, clones obtained from re-isolated strain Wil1R1 showed a distinct biological behavior. In fact, animals inoculated with Wil1R1ClB3 showed an intense acute inflammatory reaction with destructive focal hepatic lesions. These lesions were characterized as amebic abscesses. The association between bacteria and ameba has been fairly well studied because it affects the pathogenicity of the amebas and has important therapeutic implications. In this study, we demonstrated that E. dispar in association with the original microbiota is able to produce lesions in hamster liver in spite of its having been considered to be non-pathogenic in the hamster model. Based on these results we suggest that diagnosis of amebiasis needs to be made with more care and that clinical and therapeutical procedures need to be revised.

Amebiasis in four ball pythons, Python reginus

Between September 13th and November 18th in 1999, four ball pythons, Python reginus kept in the same display, showed anorexia and died one after another. At necropsy, all four snakes had severe hemorrhagic colitis. Microscopically, all snakes had severe necrotizing hemorrhagic colitis, in association with ameba-like protozoa. Some of the protozoa had macrophage-like morphology and others formed protozoal cysts with thickened walls. These protozoa were distributed throughout the wall in the large intestine. Based on the pathological findings, these snakes were infested with a member of Entamoeba sp., presumably with infection by Entamoeba invadens, the most prevalent type of reptilian amoebae.

[Relevance of Entamoeba dispar in amebiasis]

Entamoeba histolytica was redefined to recognize the existence of two morphologically indistinguishable species but genetically distinct: E. histolytica and E. dispar. The former is a pathogen responsible for amebiasis while the latter is a commensal. This redefinition has dramatically changed the understanding of amebiasis and its clinical management.

Microscopy, PCR and ELISA applied to the epidemiology of amoebiasis in Greece

Detection and differentiation between Entamoeba histolytica and E. dispar are of great importance both for diagnosis and epidemiological studies. The present study was aimed to estimate the prevalence of these species in Greece and to assess the performance of microscopy, ELISA and PCR in the field. Our results indicate that the prevalence of these parasites is very low in Greece and that PCR and ELISA are by far better than microscopy. When it comes to the choice between ELISA and PCR, it seems that in real situations the advantages of PCR are outweighed by those of ELISA.

Treatment of diarrhea caused by Giardia intestinalis and Entamoeba histolytica or E. dispar: a randomized, double-blind, placebo-controlled study of nitazoxanide

A prospective randomized, double-blind, placebo-controlled study was conducted to assess the efficacy and safety of nitazoxanide in the treatment of diarrhea caused by Giardia intestinalis or Entamoeba histolytica and/or E. dispar in 89 adults and adolescents, 22 of whom were diagnosed with G. intestinalis, 53 with E. histolytica and/or E. dispar, and 14 with both G. intestinalis and E. histolytica and/or E. dispar. The study medication was administered as 1 nitazoxanide 500-mg tablet or a matching placebo twice daily for 3 days. Thirty-eight (81%) of 47 patients in the nitazoxanide treatment group resolved diarrhea within 7 days (median, 3 days) after initiation of treatment, versus 17 (40%) of 42 in the placebo group (P=.0002). With its efficacy in treating a broad spectrum of enteric protozoan pathogens, nitazoxanide could play an important role in the management of diarrhea caused by enteric protozoa, reducing morbidity and costs associated with these diarrheal illnesses.

Evaluation of laboratory techniques for differentiation between Entamoeba histolytica and Entamoeba dispar

Incorporation of clinical, epidemiological and serological parameters to the studies of Entamoeba histolytica resulted in the conclusion that species complex comprising two morphologically identical amoeba were implicated with the disease. The two organisms are E. histolytica and E. dispar. The former is a pathogen and responsible for invasive amoebiasis while the later is a gut commensal. Clearly accurate diagnostic tools are required to distinguish the two species. The use of a stool ELISA has been shown to be useful. A monoclonal enzyme linked immunosorbent assay based kit to detect antigen of E.histolytica only in stool was evaluated in comparison to the results of the microscopical examination of the stools and that of enzyme linked immunosorbent assay used to detect the anti- E. histolytica IgG in serum. This study demonstrated that E. dispar is prevalent in the community and offers promise for E. histolytica monoclonal enzyme immunoassay for the qualitative and semiquantitative determination of sensu lato antigen in stool as a sensitive tool for detection and distinction of E. histolytica from E. dispar infections.

Modifications of Kohn's chlorazol black E staining and Wheatley's trichrome staining for temporary wet mount and permanent preparation of Entamoeba histolytica

Preparation of stained smears of Entamoeba histolytica has several drawbacks. We therefore tried to simplify the staining procedures by modifing Kohn's chlorazol black E staining and Wheatley's trichrome staining techniques. Trophozoites and cysts of axenically cultured E. histolytica and Entamoeba invadens, respectively, and trophozoites and cysts of E. histolytica in stools of patients were used. Karyosomes and peripheral chromatin of nuclei and chromatoid bodies became distinctly visible after amoebae were suspended in the basic solution of Kohn's stain. Amoebae fixed in suspension with either basic solution or Bouin's fixative were clearly stained with Kohn's and trichrome preparations, both as wet mounts directly and as permanent slides after processing for mounting. These procedures were easier when the basic solution was used as a fixative and trichrome stain was employed. Erythrocytes ingested by trophozoites, however, were not stained with either of these preparations after fixation in the basic solution but were clearly stained when Bouin's fixative was used. Cysts of E. histolytica in stools concentrated using basic solution (instead of formalin) and ether were also stained with these stains. Consequently, without employing highly toxic mercuric chloride, wet mounts and permanent smears can be prepared with permanent stains, and preserved cysts can be stained after concentration.

Multiplex polymerase chain reaction amplification and differentiation of Entamoeba histolytica and Entamoeba dispar DNA from stool samples

Due to the clinical importance of differentiating the two species of the Entamoeba histolytica/Entamoeba dispar complex, we developed a multiplex polymerase chain reaction (PCR) method that overcomes time-consuming and laborious procedures. We report here a DNA extraction protocol using non-fixed stool samples that avoid long lysis-incubation periods through the combined use of zirconium beads and a lysis-supporting buffer. We characterized 49 of 52 stool specimens from Cuban patients with amoebiosis. Among them, 36 (75.5%) were infected only with E. dispar (the nonpathogenic species), while 13 (24.5%) displayed a mixed infection with both E. dispar and E. histolytica. The multiplex PCR protocol showed a specificity of 1.00 and a sensitivity of 0.94. Furthermore, the entire procedure can be performed in one day. This approach is therefore reliable and applicable in the field for epidemiologic studies.

Genetic Variation among Human Isolates of Uninucleated Cyst-Producing Entamoeba Species

Twelve human infections with Entamoeba spp. producing uninucleated cysts were studied. DNA was extracted from infected feces and used to amplify part of the ameba small-subunit rRNA gene. Sequence analysis identified four distinct types of Entamoeba, all of which are related to Entamoeba polecki and E. chattoni and two of which have not been reported previously. Whether these genetic types represent different species is unclear. We propose that the agent of all human infections with uninucleated cyst-producing Entamoeba species be reported as "E. polecki-like."

High prevalence of infection with Entamoeba dispar, but not E. histolytica, in captive macaques

A total of 268 nonhuman primates (20 species) kept in the Primate Research Institute, Kyoto University, Japan, were surveyed for intestinal amebas. Total positive rates as based on the presence of cysts in the stool following formalin-ether sedimentation were as follows: Entamoeba histolytica/E. dispar, 53%; E. coli, 34%; E. hartmanni, 34%; Iodamoeba buetschlii, 25%; Endolimax nana, 8%; and E. chattoni, 3%. Positive rates were higher in Old World monkeys and lower in New World monkeys. All the 141 E. histolytica/E. dispar-positive animals were Macaca monkeys. The E. histolytica/E. dispar-positive samples were analyzed by polymerase chain reaction (PCR) for identification of E. histolytica and E. dispar. E. dispar DNA was detected in 137 samples, whereas no E. histolytica DNA was seen. Zymodeme analysis and reactivity to monoclonal antibodies of cultured trophozoites also supported the presence of E. dispar and the absence of E. histolytica. When the sera of 93 macaques were examined by an indirect fluorescent antibody test, only 3 animals proved to be positive for E. histolytica, showing the lowest titer. These results demonstrate that infection with E. dispar, but not E. histolytica, is predominant in macaques.

Evaluation of the Triage Micro Parasite Panel for detection of Giardia lamblia, Entamoeba histolytica/Entamoeba dispar, and Cryptosporidium parvum in patient stool specimens

A study comparing the Triage Micro Parasite Panel (Biosite Diagnostics, Inc., San Diego, Calif.) to conventional O&P examination (O&P) was performed using patient fecal specimens. Five hundred twenty-three stool samples were compared. Nineteen specimens were found to be positive by Triage, and 29 were found to be positive by O&P. Seven specimens were positive for Giardia lamblia, four were positive for Entamoeba histolytica/E. dispar, and three were positive for Cryptosporidium parvum as determined by both methods. There was one false positive by Triage (C. parvum) and four false negatives by O&P (two G. lamblia, one E. histolytica/E. dispar, and one C. parvum). The Triage test accurately detected all 18 specimens that contained one of the three organisms that it was designed to detect. The Triage test is a rapid, easy-to-use enzyme immunoassay for the detection of G. lamblia, E. histolytica/E. dispar, and C. parvum in fresh or fresh-frozen fecal specimens. These data suggest that the Triage test can be used as a screen for the immediate testing of stool specimens for these three pathogenic parasites. If Triage test results are negative, O&P can be performed if parasitic infections other than G. lamblia, E. histolytica/E. dispar, or C. parvum are suspected.

Multiyear prospective study of intestinal parasitism in a cohort of Peace Corps volunteers in Guatemala

We conducted a prospective, longitudinal study in a cohort of 36 Peace Corps volunteers (PCVs) in Guatemala to study the incidence and natural history of intestinal parasitic infections during the PCVs' >2-year overseas stay. PCVs collected stool specimens at least monthly and when ill with gastrointestinal symptoms. Of the 1,168 specimens tested, 453 (38.8%) were positive for at least one parasite and 48 (4.1%) were positive for a pathogenic parasite. A median interval of 187 days (range, 14 to 752 days) elapsed before the first documented parasitic infection, and the median intervals from arrival until subsequent infections (e.g., second or third) were >300 days. The PCVs had 116 episodes of infection with 11 parasites, including up to 4 episodes per PCV with specific nonpathogens and Blastocystis hominis. The incidence, in episodes per 100 person-years, was highest for B. hominis (65), followed by Entamoeba coli (31), Cryptosporidium parvum (17), and Entamoeba hartmanni (17). The PCVs' B. hominis episodes lasted 6,809 person-days (28.7% of the 23,689 person-days in the study), the E. coli episodes lasted 2,055 person-days (8.7%), and each of the other types of episodes lasted <2% of the person-days in the study. Gastrointestinal symptoms were somewhat more common and more persistent, but not significantly so, in association with pathogen episodes than with B. hominis and nonpathogen episodes. Although infections with pathogenic parasites could account for only a minority of the PCVs' diarrheal episodes, the continued acquisition of parasitic infections throughout the PCVs' >2-year stay in Guatemala suggests that PCVs repeatedly had fecal exposures and thus were at risk for infections with both parasitic and nonparasitic pathogens throughout their overseas service.