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Intestinal amebiasis is still an important health problem in developing regions of the world. In order to advance our knowledge on the pathogenesis and to test the relevance of recently obtained in vitro observations, suitable in vivo experimental models of intestinal amebiasis are needed. In the past a variety of laboratory animals have been used, but the mouse, whose genetics and immunology is well known, has been seldomly used. Therefore, Entamoeba histolytica strain HM1:IMSS was directly inoculated into the cecum of C3H/HeJ mice, which were sacrificed at 5, 10, 15, 20, 25 and 30 days for histopathologic analysis. An ulcerative inflammatory disease highly reminiscent of human amebiasis was observed. Early 5 day lesions consisted of tiny erosions of the surface epithelium which evolved to deeper and more extensive destructive lesions of the cecal wall. Indeed, flask-shaped ulcers, intestinal perforations and intramural abscess formation were observed at later times. It was noticeable that, despite the lack of obvious significant tissue invasion by amebae, ulcerative disease was extensive and found virtually in all mice. These observations support the view that tissue invasion by trophozoites is not necessarily required for ulcerative disease to occur, suggesting a role for toxic factors released by amebae.

Purpose: The morphologic features of fulminant amebic colitis are poorly documented. In this report, we describe the clinical and pathologic findings in four of these cases., Methods: The surgical pathology reports and accompanying histologic slides were examined from four patients who underwent surgical resections for fulminant amebic colitis. Clinical information was obtained from the patients' medical records., Results: Large, geographic mucosal ulcers were typically present and were accompanied by yellow-green pseudomembranes. The muscularis externa was usually attenuated and necrotic, imparting a "wet blotting paper" consistency. Large numbers of amebic trophozoites were present within the inflammatory exudates. The mucosa adjacent to and undermined by the ulcers was often hemorrhagic or inflamed, resembling ischemic colitis or idiopathic inflammatory bowel disease, respectively. Two patients died within four weeks of their surgery. A third patient died one year later as a result of AIDS-related complications. The remaining patient has been lost to follow-up., Conclusion: An uncommon but life-threatening manifestation of intestinal amebiasis is a fulminant colitis. Early surgical intervention and intensive antiamebic chemotherapy are essential for efficacious management.

An invasive strain-specific monoclonal antibody against Entamoeba histolytica has been used in a capture enzyme-linked immunosorbent assay (ELISA) for the detection of invasive E. histolytica fecal antigen in clinical specimens and for the diagnosis of amebic dysentery in patients from Bangladesh. The fecal antigen capture ELISA (FAC-ELISA) did not cross-react with other parasite species in the clinical specimens or with noninvasive E. histolytica present in those specimens and in experimentally seeded stools. The limit of detection of the assay for invasive E. histolytica crude antigen diluted in phosphate-buffered saline or in stools was 0.58 and 3.9 micrograms/ml, respectively, which is the equivalent of approximately 72 and 487 E. histolytica trophozoites per well, respectively. The sensitivity, specificity, and efficiency of the FAC-ELISA were 87, 100, and 98%, respectively, for the detection of invasive E. histolytica antigens and 100, 100, and 100%, respectively, for the diagnosis of amebic dysentery. The FAC-ELISA is a potential alternative for the field diagnosis of amebic dysentery and for epidemiological studies to define the distribution of invasive E. histolytica.

A 30-year-old Japanese homosexual AIDS patient was admitted to hospital because of Kaposi's sarcoma and mild diarrhea on February 4, 1993. Mud-like stool with blood and mucous was recognized after admission. Although serologic tests for Entamoeba histolytica were negative, trophozoites of E. histolytica were identified in his bloody stool. Daily doses of 1,000 mg of metronidazole were given orally for 6 days and then 750 mg for 4 days, and good results were observed. His CD4 count was 19.5/mm3. Symptomatic amebic colitis was easily treated and good results were obtained even with the extremely diminished CD4 count. This is the first published report of symptomatic amebic colitis in an AIDS patient in Japan.

The multistep invasion process of metastasis is a well-conserved mechanism of normal symbiosis and pathogenic parasitosis. To illustrate this statement, we have compared cellular and molecular aspects of metastasis from colon cancer and enteric amebiasis caused by Entamoeba histolytica. Both types of pathogenic cell, cancer cells and amebic trophozoites, follow the same metastatic route for the liver and other organs. Both establish invasion microecosystems implicating similar kinds of host cells and molecules belonging to closely related families. We have recently found indications that molecules released by trophozoites immediately after adhesion to epithelial monolayers bind to elements of the epithelial intercellular junctions. This phenomenon may lead to the functional disturbance of these junctions. Down-modulation of cell-cell adhesion molecules promotes invasion of colon cancer and other cancer cells. It is our opinion that comparative studies of apparently unrelated systems may reveal cellular and molecular mechanisms of invasion and metastasis that are of general biological importance.

Adhesion to target cells represents the first step in infection by Entamoeba histolytica. Binding of axenic amoeba (HMI strain) to human red cells in vitro was employed as a model of the adhesion process. The influence of precontact of trophozoites with suspensions of live Saccharomyces boulardii yeasts, their fractions (membranes and yeast-content supernatant before and after filtration to eliminate the membrane) or yeast culture medium before and after fermentation was investigated. N-Acetylgalactosamine (GalNAC) was employed as the reference inhibitory sugar. The percentage of amoebae bearing red cells after pretreatment of amoebae with the various suspensions and derivates was determined. Adhesion was also evaluated by scanning electron microscopy (SEM). Pretreatment of amoebae with the live yeast suspension led to a significant reduction in the percentage of adhesion [32% vs 70% in the phosphate-buffered saline (PBS) control]. Reduced adhesion was also observed with the filtered and unfiltered supernatant of the yeast suspension homogenate [32% and 34%, respectively, vs 69% in the PBS control], yeast culture medium at the end of fermentation [49% vs 76% in the PBS control] and GalNAC [32% vs 72% in the PBS control]. SEM showed a decrease in the number of amoebae bearing red cells and a reduction in the number of red cells adhering to amoebae. We conclude that substances produced by the yeasts compete with red cells for adhesion sites on amoebae.

Amoeboma was diagnosed in three patients: a Bengal seaman aged 40 and two Dutch citizens who had lived in the tropics, a man aged 41 and a woman aged 56. The first-mentioned patient had a rectal tumour easily inspected by sigmoidoscopy; a biopsy sample contained Entamoeba histolytica. The faeces contained no cysts. The two other patients had coecal amoebomas. They had been operated elsewhere on suspicion of appendicitis and had been treated with metronidazole, which had failed to eliminate the amoebae. The faeces still contained cysts. One patient had trophozoites in a biopsy sample. The serum of all three patients contained anti-amoeba antibodies. Two patients were treated successfully with a combination of metronidazole (a tissue amoebicide) and diloxanide (a lumenal amoebicide). In one patient this combination failed, and emetine had to be substituted for the metronidazole, also because of an allergic reaction. Amoeboma of colon or rectum is one of the many manifestation forms of amoebiasis, but it is rare. While in amoebic colitis tissue necrosis (histolysis) is encountered almost exclusively, in amoeboma there is a violent inflammatory reaction with formation of a pseudotumour by granulation tissue, possibly due to secondary bacterial infection. Endoscopy and determination of circulating antibodies against the causative agent E. histolytica have by now improved the diagnosis so much that adequate treatment without surgical intervention is possible in principle. As with so many exotic diseases, a stay in the tropics is the key to the diagnosis.

The present study was carried out to examine whether Entamoeba histolytica cyst passers suffer from any parasite-related bowel symptoms and to assess the frequency of spontaneous eradication of this infection. The study was carried out in two parts. In part I, stool samples were collected at random from 3536 individuals living in rural communities around Delhi. E. histolytica was isolated by the culture technique in 345 (9.7%) subjects. There was no increase in the prevalence rate of bowel symptoms in the culture-positive compared to the culture-negative subjects. One hundred twenty-four (36%) of the culture-positive subjects agreed to take part in a longitudinal study; the subjects were left untreated and clinical assessment and stool examinations were carried out at three-month intervals. One hundred eighteen (95.2%) subjects had eradicated their parasite spontaneously at the end of one year; none developed any features of invasive amebiasis. Part II of the study was carried out on 625 patients attending our Gastroenterology Clinic. Positive cultures of E. histolytica were obtained from 99 (15.2%) patients. Again, there was no increase in the prevalence rate of bowel complaints in the culture-positive compared to the culture-negative subjects. Moreover, histological appearances of the rectal biopsy specimens were not significantly different between the two groups. Twenty-eight (28.2%) patients agreed to the longitudinal study and all eradicated the parasite spontaneously within five months; none developed any evidence of invasive amebiasis.(ABSTRACT TRUNCATED AT 250 WORDS)

A case of amoebic recto-vaginal fistula is presented, with a review of literature on this rare complication of intestinal amoebiasis. A temporary defunctioning sigmoid colostomy was necessary. This in combination with oral metronidazole and tetracycline resulted in spontaneous closure of the fistulous tract. Non-traumatic recto-vaginal fistula poses a major diagnostic problem especially in the tropics where many granulomatous infections are endemic and could mimic carcinoma.

Analysis of the initial interaction between Entamoeba histolytica trophozoites and the large intestine is impossible in humans and very difficult in experimental animals. To circumvent this obstacle we treated the luminal side of full-thickness rabbit colon segments mounted in Ussing-type chambers with trophozoite lysates of the E. histolytica HM1 virulent strain. Exposure to lysates for up to 90 min produced dose- and time-dependent effects on the colon, consisting of (a) increased decay rates for potential difference, short-circuit current, and transmural resistance and (b) mucosal damage ranging from vacuolation at the bases and shortening of epithelial cells to the loss of intercellular junctions, destruction of microvilli, and necrosis of interglandular epithelial zones. This acute model of intestinal amebiasis is sensitive, fast, and reliable.

We used the polymerase chain reaction (PCR) to study the epidemiology of pathogenic and nonpathogenic Entamoeba histolytica in a rural community in Mexico. Formalin-fixed stool samples were used for extraction of DNA. The PCR amplifications were performed using two sets of primers that discriminate between pathogenic or non-pathogenic E. histolytica. A total of 201 randomly selected individuals were studied. Among them, 25 (12%) were diagnosed to be infected with E. histolytica by microscopy; PCR identified 24 of these as positive (sensitivity = 0.96) and of 176 negative individuals, only three were identified as positive (specificity = 0.98). The PCR analysis defined three populations: 14 cases were positive for both pathogenic and nonpathogenic E. histolytica, nine cases were positive for pathogenic and negative for nonpathogenic E. histolytica, and only one case was negative for pathogenic and positive for nonpathogenic E. histolytica. Infection by E. histolytica was strongly associated to infection with Entamoeba coli (odds ratio [OR] = 9.41, 95% confidence interval [CI] = 3.09, 28.65, P < 0.0004) and Endolimax nana (OR = 6.15, 95% CI = 2.03, 18.17, P < 0.0004). This new technique has high specificity and sensitivity; it is simple, reproducible, fast, avoids the need to culture trophozoites, and can be applied in the field for epidemiologic studies.

Eighty-four patients with serious infection due to Entamoeba histolytica were evaluated for systemic complications by objective criteria for dysfunction of the organ systems normally assessed in surgical sepsis. Of 71 patients with amebic liver abscess (ALA), 41% had systemic complications and 13% had more than one organ system involved. Patients > or = 40 years of age and those being treated with steroids were at significantly increased risk of developing complications (P < or = .05). The erythrocyte sedimentation rate and the levels of the acute-phase markers C-reactive protein (CRP) and serum amyloid A (SAA) were significantly elevated in patients with ALA over values in those without ALA (P < or = .05). ALA patients with complications had lower CRP and SAA concentrations than those without complications (P < or = .05). Blood and liver aspirates in ALA patients were usually bacteriologically sterile. The pathogenesis of systemic complications and the associated acute-phase response requires further study, and ways of predicting disease severity and intervening therapeutically must be devised.

Among the wide variety of clinicopathological manifestations of intestinal amebiasis, amebomas occur rarely and their pathogenesis is not well understood. When cholesterol-fed, 2- to 4-week-old guinea pigs were infected intracecally with a virulent, monoaxenic strain of Entamoeba histolytica, gross and histologically characteristic amebomas developed in 85% of the animals by the 3rd day, in 94% by the 9th day, and in 96% by the 12th day postinfection, by which time most of them had died. Amebomas were confirmed by histopathology. Thus, a model of consistent production of amebomas was documented.

E. histolytica parasites in Mexican children's stools were identified and typed as pathogenic or non-pathogenic using the polymerase chain reaction (PCR) and nonradioactive probes. PCRs were performed with primers specific for 145 base pair (bp) pathogenic or 133 bp non-pathogenic DNA sequences, which are highly repeated in E. histolytica parasites with pathogenic or non-pathogenic isoenzyme patterns, respectively. Dot-blotted PCR products were identified with a horseradish peroxidase-conjugated oligonucleotide probe specific for either the 145 bp pathogenic or 133 bp non-pathogenic sequences. The PCR and the 145 bp pathogenic probe correctly identified eight cultures with pathogenic isoenzyme types and none of nine cultures with non-pathogenic isoenzyme. The PCR and 133 bp non-pathogenic probe identified all of the non-pathogenic cultures, none of the axenized pathogenic cultures, and three of five xenic cultures with pathogenic isoenzymes. The two probes together identified all 49 stools containing E. histolytica by light microscopy (sensitivity = 1.0), which represented the entire set of the E. histolytica-positive stools diagnosed at the Hospital Infantil over a 10 week period. Most patient isolates were positive with both 145 bp pathogenic and 133 bp non-pathogenic probes, suggesting that these children, 60% of whom were dysenteric, are infected with mixed populations of amebas.

Mongolian gerbils were inoculated intracecally with E. histolytica trophozoites cultured monoxenically. During the first hours of interaction an increase in mucus production was observed. Microulcerative mucosal lesions appeared 24 to 72 h post-inoculation. Inflammatory infiltrate and edema of the lamina propria were associated with necrotic foci. At 96 h, the cecal mucosa was normal and live amebas were no longer detected. It is concluded that gerbils are useful as experimental models for studying the early stages of invasive intestinal amebiasis.

E. histolytica, pathogenic, and E. dispar, non-pathogenic, being morphologically identical are, when recovered as cysts in feces, diagnosed as E. histolytica. A survey on The Seychelles demonstrated that when culture and zymodeme characterization was used to compare against microscopy alone, the risk of overdiagnosis of E. histolytica infections was drastically reduced. From a total of 313 subjects tested 21 cultures grew amebas. By zymodeme analysis eight were E. histolytica, 40 were E. dispar and the remainder were various species of non-pathogenic intestinal amebas. Two further small comparative surveys confirmed these findings.

Genotypic differences between invasive and non-invasive E. histolytica could explain the 1:10 ratio of symptomatic/asymptomatic infection worldwide. Currently, zymodeme analysis is used to differentiate invasive from non-invasive E. histolytica strains but the technique is cumbersome and expensive. In accordance with the WHO research priorities for amebiasis we report here the further use of an invasive-specific monoclonal antibody against E. histolytica in immunofluorescence, to identify isolates cultured from stool samples of patients from three geographically distant endemic regions: Bangladesh, Colombia and Mexico. We tested 107 E. histolytica isolates and the correlation between zymodeme characterization and the immunofluorescence assay was 100%.

Three autochthonous cases of Entamoeba histolytica infection in institutionalized mentally-retarded patients are reported. Isoenzyme analysis by starch-gel electrophoresis shows the pathogenicity of the three isolates: two belong to zymodeme II, and one to zymodeme XIX. The study shows that invasive E. histolytica strains occur in Italy and can be isolated from institutionalized oligophrenic patients.

An analysis was made of the isoenzyme patterns of 61 Entamoeba histolytica strains: 42 from Cuba and 19 from Angola Mozambique and Ghana. By means of these patterns the non-pathogenic nature of the Cuban strains (Group 1) was shown. It coincided with the clinical characteristics of the infection in the carriers. Among the imported strains were 2 samples with pathogenic patterns II corresponding to 1 dysentery case and to 1 asymptomatic patient, and also non-pathogenic ones (I, II, III and XVIII).

After a stay in the far east, a man aged 20 years developed difficulty in defaecation and slight difficulty in micturition. Rectoscopy revealed a stenosing tumour resembling a carcinoma. The tumour disappeared completely following treatment with amoebicides. Surgical treatment of amoebomata is associated with complications and is warned against.

A spider monkey (Ateles geoffroyi) studied at the San Juan de Aragon Zoo died with symptoms of amoebic dysentery verified by coprologic investigation of the parasite, his female partner was cured with conventional antiamoebic treatment. At autopsy widespread ulcerations in the colon and multiple liver abscesses were found, containing trophozoites of Entamoeba histolytica. Both lesions were identical to those observed in human amoebiasis. A short review of the literature in nonhuman primates infections points out that the so-called spontaneous amoebiasis seen in colonies of captive monkeys, and transmission to their newborns within the same species of monkeys, have been in contact with humans. It is proposed that amoebiasis in monkeys should be considered as an excellent model for experimental studies on amoebiasis because other phylogenetically distant species have shown different pathology or are resistant to the infection. Also, it should raise concern that monkeys may become carriers of cysts and trophozoites of virulent strains of E. histolytica. Entamoeba histolytica DNA hybridization techniques should be considered for comparing genomic similarities with other protozoa, including the genera Amoeba to establish its pattern of evolution.

Using agarose gel electrophoresis, the electrophoretic patterns of four enzymes: malate NADP oxidoreductase (malic enzyme) (ME), glucosephosphate isomerase (GPI), phosphoglucomutase (PGM) and hexokinase (HK), were compared and analysed for five strains of Entamoeba histolytica, which had been obtained from patients with acute amebic dysentery or asymptomatic cyst carrier in Beijing, Tianjin and Fujian Province. The results showed that the electrophoretic patterns of all the five strains of E. histolytica belong to pathogenic zymodeme, zymodeme XIV, which is suggested to be the main pathogenic zymodeme in our country.

Amebas are an uncommon complication of amebic colitis. The specific medical treatment rely on the suspicion and a secure diagnosis that permits to the patient, a better clinical course.

The differential diagnostic criteria for the amebas parasitizing the human colon are described. The results of epidemiological studies carried out published in Mexico are discussed and the results of a survey performed in some hospitals in Mexico City on the current differential diagnosis of these parasites are reported. The findings showed that no carriers of E. hartmanni have been reported in the studies published in Mexico so far. However, no differentiation between E. histolytica and E. hartmanni is made in those hospitals according to the survey results. The possibility that in Mexico E. hartmanni is probably diagnosed as E. histolytica is discussed and as result the prevalence as asymptomatic intestinal amoebiasis is overestimated. The necessity of making the differential diagnosis between these parasites is emphasized.

A panoramic view of the amebiasis concept, its pathogenesis and its epidemiologic importance is presented. Besides, a brief description of the characteristic lesions of the mainly affected organs is done. Then it is proposed a sequential relationship must occur in the amebic lesion production. Finally, the best characterized amoebal infective factors are analyzed. This paper does not pretend to be an exhaustive review, but to offer an image of the pathogenetic mechanisms of amebiasis.

The paper describes a case of complicated amebic dysentery imported from India in a 39-year old man. Even in microscopic examination of feces, amebiasis diagnosis presented difficulties for clinicists.

A morphological analysis of an experimental model of invasive intestinal amebiasis was carried out using the washed-closed cecal loop model in hamsters and guinea-pigs. By light microscopy, few amebic trophozoites adhered to the intestinal epithelium, whereas many associated to the mucus blanket. Some trophozoites attached to the interglandular epithelium, during the first 10 to 15 hours of interaction. Hereafter, the parasites destroyed gradually the epithelium and were associated with normal and lysed inflammatory cells. Some amebas have cell debris and erythrocytes in their cytoplasms. Typical amebic ulcer contained abundant trophozoites at the basolateral area. The results suggest that intestinal mucus and muscularis mucosa are temporal barriers to amebic invasion and extension of the ulcer. At the mucosal and submucosal levels, lysis of inflammatory cells produced by amebas seems to play an important role in the extension of the ulcer.

The diagnostic usefulness of different laboratory tests was evaluated in 20 cases of invasive intestinal amebiasis: the direct coproparasitoscopic exam in mucus obtained by rectoscopy was positive in 90.0 per cent of cases; the same exam done in mucus obtained by the spoon technique was positive in 40.0 per cent. The serum antibodies investigated by the counterimmunoelectrophoresis technique were found in 40.0 per cent of the cases in the first blood sample obtained at the hospital admisssion, and 15 days later this percentage increased to 66.6 percent. The fecal antigen studied by the ELISA technique was positive in 70.0 per cent of the cases. Simultaneously, the therapeutic effectiveness of emetine and metronidazol was evaluated, and with both therapeutic programs total recovery was obtained in 100.0 per cent of the cases; there were no significative differences in the symptoms duration after the start of therapy, and side effects were not observed. The results must be considered preliminary, because the calculated full sample has not been concluded.

Tinidazole or metronidazole was administered at random to 56 patients with symptomatic intestinal amoebiasis. The dose of each drug given was 2 g once daily for 3 consecutive days. Tinidazole cured 92.6% patients (25/27) and metronidazole 58.6% patients (17/29). The difference was statistically significant (p less than 0.01). Tinidazole was better tolerated compared with metronidazole.

Mice naturally infected with Syphacia obvelata were challenged intracaecally with Entamoeba histolytica trophozoites. They showed a higher level of amoebic infection than mice without worms. Mice with the heaviest Syphacia infection were the most susceptible to amoebic infection. It appears that a concomitant infection with helminthic parasites residing in the caecum alters the outcome of an amoebic infection.

Uncomplicated amebic colitis is readily treated and has a mortality rate of less than 0.5%. Complications necessitating surgical intervention develop in only 6% to 11% of patients with symptomatic disease. However, the mortality rate in these patients ranges from 40% to 100% and stems in part from delays in diagnosis and treatment. Patients with known amebic colitis who show signs of systemic toxicity or of localized or generalized peritonitis are at high risk for complications; surgical consultation should be obtained. Patients who are thought to have acute appendicitis, diverticulitis, or obstructive or perforative carcinoma but have a history of dysentery atypical of that in these conditions should also be evaluated for amebiasis. Such patients should be treated presumptively until the diagnosis of amebic colitis can be excluded.

Among homosexual men the prevalence of infection with Entamoeba histolytica is high. To determine the clinical importance of this infection 55 homosexual men carrying the parasite were investigated in detail. No clinical, serological, or histological evidence of invasive amoebiasis was found in any of them. The patients were not treated and were followed up for 12 to 29 months (mean 21.6 months), during which period none developed symptoms that could be attributed to E histolytica. Spontaneous loss of the parasite occurred in 17 patients, some of whom later became reinfected. Sixteen patients had antibody to human immunodeficiency virus, and infection with E histolytica showed the same benign course in them as in the patients who did not have antibody. Throughout the study classification of the isolates of E histolytica consistently showed that they belonged only to non-pathogenic zymodemes. The findings provide further evidence that E histolytica in homosexual men is a commensal organism.

The production of cecal lesions with axenically cultivated Entamoeba histolytica in an experimental animal is reported for the first time. Forty-three newborn guinea pigs (one to five days old) were inoculated via laparatomy with 2.5 x 10(5) to 2 x 10(6) strain HM-1-IMSS amebae. Of 23 animals surviving to the 7th postinoculation day all showed cecal lesions at necropsy regardless of the age of the animal when used or the number of amebae received. Ten animals had lesions visible to the unaided eye and 13 had only microscopic lesions. No lesions were noted in other organs of the abdominal or thoracic regiosn. The use of axenically cultivated ameabae in newborn guinea pigs should prove a useful experimental model for the study of amebiasis.

The electrophoretic mobility patterns of four enzymes from trophozoites of Entamoeba histolytica were examined to determine the zymodeme of the amoebae populations involved. E. histolytica populations from aspirated liver pus belonged exclusively to types II and XI of eighteen zymodemes. E. histolytica from cases of amoebic dysentery--i.e., those patients presenting with intestinal ulceration and/or with haematophagous trophozoites in the faeces--also belonged to zymodemes II and XI. However, symptom-free cyst passers harboured E. histolytica belonging to one of several zymodemes none of which corresponded wth the zymodemes of the patients with liver abscesses or amoebic dysentery.