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Two major zymodemes from different Entamoeba histolytica strains were detected, despite different growth conditions, using isoelectrofocusing in ultrathin gels. One was associated with strains cultured from symptomatic patients, while the other was associated with microorganisms obtained from clinically symptomatic persons.
A cohort of 51 homosexuals who were either HIV-positive or had AIDS was followed prospectively with parasitologic stool examination and in vitro culture in order to determine the incidence of E. histolytica infection. Amoebic isolates were further characterized by electrophoretic isoenzyme study. Five subjects (9.8%) were found to be infected with E. histolytica. None of the amoebic isolates were found to be pathogenic by isoenzyme analysis.
The development of a vaccine against Entamoeba histolytica, the causative agent of amebic colitis and liver abscess, would reduce childhood mortality in countries such as Bangledesh where community-based studies have demonstrated a high prevalence of E. histolytica. Immunological studies from this population have shown that protection from amebiasis is associated with mucosal anti-E. histolytica Gal/GalNAc lectin antibodies, suggesting that a vaccine is an achievable goal. However, garnering resources for vaccine development is a challenge when the vaccine is targeted to poor people living in developing countries.
Amoebiasis is the second most common parasitic disease worldwIde. It occurs mainly in developing countries. A high percentage of people in countries where it is endemic are asymptomatic carriers. It results in severe disease that can be fatal in rare cases. Diabetics are at increased risk of exposure as travel to countries where it is endemic becomes more frequent, as indicated by the present case. This patient suffered from amoebiasis that produced an amoeboma which is most rare in cases of colonic amoebiasis. The clinical picture was that of an occluding gut tumor, but it was treated only with drugs. Retrospective studies show that diabetics are at increased risk of suffering severe complications after amoebic infection. The frequency and severity of this diabetes-amoeba association requires patients to take prophylactic measures, especially when travelling in developing countries.
The human pathogenic protozoan Entamoeba histolytica is a motile cell polarized into a front pseudopod and a rear uroid. The amoebic Gal/GalNAc surface lectin is a major adhesion molecule composed of an immunodominant 170-kDa heavy subunit, mostly extracellular except for a short cytoplasmic tail, and of an extracellular light subunit. The binding of multivalent ligands triggers lectin capping and recruitment to the uroid. The properties of the Gal/GalNAc lectin and its role in amoeba adhesion and uroid polarization are reviewed in the context of the molecular mechanisms underlying cell polarization and locomotion.
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Giardia and Entamoeba parasites encase themselves in a carbohydrate-rich cyst for travel from host to host. Both parasites upregulate their Golgi apparatus during this process, yielding organelles that are now found to be similar to those of higher eukaryotes. In fact, unusual enzymes and structural proteins used for cyst wall synthesis, the complexity of the secretory pathways used to transport materials to the developing cyst walls, as well as unexpected mechanisms of gene regulation and parasite-host and parasite-parasite information exchange, are revealing a high level of sophistication in these organisms that occupy low branch points in the eukaryotic lineage.
It is an exciting time in the study of Entamoeba histolytica. Over the past two years, the natural history and burden of disease in humans has been redefined, mucosal immune responses associated with protection identified, and the developmental regulation of encystation outlined. The number of genes sequenced has increased from a few hundred to a few thousand, and study of the genome structure is revealing unusual repetitive elements and plasticity. DNA microarrays promise the first ability to examine global patterns of mRNA abundance. The mechanism of transcriptional control via histone modifications and sequence-specific DNA-binding proteins are to be delineated. Advances in cell biology are providing new insights into invasion through the intestinal epithelium.
Recent studies have increased our knowledge of Entamoeba histolytica cell biology and gene regulation. In the ameba, dominant-negative mutations in the Gal/GalNAc lectin affect adhesion and cytolysis, whereas mutations in meromyosin affect cytoskeletal function. Studying these mutant proteins has improved our understanding of the role of these proteins in E. histolytica virulence. The characterization of the CP5 cysteine protease and the induction of apoptosis in host target cells has led to a better comprehension of the mechanisms by which trophozoites can lyse target cells.
One of the major soluble antigenic proteins of Entamoeba histolytica was purified to homogeneity and identified on a molecular basis. Its recombinant protein was expressed in Escherichia coli as a fusion protein with Shistosoma japonicum glutathione S-transferase. Apparent molecular weight of the purified antigenic protein was estimated to be 40-kDa and molecular-based analysis indicated that the purified protein was NADP+-dependent alcohol dehydrogenase (EhADH1). The application of the purified protein for the serodiagnosis of amebiasis was evaluated using an enzyme-linked immunosorbent assay applied to sera obtained from patients with amebiasis and healthy human controls. The purified protein was well recognized by the sera from asymptomatic amebiasis humans (22/22, 100%), whereas, it was less recognized by the sera from symptomatic amebiasis patients (5/16, 31%) with amebic colitis or liver abscess. To confirm the antigenicity of EhADH1, the recombinant glutathione S-transferase-EhADH1 fusion protein was also evaluated by the enzyme-linked immunosorbent assay using the same sera. The recombinant protein was also recognized by the sera from asymptomatic amebiasis humans (14/22, 64%) and less recognized by the sera from symptomatic amebiasis patients (2/16, 13%). These results suggest that the purified protein is applicable antigen for serodiagnostic screening of asymptomatic amebiasis humans.
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.
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Few organisms are more aptly named than Entamoeba histolytica, an intestinal protozoan parasite that can lyse and destroy human tissue. Within the past four years, new models of E. histolytica infection have begun to illuminate how amoebic trophozoites cause intestinal disease and liver abscess, and have expanded our understanding of the remarkable killing ability of this parasite. Here, I summarize recent work on the interactions between E. histolytica and human intestine, and between E. histolytica and hepatocytes, and discuss what these studies tell us about the role of inflammation and programmed cell death in the pathogenesis of amoebiasis.
A conference on Amebiasis and the Biology of Entamoeba histolytica was held in Agra, India, from 11 to14 February 2002.
A novel tetrahydroquinolinyl ester, quinfamide, administered orally in multiple doses for 3 days had an ED50 of 0.25 mg/kg/day (total dose 0.75 mg/kg) for eradicating Entamoeba criceti in hamsters in several tests. It was significantly more active by direct comparison than 3 commercially available amoebicides and at least as active as 2 other esters of the parent compound, 1-(dichloroacety)-1,2,3,4-tetrahydro-6-quinolinol. After administration of a single dose, ED50 calculations for quinfamide averaged 0.9 mg/kg. Quinfamide was considerably more active than the other tetrahydroquinolinols, diloxanide furoate and teclozan, and it was approximately 1.5 times more active than etofamide; a statistical significance between the latter 2 drugs could be demonstrated in one of 4 tests. Administered prophylactically, quinfamide was shown to protect hamsters from re-infection with E. criceti. It also inhibited propagation of E. histolytica in vitro at a concentration of 20 microgram/ml. No adverse effects were noted in rodents after a single dose as high as 10 g/kg. Daily administration to monkeys of doses up to 500 mg/kg for as long as 37 days produced no pharmacological aberrations during or after medication; haematological studies and urine analyses were normal and no gross or microscopical tissue changes attributable to quinfamide were observed. No toxicity was revealed following acute (2 g/kg) and chronic (500 mg/kg/day x 31 days) administration of the drug to dogs and rats, respectively.
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Evidence for the presence of 11 intestinal parasites in pre-school children from 4 rural villages in Ghana was obtained from an examination of stool samples. Striking differences were detected between the prevalence of some of the 6 common infections in the 4 villages. The prevalence of Ascaris lumbricoides varied from about 76% in one village (Oshiyie, coastal savanna) to apparently 0% in another (Akuma, forest zone). No differences in prevalence for any infection were observed to be sex dependent. Investigation of the relationship between age of the children and prevalence showed that the degree of prevalence of both A. lumbricoides and Trichuris trichiura had essentially levelled off by the time the children were 4 years old. There was no evidence to suggest that the prevalence of either Entamoeba sp. or spp. or hookworm was approaching a maximum value, even in the oldest children. These trends applied across the villages regardless of the differences in prevalence values for the infections. On average, the children of Oshiyie were found to harbour twice as many infections as the children of the other villages. The investigation of the prevalence data revealed evidence of associations between pairs of infections, particularly those involving hookworm and T. trichiura.