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PubMed1995

Immunogenicity of the recombinant serine rich Entamoeba histolytica protein (SREHP) amebiasis vaccine in the African green monkey.

We report the first study in non-human primates of the safety and immunogenicity of a recombinant vaccine designed to prevent amebic liver abscess. In a pilot study, a recombinant vaccine containing the serine rich Entamoeba histolytica protein (SREHP) attached to a maltose binding protein (SREHP/MBP), which has been shown to be effective in preventing amebic liver abscess in rodent models of infection, was used to immunize two African Green Monkeys. Vaccination with SREHP/MBP resulted in no systemic side-effects. The monkeys receiving the SREHP/MBP protein developed antibodies that recognized the recombinant SREHP/MBP molecule, the native SREHP protein, and the surface of amebic trophozoites. Antiserum from SREHP/MBP-vaccinated monkeys could block the adhesion of E. histolytica trophozoites to mammalian cells, a feature that may correlate with vaccine efficacy. Attempts to produce amebic liver abscess in naive African Green Monkeys by direct hepatic inoculation with virulent E. histolytica trophozoites was not successful, suggesting this species is probably not suitable for vaccine efficacy studies.

Animals↗
PubMed1988

Intestinal helminthiases in relation to the socioeconomic environment of Panamanian children.

A cross-sectional investigation was made into ascariasis and nutritional status in Panamanian preschool children from October 1983 to July 1984. Within this framework, an analysis was undertaken of possible relationships between a range of intestinal helminthiases and the socioeconomic status of the participants. Attention was paid to caregiver's education, parental occupation, family earnings, quality of housing and sanitation in the assessment of socioeconomic status. On this basis, strong associations were established between the socioeconomic status of the children and infection with Ascaris lumbricoides, Trichuris trichiura and hookworm. In general, the prevalence of single and multiple helminth infections was significantly higher in children living in housing made of wood or bamboo than in those living in housing made of concrete blocks. The same pattern applied to levels of sanitation. Ascaris lumbricoides occurred more frequently in children of mothers with the least formal education and in children living in relatively crowded conditions. Evidence was also obtained to indicate that the intensity of the intestinal helminth infections was greater in the children from the poorer environment. Since children from poorer socioeconomic conditions might be more exposed to infective stages than those from a better environment, the possible role of socioeconomic factors in contributing to the predisposition of some individuals to harbour large worm burdens of intestinal helminths was briefly discussed.

Ascariasis↗
PubMed1994

The pore-forming peptide of Entamoeba histolytica, the protozoan parasite causing human amoebiasis.

Amoebapore, the pore-forming peptide of E. histolytica has been isolated and its structure elucidated on the cDNA and protein level. The peptide is composed of 77 amino acid residues including six cysteine residues and has a molecular mass of 8244 Da. The primary translation product contains a signal sequence of 21 mostly hydrophobic amino acid residues. The active peptide has been located in the cytoplasmic granules of the amoebae. Circular dichroism spectroscopy revealed an all alpha-helical conformation and computer-aided secondary structure prediction yielded a structure of four helices. The helical conformation and three intramolecular disulfide bonds impart a highly compact and rigid structure upon the molecule. The activity of amoebapore, measured by a liposome depolarization assay, is resistant to heating at 100 degrees C in the absence of reducing agents. Synthetic peptides corresponding to the helices 1 and 3 exhibited pore-forming activity. Two minor, biologically active isoforms of amoebapore have amino acid sequence identity of 57% and 47%, respectively. Whereas amoebapore is a constituent of pathogenic E. histolytica isolates, nonpathogenic E. histolytica produce a structurally very similar peptide, the specific activity of which is approximately one third that of amoebapore. The biological significance of amoebapore for the pathogenicity of E. histolytica and specifically for its cytolytic activity remains to be determined.

Amino Acid Sequence↗
PubMed1995

The antiamoebic effect of a crude drug formulation of herbal extracts against Entamoeba histolytica in vitro and in vivo.

The antiamoebic effect of a crude drug formulation against Entamoeba histolytica was studied. In the traditional system of medicine in India, the formulation has been prescribed for intestinal disorders. It comprises of five medicinal herbs, namely, Boerhavia diffusa, Berberis aristata, Tinospora cordifolia, Terminalia chebula and Zingiber officinale. The dried and pulverized plants were extracted in ethanol together and individually. In vitro amoebicidal activity was studied to determine the minimal inhibitory concentration (MIC) values of all the constituent extracts as well as the whole formulation. The formulation had a MIC of 1000 micrograms/ml as compared with 10 micrograms/ml for metronidazole. In experimental caecal amoebiasis in rats the formulation had a curative rate of 89% with the average degree of infection (ADI) reduced to 0.4 in a group dosed with 500 mg/kg per day as compared with ADI of 3.8 for the sham-treated control group of rats. Metronidazole had a cure rate of 89% (ADI = 0.4) at a dose of 100 mg/kg per day and cured the infection completely (ADI = 0) when the dosage was doubled to 200 mg/kg per day. There were varying degrees of inhibition of the following enzyme activities of crude extracts of axenically cultured amoebae: DNase, RNase, aldolase, alkaline phosphatase, acid phosphatase, alpha-amylase and protease.

Acid Phosphatase↗
PubMed1995

Evaluation of an enzyme-linked immunoassay for the detection in serum of antibodies to Entamoeba histolytica.

A commercially available enzyme-linked immunoassay (ELISA) was compared to an indirect hemagglutination test (IHA) for the detection of antibodies to Entamoeba histolytica on 225 patients' serums. All of the 107 serums that had IHA titers of < 32 (interpreted as excluding the presence of invasive amebiasis) were ELISA negative. Sixty-three of 68 (93%) serums that had IHA titers of > or = 128 (interpreted as indicative of the presence of active or recent infection) were ELISA positive. Fifty serums had IHA titers of 32 or 64 that were considered "equivocal," and the ELISA results for these were: six positive, 35 negative, and nine "intermediate" (optical density values between the arbitrary positive cutoff and the low positive control). It was concluded that "intermediate" (and negative) ELISA results should be interpreted as excluding the presence of invasive amebiasis. Using these criteria, the results obtained with this ELISA appear to compare favorably with those of the "gold standard" IHA. Therefore, this ELISA provides a reliable alternative to the IHA for the serologic diagnosis of amebiasis, which may be advantageous for some laboratories in terms of lower cost, shorter test time, and improved efficiency.

Animals↗
PubMed1987

Development of inflammation and augmented chemotactic responsiveness of murine peritoneal macrophages following treatment with Entamoeba histolytica trophozoites.

The accumulation of inflammatory cells in the peritoneal cavity of C57BL/6 mice was examined following intraperitoneal injection of Entamoeba histolytica trophozoites. Two different strains of E. histolytica were used: a virulent strain (IP:0682:1) and a non-virulent strain (DKB). Injection of 10(6) trophozoites of either strain resulted in significant increases in the numbers of total peritoneal cells, macrophages and polymorphonuclear cells as compared to either saline-injected control mice or mice injected with 10-fold lower doses of trophozoites. The in vitro chemotactic response of macrophages from amoebae-induced exudates was also examined. Macrophages from mice treated with strain IP:0682:1 or DKB strain trophozoites were more responsive to complement-derived chemotactic factors than macrophages from saline-injected mice. This increase was significant on day 2 and persisted at enhanced levels until day 20 when the experiment was terminated. In addition, it was found that trophozoites activated normal mouse serum resulting in the production of serum-derived chemotactic activity.

Amebiasis↗
PubMed1987

Immunosuppression and splenomegaly in Entamoeba histolytica infection in mice.

Intestinal amoebiasis caused by Entamoeba histolytica trophozoites in mice is accompanied by a depression in the ability of this host to develop an immune response to sheep red blood cells. The number of splenic plaque-forming cells was reduced in mice inoculated intracecally with 2.5 x 10(5) trophozoites at 15, 25, 40, 65 and 75 days after infection when compared with non-infected mice. It was found that there was no significant difference between the spleen weight of the infected and non-infected control animals at 5 and 10 days following infection. However, a significant increase in spleen weight was observed by 15 days of infection and the spleens remained enlarged until termination of the experiment at 75 days. Thus, there was an inverse correlation between the PFC response and the spleen weight of infected animals.

Amebiasis↗
PubMed1996

Role of signalling and cytoskeletal rearrangements in the pathogenesis of Entamoeba histolytica.

Virulence of Entamoeba histolytica is characterized by intestinal tissue invasion, engulfment of host cells and the formation of liver abscesses. The actin-rich cytoskeleton of the amoeba allows rapid changes in morphology in response to signals from external stimuli. Cellular and molecular studies have described some of the proteins that participate in signalling and in cytoskeletal changes.

Animals↗
PubMedDate not supplied

An improved PCR-based method for detection and differentiation of Entamoeba histolytica and Entamoeba dispar in formalin-fixed stools.

Detection of infectious agents in faecal samples by polymerase chain reaction (PCR) can be limited by the presence of substances which inhibit DNA amplification. Here, an improved protocol is reported for directly isolating DNA from fresh and aged formalin-fixed stools, after concentration by formalin-ethyl acetate (FEA). The protocol was successfully applied to detect DNA of Entamoeba histolytica/Entamoeba dispar complex in stools by nested PCR, showing high specificity and low detection limit. Extended time of specimen storage in formalin had no influence on PCR yields. This PCR-based method offers technical advantages for routine detection and discrimination of invasive E. histolytica and non-invasive E. dispar.

Animals↗
PubMed2006

Diagnosis of amebiasis in Bangladesh.

Diagnosis of amebiasis by microscopic identification of the parasite in stool and liver abscess pus is insensitive and unable to distinguish the invasive parasite E. histolytica from the commensal parasites such as E. dispar and E. moshkovskii. New approaches to the detection of E. histolytica are based on detection of E. histolytica-specific antigen and DNA in stool and other clinical samples. Several molecular diagnostic tests for diagnosis of amebiasis have been developed and used to diagnose E. histolytica in Bangladesh. We have compared the TechLab E. histolytica-specific antigen detection test with PCR assays and with isoenzyme analysis of cultured amebas. The PCR assays are based on amplification of the multi-copy small subunit ribosomal RNA gene of E. histolytica and E. dispar. PCR assays and antigen detection test had comparable sensitivities when performed directly on fresh stool specimens. The correlation of antigen detection with PCR assays for identification of E. histolytica was excellent. TechLab's E. histolytica- specific antigen detection test was both rapid and simple to perform, making it appropriate for use in the developing world, where amebiasis is most prevalent.

Animals↗
PubMed2006

The current status of an amebiasis vaccine.

Efficient control of infectious diseases requires the development and application of suitable vaccines. Development of vaccines against amebiasis is still in its infancy. However, in recent years progress has been made in the identification of possible vaccine candidates, the route of application and the understanding of the immune response that is required for protection against amebiasis.

Administration, Oral↗
PubMed2006

Recent progress in vaccines for amebiasis.

The persistence of amebiasis as a global health problem, despite the availability of effective treatment, has led to the search for vaccines to prevent this deadly disease. Recent clinical studies suggest that mucosal immunity could provide some protection against recurrent intestinal infection with E. histolytica, but there is contradictory evidence about protective immunity after amebic liver abscess. Progress in vaccine development has been facilitated by new animal models that allow better testing of potential vaccine candidates and by the application of recombinant technology to vaccine design. Oral vaccines utilizing amebic antigens either co-administered with some form of cholera toxin or expressed in attenuated strains of Salmonella or Vibrio cholera have been developed and tested in animals for mucosal immunogenicity. Although there has been significant progress on a number of fronts, there are unanswered questions regarding the effectiveness of immune responses in preventing disease in man and, as yet, no testing of any of these vaccines in humans has been performed.

Entamoebiasis↗
PubMed2006

Diversity of clinical isolates of Entamoeba histolytica in Japan.

In Japan, amebiasis is domestically transmitted by two major populations: male homosexuals and mentally handicapped persons, which is remarkably different from most other developed countries where Entamoeba dispar infection is predominantly observed. Here we briefly summarize epidemiology of amebiasis in Japan. We also review our current understanding of the diversity of Entamoeba histolytica clinical isolates in Japan, based on polymorphic genetic markers, clinical representations, and in vivo virulence, using an animal model.

Animals↗
PubMed2006

Adherence-blocking vaccine for amebiasis.

The Gal/GalNAc lectin is a candidate vaccine antigen for an amebiasis vaccine due to its mediation of parasite adherence to the human intestine, because partial immunity in humans is associated with a mucosal IgA response against it, and because it is effective as a vaccine against amebic colitis in the murine model. The LecA domain of the Gal/GalNAc lectin contains neutralizing antibody epitopes. LecA contains the active site of the lectin (the carbohydrate recognition domain or "CRD") and has been an effective vaccine antigen in animal models of amebic colitis and liver abscess. Research needs include production of the LecA domain of the Gal/GalNAc lectin by a process that can be transferred to cGMP and optimization for immunogenicity, using adjuvants such as alum, MF59 or QS-21 adjuvants. Accomplishing this will enable testing of the ability of LecA immunizations to protect from amebic colitis in humans.

Animals↗
PubMed2006

Prevalence and incidence of Entamoeba histolytica infection in South Africa and Egypt.

There are little data on the true prevalence and incidence of Entamoeba histolytica infection in Africa. This is due to the inability, historically, to differentiate Entamoeba histolytica from the more common, but non-pathogenic, Entamoeba dispar. In addition, newer studies have demonstrated that the previous gold standard, culture with zymodeme analysis, is insensitive in detecting the presence of infection, especially when compared to PCR. Recent published articles as well as data from the authors' previous work are reviewed and summarized to elucidate what is known about prevalence and incidence of Entamoeba histolytica in Africa. The majority of data on asymptomatic infection are published from South Africa, Egypt and Cote d'Ivoire. Egypt has high rates of asymptomatic infection detected in the stool (>21%), whereas South Africa and Cote d'Ivoire rates range between 0 and 2%. Seroprevalence estimates the rate of recent infection, because anti-amebic antibodies generally persist for <5 years. Seropositivity rates (IgG, IgA) range from approximately 10 to 20%, indicating recent infection in this proportion of the population. Entamoeba histolytica infects a significant proportion of many populations of Africa; however, little data are currently available to indicate true prevalence and incidence. Further studies are needed to determine the burden of infection and disease in Africa.

Animals↗
PubMed2006

Overdiagnosis of Entamoeba histolytica and Entamoeba dispar in Nicaragua: a microscopic, triage parasite panel and PCR study.

BACKGROUND: Based on stool microscopy, an E. histolytica/E. dispar prevalence of 18.6% was found in León, Nicaragua about 10 years ago. Since then, new non-microscopic methods have been developed to discriminate between pathogenic E. histolytica and nonpathogenic E. dispar. The main objectives of the present study were to evaluate the true prevalence of E. histolytica among individuals with diarrhea and to assess the diagnostic procedures carried out at the health center level. METHODS: A descriptive study was carried out on patients with diarrhea. Parasite detection was performed by conventional microscopy on native preparations or concentrated and stained specimens, Triage Parasite Panel and by PCR for both E. histolytica and E. dispar. RESULTS: In 134 individuals with diarrhea, the prevalence of intestinal parasites was 69% as detected by direct stool examination. E. histolytica/E. dispar was found in eight (6%) of the samples, but the health centers reported 24%. In the Triage Parasite Panel only one case of E. histolytica/E. dispar was found. Analysis by PCR showed E. dispar in ten (7.5%) and E. histolytica in two cases (1.5%). The detection of intestinal coccidia and Dientamoeba fragilis required additional staining methods. CONCLUSIONS: PCR results showed that E. histolytica is a rare finding in patients with diarrhea. At the health centers, E. histolytica, E. histolytica/E. dispar were clearly overdiagnosed, with the consequence of overtreatment.

Animals↗