Prevalence and genetic diversity of Entamoeba histolytica in an institution for the mentally retarded in the Philippines

A systematic review and meta-analysis of protozoan parasite infections among patients with mental health disorders: an overlooked phenomenon

BACKGROUND

Patients with mental disorders have a high risk of intestinal parasitic infection due to poor hygiene practices. Hence, to better clarify this overlooked phenomenon, the current study is conducted to determine the global prevalence of protozoan parasite infections in patients with mental disorders and investigate the associated risk factors.

METHODS

Several databases (PubMed, Scopus, Web of Science, ProQuest, and Google Scholar) were searched for papers published until December 2022. The fixed effect meta-analysis was used to estimate the overall odds ratio (OR) and pooled prevalence was estimated using a random-effects model with a 95% confidence interval (CI).

RESULTS

Totally, 131 articles (91 case-control and 40 cross-sectional studies) met the eligibility criteria. Patients with mental disorders were significantly at higher risk for protozoan parasites than healthy controls (OR: 2.059, 1.830-2.317). The highest pooled OR (2.485, 1.413-4.368) was related to patients with neurodevelopmental disorders, and the highest pooled prevalence was detected in patients with neurodevelopmental disorders (0.341, 0.244-0.446), followed by bipolar and related disorders (0.321, 0.000-0.995). Toxoplasma gondii was the most prevalent protozoan parasite (0.343, 0.228-0.467) in cross-sectional studies and the highest pooled OR was related to Cyclospora cayetanensis (4.719, 1.352-16.474) followed by Cryptosporidium parvum (4.618, 2.877-7.412).

CONCLUSION

Our findings demonstrated that individuals afflicted with mental disorders are significantly more susceptible to acquiring protozoan parasites in comparison to healthy individuals. Preventive interventions, regular screening, and treatment approaches for parasitic diseases should be considered for patients with mental disorders.

Amebiasis as a sexually transmitted infection: A re-emerging health problem in developed countries

Amebiasis, which is caused by Entamoeba histolytica (E. histolytica), is the second leading cause of parasite-related death worldwide. It manifests from asymptomatic carriers to severe clinical conditions, like colitis and liver abscesses. Amebiasis is commonly seen in developing countries, where water and food are easily contaminated by feces because of the poor sanitation. However, a recently challenge in many developed countries is the increase in domestic cases of invasive amebiasis as a sexually transmitted infection (STI amebiasis). In contrast to food-/ waterborne transmission of E. histolytica in developing countries, transmission of STI amebiasis occurs directly through human-to-human sexual contact (e.g., men who have sex with men and people who engage in oral-anal sex); in this setting, asymptomatic infected individuals are the main reservoir of E. histolytica. The Development of screening methods for the early diagnosis of asymptomatic E. histolytica infection is the key to epidemiologic control. Moreover, delay in diagnosis of severe cases (e.g., fulminant amebiasis) leads to death even in developed countries. It is also important to increase clinical awareness of domestically transmitted STI amebiasis in the clinical settings. This review considers the changing epidemiology and clinical manifestations of STI amebiasis, and finally discusses the future strategies for the better practice.

Updates on the worldwide burden of amoebiasis: A case series and literature review

BACKGROUND

Amoebiasis is an intestinal and tissue parasitic infection caused by the protozoan Entamoeba histolytica. Despite significant medical importance and worldwide dispersion, little is known about the epidemiology and distinct geographical distribution of various clinical forms of amoebiasis in the world. In this study, we present an amoebiasis case series referred to Avicenne Hospital (Bobigny, France) from 2010 to 2022 followed by an overview of the released literature to explore diverse clinico-pathology of amoebiasis and to update the actual epidemiological situation of this parasitosis worldwide.

METHODS

The referred patients underwent a combination of clinical and parasitological examinations and imaging. The study was followed by an overview of released literature performed based on PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guideline.

RESULTS

A total of 15 patients with amoebiasis were diagnosed with an average age of 48.5 years old at the occurrence time of infection. Men (78%) were the most affected patients. Most of the cases were reported following a trip to endemic regions, such as Mali, India, Nepal, Algeria, Cameroon or Congo. All of the processed patients exhibited a hepatic amoebiasis. Amoebic abscess was observed in all cases with an average size of 6.3 cm. Of these patients, seven cases (46.7%) benefited from drainage following a risk of rupture or superinfection of the abscess. A compilation of findings extracted from 390 scientific publications via seven major medical databases, allowed us to update the main epidemiological and clinical events that has led to the current worldwide expansion of amoebiasis. We presented a clinical and epidemiological overview of the amoebiasis accompanied with a worldwide illustrative map displaying the current distribution of known amoebiasis foci in each geographical ecozone of Asia, Europe, Africa, Americas, and Australia.

CONCLUSIONS

Although Metropolitan France is not known as an endemic region of amoebiasis, amoebic liver abscess was the most frequent clinical form observed among our 15 patients processed. Most of infected patients had a history of travel to or lived-in endemic areas before arriving in France.

Development of a salivary IgA detection method for accurate diagnosis of amebiasis

An amebiasis detection method was developed based on identifying anti-Entamoeba histolytica IgA in the saliva of infected individuals. The enzyme-linked immunosorbent assay (ELISA)-based detection method was tested along with microscopy and polymerase chain reaction (PCR) on saliva and stool samples from 110 asymptomatic individuals visiting the Manila Health Department - Public Health Laboratory of the City of Manila, Philippines. A receiver operating curve (ROC) was constructed to compare the ELISA results with PCR results. E. histolytica infection was detected in 18 of the 110 individuals. The developed method had an accuracy of 90%, sensitivity of 88.89%, specificity of 90.22%, positive predictive value of 64%, and negative predictive value of 97.65% if a 1:2 dilution of crude saliva sample in phosphate-buffered saline (PBS) was used for diagnosis when compared to PCR. The area under the curve (AUC) of the ROC was 0.9436 if a 1:2 dilution of a crude saliva sample was used. The developed assay presents an easy and accurate method of detecting amebiasis in infected individuals using saliva samples instead of stool or blood samples and has potential applications in both diagnosis and epidemiological studies.

Host-parasite interactions in infections due to Entamoeba histolytica: A tale of known and unknown

Entamoeba histolytica (E. histolytica) is an enteric microaerophilic protozoan parasite responsible for millions of cases worldwide. Majority of the infections due to E. histolytica remain asymptomatic; however, it can cause an array of symptoms ranging from devastating dysentery, colitis, and abscesses in different vital organs. The interactions between the E. histolytica and its host are a multifaceted chain of events rather than merely destruction and invasion. There are manifold decisive steps for the establishment of infections by E. histolytica which includes degradation of mucosal layer, adherence to the host epithelium, invasion into the host tissues, and dissemination to vital organs. It is widely hypothesized that, for establishment of infections, the interactions at the intestinal mucosa decides the fate of the disease. The delicate communications between the parasite, the host factors, and the associated bacterial microflora play a significant role in the pathogenesis of E. histolytica. In this review, we summarize the interactions between the E. histolytica and it's host at the genetic and immunological interphases emphasizing the crucial role of microbiota in these interactions.

Multilocus sequence typing (MLST) of Entamoeba histolytica identifies kerp2 as a genetic marker associated with disease outcomes

Amoebiasis caused by protozoan parasite Entamoeba histolytica has diverse infection outcomes. The relationship between parasite genotypes and outcome of amoebic infection is still a paradox and needs to be explored. Genome information of infecting strains from endemic areas throughout the world is essential to explore this relation. Comparative genetics between E. histolytica populations from different disease outcomes have been studied to identify potential genetic markers having single nucleotide polymorphisms (SNPs) significantly associated with specific clinical outcome. Coding and non-coding regions have significantly different rates of polymorphism. Non-synonymous base substitutions were significantly more frequent than synonymous within coding loci. Both synonymous and non-synonymous SNPs within lysine- and glutamic acid rich protein 2 (kerp2) locus were significantly associated with disease outcomes. An incomplete linkage disequilibrium (LD) value with potential recombination events and significant population differentiation (F_ST) value have also been identified at kerp2 locus within the study population. Presence of disease specific SNPs, potential recombination events, and significant F_ST value at kerp2 locus indicate that kerp2 gene and its gene product are under constant selection pressure exerted by host on parasite and could also be a potential determinant of disease outcome of E. histolytica infection. Furthermore, E. histolytica isolated from asymptomatic carriers are phylogenetically closer to those causing liver abscess in human and exhibit potential inter-population recombination among them. Individuals with persistent asymptomatic E. histolytica infection may be under high risk of developing amoebic liver abscess formation in future and detailed investigation of asymptomatic individuals from endemic areas should be always required.

Analysis of D-A locus of tRNA-linked short tandem repeats reveals transmission of Entamoeba histolytica and E. dispar among students in the Thai-Myanmar border region of northwest Thailand

Intestinal parasitic infections, including those caused by Entamoeba species, are a persistent problem in rural areas of Thailand. The aims of this study were to identify pathogenic Entamoeba species and to analyze their genotypic diversity. Stool samples were collected from 1,233 students of three schools located in the Thai-Myanmar border region of Tak Province, Thailand. The prevalence of Entamoeba infection was measured by polymerase chain reaction (PCR) using species-specific primers. Thirty-one (2.5%) positive cases were detected for E. histolytica, 55 (4.5%) for E. dispar, and 271 (22.0%) for E. coli. Positive samples for E. histolytica and E. dispar were exclusively obtained from a few school classes, whereas E. coli was detected in all grades. No infections caused by E. moshkovskii, E. nuttalli, E. chattoni, and E. polecki were detected in the students studied. The D-A locus of tRNA-linked short tandem repeats was analyzed in samples of E. histolytica (n = 13) and E. dispar (n = 47) to investigate their diversity and potential modes of transmission. Five genotypes of E. histolytica and 13 genotypes of E. dispar were identified. Sequences of the D-A were divergent, but several unique genotypes were significantly prevalent in limited classes, indicating that intra-classroom transmission has occurred. As it was unlikely that infection would have been limited within school classes if the mode of transmission of E. histolytica and E. dispar had been through the intake of contaminated drinking water or food, these results suggest a direct or indirect person-to-person transmission mode within school classes. Positive rates for three Entamoeba species were 2-fold higher in students who had siblings in the schools than in those without siblings, suggesting that transmission occurred even at home due to heavy contacts among siblings.

Transmissions in endemic areas of the pathogen Entamoeba histolytica and other non-pathogenic Entamoeba species such as E. dispar and E. coli are caused by ingestion of drinking water and foods contaminated with cysts of the parasites. Cases of Entamoeba infections among school-aged children have been reported in several countries. However, it has not been demonstrated that transmission of protozoa of the Entamoeba genus occurs within school facilities. In addition, genetic information on E. histolytica and other morphologically indistinguishable species, including E. dispar and E. moshkovskii, in Thailand remains scarce. In the present study, we demonstrated that E. histolytica and/or E. dispar are prevalent among school-aged children, but limited to few classes in three rural schools in the Thai-Myanmar border region of northwest Thailand. Although various genotypes of these Entamoeba species were identified, identical genotypes were significantly more prevalent in certain school classes and also among siblings, suggesting that transmission occurred within the classrooms and at home. The possibility of person-to-person transmission among these students via direct or indirect contact during daily activities in classrooms and home is proposed.

Genetic Diversity and Gene Family Expansions in Members of the Genus Entamoeba

Amoebiasis is the third-most common cause of mortality worldwide from a parasitic disease. Although the primary etiological agent of amoebiasis is the obligate human parasite Entamoeba histolytica, other members of the genus Entamoeba can infect humans and may be pathogenic. Here, we present the first annotated reference genome for Entamoeba moshkovskii, a species that has been associated with human infections, and compare the genomes of E. moshkovskii, E. histolytica, the human commensal Entamoeba dispar, and the nonhuman pathogen Entamoeba invadens. Gene clustering and phylogenetic analyses show differences in expansion and contraction of families of proteins associated with host or bacterial interactions. They intimate the importance to parasitic Entamoeba species of surface-bound proteins involved in adhesion to extracellular membranes, such as the Gal/GalNAc lectin and members of the BspA and Ariel1 families. Furthermore, E. dispar is the only one of the four species to lack a functional copy of the key virulence factor cysteine protease CP-A5, whereas the gene's presence in E. moshkovskii is consistent with the species' potentially pathogenic nature. Entamoeba moshkovskii was found to be more diverse than E. histolytica across all sequence classes. The former is ∼200 times more diverse than latter, with the four E. moshkovskii strains tested having a most recent common ancestor nearly 500 times more ancient than the tested E. histolytica strains. A four-haplotype test indicates that these E. moshkovskii strains are not the same species and should be regarded as a species complex.

Antiamoebic drugs for treating amoebic colitis

BACKGROUND

Infection with the protozoan Entamoeba histolytica is common in low- and middle-income countries, and up to 100,000 people with severe disease die every year. Adequate therapy for amoebic colitis is necessary to reduce illness, prevent development of complicated disease and extraintestinal spread, and decrease transmission.

OBJECTIVES

To evaluate antiamoebic drugs for treating amoebic colitis.

SEARCH METHODS

We searched the available literature up to 22 March 2018. We searched the Cochrane Infectious Diseases Group Specialised Register, CENTRAL, MEDLINE, Embase, LILACS, mRCT, and conference proceedings. We contacted individual researchers, organizations, and pharmaceutical companies, and we checked reference lists.

SELECTION CRITERIA

Randomized controlled trials of antiamoebic drugs given alone or in combination, compared with placebo or another antiamoebic drug, for treating adults and children with a diagnosis of amoebic colitis.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the eligibility and methodological quality of trials and extracted and analysed the data. We calculated clinical and parasitological failure rates and rates of relapse and adverse events as risk ratios (RRs) with 95% confidence intervals (CIs), using a random-effects model. We determined statistical heterogeneity and explored possible sources of heterogeneity using subgroup analyses. We carried out sensitivity analysis by using trial quality to assess the robustness of reported results.

MAIN RESULTS

In total, 41 trials (4999 participants) met the inclusion criteria of this review. In this update, we added four trials to the 37 trials included in the first published review version. Thirty trials were published over 20 years ago. Only one trial used adequate methods of randomization and allocation concealment, was blinded, and analysed all randomized participants. Only one trial used an E histolytica stool antigen test, and two trials used amoebic culture.Tinidazole may be more effective than metronidazole for reducing clinical failure (RR 0.28, 95% CI 0.15 to 0.51; 477 participants, eight trials; low-certainty evidence) and is probably associated with fewer adverse events (RR 0.65, 95% CI 0.46 to 0.92; 477 participants, 8 trials; moderate-certainty evidence). Compared with metronidazole, combination therapy may result in fewer parasitological failures (RR 0.36, 95% CI 0.15 to 0.86; 720 participants, 3 trials; low-certainty evidence), but we are uncertain which combination is more effective than another. Evidence is insufficient to allow conclusions regarding the efficacy of other antiamoebic drugs.

AUTHORS' CONCLUSIONS

Compared with metronidazole, tinidazole may be more effective in reducing clinical failure and may be associated with fewer adverse events. Combination drug therapy may be more effective for reducing parasitological failure compared with metronidazole alone. However, these results are based mostly on small trials conducted over 20 years ago with a variety of poorly defined outcomes. Tests that detect E histolytica more accurately are needed, particularly in countries where concomitant infection with other bacteria and parasites is common.

Amoebiasis in Iran: a systematic review and meta-analysis

A comprehensive meta-analysis study was performed to estimate the reliable national prevalence and molecular epidemiology of amoebiasis in Iran. Nine English and Persian databases were searched to achieve the relevant studies. Pooled estimates were generated and meta-regression was performed. We identified 71 eligible articles involving 330 930 subjects from 25 provinces to be included in the final analysis. Moreover, 17 studies compromising 462 polymerase chain reaction (PCR)-positive isolates performed molecular analysis to inter-species differentiation. The pooled prevalence of Entamoeba infection among Iranian population was about 1% (95% CI 0.8-2.0%). Moreover, regarding Human Development Index (HDI), a higher prevalence was observed in undeveloped provinces. Out of 462 PCR-positive isolates, 83% (95% CI 69-94%) and 12% (95% CI 3-24%) were Entamoeba dispar, Entamoeba histolytica, respectively. In subgroup analysis based on molecular results, in general, population prevalence of Entamoeba dispar and E. histolytica were 91% (95% CI 80-99%) and 7%, (95% CI 0-19%), respectively, while prevalence of these species in patients with gastrointestinal disorders were 75% (95% CI 45-96%) and 18% (95% CI 1-43%), respectively. Our findings indicate the low burden of amoebiasis in Iran. E. dispar, that is mostly non-pathogenic, was identified as most prevalent species. Nevertheless, we suggest more public health interventions in areas with lower HDI.

Entamoeba histolytica and Entamoeba dispar infection in Mexican school children: genotyping and phylogenetic relationship

BACKGROUND

This study aimed to determine the frequency of Entamoeba histolytica and Entamoeba dispar infection in school children in the community of Tlaltizapan, in order to understand the dynamics of infection within the school and family spheres of this population. Amoebiasis is an unsolved public health problem and an endemic disease in Mexico. The incidence rate varies depending on the state; the most affected states show the highest numbers of new cases of amoebiasis per year. Previously, we reported the molecular frequency of infection with E. histolytica and/or E. dispar in other rural communities of the state of Morelos.

METHODS

Children from 3 schools were studied to estimate the frequency of intestinal parasites through microscopic examination of fresh stool samples. The number of studied individuals were 309 school children. The molecular characterization of E. histolytica or E. dispar was carried out by Polymerase Chain Reaction (PCR) using species-specific primers to amplify short tandem repeats (STR) in non-coding sequences associated with the tRNA gene; the amplified fragments were sequenced and analyzed.

RESULTS

Eight different genotypes were obtained from E. dispar isolates with the molecular marker NKD3-D5. None of the cases in which the species E. histolytica was detected developed symptoms attributable to an invasive process of disease. Moreover, the parasitized condition appeared to have no significant impact on the development or nutritional status of affected children. Genotype 1, which corresponds to the reference strain E. dispar SAW760, considered a non-pathogenic amoeba, was the most prevalent.

CONCLUSIONS

The comparison of the genotypes of Entamoeba species did not show a correlation between children and their relatives. In this community, the species Entamoeba dispar genotype 1 was the most widespread. Based on the indicators of growth, development and nutrition status, the studied community seems to be reasonably adapted to constant exposure to intestinal parasites, since there were no evidences of a serious impact of the parasitized condition on the children's health.

Molecular prevalence of Entamoeba histolytica/dispar infection among patients attending four health centres in north-west Ethiopia

The prevalence of amoebiasis is often overestimated owing to its epidemiological overlap with the non-pathogenic Entamoeba dispar To provide evidence for this conjecture, a cross-sectional study was conducted from November 2013 to January 2015. A range of 180-200 µg of semi-solid and formed stools and 200 µL of diarrhoeic stool samples were used for DNA extraction from microscopically E. histolytica/dispar positive samples using the QIAamp® DNA Stool Mini Kit according to manufacturers' instructions. Nested PCR targeting 18S ribosomal RNA gene was used. In 422 microscopically positive E. histolytica/dispar stools, molecular prevalence revealed that E. histolytica infestation was present in only 1.7% (95% confidence interval [CI], 0.47-2.93) and E. dispar was found in 42.2% (95% CI, 37.49-46.91), while 56.2% (95% CI, 51.47-60.93) had neither E. histolytica nor E. dispar (P < 0.001). We conclude that infestation with E. histolytica is rarer in our study areas than was previously believed. Hence, accurate differentiation of E. histolytica and E. dispar is crucial.

Prevalence of Strongyloides stercoralis and other intestinal parasitic infections among mentally retarded residents in central institution of southern Iran

OBJECTIVE

To determine the prevalence of intestinal parasitic infections among mentally retarded residents of rehabilitation center of Bandar Abbas, Hormozgan province, southern Iran.

METHODS

A cross-sectional study was carried out in central rehabilitation institute of Hormozgan province in summer 2010. Fecal samples of all 133 residents (72 males, 61 females) aged 3-52, were collected in triplicate. Specimens were examined by direct smear, formalin-ether concentration techniques and stained by permanent Trichrome, Ziehl-Neelsen stains. Statistical analysis was conducted by SPSS 13.5.

RESULTS

Intestinal parasitic infections were seen in 48.5% (64 out of 133 subjects: 53.4% in males and 46.6% in females). Strongyloides stercoralis with 17.3% showed the highest incidence followed by Entamoeba coli (9.8%), Blastocystis hominis (7.5%), Giardia lamblia (2.3%), Endolimax nana (2.3%), Hymenolepis nana (0.8%), Oxyuris vermicularis (0.8%), and Chilomasix mesnili (0.8%). Double infections were found to be as: Strongyloides stercoralis + Giardia lamblia (2.3%), Entamoeba coli + Giardia lamblia (1.5%), Entamoeba coli + Blastocystis hominis (1.5%), Oxyuris vermicularis + Entamoeba coli (0.8%), Strongyloides stercoralis + Entamoeba coli (0.8%), respectively.

CONCLUSIONS

Our findings reveal that strongyloidiasis is a common disease among mentally retarded population in southern Iran.

Evolutionary genomics and population structure of Entamoeba histolytica

Amoebiasis caused by the gastrointestinal parasite Entamoeba histolytica has diverse disease outcomes. Study of genome and evolution of this fascinating parasite will help us to understand the basis of its virulence and explain why, when and how it causes diseases. In this review, we have summarized current knowledge regarding evolutionary genomics of E. histolytica and discussed their association with parasite phenotypes and its differential pathogenic behavior. How genetic diversity reveals parasite population structure has also been discussed. Queries concerning their evolution and population structure which were required to be addressed have also been highlighted. This significantly large amount of genomic data will improve our knowledge about this pathogenic species of Entamoeba.

Molecular epidemiology of amoebiasis in Malaysia: highlighting the different risk factors of Entamoeba histolytica and Entamoeba dispar infections among Orang Asli communities

Currently, species-specific information on Entamoeba infections is unavailable in Malaysia and is restricted worldwide due to the re-description of pathogenic Entamoeba histolytica and non-pathogenic Entamoeba dispar and Entamoeba moshkovskii. Therefore, this cross-sectional study was conducted to provide the first known documented data on the true prevalence of these three species in western Malaysia using a molecular method. Another aim of this study was to determine the association of potential risk factors associated with each Entamoeba sp. A total of 500 stool samples from three Orang Asli tribes were randomly collected. The overall prevalence of E. histolytica, E. dispar and E. moshkovskii determined by microscopy was 18.6% (93/500). Molecular analysis revealed that while most Entamoeba-positive individuals were infected with E. dispar (13.4%), followed by E. histolytica (3.2%) and E. moshkovskii (1.0%), the present findings show low prevalence rates of mixed infections with E. histolytica and E. dispar (2%), E. dispar and E. moshkovskii (1.2%) and association infections of E. histolytica, E. dispar and E. moshkovskii (0.4%). Logistical regression analysis indicates that the dynamics of the transmission of the three Entamoeba spp. was different. Of six statistically significant variables observed in the univariate analysis, three were retained as significant risk factors for E. histolytica infection in the logistical regression model. These factors were (i) not washing hands after playing with soil or gardening (Odds ratio (OR)=4.7; 95% confidence level (CI)=1.38, 16.14; P=0.013), (ii) indiscriminate defecation in the river or bush (OR=5.7; 95% CI=1.46, 21.95; P=0.012) and (iii) close contact with domestic animals (OR=5.4; 95% CI=1.36, 2.51; P=0.017). However, subjects with family members who were infected with E. histolytica/E. dispar/E. moshkovskii (OR=3.8; 95 CI=2.11, 6.86; P<0.001) and those who consumed raw vegetables (OR=1.8; 95% CI=1.01, 3.23; P=0.047) were more likely to be infected with E. dispar. On the other hand, no associated factor was identified with E. moshkovskii infection. Nevertheless, diarrhoea (P=0.002) and other gastroenteritis symptoms (P<0.001) were only associated with E. histolytica infection. The present study provides new insight into the distribution and risk factors of E. histolytica, E. dispar and E. moshkovskii infections among Orang Asli communities in Malaysia. Identifying the different risk factors of E. histolytica and E. dispar infections will help in the planning specific strategies in the control and prevention of each infection in the communities. Moreover, it emphasises the need for molecular methods to determine the species-specific prevalence of Entamoeba spp.

Host-Parasite interactions in Entamoeba histolytica and Entamoeba dispar: what have we learned from their genomes?

Invasive amoebiasis caused by Entamoeba histolytica is a major global health problem. Virulence is a rare outcome of infection, occurring in fewer than 1 in 10 infections. Not all strains of the parasite are equally virulent, and understanding the mechanisms and causes of virulence is an important goal of Entamoeba research. The sequencing of the genome of E. histolytica and the related avirulent species Entamoeba dispar has allowed whole-genome-scale analyses of genetic divergence and differential gene expression to be undertaken. These studies have helped elucidate mechanisms of virulence and identified genes differentially expressed in virulent and avirulent parasites. Here, we review the current status of the E. histolytica and E. dispar genomes and the findings of a number of genome-scale studies comparing parasites of different virulence.

Intestinal microbial community diversity between healthy and orally infected rabbit with Entamoeba histolytica by ERIC-PCR

Enterobacterial repetitive intergenic consensus (ERIC)-PCR was applied to analyze the difference of intestinal microbial community diversity between healthy and orally infected rabbits with Entamoeba histolytica. The dynamic changes in different parts of digestive system including the duodenum, jejunum, ileum, caecum, and rectum in healthy and infected rabbits at different time points were also tested. The intestinal microbial community of the control healthy rabbits was steady, and the total number of ERIC-PCR bands in the control healthy rabbit was the least in the rectum and the most in the caecum. ERIC-PCR bands of orally inoculated rabbits did not obviously change until 24 h after postinoculation (p.i.). The numbers of the ERIC-PCR bands gradually decreased from 24 to 72 h p.i., and then, with the development of disease, the band numbers gradually increased until 6 days p.i. Sequence analysis showed that the nucleotide sequence homologies of the fragment about 1,200 bp of infected ileum sampled at 32 h p.i. were above 95 % with Sinorhizobium meliloti enterobacterial, Erwinia amylovora and Salmonella typhimurium, and the nucleotide sequence homologies of the fragment about 300 bp of infected ileum sampled at 48 h p.i. were more than 90 % with Xanthomonas campestris enterobacterial, Yersinia enterocolitica subsp., Shigella flexneri, S. meliloti enterobacterial, Yersinia pestis, Klebsiella pneumoniae subsp., and Escherichia coli. The prominent bacteria had changed after E. histolytica infection. The DNAstar of staple of ERIC-PCR showed that aerobe and facultative aerobe (E. coli, Shigella, and Salmonella) became preponderant bacilli in the intestine of orally infected rabbits with E. histolytica.

Evolutionary genomics of Entamoeba

Entamoeba histolytica is a human pathogen that causes amoebic dysentery and leads to significant morbidity and mortality worldwide. Understanding the genome and evolution of the parasite will help explain how, when and why it causes disease. Here we review current knowledge about the evolutionary genomics of Entamoeba: how differences between the genomes of different species may help explain different phenotypes, and how variation among E. histolytica parasites reveals patterns of population structure. The imminent expansion of the amount genome data will greatly improve our knowledge of the genus and of pathogenic species within it.

Periodicity and patterns of Entamoeba histolytica and E. dispar infection in HIV+/AIDS patients in Mexico

In a 12-month longitudinal study, a cohort of Mexican HIV+/AIDS patients was checked several times for Entamoeba infection, with the parasites identified, as E. histolytica or E. dispar, using PCR. The polymorphic region of the parasites' chitinase genes was investigated by PCR, with the variation in amplicon sizes being used as a measure of the genetic variation among the isolates. The patients found infected with Entamoeba at the start of the study displayed varied patterns of infection clearance and re-infection. The analysis of the polymorphisms in the chitinase gene revealed seven polymorphic patterns in the E. histolytica isolates investigated and three in the E. dispar isolates. Many of the patients were each re-infected with Entamoeba at least once during the 12 months of follow-up. As seen in a previous study in Mexico, none of the E. histolytica-infected patients developed any clinical symptoms of invasive amoebiasis during the follow-up period. The results highlight the complexity of the host-parasite relationship in human amoebiasis.

Entamoeba histolytica and E. dispar infections in captive macaques (Macaca fascicularis) in the Philippines

Entamoeba histolytica is a protozoan parasite that infects man and animals. This parasite has a global distribution and the disease it causes is usually characterized by diarrhea. In order to detect the parasite, it is necessary to differentiate it from Entamoeba dispar. E. dispar appears morphologically similar to E. histolytica but does not cause disease and tissue invasion. This study reports on the prevalence of E. histolytica and E. dispar among captive macaques in a primate facility in the Philippines. PCR was used to correctly identify both Entamoeba species. Indirect fluorescent antibody test (IFAT) was also performed to determine the seroprevalence of amebiasis in the captive macaques. Based on PCR targeting of the peroxiredoxin gene, of the 96 stool samples collected, 23 (24%) contained E. histolytica while 32 (33%) contained E. dispar. IFAT revealed 26 (27%) serum samples positive for antibodies against E. histolytica. Sequence analysis of the 18S rRNA gene showed that the 23 E. histolytica isolates were identical to human E. histolytica isolates deposited in the GenBank and not Entamoeba nuttalli as found in macaques in other recent reports. The Philippines is a major exporter of monkeys for biomedical research purposes, so screening animals before transporting them to other locations lessens the risk of spreading zoonoses to a wider area. This is the first report of the molecular detection of E. histolytica and E. dispar among macaques in the Philippines. This study complements the limited information available on the animal hosts of E. histolytica in the Philippines.

Antiamoebic drugs for treating amoebic colitis

BACKGROUND

Entamoeba histolytica infection is common in developing countries, and up to 100,000 individuals with severe disease die every year. Adequate therapy for amoebic colitis is necessary to reduce the severity of illness, prevent development of complicated disease and extraintestinal spread, and decrease transmission.

OBJECTIVES

To evaluate antiamoebic drugs for treating amoebic colitis.

SEARCH STRATEGY

In September 2008, we searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL (2008, Issue 3), MEDLINE, EMBASE, LILACS, mRCT, and conference proceedings. We contacted individual researchers, organizations, and pharmaceutical companies, and checked reference lists.

SELECTION CRITERIA

Randomized controlled trials of antiamoebic drugs given alone or in combination, compared with placebo or another antiamoebic drug for treating adults and children diagnosed with amoebic colitis.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the eligibility and methodological quality of trials, and extracted and analysed the data. We calculated clinical and parasitological failure rates, relapse, and adverse events as risk ratios (RR) with 95% confidence intervals (CIs), using a random-effects model. We determined statistical heterogeneity and explored possible sources of heterogeneity using subgroup analyses. We carried out sensitivity analysis using trial quality to assess the robustness of the results.

MAIN RESULTS

Thirty-seven trials, enrolling 4487 participants, met the inclusion criteria. Only one trial used adequate methods for randomization and allocation concealment, was blinded, and analysed all randomized participants. Only one trial used a E. histolytica stool antigen test. Tinidazole reduced clinical failure compared with metronidazole (RR 0.28, 95% CI 0.15 to 0.51; 477 participants, eight trials) and was associated with fewer adverse events. Compared with metronidazole, combination therapy resulted in fewer parasitological failures (RR 0.36, 95% CI 0.15 to 0.86; 720 participants, 3 trials).

AUTHORS' CONCLUSIONS

Tinidazole is more effective in reducing clinical failure compared with metronidazole and has fewer associated adverse events. Combination drug therapy is more effective in reducing parasitological failure compared with metronidazole alone. However, these results are based on trials with poor methodological quality so there is uncertainty in these conclusions. Further trials of the efficacy of antiamoebic drugs, with better methodological quality, are recommended. More accurate tests to detect E. histolytica are needed, particularly in countries where concomitant infection with other bacteria and parasites is common.

Recent discoveries in the pathogenesis and immune response toward Entamoeba histolytica

Entamoeba histolytica is an enteric dwelling human protozoan parasite that causes the disease amoebiasis, which is endemic in the developing world. Over the past four decades, considerable effort has been made to understand the parasite and the disease. Improved diagnostics can now differentiate pathogenic E. histolytica from that of the related but nonpathogenic Entamoeba dispar, thus minimizing screening errors. Classically, the triad of Gal-lectin, cysteine proteinases and amoebapores of the parasite were thought to be the major proteins involved in the pathogenesis of amoebiasis. However, other amoebic molecules such as lipophosphopeptidoglycan, perioxiredoxin, arginase, and lysine and glutamic acid-rich proteins are also implicated. Recently, the genome of E. histolytica has been sequenced, which has widened our scope to study additional virulence factors. E. histolytica genome-based approaches have now confirmed the presence of Golgi apparatus-like vesicles and the machinery for glycosylation, thus improving the chances of identifying potential drug targets for chemotherapeutic intervention. Apart from Gal-lectin-based vaccines, promising vaccine targets such as serine-rich E. histolytica protein have yielded encouraging results. Considerable efforts have also been made to skew vaccination responses towards appropriate T-helper cell immunity that could augment the efficacy of vaccine candidates under study. Thus, ongoing efforts mining the information made available with the sequencing of the E. histolytica genome will no doubt identify and characterize other important potential vaccine/drug targets and lead to effective immunologic strategies for the control of amoebiasis.

Mutation detection analysis of a region of 16S-like ribosomal RNA gene of Entamoeba histolytica, Entamoeba dispar and Entamoeba moshkovskii

BACKGROUND

The level of intra-species genetic variation in Entamoeba histolytica, Entamoeba dispar and Entamoeba moshkovskii populations in a localized geographic area, like Puducherry, India, remains unknown.

METHODS

In the present study the existence of genetic variation in the nested multiplex polymerase chain reaction (NM-PCR) amplified region of the 16S-like ribosomal RNA genes of E. histolytica, E. dispar and E. moshkovskii was investigated by riboprinting and single strand conformation polymorphism (SSCP) analysis.

RESULTS

We found that 70 stool specimens were positive for E. histolytica, 171 stool specimens were positive for E. dispar, and 37 stool specimens were positive for E. moshkovskii by NM-PCR. Ninety liver abscess pus specimens, 21 urine specimens, and 8 saliva specimens were positive for E. histolytica by NM-PCR. Riboprinting analysis detected a mutation in the PCR product of only one E. histolytica isolate from a stool specimen. However, SSCP analysis detected mutations in the PCR products of five E. histolytica isolates and three E. moshkovskii isolates from stool specimens, and one E. histolytica isolate from a saliva specimen. The mutations detected by riboprinting and SSCP analysis were confirmed by sequencing. All the nucleotide sequences showing mutations in this study have already been deposited into the NCBI GenBank database under accession numbers [GenBank: EF682200 to GenBank: EF682208].

CONCLUSION

The present study has revealed the subsistence of mutations in the ribosomal RNA genes of E. histolytica and E. moshkovskii, which points towards the existence of intra-species genetic variation in E. histolytica and E. moshkovskii isolates infecting humans.

Molecular epidemiology of amebiasis

Entamoeba histolytica, the causative agent of human amebiasis, remains a significant cause of morbidity and mortality in developing countries and is responsible for up to 100,000 deaths worldwide each year. Entamoeba dispar, morphologically indistinguishable from E. histolytica, is more common in humans in many parts of the world. Similarly Entamoeba moshkovskii, which was long considered to be a free-living ameba, is also morphologically identical to E. histolytica and E. dispar, and is highly prevalent in some E. histolytica endemic countries. However, the only species to cause disease in humans is E. histolytica. Most old epidemiological data on E. histolytica are unusable as the techniques employed do not differentiate between the above three Entamoeba species. Molecular tools are now available not only to diagnose these species accurately but also to study intra-species genetic diversity. Recent studies suggest that only a minority of all E. histolytica infections progress to the development of clinical symptoms in the host and there exist population level differences between the E. histolytica strains isolated from the asymptomatic and symptomatic individuals. Nevertheless the underlying factors responsible for variable clinical outcome of infection by E. histolytica remain largely unknown. We anticipate that the recently completed E. histolytica genome sequence and new molecular techniques will rapidly advance our understanding of the epidemiology and pathogenicity of amebiasis.

Laboratory diagnostic techniques for Entamoeba species

The genus Entamoeba contains many species, six of which (Entamoeba histolytica, Entamoeba dispar, Entamoeba moshkovskii, Entamoeba polecki, Entamoeba coli, and Entamoeba hartmanni) reside in the human intestinal lumen. Entamoeba histolytica is the causative agent of amebiasis and is considered a leading parasitic cause of death worldwide in humans. Although recent studies highlight the recovery of E. dispar and E. moshkovskii from patients with gastrointestinal symptoms, there is still no convincing evidence of a causal link between the presence of these two species and the symptoms of the host. New approaches to the identification of E. histolytica are based on detection of E. histolytica-specific antigen and DNA in stool and other clinical samples. Several molecular diagnostic tests, including conventional and real-time PCR, have been developed for the detection and differentiation of E. histolytica, E. dispar, and E. moshkovskii in clinical samples. The purpose of this review is to discuss different methods that exist for the identification of E. histolytica, E. dispar, and E. moshkovskii which are available to the clinical diagnostic laboratory. To address the need for a specific diagnostic test for amebiasis, a substantial amount of work has been carried out over the last decade in different parts of the world. The molecular diagnostic tests are increasingly being used for both clinical and research purposes. In order to minimize undue treatment of individuals infected with other species of Entamoeba such as E. dispar and E. moshkovskii, efforts have been made for specific diagnosis of E. histolytica infection and not to treat based simply on the microscopic examination of Entamoeba species in the stool. The incorporation of many new technologies into the diagnostic laboratory will lead to a better understanding of the public health problem and measures to control the disease.