Longitudinal study of intestinal Entamoeba histolytica infections in asymptomatic adult carriers

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.

Pathogenicity and virulence of Entamoeba histolytica, the agent of amoebiasis

The amoeba parasite Entamoeba histolytica is the causative agent of human amebiasis, an enteropathic disease affecting millions of people worldwide. This ancient protozoan is an elementary example of how parasites evolve with humans, e.g. taking advantage of multiple mechanisms to evade immune responses, interacting with microbiota for nutritional and protective needs, utilizing host resources for growth, division, and encystation. These skills of E. histolytica perpetuate the species and incidence of infection. However, in 10% of infected cases, the parasite turns into a pathogen; the host-parasite equilibrium is then disorganized, and the simple lifecycle based on two cell forms, trophozoites and cysts, becomes unbalanced. Trophozoites acquire a virulent phenotype which, when non-controlled, leads to intestinal invasion with the onset of amoebiasis symptoms. Virulent E. histolytica must cross mucus, epithelium, connective tissue and possibly blood. This highly mobile parasite faces various stresses and a powerful host immune response, with oxidative stress being a challenge for its survival. New emerging research avenues and omics technologies target gene regulation to determine human or parasitic factors activated upon infection, their role in virulence activation, and in pathogenesis; this research bears in mind that E. histolytica is a resident of the complex intestinal ecosystem. The goal is to eradicate amoebiasis from the planet, but the parasitic life of E. histolytica is ancient and complex and will likely continue to evolve with humans. Advances in these topics are summarized here.

Dientamoeba fragilis associated with microbiome diversity changes in acute gastroenteritis patients

This study examined the correlation between intestinal protozoans and the bacterial microbiome in faecal samples collected from 463 patients in New Zealand who were diagnosed with gastroenteritis. In comparison to traditional microscopic diagnosis methods, Multiplexed-tandem PCR proved to be more effective in detecting intestinal parasites. Among the identified protozoans, Blastocystis sp. and Dientamoeba fragilis were the most prevalent. Notably, D. fragilis was significantly associated with an increase in the alpha-diversity of host prokaryotic microbes. Although the exact role of Blastocystis sp. and D. fragilis as the primary cause of gastroenteritis remains debatable, our data indicates a substantial correlation between these protozoans and the prokaryote microbiome of their hosts, particularly when compared to other protists or patients with gastroenteritis but no detectable parasitic cause. These findings underscore the significance of comprehending the contributions of intestinal protozoans, specifically D. fragilis, to the development of gastroenteritis and their potential implications for disease management.

Glycogen Metabolism and Its Role in Growth and Encystation in Entamoeba histolytica

Entamoeba histolytica is a parasitic protozoan that causes diarrheal disease in approximately 100 million people worldwide every year. E. histolytica has two forms, the growing trophozoite and the infectious cyst. Trophozoites colonizing the large intestine form cysts that are released into the environment. The ingestion of the cysts in contaminated food and water continues the disease cycle. Here, we investigated the role of glycogen in trophozoite growth and encystation. Glycogen is thought to provide precursors for the synthesis of chitin, a major component of the protective cyst wall. We propose that glycogen also serves as an energy source during metabolic adaptation to different nutrient environments. We examined the role of glycogen in E. histolytica by analyzing the growth and encystation of RNAi strains with reduced expression of the single gene-encoding glycogen synthase (GYS) or two of three genes encoding glycogen phosphorylase (PYG). The GYS RNAi strain had a greatly reduced glycogen accumulation, and both the GYS and PYG RNAi strains exhibited reduced growth in the glucose-poor medium. Both RNAi strains also showed reduced cyst production. Our results suggest glycogen synthesis and degradation are vital to the growth and adaptation of E. histolytica to a low-glucose environment such as that encountered in the large intestine.

Combining methods for non-invasive fecal DNA enables whole genome and metagenomic analyses in wildlife biology

Non-invasive biological samples benefit studies that investigate rare, elusive, endangered, or dangerous species. Integrating genomic techniques that use non-invasive biological sampling with advances in computational approaches can benefit and inform wildlife conservation and management. Here, we used non-invasive fecal DNA samples to generate low- to medium-coverage genomes (e.g., >90% of the complete nuclear genome at six X-fold coverage) and metagenomic sequences, combining widely available and accessible DNA collection cards with commonly used DNA extraction and library building approaches. DNA preservation cards are easy to transport and can be stored non-refrigerated, avoiding cumbersome or costly sample methods. The genomic library construction and shotgun sequencing approach did not require enrichment or targeted DNA amplification. The utility and potential of the data generated was demonstrated through genome scale and metagenomic analyses of zoo and free-ranging African savanna elephants (Loxodonta africana). Fecal samples collected from free-ranging individuals contained an average of 12.41% (5.54-21.65%) endogenous elephant DNA. Clustering of these elephants with others from the same geographic region was demonstrated by a principal component analysis of genetic variation using nuclear genome-wide SNPs. Metagenomic analyses identified taxa that included Loxodonta, green plants, fungi, arthropods, bacteria, viruses and archaea, showcasing the utility of this approach for addressing complementary questions based on host-associated DNA, e.g., pathogen and parasite identification. The molecular and bioinformatic analyses presented here contributes towards the expansion and application of genomic techniques to conservation science and practice.

Sex Difference in Amebiasis

Infection with the protozoan parasite Entamoeba histolytica is much more likely to cause severe, focal liver damage in males than females, although the infection rate is the same in both sexes. The differences in disease susceptibility may be due to modulation of key mechanisms of the innate immune response by sex hormones. Complement-mediated mechanisms and estrogen-dependent activated natural killer T cells lead to early elimination of the parasite in females, whereas a pathological immune axis is triggered in males. Testosterone, which is generally thought to have more immunosuppressive properties on cells of the immune response, leads to overwhelming activation of monocytes and host-dependent destruction of liver tissue in males resulting in worse outcomes.

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.

Amebiasis and Amebic Liver Abscess in Children

Although rare in the developed world, amebiasis continues to be a leading cause of diarrhea and illness in developing nations with crowding, poor sanitation, and lack of clean water supply. Recent immigrants or travelers returning from endemic regions after a prolonged stay are at high risk of developing amebiasis. A high index of suspicion for amebiasis should be maintained for other high-risk groups like men having sex with men, people with AIDS/HIV, immunocompromised hosts, residents of mental health facility or group homes. Clinical presentation of intestinal amebiasis varies from diarrhea to colitis and dysentery. Amebic liver abscess (ALA) is the most common form of extraintestinal amebiasis. Various diagnostic tools are available and when amebiasis is suspected, a combination of stool tests and serology should be sent to maximize the yield of testing. Treatment with an amebicidal drug such as metronidazole/tinidazole and a luminal cysticidal agent such as paromomycin for clinical disease is indicated. However, for asymptomatic disease treatment with a luminal cysticidal agent to decrease chances of invasive disease and transmission is recommended.

Long non-coding RNAs as possible therapeutic targets in protozoa, and in Schistosoma and other helminths

Long non-coding RNAs (lncRNAs) emerged in the past 20 years due to massive amounts of scientific data regarding transcriptomic analyses. They have been implicated in a plethora of cellular processes in higher eukaryotes. However, little is known about lncRNA possible involvement in parasitic diseases, with most studies only detecting their presence in parasites of human medical importance. Here, we review the progress on lncRNA studies and their functions in protozoans and helminths. In addition, we show an example of knockdown of one lncRNA in Schistosoma mansoni, SmLINC156349, which led to in vitro parasite adhesion, motility, and pairing impairment, with a 20% decrease in parasite viability and 33% reduction in female oviposition. Other observed phenotypes were a decrease in the proliferation rate of both male and female worms and their gonads, and reduced female lipid and vitelline droplets that are markers for well-developed vitellaria. Impairment of female worms' vitellaria in SmLINC156349-silenced worms led to egg development deficiency. All those results demonstrate the great potential of the tools and methods to characterize lncRNAs as potential new therapeutic targets. Further, we discuss the challenges and limitations of current methods for studying lncRNAs in parasites and possible solutions to overcome them, and we highlight the future directions of this exciting field.

Molecular identification of Entamoeba histolytica, E. dispar, and E. moshkovskii in children with diarrhea from Maracaibo, Venezuela

Introducción.

Las amebas no patógenas Entamoeba dispar, Entamoeba moshkovskii y Entamoeba bangladeshi son morfológicamente idénticas a Entamoeba histolytica, parásito responsable de la amebiasis, por lo cual se necesitan técnicas moleculares para diferenciarlas.

Objetivo.

Determinar la frecuencia de las diferentes especies de Entamoeba mediante reacción en cadena de la polimerasa (Polymerase Chain Reaction, PCR) en muestras fecales de niños menores de cinco años con diarrea, provenientes de Maracaibo (Venezuela).

Materiales y métodos.

Se recolectó una muestra fecal por individuo en 75 niños con diarrea (grupo de casos) y en 25 niños sin diarrea (grupo control). Las heces se evaluaron mediante examen microscópico, método de concentración de formól-éter y PCR múltiple anidada en una sola ronda para identificar E. histolytica, E. dispar y E. moshkovskii. Además, se hizo una encuesta en la que se recopilaron los datos demográficos, signos, manifestaciones clínicas y estrato socioeconómico de los niños.

Resultados.

El 48 % de los participantes (38 del grupo de casos y 10 del grupo de control) tenían enteroparásitos. Solo en las muestras de cuatro de los niños, se encontraron quistes del complejo Entamoeba (tres en el grupo de casos y uno en el de control). Mediante PCR se amplificaron nueve muestras (9 %) para la detección de las amebas estudiadas. En el grupo de casos se registraron tres (28,13 %) de E. histolytica, cuatro (30,50 %) de E. dispar y una (9,37 %) de E. moshkovskii, en tanto que solo una (25 %) muestra amplificó para E. dispar en el grupo de control.

Conclusión.

En general, predominó E. dispar; sin embargo, todos los infectados con E. histolytica se detectaron en el grupo de niños con diarrea y se detectó el primer caso de E. moshkovskii en la región.

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.

Taxon-Specific Proteins of the Pathogenic Entamoeba Species E. histolytica and E. nuttalli

The human protozoan parasite Entamoeba histolytica can live in the human intestine for months or years without generating any symptoms in the host. For unknown reasons, amoebae can suddenly destroy the intestinal mucosa and become invasive. This can lead to amoebic colitis or extraintestinal amoebiasis whereby the amoebae spread to other organs via the blood vessels, most commonly the liver where abscesses develop. Entamoeba nuttalli is the closest genetic relative of E. histolytica and is found in wild macaques. Another close relative is E. dispar, which asyptomatically infects the human intestine. Although all three species are closely related, only E. histolytica and E. nuttalli are able to penetrate their host’s intestinal epithelium. Lineage-specific genes and gene families may hold the key to understanding differences in virulence among species. Here we discuss those genes found in E. histolytica that have relatives in only one or neither of its sister species, with particular focus on the peptidase, AIG, Ariel, and BspA families.

A Real-Time PCR Assay for Simultaneous Detection and Differentiation of Four Common Entamoeba Species That Infect Humans

There are over 40 species within the genus Entamoeba, eight of which infect humans. Of these, four species (Entamoeba histolytica, E. dispar, E. moshkovskii, and E. bangladeshi) are morphologically indistinguishable from each other, and yet differentiation is important for appropriate treatment decisions. Here, we developed a hydrolysis probe-based tetraplex real-time PCR assay that can simultaneously detect and differentiate these four species in clinical samples. In this assay, multicopy small-subunit (SSU) ribosomal DNA (rDNA) sequences were used as targets. We determined that the tetraplex real-time PCR can detect amebic DNA corresponding to as little as a 0.1 trophozoite equivalent of any of these species. We also determined that this assay can detect E. histolytica DNA in the presence of 10-fold more DNA from another Entamoeba species in mixed-infection scenarios. With a panel of more than 100 well-characterized clinical samples diagnosed and confirmed using a previously published duplex real-time PCR (capable of detecting E. histolytica and E. dispar), our tetraplex real-time PCR assay demonstrated levels of sensitivity and specificity comparable with those demonstrated by the duplex real-time PCR assay. The advantage of our assay over the duplex assay is that it can specifically detect two additional Entamoeba species and can be used in conventional PCR format. This newly developed assay will allow further characterization of the epidemiology and pathogenicity of the four morphologically identical Entamoeba species, especially in low-resource settings.

Prevalence and Molecular Differentiation of Entamoeba histolytica, Entamoeba dispar, Entamoeba moshkovskii, and Entamoeba hartmanni in Egypt

INTRODUCTION

Entamoeba histolytica-caused amoebiasis is a major cause of mortality worldwide. E. histolytica is morphologically indistinguishable from nonpathogenic species like E. dispar, E. moshkovskii, and E. hartmanni. Polymerase chain reaction (PCR) is the approved method by World Health Organization for diagnosis and differentiation of amoebiasis. This study aims to molecularly differentiate the four Entamoeba spp. using conventional PCR and correlate their prevalence with the patients' sociodemographic data.

METHODS

We collected fecal samples of 175 patients with gastrointestinal diseases at Damanhour General Hospital (El-Behira, Egypt). All microscopically positive samples were subjected to conventional PCR.

RESULTS

The overall prevalence of Entamoeba infection was 65.7% (115/175). The differentiation by PCR was successfully attained in 102 samples. The species distribution was as follows: E. histolytica (14.7%), E. dispar (61.8%), E. moshkovskii (11.8%); besides, 11.8% of samples revealed mixed infection. Of note, the infection rate was higher in men, patients from rural areas and patients who did not have sanitation facilities for sewage disposal.

CONCLUSION

This study demonstrates a high prevalence of infections caused by the nonpathogenic Entamoeba spp. E. dispar, E. moshkovskii, and E. hartmanni along with the pathogenic E. histolytica. Hence, we recommend PCR assay as an accurate, rapid, and effective diagnostic method for the detection and differentiation of the four morphologically indistinguishable Entamoeba spp. in both routine diagnosis of amoebiasis and epidemiological surveys.

Clinical features and gut microbiome of asymptomatic Entamoeba histolytica infection

Background

Entamoeba histolytica infection is a sexually transmitted disease in some developed countries. Asymptomatic infection often occurs and can be a source of transmission; however, limited data are available regarding the pathogenesis of E. histolytica.

Methods

This was a single-center, cross-sectional study. Specimens were prospectively collected from patients with clinically suspected cases. Entamoeba histolytica infection was defined as a case in which the identification of E. histolytica was confirmed by polymerase chain reaction (PCR) of a clinical specimen. Data from asymptomatic cases were compared with those from symptomatic invasive cases.

Results

Sixty-four E. histolytica–infected cases, including 13 asymptomatic cases, were identified during the study period. Microbiological diagnosis was made by endoscopic sampling in 26.6% of these cases (17/64). Endoscopy identified macroscopically visible lesions in all cases; however, the sensitivity of histopathology on biopsy samples was low (45.5%) compared with PCR (94.7%). In asymptomatic cases, infection sites were limited around the proximal colon; moreover, trophozoites were frequently identified at infection sites whereas cystic forms were commonly detected in stools. Gut microbiome analyses showed more uniform composition in asymptomatic cases than in symptomatic invasive cases, which were represented by a relatively high abundance of Ruminococcaceae, Coriobacteriaceae, and Clostridiaceae, and a low abundance of Streptococcaceae.

Conclusions

These results indicate that the encystation and attenuation of E. histolytica are highly affected by the intestinal contents, including the gut microbiome.

Genomic history of the Italian population recapitulates key evolutionary dynamics of both Continental and Southern Europeans

BACKGROUND

The cline of human genetic diversity observable across Europe is recapitulated at a micro-geographic scale by variation within the Italian population. Besides resulting from extensive gene flow, this might be ascribable also to local adaptations to diverse ecological contexts evolved by people who anciently spread along the Italian Peninsula. Dissecting the evolutionary history of the ancestors of present-day Italians may thus improve the understanding of demographic and biological processes that contributed to shape the gene pool of European populations. However, previous SNP array-based studies failed to investigate the full spectrum of Italian variation, generally neglecting low-frequency genetic variants and examining a limited set of small effect size alleles, which may represent important determinants of population structure and complex adaptive traits. To overcome these issues, we analyzed 38 high-coverage whole-genome sequences representative of population clusters at the opposite ends of the cline of Italian variation, along with a large panel of modern and ancient Euro-Mediterranean genomes.

RESULTS

We provided evidence for the early divergence of Italian groups dating back to the Late Glacial and for Neolithic and distinct Bronze Age migrations having further differentiated their gene pools. We inferred adaptive evolution at insulin-related loci in people from Italian regions with a temperate climate, while possible adaptations to pathogens and ultraviolet radiation were observed in Mediterranean Italians. Some of these adaptive events may also have secondarily modulated population disease or longevity predisposition.

CONCLUSIONS

We disentangled the contribution of multiple migratory and adaptive events in shaping the heterogeneous Italian genomic background, which exemplify population dynamics and gene-environment interactions that played significant roles also in the formation of the Continental and Southern European genomic landscapes.

Case Report: Acute Amebic Colitis Triggered by Colonoscopy: Exacerbation of Asymptomatic Chronic Infection with Entamoeba histolytica Accompanied by Dysbiosis

Recent data show that the gut microbiome plays a role in determining the clinical outcome of Entamoeba histolytica infection. We report the case of a patient who developed recurrent acute amebic colitis (second episode of acute colitis) after colonoscopy. Genotyping of E. histolytica revealed that she developed a second episode of acute amebic colitis with the same genotype as that of the first episode, indicating chronic infection had persisted asymptomatically for > 10 months between the first and second episodes. Analysis of the gut microbiome, in addition to the clinical findings, suggested that dysbiosis at colonoscopy induced the change in the clinical form of E. histolytica infection from asymptomatic chronic infection to symptomatic colitis.

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.

Trigger-induced RNAi gene silencing to identify pathogenicity factors of Entamoeba histolytica

Recently, Entamoeba histolytica clones derived from isolate HM-1:IMSS that differ in their pathogenicity were identified. Whereas some clones induce amoebic liver abscesses (ALAs) in animal models of amoebiasis, others provoke only minimal liver lesions. Based on transcriptome studies of pathogenic and nonpathogenic clones, differentially expressed genes associated with reduced or increased liver pathology can be identified. Here, to analyze the influence of these genes on ALA formation in more detail, an RNA interference-trigger mediated silencing approach was used. Using newly identified trigger sequences, the expression of 15 genes was silenced. The respective transfectants were analyzed for their ability to induce liver destruction in the murine model for the disease. Silencing of EHI_180390 (encoding an AIG1 protein) increased liver pathology induced by a nonpathogenic parent clone, whereas silencing of EHI_127670 (encoding a hypothetical protein) decreased the pathogenicity of an initially pathogenic parent clone. Additional phenotypical in vitro analyses of EHI_127670 silencing as well as overexpression transfectants indicated that this molecule has an influence on size, growth, and cysteine peptidase activity of E. histolytica. This work describes an example of how the sole operational method for effective gene silencing in E. histolytica can be used for comprehensive analyses of putative pathogenicity factors.-Matthiesen, J., Lender, C., Haferkorn, A., Fehling, H., Meyer, M., Matthies, T., Tannich, E., Roeder, T., Lotter, H., Bruchhaus, I. Trigger-induced RNAi gene silencing to identify pathogenicity factors of Entamoeba histolytica.

A Cross-Sectional Study on Intestinal Parasitic Infections in Children in Suburban Public Primary Schools, Saraburi, the Central Region of Thailand

Intestinal parasitic infection rate among school-aged children in Thailand has been decreasing. However, certain intestinal parasites remain problematic in some regions. This cross-sectional study was conducted between February and September 2016 in three suburban government primary schools (KK, BR, and HK), Saraburi, Thailand. Stool was collected from 263 asymptomatic subjects (4-15 years old), using simple direct smear, formalin-ether concentration, Boeck and Drbohlav's Locke-Egg-Serum (LES) medium culture, and agar plate culture. A self-administered questionnaire was used to collect data about lifestyle and socioeconomic status. The overall rate of intestinal parasites was 22.1% (15.6% single infection and 6.5% multiple infections). The helminths involving the digestive system found were Strongyloides stercoralis (1.5%) and Opisthorchis viverrini (0.4%). For protozoan infection, the major cause was Blastocystis hominis (17.5%). The other protozoa included Endolimax nana (4.6%), Entamoeba coli (3.4%), Entamoeba histolytica/Entamoeba dispar (1.1%), and Giardia intestinalis (0.8%). The sensitivity for the detection of B. hominis increased with the LES culture technique. The infection rate of each organism was not significantly different among the three schools except for B. hominis which showed the highest prevalence in the HK school (P = 0.001). This was correlated with the questionnaire results in which the HK school showed the highest risk of drinking contaminated water (P = 0.004). The present study emphasized the persistent problems of protozoan infections among suburban school-aged children. Lifestyle was still an important factor for intestinal parasitic infections among suburban school-aged Thai children in this study. Health education as well as routine surveillance was necessary to control the infections.

Overexpression of Differentially Expressed Genes Identified in Non-pathogenic and Pathogenic Entamoeba histolytica Clones Allow Identification of New Pathogenicity Factors Involved in Amoebic Liver Abscess Formation

We here compared pathogenic (p) and non-pathogenic (np) isolates of Entamoeba histolytica to identify molecules involved in the ability of this parasite to induce amoebic liver abscess (ALA)-like lesions in two rodent models for the disease. We performed a comprehensive analysis of 12 clones (A1–A12) derived from a non-pathogenic isolate HM-1:IMSS-A and 12 clones (B1–B12) derived from a pathogenic isolate HM-1:IMSS-B. “Non-pathogenicity” included the induction of small and quickly resolved lesions while “pathogenicity” comprised larger abscess development that overstayed day 7 post infection. All A-clones were designated as non-pathogenic, whereas 4 out of 12 B-clones lost their ability to induce ALAs in gerbils. No correlation between ALA formation and cysteine peptidase (CP) activity, haemolytic activity, erythrophagocytosis, motility or cytopathic activity was found. To identify the molecular framework underlying different pathogenic phenotypes, three clones were selected for in-depth transcriptome analyses. Comparison of a non-pathogenic clone A1^np with pathogenic clone B2^p revealed 76 differentially expressed genes, whereas comparison of a non-pathogenic clone B8^np with B2^p revealed only 19 differentially expressed genes. Only six genes were found to be similarly regulated in the two non-pathogenic clones A1^np and B8^np in comparison with the pathogenic clone B2^p. Based on these analyses, we chose 20 candidate genes and evaluated their roles in ALA formation using the respective gene-overexpressing transfectants. We conclude that different mechanisms lead to loss of pathogenicity. In total, we identified eight proteins, comprising a metallopeptidase, C2 domain proteins, alcohol dehydrogenases and hypothetical proteins, that affect the pathogenicity of E. histolytica.

The pathogen Entamoeba histolytica can live asymptomatically in the human gut, or it can disrupt the intestinal barrier and induce life-threatening abscesses in different organs, most often in the liver. The molecular framework that enables this invasive, highly pathogenic phenotype is still not well understood. In order to identify factors that are positively or negatively correlated for invasion and destruction of the liver, we used a unique tool, E. histolytica clones that differ dramatically in their pathogenicity, while sharing almost identical genetic background. Based on comprehensive transcriptome studies of these clones, we identified a set of candidate genes that are potentially involved in pathogenicity. Using ectopic overexpression of the most promising candidates, either in pathogenic or in non-pathogenic Entamoeba clones, we identified genes where high expression reduced pathogenicity and only one gene that increased pathogenicity to a certain extend.

Taken together, the current study identifies novel pathogenicity factors of E. histolytica and highlights the observation that various different genes contribute to pathogenicity.

Immune Response of Amebiasis and Immune Evasion by Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite and the causative agent of amebiasis. It is estimated approximately 1% of humans are infected with E. histolytica, resulting in an estimate of 100,000 deaths annually. Clinical manifestations of amebic infection range widely from asymptomatic to severe symptoms, including dysentery and extra-intestinal abscesses. Like other infectious diseases, it is assumed that only ~20% of infected individuals develop symptoms, and genetic factors of both the parasite and humans as well as the environmental factors, e.g., microbiota, determine outcome of infection. There are multiple essential steps in amebic infection: degradation of and invasion into the mucosal layer, adherence to the intestinal epithelium, invasion into the tissues, and dissemination to other organs. While the mechanisms of invasion and destruction of the host tissues by the amebae during infection have been elucidated at the molecular levels, it remains largely uncharacterized how the parasite survive in the host by evading and attacking host immune system. Recently, the strategies for immune evasion by the parasite have been unraveled, including immunomodulation to suppress IFN-γ production, elimination of immune cells and soluble immune mediators, and metabolic alterations against reactive oxygen and nitrogen species to fend off the attack from immune system. In this review, we summarized the latest knowledge on immune reaction and immune evasion during amebiasis.

Knockdown of Five Genes Encoding Uncharacterized Proteins Inhibits Entamoeba histolytica Phagocytosis of Dead Host Cells

Entamoeba histolytica is the protozoan parasite that causes invasive amebiasis, which is endemic to many developing countries and characterized by dysentery and liver abscesses. The virulence of E. histolytica correlates with the degree of host cell engulfment, or phagocytosis, and E. histolytica phagocytosis alters amebic gene expression in a feed-forward manner that results in an increased phagocytic ability. Here, we used a streamlined RNA interference screen to silence the expression of 15 genes whose expression was upregulated in phagocytic E. histolytica trophozoites to determine whether these genes actually function in the phagocytic process. When five of these genes were silenced, amebic strains with significant decreases in the ability to phagocytose apoptotic host cells were produced. Phagocytosis of live host cells, however, was largely unchanged, and the defects were surprisingly specific for phagocytosis. Two of the five encoded proteins, which we named E. histolytica ILWEQ (EhILWEQ) and E. histolytica BAR (EhBAR), were chosen for localization via SNAP tag labeling and localized to the site of partially formed phagosomes. Therefore, both EhILWEQ and EhBAR appear to contribute to E. histolytica virulence through their function in phagocytosis, and the large proportion (5/15 [33%]) of gene-silenced strains with a reduced ability to phagocytose host cells validates the previously published microarray data set demonstrating feed-forward control of E. histolytica phagocytosis. Finally, although only limited conclusions can be drawn from studies using the virulence-deficient G3 Entamoeba strain, the relative specificity of the defects induced for phagocytosis of apoptotic cells but not healthy cells suggests that cell killing may play a rate-limiting role in the process of Entamoeba histolytica host cell engulfment.

Epidemiology of Domestically Acquired Amebiasis in Japan, 2000-2013

Notifications of amebiasis have been increasing in Japan. Using national surveillance data during 2000-2013, reported cases of amebiasis were analyzed. A case of amebiasis was defined as laboratory-confirmed Entamoeba histolytica infection, regardless of presence of symptoms. We described temporal trends and analyzed correlates of asymptomatic versus symptomatic cases based on odds ratios (ORs) and 95% confidence intervals (CIs) using logistic regression. Of 9,946 cases reported during 2000-2013, 7,403 were domestic cases. During this period, the proportion of domestic cases increased from 63% to 85%. Among male cases, majority were middle aged, and from 2008, the number of cases attributed to heterosexual contact surpassed that of homosexual contact. During 2010-2013, increase in notifications was associated with asymptomatic cases, colonoscopy diagnosis, and males with unknown or heterosexual route of infection. Among males, colonoscopy (OR = 31.5; 95% CI = 14.0-71.0) and cases with unknown route of infection, relative to homosexual contact (OR = 2.2; 95% CI = 1.3-3.9), were associated with asymptomatic infections in multivariate analysis. Although the recent rise may have been due to enhanced detection by colonoscopy or reporting, the large number of asymptomatic cases, with reportedly unknown or heterosexual route of infection, has led to a better understanding of amebiasis in Japan and highlights the potential public health concern.

Immigrants living in an urban milieu with sanitation in Southern Italy: persistence and transmission of intestinal parasites

In the current era of globalization, the massive movement of populations to developed countries causes a greater attention to neglected tropical diseases in places where such diseases are considered unusual. The present study was planned to assess the persistence of intestinal parasitosis in immigrants stably living in the urban central area of Naples (Southern Italy) and the spread of infection within households with a lifestyle similar to that of the country of origin. A total of 2150 stool samples were analysed with the FLOTAC dual technique, and 415 subjects (19.3 %) tested positive for pathogenic intestinal parasites. One hundred ninety-six subjects were randomly selected and monitored again after 1 year in order to evaluate the persistence of intestinal parasites in immigrants having access to proper sanitation. No pathogenic parasites were found in these 196 samples. A total of 482 cohabitants of 151 positive subjects were recruited to evaluate the interfamilial spread of the identified parasites. Only in 18 households were there subjects infected with the same parasite. Monitoring of parasites in stool samples of immigrants showed a decrease of almost all pathogenic species over the years. From the analysis of households, it is not possible to assert that there is a familial transmission. Our study provides evidence that the prevalence of parasitic infections in immigrants is likely related to the poor sanitary habits of the country of origin and that acquisition of new sanitary regulations, together with the administration of pharmacological treatment, limits the transmission in the households and in the local population of their destination.

Molecular biology research to benefit patients with Entamoeba histolytica infection

The development of molecular microbiology has made it possible for us to deepen our understanding of the pathogenesis of amebiasis. Research using the trophozoite form of Entamoeba histolytica has clearly shown us the importance of the interface between the parasite and host cells in vitro. Immuno-pathogenesis after excystation was similarly well advanced by the use of a novel murine model of amebic colitis. However, it is still challenging to apply these findings to clinical and epidemiological settings. This is mainly because of the lack of a complete infection animal model of amebiasis by oral-fecal infection. Moreover, in vitro experiments have predominantly been performed using the same axenic cultured strain HM-1: IMSS isolated about 50 years ago, whereas highly diverse strains are prevalent all over the world. Translational research informed by clinical observations has the greatest potential for the development of effective interventions. Here, we highlight discoveries of the experiments designed from cohort observation and discuss remaining problems to be solved.

Noninvasive intestinal amebiasis: Entamoeba histolytica colonization without invasion

PURPOSE OF REVIEW

Entamoeba histolytica infection remains a major cause of morbidity and mortality worldwide. Although research with the organism began in the late nineteenth century, our understanding of the natural history of the infection remains incomplete and is heavily based on expert opinion. Most persons infected with E. histolytica are carriers with the organism colonizing the large intestine. Host defense mechanisms that prevent invasive diseases are poorly understood. A timely review could lead to renewed interest.

RECENT FINDINGS

We herein review 2012 and 2013 publications related to the epidemiology, diagnosis, management and potential mechanisms that enable noninvasive E. histolytica colonization without invasion.

SUMMARY

There are several publications that advance our knowledge in the first three categories listed above, but studies of mechanisms for noninvasive E. histolytica colonization are glaringly few.

Gastrointestinal symptoms in travellers

Diarrhoea is probably the single most common medical complaint in returning travellers. The most common pathogens are entero-toxigenic Escherichia coli, Shigella, Salmonella and Campylobacter. Viruses, toxigenic Arcobacter and Bacteroides fragilis, as well as parasites such as Cryptosporidium sp, are increasingly recognised but are not tested for in most diagnostic laboratories. Blood in stools is a sign of invasive disease and should trigger exclusion of invasive amoebic disease. The use of empiric antibiotics may shorten illness but is complicated by the diversity of bacterial causes and emerging resistance.

Immune markers characteristic for asymptomatically infected and diseased Entamoeba histolytica individuals and their relation to sex

BACKGROUND

The protozoan parasite Entamoeba histolytica (E. histolytica) usually asymptomatically colonizes the human intestine. In the minority of the cases, the parasite evades from the gut and can induce severe symptoms like colitis or amebic liver abscess (ALA). Interestingly, ALA predominates in adult men despite a higher prevalence of the parasite in women. The present study aimed to identify characteristic serum markers in a unique cohort of clearly defined asymptomatically infected E. histolytica individuals in comparison to patients with an E. histolytica liver manifestation of both sex.

METHODS

The following study groups were investigated: ALA patients (n = 38), healthy asymptomatic E. histolytica carriers (AC) (n = 44), and healthy E. dispar-infected controls (n = 24) out of an amebiasis endemic area. E. histolytica-specific immunoglobulin G (IgG) and the IgG subclasses against proteinaceous and non-proteinaceous amebic antigens were measured by ELISA. Serum cytokine and chemokine levels were investigated using a flow cytometry bead-based multiplex immunoassay.

RESULTS

The IgG results revealed that not only ALA patients, but also AC, developed high E. histolytica-specific titers of IgG and all IgG subclasses as well as IgA. IgG and IgG2 titers against the glycolipid E. histolytica lipophosphoglycan were highest in ALA patients. As in ALA patients, high cytokine levels of interleukin (IL-) 4 were detected in AC compared to E. dispar infected individuals, while IL-6 was exclusively elevated in ALA patients. IL-10 was lower in AC compared to ALA patients. Equal serum levels of CCL2 were found in all study groups but ALA patients showed decreased levels of CCL3. Sex dependent analysis of the data indicated significantly higher IgG and IgG1 titers in female AC compared to male AC. CCL2, the chemokine involved in immunopathology in the mouse model for the disease, was higher in male AC compared to female AC.

CONCLUSION

In this study we characterize for the first time an asymptomatic carrier stage in amebiasis that is associated with a significant immune reaction and provide immunological markers that might give first hints towards an understanding of immune mechanisms underlying the control or development of invasive amebiasis.

Sex bias in the outcome of human tropical infectious diseases: influence of steroid hormones

Numerous investigations have revealed a bias toward males in the susceptibility to and severity of a variety of infectious diseases, especially parasitic diseases. Although different external factors may influence the exposure to infection sources among males and females, one recurrent phenomenon indicative of a hormonal influence is the simultaneous increase in disease occurrence and hormonal activity during the aging process. Substantial evidence to support the influence of hormones on disease requires rigorously controlled human population studies, as well as the same sex dimorphism being observed under controlled laboratory conditions. To date, only very few studies conducted have fulfilled these criteria. Herein, we introduce tropical infectious diseases, including amebiasis, malaria, leishmaniasis, toxoplasmosis, schistosomiasis, and paracoccidioidomycosis, in which hormones are suspected to play a role in disease processes. We summarize the most recent findings from epidemiologic studies in humans and from hormone replacement studies in animal models, as well as data regarding the influence of hormones on immune responses underlying the pathology of the diseases.

Application of PCR-based methods for diagnosis of intestinal parasitic infections in the clinical laboratory

For many years PCR- and other DNA-based methods of pathogen detection have been available in most clinical microbiology laboratories; however, until recently these tools were not routinely exploited for the diagnosis of parasitic infections. Laboratories were initially reluctant to implement PCR as incorporation of such assays within the algorithm of tools available for the most accurate diagnosis of a large variety of parasites was unclear. With regard to diagnosis of intestinal parasitic infections, the diversity of parasites that one can expect in most settings is far less than the parasitological textbooks would have you believe, hence developing a simplified diagnostic triage is feasible. Therefore the classical algorithm based on population, patient groups, use of immuno-suppressive drugs, travel history etc. is also applicable to decide when to perform and which additional techniques are to be used, if a multiplex PCR panel is used as a first-line screening diagnostic.

Discrimination of Entamoeba Spp. in children with dysentery

AIM

The present study was performed in order to differentiate E. histolytica and E. dispar in children from Gorgan city, using a PCR method.

BACKGROUND

Differential detection of two morphologically indistinguishable protozoan parasites Entamoeba histolytica and E. dispar has a great clinical and epidemiological importance because of potential invasive pathogenic E. histolytica and non-invasive parasite E. dispar.

PATIENTS AND METHODS

One hundred and five dysentery samples were collected from children hospitalized in Taleghani hospital in Gorgan city. The fecal specimens were examined by light microscopy (10X then 40X) to distinguish Entamoeba complex. A single round PCR amplifying partial small-subunit rRNA gene was performed on positive microscopy samples to differentiate E. histolytica/ E. dispar and E. moshkovskii from each other.

RESULTS

Twenty-five specimens (23.8%) were positive for Enramoeba complex in direct microscopic examination. PCR using positive controls indicated E. histolytica and E. dispar in two (2/25, 8%) and three (3/25, 12%) samples, respectively.

CONCLUSION

There is a warrant to performing molecular diagnosis for stool examination at least in hospitalized children in order to prevent incorrect reports from laboratories and consequently mistreating by physicians.

Species-specific immunity induced by infection with Entamoeba histolytica and Entamoeba moshkovskii in mice

Entamoeba histolytica, the parasitic amoeba responsible for amoebiasis, causes approximately 100,000 deaths every year. There is currently no vaccine against this parasite. We have previously shown that intracecal inoculation of E. histolytica trophozoites leads to chronic and non-healing cecitis in mice. Entamoeba moshkovskii, a closely related amoeba, also causes diarrhea and other intestinal disorders in this model. Here, we investigated the effect of infection followed by drug-cure of these species on the induction of immunity against homologous or heterologous species challenge. Mice were infected with E. histolytica or E. moshkovskii and treated with metronidazole 14 days later. Re-challenge with E. histolytica or E. moshkovskii was conducted seven or 28 days following confirmation of the clearance of amoebae, and the degree of protection compared to non-exposed control mice was evaluated. We show that primary infection with these amoebae induces a species-specific immune response which protects against challenge with the homologous, but not a heterologous species. These findings pave the way, therefore, for the identification of novel amoebae antigens that may become the targets of vaccines and provide a useful platform to investigate host protective immunity to Entamoeba infections.

Diagnostic microbiologic methods in the GEMS-1 case/control study

To understand the etiology of moderate-to-severe diarrhea among children in high mortality areas of sub-Saharan Africa and South Asia, we performed a comprehensive case/control study of children aged <5 years at 7 sites. Each site employed an identical case/control study design and each utilized a uniform comprehensive set of microbiological assays to identify the likely bacterial, viral and protozoal etiologies. The selected assays effected a balanced consideration of cost, robustness and performance, and all assays were performed at the study sites. Identification of bacterial pathogens employed streamlined conventional bacteriologic biochemical and serological algorithms. Diarrheagenic Escherichia coli were identified by application of a multiplex polymerase chain reaction assay for enterotoxigenic, enteroaggregative, and enteropathogenic E. coli. Rotavirus, adenovirus, Entamoeba histolytica, Giardia enterica, and Cryptosporidium species were detected by commercially available enzyme immunoassays on stool samples. Samples positive for adenovirus were further evaluated for adenovirus serotypes 40 and 41. We developed a novel multiplex assay to detect norovirus (types 1 and 2), astrovirus, and sapovirus. The portfolio of diagnostic assays used in the GEMS study can be broadly applied in developing countries seeking robust cost-effective methods for enteric pathogen detection.

Worldwide genealogy of Entamoeba histolytica: an overview to understand haplotype distribution and infection outcome

Although Entamoeba histolytica is one of the most prevalent intestinal parasites, how the different strains of this species are distributed all over the world and how different genotypes are associated with the infection outcome are yet to be fully understood. Recently, the use of a number of molecular markers has made the characterization of several genotypes in those regions with high incidence of amoebiasis possible. This work proposes the first genealogy of E. histolytica, with an haplotype network based on two tRNA gene-linked array of Short Tandem Repeats (STRs) reported until today, and 47 sequences from 39 new isolates of Mexican Amoebic Liver Abscesses (ALA) samples. One hundred and three sequences were obtained from D-A locus, their information about the geographic region of isolation as well as clinical diagnosis were also collected. One hundred and five sequences from N-K2 locus were also obtained as well as the region of isolation, but the information about clinical diagnosis was not available in all cases. The most abundant and widely distributed haplotype in the world is the one of E. histolytica HM1:IMSS strain. This was found in Mexico, Bangladesh, Japan, China and USA and is associated to symptomatic patients as well as asymptomatic cyst passers. Many other haplotypes were found only in a single country. Both genealogies suggest that there are no lineages within the networks that may be related to a particular geographic region or infection outcome. A concatenated analysis of the two molecular markers revealed 12 different combinations, which suggests the possibility of genetic recombination events. The present study is the first to propose a global genealogy of this species and suggests that there are still many genotypes to be discovered. The genotyping of new isolates will help to understand the great diversity and genetic structure of this parasite.

Testosterone increases susceptibility to amebic liver abscess in mice and mediates inhibition of IFNγ secretion in natural killer T cells

Amebic liver abscess (ALA), a parasitic disease due to infection with the protozoan Entamoeba histolytica, occurs age and gender dependent with strong preferences for adult males. Using a mouse model for ALA with a similar male bias for the disease, we have investigated the role of female and male sexual hormones and provide evidence for a strong contribution of testosterone. Removal of testosterone by orchiectomy significantly reduced sizes of abscesses in male mice, while substitution of testosterone increased development of ALA in female mice. Activation of natural killer T (NKT) cells, which are known to be important for the control of ALA, is influenced by testosterone. Specifically activated NKT cells isolated from female mice produce more IFNγ compared to NKT cells derived from male mice. This high level production of IFNγ in female derived NKT cells was inhibited by testosterone substitution, while the IFNγ production in male derived NKT cells was increased by orchiectomy. Gender dependent differences were not a result of differences in the total number of NKT cells, but a result of a higher activation potential for the CD4(-) NKT cell subpopulation in female mice. Taken together, we conclude that the hormone status of the host, in particular the testosterone level, determines susceptibility to ALA at least in a mouse model of the disease.

TNFα-mediated liver destruction by Kupffer cells and Ly6Chi monocytes during Entamoeba histolytica infection

Amebic liver abscess (ALA) is a focal destruction of liver tissue due to infection by the protozoan parasite Entamoeba histolytica (E. histolytica). Host tissue damage is attributed mainly to parasite pathogenicity factors, but massive early accumulation of mononuclear cells, including neutrophils, inflammatory monocytes and macrophages, at the site of infection raises the question of whether these cells also contribute to tissue damage. Using highly selective depletion strategies and cell-specific knockout mice, the relative contribution of innate immune cell populations to liver destruction during amebic infection was investigated. Neutrophils were not required for amebic infection nor did they appear to be substantially involved in tissue damage. In contrast, Kupffer cells and inflammatory monocytes contributed substantially to liver destruction during ALA, and tissue damage was mediated primarily by TNFα. These data indicate that besides direct antiparasitic drugs, modulating innate immune responses may potentially be beneficial in limiting ALA pathogenesis.

Amebic liver abscess (ALA), an infectious disease caused by the protozoan parasite Entamoeba histolytica is characterized by severe focal liver damages. According to its name giving activity, destruction of liver tissue by E. histolytica has been attributed to parasite-specific effector molecules. However, abscess lesions contain considerable numbers of innate immune cells, such as neutrophils and macrophages, raising the question whether these host cells might contribute to the disease as well. We have investigated the role of the host immune response during ALA development using a mouse model for the disease. The results indicated that despite the presence of considerable numbers of neutrophils within the abscess lesions, these cells were dispensable for both the control of the disease and the tissue damage. On the other hand, two subsets of immune cells, the liver resident Kupffer cells and the inflammatory Ly6C-expressing monocytes were identified as the main effector cells responsible for liver tissue destruction. Furthermore, TNFα produced by the Ly6C-expressing monocytes, was found to be a cytokine that is critically involved in abscess development. Thus, our finding that host immune mechanisms are indeed responsible for liver tissue destruction during ALA development may change the view on the pathological mechanism of amebic disease.

Entamoeba histolytica infection in men who have sex with men

Entamoeba histolytica infection (amoebiasis) is the second leading cause of death from parasitic diseases. Epidemiological studies from developed countries have reported an increasing prevalence of amoebiasis and of invasive infections, such as amoebic colitis, among men who have sex with men (MSM) who engage in oral-anal sex. Although most infections with E histolytica are asymptomatic, clinical manifestations of invasive amoebiasis mainly include amoebic colitis and amoebic liver abscess, which are associated with substantial morbidity and medical cost. Laboratory diagnosis of amoebiasis should be based on detection of E histolytica by use of tests with high sensitivity and specificity, such as specific amoebic-antigen or PCR-based assays. Microscopy used in routine clinical laboratories is not sensitive or specific enough for detection of E histolytica. Metronidazole or tinidazole remains the mainstay of treatment for invasive amoebiasis, followed by treatment with luminal agents to prevent relapse and transmission of E histolytica to sexual partners or close contacts.

Protozoan infections of the gastrointestinal tract

The review provides current views on human protozoan parasites of the gut. The recognition of the importance of cryptosporidium, cyclospora and microsporidia over the last three decades emphasises the possibility that more pathogenic intestinal protozoa are presently unrecognized. Each of these is a zoonotic infection and the potential for a zoonotic element to the transmission of giardiasis has been recognized. A common theme in increased understanding of the biology and pathological mechanisms involved in causing disease is the application of molecular techniques to the various stages of the parasite life cycle. Molecular methods are increasingly contributing to laboratory diagnosis of these conditions with increased yields of positive results though in the tropics it is likely that fecal microscopy will remain the standard for some time to come. The nitroimidazole compounds are the mainstay of treatment for giardia and amebiasis with no major advance in therapeutics since their role was appreciated. Nitazoxanide was shown to be effective for cryptosporidiosis in the 1990s.

A Multilocus Sequence Typing System (MLST) reveals a high level of diversity and a genetic component to Entamoeba histolytica virulence

Background

The outcome of an Entamoeba histolytica infection is variable and can result in either asymptomatic carriage, immediate or latent disease (diarrhea/dysentery/amebic liver abscess). An E. histolytica multilocus genotyping system based on tRNA gene-linked arrays has shown that genetic differences exist among parasites isolated from patients with different symptoms however, the tRNA gene-linked arrays cannot be located in the current assembly of the E. histolytica Reference genome (strain HM-1:IMSS) and are highly variable.

Results

To probe the population structure of E. histolytica and identify genetic markers associated with clinical outcome we identified in E. histolytica positive samples selected single nucleotide polymorphisms (SNPs) by multiplexed massive parallel sequencing. Profile SNPs were selected which, compared to the reference strain HM-1:IMSS sequence, changed an encoded amino acid at the SNP position, and were present in independent E. histolytica isolates from different geographical origins. The samples used in this study contained DNA isolated from either xenic strains of E. histolytica trophozoites established in culture or E. histolytica positive clinical specimens (stool and amebic liver abscess aspirates). A record of the SNPs present at 16 loci out of the original 21 candidate targets was obtained for 63 of the initial 84 samples (63% of asymptomatically colonized stool samples, 80% of diarrheal stool, 73% of xenic cultures and 84% of amebic liver aspirates). The sequences in all the 63 samples both passed sequence quality control metrics and also had the required greater than 8X sequence coverage for all 16 SNPs in order to confidently identify variants.

Conclusions

Our work is in agreement with previous findings of extensive diversity among E. histolytica isolates from the same geographic origin. In phylogenetic trees, only four of the 63 samples were able to group in two sets of two with greater than 50% confidence. Two SNPs in the cylicin-2 gene (EHI_080100/XM_001914351) were associated with disease (asymptomatic/diarrhea p = 0.0162 or dysentery/amebic liver abscess p = 0.0003). This study demonstrated that there are genetic differences between virulent and avirulent E. histolytica strains and that this approach has the potential to define genetic changes that influence infection outcomes.

Entamoeba moshkovskii is associated with diarrhea in infants and causes diarrhea and colitis in mice

BACKGROUND

Entamoeba moshkovskii is prevalent in developing countries and morphologically indistinguishable from pathogenic Entamoeba histolytica and nonpathogenic Entamoeba dispar. It is not known if E. moshkovskii is pathogenic.

METHODS

Mice were intracecally challenged with the trophozoites of each Entamoeba spp. to test the ability to cause diarrhea, and infants in Bangladesh were prospectively observed to see if newly acquired E. moshkovskii infection was associated with diarrhea.

RESULTS

E. moshkovskii and E. histolytica caused diarrhea and weight loss in susceptible mice. E. dispar infected none of the mouse strains tested. In Mirpur, Dhaka, Bangladesh, E. moshkovskii, E. histolytica, and E. dispar were identified in 42 (2.95%), 66 (4.63%), and 5 (0.35%), respectively, of 1426 diarrheal episodes in 385 children followed prospectively from birth to one year of age. Diarrhea occurred temporally with acquisition of a new E. moshkovskii infection: in the 2 months preceding E. moshkvskii-associated diarrhea, 86% (36 of 42) of monthly surveillance stool samples were negative for E. moshkovskii.

CONCLUSIONS

E. moshkovskii was found to be pathogenic in mice. In children, the acquisition of E. moshkovskii infection was associated with diarrhea. These data are consistent with E. moshkovskii causing disease, indicating that it is important to reexamine its pathogenicity.

Infantile amoebiasis: a case report

Amoebiasis continues to be a major cause of morbidity and mortality in children in developing countries. Entamoeba histolytica infections are commonly observed in tropical and subtropical regions of the world including Iran. In developed countries Entamoeba histolytica infections are commonly seen in travelers, recent immigrants, homosexual men, and inmates of institutions. The disease is more severe in the two extremes of life. This paper paper describes a four-month-old male infant with Entamoeba histolytica presenting initially with refusal of feeds, hyperactive bowel sound, vomiting, and diarrhea. A fecal sample was positive for Entamoeba histolytica by Lugol's iodine solution and the concentration technique. He was successfully treated with metronidazole for 5 days. This case illustrates that Entamoeba species could be pathogenic in young infant; therefore, awareness of the infection, aggressive approach to diagnosis, and early initiation of treatment continue to be critical component of infection control.

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.

Mechanisms of adherence, cytotoxicity and phagocytosis modulate the pathogenesis of Entamoeba histolytica

The unicellular parasite Entamoeba histolytica, the causative agent of the human disease amebiasis, has traditionally been distinguished from its nonpathogenic cousin Entamoeba dispar by its propensity for the ingestion of erythrocytes. This classic feature, along with the parasite’s ability to cause extensive host cell death, are critical mechanisms of pathogenesis during human infection. Recent advances have led to a greater understanding of the molecular components that allow E. histolytica to kill and phagocytose extracellular targets during human infection and include detailed studies of the role of the parasite’s cysteine proteinases and other effectors of cytotoxicity, as well as the mechanisms of ligand recognition, signaling and intracellular trafficking during phagocytosis.