Innate and acquired resistance to amebiasis in bangladeshi children

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.

Immune Response to the Enteric Parasite Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite responsible for amoebiasis, a disease with a high prevalence in developing countries. Establishing an amoebic infection involves interplay between pathogenic factors for invasion and tissue damage, and immune responses for protecting the host. Here, we review the pathogenicity of E. histolytica and summarize the latest knowledge on immune response and immune evasion mechanisms during amoebiasis.

Entamoeba gingivalis Causes Oral Inflammation and Tissue Destruction

A metagenomics analysis showed a strongly increased frequency of the protozoan Entamoeba gingivalis in inflamed periodontal pockets, where it contributed the second-most abundant rRNA after human rRNA. This observation and the close biological relationship to Entamoeba histolytica, which causes inflammation and tissue destruction in the colon of predisposed individuals, raised our concern about its putative role in the pathogenesis of periodontitis. Histochemical staining of gingival epithelium inflamed from generalized severe chronic periodontitis visualized the presence of E. gingivalis in conjunction with abundant neutrophils. We showed that on disruption of the epithelial barrier, E. gingivalis invaded gingival tissue, where it moved and fed on host cells. We validated the frequency of E. gingivalis in 158 patients with periodontitis and healthy controls by polymerase chain reaction and microscopy. In the cases, we detected the parasite in 77% of inflamed periodontal sites and 22% of healthy sites; 15% of healthy oral cavities were colonized by E. gingivalis. In primary gingival epithelial cells, we demonstrated by quantitative real-time polymerase chain reaction that infection with E. gingivalis but not with the oral bacterial pathogen Porphyromonas gingivalis strongly upregulated the inflammatory cytokine IL8 (1,900 fold, P = 2 × 10–4) and the epithelial barrier gene MUC21 (8-fold, P = 7 × 10–4). In gingival fibroblasts, we showed upregulation of the collagenase MMP13 (11-fold, P = 3 × 10–4). Direct contact of E. gingivalis to gingival epithelial cells inhibited cell proliferation. We indicated the strong virulence potential of E. gingivalis and showed that the mechanisms of tissue invasion and destruction are similar to the colonic protozoan parasite E. histolytica. In conjunction with abundant colonization of inflamed periodontal sites and the known resistance of Entamoeba species to neutrophils, antimicrobial peptides, and various antibiotics, our results raise the awareness of this protozoan as a potential and, to date, underrated microbial driver of destructive forms of periodontitis.

Host-antibody inductivity of virulent Entamoeba histolytica and non-virulent Entamoeba moshkovskii in a mouse model

Background

Despite similarities in morphology, gene and protein profiles, Entamoeba histolytica and E. moshkovskii show profound differences in pathogenicity. Entamoeba histolytica infection might result in amoebic dysentery and liver abscess, while E. moshkovskii causes only mild diarrhea. Extensive studies focus on roles of host immune responses to the pathogenic E. histolytica; however, evidence for E. moshkovskii remains scarce.

Methods

To study differences in host-antibody response profiles between E. histolytica and E. moshkovskii, mice were immunized intraperitoneally with different sets of Entamoeba trophozoites as single species, mixed species and combinations.

Results

Mice prime-immunized with E. histolytica and E. moshkovskii combination, followed by individual species, exhibited higher IgG level than the single species immunization. Mice immunized with E. moshkovskii induced significantly higher levels and long-lasting antibody responses than those challenged with E. histolytica alone. Interestingly, E. histolytica-specific anti-sera promoted the cytopathic ability of E. histolytica toward Chinese hamster ovarian (CHO) cells, but showed no effect on cell adhesion. There was no significant effect of immunized sera on cytopathic activity and adhesion of E. moshkovskii toward both CHO and human epithelial human colonic (Caco-2) cell lines. Monoclonal-antibody (mAb) characterization demonstrated that 89% of E. histolytica-specific mAbs produced from mice targeted cytoplasmic and cytoskeletal proteins, whereas 73% of E. moshkovskii-specific mAbs targeted plasma membrane proteins.

Conclusions

The present findings suggest that infection with mixed Entamoeba species or E. moshkovskii effectively induces an antibody response in mice. It also sheds light on roles of host antibody response in the pathogenic difference of E. histolytica and E. moshkovskii trophozoites, and cell surface protein modifications of the amoebic parasites to escape from host immune system.

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.

Entamoeba Histolytica: Updates in Clinical Manifestation, Pathogenesis, and Vaccine Development

Entamoeba histolytica is the responsible parasite of amoebiasis and remains one of the top three parasitic causes of mortality worldwide. With increased travel and emigration to developed countries, infection is becoming more common in nonendemic areas. Although the majority of individuals infected with E. histolytica remain asymptomatic, some present with amoebic colitis and disseminated disease. As more is learned about its pathogenesis and the host's immune response, the potential for developing a vaccine holds promise. This narrative review outlines the current knowledge regarding E. histolytica and E. dispar and insight in the development of a vaccine.

Role of Eosinophils and Tumor Necrosis Factor Alpha in Interleukin-25-Mediated Protection from Amebic Colitis

The parasite Entamoeba histolytica is a cause of diarrhea in infants in low-income countries. Previously, it was shown that tumor necrosis factor alpha (TNF-α) production was associated with increased risk of E. histolytica diarrhea in children. Interleukin-25 (IL-25) is a cytokine that is produced by intestinal epithelial cells that has a role in maintenance of gut barrier function and inhibition of TNF-α production. IL-25 expression was decreased in humans and in the mouse model of amebic colitis. Repletion of IL-25 blocked E. histolytica infection and barrier disruption in mice, increased gut eosinophils, and suppressed colonic TNF-α. Depletion of eosinophils with anti-Siglec-F antibody prevented IL-25-mediated protection. In contrast, depletion of TNF-α resulted in resistance to amebic infection. We concluded that IL-25 provides protection from amebiasis, which is dependent upon intestinal eosinophils and suppression of TNF-α.

The intestinal epithelial barrier is important for protection from intestinal amebiasis. We discovered that the intestinal epithelial cytokine IL-25 was suppressed during amebic colitis in humans and that protection could be restored in the mouse model by IL-25 administration. IL-25 acted via eosinophils and suppressed TNF-α. This work illustrates a previously unrecognized pathway of innate mucosal immune response.

Malnutrition Is Associated with Protection from Rotavirus Diarrhea: Evidence from a Longitudinal Birth Cohort Study in Bangladesh

Rotavirus is a leading cause of dehydrating diarrhea and death among infants and children globally, particularly in communities of the developing world. While numerous studies have described the complex relationships among infectious diarrhea, growth faltering, and poverty, the impact of nutritional status on susceptibility to rotavirus diarrhea is not well understood. In a longitudinal study conducted over the first 3 years of life among 626 slum-dwelling infants enrolled at birth in Dhaka, Bangladesh, we observed that common measures of healthy growth and development were positively associated with a risk of symptomatic rotavirus infection. This finding runs counter to the idea that improving childhood nutrition will implicitly decrease the incidence of symptomatic infection by enteric pathogens. As childhood nutrition improves worldwide, rotavirus infection may remain a public health challenge, making universal vaccination of even greater importance.

Indirect Haemagglutination Test in Comparison with ELISA for Detection of Antibodies against Invasive Amoebiasis

INTRODUCTION

Diagnosis of amoebiasis is based on combination of tests like microscopy, imaging, serology and molecular methods. In absence of molecular techniques, serology can be used as an alternative aid. Various serological techniques were reported with different sensitivity and specificity. The diagnostic efficiency of these assays mainly depends on the characteristics of antigen that is being used and various conditions of performance.

AIM

To evaluate the efficiency of recombinant calcium binding domain containing protein by Indirect Haemagglutination Assay (IHA) against a commercial ELISA among amoebic liver abscess cases and control group.

MATERIALS AND METHODS

The study was carried out during the period of 2011-2015 and blood samples were collected from suspected amoebiasis cases who were attending the clinics of Medicine and Paediatrics department, JIPMER. A total of 200 sera samples which included 100 Amoebic Liver Abscess (ALA), 50 cases of other parasitic infections and liver diseases and 50 presumed healthy controls were examined by IHA and commercial ELISA. In brief, chick cells were stabilized by Double Aldehyde Sensitization (DAS) method. Optimum Sensitizing Dose (OSD) of the antigen was determined. The test was performed in a U-bottomed microtiter plate with recombinant amoebic antigen (12.5μg/ml), incubated at Room Temperature (RT) for 2 hours. RIDASCREEN Entamoeba IgG ELISA kit which is commercially available was used to evaluate the samples as per manufacturer's instruction.

RESULTS

The overall sensitivity and specificity of the IHA was 62% and 96%, respectively when compared to ELISA having sensitivity and specificity of 69% and 90%, respectively. The positive predictive value of the IHA was 91% while negative predictive value was 79%. Similarly, the positive predictive value of the ELISA was 87% while negative predictive value was 74%.

CONCLUSION

As serology heavily suffers due to lack of a standardised test system employing the native antigen, there arises need to identify alternative source of recombinant antigen which could effectively improvise the existing lacunae in the current system. Serology acts as an adjunct in clinical decision making if properly interpreted. This is an important consideration in endemic region where health services resources are limited.

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.

Mouse models of amoebiasis and culture methods of amoeba

Entamoeba histolytica is the third leading parasitic cause of man mortality in the world. Infection occurs via ingestion of food or water contaminated with cysts of E. histolytica. Amoebae primarily colonize the intestine. The majority of amoebic infections are asymptomatic, but under some conditions, approximately 4-10% of infections progress to the invasive form of the disease. To better understand the pathogenesis of amoebiasis and the interaction between amoebae and their hosts, the development of suitable animal models is crucial. Pigs, gerbils, cats and mice are used as animal models for the study of amoebiasis in the laboratory. Among these, the most commonly used model is the mouse. In addition to intestinal amoebiasis, we developed a mouse model of liver abscess by inoculating amoeba through portal vein. However, the frequency of successful infection remains low, which is dependent on the conditions of amoebae in the laboratory. As the maintenance of virulent amoebae in the laboratory is unstable, it needs further refinement. This review summarizes mouse models of amoebiasis and the current state of laboratory culture method of amoebae.

Role of the Gut Microbiota of Children in Diarrhea Due to the Protozoan Parasite Entamoeba histolytica

Background. An estimated 1 million children die each year before their fifth birthday from diarrhea. Previous population-based surveys of pediatric diarrheal diseases have identified the protozoan parasite Entamoeba histolytica, the etiological agent of amebiasis, as one of the causes of moderate-to-severe diarrhea in sub-Saharan Africa and South Asia.

Methods. We prospectively studied the natural history of E. histolytica colonization and diarrhea among infants in an urban slum of Dhaka, Bangladesh.

Results. Approximately 80% of children were infected with E. histolytica by the age of 2 years. Fecal anti-galactose/N-acetylgalactosamine lectin immunoglobulin A was associated with protection from reinfection, while a high parasite burden and expansion of the Prevotella copri level was associated with diarrhea.

Conclusions. E. histolytica infection was prevalent in this population, with most infections asymptomatic and diarrhea associated with both the amount of parasite and the composition of the microbiota.

Entamoeba dispar: Could it be pathogenic

Amebiasis is a disease caused by the protozoan parasite Entamoeba histolytica. This ameba can colonize the human intestine and persist as a commensal parasite, similar to Entamoeba dispar, an ameba considered to be non-pathogenic. The similarities between E. histolytica and E. dispar make the latter an attractive model for studies aimed at clarifying the pathogenesis of amebiasis. However, in addition to being an interesting experimental model, this relative of E. histolytica remains poorly understood. In the 1990, it was believed that E. dispar was unable to produce significant experimental lesions. This scenario began to change in 1996, when E. dispar strains were isolated from symptomatic patients in Brazil. These strains were able to produce liver and intestinal lesions that were occasionally indistinguishable from those produced by E. histolytica. These and other findings, such as the detection of E. dispar DNA sequences in samples from patients with amebic liver abscess, have revived the possibility that this species can produce lesions in humans. The present paper presents a series of studies on E. dispar that begin to reveal a new facet of this protozoan.

Entamoeba histolytica: adhesins and lectins in the trophozoite surface

Entamoeba histolytica is the causative agent of amebiasis in humans and is responsible for 100,000 deaths annually, making it the third leading cause of death due to a protozoan parasite. Pathogenesis appears to result from the potent cytotoxic activity of the parasite, which kills host cells within minutes. Although the mechanism is unknown, it is well established to be contact-dependent. The life cycle of the parasite alternates with two forms: the resistant cyst and the invasive trophozoite. The adhesive interactions between the parasite and surface glycoconjugates of host cells, as well as those lining the epithelia, are determinants for invasion of human tissues, for its cytotoxic activity, and finally for the outcome of the disease. In this review we present an overview of the information available on the amebic lectins and adhesins that are responsible of those adhesive interactions and we also refer to their effect on the host immune response. Finally, we present some concluding remarks and perspectives in the field.

The intestinal protozoa: emerging impact on global health and development

PURPOSE OF REVIEW

To highlight new findings on the relevance of gastrointestinal protozoan infections to global public health in low-income and middle-income countries and suggest new large-scale interventions.

RECENT FINDINGS

New disease burden assessments and epidemiological studies highlight the role of the major intestinal protozoa as important etiologic disease agents in low-income and middle-income countries. Despite their prevalence and adverse health impact, such information has not yet translated to the implementation of large-scale interventions as exist for helminth infections and other neglected tropical diseases. There are also several key research and development questions that must be addressed for intestinal protozoan infections and the potential need for new tools, for example, drugs, diagnostics, and vaccines. Additional studies have identified new and emerging species of intestinal protozoa relevant to global public health such as Dientamoeba fragilis and Blastocystis hominis and how they too might emerge as important gastrointestinal pathogens in the coming years.

SUMMARY

New and emerging information on intestinal protozoa are reviewed with emphasis on aspects considered relevant to global health policymakers including prospects for scaling up interventions against intestinal protozoan infections in resource-poor countries.

Immunization with the Entamoeba histolytica surface metalloprotease EhMSP-1 protects hamsters from amebic liver abscess

Diarrhea and amebic liver abscesses due to invasive Entamoeba histolytica infections are an important cause of morbidity and mortality in the developing world. Entamoeba histolytica adherence and cell migration, two phenotypes linked to virulence, are both aberrant in trophozoites deficient in the metallosurface protease EhMSP-1, which is a homologue of the Leishmania vaccine candidate leishmanolysin (GP63). We examined the potential of EhMSP-1 for use as a vaccine antigen to protect against amebic liver abscesses. First, existing serum samples from South Africans naturally infected with E. histolytica were examined by enzyme-linked immunosorbent assay (ELISA) for the presence of EhMSP-1-specific IgG. Nine of 12 (75%) people with anti-E. histolytica IgG also had EhMSP-1-specific IgG antibodies. We next used a hamster model of amebic liver abscess to determine the effect of immunization with a mixture of four recombinant EhMSP-1 protein fragments. EhMSP-1 immunization stimulated a robust IgG antibody response. Furthermore, EhMSP-1 immunization of hamsters reduced development of severe amebic liver abscesses following intrahepatic injection of E. histolytica by a combined rate of 68% in two independent animal experiments. Purified IgG from immunized compared to control animals bound to the surface of E. histolytica trophozoites and accelerated amebic lysis via activation of the classical complement cascade. We concluded that EhMSP-1 is a promising antigen that warrants further study to determine its full potential as a target for therapy and/or prevention of invasive amebiasis.

Amebic liver abscess in northern region of Bangladesh: sociodemographic determinants and clinical outcomes

Background

Amebic liver abscess (ALA) is endemic in Bangladesh since historical age but its epidemiology and sociodemographic determinants are not well described in the literatures. This paper focuses on the endemicity, sociodemographic determinants and clinical outcomes of ALA patients from certain northern districts in Bangladesh. Ninety hospitalized ALA patients enrolled from 6 northern districts of Bangladesh during July 2008 to June 2010 were analyzed.

Findings

Clinical presentations of ALA was initially substantiated by ultrasound imaging and later confirmed by detection of small subunit rRNA gene of E. histolytica using a Real Time PCR. Structured questionnaire and data sheet were used to record sociodemographic characteristics, clinical presentations and outcomes. Patients were followed for immediate and late treatment outcomes up to 2 years since diagnosis. Northern districts those situated on the Ganges basin were noted as endemic areas. Male significantly outnumbered the female with a male to female ratio of 21:1 and majority of patients (58%) were in their 3rd and 4th decades. A significant (21%) number of patients were aborigines despite their ethnic minority as population under investigation and overall 68% belonged to low socioeconomic group. Habit of indigenous alcohol consumption was very high (78%) among ALA patients with overwhelming majority was illiterate (74.44%) and from rural population (70%). Fever with right hypochondriac pain of variable duration was the principal presenting complains. Gross fluid derangements including pleural effusion, edema and ascities were observed in 39% cases and 6% had rupture of abscess. All patients were treated with standard antimicrobial regimen and discharged with initial recovery. Recurrent attack was observed in 6% cases and 3 (3.33%) patients died during 2 years follow-up period. Complicated (37.78%) ALA patients showed significant Odds ratio (P < 0.05) for major sociodemographic determinants in comparison to non-complicated patients.

Conclusions

Amebic liver abscess is endemic in certain northern districts of Bangladesh especially on the Ganges basin with relatively high prevalence among aborigines. Rural habitat, ethnicity (Aborigine) and habit of indigenous alcohol consumption were found to be strong determinants, especially for complicated ALA, which were associated with different grades of morbidity and a few mortalities.

Molecular diagnosis of infectious diarrhea: focus on enteric protozoa

Robust detection of enteric protozoa is a critical step toward determining the etiology of diarrhea. Widespread use of conventional microscopy, culturing and antigen detection in both industrial and developing countries is limited by relatively low sensitivity and specificity. Refinements of these conventional approaches that reduce turnaround time and instrumentation have yielded strong alternatives for clinical and research use. However, advances in molecular diagnostics for protozoal, bacterial, viral and helminth infections offer significant advantages in studies seeking to understand pathogenesis, transmission and long-term consequences of infectious diarrhea. Quantitation of enteropathogen burden and highly multiplexed platforms for molecular detection dramatically improve predictive power in emerging models of diarrheal etiology, while eliminating the expense of multiple tests.

Regulation of virulence of Entamoeba histolytica

Entamoeba histolytica is the third-leading cause of parasitic mortality globally. E. histolytica infection generally does not cause symptoms, but the parasite has potent pathogenic potential. The origins, benefits, and triggers of amoebic virulence are complex. Amoebic pathogenesis entails depletion of the host mucosal barrier, adherence to the colonic lumen, cytotoxicity, and invasion of the colonic epithelium. Parasite damage results in colitis and, in some cases, disseminated disease. Both host and parasite genotypes influence the development of disease, as do the regulatory responses they govern at the host-pathogen interface. Host environmental factors determine parasite transmission and shape the colonic microenvironment E. histolytica infects. Here we highlight research that illuminates novel links between host, parasite, and environmental factors in the regulation of E. histolytica virulence.

A genomewide overexpression screen identifies genes involved in the phosphatidylinositol 3-kinase pathway in the human protozoan parasite Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite that causes amoebic dysentery and liver abscess. E. histolytica relies on motility, phagocytosis, host cell adhesion, and proteolysis of extracellular matrix for virulence. In eukaryotic cells, these processes are mediated in part by phosphatidylinositol 3-kinase (PI3K) signaling. Thus, PI3K may be critical for virulence. We utilized a functional genomics approach to identify genes whose products may operate in the PI3K pathway in E. histolytica. We treated a population of trophozoites that were overexpressing genes from a cDNA library with a near-lethal dose of the PI3K inhibitor wortmannin. This screen was based on the rationale that survivors would be overexpressing gene products that directly or indirectly function in the PI3K pathway. We sequenced the overexpressed genes in survivors and identified a cDNA encoding a Rap GTPase, a protein previously shown to participate in the PI3K pathway. This supports the validity of our approach. Genes encoding a coactosin-like protein, EhCoactosin, and a serine-rich E. histolytica protein (SREHP) were also identified. Cells overexpressing EhCoactosin or SREHP were also less sensitive to a second PI3K inhibitor, LY294002. This corroborates the link between these proteins and PI3K. Finally, a mutant cell line with an increased level of phosphatidylinositol (3,4,5)-triphosphate, the product of PI3K activity, exhibited increased expression of SREHP and EhCoactosin. This further supports the functional connection between these proteins and PI3K in E. histolytica. To our knowledge, this is the first forward-genetics screen adapted to reveal genes participating in a signal transduction pathway in this pathogen.

The future for vaccine development against Entamoeba histolytica

Entamoeba histolytica is the causative agent of amebiasis, one of the top three parasitic causes of mortality worldwide. In the majority of infected individuals, E. histolytica asymptomatically colonizes the large intestine, while in others, the parasite breaches the mucosal epithelial barrier to cause amebic colitis and can disseminate to soft organs to cause abscesses. Vaccinations using native and recombinant forms of the parasite Gal-lectin have been successful in protecting animals against intestinal amebiasis and amebic liver abscess. Protection against amebic liver abscesses has also been reported by targeting other E. histolytica components including the serine-rich protein and the 29-kDa-reductase antigen. To date, vaccines against the Gal-lectin hold the most promise but clinical trials will be required to validate its efficacy in humans. Here, we review the current strategies and future perspectives involved in the development of a vaccine against E. histolytica.

"Freezing" parasites in pre-Himalayan region, Himachal Pradesh: Experience with mini-FLOTAC

BACKGROUND

Helminths and protozoa infections pose a great burden especially in developing, countries, due to morbidity caused both by acute and chronic infections. Data on distribution of intestinal parasitic infections among the native and expatriates populations in Himachal Pradesh are scarce. The aim of our survey was to analyze the intestinal parasitic burden in communities from Dharamsala, Kangra district, in clinical and public health settings. We also field-tested the mini- FLOTAC, an innovative diagnostic device.

METHODS

Subjects referring to the Tibetan Delek Hospital for abdominal discomfort and all children of the Tibetan Primary School in Dharamsala were screened for intestinal parasitic infections with direct smear, formol-ether concentration (FEC) method and mini-FLOTAC, their clinical history was recorded, and correlations between clinical symptoms and infections analyzed.

RESULTS

152 subjects were screened for intestinal parasites, of which 72 subjects in the outpatients department (OPD) (36 expatriates and 36 natives) and 80 in the school. 60% of schoolchildren and 57% of OPD patients were found positive for any infection, the most represented were protozoa infections (50%), whereas helminthic infections accounted only for 13% and 20% in OPD patients and schoolchildren, respectively. The most prevalent among helminths was Ascaris lumbricoides (11%). Giardia intestinalis was more present among schoolchildren than the OPD patients (20% vs 6%) and E. histolytica/dispar was more prevalent among the OPD patients (42%) than the school children (23%). Correlations were found between nausea and loose or watery stools and parasitic infections, particularly in expatriates, whereas schoolchildren, despite being as infected as adults, were completely asymptomatic. Mini-FLOTAC detected higher number of helminth infections whereas FEC method was more accurate for the diagnosis of protozoa.

CONCLUSIONS

This study presents an accurate snapshot of intestinal parasitic infections in Dharamsala, and their high prevalence calls for more awareness and control measures. Mini-FLOTAC is a promising and simple technique for the diagnosis of helminth infections.

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.

Imported amoebic liver abscess in France

Background

Worldwide, amoebic liver abscess (ALA) can be found in individuals in non-endemic areas, especially in foreign-born travelers.

Methods

We performed a retrospective analysis of ALA in patients admitted to French hospitals between 2002 and 2006. We compared imported ALA cases in European and foreign-born patients and assessed the factors associated with abscess size using a logistic regression model.

Results

We investigated 90 ALA cases. Patient median age was 41. The male:female ratio was 3.5∶1. We were able to determine the origin for 75 patients: 38 were European-born and 37 foreign-born. With respect to clinical characteristics, no significant difference was observed between European and foreign-born patients except a longer lag time between the return to France after traveling abroad and the onset of symptoms for foreign-born. Factors associated with an abscess size of more than 69 mm were being male (OR = 11.25, p<0.01), aged more than 41 years old (OR = 3.63, p = 0.02) and being an immigrant (OR = 11.56, p = 0.03). Percutaneous aspiration was not based on initial abscess size but was carried out significantly more often on patients who were admitted to surgical units (OR = 10, p<0.01). The median time to abscess disappearance for 24 ALA was 7.5 months.

Conclusions/Significance

In this study on imported ALA was one of the largest worldwide in terms of the number of cases included males, older patients and foreign-born patients presented with larger abscesses, suggesting that hormonal and immunological factors may be involved in ALA physiopathology. The long lag time before developing ALA after returning to a non-endemic area must be highlighted to clinicians so that they will consider Entamoeba histolytica as a possible pathogen of liver abscesses more often.

Amœbiasis is caused by Entamoeba histolytica (E. histolytica), a protozoan specific to humans which infects humans by ingestion of contaminated food and water. According to some authors, amœbiasis could be the second leading cause of death from parasitic disease worldwide. It is endemic in tropical countries but can also be diagnosed in industrialized countries, essentially in travelers. One of its main clinical manifestations is amoebic liver abscess (ALA). Abscess can be medically treated by metronidazole, but percutaneous aspiration of the abscess is sometimes performed. Few studies have been performed so far regarding the existence of cases of ALA in the industrialized world. The results of our study reported the existence of 90 cases of imported ALA in France which should raise interest among physicians as well as tourists traveling to endemic areas. Male adults and foreign-born patients presented larger abscesses, suggesting that hormonal and immunological factors could be involved in ALA physiopathology. Foreign-born patients had a longer lag time between the return to France after traveling abroad and the onset of symptoms than European-born ones. This must be highlighted to clinicians who should think about this diagnostic even if a recent travel in a tropical area is not notified by patients.

The Entamoeba histolytica serum-inducible transmembrane kinase EhTMKB1-9 is involved in intestinal amebiasis

Entamoeba histolytica possesses a family of approximately 100 putative transmembrane kinases (TMKs), indicating that the parasite has an extensive means of environmental sensing. The TMKs have been divided into nine sub-groups based on the sequence composition of their intracellular kinase as well as extracellular cysteine-rich domains. EhTMKB1-9 has been recently shown to be expressed in proliferating trophozoites and induced by serum. Interference with EhTMKB1-9 by antisense RNA knockdown or expression of a truncated protein diminished proliferation, adhesion and cytotoxicity. Here we report the involvement of EhTMKB1-9 in phagocytosis and its virulence function in the formation of amebic colitis. Trophozoites induced to express higher levels of wild type EhTMKB1-9 showed increased capacity for endocytosis. In contrast, cells compromised for the EhTMKB1-9 expression through antisense inhibition showed significantly lower levels of phagocytosis and endocytosis under the experimental conditions. The role of EhTMKB1-9 as a virulence factor was studied using animal models of amebiasis. Trophozoites expressing high levels of mutant protein lacking the kinase domain showed a competitive disadvantage with regard to survival as well as invasive phenotype in the murine model of amebic colitis. The same parasites however, were not compromised in their ability to generate abscess in the gerbil model of invasive liver amebiasis. EhTMKB1-9 is the second member from the "B" group of EhTMKs which seems to be deployed by the parasite during intestinal infection. TMKs are attractive targets for drug development because of their requirement in virulence and proliferation.

Amebic infection in humans

Clinical human infections with the protozoa Entamoeba histolytica is still estimated to occur in 50 million people worldwide, of which approximately 100,000 die annually. Although most clinical symptoms are due to involvement of the large intestine, 1 % present with involvement of the liver in the form of a liver abscess, a potentially fatal condition. Distinguishing an invasive form (E. histolytica) from a morphologically identical non-invasive one (E. dispar) requires molecular or enzymatic characterization. Further, the pattern of infection, interpretation of presence of antibodies in the host, manifestations of disease, approach to investigations and strategies for management remain complex. This article also provides a comprehensive review of the parasite and host factors that govern the complex relationship of the prozoa and humans, and tries to explain why some develop a particular form of the disease in endemic zones. Application of modern imaging and image guided therapy seems to be playing a major role in diagnosis and management of the potentially most serious form of the disease, amebic liver abscess. Despite lack of controlled studies there is a tendency to lower the threshold of their use in clinical practice, and indeed in-hospital mortality rate seems to be falling for amebic liver abscess. In a world getting increasingly swamped by non-infectious metabolic diseases, awareness of amebic infections, its bed-side diagnosis, the use of appropriate laboratory tests, and decision making in management are shrinking. This review tries to update the scientific developments in amebiasis.

Fulminant amoebic colitis mimicking intestinal vasculitis in a patient with systemic lupus erythematosus

Colitis in patients with systemic lupus erythematosus (SLE) is quite rare. It can be caused by intestinal vasculitis, mesenteric vascular thrombosis, concomitant inflammatory bowel disease or infectious colitis. It is important to make an accurate and early diagnosis as the treatments for each condition differ and a delayed diagnosis can result in life-threatening complications. However, non-specific gastrointestinal symptoms make a timely diagnosis challenging. Amoebic colitis is a rare condition in patients with SLE. Here we present a case of fulminant amoebic colitis in a patient with SLE which was initially misdiagnosed as ischemic colitis due to intestinal vasculitis. Her colitis was complicated with multiple intestinal perforations, disseminated intravascular coagulation and acute respiratory distress syndrome; but in the end, the patient was successfully treated with metronidazole and paromomycin.

CCR9+ T cells contribute to the resolution of the inflammatory response in a mouse model of intestinal amoebiasis

Analysis of the mechanisms underlying the inflammatory response in amoebiasis is important to understand the immunopathology of the disease. Mucosal associated effector and regulatory T cells may play a role in regulating the inflammatory immune response associated to Entamoeba histolytica infection in the colon. A subpopulation of regulatory T cells has recently been identified and is characterized by the expression of the chemokine receptor CCR9. In this report, we used CCR9 deficient (CCR9(-/-)) mice to investigate the role of the CCR9(+) T cells in a murine model of E. histolytica intestinal infection. Intracecal infection of CCR9(+/+), CCR9(+/-) and CCR9(-/-) mice with E. histolytica trophozoites, revealed striking differences in the development and nature of the intestinal inflammatory response observed between these strains. While CCR9(+/+) and CCR9(+/-) mice were resistant to the infection and resolved the pathogen-induced inflammatory response, CCR9(-/-) mice developed a chronic inflammatory response, which was associated with over-expression of the cytokines IFN-γ, TNF-α, IL-4, IL-6 and IL-17, while IL-10 was not present. In addition, increased levels of CCL11, CCL20 and CCL28 chemokines were detected by qRT-PCR in CCR9(-/-) mice. E. histolytica trophozoites were identified in the lumen of the cecum of CCR9(-/-) mice at seven days post infection (pi), whereas in CCR9(+/+) mice trophozoites disappeared by day 1 pi. Interestingly, the inflammation observed in CCR9(-/-) mice, was associated with a delayed recruitment of CD4(+)CD25(+)FoxP3(+) T cells to the cecal epithelium and lamina propria, suggesting that this population may play a role in the early regulation of the inflammatory response against E. histolytica, likely through IL-10 production. In support of these data, CCR9(+) T cells were also identified in colon tissue sections obtained from patients with amoebic colitis. Our data suggest that a population of CCR9(+)CD4(+)CD25(+)FoxP3(+) T cells may participate in the control and resolution of the inflammatory immune response to E. histolytica infection.

Cardiac involvement with parasitic infections

Parasitic infections previously seen only in developing tropical settings can be currently diagnosed worldwide due to travel and population migration. Some parasites may directly or indirectly affect various anatomical structures of the heart, with infections manifested as myocarditis, pericarditis, pancarditis, or pulmonary hypertension. Thus, it has become quite relevant for clinicians in developed settings to consider parasitic infections in the differential diagnosis of myocardial and pericardial disease anywhere around the globe. Chagas' disease is by far the most important parasitic infection of the heart and one that it is currently considered a global parasitic infection due to the growing migration of populations from areas where these infections are highly endemic to settings where they are not endemic. Current advances in the treatment of African trypanosomiasis offer hope to prevent not only the neurological complications but also the frequently identified cardiac manifestations of this life-threatening parasitic infection. The lack of effective vaccines, optimal chemoprophylaxis, or evidence-based pharmacological therapies to control many of the parasitic diseases of the heart, in particular Chagas' disease, makes this disease one of the most important public health challenges of our time.

Cytokine and chemokine responses in adults, newborns and children exposed to Entamoeba histolytica/dispar, Onchocerca volvulus and Plasmodium falciparum

Cytokine and chemokine response profiles were studied in newborns, 10-yr-old children and post partum mothers. All study groups were repeatedly exposed to Entamoeba histolytica, Onchocerca volvulus and Plasmodium falciparum infections as indicated by their Immunoglobulin (IgG) responses to parasite-specific antigens. As key indicators for regulatory and pro-inflammatory cytokine and chemokine responses, Interferon (IFN)gamma and regulatory IL-10 were investigated, along with the chemokines MIP-1 alpha/CCL3, MIP-1 beta/CCL4, MDC/CCL22 and TARC/CCL17. Entamoeba histolytica antigens (EhAg) strongly activated pro-inflammatory MIP-1 alpha/CCL3 and MIP-1 beta/CCL4 responses of similar magnitude in mothers, children and neonates alike. Plasmodium falciparum antigens (PfAg) enhanced MIP-1 alpha/CCL3, MIP-1 beta/CCL4 and MDC/CCL22 production in neonates, but did not trigger these chemokines in mothers or 10-yr-old children. Onchocerca volvulus antigens (OvAg) activated IFN-gamma and TARC/CCL17 production in mothers but not in neonates and children. Crude IL-10 production [i.e., without subtracting spontaneous cellular release (baseline)] was highest in mothers and somewhat lower in neonates, while the lowest IL-10 amounts of all were released by peripheral blood mononuclear cells from 10-yr-old children. In summary, strong inflammatory chemokine responses to plasmodia and ameba antigens in newborns and 10-yr-old children suggest that adequately balanced immune regulatory mechanisms may not have developed yet in these age groups and that repeated exposure to parasite infections and immune maturation during childhood is required to generate similar cytokine and chemokine profiles as in adults.

Seroprevalence of Entamoeba histolytica in the context of HIV and AIDS: the case of Vhembe district, in South Africa's Limpopo province

In a recent study in northern South Africa, the seroprevalence of Entamoeba histolytica infection among 257 HIV-positive and 117 HIV-negative individuals was determined, using an ELISA for the detection of antibodies reacting with the parasite's galactose/-acetyl-D-galactosamine(Gal/GalNAc)-inhibitable adherence lectin. Overall, 34.0% of the 374 participants (36.1% of the females and 28.1% of the males) were found seropositive for E. histolytica. Although all age-groups were affected by the amoebic pathogen, the subjects aged 50-59 years had the highest seroprevalence (69.2%). The seroprevalence of E. histolytica was also significantly higher among the HIV-positive subjects than among the HIV-negative (42.8% v. 14.5%; chi(2)=28.65; P<0.0001). Among the HIV-positive subjects, those with fewer than 200 CD4+ cells/microl were relatively more likely to be seropositive for E. histolytica (60.3% v. 43.8%; chi(2)=4.016; P=0.045). This is the first report indicating a positive association between E. histolytica infection and HIV in South Africa. Further studies, for example to determine the occurrence of diarrhoea or liver abscess in the study area, in relation to seropositivity for E. histolytica and/or HIV, are now needed.

Association of malnutrition with amebiasis

Observation of a cohort of preschool children in Dhaka, Bangladesh, is beginning to reveal the contributions of environment, host, and parasite to amebiasis. Reviewed here are the associations and interactions of malnutrition, IgA and interferon-gamma, human leukocyte antigen alleles, and parasite genotypes to the outcome of infection. Future efforts aimed at understanding the mechanisms of these effects are described.

Protection against murine intestinal amoebiasis induced by oral immunization with the 29 kDa antigen of Entamoeba histolytica and cholera toxin

Entamoeba histolytica antigens recognized by salivary IgA from infected patients include the 29 kDa antigen (Eh29), an alkyl hydroperoxide reductase. Here, we investigate the potential of recombinant Eh29 and an Eh29-cholera toxin subunit B (CTxB) fusion protein to confer protection against intestinal amoebiasis after oral immunization. The purified Eh29-CTxB fusion retained the critical ability to bind ganglioside GM(1), as determined by ELISA. Oral immunization of C3H/HeJ mice with Eh29 administered in combination with a subclinical dose of whole cholera toxin, but not as an Eh29-CTxB fusion, induced elevated levels of intestinal IgA and serum IgG anti-Eh29 antibodies that inhibited trophozoites adherence to MDCK cell monolayers. The 80% of immunized mice seen to develop IgA and IgG immune responses showed no evidence of infection in tissue sections harvested following intracecal challenge with virulent E. histolytica trophozoites. These results suggest that Eh29 is capable of inducing protective anti-amoebic immune responses in mice following oral immunization and could be used in the development of oral vaccines against amoebiasis.

The immunopathogenesis of Entamoeba histolytica

Amebiasis is the disease caused by the enteric dwelling protozoan parasite Entamoeba histolytica. The WHO considers amebiasis as one of the major health problems in developing countries; it is surpassed by only malaria and schistosomiasis for death caused by parasitic infection. E. histolytica primarily lives in the colon as a harmless commensal, but is capable of causing devastating dysentery, colitis and liver abscess. What triggers the switch to a pathogenic phenotype and the onset of disease is unknown. We are becoming increasingly aware of the complexity of the host-parasite interaction. During chronic stages of amebiasis, the host develops an immune response that is incapable of eliminating tissue resident parasites, while the parasite actively immunosuppresses the host. However, most individuals with symptomatic infections succumb only to an episode of dysentery. Why most halt invasion and a minority progress to chronic disease remains poorly understood. This review presents a current understanding of the immune processes that shape the outcome of E. histolytica infections during its different stages.

The NF-kappaB p50 subunit is protective during intestinal Entamoeba histolytica infection of 129 and C57BL/6 mice

Entamoeba histolytica is the agent of amebic colitis. In this work we examined the intestinal NF-kappaB response to this parasite. Using an enzyme-linked immunosorbent assay (ELISA) and an electrophoretic mobility shift assay, we found that the NF-kappaB subunit p50 predominated in nuclear extracts of whole cecal tissue and of isolated crypts from mice inoculated with E. histolytica. p50 was protective, since C57BL/6 and 129 mice in which there was targeted deletion of this subunit were more susceptible to E. histolytica infection as measured by culture results, cecal parasite ELISA results, and/or histologic scores. The transepithelial electrical resistance of cecal explants from C57BL/6 and 129 p50 knockout mice decreased markedly in response to the parasite compared with the transepithelial electrical resistance of their wild-type counterparts, suggesting that a protective function of p50 was present in the epithelium itself. This work shows that NF-kappaB activity, particularly activity of the p50 subunit, is one factor that contributes to resistance of the gut to E. histolytica infection.

Members of the Entamoeba histolytica transmembrane kinase family play non-redundant roles in growth and phagocytosis

Entamoeba histolytica contains a large and novel family of transmembrane kinases (TMKs). The expression patterns of the E. histolytica TMKs in individual trophozoites and the roles of the TMKs for sensing and responding to extracellular cues were incompletely characterised. Here we provide evidence that single cells express multiple TMKs and that TMK39 and TMK54 likely serve non-redundant cellular functions. Laser-capture microdissection was used in conjunction with microarray analysis to demonstrate that single trophozoites express more than one TMK gene. Anti-peptide antibodies were raised against unique regions in the extracellular domains of TMK39, TMK54 and PaTMK, and TMK expression was analysed at the protein level. Flow cytometric assays revealed that populations of trophozoites homogeneously expressed TMK39, TMK54 and PaTMK, while confocal microscopy identified different patterns of cell surface expression for TMK39 and TMK54. The functions of TMK39 and TMK54 were probed by the inducible expression of dominant-negative mutants. While TMK39 co-localised with ingested beads and expression of truncated TMK39 interfered with trophozoite phagocytosis of apoptotic lymphocytes, expression of a truncated TMK54 inhibited growth of amoebae and altered the surface expression of the heavy subunit of the E. histolytica Gal/GalNAc lectin. Overall, our data indicates that multiple members of the novel E. histolytica TMK family are utilised for non-redundant functions by the parasite.

Deficient serum mannose-binding lectin levels and MBL2 polymorphisms increase the risk of single and recurrent Cryptosporidium infections in young children

Mannose-binding lectin (MBL) is an evolutionarily conserved protein that functions in human innate immunity by binding to microbial surfaces and promoting opsonophagocytosis. MBL has been shown to bind to Cryptosporidium sporozoites, and earlier work has suggested that the protective role of MBL may be most important in childhood. We evaluated the association between polymorphisms in the MBL gene (MBL2), serum MBL deficiency, and infection with Cryptosporidium, Entamoeba histolytica, and Giardia intestinalis in children. A large, prospective cohort of Bangladeshi preschool children was followed up for >3 years. Clinical outcomes, serum MBL levels, and MBL2 polymorphisms and haplotypes were determined. Statistically significant associations with E. histolytica and G. intestinalis were not found. Serum MBL deficiency, polymorphisms in the -221 promoter region, and the YO/XA MBL2 haplotype were strongly associated with Cryptosporidium infections, particularly recurrent infection. Children with multiple infections with Cryptosporidium were more likely to be MBL deficient (odds ratio [OR], 10.45), carry the -221 promoter variant (OR, 4.02), and have the YO/XA haplotype (OR, 4.91). We have identified a potentially important component of the human innate immune response to Cryptosporidum infection. Further work is needed to evaluate the mechanism of protection of MBL in Cryptosporidium infection.

Protection against intestinal amebiasis by a recombinant vaccine is transferable by T cells and mediated by gamma interferon

We have previously shown that vaccination with purified Entamoeba histolytica Gal/GalNAc lectin or recombinant subunits can protect mice from intestinal amebiasis upon intracecal challenge. In this study, we demonstrated with adoptive-transfer experiments that this lectin vaccine protection is mediated by T cells but not serum. The cell-mediated immune (CMI) response was characterized by significant gamma interferon (IFN-gamma), interleukin 12 (IL-12), IL-2, IL-10, and IL-17 production. To move toward a human vaccine, we switched to a recombinant protein and tested a range of adjuvants and routes appropriate for humans. We found that subcutaneous delivery of LecA with IDRI's adjuvant system EM014 elicited a potent Th1-type CMI profile and provided significant protection, as measured by culture negativity (79% efficacy); intranasal immunization with cholera toxin provided 56% efficacy; and alum induced a Th2-type response that protected 62 to 68% of mice. Several antibody and CMI cytokine responses were examined for correlates of protection, and prechallenge IFN-gamma(+) or IFN-gamma-, IL-2-, and tumor necrosis factor alpha-triple-positive CD4 cells in blood were statistically associated with protection. To test the role of IFN-gamma in LecA-mediated protection, we neutralized IFN-gamma in LecA-immunized mice and found that it abrogated the protection conferred by vaccination. These data demonstrate that CMI is sufficient for vaccine protection from intestinal amebiasis and reveal an important role for IFN-gamma, even in the setting of alum.

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.

Innate immunity prevents tissue invasion by Entamoeba histolytica

Although innate and adaptive immunity both play a role in amoebiasis, the mechanisms involved in the elimination of Entamoeba histolytica are poorly understood. To provide more information about the innate immune mechanisms that may confer protection against invasive amoebiasis, we administered inflammatory substances (bacillus Calmette-Guérin, lipopolysaccharide, complete Freund's adjuvant, or mineral oil) into the peritoneum of hamsters. The animals were then challenged with pathogenic trophozoites of E. histolytica and, after 7 days, the protective host response was analysed. We found that the nonspecific inflammatory response induced in the peritoneum was sufficient to prevent liver invasion by E. histolytica. In vitro experiments showed that the killing of trophozoites was mediated by peritoneal macrophages and a protein of 68 kDa with peroxidase activity.

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.

Gender and genetic control of resistance to intestinal amebiasis in inbred mice

Resistance to the establishment of intestinal Entamoeba histolytica infection is dependent on the inbred mouse strain. In this work we used the inbred strains B6 (resistant), CBA (susceptible), B6CBAF(1) and a backcross of B6CBAF(1) to CBA to further examine the genetic basis of resistance. Mouse genotype was assessed with single nucleotide polymorphism and microsatellite markers and infection assessed by culture 9 days after intracecal E. histolytica challenge. The backcross population showed a male predisposition to culture positivity (P<0.002). F1 genotype at two loci on chromosomes 1 and 2 exhibited suggestive linkage with resistance to infection (P=0.0007 and 0.0200). Additional suggestive quantitative trait locus were observed on chromosomes 1, 9 and 13 for cecal parasite antigen load and histologic evidence of inflammation. Infection in C3H x B6 recombinant inbred mice supported the mapping data. Candidate B6 genes on chromosomes 1 and 2 were examined by microarray analysis of epithelial tissues from B6 vs CBA mice. This work shows a male predisposition to intestinal amebiasis and suggests that relatively few B6 loci can confer resistance in inbred mice. Future identification of regional candidate genes has implications for understanding the human variability to amebic infection.

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.