Diagnosis of invasive amebiasis by enzyme-linked immunosorbent assay of saliva to detect amebic lectin antigen and anti-lectin immunoglobulin G antibodies

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.

Accurate laboratory diagnosis of human intestinal and extra-intestinal amoebiasis

Accurate diagnosis of Entamoeba histolytica is important, as it is known as a causative agent for both invasive intestinal and extra-intestinal amoebiasis. Amoebiasis has a worldwide distribution, especially in developing countries, and it is responsible for up to 100,000 fatal cases annually. A number of diagnostic methods, including microscopy, culture, antigen detection, molecular based methods, and serological assays have been proposed to assist in diagnosing amoebiasis. The present study aimed to gather new data and review the available diagnostic tests of both intestinal and extra-intestinal amoebiasis and to highlight pitfalls and challenges of each of them. A broad literature of electronic databases was conducted and covered articles published up to March 2022. For laboratory diagnosis of intestinal amoebiasis, direct microscopy stool examinations and cultures should be held as the high-performance diagnostic strategies. Molecular and immunological-based assays are also recommended as complementary tests. To diagnose extra-intestinal infection, the use of serological tests is still considered the method of choice. However, serodiagnosis requires further improvement for the accurate differential diagnosis of active infection from past infections.

Lectins as virulence factors in Entamoeba histolytica and free-living amoebae

Currently, there is growing interest in the identification and purification of microbial lectins due to their involvement in the pathogenicity mechanisms of pathogens, such as Entamoeba histolytica and free-living amoebae. The Gal/GalNAc lectin from E. histolytica participates in adhesion, cytotoxicity and regulation of immune responses. Furthermore, mannose- and galactose-binding protein have been described in Acanthamoeba castellanii and Balamuthia mandrillaris, respectively and they also contribute to host damage. Finally, in Naegleria fowleri, molecules containing mannose and fucose are implicated in adhesion and cytotoxicity. Considering their relevance in the pathogenesis of the diseases caused by these protozoa, lectins appear to be promising targets in the diagnosis, vaccination and treatment of these infections.

Immunoprevalence to Six Waterborne Pathogens in Beachgoers at Boquerón Beach, Puerto Rico: Application of a Microsphere-Based Salivary Antibody Multiplex Immunoassay

Waterborne infectious diseases are a major public health concern worldwide. Few methods have been established that are capable of measuring human exposure to multiple waterborne pathogens simultaneously using non-invasive samples such as saliva. Most current methods measure exposure to only one pathogen at a time, require large volumes of individual samples collected using invasive procedures, and are very labor intensive. In this article, we applied a multiplex bead-based immunoassay capable of measuring IgG antibody responses to six waterborne pathogens simultaneously in human saliva to estimate immunoprevalence in beachgoers at Boquerón Beach, Puerto Rico. Further, we present approaches for determining cutoff points to assess immunoprevalence to the pathogens in the assay. For the six pathogens studied, our results show that IgG antibodies against antigens from noroviruses GI.I and GII.4 were more prevalent (60 and 51.6%, respectively) than Helicobacter pylori (21.4%), hepatitis A virus (20.2%), Campylobacter jejuni (8.7%), and Toxoplasma gondii (8%) in the saliva of the study participants. The salivary antibody multiplex immunoassay can be used to examine immunoprevalence of specific pathogens in human populations.

Diagnosis of Mediterranean visceral leishmaniasis by detection of Leishmania-related antigen in urine and oral fluid samples

Implementation of simple diagnostic tests using non-invasive collection of biological specimens is of great importance in the diagnosis of pediatric visceral leishmaniasis caused by Leishmania infantum. Latex agglutination kit (KAtex^®) is widely used in the diagnosis mainly in L. donovani endemic areas. However its utilization in L. infantum endemic regions remains limited and its use on noninvasive biological specimen apart urine was not reported. In this study, KAtex^® kit was used to detect Leishmania-related antigen in urine and oral fluid of 35 L. infantum visceral leishmaniasis cases and 62 controls including non-infectious disease and infectious disease controls (34 and 28 respectively). Sensitivity and specificity of urine based KAtex^® were 51.4% and 98.3% respectively, whereas, sensitivity and specificity of oral-fluid based KAtex^® were 80% and 88.3% respectively. Although, sensitivity of oral-fluid KAtex^® was high, its specificity varied significantly according to the presence or the absence of an infectious disease (71.4% versus 97%, p=0.01).

Developing a Salivary Antibody Multiplex Immunoassay to Measure Human Exposure to Environmental Pathogens

The etiology and impacts of human exposure to environmental pathogens are of major concern worldwide and, thus, the ability to assess exposure and infections using cost effective, high-throughput approaches would be indispensable. This manuscript describes the development and analysis of a bead-based multiplex immunoassay capable of measuring the presence of antibodies in human saliva to multiple pathogens simultaneously. Saliva is particularly attractive in this application because it is noninvasive, cheaper and easier to collect than serum. Antigens from environmental pathogens were coupled to carboxylated microspheres (beads) and used to measure antibodies in very small volumes of human saliva samples using a bead-based, solution-phase assay. Beads were coupled with antigens from Campylobacter jejuni, Helicobacter pylori, Toxoplasma gondii, noroviruses (G I.1 and G II.4) and hepatitis A virus. To ensure that the antigens were sufficiently coupled to the beads, coupling was confirmed using species-specific, animal-derived primary capture antibodies, followed by incubation with biotinylated anti-species secondary detection antibodies and streptavidin-R-phycoerythrin reporter (SAPE). As a control to measure non-specific binding, one bead set was treated identically to the others except it was not coupled to any antigen. The antigen-coupled and control beads were then incubated with prospectively-collected human saliva samples, measured on a high throughput analyzer based on the principles of flow cytometry, and the presence of antibodies to each antigen was measured in Median Fluorescence Intensity units (MFI). This multiplex immunoassay has a number of advantages, including more data with less sample; reduced costs and labor; and the ability to customize the assay to many targets of interest. Results indicate that the salivary multiplex immunoassay may be capable of identifying previous exposures and infections, which can be especially useful in surveillance studies involving large human populations.

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.

Diagnostic parameters of serological ELISA for invasive amoebiasis, using antigens preserved without enzymatic inhibitors

Amoebiasis is the third cause of death due to parasites in the world. Although, numerous serodiagnostic and salivary tests have been developed, the majority of these assays lack sensitivity in endemic zones to detect acute amoebic liver abscess. The two main limiting factors to develop reliable assays are the high levels of anti-amoeba antibodies in populations living in endemic zones, and the proteolysis of amoebic extracts even treated with inhibitors. Our group reported a method to preserve amoebic antigens without using enzymatic inhibitors (IC:MC fraction) that shows stability for years. Here we describe the development of a serologic ELISA to diagnose amoebiasis made with IC: MC antigens, and its validation for clinical use in endemic areas. In our study, we included sera from 66 patients diagnosed with acute amoebic liver abscess and 33 volunteers living in an endemic area for amoebiasis. Our assay was compared with an indirect haemagglutination assay (IHA) an ELISA elaborated with antigens derived from untreated trophozoites. The ELISA made with IC: MC antigens presented more reproducibility compared to other assays. Sera from 95% ALA patients showed a positive value. The ELISA (IC: MC) detected 97% of patients with ALA compared to an 81% using IHA. The parameters of ELISA (vs. IHA) were Sensitivity 98% (81%), Specificity 96% (97%), Positive predictive value 98% (96%), Negative predictive value 96% (73%) and Accuracy 98% (87%). A negative serologic test does not rule out the diagnosis of invasive amoebiasis. The ELISA made with antigens preserved without using enzymatic inhibitors has valuable serodiagnostic value to diagnose acute amoebic liver abscess, even in populations living in endemic zones of amoebiasis carrying antibodies against amoebas. In conclusion, ELISA-IC:MC presented better diagnostic parameters than IHA although a negative serologic test does not rule out acute invasive amoebiasis.

Protection against Amoebic Liver Abscess in Hamster by Intramuscular Immunization with an Autographa californica Baculovirus Driving the Expression of the Gal-Lectin LC3 Fragment

In a previous study, we demonstrated that oral immunization using Autographa californica baculovirus driving the expression of the Gal-lectin LC3 fragment (AcNPV-LC3) of Entamoeba histolytica conferred protection against ALA development in hamsters. In this study, we determined the ability of AcNPV-LC3 to protect against ALA by the intramuscular route as well as the liver immune response associated with protection. Results showed that 55% of hamsters IM immunized with AcNPV-LC3 showed sterile protection against ALA, whereas other 20% showed reduction in the size and extent of abscesses, resulting in some protection in 75% of animals compared to the sham control group. Levels of protection showed a linear correlation with the development and intensity of specific antiamoeba cellular and humoral responses, evaluated in serum and spleen of hamsters, respectively. Evaluation of the Th1/Th2 cytokine patterns expressed in the liver of hamsters showed that sterile protection was associated with the production of high levels of IFNγ and IL-4. These results suggest that the baculovirus system is equally efficient by the intramuscular as well as the oral routes for ALA protection and that the Gal-lectin LC3 fragment is a highly protective antigen against hepatic amoebiasis through the local induction of IFNγ and IL-4.

Laboratory methods of identification of Entamoeba histolytica and its differentiation from look-alike Entamoeba spp

Entamoeba histolytica, the causative agent of intestinal and extraintestinal amebiasis, is a common parasitic cause of significant morbidity and mortality in the developing countries. Hence, early detection and differentiation of pathogenic E. histolytica from nonpathogenic/commensal Entamoeba spp (Entamoeba dispar/Entamoeba moshkovskii/Entamoeba bangladeshi) plays a crucial role in clinical management of patients with amebiasis. Most diagnostic tests currently available do not reliably differentiate between the species of Entamoeba and are less sensitive, cumbersome to perform. Molecular-based methods are highly sensitive, easy to perform and differentiates the pathogenic Entamoeba from nonpathogenic species, serving the criteria for an ideal diagnostic test for amebiasis. Recently, microarray technology has been found to be a promising tool for the diagnostic and epidemiological evaluation of amebiasis.

Diagnosis of Parasitic Infections

Methods for the diagnosis of parasitic infections have stagnated in the past three decades. Labor-intensive methods such as microscopy still remain the mainstay of several diagnostic laboratories. There is a need for more rapid tests that do not sacrifice sensitivity and that can be used in both clinical settings as well as in poor resource field settings. The fields of diagnostic medical parasitology, treatment, and vaccines are undergoing dramatic change. In recent years, there has been tremendous effort to focus research on the development of newer diagnostic methods focusing on serological, molecular, and proteomic approaches. This article examines the various diagnostic tools that are being used in clinical laboratories, optimized in reference laboratories, and employed in mass screening programs.

Development of loop-mediated isothermal amplification for rapid detection of Entamoeba histolytica

OBJECTIVE

To develop a loop-mediated isothermal amplification (LAMP) assay for the detection of Entamoeba histolytica E. histolytica, the causative agent of amebiasis.

METHODS

The LAMP primer set was designed from E. histolytica hemolysin gene HLY6. Genomic DNA of E. histolytica trophozoites strain HK9 was used to optimize the LAMP mixture and conditions. Amplification of DNA in the LAMP mixture was monitored through visual inspection for turbidity of the LAMP mix as well as addition of fluorescent dye.

RESULTS

Positive LAMP reactions turned turbid while negative ones remained clear. Upon addition of a fluorescent dye, all positive reactions turned green while the negative control remained orange under ambient light. After electrophoresis in 1.5% agarose gels, a ladder of multiple bands of different sizes can be observed in positive samples while no bands were detected in the negative control. The sensitivity of the assay was found to be 5 parasites per reaction which corresponds to approximately 15.8 ng/μ L DNA. The specificity of the assay was verified by the absence of amplified products when DNA from other gastrointestinal parasites such as the morphologically similar but non-pathogenic species, Entamoeba dispar 39, and other diarrhea-causing organisms such as Blastocystis hominis and Escherichia coli were used.

CONCLUSIONS

The LAMP assay we have developed enables the detection of E. histolytica with rapidity and ease, therefore rendering it is suitable for laboratory and field diagnosis of amebiasis.

Evaluation of Entamoeba histolytica recombinant phosphoglucomutase protein for serodiagnosis of amoebic liver abscess

Background

Amoebic liver abscess (ALA) is the most frequent clinical presentation of extra-intestinal amoebiasis. The diagnosis of ALA is typically based on the developing clinical symptoms, characteristic changes on radiological imaging and serology. Numerous serological tests have been introduced for the diagnosis of ALA, either detecting circulating amoebic antigens or antibodies. However those tests show some pitfalls in their efficacy and/or the preparation of the tests are costly and tedious. The commercial IHA kit that used crude antigen was reported to be useful in diagnosis of ALA, however high antibody background in endemic areas may cause problems in its interpretation. Thus, discovery of well-defined antigen(s) is urgently needed to improve the weaknesses of current serodiagnostic tests.

Methods

Crude antigen of E. histolytica was analysed by 2-DE and Western blot to identify a protein of diagnostic potential for ALA. The corresponding gene of the antigenic protein was then cloned, expressed and the purified recombinant protein was subsequently evaluated for serodiagnosis of ALA in an indirect ELISA format.

Results

Analysis of crude antigen showed that phosphoglucomutase (PGM) has the diagnostic potential. Recombinant PGM (rPGM) showed 79.17% (19/24) sensitivity and 86.67% (195/225) specificity in diagnosis of ALA based on the COV of mean +1SD. There was no significant difference between rPGM-ELISA and IHA diagnostic kit in the diagnosis of ALA in terms of sensitivity and specificity at p-value < 0.05.

Conclusion

In conclusion, rPGM-ELISA is found to be useful for serodiagnosis of ALA. Future studies will determine whether rPGM-ELISA also detects antibodies produced in amoebic dysentery and asymptomatic cases.

Diagnostic accuracy of indirect immunofluorescence assay for intestinal invasive amebiasis and impact of HIV infection in a non-endemic country

To diagnose amebic colitis (AC), serologic tests have the advantage of being inexpensive, noninvasive, and easy to perform, but few studies have investigated their utility, especially in a non-endemic country. A total of 299 symptomatic patients (165 HIV-infected patients) who underwent endoscopy and indirect immunofluorescence (IF) assay were analyzed between 2003 and 2009. The diagnosis of AC was defined as detection of amebic trophozoites from biopsy specimens or intestinal fluid sample via endoscopy. Forty-five patients (29 HIV-infected patients) were diagnosed with AC. The area under the receiver-operating characteristic curve (ROC-AUC) for the IF assay was excellent (0.90), and a cut-off value of 100 provided 89% sensitivity and 87% specificity. ROC-AUC was slightly lower in patients with HIV infection (0.88) than in those without HIV infection (0.94). Among HIV-infected patients, ROC-AUC showed no significant differences between different CD4+ cell counts. The IF assay is useful for diagnosing AC in symptomatic patients with and those without HIV infection.

Profiles of Entamoeba histolytica-specific immunoglobulins in human sera

OBJECTIVE

To determine the profiles of anti-Entamoeba histolytica (E. histolytica) IgA, IgG, and IgM in sera of diarrheic and non-diarrheic individuals and partially characterize target antigens.

METHODS

Serum samples from thirty diarrheic and thirty non-diarrheic individuals were subjected to IgA, IgG, and IgM profiling through enzyme-linked immunosorbent assay (ELISA), flow cytometry, and immunoblot.

RESULTS

ELISA titer results showed that both diarrheic and non-diarrheic individuals possess high levels of E. histolytica-specific IgG compared to IgA and IgM. Flow cytometry data showed that diarrheic serum samples had higher mean reaction percentages against E. histolytica cells compared to non-diarrheic samples. Immunoreactive E. histolytica proteins with molecular weights ranging between 7 kDa and 292 kDa were recognized by diarrheic serum IgG, and 170 kDa and 250 kDa by non-diarrheic serum IgG.

CONCLUSIONS

Our findings suggest that serum anti-E. histolytica IgG, compared with serum anti-E. histolytica IgA and IgM responses, was generally high in both diarrheic and non-diarrheic sera, indicating a past exposure to the organism both in symptomatic patients as well as in asymptomatic carriers, respectively. In addition, serum IgG from diarrheic and non-diarrheic patients were able to detect immunogenic E. histolytica proteins.

Mucosal delivery of ACNPV baculovirus driving expression of the Gal-lectin LC3 fragment confers protection against amoebic liver abscess in hamster

Mucosal vaccination against amoebiasis using the Gal-lectin of E. histolytica has been proposed as one of the leading strategies for controlling this human disease. However, most mucosal adjuvants used are toxic and the identification of safe delivery systems is necessary. Here, we evaluate the potential of a recombinant Autographa californica baculovirus driving the expression of the LC3 fragment of the Gal-lectin to confer protection against amoebic liver abscess (ALA) in hamsters following oral or nasal immunization. Hamsters immunized by oral route showed complete absence (57.9%) or partial development (21%) of ALA, resulting in some protection in 78.9% of animals when compared with the wild type baculovirus and sham control groups. In contrast, nasal immunization conferred only 21% of protection efficacy. Levels of ALA protection showed lineal correlation with the development of an anti-amoebic cellular immune response evaluated in spleens, but not with the induction of seric IgG anti-amoeba antibodies. These results suggest that baculovirus driving the expression of E. histolytica vaccine candidate antigens is useful for inducing protective cellular and humoral immune responses following oral immunization, and therefore it could be used as a system for mucosal delivery of an anti-amoebic vaccine.

Diagnosis of amebic liver abscess and amebic colitis by detection of Entamoeba histolytica DNA in blood, urine, and saliva by a real-time PCR assay

The noninvasive diagnosis of amebic liver abscess is challenging, as most patients at the time of diagnosis do not have a concurrent intestinal infection with Entamoeba histolytica. Fecal testing for E. histolytica parasite antigen or DNA is negative in most patients. A real-time PCR assay was evaluated for detection of E. histolytica DNA in blood, urine, and saliva samples from amebic liver abscess as well as amebic colitis patients in Bangladesh. A total of 98 amebic liver abscess and 28 amebic colitis patients and 43 control subjects were examined. The real-time PCR assay detected E. histolytica DNA in 49%, 77%, and 69% of blood, urine, and saliva specimens from the amebic liver abscess patients. For amebic colitis the sensitivity of the real-time PCR assay for detection of E. histolytica DNA in blood, urine, and saliva was 36%, 61%, and 64%, respectively. All blood, urine, and saliva samples from control subjects were negative by the real-time PCR assay for E. histolytica DNA. When the real-time PCR assay results of the urine and saliva specimens were taken together (positive either in urine or saliva), the real-time PCR assay was 97% and 89% sensitive for detection of E. histolytica DNA in liver abscess and intestinal infection, respectively. We conclude that the detection of E. histolytica DNA in saliva and urine could be used as a diagnostic tool for amebic liver abscess.

Detection of the Endosomal Sorting Complex Required for Transport in Entamoeba histolytica and Characterization of the EhVps4 Protein

Eukaryotic endocytosis involves multivesicular bodies formation, which is driven by endosomal sorting complexes required for transport (ESCRT). Here, we showed the presence and expression of homologous ESCRT genes in Entamoeba histolytica. We cloned and expressed the Ehvps4 gene, an ESCRT member, to obtain the recombinant EhVps4 and generate specific antibodies, which immunodetected EhVps4 in cytoplasm of trophozoites. Bioinformatics and biochemical studies evidenced that rEhVps4 is an ATPase, whose activity depends on the conserved E211 residue. Next, we generated trophozoites overexpressing EhVps4 and mutant EhVps4-E211Q FLAG-tagged proteins. The EhVps4-FLAG was located in cytosol and at plasma membrane, whereas the EhVps4-E211Q-FLAG was detected as abundant cytoplasmic dots in trophozoites. Erythrophagocytosis, cytopathic activity, and hepatic damage in hamsters were not improved in trophozoites overexpressing EhVps4-FLAG. In contrast, EhVps4-E211Q-FLAG protein overexpression impaired these properties. The localization of EhVps4-FLAG around ingested erythrocytes, together with our previous results, strengthens the role for EhVps4 in E. histolytica phagocytosis and virulence.

Detection of Entamoeba histolytica DNA in the saliva of amoebic liver abscess patients who received prior treatment with metronidazole

Saliva is an easily-accessible and a non-invasive clinical specimen alternate to blood and liver pus. An attempt was made to detect Entamoeba histolytica DNA released in the saliva of amoebic liver abscess (ALA) patients by applying 16S-like rRNA gene-based nested multiplex polymerase chain reaction (NM-PCR). The NM-PCR detected E. histolytica DNA in the saliva of eight (28.6%) of 28 ALA patients. The NM-PCR result was negative for E. histolytica DNA in the saliva of all the eight ALA patients who were tested prior to treatment with metronidazole but was positive in the saliva of eight (40%) of 20 ALA patient who were tested after therapy with metronidazole. The NM-PCR detected E. histolytica DNA in liver abscess pus of all 28 (100%) patients with ALA. The TechLab E. histolytica II enzyme-linked immunosorbent assay was positive for E. histolytica Gal/GalNAc lectin antigen in the liver abscess pus of 13 (46.4%) of the 28 ALA patients. The indirect haemagglutination (IHA) test was positive for anti-amoebic antibodies in the serum of 22 (78.6%) of the 28 ALA patients and 2 (5.7%) of 35 healthy controls. The present study, for the first time, demonstrates the release of E. histolytica DNA in the saliva of ALA patients by applying NM-PCR.

Laboratory diagnostic techniques for Entamoeba species

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

Evaluation of Entamoeba histolytica antigen and antibody point-of-care tests for the rapid diagnosis of amebiasis

The bedside diagnosis of amebiasis could improve patient care. In Bangladesh and Vietnam, a novel and simple-to-use Entamoeba histolytica rapid antigen test had 97% sensitivity and 100% specificity compared to the results of a standard enzyme-linked immunosorbent assay antigen detection method, and a rapid antibody test had 89 to 100% sensitivity and 89 to 95% specificity.

Diagnosis of amebiasis in Bangladesh

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

Real-time-PCR assay for diagnosis of Entamoeba histolytica infection

We developed a real-time-PCR assay utilizing a molecular-beacon probe for the detection of Entamoeba histolytica and compared its sensitivity to stool antigen detection and traditional PCR. A total of 205 stool and liver abscess pus specimens from patients and controls were used for this purpose, 101 (49%) of which were positive by the TechLab E. histolytica-specific antigen detection test, while the other 104 (51%) stool and liver abscess pus specimens were negative by the antigen detection test. DNA was extracted from the stool and liver abscess pus specimens by the QIAGEN method and the small-subunit rRNA gene of E. histolytica and then amplified by traditional and real-time PCR. Out of these 205 stool and liver abscess pus specimens, 124 were positive by the real-time-PCR assay and 90 were positive by the traditional-PCR test. Compared to the real-time-PCR assay, the antigen detection test was 79% sensitive and 96% specific. When the traditional-PCR test results were compared to the real-time-PCR assay, the sensitivity of traditional PCR was 72% and the specificity was 99%. In conclusion, all three methods for the detection of E. histolytica were highly specific, with real-time PCR being the most sensitive.

Entamoeba histolytica: an update

PURPOSE OF REVIEW

Over the past decade, since it was formally recognized that Entamoeba histolytica and Entamoeba dispar were two distinct species, studies in this field have made dramatic in-roads into the understanding of E. histolytica and the pathogenesis of invasive amoebiasis. Over the same period it has also become clear that the true incidence of E. histolytica infection, particularly in vulnerable populations such as low socioeconomic children, is exceedingly high. Understanding the epidemiology, pathophysiology, and the molecular and genetic biology of the organism will not only lead to improved diagnostic and treatment options but, ultimately, to the development of a safe and efficacious vaccine.

RECENT FINDINGS

The recent advances in the genetic and molecular sciences have increased our understanding of the mechanisms that make E. histolytica unique among enteric protozoa in causing invasive disease. In addition, host factors, which predispose individuals or populations to infection or disease, are beginning to be elucidated. New diagnostic tools specific to E. histolytica are being exploited by clinicians and researchers to identify and treat patients as well as to add to the knowledge of the epidemiology and natural history of this infection. The ultimate goal - eradication of disease - is theoretically feasible since humans and primates are the only reservoirs of E. histolytica. Many talented and dedicated individuals are pursuing the development of an effective and safe amoebiasis vaccine.

SUMMARY

E. histolytica remains an important pathogen in many populations of the world and although there has been substantial progress into understanding the disease major challenges still exist.

Laboratory diagnosis of amebiasis

The detection of Entamoeba histolytica, the causative agent of amebiasis, is an important goal of the clinical microbiology laboratory. To assess the scope of E. histolytica infection, it is necessary to utilize accurate diagnostic tools. As more is discovered about the molecular and cell biology of E. histolytica, there is great potential for further understanding the pathogenesis of amebiasis. Molecular biology-based diagnosis may become the technique of choice in the future because establishment of these protozoa in culture is still not a routine clinical laboratory process. In all cases, combination of serologic tests with detection of the parasite (by antigen detection or PCR) offers the best approach to diagnosis, while PCR techniques remain impractical in many developing country settings. The detection of amebic markers in serum in patients with amebic colitis and liver abscess appears promising but is still only a research tool. On the other hand, stool antigen detection tests offer a practical, sensitive, and specific way for the clinical laboratory to detect intestinal E. histolytica. All the current tests suffer from the fact that the antigens detected are denatured by fixation of the stool specimen, limiting testing to fresh or frozen samples.

Gene discovery in the Entamoeba invadens genome

Entamoeba invadens, a parasite of reptiles, is a model for the study of encystation by the human enteric pathogen Entamoeba histolytica, because E. invadens form cysts in axenic culture. With approximately 0.5-fold sequence coverage of the genome, we were able to get insights into E. invadens gene and genome features. Overall, the E. invadens genome displays many of the features that are emerging from ongoing genome sequencing efforts in E. histolytica. At the nucleotide level the E. invadens genome has on average 60% sequence identity with that of E. histolytica. The presence of introns in E. invadens was predicted with similar consensus (GTTTGT em leader A/TAG) sequences to those identified in E. histolytica and Entamoeba dispar. Sequences highly repeated in the genome of E. histolytica (rRNAs, tRNAs, CXXC-rich proteins, and Leu-rich repeat proteins) were found to be highly repeated in the E. invadens genome. Numerous proteins homologous to those implicated in amoebic virulence, (Gal/GalNAc lectins, amoebapores, and cysteine proteinases) and drug resistance (p-glycoproteins) were identified. Homologs of proteins involved in cell cycle, vesicular trafficking and signal transduction were identified, which may be involved in en/excystation and cell growth of E. invadens. Finally, multiple copies of a number of E. invadens genes coding for predicted enzymes involved in core metabolism and the targets of anti-amoebic drugs were identified.

Diagnosis of amoebic colitis by antigen capture ELISA in patients presenting with acute diarrhoea in Cairo, Egypt

We studied 84 consecutive patients presenting with acute diarrhoea (less than 1 week in duration) at an outpatient tropical medicine clinic in Cairo, Egypt. The diagnosis of amoebic colitis was established by the presence of Entamoeba histolytica galactose-inhibitable lectin antigen and the presence of occult blood in stool. Controls were 182 healthy regional people and 64 patients complaining of prolonged diarrhoea lasting more than 1 week. Entamoeba histolytica infection was found more frequently in patients with acute diarrhoea (57.1%) than in healthy controls (21.4%) or patients with prolonged diarrhoea (25%) (P < 0.001). There was a higher prevalence of Entamoeba dispar infection in the two control groups (24.2 and 20.3%, respectively, P=0.004 and 0.061) compared with those with acute diarrhoea (8.3%). Of the 84 patients with acute diarrhoea 32 had amoebic colitis (38%), and of these, 31 (97%) had at least one positive assay for serum amoebic antibodies (P < 0.001 compared with control groups). In summary, as determined by antigen-detection enzyme-linked immunosorbent assay, there is an unexpectedly high prevalence of amoebic colitis among patients presenting with acute diarrhoea to a tropical disease clinic in Cairo, Egypt.

Hepatobiliary infections

The major hepatobiliary infections (excluding the viral hepatitides) include amebic and pyogenic liver abscess and cholangitis. Little new information has been published in the area of cholangitis during the last several years. In contrast, the clinical presentation and management of liver abscess have evolved considerably, not only in the last several years but also during a more extended period spanning the last two decades. In the United States, amebic liver abscess occurs largely in individuals from endemic areas or in those traveling to endemic areas. Recent data suggest that patients with human immunodeficiency virus (HIV) infection are at an increased incidence of amebic liver abscess. New serologic tests and molecular techniques are being added to the diagnostic armamentarium for amebic liver abscess. In most cases, amebic liver abscess is associated with an excellent prognosis (up to 100% survival) if properly managed. Pyogenic liver abscess, although commonly occurring in patients with known biliary tract disease, is often cryptogenic in origin (ie, no clear causal factor can be identified) or often is caused by underlying medical disorders. An emerging population of patients with pyogenic liver abscess includes those with complications of aggressive interventions (hepatic chemoembolization, cryoablation, liver transplantation). Pyogenic liver abscess was predominantly managed by surgical methods up until the early 1980s, but almost entirely has changed to being managed by interventional techniques; in 2000, this trend has continued. In contrast to amebic liver abscess, pyogenic liver abscess is associated with greater morbidity and mortality, ostensibly caused by the severity of the underlying disease in many patients. However, it should be emphasized that the prognosis of patients with pyogenic liver abscess, who do not have underlying comorbid conditions, is excellent.