Longitudinal anti-SARS-CoV-2 antibody immune response in acute and convalescent patients

Despite global efforts to assess the early response and persistence of SARS-CoV-2 antibodies in patients infected with or recovered from COVID-19, our understanding of the factors affecting its dynamics remains limited. This work aimed to evaluate the early and convalescent immunity of outpatients infected with SARS-CoV-2 and to determine the factors that affect the dynamics and persistence of the IgM and IgG antibody response. Seropositivity of volunteers from Mexico City and the State of Mexico, Mexico, was evaluated by ELISA using the recombinant receptor-binding domain (RBD) of the SARS-CoV-2 Spike protein for 90 days, at different time points (1, 15, 45, 60, and 90 days) after molecular diagnosis (RT-qPCR). Gender, age range, body mass index (BMI), comorbidities, and clinical spectrum of disease were analyzed to determine associations with the dynamics of anti-SARS-CoV-2 antibodies. On 90 days post-infection, individuals with moderate and asymptomatic disease presented the lowest levels of IgM, while for IgG, at the same time, the highest levels occurred with mild and moderate disease. The IgM and IgG levels were related to the clinical spectrum of disease, BMI, and the presence/absence of comorbidities through regression trees. The results suggest that the dynamics of anti-SARS-CoV-2 IgM and IgG antibodies in outpatients could be influenced by the clinical spectrum of the disease. In addition, the persistence of antibodies against SARS-CoV-2 could be related to the clinical spectrum of the disease, BMI, and the presence/absence of comorbidities.

Amoebiasis: Advances in Diagnosis, Treatment, Immunology Features and the Interaction with the Intestinal Ecosystem

This review of human amoebiasis is based on the most current knowledge of pathogenesis, diagnosis, treatment, and Entamoeba/microbiota interactions. The most relevant findings during this last decade about the Entamoeba parasite and the disease are related to the possibility of culturing trophozoites of different isolates from infected individuals that allowed the characterization of the multiple pathogenic mechanisms of the parasite and the understanding of the host-parasite relationship in the human. Second, the considerable advances in molecular biology and genetics help us to analyze the genome of Entamoeba, their genetic diversity, and the association of specific genotypes with the different amoebic forms of human amoebiasis. Based on this knowledge, culture and/or molecular diagnostic strategies are now available to determine the Entamoeba species and genotype responsible for invasive intestinal or extraintestinal amoebiasis cases. Likewise, the extensive knowledge of the immune response in amoebiasis with the appearance of new technologies made it possible to design diagnostic tools now available worldwide. Finally, the understanding of the interaction between the Entamoeba species and the intestinal microbiota aids the understanding of the ecology of this parasite in the human environment. These relevant findings will be discussed in this review.

The regulatory function of Blastocystis spp. on the immune inflammatory response in the gut microbiome

Blastocystis spp. is a unicellular organism that resides in digestive tract of various vertebrates, with a worldwide distribution and a variable prevalence. For many years, Blastocystis spp. was considered a cyst of a flagellate, a fungus, or a saprophyte yeast of the digestive tract; in 1996, it is placed in the group of stramenopiles (heterokonts). Since its new classification, many questions have arisen around this protist about its role as a pathogen or non-pathogen organism. Recent evidence indicates that Blastocystis spp. participates in the immune inflammatory response in the intestinal microbiome generating an anti-inflammatory response, showing a lower concentration of fecal inflammatory markers in infected human hosts. Here, we review recent findings on the regulatory function of Blastocystis spp. in the immune inflammatory response to comprehend the purpose of Blastocystis spp. in health and disease, defining if Blastocystis spp. is really a pathogen, a commensal or even a mutualist in the human gut microbiome.

Tobamoviruses can be frequently present in the oropharynx and gut of infants during their first year of life

Plant viruses have been reported to be common in the gut of human adults, presumably as result of food ingestion. In this work, we report that plant viruses can also be found frequently in the gut and oropharynx of children during their first year of life, even when they are exclusively breast-fed. Fecal and oropharynx samples were collected monthly, from birth to 1 year of age, from three apparently healthy children in a semi-rural community and analyzed by next generation sequencing. In 100% of the fecal samples and 65% of the oropharynx samples at least one plant virus was identified. Tobamoviruses in the Virgaviridae family were by far the most frequently detected, with tropical soda apple mosaic virus, pepper mild mottle virus, and opuntia tobamovirus 2 being the most common species. Seventeen complete virus genomes could be assembled, and phylogenetic analyses showed a large diversity of virus strains circulating in the population. These results suggest that children are continuously exposed to an extensive and highly diverse collection of tobamoviruses. Whether the common presence of plant viruses at an early age influences the infant's immune system, either directly or through interaction with other members of the microbiota, remains to be investigated.

Use of next-generation amplicon sequencing to study Blastocystis genetic diversity in a rural human population from Mexico

BACKGROUND

The intestinal parasite Blastocystis is found in humans and animals around the world. It is spread through the consumption of contaminated food and water and has been associated with a variety of intestinal symptoms. Blastocystis is one of the most common intestinal parasites in humans, yet its prevalence and distribution in humans in North America is not well characterized.

METHODS

Next-generation amplicon sequencing of a region of the Blastocystis SSU rRNA gene was applied to DNA extracted from fecal specimens obtained from 182 inhabitants of a rural population in Mexico to characterize Blastocystis prevalence, subtype distribution, and intra-host subtype diversity in humans.

RESULTS

Of the 182 samples tested in this study, 68.1% (124) contained one or more Blastocystis subtypes. Subtype 3 was the most common subtype observed and was found in 81.5% of the positive samples. Subtype 1, 16.9% of the positive samples, and subtype 2, 17.7% of the positive samples, were also found in this population. Mixed infections were observed in 13.7% of the positive samples. In this population, the odds of having Blastocystis increased in adulthood (> 15 years; OR: 1.72, P < 0.0001), and the odds of having subtype 1 increased in the presence of farm animals (OR: 1.51, P = 0.03). The odds of having subtype 1, subtype 2, or a mixed infection decreased in the presence of cement flooring (OR: - 1.61, P = 0.005; OR: - 1.14, P = 0.03; OR: - 1.48, P = 0.02) possibly indicating socioeconomic factors are involved in the risk of acquiring one of these subtypes.

CONCLUSIONS

These data contribute to our understanding of the epidemiology of Blastocystis infection in humans and can be used to shape future studies which aim to better characterize the transmission pathways and health outcomes of Blastocystis infections.

Genetic Diversity and Distribution of Blastocystis Subtype 3 in Human Populations, with Special Reference to a Rural Population in Central Mexico

Blastocystis subtype 3 (ST3) is a parasitic protist found in the digestive tract of symptomatic and asymptomatic humans around the world. While this parasite exhibits a high prevalence in the human population, its true geographic distribution and global genetic diversity are still unknown. This gap in knowledge limits the understanding of the spread mechanisms, epidemiology, and impact that this parasite has on human populations. Herein, we provided new data on the geographical distribution and genetic diversity of Blastocystis ST3 from a rural human population in Mexico. To do so, we collected and targeted the SSU-rDNA region in fecal samples from this population and further compared its genetic diversity and structure with that previously observed in populations of Blastocystis ST3 from other regions of the planet. Our analyses reveled that diversity of Blastocystis ST3 showed a high haplotype diversity and genetic structure to the world level; however, they were low in the Morelos population. The haplotype network revealed a common widespread haplotype from which the others were generated recently. Finally, our results suggested a recent expansion of the diversity of Blastocystis ST3 worldwide.

Differential expression of pathogenic genes of Entamoeba histolytica vs E. dispar in a model of infection using human liver tissue explants

We sought to establish an ex vivo model for examining the interaction of E. histolytica with human tissue, using precision-cut liver slices (PCLS) from donated organs. E. histolytica- or E. dispar-infected PCLS were analyzed at different post-infection times (0, 1, 3, 24 and 48 h) to evaluate the relation between tissue damage and the expression of genes associated with three factors: a) parasite survival (peroxiredoxin, superoxide dismutase and 70 kDa heat shock protein), b) parasite virulence (EhGal/GalNAc lectin, amoebapore, cysteine proteases and calreticulin), and c) the host inflammatory response (various cytokines). Unlike E. dispar (non-pathogenic), E. histolytica produced some damage to the structure of hepatic parenchyma. Overall, greater expression of virulence genes existed in E. histolytica-infected versus E. dispar-infected tissue. Accordingly, there was an increased expression of EhGal/GalNAc lectin, Ehap-a and Ehcp-5, Ehcp-2, ehcp-1 genes with E. histolytica, and a decreased or lack of expression of Ehcp-2, and Ehap-a genes with E. dispar. E. histolytica-infected tissue also exhibited an elevated expression of genes linked to survival, principally peroxiredoxin, superoxide dismutase and Ehhsp-70. Moreover, E. histolytica-infected tissue showed an overexpression of some genes encoding for pro-inflammatory interleukins (ILs), such as il-8, ifn-γ and tnf-α. Contrarily, E. dispar-infected tissue displayed higher levels of il-10, the gene for the corresponding anti-inflammatory cytokine. Additionally, other genes were investigated that are important in the host-parasite relationship, including those encoding for the 20 kDa heat shock protein (HSP-20), the AIG-1 protein, and immune dominant variable surface antigen, as well as for proteins apparently involved in mechanisms for the protection of the trophozoites in different environments (e.g., thioredoxin-reductase, oxido-reductase, and 9 hypothetical proteins). Some of the hypothetical proteins evidenced interesting overexpression rates, however we should wait to their characterization. This finding suggest that the present model could be advantageous for exploring the complex interaction between trophozoites and hepatocytes during the development of ALA, particularly in the initial stages of infection.

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

Background

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

Methods

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

Results

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

Conclusions

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

Analysis of the Bacterial Diversity in Liver Abscess: Differences Between Pyogenic and Amebic Abscesses

Several recent studies have demonstrated that virulence in Entamoeba histolytica is triggered in the presence of both pathogenic and nonpathogenic bacteria species using in vitro and in vivo experimental animal models. In this study, we examined samples aspirated from abscess material obtained from patients who were clinically diagnosed with amebic liver abscess (ALA) or pyogenic liver abscess (PLA). To determine the diversity of bacterial species in the abscesses, we performed partial 16S rRNA gene sequencing. In addition, the E. histolytica and Entamoeba dispar species were genotyped using tRNA-linked short tandem repeats as specific molecular markers. The association between clinical data and bacterial and parasite genotypes were examined through a correspondence analysis. The results showed the presence of numerous bacterial groups. These taxonomic groups constitute common members of the gut microbiota, although all of the detected bacterial species have a close phylogenetic relationship with bacterial pathogens. Furthermore, some patients clinically diagnosed with PLA and ALA were coinfected with E. dispar or E. histolytica, which suggests that the virulence of these parasites increased in the presence of bacteria. However, no specific bacterial groups were associated with this effect. Together, our results suggest a nonspecific mechanism of virulence modulation by bacteria in Entamoeba.

Prevalent HLA Class II Alleles in Mexico City Appear to Confer Resistance to the Development of Amebic Liver Abscess

Amebiasis is an endemic disease and a public health problem throughout Mexico, although the incidence rates of amebic liver abscess (ALA) vary among the geographic regions of the country. Notably, incidence rates are high in the northwestern states (especially Sonora with a rate of 12.57/100,000 inhabitants) compared with the central region (Mexico City with a rate of 0.69/100,000 inhabitants). These data may be related to host genetic factors that are partially responsible for resistance or susceptibility. Therefore, we studied the association of the HLA-DRB1 and HLA-DQB1 alleles with resistance or susceptibility to ALA in two Mexican populations, one each from Mexico City and Sonora. Ninety ALA patients were clinically diagnosed by serology and sonography. Genomic DNA was extracted from peripheral blood mononuclear cells. To establish the genetic identity of both populations, 15 short tandem repeats (STRs) were analyzed with multiplexed PCR, and the allelic frequencies of HLA were studied by PCR-SSO using LUMINEX technology. The allele frequencies obtained were compared to an ethnically matched healthy control group (146 individuals). We observed that both affected populations differed genetically from the control group. We also found interesting trends in the population from Mexico City. HLA-DQB1*02 allele frequencies were higher in ALA patients compared to the control group (0.127 vs 0.047; p= 0.01; pc= NS; OR= 2.9, 95% CI= 1.09-8.3). The less frequent alleles in ALA patients were HLA-DRB1*08 (0.118 vs 0.238 in controls; p= 0.01; pc= NS; OR= 0.42, 95% CI= 0.19-0.87) and HLA-DQB1*04 (0.109 vs 0.214; p= 0.02; pc= NS; OR= 0.40, 95% CI= 0.20-0.94). The haplotype HLA-DRB1*08/-DQB1*04 also demonstrated a protective trend against the development of this disease (0.081 vs. 0.178; p=0.02; pc=NS; OR= 0.40, 95% CI= 0.16-0.93). These trends suggest that the prevalent alleles in the population of Mexico City may be associated with protection against the development of ALA.

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

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

Case report: Cutaneous amebiasis: the importance of molecular diagnosis of an emerging parasitic disease

Cutaneous amebiasis is the least common clinical form of human amebiasis in Mexico, sexual amebiasis was only occasionally observed before the late 1980s. However, in the last few decades, most of the documented cases of cutaneous amebiasis from around the world are sexually transmitted. We present two cases of sexually transmitted genital amebiasis. The molecular characterization of the Entamoeba species in the affected tissues underlines the importance of an etiological diagnosis using specific and sensitive techniques that avoid the rapid destruction of tissues and the irreversible sequelae to the anatomy and function of the affected organs. In addition, for those interested in the study of the human-amoebic disease relationship and its epidemiology, the detection of a new, mixed infection in an invasive case of amebiasis reveals new perspectives in the study of the extraordinarily complex host-parasite relationship in amebiasis.

Amoebic liver abscess production by Entamoeba dispar

Although Entamoeba dispar displays a similar morphology to Entamoeba histolytica, cellular and molecular studies have revealed significant differences between these two amoebae, including the former being characterized as non-pathogenic and the later as pathogenic. However, recent in vivo and in vitro experiments have shown that E. dispar strains of different origin are capable of causing liver damage and destroying cell culture lines in the presence of common intestinal bacteria. These results suggested that E. dispar may present pathogenic behavior according to the specific E. dispar strain, culture and environmental conditions. To investigate this possibility, we carried out in vivo and in vitro studies using a xenic strain E. dispar (ICB-ADO) isolated from a symptomatic non-dysenteric Brazilian patient. This strain was able to induce liver necrosis in a hamster model that was more severe than that produced by E. histolytica. The ICB-ADO isolate also caused significantly more destruction of cultured MDCK cells and increased loss of transepithelial resistance than did the E. histolytica. Xenic E. dispar exhibited high proteolytic activity, which was partially inhibited by the addition of cysteine-protease inhibitors. Based on our biochemical and molecular characterization of E. dispar (ICB-ADO) xenic culture and its ability to produce liver abscesses, we conclude that this specific strain can indeed produce tissue damage, distinct from the frequently used non- pathogenic E. dispar SAW 760 strain.

Novelties on amoebiasis: a neglected tropical disease

In accordance with the 1997 documents of the World Health Organization (WHO), amoebiasis is defined as the infection by the protozoan parasite Entamoeba histolytica with or without clinical manifestations. The only known natural host of E. histolytica is the human with the large intestine as major target organ. This parasite has a very simple life cycle in which the infective form is the cyst, considered a resistant form of parasite: The asymptomatic cyst passers and the intestinal amoebiasis patients are the transmitters; they excrete cysts in their feces, which can contaminate food and water sources. E. histolytica sensu stricto is the potentially pathogenic species and E. dispar is a commensal non-pathogenic Entamoeba. Both species are biochemical, immunological and genetically distinct. The knowledge of both species with different pathogenic phenotypes comes from a large scientific debate during the second half of the 20^th century, which gave place to the rapid development of diagnostics technology based on molecular and immunological strategies. During the last ten years, knowledge of the new epidemiology of amoebiasis in different geographic endemic and non-endemic areas has been obtained by applying mostly molecular techniques. In the present work we highlight novelties on human infection and the disease that can help the general physician from both endemic and non-endemic countries in their medical practice, particularly, now that emigration is undoubtedly a global phenomenon that is modifying the previous geography of infectious diseases worldwide.

Human amebiasis: breaking the paradigm?

For over 30 years it has been established that the Entamoeba histolytica protozoan included two biologically and genetically different species, one with a pathogenic phenotype called E. histolytica and the other with a non-pathogenic phenotype called Entamoeba dispar. Both of these amoebae species can infect humans. E. histolytica has been considered as a potential pathogen that can cause serious damage to the large intestine (colitis, dysentery) and other extraintestinal organs, mainly the liver (amebic liver abscess), whereas E. dispar is a species that interacts with humans in a commensal relationship, causing no symptoms or any tissue damage. This paradigm, however, should be reconsidered or re-evaluated. In the present work, we report the detection and genotyping of E. dispar sequences of DNA obtained from patients with amebic liver abscesses, including the genotyping of an isolate obtained from a Brazilian patient with a clinical diagnosis of intestinal amebiasis that was previously characterized as an E. dispar species. The genetic diversity and phylogenetic analysis performed by our group has shown the existence of several different genotypes of E. dispar that can be associated to, or be potentiality responsible for intestinal or liver tissue damage, similar to that observed with E. histolytica.

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

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

Reassessment of the epidemiology of amebiasis: state of the art

The epidemiology of amebiasis has dramatically changed since the separation of Entamoeba histolytica and Entamoeba dispar species, and the worldwide prevalence of these species has not been estimated until recently. The most cited data regarding prevalence, morbidity, or mortality due to amebiasis is the 1986 Walsh report, in which 100,000 deaths are reported to occur worldwide each year due to medical complications of invasive amebiasis. However, the prevalence values of Entamoeba histolytica infection could be completely erroneous since the estimations were performed prior to the molecular characterization of E. histolytica and E. dispar species. Moreover, Entamoeba moshkovskii, another morphologically indistinguishable human parasitic Entamoeba, was not mentioned or considered as a contributor to the prevalence figures in endemic areas. However, recent available prevalence and morbidity data obtained through molecular techniques allow the construction of a more reliable map of endemic regions of amebiasis all over the world [the Asian subcontinent (India, Bangladesh), Africa, Asian Pacific Countries (Thailand, Japan), South and Central America (Mexico, Colombia)]. The epidemiology of infectious diseases focuses on identification of factors that determine disease distribution in time and space, transmission factors responsible for the disease, clinical manifestations, and progression in the host, with the goal being the design of realistic intervention and prevention strategies in a reasonable period of time. In the present review, we will describe how molecular tools have made actual knowledge regarding the epidemiology of amebiasis possible. We will also analyze the most relevant available data on prevalence, morbidity, geographic distribution, patterns of transmission, exposure, and risk factors for infection in the human host. Our intention is to emphasize the recent molecular typing methods applied in genotyping Entamoeba species and strains, and to assess their value and limitations. Finally, we will discuss those areas of the host-parasite relationship that are still not fully understood, and the scientific challenges to approach this important public health problem in the future.

Two different chitinase genotypes in a patient with an amebic liver abscess: a case report

The present work deals with the identification of a patient with two liver abscesses containing two different strains of Entamoeba histolytica, as defined by chitinase gene plymorphisms.

Epidemiology of amebiasis in Mexico: a molecular approach

The differentiation of the two Entamoeba species E. histolytica and E. dispar through molecular characterization in the last decade of the twentieth century led to the need to re-evaluate the epidemiology of amebiasis in terms of prevalence and morbidity of the infection in the world's population, particularly in those geographic regions with high endemic rates.

Infection by human immunodeficiency virus-1 is not a risk factor for amebiasis

The purpose of this study was to determine whether HIV-1 infected patients in our community were more susceptible to Entamoeba histolytica and Entamoeba dispar infection than non-HIV-infected individuals. The prevalence and frequency of invasive amebiasis was determined in 203 HIV+/AIDS subjects and 140 close relatives or sexual partners, all of whom were HIV-. Anti-E. histolytica antibodies (IgG, IgA) were assessed as indicators of E. histolytica invasive infection. Polymerase chain reaction (PCR) was used for the characterization of the Entamoeba species. The prevalence estimated with PCR data showed that E. histolytica infection was more common in the HIV+/AIDS group (25.32%), than in HIV- contacts (18.46%). E. histolytica + E. dispar infection was more frequent in HIV+/AIDS patients (13.3%), than in HIV- contacts (0.7%). E. histolytica and/or E. dispar infection was highly prevalent in HIV+/AIDS patients (34.1%) without evidence of recent or current invasive disease. Contacts of HIV+/AIDS patients who were infected with E. histolytica were asymptomatic cyst passers. Our results suggest that E. histolytica strains prevalent in the studied community appear to be of low pathogenic potential.

Entamoeba histolytica and/or Entamoeba dispar: infection frequency in HIV+/AIDS patients in Mexico city

The objective of this work was to evaluate the frequency of Entamoeba histolytica/Entamoeba dispar intestinal infection in HIV+/AIDS subjects and their HIV- close relatives or sexual partners. Enteric parasites were investigated in stool samples by microscopic examination and E. histolytica and E. dispar were identified by PCR. We found by microscopic analysis in HIV+/AIDS group that the E. histolytica/E. dispar complex was present in 5.9% of the members, while in the HIV- group was 2.9%. With PCR we found that the E. histolytica prevalence was 25.3% in the HIV+/AIDS group and 18.5% in the HIV-group. The difference in the results obtained with the microscopic and PCR is due to the different sensibility of the procedures. Besides, we found patients who were infected with E. histolytica in both groups were asymptomatic cyst passers. Our results suggest that E. histolytica strains prevalent in the studied community appear to be of low pathogenic potential.

High prevalence rate of Entamoeba histolytica asymptomatic infection in a rural Mexican community

The frequency of Entamoeba histolytica and Entamoeba dispar infection was analyzed in a rural community in the state of Morelos, Mexico, using polymerase chain reaction (PCR). Sociodemographic variables as risk factors for the infection were assessed. Results highlighted the number of individuals with intestinal parasites (43.1%) in the community, indicating extensive fecalism. A high frequency of E. histolytica asymptomatic infection, higher than E. dispar infection (13.8% versus 9.6%), was detected by PCR. Anti-amebic antibody levels (IgG) in serum and saliva (IgA) samples were not associated with E. histolytica intestinal infection. These findings suggest a predominant distribution of E. histolytica strains of low invasive potential in this community.

Entamoeba histolytica and Entamoeba dispar: prevalence infection in a rural Mexican community

The frequency of Entamoeba histolytica and Entamoeba dispar infection was analyzed in a rural community in the state of Morelos, Mexico, through PCR technique by using specie specific primer. The E. histolytica specie was detected in 33 of 290 analyzed stool samples (11.4%), E. dispar specie was observed in 21 samples (7.2%) and both species of Entamoeba were detected in seven samples (2.4%). So a higher E. histolytica than E. dispar frequency infection was detected (13.8 versus 9.6%). Even though in our design we did not considered the follow-up of included individuals, the absence of invasive amebiasis cases in the studied population during our stay in town was unexpected.

E. dispar strain: analysis of polymorphism as a tool for study of geographic distribution

The intra-species polymorphism of E. histolytica and E. dispar species in endemic area is an important tool for geographic distribution and spread mechanism studies. Since E. dispar and E. histolytica shears ecological niche, cell cycle, and transmission mechanism for human host, we studied the intra-specie variation and distribution of E. dispar strains obtained from cyst passers, in two neighbor rural communities in Morelos Mexico. We analyzed the polymorphic region of the quitinase protein gene in isolates of E. dispar. In 45 isolates from one community we identified 12 different CHI patterns while in 15 isolates from the other community we identified 5 different patterns. However both communities share 4 patterns. This finding suggests the presence of strains with different geographic mobility.

Defective production of reactive oxygen intermediates (ROI) in a patient with recurrent amebic liver abscess

Previously, we reported the case of a man in the fourth decade of life afflicted with three independent episodes of amebic liver abscesses over a period of 4 years. Previous evidence has indicated that the cellular immune response is involved in protection against recurrent invasive amebic infection, and macrophage-mediated effector mechanisms appear important for host resistance to Entamoeba histolytica infection. The aim of the present work was to investigate locomotor activity and oxidative burst function of peripheral mononuclear cells of this individual after healing of the third amebic liver abscess. A locomotion assay using Boyden chemotaxis chambers and the respiratory burst evaluated by chemiluminescence were performed in both mononuclear phagocytes (MPs) and polymorphonuclear (PMN) leukocytes. Levels of salivary IgA and serum IgG anti-amebic antibodies were followed during 48 months after the second amebic liver abscess. Results obtained showed a deficiency in MP but not in PMN leukocyte respiratory burst. Respiratory burst is a major microbicidal mechanism in MP leukocytes; this also has been considered as a host resistance strategy against E. histolytica. It may be at least one risk factor in our patient that was responsible for recurrence of amebic liver abscess.

Calreticulin-like molecule in trophozoites of Entamoeba histolytica HM1:IMSS (Swissprot: accession P83003)

In this work, we report the partial sequence of a 51 kDa protein of Entamoeba histolytica that is highly immunogenic in humans. Partial sequencing of the N-terminal end showed that 18 of the first 20 amino acid residues of the protein were identified uniquely, indicating that the final product was a homogeneous protein preparation. The N-terminal sequence that was found was: KVYFEETFENGWKXIWSKW. Comparing the 19-amino acid sequence of the protein in automated databases shows significant similarity with amino acid sequences of the calreticulin-like protein of spinach leaves (77%) and of the calreticulin precursor of Dictyostelium discoideum (60%).

Persistence of secretory antiamoebic antibodies in patients with past invasive intestinal or hepatic amoebiasis

In the present work, it was demonstrated that in amoebic dysentery and amoebic liver abscess patients, the secretory response is long-lasting (> 12 months); and 50% of amoebic dysentery patients developed circulating antiamoebic IgG in comparison with 100% of amoebic liver abscess individuals. A total of 83% of these individuals developed high levels of serum anti-Entamoeba histolytica IgA. However, only 10.4% of the dysentery patients showed this anti-E. histolytica antibody isotype in serum. There was no correlation between secretory and serum antiamoebic response, suggesting independent inductive and effector sites in both compartments.

HLA characterization in adult asymptomatic cyst passers of Entamoeba histolytica/E. dispar

The present work aimed at studying the possible association of HLA antigens with Entamoeba histolytica/E. dispar asymptomatic infection in a Mexican mestizo population. A case-control design was selected for evaluation of the role of genetic markers in parasite infection. For this purpose the HLA-A, HLA-B, and HLA-DR profiles of a population of asymptomatic E. histolytica/E. dispar adult cyst passers (cases) and a corresponding nonparasitized adult group (controls) followed for 12 months were identified. Entamoeba species were identified through zymodeme patterns and/or amplification of species-specific DNA sequences. A healthy, nonparasitized group of individuals was included as a control. Our results show that apparently, no specific HLA marker is associated with the asymptomatic cyst passers' condition. These findings have to be added to previous results in which, in contrast to a demonstrated association between HLA-DR3 and amebic liver abscess in Mexican mestizo adults and infants, no significant association with amebic rectocolitis was found.

The effect of formalin fixation on the polymerase chain reaction characterization of Entamoeba histolytica

Formalin fixation is the most common storage, transportation and preservation method for stool samples. However, fixation dramatically reduces our ability to extract from stool samples DNA that is a suitable template for polymerase chain reaction (PCR)-based diagnostic tests. In this study we evaluated the effects of formalin concentration and of the time stored in fixative on the success of PCR amplification. We found that the deleterious effects of formalin are both time and concentration dependent and may result from fragmentation of fixed DNA during its purification.

Human cell-mediated immune responses to antigenic fractions of Salmonella typhi

The proliferative responses of peripheral blood mononuclear cells of 10 subjects that had typhoid fever, and healthy volunteers without history of typhoid fever or immunization against disease, were analysed with antigen fractions from two protein extracts of Salmonella typhi. Fractions from each extract were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) electrophoresis, transferred to nitrocellulose filters by electroblotting and processed to obtain antigen-bearing nitrocellulose particles for use in lymphocyte cultures. Although the individual proliferative responses were heterogeneous we identified two main immunogenic regions of 29-32 10(3) MW and 45-56 x 10(3) MW for both extracts. Even though there was no one particular antigenic fraction capable of stimulating lymphocytes from all individuals with a previous history of typhoid fever, the combination of three fractions 29-32, 41-45, 63-71 x 10(3) MW could be stimulatory for cells of 90% of these individuals. Also, four subjects that did not respond to unfractionated antigens gave proliferative responses to several fractions of the same extract. We have identified the main immunogenic fractions of S. typhi that might play a role during typhoid infection and postinfection immunity, and merit further purification and characterization.

Cellular immune response to fractionated avian antigens by peripheral blood mononuclear cells from patients with pigeon breeder's disease

Pigeon breeder's disease (PBD), a form of hypersensitivity pneumonitis caused by repeated inhalation of antigens of pigeon origin, is characterized by a diffuse inflammation of the lower respiratory tract. Although a variety of immunologic and nonimmunologic mechanisms have been described in the development of the disease, the pathogenesis is still far from clear. In this study we analyzed the T-lymphocyte proliferative response to a variety of avian antigens with use of peripheral blood mononuclear cells from 11 patients who had PBD and 10 healthy volunteers. We used a new method based on avian antigen-bearing nitrocellulose particles derived from Western blots to study the T-cell proliferative response to 15 antigenic fractions obtained from pigeon serum. With this technique, complex mixtures of antigens can be fractionated by polyacrylamide gel electrophoresis, transferred to nitrocellulose membranes, and used for T-cell proliferation assays with selected antigenic determinants. A wide variety of responses were observed, and there were no reproducible patterns of reaction within either group. Nine of 10 healthy subjects responded to some soluble fractions. However, patients with PBD displayed the strongest response and responded to a significantly greater number of antigenic fractions. Fraction 2, representing a 220 kd molecular weight protein, was the only immunodominant antigen when both groups were compared; it was recognized by 73% of the patients with PBD and by only 20% of control subjects (p < 0.03). These findings show that T lymphocytes of patients with PBD recognize a wide range of bird proteins, which induce marked T-cell proliferation.

Entamoeba histolytica: antibody response to recent and past invasive events

Sero-epidemiological data from endemic amoebiasis areas are difficult to evaluate because the serology of individuals affected by an active process of Entamoeba histolytica tissue invasion is, at present, almost impossible to distinguish from that of individuals who have had an invasive event in the past. The present study compares serum antigenic recognition frequencies among three groups of individuals with different infective conditions: amoebic liver abscess patients; asymptomatic cyst passers; and individuals who have had amoebic liver abscess from one to three years before the study. Control groups consisted of Mexican and Canadian healthy adults. Western blots of E. histolytica membrane extract antigen were reacted with sera from the studied individuals, recognition frequency values were calculated and immunoplots of frequency differences were constructed. The results obtained suggest that the identification and purification of antigenic fractions, which are frequently recognized by sera of amoebic liver abscess patients (136, 132, 93, 70 and 62 kDa), or preferentially associated with past invasive events (144, 140 and 49 kDa), or related to the E. histolytica cyst passer condition (62 and 136 kDa), are important improvements in the use of serology for diagnosis and epidemiological studies in endemic areas of amoebiasis.

Western blot of Entamoeba histolytica antigenic fractions: reactivity analysis with sera from intestinal amoebiasis patients

The reactivity of sera from acute-phase intestinal amoebiasis patients (two weeks evolution) was studied to determine which of the Entamoeba histolytica antigens are most frequently immunogenic. Sera were examined by means of immunoelectrotransferase assay using crude extract of HM1:IMSS E. histolytica trophozoites. Three populations of clinically healthy adults from Mexico, Canada and Germany, with no evidence of parasites in faeces, were used as controls. The frequency of antigen recognition was analysed. In ailing individuals, the bands of 23, 24, 26 and 51 kDa were recognized most frequently (65 and 60%) followed by the 62 kDa band (56%). The combination of some of these bands, namely 3.4, 4.1 and 6.7, with molecular weights of 62, 51 and 24 kDa, increased the recognition frequency of patients to 91.4%. These results constitute a first but important step towards the design of more accurate methods for the successful immunodiagnosis and epidemiology of acute intestinal amoebiasis.

Entamoeba histolytica: specific antigen recognized by a monoclonal antibody

Specific antigenic determinants on the membrane surface of Entamoeba histolytica that distinguish it from other Entamoeba species were demonstrated. Evidence for these antigenic determinants was obtained with a monoclonal antibody to E. histolytica which showed not only specificity but also sensitivity as demonstrated in enzyme linked immunosorbent assay. Immunofluorescence microscopy showed that the monoclonal antibody recognized an epitope present on the membrane surface of E. histolytica trophozoites. The epitope detected by the monoclonal antibody was present in three components of different molecular weight. These components may have a common precursor or may be the result of enzymatic degradation under the conditions tested.

Resistance to Nocardia brasiliensis infection in mice immunized with either Nocardia or BCG

Different vaccination procedures to increase the mechanisms of host resistance to Nocardia brasiliensis were studied in mice. When mice were challenged in the footpad, 2 x 10(8) N. brasiliensis 20 days after footpad inoculation with either viable or killed N. brasiliensis, the mice demonstrated significant resistance to infection when compared with noninfected and nonimmunized mice. The degree of resistance seems to be correlated with the delayed-type hypersensitivity response in the vaccinated animals. Vaccination with another acid-fast bacilli, BCG, afforded both a mild protection and low DTH reactivity. Antibody levels to Nocardia were similar in either Nocardia- or BCG-treated groups indicating that they do not play an important role in resistance to infection by N. brasiliensis.