Evolution and pathology in chagas disease--a review

Trypanosoma cruzi acute infections often go unperceived, but one third of chronically infected individuals die of Chagas disease, showing diverse manifestations affecting the heart, intestines, and nervous systems. A common denominator of pathology in Chagas disease is the minimal rejection unit, whereby parasite-free target host cells are destroyed by immune system mononuclear effectors cells infiltrates. Another key feature stemming from T. cruzi infection is the integration of kDNA minicircles into the vertebrate host genome; horizontal transfer of the parasite DNA can undergo vertical transmission to the progeny of mammals and birds. kDNA integration-induced mutations can enter multiple loci in diverse chromosomes, generating new genes, pseudo genes and knock-outs, and resulting in genomic shuffling and remodeling over time. As a result of the juxtaposition of kDNA insertions with host open reading frames, novel chimeric products may be generated. Germ line transmission of kDNA-mutations determined the appearance of lesions in birds that are indistinguishable from those seen in Chagas disease patients. The production of tissue lesions showing typical minimal rejection units in birds' refractory to T. cruzi infection is consistent with the hypothesis that autoimmunity, likely triggered by integration-induced phenotypic alterations, plays a major role in the pathogenesis of Chagas disease.     

Genetic susceptibility to chronic Chagas disease: an overview of single nucleotide polymorphisms of cytokine genes

Chagas disease is a parasitic infection that is a significant public health problem in Latin America. The mechanisms responsible for susceptibility to the infection and the mechanisms involved in the development of cardiac and digestive forms of chronic Chagas disease remain poorly understood. However, there is growing evidence that differences in susceptibility in endemic areas may be attributable to host genetic factors. The aim of this overview was to analyze the genetic susceptibility to human Chagas disease, particularly that of single nucleotide polymorphisms of cytokine genes. A review of the literature was conducted on the following databases: PubMed/MEDLINE and Scopus. The search strategy included using the following terms: "Cytokines", "Single Nucleotide Polymorphisms" and "Chagas Disease". After screening 25 citations from the databases, 19 studies were selected for the overview. A critical analysis of the data presented in the articles suggests that genetic susceptibility to Chagas disease and chronic Chagas cardiomyopathy is highly influenced by the complexity of the immune response of the host. Follow-up studies based on other populations where Chagas disease is endemic (with distinct ethnic and genetic backgrounds) need to be conducted. These should use a large sample population so as to establish what cytokine genes are involved in susceptibility to and/or progression of the disease.     

Discovery and characterization of an antibody, anti-egressin, that is able to inhibit Trypanosoma cruzi egress in vitro

Trypanosoma cruzi, a protozoan parasite, is the etiologic agent of Chagas disease. The disease is characterized by acute and chronic phases, with high and low parasitemia, respectively. A strong immune activation is necessary for the host to enter the chronic phase; however, immune mechanisms participating in the reduction of parasites between the acute and chronic phases of the disease have been very difficult to elucidate. We report here the discovery of anti-egressin, an antibody present in serum from chronically infected BALB/c mice that is able to inhibit parasite egress from infected BALB/c fibroblast cultures in vitro. The antibody is very concentrated in serum from these mice; chronic serum may be diluted 1:20 while still maintaining functional activity. Isotype analysis of anti-egressin has suggested it to be IgG2a. Further analysis revealed that anti-egressin was specific for a component expressed on the surface of infected host cells. The specificity of anti-egressin toward the extracellular portion of infected host cells was demonstrated both by using a quantitative assay measuring released trypomastigotes and through immunocytochemical staining. The novel role of anti-egressin in the inhibition of parasite egress from infected host cells has not been described in the literature to date. We believe that anti-egressin plays an important role in achieving the low parasitemia characteristic of chronic Chagas disease.     

Ecological patterns of blood-feeding by kissing-bugs (Hemiptera: Reduviidae: Triatominae)

Host use by vectors is important in understanding the transmission of zoonotic diseases, which can affect humans, wildlife and domestic animals. Here, a synthesis of host exploitation patterns by kissing-bugs, vectors of Chagas disease, is presented. For this synthesis, an extensive literature review restricted to feeding sources analysed by precipitin tests was conducted. Modern tools from community ecology and multivariate statistics were used to determine patterns of segregation in host use. Rather than innate preferences for host species, host use by kissing-bugs is influenced by the habitats they colonise. One of the major limitations of studies on kissing-bug foraging has been the exclusive focus on the dominant vector species. We propose that expanding foraging studies to consider the community of vectors will substantially increase the understanding of Chagas disease transmission ecology. Our results indicate that host accessibility is a major factor that shapes the blood-foraging patterns of kissing-bugs. Therefore, from an applied perspective, measures that are directed at disrupting the contact between humans and kissing-bugs, such as housing improvement, are among the most desirable strategies for Chagas disease control.     

The role of astrocytes in the immunopathogenesis of toxoplasmic encephalitis

Challenge with the parasite Toxoplasma gondii eventually leads to persistent infection characterised by the presence of tissue cysts in the brain of the host. In immunocompetent individuals the parasite rarely leads to disease but in the immunocompromised host reactivation of these cysts can lead to toxoplasmic encephalitis. It is known that both CD4(+) and CD8(+) T cells are important in preventing reactivation of the parasite, however there is also evidence that astrocytes, a subset of glial cells dominant in the CNS, may be important in resistance to T. gondii. The aim of this paper is to review what is known about the immune functions of astrocytes, and the possible role they may play during toxoplasmic encephalitis.     

Don't bother to knock--the cell invasion strategy of Trypanosoma cruzi

The protozoan parasite Trypanosoma cruzi is responsible for Chagas disease, a serious debilitating disease that affects millions of people in Latin America. Trypomastigotes, the infective forms, are capable of invading and replicating in different cell types. The invasion process involves a gradual recruitment and fusion of host cell lysosomes at the parasite entry site, and is regulated by intracellular free Ca2+ transients triggered by trypomastigotes in host cells. This unusual, Ca2+-dependent lysosome exocytosis pathway was recently shown to be involved in the mechanism by which mammalian cells repair lesions on their plasma membrane.     

The effect of Blastocrithidia triatomae (Trypanosomatidae) on the reduviid bug Triatoma infestans: influence of group size

Developmental time and mortality in uninfected larvae of the reduviid bug Triatoma infestans and in those infected by feeding a mixture of blood and cysts of the homoxenous trypanosomatid Blastocrithidia triatomae were compared. Larvae were maintained isolated in 77-cm3 (area 9.6 cm2) beakers or in groups of 20, 30, 40, and 50 bugs per 1-liter beaker (area 722 cm2). In uninfected groups, only a minor proportion of isolated bugs showed delayed development, but in groups infected with B. triatomae, additionally, a retardation in groups of 50 larvae occurred. Infected bugs needed more time to complete development in fourth and fifth instar than did uninfected bugs. Mean mortality rates of about 10% in uninfected groups were unaffected by group size. Mortality rates in most groups of infected bugs were about 50%, but in groups consisting of 50 larvae a statistically significant higher mortality rate of 75% was observed. This indicates a subpathological overcrowding stress, increased by the synergistic action of the flagellate.     

Chemokines,inflammation and Trypanosoma cruzi infection

The inflammatory response that follows the infection with Trypanosoma cruzi is essential for host resistance to infection but is also responsible for the diverse pathology observed in Chagas disease. Here, we examine the stimuli and mechanisms underlying chemokine production following infection in vitro and in vivo, and the ability of chemokines to coordinate the influx of inflammatory and immune cells to the site of parasite infection, and to control T. cruzi growth.     

Effects of mammal host diversity and density on the infection level of Trypanosoma cruzi in sylvatic kissing bugs

Several reports have described host species diversity and identity as the most important factors influencing disease risk, producing either dilution or amplification of the pathogen in a host community. Triatomine vectors, mammals and the protozoan Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) Chagas are involved in the wild cycle of Chagas disease, in which infection of mammals occurs by contamination of mucous membranes or skin abrasions with insect‐infected faeces. We examined the extent to which host diversity and identity determine the infection level observed in vector populations (i.e. disease risk in humans). We recorded infection in triatomine colonies and on the coexisting host mammalian species in semi‐arid Chile. Host diversity, and total and infected host species densities are used as predictor variables for disease risk. Disease risk did not correlate with host diversity changes. However, the densities of each infected rodent species were positively associated with disease risk. We suggest that the infected host density surrounding the vector colonies is a relevant variable for disease risk and should be considered to understand disease dynamics. It is crucial to pay attention on the spatial scale of analysis, considering the pattern of vector dispersal, when the relationship between host diversity and disease risk is studied.     

The effect of azadirachtin on Blastocrithidia triatomae and Trypanosoma cruzi in Triatoma infestans (Insecta, Hemiptera).

The effect of azadirachtin on Blastocrithidia triatomae and Trypanosoma cruzi, which colonise the intestinal tract of the blood-sucking bug Triatoma infestans, was investigated. In established infections of controls without azadirachtin treatment, the small intestine of fifth-instar T. infestans contained up to 7 x l0(6) B. triatomae and the rectum 3 x 10(6). In comparison to this homoxenous flagellate, the population densities of T. cruzi in the respective regions were 99.3 and 76% lower. Treatment with azadirachtin (1 microg ml(-1)) via a blood meal and a concurrent infection with B. triatomae resulted in an increase of the population density (3 weeks p.i.), caused mainly by the mastigote stages in the rectum. In an established B. triatomae infection (12 weeks p.i.), feeding of azadirachtin did not affect the population density and composition. In an optimal T. cruzi-vector system, i.e. parasite and bug originate from the same locality, the treatment with azadirachtin at 20 weeks p.i. strongly reduced the population density in the small intestine of all bugs up to 100 days after treatment, but only in a minor percentage of the bugs in the rectum. Trypanosoma (cruzi incubated for up to 24 h in faeces of azadirachtin-treated bugs were not affected, indicating that the rectum of these bugs contained no toxic substances. The importance of these findings is that investigations of the mechanisms of action of azadirachtin offer a possibility to identify vector-derived compounds, which are necessary for the development of T. cruzi, thereby, giving us a possible new strategy to combat Chagas' disease.     

Trypanosoma cruzi and human ubiquitin are immunologically distinct proteins despite only three amino acid difference in their primary sequence

The high similarity between Trypanosoma cruzi and human ubiquitin prompted us to characterize the human humoral immunity to host and parasite ubiquitin in Chagas disease and its possible role in Chagas autoimmunity. We have used a simplified one step purification procedure to partially purify T. cruzi ubiquitin. Using this preparation we have performed ELISA and Western blots, to show that chagasic sera recognise T. cruzi but not human or Leishmania ubiquitin indicating a species-specific response. Our results show that despite the high degree of similarity in the primary structure of human and T. cruzi ubiquitins, the three amino acid difference is sufficient to distinguish parasite versus host proteins.     

Genetic Variability of Trypanosoma cruzi:Implications for the Pathogenesis of Chagas Disease

Chagas disease, caused by the protozoan Trypanosoma cruzi, has a variable clinical course, ranging from symptomless infection to severe chronic disease with cardiovascular or gastrointestinal involvement or even overwhelming acute episodes. The factors influencing this clinical variability have not been elucidated, but genetic variation of both the host and parasite is likely to be important. Here, Andréa M. Macedo and Sérgio D.J. Pena review the evidence showing a role for the genetic constitution of T. cruzi in determining the clinical characteristics of Chagas disease, and propose a ;clonal-histotropic model' for the pathogenesis of this disease.     

The Trypanosoma cruzi-host-cell interplay: location, invasion, retention

Chagas disease is a debilitating human illness caused by infection with the protozoan Trypanosoma cruzi. A capacity to invade and replicate within many different cell types is a cornerstone of the remarkable fitness of this parasite. Although invasion occurs independently of actin polymerization, the host cell still participates in the process, often in unexpected ways. Recent surprising findings indicate that host-cell lysosomes are indispensable, either by directly mediating invasion or by retaining these highly motile parasites inside cells.     

Severity of chronic Chagas disease is associated with cytokine/antioxidant imbalance in chronically infected individuals

Understanding the pathogenic mechanisms in chronic Chagas disease, a major cause of morbidity and mortality in Latin America, is essential for the design of rational therapeutic strategies. In this paper we show that the development of Chagas disease is a consequence of a long-term and complex relationship between parasite persistence and maladapted homeostatic mechanisms in the host which leads to pathologic changes. We performed a retrospective study on 50 patients with chronic Chagas disease and 50 healthy control individuals. The specific immune response was detected by ELISA and IHA tests using autochthonous antigens, inflammatory process with the cytokine tumour necrosis factor (TNF)-alpha and nitric oxide (NO), and antioxidant protection with glutathione peroxidase and superoxide dismutase (SOD) levels. We developed generalised linear modelling procedures to assess simultaneously which explanatory variables and/or their interactions better explained disease severity in patients. Our results show the existence of a strong relationship between anti-Trypanosoma cruzi levels and chronic Chagas disease (P<0.0001). Taken together, the statistical data indicate both cumulative and complementary effects, where the increase in TNF-alpha (P=0.004) and NO (P=0.005) levels correlated with a reduction in glutathione peroxidase (P=0.0001) and SOD (P=0.01) levels drives the disease pathology in chronically infected patients. Our findings may have important implications for understanding host susceptibility to develop severe chronic infectious disease. In addition we show putative targets for the design of new therapeutic strategies to prevent disease progression, considering both specific treatment against the aetiological agent and modulation of the different immunopathological reactions in chronically infected individuals with chronic Chagas disease.     

Global Metabolomic Profiling of Acute Myocarditis Caused by Trypanosoma cruzi Infection

Chagas disease is caused by Trypanosoma cruzi infection, being cardiomyopathy the more frequent manifestation. New chemotherapeutic drugs are needed but there are no good biomarkers for monitoring treatment efficacy. There is growing evidence linking immune response and metabolism in inflammatory processes and specifically in Chagas disease. Thus, some metabolites are able to enhance and/or inhibit the immune response. Metabolite levels found in the host during an ongoing infection could provide valuable information on the pathogenesis and/or identify deregulated metabolic pathway that can be potential candidates for treatment and being potential specific biomarkers of the disease. To gain more insight into those aspects in Chagas disease, we performed an unprecedented metabolomic analysis in heart and plasma of mice infected with T. cruzi. Many metabolic pathways were profoundly affected by T. cruzi infection, such as glucose uptake, sorbitol pathway, fatty acid and phospholipid synthesis that were increased in heart tissue but decreased in plasma. Tricarboxylic acid cycle was decreased in heart tissue and plasma whereas reactive oxygen species production and uric acid formation were also deeply increased in infected hearts suggesting a stressful condition in the heart. While specific metabolites allantoin, kynurenine and p-cresol sulfate, resulting from nucleotide, tryptophan and phenylalanine/tyrosine metabolism, respectively, were increased in heart tissue and also in plasma. These results provide new valuable information on the pathogenesis of acute Chagas disease, unravel several new metabolic pathways susceptible of clinical management and identify metabolites useful as potential specific biomarkers for monitoring treatment and clinical severity in patients.     

Chagas Disease Etiology: Autoimmunity or Parasite Persistence?

The question of the cause and the mechanisms of disease in chronic Trypanosoma cruzi infection continues to attract debate. Chagas disease, characterized by cardiomyopathy and/or megasyndrome involving the esophagus or colon, occurs in approximately 30% of individuals with chronic T. cruzi infections. Although the pathogenesis of Chagas disease is often attributed to autoimmune mechanisms, definitive proof of anti-self responses as the primary cause of disease in T. cruzi-infected hosts is lacking. Rick Tarleton and Lei Zhang here consider an alternative view that the primary cause of chronic Chagas disease is the failure of the host to clear the infection, resulting in infection-induced, immune-mediated tissue damage.     

Polyamine depletion inhibits the autophagic response modulating Trypanosoma cruzi infectivity

Autophagy is a cell process that in normal conditions serves to recycle cytoplasmic components and aged or damaged organelles. The autophagic pathway has been implicated in many physiological and pathological situations, even during the course of infection by intracellular pathogens. Many compounds are currently used to positively or negatively modulate the autophagic response. Recently it was demonstrated that the polyamine spermidine is a physiological inducer of autophagy in eukaryotic cells. We have previously shown that the etiological agent of Chagas disease, the protozoan parasite Trypanosoma cruzi, interacts with autophagic compartments during host cell invasion and that preactivation of autophagy significantly increases host cell colonization by this parasite. In the present report we have analyzed the effect of polyamine depletion on the autophagic response of the host cell and on T. cruzi infectivity. Our data showed that depleting intracellular polyamines by inhibiting the biosynthetic enzyme ornithine decarboxylase with difluoromethylornithine (DFMO) suppressed the induction of autophagy in response to starvation or rapamycin treatment in two cell lines. This effect was associated with a decrease in the levels of LC3 and ATG5, two proteins required for autophagosome formation. As a consequence of inhibiting host cell autophagy, DFMO impaired T. cruzi colonization, indicating that polyamines and autophagy facilitate parasite infection. Thus, our results point to DFMO as a novel autophagy inhibitor. While other autophagy inhibitors such as wortmannin and 3-methyladenine are nonspecific and potentially toxic, DFMO is an FDA-approved drug that may have value in limiting autophagy and the spread of the infection in Chagas disease and possibly other pathological settings.     

The importance of aberrant T-cell responses in Chagas disease

Persistence of Trypanosoma cruzi is associated with damage to the heart, which is a characteristic of Chagas disease. In this article, we discuss recently identified mechanisms of aberrant T-cell activation that are responsible for persistence of T. cruzi and cardiac injury. Among them, apoptosis of host cells drives T. cruzi replication in macrophages and is present in cardiac inflammation. It is proposed that phagocytic removal of infected apoptotic cardiomyocytes, combined with signaling through innate immune receptors, is required to initiate immune responses that damage the heart.     

Etiological treatment during early chronic indeterminate Chagas disease incites an activated status on innate and adaptive immunity associated with a type 1-modulated cytokine pattern

Pro-inflammatory immune response is usually associated with Chagas disease pathogenesis, but is also relevant to treatment effectiveness. Cross-sectional studies have suggested that this activated state may persist for years after therapeutic intervention. However, short-term longitudinal investigation has suggested that the Benznidazole treatment (Bz-treatment) leads to decreased immunological activation. In order to elucidate this issue, we performed a longitudinal study to evaluate the immunological status following Bz-treatment during early indeterminate Chagas disease. Our results demonstrated that Bz-treatment led to higher activation status of circulating monocytes but was negatively associated with the number of IL-12(+)CD14(+) cells. Moreover, Bz-treatment triggered a high frequency of circulating CD3(-)CD16(+)CD56(-) NK cells, in addition to elevated activation status associated with a type 1-modulated cytokine pattern. Bz-treatment induced substantial T and B-cell activation status associated with an overall IL-10 modulated type 1 cytokine profile. In summary, these findings provide new information regarding immune activation status following the etiological treatment of Chagas disease. These results suggest that in addition to the increased number of activated leukocytes in the peripheral blood, Bz-treatment may also involve a qualitative change in their functional capacity that drives their activation state toward a modulated cytokine profile. These changes may account for the benefits of etiological treatment of Chagas disease.     

Macrophage signaling by glycosylphosphatidylinositol-anchored mucin-like glycoproteins derived from Trypanosoma cruzi trypomastigotes

Activation of cells from the innate immune system has an important role in host resistance to early infection with the intracellular protozoan parasite, Trypanosoma cruzi. Here we review the studies that have identified and structurally characterized the glycosylphosphatidylinositol (GPI) anchors, as parasite molecules responsible for the activation of cells from the macrophage lineage. We also cover the studies that have identified the receptor, signaling pathways as well as the array of genes expressed in macrophages that are activated by these glycoconjugates. We discuss the possible implications of such response on the host resistance to T. cruzi infection and the pathogenesis of Chagas disease.