Evolution and pathology in chagas disease--a review

Comments on the article by Ribeiro et al. 'Enhanced parasympathetic activity in Chagas' disease still stands in need of proof': definitions and biases

It has been hypothesized that impaired cardiac autonomic function in chagasic subject carriers of anti-muscarinic type 2 antibodies (Anti-M2) is a consequence of tonic stimulation (enhancement) of M2 receptors, thus damping high frequency spontaneous heart rate fluctuations. However, expected reduction in baseline average heart rate response as a consequence of M2 receptors stimulation has not been confirmed, imposing a query on current hypothesis for explaining autonomic impairment in Chagas' disease. In this context, possible explanations for the lack of heart rate reduction in the setting of chronic muscarinic stimulation in Chagas' disease have been discussed, based on current knowledge. Among possible factors implicated, stands out: i) spontaneous heart rate recovery after chronic vagal stimulation, ii) simultaneous anti-M2 and anti-beta 1 adrenergic receptors antibodies environments, iii) underlying cardiac function as assessed by both mechanical and humoral indexes, iv) age, v) immune status. Rigorous experimental settings may be necessary to mechanistically demonstrate eventually the association between agonistic anti-M2 environments and reduced autonomic modulation of the heart, in both humans and animal models, associated with short term and long term singular average resting heart rate balance secondary to parasympathetic stimulation.

Entomological factors affecting the low endemicity of Chagas disease in Nazca, Southwestern Peru

Chagas disease is prevalent in Peru. The province of Nazca, in the southwestern region of the country, shows a high intradomiciliary infestation rate of Triatoma infestans bugs. Although the vector is present, the number of Chagas disease cases appears to be much lower than those reported in the neighboring region of Arequipa. We examined 624 T. infestans from Nazca to determine the current Trypanosoma cruzi infection rates, and found that no bugs were infected with this parasite. These results contrast with those found in Arequipa, where 19-30% triatomines have been reported infected. To compare their vectorial capacity, we infected 30 T. infestans specimens, selected both from Nazca and Arequipa, by feeding bugs on T. cruzi-infected mice. The parasites developed all stages expected in the vector; furthermore, the infective stage, metacyclic trypomastigote, was found in both insect populations from the second week after infection. In addition, those insects that accepted to be fed with mice blood defecated immediately after finishing blood meal, indicating that they might be efficient vectors. We maintain that differences observed in infection rates between vectors from Nazca and Arequipa may be explained by differences in host availability. In Arequipa hosts are mainly small animals, whereas in Nazca the main blood source comes from birds, which are refractory to the infection.

Anti-trypanosomatid benzofuroxans and deoxygenated analogues: synthesis using polymer-supported triphenylphosphine, biological evaluation and mechanism of action studies

Hybrid vinylthio-, vinylsulfinyl-, vinylsulfonyl- and vinylketo-benzofuroxans developed as anti-trypanosomatid agents, against Trypanosoma cruzi and Leishmania spp., have showed low micromolar IC(50) values. The synthetic route to access to these derivatives was an efficient Wittig reaction performed in mild conditions with polymer-supported triphenylphosphine (PS-TPP). Additionally, the benzofurozan analogues, deoxygenated benzofuroxans, were prepared using PS-TPP as reductive reagent in excellent yields. The trypanosomicidal and leishmanocidal activities of the benzofuroxan derivatives were measured and also some aspects of their mechanism of action studied. In this sense, inhibition of mitochondrial dehydrogenases activities, production of intra-parasite free radicals and cruzipain inhibition were studied as biological target for the anti-trypanosomatid identified compounds. The trypanosomicidal activity could be the result of both the parasite-mitochondrion function interference and production of oxidative stress into the parasite.

Environment, interactions between Trypanosoma cruzi and its host, and health

An epidemiological chain involving Trypanosoma cruzi is discussed at the environmental level, and in terms of fine molecular interactions in invertebrate and vertebrate hosts dwelling in different ecosystems. This protozoan has a complex, genetically controlled plasticity, which confers adaptation to approximately 40 blood-sucking triatomine species and to over 1,000 mammalian species, fulfilling diverse metabolic requirements in its complex life-cycle. The Tr. cruzi infections are deeply embedded in countless ecotypes, where they are difficult to defeat using the control methods that are currently available. Many more field and laboratory studies are required to obtain data and information that may be used for the control and prevention of Tr. cruzi infections and their various disease manifestations. Emphasis should be placed on those sensitive interactions at cellular and environmental levels that could become selected targets for disease prevention. In the short term, new technologies for social mobilization should be used by people and organizations working for justice and equality through health information and promotion. A mass media directed program could deliver education, information and communication to protect the inhabitants at risk of contracting Tr. cruzi infections.

Trypanosoma cruzi: biodistribution of technetium-99m pertechnetate in infected rats

With the aim of investigating the biodistribution of technetium-99m pertechnetate ((99m)TcO4-) in rats infected with Y strain of Tripanosoma Cruzi, at the peak of parasitemia, (14th day of infection), we injected Wistar rats with 0.1 ml of (99m)TcO4- (3.7MBq). After 60 min, the percentage of radioactivity per gram was counted in several isolated organs and blood, using a gamma counter (1470 Wizard, PerkinElmer Finland). The uptake of (99m)TcO4- increased significantly in blood and decreased in the colon of infected animals (p<0.05). A significant reduction in serum iron and red blood cells and a significant increase in total proteins, leukocytes and lymphocytes in the infected rats were observed, compared with controls (p<0.05). A reduction in muscle layer thickness of the colon and mononuclear inflammation were observed. These results conclusively demonstrate that T. cruzi infection would be associated with changes in the biodistribution of (99m)TcO4- and in colon morphology, with potential clinical implications.

What is the role of small rodents in the transmission cycle of Trypanosoma cruzi and Trypanosoma evansi (Kinetoplastida Trypanosomatidae)? A study case in the Brazilian Pantanal

Determining the reservoir hosts for parasites is crucial for designing control measures, but it is often difficult to identify the role that each host species plays in maintaining the cycle of infection in the wild. One way to identify potential maintenance hosts is to estimate key parameters associated with transmission and pathogenicity. Here we assess the potential for three native rodent species of the Brazilian Pantanal (Clyomys laticeps, Thrichomys pachyurus and Oecomys mamorae) to act as reservoir or maintenance hosts of Trypanosoma evansi, an important parasite of domestic livestock. By analyzing blood parameters of naturally infected wild-caught rodents of these species, we compared their levels of parasitemia and anemia due to T. evansi infection with literature values for other host species infected by this parasite. We also analyzed levels of these blood parameters relative to infection by Trypanosoma cruzi, the causative agent of Chagas disease in humans, for which wild rodents are already thought to be important reservoir species. All three species showed low impacts of the two trypanosomes on their blood parameters compared to other species, suggesting that they experience a low virulence of trypanosome infection under natural conditions in the Pantanal and might act as maintenance hosts of trypanosome infections. The low parasitemia of trypanosome infections suggests that these rodents play a secondary role in the transmission cycle compared to other species, especially compared to the capybara (Hydrochaeris hydrochaeris) which also experiences low pathogenicity due to infection despite much higher levels of parasitemia.

Involvement of the beta-adrenergic system in the cardiac chronic form of experimental Trypanosoma cruzi infection

Changes in the cardiac beta-adrenergic system in early stages of Trypanosoma cruzi infection have been described. Here, we studied an early (135 days post-infection-p.i.) and a late stage (365 days p.i.) of the cardiac chronic form of the experimental infection (Tulahuen or SGO-Z12 strains), determining plasma epinephrine and norepinephrine levels, beta-receptor density, affinity and function, cardiac cAMP concentration and phosphodiesterase activity, cardiac contractility, and the presence of beta-receptor autoantibodies. Tulahuen-infected mice presented lower epinephrine and norepinephrine levels; lower beta-receptor affinity and density; a diminished norepinephrine response and higher cAMP levels in the early stage, and a basal contractility similar to non-infected controls in the early and augmented in the late stage. The Tulahuen strain induced autoantibodies with weak beta-receptor interaction. SGO-Z12-infected mice presented lower norepinephrine levels and epinephrine levels that diminished with the evolution of the infection; lower beta-receptor affinity and an increased density; unchanged epinephrine and norepinephrine response in the early and a diminished response in the late stage; higher cAMP levels and unchanged basal contractility. The SGO-Z12 isolate induced beta-receptor autoantibodies with strong interaction with the beta-receptors. None of the antibodies, however, acted a as beta-receptor agonist. The present results demonstrate that this system is seriously compromised in the cardiac chronic stage of T. cruzi infection.

Chagasic encephalitis in HIV patients: common presentation of an evolving epidemiological and clinical association

We present a case of chagasic meningoencephalitis reactivation in an HIV-infected woman with advanced immunosuppression. Prolonged survival was attained with antiparasitic therapy and secondary prophylaxis, in conjunction with the use of highly-active antiretroviral therapy. The geographic expansion of the HIV epidemic around the world coupled with global migration and international travel have created a favourable situation for Trypanosoma cruzi and HIV coinfection. The clinical manifestations of Chagas disease in HIV-positive people usually represent reactivation and not acute infection with T cruzi (coinfection). Symptomatic reactivation of chronic latent T cruzi infection can be triggered by severe immunosuppression associated with HIV infection. In this setting, Chagas disease reactivation often presents as meningoencephalitis resembling toxoplasma encephalitis. We review, in this Grand Round, the clinical manifestations, diagnostic approach, pathogenesis, natural history, treatment, prognosis, and prevention of Chagas disease reactivation among HIV-infected people with an emphasis on CNS manifestations.

Nonlinear mathematical model for predicting long term cardiac remodeling in Chagas' heart disease: introducing the concepts of 'limiting cardiac function' and 'cardiac function deterioration period'

Cardiac remodeling has been recently investigated in long term follow-up introducing a simple exponential model to describe the time course of cardiac function and dimension changes in Chagas' disease. In the present study, an improved mathematical model to equate time course and cardiac functional changes has been proposed. Present model has been derived from previously validated intuitive assumptions and tested on data set of outpatients with chronic Chagas' disease (51.3±9.4 years old), followed for up to 10 years in Rio de Janeiro, Brazil. The variables representing cardiac status at admission were plotted against respective time derivative, which appropriately fit a second order polynomial (adjusted r(2)=0.956; p<0.001), indicating that long term cardiac remodeling followed a Verhulst-Pearl (Logistic) model. The derived Logistic model provided two output constants: a time-function (2.0·10(-3)±5.4·10(-4) months(-1)·%(-1); p<0.001) and an inferior limit for left ventricular ejection fraction (19.0±0.9%; p<0.001), standing for a limit beyond life expectation is unsustainable, in Chagas' disease. Cardiac function deterioration period was promptly derived from the model, representing the period of time following indeterminate stages of the disease when cardiac function start deteriorating, and ranged from 3 to 15.8 years. An example of data of left ventricular ejection fraction of a subject followed during 10 years illustrated the model, further validating its robustness. Present data confirms that, in chronic Chagas' disease, initial insult is connected to the progression of myocardial remodeling and introduces the concepts of limiting cardiac function and cardiac deterioration period.

Placental infection by two subpopulations of Trypanosoma cruzi is conditioned by differential survival of the parasite in a deleterious placental medium and not by tissue reproduction

Chagas disease is caused by Trypanosoma cruzi, which can be transmitted to the fetus via the transplacental route. Factors that may be involved in transplacental transmission include parasite strain and placental immunological competence. The aim of this work was to compare the biological differences between two subpopulations of T. cruzi with respect to their interaction with the human placenta in vitro. We found that the Tulahuen strain (sublineage TcIIe) and another strain isolated from a congenitally infected newborn child had similar rates of productive infection in human chorionic villi in vitro, with similar deleterious nitric oxide levels between the two strains. We also found that the congenital T. cruzi stock had a greater ability than the Tulahuen strain to survive in the placental deleterious media, with the difference acquiring more importance considering the low reproductive rate of both subpopulations of T. cruzi within placental cells. As the presence of T. cruzi is a necessary condition to produce congenital transmission, we propose that the different survival rates of strains of T. cruzi in an adverse placental environment offer an opportunity for the parasite to infect the placenta in order to produce a sustainable infection during pregnancy, with the subsequent possibility of infecting the fetus.

Pediatric clinical pharmacology studies in Chagas disease: focus on Argentina

Chagas disease is a neglected parasitic disease endemic in the Americas. It mainly affects impoverished populations and the acute phase of the infection mostly affects children. Many cases have also been detected in nonendemic countries as a result of recent migratory trends. The chronic phase is relatively asymptomatic, but 30% of patients with chronic infection eventually develop cardiac and digestive complications that commonly lead to death or disability. Only two drugs are available for the treatment of Chagas disease, benznidazole and nifurtimox. These drugs have been shown to be effective in the treatment of both acute and early chronic phases in children, but the pharmacokinetics of these drugs have never been studied in this population. We have set out to conduct a pharmacokinetics study of benznidazole in a pediatric population with Chagas disease. The results of this study are expected to allow better estimation of the optimal doses and schedule of pharmacotherapy for Chagas disease in children.

Acute heart inflammation: ultrastructural and functional aspects of macrophages elicited by Trypanosoma cruzi infection

The heart is the main target organ of the parasite Trypanosoma cruzi, the causal agent of Chagas' disease, a significant public health issue and still a major cause of morbidity and mortality in Latin America. During the acute disease, tissue damage in the heart is related to the intense myocardium parasitism. To control parasite multiplication, cells of the monocytic lineage are highly mobilized. In response to inflammatory and immune stimulation, an intense migration and extravasation of monocytes occurs from the bloodstream into heart. Monocyte differentiation leads to the formation of tissue phagocytosing macrophages, which are strongly activated and direct host defence. Newly elicited monocyte-derived macrophages both undergo profound physiological changes and display morphological heterogeneity that greatly differs from originally non-inflammatory macrophages, and underlie their functional activities as potent inflammatory cells. Thus, activated macrophages play a critical role in the outcome of parasite infection. This review covers functional and ultrastructural aspects of heart inflammatory macrophages triggered by the acute Chagas' disease, including recent discoveries on morphologically distinct, inflammation-related organelles, termed lipid bodies, which are actively formed in vivo within macrophages in response to T. cruzi infection. These findings are defining a broader role for lipid bodies as key markers of macrophage activation during innate immune responses to infectious diseases and attractive targets for novel anti-inflammatory therapies. Modulation of macrophage activation may be central in providing therapeutic benefits for Chagas' disease control.

Trypanosoma cruzi and myoid cells from seminiferous tubules: interaction and relation with fibrous components of extracellular matrix in experimental Chagas' disease

The main transmission route of Trypanosoma cruzi is by triatomine bugs. However, T. cruzi is also transmitted through blood transfusion, organ transplantation, ingestion of contaminated food or fluids, or is congenital. Sexual transmission, although suggested since the discovery of Chagas' disease, has remained unproven. Sexual transmission would require T. cruzi to be located at the testes and ovaries. Here we investigated whether T. cruzi is present in the gonads of mice infected with 10(4) T. cruzi trypomastigotes from the CL strain. Fourteen days after experimental infection, histopathological examination showed alterations in the extracellular matrix of the lamina propria of the seminiferous tubules. Furthermore, amastigotes were present in seminiferous tubules, within myoid cells, and in the adjacencies of the basal compartment. These results indicate that T. cruzi is able to reach seminiferous tubule lumen, thus suggesting that Chagas' disease could potentially be transmitted through sexual intercourse. Complementary studies are required to demonstrate that Chagas' disease can be transmitted by coitus.

TNF/TNFR1 signaling up-regulates CCR5 expression by CD8+ T lymphocytes and promotes heart tissue damage during Trypanosoma cruzi infection: beneficial effects of TNF-alpha blockade

In Chagas disease, understanding how the immune response controls parasite growth but also leads to heart damage may provide insight into the design of new therapeutic strategies. Tumor necrosis factor-alpha (TNF-alpha) is important for resistance to acute Trypanosoma cruzi infection; however, in patients suffering from chronic T. cruzi infection, plasma TNF-alpha levels correlate with cardiomyopathy. Recent data suggest that CD8-enriched chagasic myocarditis formation involves CCR1/CCR5-mediated cell migration. Herein, the contribution of TNF-alpha, especially signaling through the receptor TNFR1/p55, to the pathophysiology of T. cruzi infection was evaluated with a focus on the development of myocarditis and heart dysfunction. Colombian strain-infected C57BL/6 mice had increased frequencies of TNFR1/p55+ and TNF-alpha+ splenocytes. Although TNFR1-/- mice exhibited reduced myocarditis in the absence of parasite burden, they succumbed to acute infection. Similar to C57BL/6 mice, Benznidazole-treated TNFR1-/- mice survived acute infection. In TNFR1-/- mice, reduced CD8-enriched myocarditis was associated with defective activation of CD44+CD62Llow/- and CCR5+ CD8+ lymphocytes. Also, anti-TNF-alpha treatment reduced the frequency of CD8+CCR5+ circulating cells and myocarditis, though parasite load was unaltered in infected C3H/HeJ mice. TNFR1-/- and anti-TNF-alpha-treated infected mice showed regular expression of connexin-43 and reduced fibronectin deposition, respectively. Furthermore, anti-TNF-alpha treatment resulted in lower levels of CK-MB, a cardiomyocyte lesion marker. Our results suggest that TNF/TNFR1 signaling promotes CD8-enriched myocarditis formation and heart tissue damage, implicating the TNF/TNFR1 signaling pathway as a potential therapeutic target for control of T. cruzi-elicited cardiomyopathy.

Cardiac involvement in African and American trypanosomiasis

American trypanosomiasis (Chagas disease) and human African trypanosomiasis (HAT; sleeping sickness) are both caused by single-celled flagellates that are transmitted by arthropods. Cardiac problems are the main cause of morbidity in chronic Chagas disease, but neurological problems dominate in HAT. Physicians need to be aware of Chagas disease and HAT in patients living in or returning from endemic regions, even if they left those regions long ago. Chagas heart disease has to be taken into account in the differential diagnosis of cardiomyopathy, primarily in patients with pathological electrocardiographic (ECG) findings, such as right bundle branch block or left anterior hemiblock, with segmental wall motion abnormalities or aneurysms on echocardiography, and in young patients with stroke in the absence of arterial hypertension. In HAT patients, cardiac involvement as seen by ECG alterations, such as repolarisation changes and low voltage, is frequent. HAT cardiopathy in general is benign and does not cause relevant congestive heart failure and subsides with treatment. We review the differences between the American and African trypanosomiasis with the main focus on the heart.

Pivotal role for TGF-beta in infectious heart disease: The case of Trypanosoma cruzi infection and consequent Chagasic myocardiopathy

This paper summarizes recent data from the literature suggesting that transforming growth factor-beta (TGF-beta) participates at least in four different processes influencing development of myocardiopathy in Chagas disease, a major parasitic illness caused by Trypanosoma cruzi infection: (a) invasion of cardiac fibroblasts and myocytes; (b) intracellular parasite cycle; (c) regulation of inflammation and immune response; (d) fibrosis and heart remodeling during acute and chronic disease. All these effects point to an important role of TGF-beta in Chagas disease myocardiopathy and suggest that monitoring the circulating levels of this cytokine could be of help in clinical prognosis and management of patients. Moreover, TGF-beta-interfering therapies appear as interesting adjuvant interventions during acute and chronic phases of T. cruzi infection.

Chagas heart disease pathogenesis: one mechanism or many?

Chagas heart disease (CHD), caused by the protozoan parasite Trypanosoma cruzi, is the leading cause of infectious myocarditis in the world. The etiology of CHD is unclear and multiple mechanisms have been proposed to explain the pathogenesis of the disease. This review describes the proposed mechanisms of CHD pathogenesis and evaluates the historical significance and evidence supporting each. Although the majority of CHD-related pathologies are currently attributed to parasite persistence in the myocardium and autoimmunity, there is strong evidence that CHD develops as a result of additive and even synergistic effects of several distinct mechanisms rather than one factor.

Glial fibrillary acidic protein and S-100 colocalization in the enteroglial cells in dilated and nondilated portions of colon from chagasic patients

After acute immunoreactive infestation with the Chagas' disease parasite, Trypanosoma cruzi, some patients develop chronic megacolon, whereas others remain asymptomatic. Chronic chagasic patients with gastrointestinal involvement exhibit inflammation and degeneration of enteric neurons. Our hypothesis is that enteric glial cells may be involved in the modulation of enteric inflammatory responses or even control the colon's dilatation. The aims of this study were to characterize the phenotype of enteric glial cells according to the expression of S-100 and glial fibrillary acidic protein and to look for correlation between these data and the neuronal loss in the colon of chagasic patients. We studied both dilated and nondilated portions of chagasic megacolon. We used a pan-enteric glial cell marker (anti-S-100), a subpopulation enteric glial cell marker (anti-glial fibrillary acidic protein), and a pan-neuronal marker (anti-Human protein C and protein D) with double-labeled sheets using a confocal microscope. Our results demonstrate that neuronal loss is similar in dilated and nondilated portions of chagasic megacolon. Moreover, the results indicate that neuronal destruction present in chagasic megacolon is preceded by glial component loss. The nondilated portion of chagasic megacolon exhibited increased expression of glial fibrillary acidic protein comparable with the dilated portion and also to the noninfected group. Our results suggest that glial fibrillary acidic protein enteric glial cells prevent dilatation of the organ and protect the enteric nervous system against the inflammatory process and neuronal destruction, preventing the destruction from expanding to unaffected areas of the colon.

Viridamides A and B, lipodepsipeptides with antiprotozoal activity from the marine cyanobacterium Oscillatoria nigro-viridis

Parallel chemical and phylogenetic investigation of a marine cyanobacterium from Panama led to the isolation of two new PKS-NRPS-derived compounds, viridamides A and B. Their structures were determined by NMR and mass spectroscopic methods, and the absolute configurations assigned by Marfey's method and chiral HPLC analysis. In addition to six standard, N-methylated amino and hydroxy acids, these metabolites contained the structurally novel 5-methoxydec-9-ynoic acid moiety and an unusual proline methyl ester terminus. Morphologically, this cyanobacterium was identified as Oscillatoria nigro-viridis, and its 16S rDNA sequence is reported here for the first time. Phylogenetic analysis of these sequence data has identified O. nigro-viridis strain OSC3L to be closely related to two other marine cyanobacterial genera, Trichodesmium and Blennothrix. Viridamide A showed antitrypanosomal activity with an IC50 of 1.1 microM and antileishmanial activity with an IC50 of 1.5 microM.

Chagas disease: what is known and what is needed--a background article

Chagas disease began millions of years ago as an enzootic disease of wild animals and started to be transmitted to man accidentally in the form of an anthropozoonosis when man invaded wild ecotopes. Endemic Chagas disease became established as a zoonosis over the last 200-300 years through forest clearance for agriculture and livestock rearing and adaptation of triatomines to domestic environments and to man and domestic animals as a food source. It is estimated that 15 to 16 million people are infected with Trypanosoma cruzi in Latin America and 75 to 90 million people are exposed to infection. When T. cruzi is transmitted to man through the feces of triatomines, at bite sites or in mucosa, through blood transfusion or orally through contaminated food, it invades the bloodstream and lymphatic system and becomes established in the muscle and cardiac tissue, the digestive system and phagocytic cells. This causes inflammatory lesions and immune responses, particularly mediated by CD4+, CD8+, interleukin-2 (IL) and IL-4, with cell and neuron destruction and fibrosis, and leads to blockage of the cardiac conduction system, arrhythmia, cardiac insufficiency, aperistalsis, and dilatation of hollow viscera, particularly the esophagus and colon. T. cruzi may also be transmitted from mother to child across the placenta and through the birth canal, thus causing abortion, prematurity, and organic lesions in the fetus. In immunosuppressed individuals, T. cruzi infection may become reactivated such that it spreads as a severe disease causing diffuse myocarditis and lesions of the central nervous system. Chagas disease is characterized by an acute phase with or without symptoms, and with entry point signs (inoculation chagoma or Romaña's sign), fever, adenomegaly, hepatosplenomegaly, and evident parasitemia, and an indeterminate chronic phase (asymptomatic, with normal results from electrocardiogram and x-ray of the heart, esophagus, and colon) or with a cardiac, digestive or cardiac-digestive form. There is great regional variation in the morbidity due to Chagas disease, and severe cardiac or digestive forms may occur in 10 to 50% of the cases, or the indeterminate form in the other asymptomatic cases, but with positive serology. Several acute cases have been reported from Amazon region most of them by T. cruzi I, Z3, and a hybrid ZI/Z3. We conclude this article presenting the ten top Chagas disease needs for the near future.

Trypanosoma cruzi infection in the sylvatic kissing bug Mepraia gajardoi from the Chilean Southern Pacific Ocean coast

The Southern Pacific Ocean coast has been traditionally considered a non-active transmission area for Chagas disease. In this report, we show evidence of Trypanosoma cruzi infection in the sylvatic kissing bug Mepraia gajardoi from the northern Chilean coast.

Atrial mechanical remodeling and new onset atrial fibrillation in chronic Chagas' heart disease

Atrial fibrillation (AF) is a common arrhythmia, mechanistically linked to underlying heart disease. AF affects about one fifth of subjects with Chagas' heart disease and is a harbinger of poor prognosis. In a retrospective longitudinal analysis, 50 subjects were investigated in long-term follow-up for the first documented atrial fibrillation (AF) episode. During a follow-up of (mean+/-SD) 84.2+/-39.0 months, nine subjects developed AF (incidence: 3.3+/-1.0%/year). Five subjects had nonfatal embolic stroke and nine died due to cardiac causes. The relative risk of AF for stroke was 3.0 (p=0.22) and for cardiac death was 3.6 (p=0.04). A faster left atrial diameter (LAD) enlargement during follow-up was tracked in subjects with more severe cardiac damage at presentation, and large LAD was detected at both presentation (p=0.02) and end of follow-up (p=0.002) in subjects who experienced AF. Atrial remodeling in chronic Chagas' disease is associated with severity of underlying heart disease at presentation and impacts AF incidence in this population.

In silico, biologically-inspired modelling of genomic variation generation in surface proteins of Trypanosoma cruzi

BACKGROUND

Protozoan parasites improve the likelihood of invading or adapting to the host through their capacity to present a large repertoire of surface molecules. The understanding of the mechanisms underlying the generation of antigenic diversity is crucial to aid in the development of therapies and the study of evolution. Despite advances driven by molecular biology and genomics, there is a need to gain a deeper understanding of key properties that may facilitate variation generation, models for explaining the role of genomic re-arrangements and the characterisation of surface protein families on the basis of their capacity to generate variation. Computer models may be implemented to explore, visualise and estimate the variation generation capacity of gene families in a dynamic fashion. In this paper we report the dynamic simulation of genomic variation using real T. cruzi coding sequences as inputs to a computational simulation system. The effects of random, multiple-point mutations and gene conversions on genomic variation generation were quantitatively estimated and visualised. Simulations were also implemented to investigate the potential role of pseudogenes as a source of antigenic variation in T. cruzi.

RESULTS

Computational models of variation generation were applied to real coding sequences from surface proteins in T. cruzi: trans-sialidase-like proteins and putative surface protein dispersed gene family-1. In the simulations the sequences self-replicated, mutated and re-arranged during thousands of generations. Simulations were implemented for different mutation rates to estimate the relative robustness of the protein families in the face of DNA multiple-point mutations and sequence re-arrangements. The gene super-families and families showed distinguishing evolutionary responses, which may be used to characterise them on the basis of their capacity to generate variability. The simulations showed that sequences from T. cruzi nuclear genes tend to be relatively more robust against random, multiple-point mutations than those obtained from surface protein genes. Simulations also showed that a gene conversion model may act as an effective variation generation mechanism. Differential variation responses can be used to characterise the sequence groups under study. For example, unlike other families, sequences from the DGF1 family have the capacity to maximise variation at the amino acid level under relatively low mutation rates and through gene conversion. However, in relation to the other protein families, they exhibit more robust behaviour in response to more severe modifications through intra-family genomic sequence exchange. Independent simulations indicate that DGF1 pseudogenes might play a role in the generation of greater genomic variation in the DFG1 gene family through gene conversion under different experimental conditions.

CONCLUSION

Digital, dynamic simulations may be implemented to characterise gene families on the basis of their capacity to generate variation in the face of genomic perturbations. Such simulations may be useful to explore antigenic variation mechanisms and hypotheses about robustness at the genomic level. This investigation illustrated how sequences derived from surface protein genes and computer simulations can be used to investigate variation generation mechanisms. Such in silico experiments of self-replicating sequences undergoing random mutations and genomic re-arrangements can offer insights into the diversity generation potential of the genes under study. Biologically-inspired simulations may support the study of genomic variation mechanisms in pathogens whose genomes have been recently sequenced.

Exposure to mixed asymptomatic infections with Trypanosoma cruzi, Leishmania braziliensis and Leishmania chagasi in the human population of the greater Amazon

Lack of conservation of the Amazon tropical rainforest has imposed severe threats to its human population living in newly settled villages, resulting in outbreaks of some infectious diseases. We conducted a seroepidemiological survey of 1100 inhabitants of 15 villages of Paço do Lumiar County, Brazil. Thirty-five (3%) individuals had been exposed to Trypanosoma cruzi (Tc), 41 (4%) to Leishmania braziliensis (Lb) and 50 (4.5%) to Leishmania chagasi (Lc) infections. Also, 35 cases had antibodies that were cross-reactive against the heterologous kinetoplastid antigens. Amongst these, the Western blot assays revealed that 11 (1%) had Tc and Lb, that seven (0.6%) had Lc and Tc, and that 17 (1.6%) had Lb and Lc infections. All of these cases of exposures to mixed infections with Leishmania sp, and eight of 11 cases of Tc and Lb were confirmed by specific PCR assays and Southern hybridizations. Two cases had triple infections. We consider these asymptomatic cases showing phenotype and genotype markers consistent with mixed infections by two or more kinetoplastid flagellates a high risk factor for association with Psychodidae and Triatominae vectors blood feeding and transmitting these protozoa infections. This is the first publication showing human exposure to mixed asymptomatic kinetoplastid infections in the Amazon.

Hitchhiking Trypanosoma cruzi minicircle DNA affects gene expression in human host cells via LINE-1 retrotransposon

The horizontal transfer of Trypanosoma cruzi mitochondrial minicircle DNA to the genomes of naturally infected humans may play an important role in the pathogenesis of Chagas disease. Minicircle integrations within LINE-1 elements create the potential for foreign DNA mobility within the host genome via the machinery associated with this retrotransposon. Here we document integration of minicircle DNA fragments in clonal human macrophage cell lines and their mobilization over time. The movement of an integration event in a clonal transfected cell line was tracked at three months and three years post-infection. The minicircle sequence integrated into a LINE-1 retrotransposon; one such foreign fragment subsequently relocated to another genomic location in association with associated LINE-1 elements. The p15 locus was altered at three years as a direct effect of minicircle/LINE-1 acquisition, resulting in elimination of p15 mRNA. Here we show for the first time a molecular pathology stemming from mobilization of a kDNA/LINE-1 mutation. These genomic changes and detected transcript variations are consistent with our hypothesis that minicircle integration is a causal component of parasite-independent, autoimmune-driven lesions seen in the heart and other target tissues associated with Chagas disease.