Central nervous system involvement in experimental trypanosomiasis cruzi

A review of the available literature on central nervous system involvement in experimental trypanosomiasis cruzi is undertaken. From a critical analysis of 26 works on experimental infections with Trypanosoma cruzi (23 on the acute phase, 2 on the chronic phase, and one describing sequentially both phases), all supported by neuropathologic studies, it can be concluded that: 1) central nervous system involvement during the acute phase, in the form of encephalitis in multiple foci, with variable intensity of the parasitism and inflamatory changes, is frequent and well documented; 2) in animals with more severe central nervous system involvement death occurs as a result of the brain lesions or acute chagasic myocarditis, the latter being always present; 3) in animals with more discrete brain involviment death during the acute phase is due to complications not related to the nervous system, among which congestive heart failure second to acute chagasic myocarditis, a condition that is always present, regardless of whether or not the central nervous system is infected; 4) it is possible that in surviving animals that had mild encephalitis the inflammatory changes from the acute phase usually regress as the infection progress to the chronic phase.

Cell mediated immunity in Chagas' disease: Trypanosoma cruzi antigens induce suppression of the in vitro proliferative response of mononuclear cells

The partial suppression of the cell-mediated immune response by Trypanosoma cruzi antigens in patients with Chagas' disease is demonstrated in a costimulation assay with T. cruzi antigens and Mycobacterium tuberculosis purified protein derivative (PPD) or Tetanus toxoid (TT). ononuclear cells from 13 patients with chagasic infection without evidence of heart disease, 10 patients with chagasic cardiomyopathy and 7 healthy blood donors were stimulated with antigen A (autoclaved epimastigotes), PPD, TT, PPD + A, PPD + TT and TT + A. The average percentage of suppression induced by costimulation of mononuclear cells with PPD and antigen A was 47.1% in patients with chagasic infection without heart disease (INF), 38.8% in patients with chagasic cardiomyopathy (CDM) and 23.3% in healthy controls. Similar values were observed when living trypomastigotes were used. A costimulatory study with PPD and TT, PPD and A and TT and A was carried out in 8 patients with chagasic infection, in order to evaluate the possibility that this difference could be due to a nonspecific inhibitory effect. The mean suppression induced by TT + PPD was -8.9, with TT + A was 52.7 and with PPD + A was 50.1. The data reported show that T. cruzi antigens induce a specific suppression of the proliferative responseof mononuclear cells, that might be relevant to the persistence of the parasite in the host.

Are dead Triatoma infestans a competent vector of Trypanosoma cruzi?

After Triatoma infestans death, Trypanosoma cruzi survived several days, maintaining the ability to infect a vertebrate host. Dead bugs from an endemic area collected during an official spraying comapign showed mobile rectal tripanosomes up to 14 days after vector death. Two days after vector death2, 760 tripomastigotes were found alive in its rectal material. However, the number of mobile tripomastigotes decreased significantly from the 5th day after death. Laboratory proofs with third and fifth nymphal stage showed similar results. Living tripanosomes were found in their rectal material at 10 days in third stage and even at 30 days in fifth nymphal stage. The mean number of tripomastigotes had no changes up to 10 days in third nymphal stage and increased significantly from 1 to 10 days in the fifth stage. Conjuctival instillation as well as intraperitoneal innoculation to mice, of metacyclic forms from dead T. infestans produced infection in the vertebrate host. Present results show that human contact with dead vector highly probable in summer and living and infective T. cruzi are available for transmision in the vector.

Biological characterization of Trypanosoma cruzi strains from different zymodemes and schizodemes

The development in C3H mice of thirteen strains of Trypanosoma cruzi belonging to different zymodemes ans schizodemes was studied. Host mortality, virulence, histiotropism, parasitemia and polymorphism of the parasites were recorded. The strains were grouped into: a) high virulence - causing 100% mortality and characterized by predominance of bery broad trypomastigotes in the bloodstream at the end of infection; b) medium virulence - causing no mortality and with a predominance of broad trypomastigotes; c) low virulence - causing no mortality with blood forms not described due to the very low parasitemia. During 18 months maintenance the parasitemia curves were kept constant for all strains except one. A direct correlation between either zymodeme or schizodeme and experimental biological properties of T. cruzi strains was not found. However, the parasitemia was subpatent and patent for strains from zymodeme C and the others respectively. Furthermore the high virulence seems to be related to one of two shizodemes found within zymodeme B strains. All strains presenting patent parasitemia independent of shizodeme and ymodeme showed a myotropism towards heart and skeletal muscle with varible inflammatory intensity. The present study confirmed the heterogeneity found by isoenzyme and K-DNA patterns among the strains of T. cruzi isolated from chagasic patients in Bambuí, Minas Gerais State, Brasil.

Trypanosoma cruzi: effect of phenothiazines on the parasite and its interaction with host cells

Phenothiazines were observed to have a direct effect on Trypanosoma cruzi and on its in vitro interaction with host cells. They caused lysis of trypomastigotes (50 uM/24 h) and,to a lesser extent, epimastigote proliferation. Treatment of infected peritoneal macrophages with 12.5 uM chlorpromazine or triflupromazine inhibited the infection; this effect was found to be partially reversible if the drugs were removed after 24 h of treatment. At 60 uM, the drugs caused damage to amastigotes interiorized in heart muscle cells. However, the narrow margin of toxity between anti-trypanossomal activity and damage to host cells mitigates against in vivo investigation at the present time. Possible hypothesis for the mechanism of action of phenothiazines are discussed.

Macrophage activation and histopathological findings in Calomys callosus and Swiss mice infected with several strains of Trypanosoma cruzi

Peritoneal macrophage activation as measured by H2O2 release and histopathology was compared between Swiss mice and Calomys callosus, a wild rodent, reservoir of Trypanosoma cruzi, during the course of infection with four strains of this parasite. In mice F and Y strain infections result in high parasitemia and mortality while with silvatic strains Costalimai and M226 parasitemia is sub-patent, with very low mortality. H2O2 release peaked at 33,6 and 59 nM/2 x 10(elevado a sexta potência) cells for strains Y and F, respectively, 48 and 50 nM/2 x 10 (elevado a sexta potência) for strains Costalimai and M226, at different days after infection. Histopathological findings of myositis, myocarditis, necrotizing artheritis and abscence of macrophage parasitism were foud for strains F and Costalimai. Y strain infection presented moderate myocarditis and myositis, with parasites multiplying within macrophages. In C. callosus all four strains resulted in patent parasitemia wich was eventually overcome, with scarce mortality. H2O2 release for strains Y or F was comparable to that of mice-peaks of 27 and 53 nM/2 x 10 (elevado a sexta potência) cells, with lower values for strains Costalimai and M226 - 16.5 and 4.6 nM/2 x 10(elevado a sexta potência)cells, respectively. Histopathological lesions with Y and F strain injected animals were comparable to those of mice at the onset of infections; they subsided completely at the later stages with Y strain and partially with F strain infected C. callosus. In Costalimai infected C. callosus practically no histopathological alterations were observed.

Quantification of Trypanosoma cruzi in the heart, lymph nodes and liver of experimentally inffected mice, using limiting dilution analysis

Limiting dilution analysis was used to quantify Trypanosoma cruzi in the lymph nodes, liver and heart of Swiss and C57 B1/10 mice. The results showed that, in Swiss and B1/10 mice infected with T. cruzi Y strain, the number of parasites/mg of tissue increased during the course of the infection in both types of mice, although a grater number of parasites were observed in heart tissue from Swiss mice than from B1/10. With regard to liver tissue, it was observed that the parasite load in the initial phase of infection was higher than in heart. In experiments using T. cruzi Colombian strain, the parasite load in the heart of Swiss and B1/10 mice increased relatively slowly, although high levels of parasitization were nonetheless observable by the end of the infection. As for the liver and lymph nodes, the concentration of parasites was lower over the entire course of infection than in heart. Both strains thus maintained their characteristic tissue tropisms. The limiting dilution assay (LDA) proved to be an appropriate method for more precise quantification of T. cruzi, comparing favorably with other direct microscopic methods that only give approximate scores.

Trypanosoma cruzi recognition by macrophages and muscle cells: perspectives after a 15-year study

Macrophages and muscle cells are the main targets for invasion of Trypanosoma cruzi. Ultrastructural studies of this phenomenon in vitro showed that invasion occurs by endocytosis, with attachment and internalization being mediated by different components capable of recognizing epi-or trypomastigotes (TRY). A parasitophorus vacuole was formed in both cell types, thereafter fusing with lysosomes. Then, the mechanism of T. cruzi invasion of host cells (HC) is essentially similar (during a primary infection in the abscence of a specific immune response), regardless of wether the target cell is a professional or a non-professional phagocytic cell. Using sugars, lectins, glycosidases, proteinases and proteinase inhibitors, we observed that the relative balance between exposed sialic acid and galactose/N-acetyl galactosamine (GAL) residues on the TRY surface, determines the parasite's capacity to invade HC, and that lectin-mediated phagocytosis with GAL specificity is important for internalization of T. cruzi into macrophages. On the other hand, GAL on the surface to heart muscle cells participate on TRY adhesion. TRY need to process proteolytically both the HC and their own surface, to expose the necessary ligands and receptors that allow binding to, and internalization in the host cell. The diverse range of molecular mechanisms which the parasite could use to invade the host cell may correspond to differences in the available "receptors"on the surface of each specific cell type. Acute phase components, with lectin or proteinase inhibitory activities (a-macroglobulins), may also be involved in T. cruzi-host cell interaction.

Reversibility of muscle and heart lesions in chronic Trypanosoma cruzi infected mice after late trypanomicidal treatment

The effect of trypanomicidal treatment upon established histopathological Trypanosoma cruzi induced lesions was studied in Swiss mice. The animals were inoculated with 50 trypomastigotes and infection was allowed to progress without treatment for 99 days. After this period, the animals were divided in three groups, treated for 30 days with either placebo, benznidazole (200 mg/kg/day) or nifurtimox (100 mg/kg/day). These treatments induced 94 and 100 (per cent) cure rates respectively as detected by xenodiagnosis and reduction of antibody levels. Autopsies and histopathological studies of heart, urinary bladderand skeletal muscle performed on day 312 after infection showed almost complete healing without residual lesions. As long periods were allowed between infection, treatment and autopsy, the results indicate that tissue lesions depend, up to advances stages, on the continuous presence of the parasite.

Morphological aspects of the myocarditis and myositis in Calomys callosus experimentally infected with Trypanosoma cruzi: fibrogenesis and spontaneous regression of fibrosis

Calomys callosus a wild rodent, is a natural host of Trypanosoma cruzi. Twelve C. callosus were infected with 10(5) trypomastigotes of the F strain (a myotropic strain) of T. cruzi. Parasitemia decreased on the 21 st day becoming negative around the 40th day of infection. All animals survived but had positive parasitological tests, until the end of the experiment. The infected animals developed severe inflammation in the myocardium and skeletal muscle. This process was pronounced from the 26 th to the 30th day and gradually subsided from the 50 th day becoming absent or residual on the 64 th day after infection. Collagen was identified by the picro Sirius red method. Fibrogenesis developed early, but regression of fibrosis occurred between the 50th and 64th day. Ultrastructural study disclosed a predominance of macrophages and fibroblasts in the inflammatory infiltrates, with small numbers of lymphocytes. Macrophages had active phagocytosis and showed points of contact with altered muscle cells. Different degrees of matrix expansion were present, with granular and fibrilar deposits and collagen bundles. These alterations subsided by the 64th days. Macrophages seem to be the main immune effector cell in the C. callosus model of infection with T. cruzi. The mechanisms involved in the rapid fibrogenesis and its regression deserve further investigation.

In vivo differentiation of Trypanosoma cruzi - 1. Experimental evidence of the influence of vector species on metacyclogenesis

Vector species has not hitherto been studied as influencing metacyclogenesis of Trypanosoma cruzi, while the role of the parasite strain has been frequently stressed as of dominant importance in this process. In order to fill this gap in our knowledge, metacyclogenesis was monitored in nine triatomine species. The first part of this paper presents photographs of the main and intermediate parasite stages in each vector species studied. In the second part of the study the proportional distribution of all these forms, as seen in Giemsa stained smears is summarized, thus providing an opportunity to analyze both: the length of time between the ingestion of the blood trypomastigotes and the appearance of metacyclic forms and the rates of developmental stages leading to these latter. The most remarkable observation was that metacyclogenesis rates in vivo appear to be vector dependent, reaching 50 in Rhodnius neglectus, 37 in its congener R. prolixus and being dramatically lower in the majority of Triatoma species (5 in T. sordida, 3 in T. brasiliensis and 0 in T. pseudomaculata) at the 120th day of infection. These observations suggest that through screening of different vector species it is possible to find some that are capable of minimizing or maximizing metacyclic production.

Inter-relation of sylvatic and domestic transmission of Trypanosoma cruzi in areas with and without domestic vectorial transmission in Minas Gerais, Brazil

During the period 1980-1986, we captured triatomine bugs and mammalian reservoir hosts from sylvatic and domestic situations in different municipalities of the State of Minas Gerais. Trypanosoma cruzi was isolated from captured bugs, mammals and patients. After cultivation in LIT medium, the electrophoretic enzyme profiles were determined. We obtained atotal of 32 parasite isolates from regions with active domestic transmission, and 24 isolates form areas under control. For the first areas the results suggest introduction of T. cruzi from sylvatic habitats, through incursion of infected opossums and/or sylvatic T. sordida, which appears to have given rise to at least one acute human infection. Of particular interest is the finding of sylvatic opossums and a T. sordida nymph infected with ZB, that could indicate return of parasites from chronic human infections to sylvatic transmission cycles. For the areas under control we also interpret the results as interaction between sylvatic and domestic cycles of transmission, here through the invasion of houses by bugs carrying the Z1 zymodeme from the sylvatic environment. The Multivariate Correspondence Analysis gives a spatial description between the different parasite isolates and confirms the existence of a bridge in the opposite direction in the region with active vectorial transmission including the exporting of Z2 through the peridomestic environment into the sylvatic cycle. For the others areas this bridge corresponds especially to Panstrongylus megistus, importing Z1 into the domestic environment.

Interaction between Didelphis albiventris and Triatoma infestans in relation to Trypanosoma cruzi transmission

This paper attempts to prove if a high Trypanosoma cruzi prevalence of opossums might be reached with few potential infective contacts. One non-infected Didelphis albiventris to T. cruzi and 10 infected nymphs of Triatoma infestans were left together during 23 hr in a device that simulated a natural opossum burrow. Twenty-six replicates were perfomed using marsupials and triatomines only once. Potentially infective contacts occurred in all the trials. From the 26 opossums used in trials, 54% did not eat any bug. Of the 260 bugs used, 21% were predated. In the 25 trials involving 205 surving bugs, 36 % of them did not feed. In 15/25 cases, maior ou igual a 60% of the triatomines were able to feed. The parasitological follow-up of 24 opossums showed that among 10 that had eaten bugs, 4 turned out infected and among the 14 that had not predate, 3 (21%) became positive. In sum, 7/24 (29%) of the marsupials acquired the infection after the experiment. This infection rate was similar to the prevalences found for the opossum population of Santiago del Estero, Argentina, suggesting that the prevalences observed in the field might be reached if each marsupial would encounter infected bugs just once in its lifetime.

Complete immunization against Trypanosoma cruzi verified in individual mice by complement-mediated lysis

Experimental systems to assay immunity against Trypanosoma cruzi usually demonstrate partial resistance without excluding the establishment of sub-patent infections in protected animals. To test whether Swiss mice immunized with attenuated parasites might develop complete resistance against virulent T. cruzi, experiments were performed involving challenge with low numbers of parasites, enhancement of local inflammation and the combination of natural and acquired resistance. Absence of infection was established after repeated negative parasitological tests (including xenodiagnosis and hemoculture), and lack of lytic antibody was tested by complement mediated lysis. Immunization with 10(7) attenuated epimastigotes conferred protection against the development of high levels of parasitemia after challenge with Tulahuen strain, but was unable to reduce the number of infected animals. However, when a strong, delayed-type hypersensitivity reaction was triggered at the site of infection by injecting a mixture of virulent and attenuated T. cruzi, a significant proportion of immunized animals remained totally free of virulent infection. The same result was obtained when the immunization experiment was performed in four month old Swiss mice, displaying a relatively high natural resistance and challenged with wild, vector-borne parasites. These experiments demonstrate that complete resistance against T. cruzi can be obtained in a significant proportion of animals, under conditions which replicate natural, vector delivered infection by the parasite.

Trypanosoma cruzi strains and autonomic nervous system pathology in experimental chagas disease

Lesions involving the sympathetic (para-vertebral ganglia) and para-sympathetic ganglia of intestines (Auerbach plexus) and heart (right atrial ganglia) were comparatively analyzed in mice infected with either of three different strain types of Trypanosoma cruzi, during acute and chronic infection, in an attempt to understand the influence of parasite strain in causing autonomic nervous system pathology. Ganglionar involvement with neuronal destruction appeared related to inflammation, which most of the times extended from neighboring adipose and cardiac, smooth and striated muscular tissues. Intraganglionic parasitism was exceptional. Inflammation involving peripheral nervous tissue exhibited a focal character and its variability in the several groups examined appeared unpredictable. Although lesions were generally more severe with the Y strain, comparative qualitative study did not allow the conclusion, under the present experimental conditions, that one strain was more pathogenic to the autonomic nervous system than others. No special tropism of the parasites from any strain toward autonomic ganglia was disclosed.