Showing papers by "Oswaldo Cruz Foundation published in 1994"
Journal Article•
TL;DR: The rapid staining protocol significantly decreases the processing time required for silver-stained polyacrylamide gels, which is of particular importance in diagnostic situations, and allows individual bands from complex mixtures to be easily recovered for sequencing or probe preparation.
Abstract: A rapid silver-staining procedure for DNA fragments in polyacrylamide gels is described. The time required for band detection is 15 min and the limit of sensitivity 3 pg/mm2. PCR products subjected to this rapid staining protocol are readily recovered from the gel by excision and elution by incubation at 95 degrees C for 20 min. Bands of up to 3 kb have been recovered and reamplified from either recently prepared or dried gels. The rapid staining protocol significantly decreases the processing time required for silver-stained polyacrylamide gels, which is of particular importance in diagnostic situations. The recovery protocol allows individual bands from complex mixtures to be easily recovered for sequencing or probe preparation.
1,175 citations
TL;DR: Leishmania braziliensis and L. naiffi were shown to be the most polymorphic species, while L. guyanensis, in spite of being the most common species found in this study, was remarkably homogeneous.
Abstract: More than 250 strains of Leishmania isolated from different localities and hosts in the New World were analyzed by enzyme electrophoresis, and their electromorphic profiles were compared with 19 reference strains representing most of the described species of this parasite. The 18 enzymic loci analyzed were very polymorphic, and the strains were classified into 44 zymodemes, each grouping strains with the same enzyme profiles. Each zymodeme was considered as an elementary taxon and the phenetic and phylogenetic relationships were determined by agglomerative hierarchical, ordination, and cladistic techniques. The different classification methods produced very similar results. The 44 zymodemes could be clustered into two groups, corresponding to the subgenera Leishmania and Viannia, by the numerical methods. The subgenus Viannia was shown to be monophyletic and could be further divided into species complexes representing L. braziliensis, L. naiffi, and L. guyanensis/L. panamensis/L. shawi, as well as some isolated taxa including L. lainsoni. The subgenus Leishmania, on the other hand, was polyphyletic, with New World isolates related to L. major clustered separately from the L. mexicana species complex. Most of the other zymodemes in this group represented independent taxa. The results confirm Viannia as a valid taxon but suggest that the status of the subgenus Leishmania should be further investigated. Leishmania braziliensis and L. naiffi were shown to be the most polymorphic species, while L. guyanensis, in spite of being the most common species found in this study, was remarkably homogeneous. The only variants were found south of the Amazon river. North of this river, the species was monomorphic.
344 citations
TL;DR: The results suggest that the PCR may be a useful complement to serology in the diagnosis of Chagas' disease, and that it is the most powerful technique available for parasite detection in patients with chronic disease.
Abstract: The feasibility of using DNA amplification by the polymerase chain reaction (PCR) for specific detection of Trypanosoma cruzi in human blood specimens was investigated. One hundred blood samples were collected in an endemic area of Minas Gerais, Brazil. They were submitted to DNA extraction and PCR amplification with kinetoplast DNA-specific primers using a simplified boiling procedure that linearized most minicircle molecules without the aid of chemical reagents. Samples that gave negative results were checked for possible inhibition of amplification using primers derived from a human-specific sequence, and those showing some level of inhibition were retested after a new DNA extraction. Of 86 patients previously diagnosed as chagasic by serologic techniques, 83 were positive in our PCR test (sensitivity = 96.5%), including all the xenodiagnosis-positive patients and 21 (87.5%) of 24 xenodiagnosis-negative individuals. In addition, four of six patients with doubtful serologic results were confirmed as positive by PCR. Our results suggest that the PCR may be a useful complement to serology in the diagnosis of Chagas' disease, and that it is the most powerful technique available for parasite detection in patients with chronic disease.
266 citations
TL;DR: Different molecular targets used in the laboratory, aiming at the detection and specific typing of these protozoa, including kinetoplast and nuclear targets are described and the results obtained from their use are reported.
Abstract: The use of molecular tools to detect and type Leishmania species in humans, reservoirs or sandflies has been pursued using different approaches. The polymerase chain reaction provided sensitivity to case this task, since the use of hybridization procedures alone employing specifics probes is hampered due to the low detection limit. In this report, we describe the different molecular targets used in our laboratory, aiming at the detection and specific typing of these protozoa. Different kits based on hybridization assays and PCR amplification using kinetoplast and nuclear targets are described and the results obtained from their use are reported.
214 citations
TL;DR: Rotavirus serotype G5 in fecal specimens of 38 Brazilian children with diarrhea was identified by PCR and enzyme immunoassays and exhibited long RNA electropherotypes and either subgroup II or nonsubgroup I-nonsubgroup II specificities.
Abstract: Rotavirus serotype G5 in fecal specimens of 38 Brazilian children with diarrhea was identified by PCR and enzyme immunoassays The strains exhibited long RNA electropherotypes and either subgroup II or nonsubgroup I-nonsubgroup II specificities Serotype G5 has been found in piglets and horses but not yet in humans Images
210 citations
TL;DR: The relevance, specificity, and potential of the anthropological approach to health and illness, as complementary to other approaches that currently deal with public health problems, are discussed.
Abstract: This paper discusses the relevance, specificity, and potential of the anthropological approach to health and illness. Medical anthropology is shown as complementary to other approaches that currently deal with public health problems. The impact of social and cultural factors on health-related perceptions and behaviors is illustrated and commented. A conceptual and methodological framework is also proposed to systematize the study of representations and practices of communities in the area of public health. The specific contribution of the anthropological approach is discussed in terms of the effectiveness of public health programs.
151 citations
TL;DR: DNA sequence analysis of the cloned products reveals high conservation of both the exon and intron of Leishmania strains, and variation is evident in both the length and primary sequence of the non-transcribed spacers of the mini-exon genes.
150 citations
TL;DR: Brazilian HIV-1 B strains may have important antigenic differences from prototype subtype B strains currently being evaluated for use in HIV vaccines, suggesting that future vaccine programs in Brazil should be taken into account.
Abstract: Viral DNA sequences were determined over the V3 region of env from 28 infected individuals living in the high HIV-1 prevalence Brazilian cities of Rio de Janeiro and Sao Paulo. Twenty-six belonged to envelope sequence subtype B, prevalent in North America and Europe, and one was classified as subtype F, found recently in Brazil and in Romania (one appeared to be a B/F recombinant). Octameric sequences at the tip of the subtype B V3 loops were variable and distinct from those prevalent in North America and Europe. The GPGR motif, prevalent in North American/European strains, was found in only 8 (28.5%) sequences, whereas GWGR was found in 12 (43%) and novel sequences in 8 (28.5%). Brazilian subtype B sequences also diverged from the consensus North American/European strains over the remainder of the V3 loop. These results suggest that Brazilian HIV-1 B strains may have important antigenic differences from prototype subtype B strains currently being evaluated for use in HIV vaccines. These results should be taken into account for future vaccine programs in Brazil.
149 citations
TL;DR: Patients suffering from American cutaneous leishmaniasis showed an increase in the percentage of CD8+ blast T cells and a decline in the proportion of CD4+ Blast T cells in cultures and the levels of gamma interferon in T-cell culture supernatants showed a tendency to increase when the patients were cured.
Abstract: Fourteen patients suffering from American cutaneous leishmaniasis were studied. Assays of the lymphocyte proliferative response induced in vitro by Leishmania braziliensis antigens were performed. After 5 days in culture, L. braziliensis-stimulated blast T cells were harvested for CD4+ and CD8+ phenotype analysis. When results before and at the end of therapy were compared, leishmaniasis patients showed an increase in the percentage of CD8+ blast T cells and a decline in the proportion of CD4+ blast T cells in cultures. The levels of gamma interferon in T-cell culture supernatants showed a tendency to increase when the patients were cured. These results show a pattern of higher proportions of Leishmania-reactive CD8+ T cells and lower proportions of Leishmania-reactive CD4+ T cells after cure.
136 citations
TL;DR: Data is reviewed showing that peptidic hormones and neuropeptides can influence the thymus pleiotropically, and such neuroendocrine influences appear to be part of a bidirectional circuitry, since thymic-derived peptides also regulate the release of hormones from the pituitary and hypothalamus.
121 citations
TL;DR: A pesquisa analisou a atuacao dos Centros Regionais de Atencao aos MausTratos na Infância (Cramis) no atendimento a criancas e adolescentes (e familiares) vitimas da violencia intrafamiliar.
Abstract: Este artigo efetua uma sintese parcial do estudo "Prevenir e Proteger: Analise de um servico de atencao a crianca vitima de violencia domestica". A pesquisa analisou a atuacao dos Centros Regionais de Atencao aos MausTratos na Infância (Cramis) no atendimento a criancas e adolescentes (e familiares) vitimas da violencia intrafamiliar. Buscou-se um dialogo teorico-metodologico entre as abordagens quantitativa e qualitativa, focalizando a estrutura, os processos e as representacoes presentes na atuacao dos Cramis, alem da caracterizacao das familias atendidas no periodo de 1988 a 1992. Apresenta-se como resultado o perfil dessas familias, bem como o perfil de atuacao dos servicos. Diante dos dados analisados, discute-se a potencial contribuicao da experiencia dos Cramis a implementacao de acoes no sistema publico de saude.
TL;DR: Increased levels of activated T cells and CD5+ B cells are present in the circulation of people with chronic Chagas' disease, which are cell phenotypes that have been associated in other conditions with autoimmune, polyclonal, and hyperimmune responses.
Abstract: Whole blood preparations from patients with either the indeterminate (asymptomatic) or cardiac clinical forms of chronic Trypanosoma cruzi infection were analyzed by flow cytometry using double-labeling to identify subsets of circulating lymphocytes. Several significant differences were demonstrated between the blood lymphocyte profiles of chagasic patients and non-chagasic controls. Clear increase in the percentages and actual numbers of double-positive cells of the phenotype CD3+/HLA-DR+, as well as decrease in the percentage of CD45RA+/CD4+ and CD45RA+/CD8+ T cells, indicate greater numbers of activated T cells circulating in the blood of infected patients. Consistent parallel increases were seen also in the B lymphocyte subset which stained double-positive for CD19/CD5. There were no significant differences in the circulation of these chronic chagasic patients in the CD4:CD8 ratios. Also, no substantive phenotypic differences were observed in the lymphocyte populations between the two ends of the clinical spectrum (indeterminate versus cardiac) in chronic human Chagas' disease. These observations demonstrate that increased levels of activated T cells and CD5+ B cells are present in the circulation of people with chronic Chagas' disease. These are cell phenotypes that have been associated in other conditions with autoimmune, polyclonal, and hyperimmune responses. The specificities of these activated cells and the roles they may play in resistance or pathogenesis during chronic Chagas' disease need now to be determined.
TL;DR: This study evaluated production of interferon gamma in vitro by schistosome antigen-stimulated peripheral blood mononuclear cells from asymptomatic patients, and by PBMCs from apparently uninfected, untreated persons living in areas endemic for Schistosoma mansoni ('endemic normals').
Abstract: During human schistosomiasis host responses to antigens of various parasite life-cycle stages may contribute to whether the severe, hepatosplenic state develops or the patient remains relatively asymptomatic throughout infection, and may play a role in resistance. This study evaluated production of interferon gamma (IFN-gamma) in vitro by schistosome antigen-stimulated peripheral blood mononuclear cells (PBMCs) from asymptomatic patients, and by PBMCs from apparently uninfected, untreated persons living in areas endemic for Schistosoma mansoni ('endemic normals'). IFN-gamma production parallels PBMC proliferation in that schistosomal egg antigens stimulate patent patients' cells poorly, but strongly stimulate PBMCs from 'endemic normals'. This is proportionally true for antigens from adult worms and cercariae. Although asymptomatic patent patients' cells produced little or no IFN-gamma in response to the 3 schistosomal antigenic extracts, their PBMCs, and PBMCs from 'endemic normals', produced expected amounts of IFN-gamma when exposed to phytohaemagglutinin. This implies that persons with patent infections have schistosome antigen-specific defects in their ability to respond to IFN-gamma production that are not exhibited by putatively resistant 'endemic normals'.
TL;DR: Results suggest that PCR detection of T. cruzi DNA in blood can be a very useful complement to serology in Chagas' disease diagnosis in Bolivia.
Abstract: The detection of Trypanosoma cruzi kinetoplast DNA by polymerase chain reaction (PCR) amplification is a potentially powerful tool for the parasitological diagnosis of Chagas' disease. We have applied this technique in a field situation in Bolivia, where 45 children from a primary school were subjected to serological testing, buffy coat analysis and PCR diagnosis. 26 of the 28 serology-positive individuals were also positive by PCR. In addition, two serology-negative children gave a positive result by PCR, including one who was positive in the buffy coat test. These results suggest that PCR detection of T. cruzi DNA in blood can be a very useful complement to serology in Chagas' disease diagnosis in Bolivia.
TL;DR: Visceral leishmoniosis has recently become established in the peri-urban areas of the city of Rio de Janeiro and the factors involved in its establishment and propagation are considered, including environmental, human, social, economic and historical factors.
Journal Article•
TL;DR: The findings suggest that immune effector cells play a major role in the pathogenesis of the myocyte damage and the microangiopathy in acute Chagas' disease.
Abstract: Histological and ultrastructural studies of the hearts of dogs sacrificed 18 to 26 days after intraperitoneal inoculation with 4 x 10(5) blood forms of the 12 SF strain of Trypanosoma cruzi/kg of body weight disclosed myocarditis characterized by parasitic invasion of some myocytes, damage and necrosis of nonparasitized myocytes, and interstitial infiltration by mononuclear cells. Nonparasitized myocytes showed alterations ranging from mild edema to severe myocytolysis. These changes often were accompanied by contacts of myocytes with lymphocytes (both granular and agranular) and macrophages. These contacts were characterized by focal loss of the myocyte basement membrane and close approximation of the plasma membranes of the two cells. Contacts between lymphocytes and capillary endothelial cells were also frequent. Platelet aggregates and fibrin microthrombi were observed in some capillaries. Our findings suggest that immune effector cells play a major role in the pathogenesis of the myocyte damage and the microangiopathy in acute Chagas' disease.
TL;DR: The results showed a large genetic variability of Brazilian strains, with the number of different restriction patterns of strains isolated in Rio de Janeiro was at least as large as that of the reference strains isolate in the rest of the world.
Abstract: Hepatitis B virus (HBV) genomes have been classified into six groups, A-F, group F being the most divergent. South America has provided the smallest number of strains studied at the genome level. The only HBV strain from this region sequenced completely has been classified in group F, and contains the most divergent of the HBV genomes presently known [Naumann et al. (1983): Journal of General Virology 74:1627-1632]. To evaluate genetic relatedness between strains isolated in South America and in the rest of the world, a restriction endonuclease analysis was carried out on 14 HBV strains (4 adw2, 3 adw4, 3 ayw2, and 4 ayw3) isolated in Rio de Janeiro, Brazil. C, pre-S, and X genes along with the 5' part of the P gene from these strains were amplified by the polymerase chain reaction. The DNA fragments were digested by BamHI, BstEII, EcoRI, HhaI, and TaqI endonucleases. The restriction patterns obtained were compared with those deduced from the nucleotide sequence of 26 HBV strains isolated in other continents. The results showed a large genetic variability of Brazilian strains. Taking into account that all the samples examined possessed the w antigenic subdeterminant, the number of different restriction patterns of strains isolated in Rio de Janeiro was at least as large as that of the reference strains isolated in the rest of the world. Some original restriction patterns were found in adw4 and ayw2 HBV strains.
TL;DR: The scope of this investigation has been widened to also include morphometric data on the parasites, to further simplify their identification, since the presence of helminths in laboratory animals is regarded as a restricting factor for the proper attainment of experimental protocols.
Abstract: The spectrum of intestinal parasites present in the Swiss Webster, C57B1/6 and DBA/2 mice strains from different animal houses was identified and prevalences compared. Three parasites were observed during the course of this study, namely the cestode Vampirolepis nana (Siebold, 1852) Spasskii, 1954 (= Hymenolepis nana) and the nematodes Aspiculuris tetraptera (Nitzsch, 1821) Schultz, 1924 and Syphacia obvelata (Rudolphi, 1802) Seurat, 1916. The scope of this investigation has been widened to also include morphometric data on the parasites, to further simplify their identification, since the presence of helminths in laboratory animals is regarded as a restricting factor for the proper attainment of experimental protocols.
TL;DR: The great variety of polymorphic genetic markers identified in this restricted survey indicates that RAPD analysis may make a major contribution to the study of the genetics of Biomphalaria.
TL;DR: Sex and twinning of affected infants and fetuses, according to type of neural tube defect (NTD), varied by type of NTD, vital status at birth, presence of associated malformations, and year of birth, with an increasing sex ratio for anencephaly during the 1960s and 1970s.
Abstract: The goal of this study, based on information collected from eight congenital malformation registry programs around the world, was to analyze sex and twinning of affected infants and fetuses, according to type of neural tube defect (NTD) and other variables. The type of defect and its location, whether it occurred in isolated form or was associated with other malformations, population from which data were retrieved, vital status of the infant, and gestational age of the fetus/infant were considered. The material included 3,416 infants and 168 selectively aborted fetuses with anencephaly, 4,830 infants and 76 fetuses with spina bifida, and 1,022 infants and 19 fetuses with encephalocele. Less than 20% of infants with anencephaly or spina bifida and more than one-third of infants with encephalocele had associated malformations. A female excess was found among all infants with NTD but a male excess in fetuses delivered spontaneously before week 20, indicating selective male late fetal deaths. Sex ratio varied by type of NTD, vital status at birth, presence of associated malformations, and year of birth, with an increasing sex ratio for anencephaly during the 1960s and 1970s. Twinning was positively associated with NTD but the extent of this association varied with NTD type and program, while the distribution by sex type of pair of twin appeared to be similar to that of all births. Twins concordant for anencephaly or encephalocele were mainly found when the defect occurred as part of a syndrome, and only in like-sexed pairs. Twins concordant for spina bifida had the isolated form of the defect and 5 of 6 pairs were like-sexed.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: An "attack" of wild triatomines (Rhodnius brethesi) topiacaca workers (Leopoldinia piacaba) is confirmed in the locality of Acuquaia, at Padauari river, affluent of Rio Negro in the municipality of Barcelos, Brazil.
Abstract: An "attack" of wild triatomines (Rhodnius brethesi) topiacaca workers (Leopoldinia piacaba) is confirmed in the locality of Acuquaia, at Padauari river, affluent of Rio Negro in the municipality of Barcelos, State of Amazonas, Brazil. A serological prevalence of 12.5% for T. cruzi antibodies in human population, in the city of Barcelos, has already been described in a previous paper. A strong association between the serological positivity and the population contact with wild triatomines, known in the area as "piacava's lice", was verified.
TL;DR: Investigation of biosynthesis, enzymatic processing, and immunocytochemical localization of an abundant developmentally regulated cysteine proteinase of Leishmania pifanoi, Lpcys2, indicated that proteolytic activity is associated with the intermediate form as well as the mature proteinase, and cleavage of the COOH-terminal domain probably occurs in the megasome.
TL;DR: Salivary infection of T. rangeli impairs the ability of the vector to locate blood vessels by affecting salivary antihemostatic properties, thus enhancing the possibility of intradermal inoculation of parasites into the mammalian host.
TL;DR: The results indicate that the occurrence of systemic and local adverse reactions was unrelated to either the dose of DEC or the pretreatment microfilarial density, and side effects were dependent on the drug dosage irrespective of infection status.
Abstract: To determine the tolerance to diethylcarbamazine (DEC) treatment of patients with Bancroftian filariasis, 193 individuals (138 asymptomatic microfilaraemic, 30 amicrofilaraemic diseased patients and 25 asymptomatic amicrofilaraemic endemic residents) were enrolled in a prospective trial with different dose schedules, in a hospital and outpatient clinic setting in Brazil. Systemic adverse reactions, localized adverse reactions, and side effects, related to microfilariae, adult worms and the drug itself, were evaluated. Systemic reactions occurred irrespective of the DEC dose and schedule in about 40% of the microfilariae carriers, but not in amicrofilaraemic diseased patients or residents; they usually consisted of microscopic haematuria, followed by fever and malaise. Localized reactions were manifested by the appearance of inflammatory reactions, mainly in the scrotal area. Nodules containing degenerating adult worms developed mainly in the scrotal lymphatics of microfilaraemic patients, diseased amicrofilaraemic patients, and residents. Drowsiness, which increased with higher doses of DEC, was the most common side effect in both microfilaraemic and amicrofilaraemic individuals, followed by nausea and gastric upset. The results indicate that the occurrence of systemic and local adverse reactions was unrelated to either the dose of DEC or the pretreatment microfilarial density. The severity of systemic reactions was proportional to the microfilarial density. Side effects were dependent on the drug dosage irrespective of infection status.
TL;DR: The authors revalidate the genus Mepraia, described in 1940 by Mazza, Gajardo & Jorg, which is monotypic and represented by the species M. spinolai (Porter, 1934).
Abstract: The authors revalidate the genus Mepraia, described in 1940 by Mazza, Gajardo & Jorg. The genus is monotypic and represented by the species M. spinolai (Porter, 1934). Based on the characteres described below the authors considered the separation of the genus Triatoma Laporte, 1832 and the return of the genus Mepraia. Strongly alar polymorphism, the abdomen of female with connexivum like in genus Dipetalogaster Usinger 1939, seven testicular follicles, like in Triatoma, however with a different relation of lenghts; external male genitalia showing a big and foliar process of the conjunctiva, vesica with an arch-shape, struts and endosoma process absent.
TL;DR: Analysis of the frequency and distribution of several microsatellite DNAs in the genome of Leishmania showed an uneven distribution among heterologous chromosomes of the same strain, and specific polymerase chain reaction amplification of two cloned (CA)n loci demonstrated allelic size polymorphisms among strains within L. infantum and LeishMania donovani.
TL;DR: A survey of wild and domestic animals and monthly sandflies captures indicate a strong evidence on the vector and the potential reservoirs of L. braziliensis in this region.
Abstract: American cutaneous leishmaniasis (ACL) has been increasing in Pernambuco, thus becoming an important problem for Public Health. The incindence is predominant in the region called 'Zona da Mata', in the east of this state. This region corresponds geographically to the primitive area of the Atlantic forest. In order to characterize the eco-epidemiology expression of ACL in this region, two localities situated in the municipalities of Amaraji e Cortes have been selected by the criterion of higher incindence of human cases. Five stocks of patients were characterized and identified on the basis of enzyme profiles as a new variant of Leishmania (V.) braziliensis. A survey of wild and domestic animals was carried out by means of a parasitological and serological diagnosis. Through the analysis of the spleen and liver imprints, were detected amastigotes compatible with Leishmania in five Nectomys s. squamipes, five Bolomys 1. pixuna, two Rattus r. alexandrinus and one Rattus r. frugivorus. For two years we carried out monthly sandflies captures using CDC light traps as well as manual captures. Lutzomyia whitmani was predominant, which accounted for 97.4% of the total. These data indicate a strong evidence on the vector and the potential reservoirs of L. braziliensis in this region.
TL;DR: Risks that Chagas' disease will become endemic to the Amazon appear to be linked to the transposition of the wild cycle to the domestic cycle in that area or to transfer of the domestic Cycle from endemic areas to theAmazon.
Abstract: At least eighteen species of triatominae have been found in the Brazilian Amazon, nine of them naturally infected with Trypanosoma cruzi or "cruzi-like" trypanosomes and associated with numerous wild reservoirs. Despite the small number of human cases of Chagas' disease described to date in the Brazilian Amazon the risk that the disease will become endemic in this area is increasing for the following reasons: a) uncontrolled deforestation and colonization altering the ecological balance between reservoir hosts and wild vectors; b) the adaptation of reservoir hosts of T. cruzi and wild vectors to peripheral and intradomiciliary areas, as the sole feeding alternative; c) migration of infected human population from endemic areas, accompanied by domestic reservoir hosts (dogs and cats) or accidentally carrying in their baggage vectors already adapted to the domestic habitat. In short, risks that Chagas' disease will become endemic to the Amazon appear to be linked to the transposition of the wild cycle to the domestic cycle in that area or to transfer of the domestic cycle from endemic areas to the Amazon.
TL;DR: 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
Abstract: 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.