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R M Silva

Publications and source records attributed to R M Silva.

61 records · Page 4Linked to original sources
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Molecular motions in chitosan studied by dielectric relaxation spectroscopy.

Neutralized and nonneutralized chitosan films subject to different thermal treatments were studied by dielectric relaxation spectroscopy from -130 to +150 degrees C in the frequency range between 20 Hz and 1 MHz. Two main relaxation processes, both arrhenian type, were detected: process I at temperatures below 0 degrees C with a mean activation energy of 49 +/- 1 kJ mol(-1), which has the characteristics of a secondary relaxation process related with local chain dynamics, and process II observable at higher temperatures with an activation energy of 94 +/- 2 kJ mol(-1), correlated with dc conductivity, which is found in dried polysaccharides systems. Process I is always observed in neutralized chitosan, but it is strongly depleted in the wet nonneutralized form. Although the location of process I is independent of NH2/NH3+ side group, process II deviates to higher temperatures with dryness in both chitosan forms, being located at lower temperatures in nonneutralized chitosan.

Chitosan↗
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Dot-ELISA for the detection of IgM and IgG antibodies to Schistosoma mansoni worm and egg antigens, associated with egg excretion by patients.

Human schistosomiasis, caused by Schistosoma mansoni, is highly prevalent in Brazil and usually diagnosed by time consuming stool analysis. Serological tests are of limited use in this disease, mainly for epidemiological studies, showing no discrimination between previous contact with the parasite and active infections. In the present study, we standardized and compared a Dot-ELISA for IgM and IgG antibodies against S. mansoni antigens from eggs and worms with a routine IgG and IgM immunofluorescence assay using similar antigens, in the study of sera from 27 patients who had quantified egg stool excretion. The positivity obtained for IgG Dot-ELISA was 96.3% and 88.9% for IgM Dot-ELISA with worm antigen and 92.6% and 90.9% with egg antigen. The IFI presented similar positivities using worm antigen, 92.6% (IgG) and 96.3% (IgM), and lower results with egg antigen, 77.8%(IgG and IgM). The patients studied were divided into two groups according to their egg excretion, with greater positivity of serological tests in higher egg excreters. When comparing the quantitative egg excretion and the serological titers of the patients, we detected a correlation only with IgM Dot-ELISA, with r = 0.552 (p = 0.0127). These data show that Dot-ELISA can be used for the detection of specific antibodies against S. mansoni in sera from suspected patients or in epidemiological studies and, with further purification of egg antigen and larger samples, IgM Dot-ELISA could be a possible tool for rough estimates of parasite burden in epidemiological studies.

Adolescent↗
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[Enteropathogens associated with acute diarrheal disease in children]

OBJECTIVE: Aiming a better understanding of the distribution of enteropathogens in Brazil, we have investigated the prevalence of enteropathogens in acute infantile diarrhea in children of low economic level from São José do Rio Preto, SP.METHODS: A prospective study with 196 children under age five, all with diarrhea, and 33 control subjects was conducted at Hospital de Base de São José do Rio Preto during 1995. This Hospital is associated to a Medicine School and offers free assistance to patients of low economic level who live in the area. RESULTS: Enteropathogens were identified in 48% of the cases and 27% of the controls. Shigella species were isolated in 21% of the cases, EPEC in 10.7%, Salmonella species in 5.6%. The other enteropathogens studied represented 12 % of the isolate pathogens from case children. In the controls 18.2% of atypical EPEC were isolated. Isolation of Shigella species increased with increasing age of cases and peaked in spring, whereas EPEC was common in early infancy and peaked in spring and winter.CONCLUSIONS: Among São José do Rio Preto children, Shigella species and diarrheiogenic E. coli strains (EPEC, ETEC, EAggEC, EIEC) were isolated throughout the year as a cause of diarrhea bringing children to a medical attention. Most of the pathogens were isolated in spring (mainly Shigella and Salmonella), so the temperature and humidity of the environment must be very important.

Journal Article↗
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[Association of patterns of Escherichia coli adherence to HEp-2 cells with acute and persistent diarrhea].

In Brazil diarrhea is the cause of approximately 15% of death among infants. Enteropathogenic E coli is the most important bacterial agent causing acute diarrhea, which is defined as less than 14 days of duration. About 30% of these cases may evolve to persistent diarrhea, defined as lasting more than 14 days. In this work it was carried out a case-control study including 34 children under 2 years of age, and admitted to hospital facilities in São Paulo for rehydration therapy. Thirty-four age matched children hospitalized in the same facilities, and presenting no gastrointestinal symptoms were included as controls. Stool samples were analyzed for the presence of bacterial pathogens (diarrheagenic E coli, Shigella, Salmonella, Yersinia, and Campylobacter), protoparasytes, rotavirus, and enteric adenovirus. The E coli strains isolated were analyzed for their ability to adhere to HEp-2 cultured cells, in a 3 h adhesion assay. Search for homology with DNA probes for localized adherence (EAF, eaeA probes), AA (enteroagregative adherence) (AA probe), and diffuse adherence (F1845, AIDA-I probes) was carried out by the colony hybridization method. Twenty-four of the cases were acute diarrhea and 10 persistent diarrhea. Strains with localized adherence were associated with acute and persistent diarrhea. About 23.5% of E coli were associated with typical Enteropathogenic E coli strains (EAF+, eaeA+). Enteroaggregative E coli (EAggEC) (AA+) was isolated only from cases and in similar frequency for acute and persistent diarrhea. Diffusely adherent E coli (DAEC) which did not hybridize with the diffuse adherence probes were isolated among cases and controls. E coli eaeA+ with localized-like adherence was isolated from cases in a frequency three times higher than in controls, suggesting that it may really have a pathogenic potential.

Acute Disease↗
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[Serological and epidemiological features of canine American tegumentary Leishmaniasis from Maricá, Rio de Janeiro, Brazil].

A sample of 261 dogs from 134 households located in a periurban area of Maricá, Rio de Janeiro, Brazil, was studied to evaluate serologic reactions and active infection of american tegumentary leishmaniasis (ATL). Eight dogs presented lesions suggestive of ATL, but this was isolated in only three. Using ELISA, 24.5% (64/261) of the dogs studied were positive (sensitivity = 66% and specificity = 76%), associated with isolation in 2 animals and 0.4% (1/261) by indirect immunofluorescence assay (IIF) with no association with isolation. In order to reduce the unspecific reactions to ELISA, a second criterion was used to obtain the cutoff (sensitivity = 33% and specificity = 93%), resulting in a reactivity of 6.9 % (18/261) associated to isolation in a single animal. As observed in this study, serologic results by IIF were not associated with active infection and ELISA showed high unspecific reactions, indicating that the serologic reactions alone are not recommended for ATL diagnosis. ATL scars were been observed in 7 persons in the region and active lesion, under treatment, was observed in one patient. The finding of active lesions, either in dogs or humans, confirmed the existence of active tegumentary leishmaniasis in Maricá, indicating the need for further studies to evaluate the importance of this infection in the municipality.

Animals↗