Chagas disease vector control through different intervention modalities in endemic localities of Paraguay.
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In a field study carried out in three rural communities in Paraguay in a zone endemic for Chagas disease, we implemented three different vector control interventions--spraying, housing improvement, and a combination of spraying plus housing improvement--which effectively reduced the triatomine infestation. The reduction of triatomine infestation was 100% (47/47) in the combined intervention community, whereas in the community where housing improvement was carried out it was 96.4% (53/55). In the community where fumigation alone was used, the impact was 97.6% (40/41) in terms of domiciliary infestation. In all the houses where an intervention was made, an 18-month follow-up showed reinfestation rates of less than 10%. A serological survey of the population in the pre- and post-intervention periods revealed a shift in positive cases towards older age groups, but no significant differences were observed. The rate of seroconversion was 1.3% (three new cases) in the community with housing improvement only, but none of these cases could have resulted from vector transmission. The most cost-effective intervention was insecticide spraying, which during a 21-month follow-up period had a high impact on triatomine infestation and cost US$ 29 per house as opposed to US$ 700 per house for housing improvement. (+info)
Epidemiology of hookworm infection in Itagua, Paraguay: a cross sectional study.
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A cross-sectional study in Itagua, Paraguay tested 192 people for the presence, intensity and species of hookworm infection. Fifty-nine percent of these individuals were found to be infected. Intensity of infection was determined on 92% of infected individuals by quantitative egg counts. The high intensity hookworm infections, which cause the greatest morbidity, were clustered between the ages of five and 14 years. No differences were seen between genders. The species of hookworm was determined for parasites reared from 72% of infected individuals. Both Necator americanus and Ancylostoma duodenale were identified, although the former species predominated. We conclude that hookworm infection continues to be a public health problem in Paraguay, particularly among children and adolescents who suffer from high intensity infections. A. duodenale continues to persist in the Western Hemisphere and has not been completely displaced by N. americanus. (+info)
Genetic characterization of soybean rhizobia in Paraguay.
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The soybean is an exotic plant introduced in Paraguay in this century; commercial cropping expanded after the 1970s. Inoculation is practiced in just 15 to 20% of the cropping areas, but root nodulation occurs in most sites where soybeans grow. Little is known about rhizobial diversity in South America, and no study has been performed in Paraguay until this time. Therefore, in this study, the molecular characterization of 78 rhizobial isolates from soybean root nodules, collected under field conditions in 16 sites located in the two main producing states, Alto Parana and Itapua, was undertaken. A high level of genetic diversity was detected by an ERIC-REP-PCR analysis, with the majority of the isolates representing unique strains. Most of the 58 isolates characterized by slow growth and alkaline reactions in a medium containing mannitol as a carbon source were clustered with strains representative of the Bradyrhizobium japonicum and Bradyrhizobium elkanii species, and the 16S ribosomal DNA (rDNA) sequences of 5 of those isolates confirmed the species identities. However, slow growers were highly polymorphic in relation to the reference strains, including five carried in commercial inoculants in neighboring countries, thus indicating that the Paraguayan isolates might represent native bradyrhizobia. Twenty isolates highly polymorphic in the ERIC-REP-PCR profiles were characterized by fast growth and acid reactions in vitro, and two of them showed high 16S rDNA identities with Rhizobium genomic species Q. However, two other fast growers showed high 16S rDNA identity with Agrobacterium spp., and both of these strains established efficient symbioses with soybean plants. (+info)
trans-sialidase inhibition assay, a highly sensitive and specific diagnostic test for Chagas' disease.
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For the diagnosis of Chagas' disease, the trans-sialidase inhibition assay was able to resolve the results for samples with borderline results, to detect as positive 60% of samples that were negative by conventional serology, and to discriminate idiopathic from chagasic megaviscera or cardiopathy. No cross-reaction with sera from patients with other diseases was observed. (+info)
Prediction of colonization by macrophytes in the Yacireta reservoir of the Parana River (Argentina and Paraguay).
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The potential colonization by anchored plants (PCAP) and the potential areas for initial colonization of free floating plants were estimated during the early filling phase for the Yacireta reservoir. In order to obtain the PCAP, the observed maximum depth of colonization of the anchored macrophytes before impoundment and the hypsographic curves were used. The species inhabiting the pre-impoundment area were classified according to the different bioforms before the inclussion in the analysis. The areal extent of PCAP (from depths between 0-4 m) could reach 275 km2 at 76 m above sea level (current water level), whereas at 82 m above sea level (final filling level) the littoral zone will be increased by about 21.5%. The potential area for geophytes was estimated to be 99 km2; 131 km2 for root-floating leaved plants and 120 km2 for submerged plants, at 76 m above sea level. At 82 m above sea level, the geophytes could reach 271 km2. The data for wind frequency, velocity and fetch, together with depth were used to calculate shallow and sheltered areas in which free floating plants could find favourable conditions to initial colonization. Physical and chemical features recorded at eight stations during the early filling phase are discussed in relation to potential plant development. (+info)
Isoenzyme profiles of Trypanosoma cruzi stocks from different areas of Paraguay.
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Twenty one Trypanosoma cruzi stocks from humans, domiciliary triatomines and one sylvatic animal of different areas of Paraguay were subjected to isoenzyme analysis. Thirteen enzyme systems (15 loci in total) were studied. MN cl2 (clonets 39) and SO34 cl4 (clonets 20) were used as references. Relationships between stocks were depicted by an UPGMA dendrogram constructed using the Jaccard's distances matrix. Among the Paraguayan stocks 14 zymodemes were identified (Par1 to Par14), Par 5 being the most frequent. Polymorphism rate and clonal diversity were 0.73 and 0.93, respectively. Average number of alleles per polymorphic locus was 2.5 (range 2-4). These measurements show a high diversity, which is confirmed by the dendrogram topology. All stocks belong to the same lineage, as MN cl2 reference strain (T. cruzi II). Moreover three distinct subgroups were identified and two of them correspond to Brazilian and Bolivian zymodemes, respectively. The third subgroup, the most common in Paraguay, is related to Tulahuen stock. The large geographical distribution of some zymodemes agrees with the hypothesis of clonality for T. cruzi populations. However sample size was not adequate to detect genetic recombination in any single locality. (+info)
Chagas disease prevention through improved housing using an ecosystem approach to health.
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This Chagas disease prevention project via housing improvement aims to determine the efficiency of different interventions in vector control. The following study describes the target communities, disease magnitude, and housing improvements. Transmission levels are analysed from an ecological and socioeconomic perspective. Special interest was focused on the peridomicile as the origin of domiciliary reinfestation. In the original project, three intervention programs were proposed, one for each of the three communities: (a) an insecticide spraying program; (b) a housing improvement program; and (c) a combined program of spraying and housing improvement. The three communities currently have different risks of exposure to triatominae reinfestation as a consequence of the type of intervention carried out. A new multidisciplinary approach which integrates participatory, community-based research and socioeconomic dimensions will allow to determine the efficiency of models for territorial ordering, community education, and environmental interventions in Chagas disease control. (+info)
Patterns of infection with Laguna Negra virus in wild populations of Calomys laucha in the central Paraguayan chaco.
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In 1995, an outbreak of hantavirus pulmonary syndrome occurred in the central Paraguayan chaco. The primary reservoir of the virus, Laguna Negra virus, was identified as the vesper mouse, Calomys laucha. Over a 15-month period, we collected 1,090 small mammals at 12 locations representing 4 habitats common in the central Paraguayan chaco. Calomys laucha was common in agricultural habitats and uncommon in the native forest habitat. Populations of C. laucha were greater during the dry season months and declined during the wet season. A total of 643 small mammals were tested for antibodies cross-reactive to Sin Nombre virus. All of the antibody-positive animals were C. laucha (crude antibody prevalence ratio 12.1% [25 of 206]). Antibody prevalence ratio increased with body size and was more common among male (18%; n = 115) than among female (4%; n = 96) vesper mice. Antibody prevalence ratio was highest among animals from cropland habitats (18%; n = 72), followed by thorn scrub (13%; n = 46) and pastureland (7%; n = 81) and may be positively correlated to the proportion of C. laucha in the small mammal community. These data suggest that community-level dynamics, in addition to population-level dynamics, may be involved in the transmission of the virus through natural populations of vesper mice. (+info)