Seroprevalence and risk factors for Trypanosoma cruzi infection in the Amazon region of Ecuador.

Trypanosoma cruzi infection in the Ecuadorian Amazon region has recently been reported. A seroepidemiologic survey conducted in four provinces in this region indicates a seroprevalence rate of 2.4% among the 6,866 samples collected in 162 communities. Among children < OR = 10 years of age, 1.2% were seropositive. Risk factors for T. cruzi seropositivity were having been born and remaining in the Ecuadorian Amazon provinces, age, living in a house with a thatch roof and open or mixed wall construction, recognizing the vector insects, and reporting being bitten by a triatomine bug. These data suggest active transmission of Chagas' disease in the Ecuadorian Amazon region is associated with poor housing conditions, and highlight the need for further studies aimed at understanding the biology of the insect vectors, reservoir species, and the clinical impact of T. cruzi infection as the basis for future educational and control programs in this region.

Modeling disease vector occurrence when detection is imperfect: infestation of Amazonian palm trees by triatomine bugs at three spatial scales.

BACKGROUND: Failure to detect a disease agent or vector where it actually occurs constitutes a serious drawback in epidemiology. In the pervasive situation where no sampling technique is perfect, the explicit analytical treatment of detection failure becomes a key step in the estimation of epidemiological parameters. We illustrate this approach with a study of Attalea palm tree infestation by Rhodnius spp. (Triatominae), the most important vectors of Chagas disease (CD) in northern South America. METHODOLOGY/PRINCIPAL FINDINGS: The probability of detecting triatomines in infested palms is estimated by repeatedly sampling each palm. This knowledge is used to derive an unbiased estimate of the biologically relevant probability of palm infestation. We combine maximum-likelihood analysis and information-theoretic model selection to test the relationships between environmental covariates and infestation of 298 Amazonian palm trees over three spatial scales: region within Amazonia, landscape, and individual palm. Palm infestation estimates are high (40-60%) across regions, and well above the observed infestation rate (24%). Detection probability is higher ( approximately 0.55 on average) in the richest-soil region than elsewhere ( approximately 0.08). Infestation estimates are similar in forest and rural areas, but lower in urban landscapes. Finally, individual palm covariates (accumulated organic matter and stem height) explain most of infestation rate variation. CONCLUSIONS/SIGNIFICANCE: Individual palm attributes appear as key drivers of infestation, suggesting that CD surveillance must incorporate local-scale knowledge and that peridomestic palm tree management might help lower transmission risk. Vector populations are probably denser in rich-soil sub-regions, where CD prevalence tends to be higher; this suggests a target for research on broad-scale risk mapping. Landscape-scale effects indicate that palm triatomine populations can endure deforestation in rural areas, but become rarer in heavily disturbed urban settings. Our methodological approach has wide application in infectious disease research; by improving eco-epidemiological parameter estimation, it can also significantly strengthen vector surveillance-control strategies.