Modeling Disease Vector Occurrence when Detection Is Imperfect: Infestation of Amazonian Palm Trees by Triatomine Bugs at Three Spatial Scales

Abstract

BackgroundFailure 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 FindingsThe 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 (∼0.55 on average) in the richest-soil region than elsewhere (∼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/SignificanceIndividual 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.

2 nd Brazilian Consensus on Chagas Disease, 2015

“…To this end, the understanding of the processes of habitat selection by triatomines is fundamental for the construction of epidemiological evidence, in order to plan and develop local systems of epidemiological surveillance and control, thus reinforcing the role of surveillance (22) (39) (82) . However, operational failures identified in the detection of vectors can generate critical classification errors and, therefore, prevent the scope of the actions, hampering the composition of scenarios and dynamics of these insects in their habitat (70) (71) (82) .…”

“…Assuming that no sampling technique is perfect, some studies in Brazil have applied methods that explicitly incorporate the failures in the detection of infestation foci in the research of the ecology and the surveillance of vectors of Chagas disease in different environments, including the Amazon and Northeast region (70) (71) (82) . This approach has and will increasingly enable future improvement of the estimates of eco-epidemiological indicators and may significantly strengthen the strategies for integrated monitoring and control of vectors (70) (71) (83) (84) .…”

Attraction of Chagas disease vectors (Triatominae) to artificial light sources in the canopy of primary Amazon rainforest

“…Flying from such ecotopes, adult specimens may enter a house or fall into a food-processing device; this is currently regarded as the main mechanism underlying Chagas disease epidemiology in Amazonia (Coura et al 2002, Aguilar et al 2007, Valente et al 2009). For instance, large peridomestic palm trees are often infested and can act as a major source of adventitious Rhodnius specimens in several Latin American biomes, including Amazonia (Romaña et al 1999, Fitzpatrick et al 2008, Gurgel-Gonçalves et al 2008, Abad-Franch et al 2010, Calzada et al 2010.…”

Enfermedad de Chagas y su seroprevalencia en tres departamentos de la Amazonia colombiana.

“…Debido al hallazgo de casos agudos en esta zona con alta intervención humana que produce deforestación. (2) La relación ecológica de palmeras que contienen colonias de vectores y la dinámica de transmisión a la población humana por vectores silvestres que invaden casas sin llegar a colonizarlas es un fenómeno bien establecido (2). La Amazonia contiene de manera natural gran variedad de vectores y reservorios infectados con T. cruzi, que generan ciclos de transmisión en focos naturales selváticos; invasión de domicilios por vectores silvestres altamente infectados (60%), adaptación gradual de vectores como Triatoma maculata, ambiente domiciliario y patrones de baja transmisión hipoendémica de T. cruzi con seroprevalencias que varían entre 1 y 3%.…”