Modeling Disease Vector Occurrence When Detection Is Imperfect II: Drivers of Site-Occupancy by Synanthropic Triatoma brasiliensis in the Brazilian Northeast

Abstract

BackgroundUnderstanding the drivers of habitat selection by insect disease vectors is instrumental to the design and operation of rational control-surveillance systems. One pervasive yet often overlooked drawback of vector studies is that detection failures result in some sites being misclassified as uninfested; naïve infestation indices are therefore biased, and this can confound our view of vector habitat preferences. Here, we present an initial attempt at applying methods that explicitly account for imperfect detection to investigate the ecology of Chagas disease vectors in man-made environments.MethodologyWe combined triplicate-sampling of individual ecotopes (n = 203) and site-occupancy models (SOMs) to test a suite of pre-specified hypotheses about habitat selection by Triatoma brasiliensis. SOM results were compared with those of standard generalized linear models (GLMs) that assume perfect detection even with single bug-searches.Principal Findings Triatoma brasiliensis was strongly associated with key hosts (native rodents, goats/sheep and, to a lesser extent, fowl) in peridomestic environments; ecotope structure had, in comparison, small to negligible effects, although wooden ecotopes were slightly preferred. We found evidence of dwelling-level aggregation of infestation foci; when there was one such focus, same-dwelling ecotopes, whether houses or peridomestic structures, were more likely to become infested too. GLMs yielded negatively-biased covariate effect estimates and standard errors; both were, on average, about four times smaller than those derived from SOMs.Conclusions/SignificanceOur results confirm substantial population-level ecological heterogeneity in T. brasiliensis. They also suggest that, at least in some sites, control of this species may benefit from peridomestic rodent control and changes in goat/sheep husbandry practices. Finally, our comparative analyses highlight the importance of accounting for the various sources of uncertainty inherent to vector studies, including imperfect detection. We anticipate that future research on infectious disease ecology will increasingly rely on approaches akin to those described here.

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) .…”

“…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) . The failures were observed in areas with well-established triatomine infestation, where active searches by trained and motivated agents usually detect approximately 40-60% of intradomiciliary and extradomiciliary infestation outbreaks, while undetected foci are not eliminated (70) .…”

“…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) . The failures were observed in areas with well-established triatomine infestation, where active searches by trained and motivated agents usually detect approximately 40-60% of intradomiciliary and extradomiciliary infestation outbreaks, while undetected foci are not eliminated (70) . In addition, from the analysis of the monitoring process by means of active searches conducted by control agents, its sensitivity is estimated at approximately 20% for locations with low intensity infestation (few outbreaks, with few triatominae) and at approximately 40% in locations with more intense infestation (71) .…”

“…In addition to this approach, the integrated use of spatial analysis techniques to extend the analytical capability, with insertion of spatial and temporal dimensions of the transmission of Chagas disease, has shown great potential, in particular by the significant development of portable electronic equipment and software for data processing and analysis (70) (85) (86) (87) .…”