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Spatial analysis on the impact of Ultra-low Volume indoor insecticide spraying on Aedes aegypti household density

Anna B. Kawiecki1, 2*, Amy C. Morrison1, 2, 3 and Christopher M. Barker1, 2
  • 1 Department of Pathology, Microbiology & Immunology, School of Veterinary Medicine, University of California, Davis, United States
  • 2 Pacific Southwest Center of Excellence in Vector-Borne Diseases (PacVec), United States
  • 3 Naval Medical Research Unit Six, Peru

Vectorborne diseases are a growing threat to global public health, causing a high burden of disease and mortality, especially in developing nations in the tropics (Bhatt et al. 2013). The Aedes aegypti mosquito is the primary vector for several arboviruses that can cause severe epidemics, such as dengue, Zika and chikungunya, and is especially concerning due to the expansion of its geographic range and adaptation to urban environments. Control and prevention of Aedes-transmitted diseases rely on vector control strategies, however there is insufficient understanding of the efficacy of any given strategy on vector density and disease reduction in natural field conditions (Wilson et al. 2015). In addition, there are few studies that investigate the effects of vector control interventions on the vector populations in neighboring areas not covered by the intervention, or how these effects change over space and time. Ultra-low Volume (ULV) indoor insecticide spraying has been shown to be effective at reducing Ae. aegypti density for short periods of time (approximately two weeks post-intervention; Gunning et al. 2018). Unsprayed areas near the spray zone may see a reduction in the Ae. aegypti population as well, however the spatial extent of the vector control effect beyond the spray zone is unclear, as is the effect of incomplete spray coverage within the intervention area. The effect may be limited by the flight range of Ae. aegypti mosquitoes, which generally cluster within 10-30 m of their source household (Getis et al. 2010). However, these behaviors may change in the presence of vector control interventions. In this study, we characterize the impact of ULV indoor spraying on the A. aegypti population within households in relation to the spray events occurring in the proximity of that household in time and space. We will use data from two large-scale experiments that involved six cycles of indoor pyrethroid spray applications in two distinct neighborhoods of the Amazonian city of Iquitos, Peru. These experiments divided the study area into a central “spray zone” that received the intervention, surrounded by a “buffer zone” that did not. Adult mosquitoes were collected by hand aspirators across the entire study area before, during and after the intervention. Two candidate models will be compared for each experiment: (1) at the household level, a general linear mixed model will estimate the Ae. aegypti count per household by including a fixed effect for the intervention on the household weighted by the distance in time and space of nearby houses that received the intervention, thereby adding spatiotemporal effects to the intervention variable; (2) at the zone level, a negative binomial regression model will estimate the spillover of the intervention effect into unsprayed neighboring houses by estimating the relationship between the number of Ae. aegypti in houses in the buffer zone and the distance in space and time to the spray zone. With this analysis we provide evidence for the spatial coverage necessary to achieve vector reductions as well as the impact of ULV indoor spraying on neighboring vector populations outside the intervention area. This knowledge can be used to inform targeted and more cost-effective vector control programs, decreasing the economic burden caused by arboviral diseases in developing regions.

Acknowledgements

This research was funded by the National Institutes of Health (NIH) grant P01-AI098670-03, the National Institutes of Health (NIH) grant R01-AI091980, the W. M. Keck Foundation, and the National Science Foundation (RTG/DMS - 1246991 and NSF-IGERT-1068676).

References

Bhatt, S, P W Gething, O J Brady, J P Messina, A W Farlow, C L Moyes, J M Drake, et al. 2013. “The Global Distribution and Burden of Dengue.” Nature 496 (7446): 504–7. https://doi.org/10.1038/nature12060. Getis, Arthur, Amy C. Morrison, Kenneth Gray, and Thomas W. Scott. 2010. “Characteristics of the Spatial Pattern of the Dengue Vector, Aedes Aegypti, in Iquitos, Peru.” In Perspectives on Spatial Data Analysis, edited by Luc Anselin and Sergio J. Rey, 203–25. Berlin, Heidelberg: Springer Berlin Heidelberg. https://doi.org/10.1007/978-3-642-01976-0_15. Gunning, Christian E., Kenichi W. Okamoto, Helvio Astete, Gissella M. Vasquez, Erik Erhardt, Clara Del Aguila, Raul Pinedo, et al. 2018. “Efficacy of Aedes Aegypti Control by Indoor Ultra Low Volume (ULV) Insecticide Spraying in Iquitos, Peru.” Edited by Roberto Barrera. PLOS Neglected Tropical Diseases 12 (4): e0006378. https://doi.org/10.1371/journal.pntd.0006378. Wilson, Anne L., Marleen Boelaert, Immo Kleinschmidt, Margaret Pinder, Thomas W. Scott, Lucy S. Tusting, and Steve W. Lindsay. 2015. “Evidence-Based Vector Control? Improving the Quality of Vector Control Trials.” Trends in Parasitology 31 (8): 380–90. https://doi.org/10.1016/j.pt.2015.04.015.

Keywords: vector control, Dengue, spatial model, Aedes (Ae.) aegypti, Iquitos Peru

Conference: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data, Davis, United States, 8 Oct - 10 Oct, 2019.

Presentation Type: Student Poster-session

Topic: Spatio-temporal surveillance and modeling approaches

Citation: Kawiecki AB, Morrison AC and Barker CM (2019). Spatial analysis on the impact of Ultra-low Volume indoor insecticide spraying on Aedes aegypti household density. Front. Vet. Sci. Conference Abstract: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data. doi: 10.3389/conf.fvets.2019.05.00036

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Received: 01 Jun 2019; Published Online: 27 Sep 2019.

* Correspondence: Mx. Anna B Kawiecki, Department of Pathology, Microbiology & Immunology, School of Veterinary Medicine, University of California, Davis, Davis, California, 95616, United States, akawiecki@ucdavis.edu