The effect of spatial scale on entomological thresholds for the prevention of West Nile virus disease
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1
Davis Arbovirus Research and Training, University of California, Davis, United States
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2
Department of Pathology, Microbiology & Immunology, School of Veterinary Medicine, University of California, Davis, United States
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3
Pacific Southwest Center of Excellence in Vector-Borne Diseases (PacVec), United States
The vector index (VI) is used to estimate the relative abundance of arbovirus-infected mosquitoes as the product of two commonly monitored quantities: mosquito trap counts and mosquito infection prevalence. It is used increasingly to guide mosquito control programs as an entomological indicator of human infection risk for arboviruses, especially for zoonotic pathogens such as West Nile virus (WNV). Despite studies showing a positive relationship between the VI and human incidence, an established VI threshold below which risk of spillover is low has not been established. With this study, we aimed to 1) determine the spatial scale at which the VI is most predictive of human WNV disease occurrence and 2) estimate VI threshold(s) at which effective adult mosquito control would prevent spillover from occurring. To provide a better evidence basis for adult mosquito control decisions, we have characterized the relationship between the VI and human WNV disease using surveillance data from several mosquito control districts using Poisson regression models for the data aggregated to each of four spatial scales: mosquito control agency, census county division, city, and zip code. Our models controlled for the effect of the trap type used for the mosquito collection and variation among agencies to account for different operational practices. We considered the predictive value of the VI at these different spatial scales to determine whether the VI is capable of providing sensitive and specific predictions at scales relevant for targeting mosquito control, then we estimated optimal population-adjusted VI thresholds for cities within each agency. We found the VI to be a significant predictor of WNV incidence at all spatial scales and that city-scale VI thresholds provided the best balance between being small enough to target vector control but large enough to minimize noise in the VI-WNV disease relationship. Overall, these results will help to inform decisions about the most relevant entomological thresholds and geographic scales for targeting broad-scale control measures.
Acknowledgements
We would like to thank Robert Cummings of Orange County MVCD for coordinating the funding for this study and Jacklyn Wong and Anne Kiemtrup, Vector-Borne Disease Section, CDPH for providing the data on cases of WNV disease in humans. We acknowledge funding from Orange County, Greater LA County, San Gabriel Valley, Sacramento-Yolo, Placer, and Turlock MVCDs. CMB also acknowledges support from and the PacVec Regional CoE funded by the CDC (Cooperative Agreement U01CK000516).
Keywords:
Vector-borne disease,
West Nile virus,
Mosquitoes,
vector control,
surveillance
Conference:
GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data, Davis, United States, 8 Oct - 10 Oct, 2019.
Presentation Type:
Regular oral presentation
Topic:
Spatio-temporal surveillance and modeling approaches
Citation:
Stiles
PC and
Barker
CM
(2019). The effect of spatial scale on entomological thresholds for the prevention of West Nile virus disease.
Front. Vet. Sci.
Conference Abstract:
GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data.
doi: 10.3389/conf.fvets.2019.05.00076
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Received:
03 Jun 2019;
Published Online:
27 Sep 2019.
*
Correspondence:
Mx. Pascale C Stiles, Davis Arbovirus Research and Training, University of California, Davis, Davis, United States, pcstiles@ucdavis.edu