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UBC Theses and Dissertations

Determinants of West Nile Virus (WNV) incidence in select regions of Canada : an examination of climate and ecological drivers in British Columbia and Saskatchewan Roth, David Z


Background: West Nile Virus (WNV) is a zoonotic arbovirus that has caused significant disease in Canada, yet remains rare in British Columbia (BC). WNV is spread between avian reservoirs by Culex mosquitoes, and incidental transmission to humans can occur. Understanding temporal and spatial changes in WNV risk is di cult because of the complexity of the transmission cycle. Nonetheless, public health agencies require decision support in order to guide resource allocation. Understanding the climate and ecological drivers of WNV disease can help with the development of such tools. Methods: Descriptive analyses were used to compare ecological and climate conditions in years with and without WNV transmission in BC from 2009 to 2015. Generalized linear mixed models were used to evaluate associations between WNV incidence in Saskatchewan (2003-2007) and: 1) total irrigated landscape, and 2) avian community structure. Results were combined with a literature review to develop a WNV decision-support tool for BC which was evaluated via a user survey. Results: WNV activity in BC between 2009-2015 was limited to select locations during hot summers when temperatures remained above key temperature thresholds during the amplification period. In Saskatchewan, human incidence was positively associated with irrigated landscapes in 2003 but not 2007. Non-passerine species richness and abundance was positively associated with incidence from 2003-2007, and the dilution hypothesis was not supported. Heat was consistently associated with incidence, but other predictors had varying effects between years and models. The resulting decision support tool contained seven surveillance inputs and three hazard levels. Survey results supported the choice of surveillance inputs and the recommended prevention measures. Discussion: Ecological complexity challenges quantitative risk prediction for WNV and necessitates the use of simpler tools for public health decision support. Public health agencies in low-incidence areas should invest public health resources in improving situational awareness and preparedness instead of risk prediction. The decision support tool created here provides a general estimate of WNV amplification as a proxy of WNV hazard. Continued refinement of the tool as more is learned about the ecology of WNV would increase its utility

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