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UBC Theses and Dissertations

Exploring the ecological factors behind the 1999 outbreak of Cryptococcus gattii sensu lato on Vancouver Island Acheson, Emily Sohanna


Cryptococcus gattii sensu lato, a species complex of fungi that causes life-threatening infections in humans and other animals, was responsible for an outbreak of infections on Vancouver Island beginning around 1999. The possible ecological triggers for this outbreak, the first ever recorded in Canada, remain unknown. In this thesis, I apply a geospatial lens to explore the ecology of C. gattii s.l.. I aim to better understand the biophysical factors upon which C. gattii s.l. is most dependent and, through this, which factors may have led to the outbreak. Through a review of the C. gattii s.l. literature, I show that no studies directly tested the potential effects of climatic changes on C. gattii s.l., while only one study directly assessed those of land use change. I then use geographic information systems (GIS) and remote sensing to map global environmental isolations of C. gattii s.l. and challenge the long-held hypothesis that this fungus was only previously found in tropical and subtropical areas. I further demonstrate that GIS can provide a systematic method to classify the climates of disease emergence areas for public health research. In my studies of the potential effects of forest disturbance and climate on C. gattii s.l. occurrence on Vancouver Island, I found weak or no effects of forest disturbance on C. gattii s.l. occurrence. However, I found significant effects of the number of frost-free days in the year prior to, and the mean precipitation in the summer preceding, fungal sampling. These findings support previous studies that also found C. gattii s.l. has an increased survival in areas of Vancouver Island that have average winter temperatures above freezing, as well as warm, dry summers that may support aerosolization of spores. This research is also the first to examine the potential effects of forest disturbance, as well as possible interactions with climate, on C. gattii s.l.. Beyond exploring the ecology of C. gattii s.l., I propose geospatial methods to deal with spatiotemporal biases in secondary-use GIS data as well as to quantify the effects of ecological disturbance on infectious disease emergence in the natural environment.

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