UBC Theses and Dissertations
Ecological niche modeling of Cryptococcus gattii in British Columbia Mak, Sunny Y.
Cryptococcus gattii unexpectedly emerged on Vancouver Island, British Columbia (BC), Canada in 1999 causing human and animal illness. Prior to its discovery on Vancouver Island, this microscopic fungal organism was limited to tropical and sub-tropical regions of the world with eucalyptus trees as the environmental reservoir. Environmental sampling for C. gattii in southwestern BC has isolated the organism from native vegetation, soil, air and water. Since it is not possible to sample every location for the presence or absence of C. gattii on Vancouver Island or the BC mainland, ecological niche modeling using the Genetic Algorithm for Rule-set Prediction (GARP) was performed to identify the optimal and potential ecological niche areas of C. gattii in BC. Human and animal surveillance and environmental sampling data were used as input data points to build and test the ecological niche models based on 15 predictor environmental data layers (topographic, climatic, biogeoclimatic, and soil). Training and testing accuracy of the C. gattii ecological niche models were 99.4% and 99.2% based on the distribution of human cases, 98.7% and 98.3% based on the distribution of animal cases, and 99.7% and 99.7% based on the distribution of positive environmental sampling locations (p-value <0.0001 for all models). Forecasted optimal C. gattii ecological niche areas in BC include the central and south eastern coast of Vancouver Island, Gulf Islands, Sunshine Coast and Vancouver Lower Mainland. They are characterized by areas of low lying elevations, daily January average temperatures above freezing, and presence within the Coastal Douglas-fir and Coastal Western Hemlock xeric maritime biogeoclimatic zones. The results of these analyses are visualized using Geographic Information Systems, and shared with public health to prioritize future C. gattii environmental sampling in previously unidentified areas and increase public and physician awareness of cryptococcal disease in BC.
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