Foxes and Lynx as Sentinels for Toxoplasma gondii across the Canadian North

Toxoplasma gondii is one of the most successful parasites in the world and can have serious adverse effects on immunocompromised individuals and foetuses. It is thus a parasite of public health concern, especially in the Canadian North where seroprevalence in some Inuit communities is much higher than in other parts of North America. Food-borne transmission is likely a significant route of transmission among northern residents as well as Arctic carnivores, where transmission may be altered by the rapid demographic and environmental changes affecting Arctic and subarctic regions. I focused on lynx as the only definitive host that can produce oocysts in subarctic regions, and foxes as intermediate hosts at high risk of exposure. The aim of this research was first to assess T. gondii exposure, prevalence and genetic diversity in foxes and lynx in northern Canada. I hypothesized that foxes would act as good sentinel species for T. gondii in the North since they occupy a high trophic position in the Arctic and are widespread in northern Canada. I also sought to determine if lynx are serving as definitive hosts for T. gondii using DNA based methods (real time PCR with melting-curve analysis) which are more sensitive than efforts to detect oocysts in feces. I used a sequence specific magnetic capture DNA extraction and real-time PCR to test whole hearts and brains of foxes and lynx. I tested samples serologically by enzyme-linked immunosorbent assay (ELISA) using fluids from thawed hearts. I targeted foxes from all four Inuit regions of Canada: Inuvialuit Settlement Region in Canada’s Western Arctic, Nunavut, Nunavik in northern Québec, and Nunatsiavut in Labrador. Exposure and tissue infection were lower in fox and lynx in Canada’s Western Arctic, and higher in the Eastern Arctic, especially the Hudson Bay region of Nunavik. These results are compatible with recent serological findings in people from Inuit Health Surveys, supporting the hypothesis that fox are indeed suitable sentinels of environmental transmission and human exposure to T. gondii. DNA consistent with that of T. gondii was detected in feces of one lynx from boreal regions of Québec, but was detected far more commonly in lynx tissues. While lynx are a potential source of oocysts, they may also contribute to transmission of this parasite through consumption of their tissues by other carnivores and harvesters. This supports my hypothesis that fox are primarily exposed to T. gondii through carnivory rather than consumption of oocysts produced locally by lynx. In order to determine the role prey species play in T. gondii prevalence, I used stable isotopes on muscle and hair of Nunavik foxes to reconstitute their diet and link diet with their infection status. I concluded that marine food sources and migratory birds are likely a major source of exposure in foxes to T. gondii in Nunavik, again similar to recent findings on consumption trends in people in Nunavik. This work reveals a better understanding of the distribution and introduction of T. gondii in fragile Arctic ecosystems. Ultimately, these findings inform future risk assessments to determine the potential human and animal health risks associated with T. gondii in northern ecosystems.

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