TRANSMISSION DYNAMICS OF TOXOPLASMA GONDII IN TERRESTRIAL ECOSYSTEMS OF THE CANADIAN WESTERN ARCTIC
Bouchard, Emilie 1989-
Toxoplasma gondii is a single-celled parasite infecting a wide range of birds and mammals worldwide. In these warm-blooded animals, it usually causes no symptoms but can cause neurological, ocular, and reproductive problems, especially if the immune system is compromised or if a mammal becomes infected while pregnant. Seroprevalence in some Inuit communities is much higher than in other parts of North America. Inuit are thought to be exposed through handling and consumption of Arctic wildlife. As T. gondii are known to produce oocysts in the intestines of felids, and wild and domestic felids are rare in the tundra regions of the Arctic, there are other transmission mechanisms occurring. Previous work has demonstrated that migratory birds are a potential source for introduction of toxoplasmosis, and that Arctic foxes are likely infected through carnivory. The aim of this research was, first, to determine major routes of transmission of T. gondii in a terrestrial Arctic ecosystem at Karrak Lake in the Queen Maud Gulf Bird Sanctuary, Nunavut, in Arctic foxes and Arctic-nesting geese. We also compared molecular and serological techniques used to detect and characterize T. gondii. Finally, reindeer were experimentally infected to determine effects and tissue distribution of the parasite. This work will address important food safety and public health aspects by looking for T. gondii in two key species, geese and caribou, which are important food sources in northern communities. Caribou populations are declining throughout the Arctic. Knowing what effects this parasite can have on caribou gives us information on whether it causes health problems or not. As for Arctic foxes, looking into seroprevalence and mode of transmission will help us understand how this parasite persists in this particular ecosystem. We hypothesize that T. gondii is maintained via vertical transmission (i.e., female foxes to the pups), in addition to transmission by carnivory. To test this hypothesis, and to determine if any changes in serostatus occurred throughout multiple years, we collected and tested blood samples from live-trapped adult and juvenile Arctic foxes. Samples were analyzed in laboratories by serological methods (Indirect Fluorescent Antibody Test (IFAT), Modified Agglutination Test (MAT)) developed and improved previously. We also tested wild goose samples serologically, using filter papers, thoracic fluids and fluids from frozen hearts, and via 2 different methods of DNA extraction followed by PCR for a 529 bp repeating segment. The magnetic capture technique allowed use of up to 100g of tissues compared to ≤25mg with traditional DNA extraction methods, thus increasing the chance to find true positives in heart and brain samples. Finally, we investigated the pathology and tissue distribution of T. gondii in experimentally infected reindeer to determine which tissues pose the greatest risk for human exposure. Our work suggests that T. gondii is present in newborn Arctic foxes, supporting the hypothesis of vertical transmission. We also proposed that subsequent litters can be infected congenitally, not just litters of females infected for the first time in pregnancy, which are pregnant females without T. gondii antibodies at the moment of infection. This can have important implications regarding reproductive success. Changes in serostatus in adult Arctic foxes throughout the years were also noticed, with a higher rate of exposure and seroconversion in mature foxes, as well as a shift of serostatus from positive to negative in an older fox. These findings give us a better understanding of how the parasite can be transmitted and maintained in a terrestrial Arctic ecosystem. Magnetic capture succeeded in detecting higher levels of T. gondii in reindeer tissues than traditional DNA extraction, suggesting the use of this technique when large amount of tissues are available. Toxoplasma gondii was not detected in wild goose tissues (i.e., brain, heart) following conventional PCR and sequencing, possibly due to low infection rates in Ross’s and Lesser Snow Geese, and low sensitivity of the conventional PCR. Antibodies against T. gondii were found serologically in both goose species using body fluids, but not following a chloroform clean-up centrifugation on the samples used to remove fat particles. The quality of samples at the time of serological testing as well as the type of samples (body fluids instead of serum) could explain the negative results after using the chloroform centrifugation. We successfully performed MAT for the first time in the field, suggesting that the use of this technique in remote field areas and northern communities is feasible. Finally, T. gondii was successfully detected in commonly consumed muscles of experimentally infected reindeer. This result gives us important insight on a potential mechanism for food-borne transmission of T. gondii in northern communities and raises concern regarding the safety of caribou meat in naturally infected animals. Subtle behavioral changes were observed in reindeer after infection, as well as respiratory problems in one animal. Numerous studies have demonstrated that T. gondii is capable of vertical transmission in a variety of hosts, including humans. High prevalences of the parasite in host populations that are geographically isolated from definitive felid hosts, as is the case in arctic fox populations, are intriguing scenarios to explore the importance of vertical transmission. It may also help to explain the extent of genetic diversity and the relative roles of sexual recombination (oocysts) vs clonal propagation (asexual reproduction). Moreover, using seroprevalence studies, Arctic foxes can be used as sentinels for T. gondii in this specific ecosystem. This research will provide information about how Arctic peoples become exposed through important food sources (i.e., geese and caribou) and the health effects of toxoplasmosis in threatened wildlife. We need more information on the significance of food-borne routes of transmission of T. gondii in the North in order to implement culturally appropriate and effective local prevention measures.
DegreeMaster of Science (M.Sc.)
CommitteeHill, Janet; Brook, Ryan; Alisauskas, Ray; Gajadhar, Alvin; Soos, Catherine; Elkin, Brett
Copyright DateAugust 2016