Toxoplasma gondii is a zoonotic protozoan that causes serious illness in humans and infects animals worldwide, including the Canadian Arctic. Indeed, high prevalence of infection amongst Inuit has been recorded, possibly due to consumption of raw infected seal meat. Here we explore the hypothesis that T. gondii oocysts contaminate the coastal marine environment via surface runoff from across the boreal watershed, particularly during the snowmelt period. We propose a conceptual framework of the different processes governing the fate and transport of T. gondii oocysts from the melting snowpack to the Canadian arctic coast via the freshwater runoff. This framework identifies the feasibility of a transmission pathway of oocysts from contaminated soil to the marine environment, but also the complexity and multiplicity of mechanisms involved. In addition, the framework identifies knowledge gaps for guiding future studies on T. gondii oocysts. Furthermore, this work could be used as a tool to investigate the possible estuarine contamination by other faeces-borne pathogens transported via the spring freshet in seasonally snow covered watersheds.

SUMMARY: Toxoplasmosis is a significant public health threat for Inuit in the Canadian Arctic. This study aimed to investigate arctic seals as a possible food-borne source of infection. Blood samples collected from 828 seals in 7 Canadian Arctic communities from 1999 to 2006 were tested for Toxoplasma gondii antibodies using a direct agglutination test. Polymerase chain reaction (PCR) was used to detect T. gondii DNA in tissues of a subsample of seals. Associations between seal age, sex, species, diet, community and year of capture, and serological test results were investigated by logistic regression. Overall seroprevalence was 10·4% (86/828). All tissues tested were negative by PCR. In ringed seals, seroprevalence was significantly higher in juveniles than in adults (odds ratio=2·44). Overall, seroprevalence varied amongst communities (P=0·0119) and by capture year (P=0·0001). Our study supports the hypothesis that consumption of raw seal meat is a significant source of infection for Inuit. This work raises many questions about the mechanism of transfer of this terrestrial parasite to the marine environment, the preponderance of infection in younger animals and the natural course of infection in seals. Further studies to address these questions are essential to fully understand the health risks for Inuit communities.

Toxoplasma gondii, one of the more common zoonotic parasites in the world, can cause serious illness in humans and other animals worldwide. Felids are the only known host that can shed T. gondii oocysts, which are essential to the perpetuation of the parasite. In much of boreal Canada, the Canadian lynx (Lynx canadensis) is the only wild felid host that could contribute to environmental contamination with T. gondii oocysts. We estimated the prevalence of T. gondii antibodies in Canadian lynx from western Québec and compared our results with earlier findings in the same region 12 yr earlier. We investigated factors associated with seroconversion, including age, sex, geographic location, and possible co-occurrence with domestic cats (Felis catus), and we assessed the proportion of lynx shedding T. gondii oocysts. Blood and fecal samples were collected from 84 lynx harvested by trappers in the eastern part of the study area during winter 2009-2010. Sera were tested for antibodies to T. gondii by the modified agglutination test (cutoff titer 1:50) and fecal samples for parasite eggs by fecal flotation. Antibodies to T. gondii were detected in sera of 14% of 84 lynx. Numerous helminth ova and coccidian oocysts were found in feces, whereas T. gondii-like oocysts were not detected. Antibody prevalence increased with age class (odds ratio [OR]=4.33, 95% confidence interval [CI]=1.57-11.99, P<0.01). Antibody prevalence (14%) in our study was significantly lower than in 84 lynx (36%) trapped in the western part of the study area during winter 1997-1998 (OR=0.18, 95% CI=0.08-0.44, P<0.001). Our results suggest there may be significant spatiotemporal dynamics of T. gondii infection in lynx in Canada, and we review possible abiotic and biotic ecologic factors supporting these findings.

Background: In changing northern ecosystems, understanding the mechanisms of transmission of zoonotic pathogens, including the coccidian parasite Toxoplasma gondii, is essential to protect the health of vulnerable animals and humans. As high-level predators and scavengers, foxes represent a potentially sensitive indicator of the circulation of T. gondii in environments where humans co-exist. The objectives of our research were to compare serological and molecular assays to detect T. gondii, generate baseline data on T. gondii antibody and tissue prevalence in foxes in northern Canada, and compare regional seroprevalence in foxes with that in people from recently published surveys across northern Canada. Methods: Fox carcasses (Vulpes vulpes/Vulpes lagopus, n = 749) were collected by local trappers from the eastern (Labrador and Québec) and western Canadian Arctic (northern Manitoba, Nunavut, and the Northwest Territories) during the winters of 2015–2019. Antibodies in heart fluid were detected using a commercial enzyme-linked immunosorbent assay. Toxoplasma gondii DNA was detected in hearts and brains using a magnetic capture DNA extraction and real-time PCR assay. Results: Antibodies against T. gondii and DNA were detected in 36% and 27% of foxes, respectively. Detection of antibodies was higher in older (64%) compared to younger foxes (22%). More males (36%) than females (31%) were positive for antibodies to T. gondii. Tissue prevalence in foxes from western Nunavik (51%) was higher than in eastern Nunavik (19%). At the Canadian scale, T. gondii exposure was lower in western Inuit regions (13%) compared to eastern Inuit regions (39%), possibly because of regional differences in fox diet and/or environment. Exposure to T. gondii decreased at higher latitude and in foxes having moderate to little fat. Higher mean infection intensity was observed in Arctic foxes compared to red foxes. Fox and human seroprevalence showed similar trends across Inuit regions of Canada, but were less correlated in the eastern sub-Arctic, which may reflect regional differences in human dietary preferences. Conclusions: Our study sheds new light on the current status of T. gondii in foxes in northern Canada and shows that foxes serve as a good sentinel species for environmental circulation and, in some regions, human exposure to this parasite in the Arctic. Graphical