Ecology of Francisella tularensis in Sympatric Rodent and Lagomorph Species in Urban and Non-urban Settings in Prairie Canada

Francisella tularensis, the bacterium causing tularemia, is endemic in rodents and lagomorphs in the Canadian Prairies. Recent cases include two wild animals in Saskatoon Saskatchewan (SK) in 2017, and a tamarin at the Assiniboine Park Zoo (APZ), in Winnipeg Manitoba (MB) in 2015. The latter was the second incidence of tularemia being diagnosed in non-human primates at the zoo. Little is known about the disease’s ecology in Prairie Canada, hence this study attempted to determine the prevalence, and assess potential candidates for reservoir species in SK and MB. This study attempted to determine tularemia’s temporal and spatial prevalence in rodents and lagomorphs (possible reservoir species), as well as mesocarnivores and mosquitoes (possible sentinel species). Animals were live trapped across SK (2018-2020) and MB (2018-2019). Locations included non-urban and urban settings, with a mix of terrestrial and aquatic habitats. Mammals caught were sampled for blood and ectoparasites, then euthanized for tissue collection or released. A microagglutination test (MAT) was used to determine antibody status, while an in-house polymerase chain reaction (PCR) test was used on tissues and mosquitoes to detect F. tularensis DNA. A total of 730 blood samples from rodents and lagomorphs were tested and 29 from mesocarnivores: 16 animals were positive (12 from MB and four from SK, of which nine were Richardson’s ground squirrels, two American red squirrels, two stripped skunks, one prairie vole, one raccoon and one American mink). A total of 1,040 tissue and 105 mosquito pools underwent PCR testing. None had detectable F. tularensis DNA. Presence of F. tularensis in many SK and MB locations was confirmed. Antibodies, along with negative PCR, seems to indicate squirrels can be infected and survive. Although all rodent with titers had seemingly cleared the infection, there may be individuals that fail to do so and become chronic carriers (reservoir species). On the other hand, should morbidity within these squirrel species increase they may play a recipient (spillover) or donor role in their habitat. Although the number of mesocarnivore sera available was low, each year at least one animal had F. tularensis antibodies. This supports the hypothesis that mesocarnivores could be good sentinels for tularemia activity. In contrast, none of the mosquito samples tested yielded positive results. While it was not possible to rule out mosquitoes as potential vectors, it seems they are not useful sentinels in locations where F. tularensis prevalence is low