Risk Factors for Exposure to Toxoplasma gondii in Bighorn Sheep (Ovis canadensis)

Toxoplasma gondii is a globally distributed protozoan parasite that can spill over into wildlife, including bighorn sheep (Ovis canadensis). Members of the Felidae are the definitive hosts of T. gondii and can spread the parasite via their feces. Vertical transmission can also occur, resulting in abortion and neonate loss in wild sheep. Toxoplasma gondii infection in wildlife is associated with higher human densities, higher urbanization, and broader distribution and higher density of domestic cats. The goal of this study was to investigate factors potentially associated with seropositivity for T. gondii in bighorn sheep, including age class and metrics of urbanization as measures of free-roaming domestic cat habitat use and overlap with wild sheep (number of buildings, building density, and proportion of cat home range overlap). These metrics were analyzed at two different spatial scales of bighorn sheep habitat: escape terrain (as a measure of habitat use throughout the year) and winter home range (as a measure of winter seasonal habitat use). Two hundred seventy-six bighorn sheep were sampled from Idaho and Washington; a total of 42 (15%) were seropositive for T. gondii. I found that the number of buildings in escape terrain was positively associated with bighorn sheep seroprevalence, indicating a relationship between urbanization and T. gondii spillover into bighorn sheep.