Range Expansion of and in Ontario, Canada, from 2017 to 2019.

Range expansion of the vector tick species, , has been detected in Ontario over the last two decades. This has led to elevated risk of exposure to , the bacterium that causes Lyme disease. Previous research using passive surveillance data suggests that populations establish before the establishment of transmission cycles, with a delay of ∼5 years. The objectives of this research were to examine spatial and temporal patterns of and its pathogens from 2017 to 2019 in southwestern, eastern, and central Ontario, and to explore patterns of invasion. Over the 3-year study period, drag sampling was conducted at 48 sites across Ontario. ticks were tested for , , , and species, including and , and Powassan virus. was detected at 30 sites overall, 22 of which had no history of previous tick detection. was detected at nine sites, eight of which tested positive for the first time during this study and five of which had detected concurrently with initial tick detection. Tick and pathogen hotspots were identified in eastern Ontario in 2017 and 2018, respectively. These findings provide additional evidence on the range expansion and population establishment of in Ontario and help generate hypotheses on the invasion of in Ontario. Ongoing public health surveillance is critical to monitor changes in and its pathogens in Ontario.