Abstract
Canadians face an emerging threat of Lyme disease due to the northward expansion of the tick vector, Ixodes scapularis. We evaluated the degree of I. scapularis population establishment and Borrelia burgdorferi occurrence in the city of Ottawa, Ontario, Canada from 2017–2019 using active surveillance at 28 sites. We used a field indicator tool developed by Clow et al. to determine the risk of I. scapularis establishment for each tick cohort at each site using the results of drag sampling. Based on results obtained with the field indicator tool, we assigned each site an ecological classification describing the pattern of tick colonization over two successive cohorts (cohort 1 was comprised of ticks collected in fall 2017 and spring 2018, and cohort 2 was collected in fall 2018 and spring 2019). Total annual site-specific I. scapularis density ranged from 0 to 16.3 ticks per person-hour. Sites with the highest density were located within the Greenbelt zone, in the suburban/rural areas in the western portion of the city of Ottawa, and along the Ottawa River; the lowest densities occurred at sites in the suburban/urban core. B. burgdorferi infection rates exhibited a similar spatial distribution pattern. Of the 23 sites for which data for two tick cohorts were available, 11 sites were classified as “high-stable”, 4 were classified as “emerging”, 2 were classified as “low-stable”, and 6 were classified as “non-zero”. B. burgdorferi-infected ticks were found at all high-stable sites, and at one emerging site. These findings suggest that high-stable sites pose a risk of Lyme disease exposure to the community as they have reproducing tick populations with consistent levels of B. burgdorferi infection. Continued surveillance for I. scapularis, B. burgdorferi, and range expansion of other tick species and emerging tick-borne pathogens is important to identify areas posing a high risk for human exposure to tick-borne pathogens in the face of ongoing climate change and urban expansion.
Highlights
Canadians face an emerging risk of Lyme disease (LD) and other tick-borne pathogens due to the northward expansion of the tick vector, the blacklegged tick, Ixodes scapularis
While passive surveillance is useful for signalling the presence of a potential emerging risk area for tick-borne illness, active surveillance is required for determining whether a reproducing tick population is established [9]
We collected a total of 782 I. scapularis ticks over 317.49 person-hours of field sampling including 603 adults, 132 nymphs, and 47 larvae
Summary
Canadians face an emerging risk of Lyme disease (LD) and other tick-borne pathogens due to the northward expansion of the tick vector, the blacklegged tick, Ixodes scapularis (sometimes called the deer tick). Given Ottawa’s geographic location within the climatically suitable range for I. scapularis and the recent increase in LD cases, there is a need for ongoing surveillance of I. scapularis and Borrelia burgdorferi sensu stricto (s.s.), the causative agent of LD in Ontario [1, 6,7,8]. While passive surveillance is useful for signalling the presence of a potential emerging risk area for tick-borne illness, active surveillance is required for determining whether a reproducing tick population is established [9]. Adventitious ticks collected in passive tick surveillance represent a low but persistent risk of LD, the presence of a reproducing tick population in a given geographic area signals a higher potential risk for human LD exposure
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