| Čoahkkáigeassu: | Ticks are vectors of many diseases, including Lyme disease (Ld). Lyme disease is an emerging disease in Canada caused by infection with the Lyme borreliosis (Lb) members of the <i>Borrelia</i> genus of spirochaete bacteria, of which <i>Borrelia</i> <i>burgdorferi</i> is regionally the most prevalent. The primary tick vector in central and eastern Canada, <i>Ixodes scapularis</i>, is increasing in numbers and in the geographical extent of established populations. This study documents the distribution of ticks recovered by passive surveillance, and their <i>B.</i> <i>burgdorferi</i> infection prevalence, in three Canadian Maritime provinces from 2012–2020. These regions represent areas in which tick populations are widely established, establishing, and considered non-established. Using a community science approach by partnering with veterinarians and members of the public, we collected over 7000 ticks from the 3 provinces. The three species found most often on companion animals and humans were <i>I. scapularis</i> (76.9%), <i>Ixodes cookei</i> (10.4%) and <i>Dermacentor variabilis</i> (8.9%). The most common hosts were dogs (60.5%), cats (16.8%) and humans (17.6%). As is typical of passive surveillance tick collections, the majority of ticks recovered were adult females; for <i>I. scapularis</i> 90.2%, 5.3%, 3.9% and 0.6% of the total of 5630 ticks recovered for this species were adult females, adult males, nymphs and larvae, respectively. The majority of <i>B. burgdorferi</i>-infected ticks were <i>I. scapularis</i>, as expected. <i>Borrelia</i> infection prevalence in <i>I scapularis</i> was higher in Nova Scotia (20.9%), the province with the most endemic regions, than New Brunswick (14.1%) and Prince Edward Island (9.1%), provinces thought to have established and non-established tick populations, respectively. The province-wide <i>Borrelia</i> infection prevalence generally increased in these latter tow provinces over the course of the study. The host did not have a significant effect on <i>B. burgdorferi</i> infection prevalence; <i>I. scapularis</i> ticks from dogs, cats, humans was, 13.3% (n = 3622), 15.6% (n = 817), 17.9% (n = 730), respectively. No <i>I. scapularis</i> larvae were found infected (n = 33) but <i>B. burgdorferi</i> was detected in 14.8% of both adults (n = 5140) and nymphs (n = 215). The incidence of <i>B. burgdorferi</i> infection also did not differ by engorgement status 15.0% (n = 367), 15.1% (n = 3101) and 14.4% (n = 1958) of non-engorged, engorged and highly engorged ticks, respectively, were infected. In New Brunswick, at the advancing front of tick population establishment, the province-wide infection percentages generally increased over the nine-year study period and all health district regions showed increased tick recoveries and a trend of increased percentages of <i>Borrelia</i>-infected ticks over the course of the study. Within New Brunswick, tick recoveries but not <i>Borrelia</i> infection prevalence were significantly different from endemic and non-endemic regions, suggesting cryptic endemic regions existed prior to their designation as a risk area. Over the 9 years of the study, tick recoveries increased in New Brunswick, the primary study region, and <i>I. scapularis</i> recoveries spread northwards and along the coast, most but not all new sites of recoveries were predicted by climate-based models, indicating that ongoing tick surveillance is necessary to accurately detect all areas of risk. Comparison of tick recoveries and public health risk areas indicates a lag in identification of risk areas. Accurate and timely information on tick distribution and the incidence of <i>Borrelia</i> and other infections are essential for keeping the public informed of risk and to support disease prevention behaviors.
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