Population-based passive tick surveillance and detection of expanding foci of blacklegged ticks Ixodes scapularis and the Lyme disease agent Borrelia burgdorferi in Ontario, Canada

Abstract

We identified ticks submitted by the public from 2008 through 2012 in Ontario, Canada, and tested blacklegged ticks Ixodes scapularis for Borrelia burgdorferi and Anaplasma phagocytophilum. Among the 18 species of ticks identified, I. scapularis, Dermacentor variabilis, Ixodes cookei and Amblyomma americanum represented 98.1% of the 14,369 ticks submitted. Rates of blacklegged tick submission per 100,000 population were highest in Ontario's Eastern region; D. variabilis in Central West and Eastern regions; I. cookei in Eastern and South West regions; and A. americanum had a scattered distribution. Rates of blacklegged tick submission per 100,000 population were highest from children (0-9 years old) and older adults (55-74 years old). In two health units in the Eastern region (i.e., Leeds, Grenville & Lanark District and Kingston-Frontenac and Lennox & Addington), the rate of submission for engorged and B. burgdorferi-positive blacklegged ticks was 47× higher than the rest of Ontario. Rate of spread for blacklegged ticks was relatively faster and across a larger geographic area along the northern shore of Lake Ontario/St. Lawrence River, compared with slower spread from isolated populations along the northern shore of Lake Erie. The infection prevalence of B. burgdorferi in blacklegged ticks increased in Ontario over the study period from 8.4% in 2008 to 19.1% in 2012. The prevalence of B. burgdorferi-positive blacklegged ticks increased yearly during the surveillance period and, while increases were not uniform across all regions, increases were greatest in the Central West region, followed by Eastern and South West regions. The overall infection prevalence of A. phagocytophilum in blacklegged ticks was 0.3%. This study provides essential information on ticks of medical importance in Ontario, and identifies demographic and geographic areas for focused public education on the prevention of tick bites and tick-borne diseases.

Figure 1. Seasonality of adult ticks submitted in Ontario, Canada (2008–2012).

Figure 2. Age distribution of Ixodes scapularis submitters, counts and rates per age group, Ontario, Canada (2008–2012).

* *For blacklegged ticks submitted in which age was reported by submitter (n = 4,793).

Figure 3. Distribution of ticks submitted for identification in Ontario, Canada (2008–2012) as rates of submission per 100,000 population (based on submitter CSD of residence).

A) Ixodes scapularis, B) Dermacentor variabilis, C) Ixodes cookei and D) Amblyomma americanum.† †CSD, census subdivision. All CSDs not visible because of their small size.

Figure 4. Percentage Borrelia burgdorferi-positivity and total Ixodes scapularis by submitter town of exposure in Ontario, Canada (2008–2012).

Figure 5. Trends in Ixodes scapularis counts in Ontario, Canada, by region (2008–2012).

Figure 6. Rate of spread of Ixodes scapularis, measured in cumulative number towns with blacklegged ticks submissions along the northern shores of Lake Ontario/St. Lawrence River and Lake Erie, Ontario, Canada (2008–2012).

* *Includes I. scapularis submitted from: human (n = 6,147), dog (1,961), cat (206), environment (24), white-tailed deer (6), horse (3) and other animals not specified or unknown (51).