Distribution of Ticks and the Risk of Lyme Disease and Other Tick-Borne Pathogens of Public Health Significance in Ontario,Canada

Abstract

Over the past two decades, the northward spread of Ixodes scapularis across Ontario, Canada, has accelerated and the risk of Lyme disease has increased. Active surveillance is a recognized and effective method for detecting reproducing populations of I. scapularis. In this study, we conducted field sampling consistent with an active surveillance approach from May to October 2014 at 104 sites in central, eastern, and southern Ontario to determine the current distribution of I. scapularis and other tick species, and enhance our understanding of the geographic risk associated with Borrelia burgdorferi and other tick-borne pathogens of public health significance in this region. I. scapularis was present at 20 of the 104 sites visited. Individuals of the tick species Dermacentor variabilis, Haemaphysalis leporispalustris, and Ixodes dentatus were also collected. I. scapularis was positive by PCR for B. burgdorferi at five sites. These sites formed a significant spatial cluster in eastern Ontario. No ticks were PCR positive for Borrelia miyamotoi, Anaplasma phagocytophilum, and Babesia microti. This study provides an up-to-date picture of the distribution of I. scapularis and other tick species, and the risk of B. burgdorferi and other pathogens of public health significance in central, eastern, and southern Ontario. This information may allow for more effective surveillance efforts and public health interventions for Lyme disease and other tick-borne diseases in this region.

Introduction

Globally, ticks represent one of the most significant public health risks, second only to mosquitoes as vectors for pathogen transmission (Parola and Raoult 2001). Although tick-borne diseases have been recognized for centuries, interest has intensified in the recent past due to the potential impact that climate change may have on the expanded distribution of tick species and subsequent introduction of tick-borne diseases (Estrada-Peña and De La Fuente 2014).

Lyme disease is the most important tick-borne disease in North America, with over 22,000 cases reported in the United States in 2012 (Centers for Disease Control and Prevention 2015), although the true annual incidence may be in the order of 300,000 cases (Hinckley et al. 2014). In the eastern United States and Canada, the causative agent of Lyme disease, Borrelia burgdorferi, is transmitted by the blacklegged tick, Ixodes scapularis (Burgdorfer et al. 1982). I. scapularis can also transmit other pathogens of public health significance, most notably Anaplasma phagocytophilum (Dumler and Bakken 1995), Babesia microti (Spielman et al. 1984), as well as the recently recognized Borrelia miyamotoi (Scoles et al. 2001).

Before 1990, only one isolated population of I. scapularis was known to exist in Canada (Watson and Anderson 1976). Over the past two decades the northward spread of I. scapularis has accelerated. Large numbers of ticks are carried northward annually by migratory birds (Ogden et al. 2008a), and the areas into which these ticks are being introduced are becoming increasingly suitable for tick development due to climate change (Ogden et al. 2008c, 2014c). In Ontario, there are now eight recognized endemic sites, although the distribution of this tick is believed to be much wider (Sider et al. 2012, Ogden et al. 2014b). The spread of I. scapularis has coincided with a notable increase in the incidence of human Lyme disease cases (Ogden et al. 2015a).

Surveillance for ticks to assess the risk of tick-borne disease has been a long-standing practice in Ontario (Scholten 1977). Passive surveillance, through which ticks that are found by the public are brought to public health units and healthcare providers, is an important component of the surveillance program. These ticks are identified and I. scapularis are sent to the National Microbiology Laboratory (NML) of the Public Health Agency of Canada (PHAC) for pathogen screening by PCR (Ogden et al. 2006b). In the mid 1900s, the predominate tick species collected through passive surveillance were Dermacentor variabilis and Ixodes cookei (Scholten 1977). As the northward expansion of I. scapularis accelerated, the number of I. scapularis submitted grew substantially and by 2009, exceeded any other tick species (Nelder et al. 2014). Passive surveillance has been instrumental in monitoring the risk of Lyme disease and tick-borne disease in the province, but enhanced analyses of these passive surveillance data are needed to further understand the risk of disease (Ogden et al. 2010, Koffi et al. 2012).

Active surveillance is recognized as an effective approach for the detection of I. scapularis populations. As outlined at the consensus conference on Lyme disease (Health Canada 1991), active surveillance involves collecting ticks from the environment through drag sampling and testing I. scapularis for the presence of B. burgdorferi. Small mammal trapping is also indicated. Although small mammal trapping is the most sensitive method for detecting ticks, it is not as frequently used as drag sampling due to the associated costs and intensive time and labor demands (Ogden et al. 2014a).

In this study, we conducted field sampling consistent with an active surveillance approach across a widespread area of central, eastern, and southern Ontario from May to October 2014 to determine the current distribution of I. scapularis and other tick species, and to enhance our current understanding of the geographical risk associated with B. burgdorferi and other tick-borne pathogens of public health significance in the province.

Materials and Methods

Site selection

Sites were selected to compare the prevalence of I. scapularis-positive sites between the three ecoregions of central, eastern, and southern Ontario (Lake Erie–Lake Ontario ecoregion 7E, Lake Simcoe–Rideau ecoregion 6E, and Georgian Bay ecoregion 5E) (Fig. 1). Ecoregions are defined by the Ministry of Natural Resources, Government of Ontario, and are based on coarse-scale climate, demographic, and watershed analysis (Ontario Ministry of Natural Resources 2007). We chose these divisions as they represent three distinct ecological regions where the climate (annual accumulated number of degree-days >0°C) is likely sufficient to support I. scapularis development (Ogden et al. 2005). Areas with known established populations of I. scapularis were excluded (Sider et al. 2012). The sample size was calculated to detect a difference in the prevalence of I. scapularis-positive sites between ecoregions of 0.6 and 0.2. These values reflect the expected prevalence in an area with a highly suitable habitat and climatic conditions for I. scapularis and an area with relatively limited suitability, respectively (Brownstein et al. 2003, Diuk-Wasser et al. 2006). Based on these prevalence values, a power of 80% and an α = 0.05, 28 sites per ecoregion were required. We opportunistically selected forested sites with a minimum area of 0.25 km² for inclusion in this study. Sites were limited to forested land cover since this environment is the preferred habitat of I. scapularis, which was the target tick species in this study (Lindsay et al. 1998). Permission to access each site was secured by field personnel.

FIG. 1.

One hundred and four research sites in ecoregions 5E, 6E, and 7E were surveyed by drag sampling from May to October 2014. Four species of ticks were collected: Ixodes scapularis, Dermacentor variabilis, Haemaphysalis leporispalustris, and Ixodes dentatus. An area with a high prevalence of sites that were positive for I. scapularis was detected in eastern Ontario. Endemic sites are provided for reference. Status of I. scapularis: white circle = absent, black star = present. Other tick species: gray diamond = D. variabilis, gray square = H. leporispalustris; gray triangle = I. dentatus. Semitranslucent circle = cluster of sites with I. scapularis present. Black asterisk = endemic site.

Field sampling

Field sampling was conducted from May to October 2014 at 104 sites within ecoregions 5E, 6E, and 7E. Handheld global positioning systems were used to record the longitude and latitude values at each site. Ticks were collected by dragging a 1 meter squared white flannel drag cloth attached to a 1.25 meters pole across the forest floor and over surface vegetation in parallel transects for the equivalent of three person-hours. Every 3 min, the timer was stopped and the drag cloth and researcher's clothing were examined for ticks. All adults, nymphs, and larvae were removed and counted. If the larval number was high (>100), an estimate was made, rounding to the nearest tens. Adults and nymphs were collected and stored in 70% ethanol for further processing. When only larvae were found, they were collected and stored in 70% ethanol for species identification. Tick dragging was not conducted on days when it rained.

Laboratory analysis

Nymphal, adult, and when required, larval tick samples were submitted to the NML (Public Health Agency of Canada, Winnipeg, Manitoba, Canada) for species identification. Adult and nymphal ticks identified as I. scapularis were tested for the presence of B. burgdorferi, B. miyamotoi, A. phagocytophilum, and B. microti by real-time PCR as previously described (Ogden et al. 2006b, Dibernardo et al. 2014). Briefly, QIAGEN DNeasy 96 tissue kits (QIAGEN, Inc., Mississauga, Canada) were used for DNA extraction. A duplex screening assay was chosen to screen the samples for Borrelia spp. using the 23S ribosomal RNA (rRNA) real-time PCR assay and for A. phagocytophilum using the msp2 real-time PCR assay (Courtney et al. 2004). Analysis for B. microti was conducted using the methods described by Nakajima et al. (2009) for the detection of the CCTeta gene. All Borrelia spp.-positive samples were subsequently tested for B. burgdorferi using a confirmatory ospA real-time PCR assay and for B. miyamotoi using an IGS real-time PCR assay. B. miyamotoi-positive samples were further verified using the glpQ real-time PCR assay (Dibernardo et al. 2014). To account for possible contamination during DNA extraction and PCR, water or blank controls were included in all extractions and PCR runs. All of these controls were negative during the course of this study.

Statistical analyses

Exact logistic regression was conducted to determine if there was a difference in the prevalence of positive sites for each tick species (I. scapularis, D. variabilis, Haemaphysalis leporispalustris, and Ixodes dentatus) between ecoregions and to evaluate the difference in the prevalence of B. burgdorferi-positive sites between ecoregions. Exact logistic regression was chosen because for each regression analysis at least one ecoregion had a small (<5) number of sites with a positive outcome. All statistical analyses were completed in STATA version 13.1 (STATACorp, College Station, TX; 2014).

The spatial scan statistic was implemented using SaTScan 9.4 (www.satscan.org, 2015). A purely spatial retrospective analysis using the Bernoulli probability model was chosen to assess areas of high prevalence. The spatial window was set at a maximum spatial cluster size no greater than 50% of the population at risk. Monte Carlo replications were limited to 999 replications. Only statistically significant secondary clusters with no geographical overlap were reported; hierarchical and Gini clusters (i.e., clusters based on the Gini index) were reported if they met these criteria (Kulldorff 2015). The spatial scan statistic was conducted twice. The first analysis examined the site data categorized according to the presence or absence of I. scapularis and the second analysis examined the data based on whether a site was positive or negative for B. burgdorferi. A significance level of α = 0.05 was used for all statistical and spatial analyses.

Spatial data were prepared using QGIS version 2.6.0 Brighton (www.qgis.org; 2014). Briefly, the vector layer for ecoregion (Ontario Ministry of Natural Resources 2007) was accessed through the Scholars GeoPortal at the University of Guelph (http://geo2.scholarsportal.info). Ecoregions 5E, 6E, and 7E were selected to form the base layer. Site data were plotted using the recorded longitude and latitude values. In the first spatial display, two geographical information system layers were created to categorize the findings of field sampling. The presence or absence of I. scapularis at each site was used as the first layer, and an additional layer was added to classify each site based on the presence of another tick species. A second spatial display was created for the presence of I. scapularis and detection of B. burgdorferi. Using one data layer, the sites were categorized as “absent” if no I. scapularis were collected and “present” if at least one I. scapularis of any life stage was collected. Each I. scapularis “present” site was further categorized as “negative for B. burgdorferi” if all samples analyzed were negative for the bacteria, “positive for B. burgdorferi” if at least one sample was positive for the bacteria, and “only larvae” if only larvae were collected and therefore no laboratory testing was completed.

Results

Four species of ticks were found at the 104 field sampling sites. I. scapularis was the most prevalent tick species collected and was present at 20 sites (19.2%; 95% confidence interval [95% CI] 12.2–28.1) across all three ecoregions (Table 1). A total of 66 I. scapularis were collected (median 2 per site; range 1–15), comprising 31 adults and 35 nymphal ticks. A total of 152 H. leporispalustris were found at nine sites (8.7%; 95% CI 4.0–15.8) within ecoregions 5E and 6E, and a total of 18 D. variabilis were found at seven sites (6.7%; 95% CI 2.7–13.4) in ecoregions 6E and 7E. The least prevalent tick species was I. dentatus, with only one tick collected at one site in ecoregion 7E (1.0%; 95% CI 0.02–5.2). The odds of detecting a site that was positive for H. leporispalustris were significantly less likely in ecoregion 7E, when compared to ecoregion 5E. There were no other significant differences in the prevalence of sites with I. scapularis or the two other tick species among the ecoregions (Table 2).

Table 1.

Number of Ixodes scapularis and Prevalence of Borrelia burgdorferi in Nymphal and Adult I. scapularis from Ecoregions 5E, 6E, and 7E

	Ecoregion ^a 5E (27 sites)	Ecoregion 6E (43 sites)	Ecoregion 7E (34 sites)	Total (104 sites)
Prevalence of sites with I. scapularis (95% CI)^b	22.2 (8.6–42.3)	23.3 (11.7–38.6)	11.8 (3.3–27.5)	19.2 (12.2–28.1)
Total number of ticks collected	49	569	8	626
Total number of adult ticks collected	10	16	5	31
Total number of nymphal ticks collected	15	20	0	35
Median number of adult and nymphal ticks/site (range)	2 (2–15)	2 (1–10)	1 (1–4)	2 (1–15)
Prevalence of sites with B. burgdorferi-infected ticks (95% CI)	7.4 (0.9–24.3)	7.1 (1.5–19.5)^c	0	4.9 (1.6–11.2)^d
Number of adult and nymphal ticks infected with B. burgdorferi	3	7	0	10
Median number of adult and nymphal ticks infected with B. burgdorferi/site (range)	1 (1–2)	2 (2–3)	0	2 (1–3)
Odds ratio^e (95% CI; p value)	Referent	0.96 (0.1–12.28; 1.0)	0.34 (0–4.45; 0.41)

As outlined by the Ontario Ministry of Natural Resources (2007).

95% confidence interval.

Based on the results of 42 sites. One site did not have laboratory results, as only I. scapularis larvae were collected.

Based on the results of 101 sites. Three sites did not have laboratory results, as only I. scapularis larvae were collected.

The odds of a site being positive for B. burgdorferi in either ecoregion 6E or 7E compared to the referent 5E.

Table 2.

Prevalence of Sites with Ixodes Scapularis, Haemaphysalis leporispalustris, Dermacentor variabilis, and Ixodes dentatus and the Association Between the Prevalence of Sites with Each Tick Species and Ecoregions 5E, 6E and 7E in Ontario Based on Exact Logistic Regression

Tick species	Ecoregion ^a 5E (27 sites)	Ecoregion 6E (43 sites)	Ecoregion 7E (34 sites)
I. scapularis
Prevalence (95% CI)	22.2 (8.6–42.3)	23.3 (11.7–38.6)	11.8 (3.3–27.5)
Odds ratio^b (95% CI; p value)	Referent	1.00 (0.30–4.10; 1.0)	0.47 (0.09–2.28; 0.45)
H. leporispalustris
Prevalence (95% CI)	18.5 (6.3–38.1)	9.3 (2.6–22.1)	0
Odds ratio (95% CI; p value)	Referent	0.46 (0.08–2.37; 0.45)	0.10^c (0–0.79; 0.03)
D. variabilis
Prevalence (95% CI)	0	9.3 (2.6–22.1)	8.8 (1.8–23.7)
Odds ratio (95% CI; p value)	Referent	3.52^c (0.42–∞; 0.27)	3.20^c (0.33–∞; 0.33)
I. dentatus
Prevalence (95% CI)	0	0	2.9 (0.07–15.3)
Odds ratio (95% CI; p value)	Referent	1 (0–∞)	0.79^c (0.2–∞; 1.0)

As outlined by the Ontario Ministry of Natural Resources (2007).

The odds of a site being positive for the tick species in either ecoregion 6E or 7E compared to the referent 5E.

Median unbiased estimate.

More than one tick species was present at six sites. When more than one tick species was present, it was either I. scapularis and D. variabilis, or I. scapularis and H. leporispalustris together.

B. burgdorferi was found in 10 adult I. scapularis from five sites (4.9%; 95% CI 1.6–11.2; Table 1). The number of positive ticks at each site ranged from 1 to 3, with a median of 2. There was no significant difference in the prevalence of B. burgdorferi between the ecoregions (Table 1). B. miyamotoi, A. phagocytophilum, and B. microti were not detected in any of the 31 adult and 35 nymphal I. scapularis tested (0%; one-sided 97.5% CI 0–5.4).

A spatial cluster of I. scapularis positive sites was identified in eastern Ontario, covering parts of ecoregions 5E and 6E (Fig. 1). A spatial cluster of B. burgdorferi-positive sites was found in the same area of eastern Ontario (Fig. 2).

FIG. 2.

The presence and absence of I. scapularis and B. burgdorferi at 104 research sites in ecoregions 5E, 6E, and 7E were determined by drag sampling from May to October 2014. Twelve sites had the presence of I. scapularis, but tested negative for B. burgdorferi. Five sites had both the presence of I. scapularis and tested positive for B. burgdorferi. An area with a high prevalence of sites that were positive for B. burgdorferi was detected in eastern Ontario. The status of three sites was unknown as only the larval stage was collected. I. scapularis site status: white circle = absent; light gray triangle = present, larvae only; dark gray triangle = present and negative for B. burgdorferi; black triangle = present and positive for B. burgdorferi. Semitranslucent circle = cluster of sites with B. burgdorferi present.

Discussion

Passive surveillance has been invaluable for studying the emergence of Lyme disease in Canada. Analysis of samples submitted from 1990 to 2003 by Ogden et al. (2006b) indicated that the distribution of I. scapularis may be much greater than initially thought and expand far beyond the endemic areas. Monitoring the number of ticks submitted and the infection prevalence has been used as an indication for I. scapularis establishment within an area (Ogden et al. 2010), and epidemiological risk factors for tick acquisition and disease exposure have been elucidated from demographic information collected from submitters (Nelder et al. 2014).

However, there are a number of drawbacks associated with passive surveillance. Passive surveillance lacks specificity due to the incidence of adventitious ticks, which are ticks that are sporadically introduced into an area, most commonly by migratory birds (Ogden et al. 2014a). Furthermore, sensitivity can be low because an absence of submissions does not necessarily indicate an area without ticks. This is especially true in areas of low human population density, where there is a very low probability of gathering sufficient data through passive surveillance (Nelder et al. 2014). Low specificity and sensitivity can lead to an elevation of false-positive and false-negative areas, respectively. For these reasons, active surveillance has been considered the gold standard method for identifying areas where I. scapularis ticks have become established.

Passive surveillance also has reduced capacity to detect all the life stages of the tick. Adult ticks are the most common instar of ticks submitted by the public. Nymphs and larvae are difficult for the public to recognize due to their small size and are rarely submitted through passive surveillance (Ogden et al. 2006b). However, these stages provide valuable information on the tick population and disease risk. The presence of the immature stages of ticks and/or the presence of more than one stage of tick at a site provide stronger evidence of a reproducing population of I. scapularis (Koffi et al. 2012). Nymphs also provide the best indication of disease risk. Peak nymphal activity occurs in early summer, when humans are more likely to engage in outdoor activities; often in clothing that provides limited protection from tick bites. This factor, along with the decreased detection as a result of their small size, leads to an elevated risk of transmission of B. burgdorferi from nymphal I. scapularis (Ogden et al. 2008b).

Using an approach consistent with active surveillance, we detected I. scapularis in all three ecoregions of southern, eastern, and central Ontario. These sites represent new areas outside of the known endemic sites of Point Pelee National Park, Rondeau Provincial Park, Long Point Provincial Park, Turkey Point Provincial Park, Wainfleet Bog Conservation Area, Prince Edward Point National Wildlife Area, and Saint Lawrence Islands National Park (Fig. 1) (Sider et al. 2012). No significant differences were noted in the prevalence of sites positive for I. scapularis or B. burgdorferi between ecoregions. Spatial clusters indicated a high prevalence of sites with I. scapularis and positive for B. burgdorferi-infected ticks in the area of eastern Ontario.

Based on these findings, eastern Ontario may represent a “hot spot” for I. scapularis and the transmission of B. burgdorferi. We hypothesize that this “hot spot” is a result of a large area of highly suitable habitat, as well as an intensified rate of localized spread through small mammals and white-tailed deer. More research is required to investigate this hypothesis. Eastern Ontario has previously been labeled as an area of elevated risk due to a significantly higher rate of tick submissions from the public. Our findings validate and strengthen these data gathered by passive surveillance (Ogden et al. 2010, Nelder et al. 2014).

It may be expected that if a significant cluster was detected, there would also be a significant difference between the ecoregions; however, this was not the case. This discrepancy is likely due to the inclusion of portions of both 5E and 6E within each cluster, and therefore, minimal difference in the prevalence of positive sites between each ecoregion. It is also important to consider the modifiable areal unit problem (Waller and Gotway 2004). In our study, we used the boundaries of each ecoregion to aggregate the site data. The unit of ecoregion was chosen because the boundaries define areas with coarse-scale ecological differences, and these differences may have an impact on the ecology of Lyme disease. However, it appears that these boundaries may not be the most appropriate level at which to aggregate and analyze the data. The criteria used to create these ecoregions may not reflect the significant ecological factors present in the microhabitat of the tick (Estrada-Peña et al. 2013) and may explain our inability to detect differences based on our regression analyses. In contrast, the spatial scan statistic has a flexible scanning window and was not restricted to the ecoregion boundaries. It also should be noted that we did not reach our minimum sample size for ecoregion 5E due to weather and time constraints, and this may have affected our ability to detect a significant difference between the ecoregions (Type II error).

Importantly, we did not detect I. scapularis at a large number of sites. Many of these negative sites were located in areas with lower population density where passive surveillance is inadequate (Nelder et al. 2014). Both positive and negative findings are of significant benefit to public health. Currently, there is no human vaccine for B. burgdorferi or widespread, effective tick control measures. Therefore, disease prevention focuses on public health education and preventive measures that include personal protective measures and landscape modification. These efforts need to be targeted to the areas of elevated risk because they require considerable effort and investment by the public (Ogden et al. 2015b). Knowledge of the presence and absence of I. scapularis populations assists with risk assessment and appropriate planning of public health interventions (Ogden et al. 2008b).

Seasonal life stage patterns as well as changes in daily tick activity due to temperature and humidity fluctuations can affect the results of tick dragging (Estrada-Peña et al. 2013). We conducted tick dragging throughout the active season of I. scapularis and collected adult, nymphal, and larval stages in varying abundance. Although this should be acknowledged as a limitation of this study, our approach also provided a number of benefits. The presence of host seeking larvae (and to a lesser extent, nymphs) indicates that reproducing populations of ticks is establishing at some of our study sites and highlights key areas that should be targeted for ongoing surveillance. In addition, nymphal ticks represent the greatest risk of disease. Our tick dragging efforts were effective in collecting nymphal ticks and illustrate the necessity of an active surveillance approach to more accurately determine disease risk. Conducting field sampling throughout the season is supported by work conducted by Ogden et al. (2014a), who illustrated that tick dragging can be completed at any time during the season to provide adequate evidence of a risk area.

A. phagocytophilum, B. microti, and B. miyamotoi were not detected in any I. scapularis ticks collected in this study. Since we did not collect a large number of ticks, the power of our sample size was low, limiting our ability to detect these pathogens in our study. Previous studies report a low infection prevalence of 0.3% for both A. phagocytophilum (Nelder et al. 2014) and B. miyamotoi (Dibernardo et al. 2014). Based on the one-sided 97.5% CI, we expect the true infection prevalence to be between 0% and 5.4%, so larger sample sizes of ticks would need to be tested to rule out the presence of these pathogens at I. scapularis-positive sites.

D. variabilis, H. leporispalustris, and I. dentatus were also collected through dragging. H. leporispalustris was significantly less likely to be detected at a site in ecoregion 7E, when compared to ecoregion 5E. Research conducted by Gabriele-Rivet et al. (2015) in New Brunswick, Canada, found significant associations with the presence of H. leporispalustris and a number of ecological variables, including degree-days >0°C, proportion of clay in the soil, site elevation, season, and mean annual precipitation. Ecological differences exist between ecoregions 5E and 7E and these differences may help to explain the presence of this tick at specific sites. More field research examining the preferred habitat of H. leporispalustris should be conducted in Ontario to investigate this hypothesis.

H. leporispalustris and D. variabilis pose a potential public health risk from zoonotic pathogens other than B. burgdorferi (e.g., Rickettsia rickettsii, the causative agent of Rocky Mountain Spotted Fever, and Francisella tularensis, the causative agent of tularemia), although in Canada the prevalence of infection with these pathogens associated with these tick species is usually very low (Wood and Artsob 2012). I. dentatus rarely feed on humans and therefore poses little, if any risk to public health (Kollars and Oliver 2003).

It is important to note that the field sampling approach used in this study was biased toward detecting I. scapularis. Each species of tick has a preferred habitat (Estrada-Peña et al. 2013, Gabriele-Rivet et al. 2015), and the field sampling sites were selected based on the preferred habitat of I. scapularis. Nonetheless, our findings illustrate that an active surveillance approach can provide the added benefit of monitoring other species of ticks, including emerging or invasive species that may pose a risk to public health.

The findings of our widespread field sampling can be used to establish a current baseline for I. scapularis distribution in Ontario. As this tick species continues to spread northward on migratory birds (Ogden et al. 2008a) and is able to establish populations in areas at higher latitudes that have become suitable for tick development due to climate change (Ogden et al. 2014c), the risk of Lyme disease will increase.

It is therefore pertinent for risk assessment to have a baseline for comparison. This baseline measurement allows for more effective monitoring of risk and can be used to appropriately direct future surveillance efforts and public health interventions.

In addition to surveillance efforts to monitor ticks and tick-borne disease, the ecology of each tick and the cycle of pathogen transmission must be understood. This will greatly enhance surveillance efforts and the implementation of effective control strategies (Estrada-Peña et al. 2013). The ecology of Lyme disease is complex, involving a number of abiotic and biotic factors. These factors can differ depending on the geographic area, which has been illustrated by extensive research conducted in many states, as well as in the province of Quebec (Ostfeld and Keesing 2000, Bouchard et al. 2011). Smaller scale studies in Ontario have begun to elucidate some of the ecological factors influencing the establishment and spread of I. scapularis and Lyme disease in the province, including the role of habitat type in egg hatching and tick survival, and the influence of deer and microclimatic factors on tick abundance (Lindsay et al. 1998, Ogden et al. 2006a, Werden et al. 2014). Widespread ecological research is warranted in Ontario to complement the current body of knowledge, including data gathered by passive and active surveillance.

Conclusion

In this study, we used an active surveillance approach to better understand the distribution of I. scapularis and the risk of B. burgdorferi in Ontario, as well as other tick species and tick-borne pathogens of public health significance. I. scapularis and B. burgdorferi were detected outside of the known endemic areas, including a spatial cluster of positive sites in eastern Ontario, which indicates that this region may represent a “hot spot” for Lyme disease risk. This information can help to direct future surveillance efforts and public health interventions. Furthermore, we can now expand upon our knowledge of tick distribution and disease risk by conducting studies on the ecology of I. scapularis and B. burgdorferi to better understand the abiotic and biotic factors influencing the establishment and spread of Lyme disease in Ontario.

Footnotes

Acknowledgments

We thank the Public Health Agency of Canada (PHAC), the Canadian Wildlife Health Cooperative (CWHC), and the National Sciences and Engineering Research Council (NSERC) for financial support. K.M.C. was supported by an NSERC scholarship, an Ontario Veterinary College Fellowship, and the Blake Graham Fellowship. We thank the Ontario Ministry of National Resources and Forestry and conservation authorities across Ontario for providing access to their parks and conservations areas. We also thank Dr. Curtis Russell (Public Health Ontario) and numerous public health units in Ontario for partnering with our research project to assist with fieldwork and data sharing. Sincere appreciation is extended to the field research team composed of K. Schutten, A. Finley, Q. Marshall, H. Marshall, K. Puskas, and F. Tansil.

Author Disclosure Statement

No competing financial interests exist.

References

Bouchard

, Beauchamp

, Nguon

, Trudel

, et al. Associations between Ixodes scapularis ticks and small mammal hosts in a newly endemic zone in southeastern Canada: Implications for Borrelia burgdorferi transmission. Ticks Tick Borne Dis, 2011; 2:183–190.

Brownstein

, Holford

, Fish

. A climate-based model predicts the spatial distribution of the Lyme disease vector Ixodes scapularis in the United States. Environ Health Perspect, 2003; 111:1152–1157.

Burgdorfer

, Barbour

, Hayes

, Benach

, et al. Lyme disease—A tick-borne spirochetosis?. Science, 1982; 216:1317–1319.

Centers for Disease Control and Prevention.. Reported cases of Lyme disease by year, United States, 1995–2013. 2015. Available at www.cdc.gov/lyme/stats/chartstables/casesbyyear.html

Courtney

, Kostelnik

, Zeidner

, Massung

. Multiplex real-time PCR for detection of Anaplasma phagocytophilum and Borrelia burgdorferi . J Clin Microbiol, 2004; 42:3164–3168.

Dibernardo

, Cote

, Ogden

, Lindsay

. The prevalence of Borrelia miyamotoi infection, and co-infections with other Borrelia spp. in Ixodes scapularis ticks collected in Canada. Parasit Vectors, 2014; 7:183–190.

Diuk-Wasser

, Gatewood

, Cortinas

, Yaremych-Hamer

, et al. Spatiotemporal patterns of host-seeking Ixodes scapularis nymphs (Acari: Ixodidae) in the United States. J Med Entomol, 2006; 43:166–176.

Dumler

, Bakken

. Ehrlichial diseases of humans: Emerging tick-borne infections. Clin Infect Dis, 1995; 20:1102–1110.

Estrada-Peña

, De La Fuente

. The ecology of ticks and epidemiology of tick-borne viral diseases. Antiviral Res, 2014; 108:104–128.

10.

Estrada-Peña

, Gray

, Kahl

, Lane

, et al. Research on the ecology of ticks and tick-borne pathogens—Methodological principles and caveats. Front Cell Infect Microbiol, 2013; 3:29.

11.

Gabriele-Rivet

, Arsenault

, Badcock

, Cheng

, et al. Different ecological niches for ticks of public health significance in Canada. PLoS One, 2015; 10: e0131282.

12.

Health Canada. Consensus conference on Lyme disease. Can J Infect Dis, 1991; 2:49–54.

13.

Hinckley

, Connally

, Meek

, Johnson

, et al. Lyme disease testing by large commercial laboratories in the United States. Clin Infect Dis, 2014; 59:676–681.

14.

Koffi

, Leighton

, Pelcat

, Trudel

, et al. Passive surveillance for I. scapularis ticks: Enhanced analysis for early detection of emerging Lyme disease risk. J Med Entomol, 2012; 49:400–409.

15.

Kollars

, Oliver

. Host associations and seasonal occurrence of Haemaphysalis leporispalustris, Ixodes brunneus, I. cookei, I. dentatus, and I. texanus (Acari: Ixodidae) in Southeastern Missouri. J Med Entomol, 2003; 40:103–107.

16.

Kulldorff

. SaTScan user guide v.9.4. 2015. Available at www.satscan.org

17.

Lindsay

, Barker

, Surgeoner

, McEwen

, et al. Survival and development of the different life stages of Ixodes scapularis (Acari: Ixodidae) held within four habitats on Long Point, Ontario, Canada. J Med Entomol, 1998; 35:189–199.

18.

Nakajima

, Tsuji

, Oda

, Zamoto-Niikura

, et al. Babesia microti-group parasites compared phylogenetically by complete sequencing of the CCTeta gene in 36 isolates. J Vet Med Sci, 2009; 71:55–68.

19.

Nelder

, Russell

, Lindsay

, Dhar

, et al. 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. PLoS One, 2014; 9:e105358.

20.

Ogden

, Barker

, Beauchamp

, Brazeau

, et al. Investigation of ground level and remote-sensed data for habitat classification and prediction of survival of Ixodes scapularis in habitats of southeastern Canada. J Med Entomol, 2006a; 43:403–414.

21.

Ogden

, Bigras-Poulin

, O'Callaghan

, Barker

, et al. A dynamic population model to investigate effects of climate on geographic range and seasonality of the tick Ixodes scapularis . Int J Parasitol, 2005; 35:375–389.

22.

Ogden

, Bouchard

, Kurtenbach

, Margos

, et al. Active and passive surveillance and phylogenetic analysis of Borrelia burgdorferi elucidate the process of Lyme disease risk emergence in Canada. Environ Health Perspect, 2010; 118:909–914.

23.

Ogden

, Koffi

, Lindsay

. Assessment of a screening test to identify Lyme disease risk. Can Commun Dis Rep, 2014a; 40:1–5.

24.

Ogden

, Koffi

, Lindsay

, Fleming

, et al. Surveillance for Lyme disease in Canada, 2009 to 2012. Can Commun Dis Rep, 2015a; 411–414.

25.

Ogden

, Koffi

, Pelcat

, Lindsay

. Environmental risk from Lyme disease in central and eastern Canada: A summary of recent surveillance information. Can Commun Dis Rep, 2014b; 40:1–9.

26.

Ogden

, Lindsay

, Hanincova

, et al. Role of migratory birds in introduction and range expansion of Ixodes scapularis ticks and of Borrelia burgdorferi and Anaplasma phagocytophilum in Canada. Appl Environ Microbiol, 2008a; 74:1780–1790.

27.

Ogden

, Lindsay

, Morshed

, Sockett

, et al. The rising challenge of Lyme borreliosis in Canada. Can Commun Dis Rep, 2008b; 34:1–19.

28.

Ogden

, Lindsay

, Schofield

. Methods to prevent ticks bites and Lyme disease. Clin Lab Med, 2015b; 35:883–899.

29.

Ogden

, Radojević

, Wu

, Duvvuri

, et al. Estimated effects of projected climate change on the basic reproductive number of the Lyme disease vector Ixodes scapularis . Environ Health Perspect, 2014c; 122:631–638.

30.

Ogden

, St-Onge

, Barker

, Brazeau

, et al. Risk maps for range expansion of the Lyme disease vector, Ixodes scapularis, in Canada now and with climate change. Int J Health Geogr, 2008c; 7:24.

31.

Ogden

, Trudel

, Artsob

, Barker

, et al. Ixodes scapularis ticks collected by passive surveillance in Canada: Analysis of geographic distribution and infection with Lyme borreliosis agent Borrelia burgdorferi . J Med Entomol, 2006b; 43:600–609.

32.

Ontario Ministry of Natural Resources. Ecological Land Classification Primer Central and Southern Ontario. Peterborough: Ontario Ministry of Natural Resources; 2007:1–8.

33.

Ostfeld

, Keesing

. Biodiversity series: The function of biodiversity in the ecology of vector-borne zoonotic diseases. Can J Zool, 2000; 78:2061–2078.

34.

Parola

, Raoult

. Ticks and tickborne bacterial diseases in humans: An emerging infectious threat. Clin Infect Dis, 2001; 32:897–928.

35.

Scholten

. Human tick infestations in Ontario: Findings at the Toronto Public Health Laboratory, 1967–1977. Can J Public Health, 1977; 68:494–496.

36.

Scoles

, Papero

, Beati

, Fish

. A relapsing fever group spirochete transmitted by Ixodes scapularis ticks. Vector Borne Zoonotic Dis, 2001; 1:21–34.

37.

Sider

, Patel

, Russell

, Jain-Sheehan

, et al. Technical Report: Update on Lyme Disease Prevention and Control. Toronto: Public Health Ontario, 2012.

38.

Spielman

, Levine

, Wilson

. Vectorial capacity of North American Ixodes ticks. Yale J Biol Med, 1984; 57:507–513.

39.

Waller

, Gotway

. Visualizing spatial data. In: Waller LA, Gotway CA. Applied Spatial Statistics for Public Health Data. New Jersey: John Wiley & Sons, Inc.; 2004:104–108.

40.

Watson

, Anderson

. Ixodes scapularis say on white-tailed deer (Odocoileus virginianus) from Long Point, Ontario. J Wildl Dis, 1976; 12:66–71.

41.

Werden

, Barker

, Bowman

, Gonzales

, et al. Geography, deer, and host biodiversity shape the pattern of Lyme disease emergence in the Thousand Islands archipelago of Ontario, Canada. PLoS One, 2014; 9:e85640.

42.

Wood

, Artsob

. Spotted fever group rickettsiae: A brief review and a Canadian perspective. Zoonoses Public Health, 2012; 59 Suppl 2:65–79.