Species distribution models for the eastern blacklegged tick, Ixodes scapularis, and the Lyme disease pathogen, Borrelia burgdorferi, in Ontario, Canada

Abstract

The blacklegged tick, Ixodes scapularis, is established in several regions of Ontario, Canada, and continues to spread into new geographic areas across the province at a rapid rate. This poses a significant public health risk since I. scapularis transmits the Lyme diseasecausing bacterium, Borrelia burgdorferi, and other pathogens of potential public health concern. The objective of this study was to develop species distribution models for I. scapularis and B. burgdorferi to predict and compare the potential distributions of the tick vector and the Lyme disease pathogen as well as the ecological factors most important for species establishment. Ticks were collected via tick dragging at 120 sites across southern, central, and eastern Ontario between 2015 and 2018 and tested for tick-borne pathogens. A maximum entropy (Maxent) approach was used to model the potential distributions of I. scapularis and B. burgdorferi. Two independent datasets derived from tick dragging at 25 new sites in 2019 and ticks submitted by the public to local health units between 2015 and 2017 were used to validate the predictive accuracy of the models. The model for I. scapularis showed high suitability for blacklegged ticks in eastern Ontario and some regions along the shorelines of the Great Lakes, and moderate suitability near Algonquin Provincial Park and the Georgian Bay with good predictive accuracy (tick dragging 2019: AUC = 0.898; ticks from public: AUC = 0.727). The model for B. burgdorferi showed a similar predicted distribution but was more constrained to eastern Ontario, particularly between Ottawa and Kingston, and along Lake Ontario, with similarly good predictive accuracy (tick dragging 2019: AUC = 0.958; ticks from public: AUC = 0.863. The ecological variables most important for predicting the distributions of I. scapularis and B. burgdorferi included elevation, distance to deciduous and coniferous forest, proportions of agricultural land, water, and infrastructure, mean summer/spring temperature, and cumulative annual degree days above 0˚C.

Monitoring Risk: Tick and Borrelia burgdorferi Public Participatory Surveillance in the Canadian Maritimes, 2012–2020

“…In this case, tick presence, abundance, the nature and prevalence of infection should be communicated to the public in a timely manner to promote strategies that reduce tick encounters and reduce the duration of tick feeding. While the saltatory and fluid seeding of adventitious ticks is difficult to model, modeling climate and biotic factors that promote establishment of new tick populations can be used to provide predictive power for public health messaging [ 36 , 46 , 79 , 80 ]. Tick establishment is driven by climate conditions, geography and the movement of animal hosts [ 36 , 46 , 81 , 82 , 83 ].…”

Earth Observation-Informed Risk Maps of the Lyme Disease Vector Ixodes scapularis in Central and Eastern Canada

“…This was evident in the validation analyses. Evaluating these qualities by field study is a work in progress, and the outcomes of these studies will allow more granular identification of Lyme disease risk habitats according to woodland types, which will likely also be identifiable using EO data [25].…”

“…Previous studies have used EO data to explore spatial variation in environmental suitability, over relatively short timescales, for vector-borne diseases [17,18,20,[25][26][27], mostly from the perspective of ecological studies. However, here, we explore the use of EO data for public health purposes to identify how environmental suitability for the Lyme disease vector I. scapularis has changed over a 16-year timescale when it is thought that a warming climate has driven the range expansion of the tick and Lyme disease risk into Canada.…”

Tick infestation on medium–large-sized mammalian hosts: are all equally suitable to Ixodes ricinus adults?

“…Tick-borne diseases are emerging across northern latitudes in both Europe [1] and North America [2], and understanding the role of the host community for limiting tick-borne diseases is a key issue for management. In Europe, the generalist tick Ixodes ricinus is the main vector of the pathogens causing Lyme borreliosis [3] and other pathogens that are of medical importance [4].…”