Ticks in a changing climate

Certain species of ticks are vectors of bacterial, viral and protozoan pathogens and are capable of infecting humans and animals alike through prolonged attachment during a blood meal. Tick species that act as such vectors in Canada include the blacklegged tick (Ixodes scapularis), the Western blacklegged tick (Ixodes pacificus), the American dog tick (Dermacentor variabilis), the Rocky Mountain wood tick (Dermacentor andersoni) and the Lone Star tick (Amblyomma americanum). Each of these tick species has a preferred habitat where it is often found.  

Lyme disease is the most commonly reported tick-borne disease for humans in Canada, with 3,147 cases reported in 2021. Other human tick-borne diseases that have been reported in Canada include Anaplasmosis, Babesiosis, Rocky Mountain Spotted Fever, Powassan virus disease, Colorado tick fever virus, tick-borne relapsing fever, and ularemia, though cases have remained low overall. Nonetheless,  this may change: researchers estimate ticks are expanding northwards at a rate of 35-55 kilometers a year as a result of climate change, shifts in animal migration patterns, and land use changes. This is likely to put more Canadians at greater risk of tick exposure and consequently tick-borne diseases. Moreover, climate change may accelerate the tick life cycle, increasing both tick abundance and seasonal questing activity.

The resources below are intended to assist Environmental Public Health practitioners to understand and address the changing risk of tick-borne infections in Canada.

The impact of climate change on tick-borne diseases in Canada

• The impacts of climate and land use change on tick-related risks (NCCEH, 2022)
  This evidence review examines the natural environments that increase the risk of tick exposure, and how climate change and land use changes are impacting these environments.
   
• Possible Effects of Climate Change on Ixodid Ticks and the Pathogens They Transmit: Predictions and Observations (Ogden et al., 2020)
  This journal article explores how climate and weather could impact the occurrence and abundance of ticks and the transmission of tick-borne diseases, and how projected changes to climate may alter the geographical ranges of ticks and tick-borne diseases.
   
• Increased risk of tick-borne diseases with climate and environmental changes (Government of Canada, 2019)
  This evidence review summarizes the impacts of climate and environmental changes on the number, activity, and range of ticks and their hosts. The review also examines how climate change may alter human behaviour in ways that increase exposure to ticks and consequently tick-borne diseases.
   
• Range Expansion of Tick Disease Vectors in North America: Implications for Spread of Tick-Borne Disease (Sonenshine, 2018)
  This evidence review focuses on the impacts that climate change will have on biotic (i.e., dense vegetation, leaf litter, etc.) and abiotic factors (relative humidity, soil moisture, etc.) that in turn are likely to influence the future range expansion of tick species in the US and Canada.

 Monitoring and surveillance of tick vectors, range, and disease risk in Canada

• Lyme disease: Surveillance (Government of Canada, 2023)
  This website provides an overview of the surveillance of human cases of Lyme disease in Canada by provincial and territorial public health authorities. The website also provides a tool to check whether you are in a risk area where tick populations may be emerging or where people are at greater risk of getting Lyme disease.
   
• Epidemiology of ticks submitted from human hosts in Alberta, Canada (2000–2019) (Kanji et al., 2022)
  This peer-reviewed article presents a retrospective review of ticks recovered from humans and submitted for identification in Alberta over a 19-year period. Infection prevalence was also determined to better understand pathogen epidemiology.
   
• Monitoring Risk: Tick and Borrelia burgdorferi Public Participatory Surveillance in the Canadian Maritimes, 2012-2020 (Lewis et al. 2021)
  This peer-reviewed article characterizes the distribution of ticks recovered by passive surveillance, and their pathogen prevalence, in three Canadian Maritime provinces from 2012-2020.
   
• Monitoring the patterns of submission and presence of tick-borne pathogens in Ixodes scapularis collected from humans and companion animals in Ontario, Canada (2011–2017) (Nelder et al., 2021)
  This peer-reviewed article describes the spatiotemporal trends for blacklegged tick (Ixodes scapularis) submissions from humans and companion animals in Ontario from 2011-2017, along with pathogen prevalence.
   
• Public platform for image-based identification and population monitoring in Canada (eTick, 2021)
  This website is a citizen science project that invites the public to participate in the monitoring of ticks in Canada by submitting tick photos via a web platform or mobile app for identification by a professional. The website also allows users to visualize information submitted by species, date and geographical area. More information about eTick can be found on the NCCEH website here and here. 
   
• Surveillance for Ixodes scapularis and Ixodes pacificus ticks and their associated pathogens in Canada, 2019 (Government of Canada, 2019)
  This peer-reviewed article characterizes passive and active surveillance of the main Lyme disease tick vectors and their pathogen prevalence in Canada in 2019, highlighting emerging risk areas.
   
• Canadian Databases for Ticks and Mosquitoes (NCCID & NCCEH, 2018)
  This provincial and territorial mosquito and tick database includes information on which government entity (if any) performs the surveillance of mosquitoes and/or ticks with the potential to transmit infections to humans and how this surveillance is carried out.

Individual and community-level tick prevention strategies

• A review of ticks in Canada and health risks from exposure (NCCEH 2022)
  This evidence review outlines the health risks of tick-borne diseases in Canada and provides an overview of several personal protective measures that can help reduce risk of exposure, and subsequently infection.
   
• Behavioral risk factors associated with reported tick exposure in a Lyme disease high incidence region in Canada (Aenishaenslin et al., 2022)
  This peer-reviewed article investigates the adoption of preventive behaviours towards tick bites and Lyme Disease and the association between behavioural risk factors and reported tick exposure in an area of Quebec with high Lyme Disease incidence.
   
• Preventing mosquito and tick bites: A Canadian update (Canadian Paediatric Society, 2020
  This webpage provides basic guidance on personal protective measures to safely and effectively prevent tick bites in Canada, including avoiding tick habitats, using physical and chemical barriers, and insecticides.
   
• Case Studies in Tick Surveillance and Tick-borne Disease Prevention (Association of state and territorial health officials, 2020)
  This report comprises three case studies documenting how US vector-borne disease control officials for three different states have responded to specific concerns related to the public health threats posed by ticks. While these cases are US-based, they serve as helpful guides for responding to similar problems in Canada.
   
• Evidence for Personal Protective Measures to Reduce Human Contact With Blacklegged Ticks and for Environmentally Based Control Methods to Suppress Host-Seeking Blacklegged Ticks and Reduce Infection with Lyme Disease Spirochetes in Tick Vectors and Rodent Reservoirs (Eisen & Dolan 2016)
  This evidence review documents the progress made over the last three decades in 1) preventing human–tick contact with repellents and permethrin-treated clothing, and 2) suppressing Ixodes scapularis and disrupting enzootic transmission of Lyme Disease with environmentally-based control methods.