In the summer, many species of insect and arthropods are active and proliferating. One of them is the deer tick, also known as the black-legged tick (Ixodes scapularis), an invasive species responsible for the transmission of Lyme disease. Originally from the United States, this tick has now been established in Quebec for several years, a situation linked with climate change. We speak of an established tick population when it manages to survive and reproduce from one year to the next. But what role has climate change played in this, and what will happen in the future?

A climate conducive to the migration of the black-legged tick

The higher temperatures induced by climate change have a strong influence on the geographic progression of deer ticks. In Canada, warming could allow them to move northward at a rate of 35 to 55 kilometres per year. 

In Quebec, the issue is already present in the southern part of the territory, where surveillance data has detected established tick populations in several regions.

Figure 1: Current distribution of Ixodes scapularis tick populations in Quebec.

The Institut national de santé publique du Québec (INSPQ), in collaboration with Ouranos, has produced new maps this year showing that by 2080, most of Quebec’s inhabited areas could offer favourable conditions for the establishment of these ticks, increasing everyone’s risk of getting bitten and contracting Lyme disease.

Although ticks are present throughout the year, the species becomes active when the temperature rises above 4°C and there is no snow cover on the ground. Increasingly hot summers are likely to boost tick activity, which is highest when the temperature is around 25°C. And with rising temperatures, the period of tick activity tends to lengthen, starting earlier in the spring and ending later in the fall. 

The changing climate is also causing the ranges of the host species that carry ticks to expand. Deer, birds and rodents that are displaced due to climate change or human-induced changes in their habitats contribute to the geographic expansion of ticks in the province.

The future distribution of deer ticks in Quebec

In the coming decades, climate projections suggest there will be an increase in the range of this species. As a result, the presence of Lyme disease in most of Quebec’s inhabited regions is also likely to increase.  

Based on median and high greenhouse gas emission scenarios, the climate zone favourable to the establishment of deer tick populations will tend to increase in almost all of southern Quebec by 2080. Tick distribution projections are similar for both scenarios for 2030. In projections for 2050 and 2080, ticks are expected to advance northwards under both scenarios, but more under the high emissions scenario.

Figure 2: Climate zone favourable to the establishment of deer tick populations in a median greenhouse gas emission scenario for the years 2030 (red), 2050 (orange) and 2080 (yellow).

Figure 3: Climate zone favourable to the establishment of deer tick populations in a high greenhouse gas emission scenario for the years 2030 (red), 2050 (orange) and 2080 (yellow).

To produce these projections, Ouranos calculated the number of degree-days in °C, a measure that corresponds to the difference between the daily average temperature and a reference value. This helps determine if the climate conditions in an area will allow deer ticks to become established.

Here, the indicator used is the annual number of degree-days above 0°C, greater than or equal to 2800. If the projected conditions at a given location exceed this threshold, a deer tick population can be expected.

Deer ticks: Vectors of Lyme disease 

A deer tick bite is not automatically synonymous with Lyme disease. In fact, a little less than one tick out of three is infected with the bacteria Borrealia burgdorferi and can transmit it. They can contaminate humans and animals through a bite and lead to skin, joint, heart and eye problems, and even neurological issues. Other diseases can also be transmitted by deer ticks, including anaplasmosis. 

There have been more and more cases of Lyme disease in the province over the past ten years. Between 2014 and 2018, the average number of cases reported annually was 219, but this number climbed to 524 between 2019 and 2023. 

Several factors have increased the risks of exposure to ticks and Lyme disease, such as the presence of favorable habitats to ticks (woods, forests, tall grass, etc.) and greater human density near established tick populations.

A deer tick. Photo by David Cappaert.

Lowering the risk of contracting Lyme disease

With the return of the warm weather, you should take the necessary precautions to avoid being infected. The month of May was Lyme Disease Awareness Month, and the  Gouvernement du Québec and the Gouvernement du Canada provided the public with valuable advice on the measures to be taken to reduce the risk of exposure to deer ticks and avoid contracting Lyme disease. Many solutions exist. All you have to do is take a few simple steps that can make all the difference!