For the better part of the 21st century, the topic of climate change has been at the forefront of environmental and political discussions. But perhaps an overlooked aspect of climate change is the impact it could have on increasing the threat of tick-borne illnesses.

Heinz College Professor and environmental economist Edson Severnini has researched the correlation between climate change and tick-borne illnesses extensively, and is convinced that the warming climate is creating conditions that are favourable to ticks and expanding their range. Severnini notes that “climate change is making the natural habitat of areas historically not prone to ticks suitable for them, which expands the area where exposure could happen”, going as far as predicting a surge in Lyme disease in North America of about 21 percent by mid-century, citing warmer temperatures as the primary factor. A consequence of the temperature being warm for a greater part of the year is that humans will spend more time outdoors, particularly in wooded areas where ticks can be found in droves, driving up the chances they will be bitten. Severneni believes the impact of global warming will be wide ranging, potentially overwhelming health care infrastructure and compromising other services provided by hospitals and clinics due to an increase in tickborne illnesses.

So why do warmer temperatures lead to a greater abundance of ticks? Generally, ticks begin questing for a host when temperatures reach around 4 to 10 Celsius. Because of climate change, ticks are beginning to quest earlier in the spring and later into the summer as their ideal conditions are present for a greater portion of the year. This is particularly the case in regions like the American Midwest and northeast where ticks already thrive. Another factor that must be taken into consideration is the fact that the increased temperature also increases the range, abundance, and activity of reservoir and tick hosts like rodents and deer, making it easier for ticks to find hosts.

The Center for Disease Control and Prevention (CDC) confirms that tick development, activity, survival, and behaviour are all directly influenced by environmental factors like temperature and humidity. The CDC logs about 30,000 cases of Lyme disease each year, but estimate that number only accounts for about 10 percent of the people who contract the disease each year due to misdiagnosis and underreporting. While Lyme disease is by far the most commonly reported tickborne disease, rare illnesses such as anaplasmosis, Powassan virus, and babesiosis are also expected to become more of a threat as temperatures rise.