And, as with many questions related to nature these days, the answer is because of climate change. A 2005 study by Yale Medical School’s John S. Brownstein, Theodore Holford, and Durland Fish found that, as the planet warms, an increasingly large swath of the continent will become suitable habitat for Ixodes scapularis. Identifying this expansion of habitat as a “public health concern,” the authors note that, while the overall distribution area may initially contract (as parts of the American South become too hot for the disease-bearing ticks to thrive), the ticks will ultimately expand their suitable habitat into currently unaffected regions. Among these regions will be the central U.S., which will become home to ticks migrating north from states like Texas and Florida. But the most dramatic change could take place in Canada, where, by the 2080s, climate change will expand the total suitable habitats for I. scapularis by 213 percent.
At the time of writing, the scientists noted that Canada faced little risk from I. scapularis: “established populations … are currently limited to a small number of foci in southern Ontario.” But, over the next several decades, the study “specifically forecasts the emergence of a tick-borne infectious disease in Canada” as suitable habitats expand to northern Ontario and Manitoba. Events seem to confirm this prediction: In 2010, Canada began to require doctors to report cases of Lyme disease, and Canadian health officials now warn that “the incidence of Lyme disease in Canada is increasing.”