Tick-Borne Diseases are on the Rise in the United States: An Analysis of the Explanations Behind Tick Expansion

The visible range expansion of numerous tick species in the United States over the past century has caused much concern among disease ecologists and public health officials. It has also led to an increase in tick-borne disease cases, specifically Lyme disease, which has driven scientists to explore the reasons why we are seeing more ticks in the United States. Much of the literature attributes the recent alterations in tick ranges to climate change. A closer reading of the literature however, showed that climate change does not support range expansion in every region of the United States. I conducted a literature review on the changes in range the black-legged tick, Ixodes scapularis, to see which hypotheses best support the observed range expansions in different regions of the United States. Both the northward and westward expansion of the black-legged tick, Ixodes scapularis, were considered, as well as the factors contributing to changes in geographical distribution.  Two different hypotheses, the impact of climate change and the changes in abundance of host species, were discussed in relation to each expansion, to explore how I. scapularis is affected by different climatic and ecological factors. Analysis showed variation in the cause for tick expansion across different regions, and that multiple factors can impact a single tick species in one region. These findings indicated that there are multiple ways to explain the increase of tick-borne diseases cases. The results suggest that further studies in other similar geographic regions, such as northern Europe, would help to further test the findings of this study.