US Geographic Distribution of the Blacklegged Tick

Range expansion of Ixodes scapularis in the USA 2022
Estimated geographic ranges for Ixodes scapularis in the United States based on knowledge of tick collection records by 2022 (CDC, 2023a). 2023a. Regions where ticks live. Accessed 21 March, 2023. Fish, D., 2022; Fig. 1 licensed under CCs*.

The Tick and Tick-borne Diseases Journal (Eisen L. & Eisen R. J.) 07.24.2023, published “Changes in the Geographic Distribution of the Blacklegged Tick, Ixodes scapularis, in the United States.” The study aims to provide a geographical history of the occurrence of Ixodes scapularis (the blacklegged tick) in the US from the 1800s to present. Over time, changes in tick surveillance have made it hard to distinguish between the actual expansion of the tick’s range and better detection of existing populations.

The blacklegged tick was not considered a threat to humans until the mid-1970s, where it was believed to be mostly found in the southeastern United States, but later it was discovered to have spread widely across the eastern US up to the border with Canada, and across the south into Mexico, leading to an increase in tick-borne diseases such as Lyme disease. In studies from the 1940s, “I. scapularis was described to occasionally infest humans but still without any known association with transmission of disease agents.” Since then, there have been more than 150,000 I. scapularis ticks recorded to infest humans in the US, with this tick being now described as a vector of seven human pathogens, causing vector-borne diseases.

Factors like reforestation, increasing deer populations, and changing climate likely played a role in the tick’s geographical changes. Continuous surveillance of ticks is crucial to gather data to understand the roles of land cover, tick hosts, and climate in explaining and predicting the expansion of ticks and tick-borne diseases.

*Creative Commons License

For more information:

Read the full article on the ScienceDirect website here.