Lyme-Carrying Ticks Are Now Found in Half of U.S. Counties

The number of areas with ticks increased by almost 45 percent since 1998.


Tick photo via Shutterstock

In 2014, 96 percent of Lyme disease cases came from just 14 states, most of them in the Northeast. A new study may shed some light on why that is.

The study, conducted by the CDC and published in the Journal of Medical Entomology, tracked the prevalence of two species of Lyme-carrying ticks in every county in the country. The researchers found that, since a similar study was done in 1998, the number of counties that are home to a significant number of the ticks increased by almost 45 percent. The species were found in roughly half of the counties in the U.S., spread across 43 states.

Where does the Northeast fit into all of this? Though the northern states have always seen more ticks than our neighbors to the south and west, one variety of tick, I. scapularis, spread significantly from 1998 to the current study, with higher levels in almost all of the New England and Mid-Atlantic states, as well as Ohio, Virginia, West Virginia, and North Carolina. The other species, I. pacificius, is mostly contained to California, Oregon, and Washington. Perhaps the most dramatic change happened in the Midwest. Minnesota went from nine counties in the ’90s to 45, while Ohio went from zero to 33.

Massachusetts has been a hub for ticks long before the CDC study—in 2014, it had the third-highest rate of Lyme disease contraction nationwide—and the latest round of data shows no sign of that stopping.

To see the full map of tick locations, see the study here.