According to a new study from the Centers for Disease Control and Prevention, ticks that can spread Lyme disease now live in almost half of U.S. counties. Researchers found that varieties of the blacklegged tick that may carry bacteria responsible for Lyme disease are present in 45 percent of counties nationwide, compared with just 30 percent in 1998. The study results were recently reported on by Reuters.
Based on recent research, since the late 1990s, the number of reported Lyme disease cases in the U.S. has more than tripled. To assess changes in the tick population, researchers analyzed data reported by counties using the same surveillance methods from 1998 and discovered the following:
- Deer ticks in 1,420 out of 3,110 counties in the continental U.S., or about 46 percent of counties.
- Western blacklegged ticks in 111 counties, or about 4 percent.
- Deer ticks are now established in 842 counties across 35 states, compared with 396 counties in 32 states in 1998. These ticks used to be concentrated in northeastern states but have moved west and south.
- Western blacklegged ticks are now established in 95 counties across six states, up from 90 counties in 1998. These ticks remain concentrated in Pacific coast states.
- Outside of the U.S., ticks carry the disease in forested areas of Asia, northwestern, central, and eastern Europe.
According to Bobbi Pritt, M.D., Director of Clinical Parasitology at the Mayo Clinic in Rochester, Minnesota, Environmental and climate changes may be helping ticks to expand their territory in the U.S.
“Warmer temperatures, increases in rainfall, and milder winters can favor tick survival,” Dr. Pritt, who wasn’t involved in the study, commented by email. “These factors can also favor survival and expansion of the mammals and birds that the ticks feed on.”