Your favorite hiking spots might have some new inhabitants.

Researchers at the U.S. Centers for Disease Control and Prevention (CDC) say the range of ticks capable of carrying the bacteria that causes Lyme disease is spreading.

The research, published in the Journal of Medical Entomology, is the first update on blacklegged tick distribution in the United States since 1998.

Dr. Rebecca Eisen, a research biologist at the CDC, noticed the lapse in surveillance and assembled a team to look at the populations of ticks that can spread Lyme disease, the blacklegged tick (Ixodes scapularis) and the western blacklegged tick (Ixodes pacificus).

Their research determined the blacklegged tick is now present in more than 45 percent of U.S. counties, compared to 30 percent 18 years ago. They also found blacklegged ticks are now considered established in twice the number of counties as in 1998.

The areas most affected, researchers say, appear to be in the northern U.S., while the south’s numbers remain relatively stable. The range of the western blacklegged tick, however, only increased from 3.4 to 3.6 percent of counties.

“Our study shows that over that time period, the distribution of Lyme disease vectors has changed substantially, with notable increases in the northeastern and north-central states,” Eislen told Healthline. “The tick is now established in areas where it was absent 20 years ago.”

The CDC estimates that 300,000 Americans are diagnosed with Lyme disease each year. The estimates are now 10 times higher than they once were after 2013, when the CDC adjusted their annual estimates.

Cases of Lyme disease were lowest in 1995, but peaked at 30,000 in 2013. Of those cases, 95 percent occurred in 14 states, with the most infections occurring in the Northeast and along the Mississippi River border between Minnesota and Wisconsin.

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Factors Driving the Spread of Ticks

Some research suggests that climate change could impact the spread of Lyme disease by giving ticks a longer feeding season. One field study determined warmer years give ticks three more weeks of their lifecycle when they’re most likely to infect humans.

Eislen conducted a study that was published in December in the Journal of Medical Entomology and concluded meteorological variables are most influential in determining when ticks will seek a host.

“Although the ability of ticks to survive and reproduce is influenced by temperature and precipitation, climate is only one of many factors influencing the distribution of ticks,” she said. “Other factors include, but are not limited to, availability of hosts, and suitable habitat, such as wooded or brushy vegetation.”  

With a multitude of factors affecting tick population, Eislen says during any given year, people may not notice the changes depending on the amount of time they or their pets spend outdoors.

While there may be more ticks carrying the bacteria that causes Lyme disease — also known as spirochetes — Eislen says the risk of people contracting Lyme disease is not equal across areas of the country, even where the tick is present. 

“This is largely because of differences in how ticks in the north and the south find their hosts and how many of these ticks are infected with LD spirochetes,” she said.

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Tips to Prevent Lyme Disease

Summer is the blacklegged tick’s prime season for feasting.

The two types of blacklegged ticks that spread Lyme disease live in wooded and high grass areas, so extra precaution should be taken in those places.

To reduce the risk of Lyme disease, CDC officials recommend that people:

  • learn which tickborne diseases are common in their area.
  • walk in the center of trails when hiking.
  • avoid areas with thick vegetation, high grass, and leaf litter.
  • use repellent that contains 30 percent DEET on exposed skin. (American Academy of Pediatrics recommends products with up to 30 percent DEET for children.)
  • treat clothing and gear with products containing permethrin.
  • bathe or shower after coming indoors and look for crawling ticks before they bite you.
  • remove all attached ticks immediately.
  • regularly treat dogs with products that kill and/or repel ticks.

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