Lyme Disease Ticks Spreading Across U.S.
More Americans are likely to encounter ticks carrying Lyme disease than ever before, according to a study published in the Journal of Medical Entomology.
Researchers mapped the distribution of those ticks and found that they are ranging farther north than before, and are now living in nearly half of the counties in the U.S.
There are two tick species that can carry the bacteria that cause Lyme disease: the blacklegged tick, also known as the deer tick, and the western blacklegged tick. The bacteria can be transmitted to people only through tick bites.
After evaluating data for the 3,110 counties in the continental U.S., the researchers found recorded evidence that the eastern tick is in 1,420 counties and the western tick is in 111 counties. Together, the two tick species now span 49 percent of U.S. counties across 43 states.
Lyme cases have risen, too. In 1991, about 10,000 Lyme disease cases were reported in the U.S., but in 2014, more than 33,000 cases were reported, according to the Centers for Disease Control and Prevention. Early-stage Lyme symptoms include fever, chills, joint pain and often a distinctive "bull's-eye" rash at the site of the tick bite. If untreated, the disease can cause arthritis, heart palpitations, brain inflammation, and weakness of the facial muscles.
One reason for expansion of the ticks' range may be climate change, since they don’t survive in severe cold or dry areas.
Not every one of those types of ticks carry the bacteria that causes Lyme disease, so the researchers did not speculate on how much the expansion of their range will increase the number of Lyme disease cases.
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