The number of cases of Lyme disease in the U.S. has increased dramatically over the past several years, and its reach is spreading across more of the country, according to a new report from the Centers for Disease Control and Prevention.
Cases of Lyme disease are still concentrated in the Northeast and upper Midwest. But now more areas in those regions are considered high risk, the study notes.
“The risk is expanding, in all directions,” said the lead author, Kiersten Kugeler of the CDC, according to the Associated Press.
There are now 260 counties in the country where the number of Lyme disease cases is at least twice what’s expected, given the size of each county’s population. That’s up from 130 a decade earlier, according to the report.
The bacteria that causes Lyme disease is spread by infected deer ticks, and researchers suspect warmer temperatures caused by climate change are allowing the ticks to thrive in more areas of the country.
More development in wooded areas, where ticks live, may also be a factor, Kugeler said, according to the Associated Press.
According to the study, 17 states have high-risk counties, including several in the Northeast - Connecticut, Massachusetts, New Hampshire, Maine and Vermont.
In the upper Midwest, Minnesota and Wisconsin have several high-risk counties, as do Iowa and Michigan.
More Minnesota counties are now considered high risk. But the study found that Lyme disease isn't spreading as much in Wisconsin, staying primarily in the northwestern part of the state, according to NBC News, although the study didn't say why.
Minnesota recorded 1,431 confirmed cases of Lyme disease in 2013, along with another 909 suspected cases. That compares with just 252 confirmed cases in 1996.
In Wisconsin, the numbers are fairly similar: 1,741 confirmed cases in 2013 and another 527 probable.
Nationwide about 20,000 to 30,000 cases are reported each year, but experts say the actual number is probably 10 times higher.
Symptoms of Lyme disease include a fever, headache and fatigue, and sometimes a rash that looks like a bull’s-eye on the tick bite. Most people recover with antibiotics. If left untreated, the infection can cause arthritis and more severe problems.