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Tick-borne illnesses have more than doubled in the United States over the past decade. 

Tick-borne Lyme disease, which can cause life-threatening illness, remains a concern in Florida.

Until very recently it was thought that just one bacterium was to blame for causing Lyme disease in humans. But it turns out that a second, related bug can cause it too.

In 2013, during routine testing of bacterial DNA floating around in the blood samples of people suspected of having Lyme disease, researchers at the Mayo Clinic in Rochester, Minn., realized they were looking at something different.

Rocky Mountain spotted fever is a nasty disease.

"It's super, super scary," says F. Scott Dahlgren, an epidemiologist with the Centers for Disease Control and Prevention.

"If you don't treat for Rocky Mountain spotted fever by the fifth day of illness, there's a really good chance you're going to die," says Dahlgren. "And it's an ugly, ugly death, too," he adds. "It's a horrific thing to go through and to see a loved one go through."