The black-legged tick is on the move.

Cases of Lyme disease -- traditionally more prevalent in the Northeast -- have now been found in all 50 states and the District of Columbia, a 2018 study from Quest Diagnostics found. While the Northeast still reported the highest number of cases, California and Florida had the highest percentage increase in positive test results from 2015 to 2017.

Experts say the tick has been expanding its range into the southern and western U.S. and into Canada. However, after years of increases in Lyme case numbers, the CDC reported a 21-percent decrease in the number of confirmed and probable cases between 2017 and 2018 (33,666).

Those are the reported cases. The CDC estimates there are more than 300,000 cases of Lyme infection in the U.S. each year -- or 10 times as many as what is reported.

Most cases are clustered in 14 states in the Northeast and Upper Midwest, but Lyme has been reported as far south as Mexico, and increasingly, in Canada.

The black-legged tick (Ixodes scapularis), also known as the deer tick, carries the bacteria that causes Lyme infection. The same tick also can spread other diseases, including babesiosis, anaplasmosis, and Powassan virus -- other diseases on the rise in the U.S.

Here's more about the disease and what to expect this year and beyond.