Ticks that carry Lyme Disease live in almost half of US counties – study

Black-legged tick inhabits twice as many counties as in 1998, CDC reports, with 320% increase in number of north-eastern counties seen as high risk for disease

Ticks that can carry the debilitating illness Lyme disease have significantly spread across the US over the past 20 years and are now found in nearly half of all American counties, including areas where they've never previously been documented, a new analysis has found.

The black-legged tick is now established in twice the number of counties it inhabited in 1998, according to the US Centers for Disease Control, and has expanded its range in the northeastern states and the upper midwest. Following its onward march, or hop, across the Ohio river valley, western New York and the shores of Lake Michigan since the 1990s, there has been a tripling in the incidents of Lyme disease in the US.