New Delhi, July 3 -- the United States is experiencing the highest rate of emergency room visits from tick bites since 2017, according to the Centers for Disease Control and Prevention's tick bite data tracker.

The timing is not incidental. Tens of millions of Americans will spend July Fourth outdoors over the coming days, in the parks, campgrounds, and backyards where ticks are most active. This year they are heading into a season that public health officials describe as distinctly worse than normal, one in which the geography of risk is shifting faster than many people outside the affected communities realize.

Rebecca Osborn, an epidemiologist at the Wisconsin Department of Health Services, has tracked the movement of tick species acr...