Five years ago, finding a blacklegged tick in most of southern Michigan was uncommon enough to surprise a county health worker. That is no longer the case. The Michigan Department of Health and Human Services reported 1,215 Lyme disease cases in 2024, up from 452 in 2020, a 168% increase driven by the rapid geographic spread of Ixodes scapularis, the blacklegged tick responsible for transmitting the disease.
The MDHHS spring 2025 advisory warned that blacklegged ticks are now established in more Michigan counties than at any point on record. The agency’s public data highlights the 2020-to-2024 arc, and the overall trajectory, a 168% rise over five years with the steepest gains in the most recent years, underscores a dramatic acceleration in both tick spread and case detection across the state.
Where the ticks are showing up
Blacklegged ticks were once concentrated in western Michigan’s lakeshore counties and parts of the Upper Peninsula. Field surveillance now finds established populations across much of the Lower Peninsula, including counties in the southeast and central regions that had little recorded tick activity a decade ago.
In Kalamazoo County, health officials collected 24 blacklegged ticks during 2024 surveillance sweeps. Of those, seven tested positive for Borrelia burgdorferi, the bacterium that causes Lyme disease, and one carried Anaplasma phagocytophilum, the pathogen behind anaplasmosis. A nearly 30% Lyme positivity rate in a single county sample is not generalizable statewide, but it illustrates the kind of local risk that was virtually absent from that part of the state a few years ago…