County-level surveillance for the American dog tick (Dermacentor variabilis) and Rickettsia species in Kentucky

Spotted fever group (SFG) rickettsiosis includes a group of illnesses with similar symptoms caused by Rickettsia species bacteria. While Rickettsia rickettsii, the agent of Rocky Mountain spotted fever (RMSF) is a well-known pathogen, other SFG Rickettsia spp. can infect ticks and occasionally contribute to human disease. We conducted county-level surveillance of Dermacentor variabilis ticks in Kentucky to characterize the distribution and diversity of SFG Rickettsia. Ticks were collected from the environment from 2019 to 2024 by dragging a white cloth and through our Kentucky Tick Submission Program. In total, 2,023 D. variabilis ticks were collected from 114 counties. Rickettsia species were detected in 1% of Dermacentor variabilis ticks, including R. montanensis (0.47%), R. amblyommatis (0.13%), and R. parkeri (0.13%). These findings indicate that, while SFG Rickettsia are present at low levels in D. variabilis ticks in Kentucky, continued surveillance in counties with reported SFG rickettsiosis cases is essential to improve clinical recognition and guide public health efforts to monitor and prevent SFG rickettsiosis.