Expanding range of Ixodes scapularis Say (Acari: Ixodidae) and Borrelia burgdorferi infection in North Carolina counties, 2018-2023.

North Carolina (NC) has been experiencing a recent surge in human Lyme disease (LD) cases. Understanding the distribution of tick-borne diseases necessitates understanding the distribution of the ticks that transmit their causative pathogens. Unfortunately, in NC, knowledge on tick distribution is outdated. In this manuscript, we report the results of a state-wide entomologic survey conducted in 42 NC counties by flagging/dragging from spring 2018 to summer 2023. Ixodes scapularis nymphs and adults were screened for Borrelia burgdorferi (the causative agent of LD) and four other tick-borne bacterial pathogens (Anaplasma phagocytophilum, B. mayonii, B. miyamotoi, and Babesia microti) by the Centers for Disease Control and Prevention (CDC). Consistent with current data on human LD cases incidence and distribution, results of this study indicated a range expansion of I. scapularis with higher tick densities and B. burgdorferi infection prevalence now occurring in the Blue Ridge Mountains province of western NC. Temporal analysis of I. scapularis presence data indicated that this shift is fairly recent (about 10 years). Finally, in the Blue Ridge Mountains we detected a northeast-to-southwest gradient in I. scapularis tick and B. burgdorferi infection prevalence suggesting that this trend is driven by a spread of the northern clade I. scapularis ticks into NC from southwestern Virginia, along the Appalachian Mountains. Other pathogenic bacteria detected in I. scapularis ticks included B. miyamotoi and A. phagocytophilum, that were limited to the Blue Ridge Mountains. These results have important public health implications, including the need for enhanced tick surveillance, updated clinical awareness, and targeted public education in newly affected areas.