Current Status, Public Health Implications, and Potential Future Establishment of <i>Amblyomma americanum</i>, the Lone Star Tick, in Maine

Introduction: Amblyomma americanum is a medically important tick species established in the southeastern United States, with populations gradually spreading northward into New England. This study aimed to evaluate the current presence, distribution, and density of A. americanum in Maine. Methods: Surveillance efforts focused on Ixodes scapularis have been conducted by the Vector-Borne Disease Laboratory of MaineHealth Institute for Research since 1989. This surveillance uses tick flagging, examination of hunter-harvested game and trapped wild hosts for feeding ticks, and a statewide passive surveillance program. Effort focused on A. americanum surveillance began in 2019 using flagging, carbon dioxide-baited trapping, and serosurveillance (Heartland virus, Bourbon virus) in cervids. Results: Maine’s passive tick surveillance program has received low numbers of A. americanum (0–17 per year, 1989–2024) from across the state. Immature A. americanum have also been repeatedly collected from migratory birds (0–6 per year, 1991–2024). Serosurveillance of cervids (n = 217) identified 1 deer with Heartland virus. Zero A. americanum were returned from targeted flagging or carbon dioxide-baited trapping. Discussion: Uncertainties surrounding the seasonality of possible A. americanum populations in Maine may account for the low numbers seen from active surveillance and examination of game. The low, yet continual, collections from migratory birds and passive surveillance over time mirror patterns of establishment seen previously in New England and indicate repeated introductions into Maine. Conclusions: Although collections from Maine do not yet meet the US Centers for Disease Control and Prevention requirements for an established population, evidence shows that low numbers are present in the state, and that further range expansion and increased abundance are likely in years to come.