Areas of the United States where I. scapularis, A. americanum, and I. pacificus are endemic. Pathogens that can be transmitted by I. scapularis include A. phagocytophilum, B. burgdorferi, B. miyamotoi, Babesia microti, Babesia divergens, and POWV. Pathogens that can be transmitted by I. pacificus include A. phagocytophilum, B. burgdorferi, B. miyamotoi, Babesia microti, and Babesia duncani. Pathogens that are transmitted by A. americanum include E. chaffeensis, E. ewingii, Heartland virus, and Bourbon virus. Where tick species ranges overlap, all pathogens need to be considered in making a diagnosis.