any of a group of parasitic microorganisms that live in arthropods (as ticks and mites) and can cause disease if transmitted to human beings
any of a group of parasitic bacteria that live in arthropods (as ticks and mites) and can cause disease if transmitted to human beings
any of a group of very small rod-shaped bacteria that live in biting arthropods (as ticks and mites) and cause disease in vertebrate hosts; they cause typhus and other febrile diseases in human beings