rickettsia

Any of various bacteria of the genus Rickettsia, carried as parasites by many ticks, fleas, and lice, that cause diseases such as typhus and Rocky Mountain spotted fever in humans.

Any of a group of gram-negative bacteria, of the genus Rickettsia, carried as parasites by ticks, fleas and lice; they cause typhus and other diseases

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