Rickettsiae is a genus of coccobacilli, 0.5-1 µm long, oval or irregular in shape, with one polar flagellum and one reduced mouthpart.
They cause rickettsioses in humans and other mammals, as well as febrile diseases in birds. A significant part of the causative agents of rickettsial diseases belongs to the family Rickettsiaceae, order Alphaproteobacteria. Previously classified as bacteria, they are currently classified as primitive organisms. In case of infection, prototype pathogens exist, as in the case of R. prowazekii—Brick fever peaks