Bacteria of the genus Rickettsia are carried as parasites by many ticks, fleas, and lice, and cause diseases such as typhus, scrub typhus, rickettsialpox, Brill-Zinsser disease, Boutonneuse fever, and Rocky Mountain spotted fever in human beings. Like viruses, they grow only in living tissue. Judging by the scientific literature, research into the genetics of rickettsiae has been less intense than into that of viruses and other bacteria. Diseases caused by some other bacteria, such as Coxiella burnetii, the cause of Q fever, are also considered rickettsial diseases, though the organisms are no longer considered particularly close relatives.
The genus Rickettsia is named after Howard Taylor Ricketts (1871-1910). Despite the similar name, Rickettsia bacteria do not cause rickets. The disease of rickets takes its name from the Greek word for spine, rhakhis, and is a vitamin deficiency disease, not an infectious disease.