Rickettsial diseases: The infectious diseases caused by the rickettsiae fall into 4 groups:(1) typhus: epidemic typhus, Brill-Zinsser disease, murine (endemic) typhus, and scrub typhus; (2) spotted fever-Rocky Mountain spotted fever, Eastern tick-borne rickettsioses, and rickettsialpox; (3) Q fever; and (4) trench fever.