This chapter identifies animal diseases that are host specific and reviews the effects of various human diseases on animals. It also identifies history, etiologic, human Infection, diagnosis, public health aspects and therapeutic aspects of each disease important to epidemiology and prevention. The typhus group of rickettsiae includes three morphologically and biologically similar species: Rickettsia typhi, the etiologic agent of murine typhus; R. prowazekii, the agent of epidemic or louse-borne typhus; and R. canada, an agent of mild febrile illness in humans. Typhus rickettsiae are apparently innocuous to both reservoir and vector hosts, although lifelong infection results. Diagnosis of murine typhus may be accomplished by isolation of the organism, immunofluorescence microscopy, animal inoculation, genetic analysis, or serology. Murine typhus is worldwide in distribution, but many cases go unrecognized and/or unreported. Endemic foci have been described in Australia, Asia, Africa, and Mexico.