Doctor of Philosophy (PhD)


Veterinary Medical Sciences - Pathobiological Sciences

Document Type



Rickettsia felis is an emerging insect-borne rickettsial pathogen and the causative agent of flea-borne spotted fever. First described as a human pathogen from the United States in 1991, R. felis is now identified throughout the world and considered a common cause of fever in Africa. The cosmopolitan distribution of this pathogen is credited to the equally widespread occurrence of cat fleas (Ctenocephalides felis), the primary vector and reservoir of R. felis. Additionally, R. felis has been identified in other hematophagous arthropods (including numerous species of fleas, ticks, mosquitoes, and mites). Most transmission cycles of pathogenic Rickettsia include transovarial and transstadial passages in their arthropod hosts as well as transmission to new vectors through the infectious blood of vertebrate amplifying hosts. The continuous molecular detection of R. felis from other blood-feeding vectors supports the notion of infectious transmission cycles; however, naturally infected mammalian blood or tissues have never been shown to be a source of R. felis infection from vertebrate to arthropod host. Here we demonstrate that horizontal transmission of R. felis occurs independent of a rickettsemic vertebrate host. The combination of intraspecific and interspecific cofeeding transmission of R. felis on a vertebrate host, sustained transmission of R. felis between cofeeding cat fleas in an artificial host system, and support by modeling demonstrated cofeeding as an important mechanism of pathogen maintenance and transmission within flea populations. Additionally, our results indicate that not only are R. felis-exposed cat fleas infectious following a brief incubation period, but utilization of a mechanical mechanism may also explain the rapid rate of spread that typifies R. felis flea-borne transmission within experimental and computational models. Elucidation of the R. felis transmission cycle is necessary to further our understanding of this emerging rickettsiosis.



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Committee Chair

Macaluso, Kevin