Date of Award


Document Type


Degree Name



Basic Medical Sciences

Committee Chair

Kevin R. Macaluso, Ph.D.


Dr. Meghan Hermance, Dr. Jonathan Rayner, Dr. Robert Barrington, Dr. John McCreadie


Rickettsia felis is an emerging arthropod-borne rickettsial pathogen and the causative agent of flea-borne spotted fever, which can cause serious disease in humans. More than 40 arthropod species, including fleas, ticks, and mosquitoes are identified as potential vectors of R. felis. Current paradigms assign cat fleas (Ctenocephalides felis) as the primary vector and reservoir of R. felis, which correlates with the widespread occurrence of the agent. Although it is known that R. felis can be maintained in cat flea populations through both vertical and horizontal transmission, R. felis transmission from mother to offspring is highly variable. Several studies have reported the inability to introduce R. felis into adult fleas and drive vertical transmission in the laboratory; impeding further understanding of how R. felis circulates in flea populations. The failure to observe vertical transmission by Rickettsia naïve fleas might be explained by several factors, including the presence of endosymbionts within the vector population, possibly restricting the vertical transmission mechanism for the maintenance of R. felis. Vertically transmitted endosymbionts, particularly Wolbachia, can impact the spread of pathogenic bacteria within arthropods. In fleas, both Rickettsia and Wolbachia have been identified; however, the interaction of bacterial endosymbionts relative to vertical transmission of R. felis in cat fleas has not been explored. Therefore, the broad hypothesis to be examined is that the diversity of the bacterial community affects rickettsial infection and vertical transmission within cat flea populations. The ultimate goal is to investigate the interaction of Wolbachia endosymbionts and R. felis in cat fleas, as well as the influence of Wolbachia on R. felis transmission mechanisms in cat fleas. Here we demonstrate factors that likely contribute to the variation of R. felis vertical transmission mechanism. The findings of this study provide evidence that endosymbionts, Wolbachia, can impact R. felis transmission in cat flea populations, and that microbiome changes can also affect pathogen transmission. Furthermore, the data indicate a negative relationship between Wolbachia and R. felis in the cat flea. Thus, understanding the relationship between Rickettsia and bacterial endosymbionts in this study has expanded the current knowledge of R. felis transmission mechanisms and provided a better understanding of R. felis ecology in nature.

Available for download on Saturday, December 16, 2023