Semester of Graduation

Spring 2018

Degree

Master of Science (MS)

Department

Pathobiological Sciences

Document Type

Thesis

Abstract

Rickettsia felis, the causative agent of flea-borne spotted fever, is an emerging pathogen of the transitional group Rickettsiae and an important cause of febrile illness in Africa. Since the organism’s original discovery in the early 1990s, much research has been directed towards elucidating transmission mechanisms within the believed primary host and reservoir, the cat flea (Ctenocephalides felis). However, while a growing number of human cases are being reported throughout the world, a definitive transmission mechanism from arthropod host to vertebrate host resulting in clinical disease has not been found. Several possible mechanisms, including bite of infected arthropods and association with infectious arthropod feces, are currently being investigated. This current study was undertaken to examine the role of infectious cat flea feces in dissemination of the organism to vertebrates. It was hypothesized that if cat fleas excrete viable R. felis during feeding, then the feces are capable of producing infection in vertebrates through cutaneous inoculation. Feces of cat fleas infected with R. felis were analyzed for the presence of the organism, and these potentially infectious feces were then used to intradermally inoculate naïve BALB/c mice. The results of this research show that R. felis is present in high numbers in infected cat flea feces post-exposure to an infectious blood meal, and these bacteria are presumed viable due to the detection of rickettsial transcripts within the feces. Detectable amounts of R. felis were found in the skin of mice inoculated both with R. felis from culture and R. felis-infected flea feces, and rare animals injected with R. felis from culture showed possible systemic dissemination. The response of mice inoculated with R. felis-infected cat flea feces is primarily a neutrophilic dermatitis with positive anti-Rickettsia IgG titers at 14 days post-exposure. No mice developed any overt clinical or physical signs. This study demonstrates that cutaneous inoculation with infectious arthropod feces is an effective transmission medium for the organism to mice. Further work is needed to define the role of this route of exposure in the epidemiology of the human disease.

Date

3-25-2018

Committee Chair

Macaluso, Kevin

Available for download on Monday, March 25, 2019

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