Semester of Graduation

Summer 2019

Degree

Master of Science (MS)

Department

Pathobiological Sciences

Document Type

Thesis

Abstract

Rickettsia felis is the etiologic agent of flea-borne spotted fever (FBSF) in humans and a poorly described cause of fever in animals. It is transmitted by its primary arthropod vector and reservoir host, the cat flea Ctenocephalides felis. Known routes of Rickettsia felis transmission between Rickettsia felis-infected cat fleas and vertebrate hosts include cutaneous bites and contamination of cutaneous wounds with infective flea feces. The bulk of FBSF infections occur in young children in Africa, though infections of people at all ages all over the world have been confirmed. As mammals and young children frequently come into contact with flea feces through routine grooming and indiscriminate oral hygiene, respectively, we speculate that ingestion of infective flea feces may potentially account for a portion of natural Rickettsia felis infections. To investigate the potential role ingestion of Rickettsia felis plays in transmission of the bacterium to vertebrates, we designed sister experiments using a BALB/c mouse model to determine 1) if Rickettsia felis could establish an infection via an oral route and 2) if Rickettsia felis could establish an infection via an oral route in the form of infective cat flea feces. For our first objective, Rickettsia felis was cultured in ISE6 cells, purified, and administered orally in SPG buffer. Our second objective was executed by feeding a viable Rickettsia felis-spiked blood meal to Ctenocephalides felis, collecting infective flea feces, and administering the feces orally in SPG buffer. In both experiments necropsy was performed at 1, 7, and 14 days post-exposure and heart, liver, spleen, stomach, and intestine were collected for DNA extraction, RNA extraction, and qPCR analysis. Tissues with positive results were subsequently submitted for histopathology using hematoxylin and eosin staining as well as anti-Rickettsia immunohistochemistry. Select tissues were tested via RT-qPCR and a single serum sample via an indirect immunofluorescence assay. Our results indicate that R. felis from culture is transmissible via ingestion in mice and may be found in organs distant from the gastrointestinal tract at all time-points tested without evoking inflammation. Further studies are needed to characterize all aspects of R. felis transmission via ingestion in vertebrates.

Committee Chair

Macaluso, Kevin

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