Term of Award

Fall 2022

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.


Department of Biology

Committee Chair

Lisa Brown

Committee Member 1

Joshua Gibson

Committee Member 2

Lance Durden


Despite their continued medical and veterinary importance, the vectorial capacity of fleas (Order Siphonaptera) is often underestimated. Fleas are best described as ectoparasites of a variety of mammalian and aviary hosts. In humans, fleas are infamous for the transmission of several detrimental agents, including those that cause plague, murine typhus, and cat-scratch disease. Although their significance in flea immune responses remains unknown, phagocytic immune cells, known as hemocytes, are important players in the cell mediated immune response of insects. Among invertebrates, hemocytes provide defense against foreign microbes via phagocytosis, cellular encapsulation, and the production of humoral immune factors. As mentioned above, current information on the types of hemocytes fleas produce, their relative abundance, and their functions is limited. This is a significant gap in knowledge, as improved understanding of how fleas defend themselves from infection could lead to the refinement of disease control strategies. To investigate the role of hemocytes in flea immunity, cat fleas (Ctenocephalides felis) were infected with the Gram-negative bacterium, Escherichia coli. Specifically, an E.coli infection was delivered via a septic pinprick, and the following parameters were measured: (1) in vivo bacteria killing efficiency; (2) quantification of circulating hemocytes; and (3) the relative capacity of hemocyte phagocytosis. The data show that hemocytes proliferate in response to a bacterial infection, and that these immune cells are highly phagocytic. Overall, this study provides important insight into how fleas interact with Gram-negative bacterial pathogens in their hemocoel, which can directly affect transmission of flea-borne diseases.

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