Term of Award

Spring 2021

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

Lance Durden

Committee Member 2

Joshua Gibson


Fleas (Order Siphonaptera) are opportunistic blood feeders that parasitize a wide variety of mammals and birds. They also transmit bacterial pathogens that cause diseases in humans (e.g., murine typhus, flea-borne spotted fever, cat scratch disease, and plague). Because they acquire infectious pathogens while blood feeding, the flea gut is considered to be the initial site of infection. While immune responses have been well documented in other disease vectors, few studies have identified the immune mechanisms involved in defense of the flea gut. In other hematophagous insects, the synthesis of reactive oxygen species (ROS) is the immediate immune defense mechanism against foreign microbes. To investigate the role of ROS in flea gut immunity, cat fleas (Ctenocephalides felis) were orally infected with the model insect pathogen Serratia marcescens. Specifically, fleas were treated with an antioxidant to reduce the amount of microbicidal ROS before infection, and then S. marcescens infection loads were measured. Additionally, we measured hydrogen peroxide (ROS) levels, and the relative quantity of mRNA for select genes associated with DUOX, a surface protein of epithelial cells responsible for ROS production. Four experimental groups were examined: (1) S. marcescens-infected fleas; (2) fleas fed an antioxidant; (3) fleas fed an antioxidant and then infected with S. marcescens, and (4) fleas fed on untreated blood (control). Overall, these results show that ROS levels in the gut increase in response to infection, and the signaling pathway for DUOX activation is tightly regulated. This study provides evidence that ROS is a key mechanism for early gut defense in cat fleas.

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Research Data and Supplementary Material