College of Graduate Studies: Theses & Dissertations

Term of Award

Spring 2026

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

Department of Biology

Committee Chair

Lisa Brown

Committee Member 1

Josh Gibson

Committee Member 2

Stephen Greiman

Abstract

Fleas defend against infection through the activation of both humoral and cellular innate immune responses. Previous research in female cat fleas demonstrated increased immune activity following a systemic bacterial infection. However, comparable data for males and sex-based comparisons are limited. In this study, we investigated differences in innate cellular immune responses between male and female cat fleas following systemic infection with Gram-negative Escherichia coli. Bacterial load was quantified using colony-forming units 24 h post-infection. Immune function was assessed via phagocytic index and capacity. Survival and total circulating hemocyte counts were evaluated across infected, sterile-injected, and untreated groups. Male fleas exhibited a reduced immune response compared to females, with no significant difference in phagocytic capacity. Males also showed a significantly higher prevalence of bacteria 24 h post-bacterial infection. Although the number of bacteria per hemocyte did not differ significantly between sexes, our analyses showed that females had more circulating hemocytes and a higher phagocytic index, indicating a greater proportion of actively phagocytosing cells. Survival assays further showed that females had higher survival following a bacterial infection than males. These findings indicate that females mount a stronger cellular immune response and exhibit better survival, highlighting possible sex-based differences in flea immunity.

Research Data and Supplementary Material

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