Associate Professor Georgia Southern University Statesboro, Georgia
Fleas serve as insect vectors for numerous bacterial pathogens that cause human diseases (cat scratch disease, plague, murine typhus). However, relatively few laboratories have studied the biology of fleas to the same extent as other disease vectors. Current research in my laboratory seeks to investigate the immune system of an important flea pest to humans, the cat flea (Ctenocephalides felis). Similar to other studies on arthropod vectors, we developed an infection model to study immunity in the digestive tract and hemocoel of cat fleas using laboratory strains of bacteria. Next, we conducted a variety of assays to measure flea immunity, including (1) reactive oxygen species (ROS) synthesis, (2) antimicrobial activity of hemolymph, (3) number of circulating hemocytes, (4) phagocytosis activity of circulating hemocytes, and (5) in vivo bacteria killing efficiency when phagocytosis activity is limited. Our results show that ROS levels increase in response to infection in the flea gut, and that this increase helps to strengthen gut immunity through the microbicidal activity of ROS. Additionally, the antimicrobial activity of flea hemolymph increases in response to certain species of bacteria; yet, an infection with the same bacterial species does not influence levels of ROS in the flea hemocoel. Moreover, the number of circulating hemocytes increases in response to infection, and these cells display strong phagocytic activity. Finally, limiting phagocytosis by injecting polystyrene beads subsequently increases flea susceptibility to infection. Overall, this work yields significant insight into how fleas interact with bacterial pathogens in their digestive tract and hemocoel.
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