Date of Award


Document Type

Master's Thesis - Open Access

Degree Name

Master of Science


Basic Medical Sciences

First Advisor

Dana Mordue, Ph.D

Second Advisor

Paul Arnaboldi, Ph.D

Third Advisor

Mary Petzke, Ph.D


Babesia microti is an apicomplexan parasite transmitted by tick bite that infects red blood cells. It is increasingly associated with transfusion-transmitted infections including fatal infection as the parasite survives blood banking procedures. The infection can range from asymptomatic to fatal. The parasite can persist in relatively asymptomatic individuals for up to two years. The host and parasite determinants of severity of infection and/or parasite clearance remain largely unknown. However, asplenic and immune suppressed individuals including the very young and relatively old, greater than 50 years of age, are more vulnerable to severe disease. The goal of the current research is to evaluate the role of reactive oxygen species in parasite clearance during babesiosis. A mouse model of babesiosis was developed in which infection results in nearly 40% parasitemia over the first week of infection, followed by parasite clearance. Dual RNA sequencing was performed on peripheral blood mononuclear cells, granulocytes and parasites to identify changes in gene expression within the parasite and host at key points during infection. Day 5 post-infection represents parasite replication and proliferation and day 7 post-infection correlates with the onset of parasite clearance. Analysis of the parasite RNA-seq data reveal an increase in the expression of genes critical for resistance to reactive oxygen (ROS) and nitrogen species (RNS) as well as repairing damage induced by nitrosative and oxidative stress. To directly test whether cellular ROS and RNS are produced during babesiosis, we used intra-vital- fluorescent probes to measure intracellular splenic and peripheral blood production of ROS (CellROX) and RNS (DAF-FM) during infection. Consistent with the dual RNA-sequencing data, splenic production of ROS correlated with the onset of parasite clearance. Later in infection, cells within the blood also produced ROS. Overall, nitric oxide (NO) production was only modestly increased compared to that of ROS. Because ROS was increased in the spleen, we directly tested the role of NADPH oxidase and TNF in control of Babesia microti infection using P47 phox, and TNF receptor 1 and 2 gene deletion mice, respectively. Mice deficient in NADPH oxidase were not more sensitive to infection. By contrast, mice that lacked TNF receptors were unable to clear infection, displayed a reduction of parasite death inside infected red blood cells and maintained prolonged parasitemia compared to wild type mice. Thus, our studies are the first to demonstrate that TNF receptors are important for control of infection including death of the parasites within infected red blood cells. The goal of future studies is to determine the source of reactive oxygen species during infection and the mechanisms of TNF receptors’ resistance to the parasite.