Date of Award


Degree Name

Doctor of Philosophy


Biological Sciences


Siddhartha Das


Giardia lamblia, a protozoan parasite, is a major cause of waterborne infection, worldwide. While the trophozoite form of this parasite induces pathological symptoms in the gut, the cyst forms transmit the infection via contaminated water. Since Giardia is a non-invasive parasite, the actual mechanism by which it causes infection remains elusive. We have previously reported that Giardia assembles cholesterol and GM1 glycolipid-enriched lipid rafts (LRs) that participate in encystation and cyst production. To further delineate the role of LRs in pathogenesis, we isolated LRs from Giardia and subjected them to proteomic analysis. Various cellular proteins including the virulent proteins—e.g., giardins, variant surface proteins (VSPs), arginine deaminases (ADAs), elongation factors (EFs), ornithine carmoyltransferases (OTCs) and high cysteine-rich membrane proteins (HCMPs)—were found to be present in LRs. Since Giardia secretes virulent proteins (secretome) encapsulated in extracellular vesicles that induce proinflammatory responses in hosts, vesicles released by the parasite were isolated and subjected to nanoparticle tracking and proteomic analyses. Two types of vesicles—i.e., exosome-like small vesicles (SVs; <100nm) and microvesicles-like large vesicles (LVs; 100–400 nm)—were identified and found to contain diverse group of proteins including the virulent proteins. Pretreatment of the parasite with two giardial LRs disruptors, nystatin (27 µM) and oseltamivir (20 µM), altered the expression profiles of virulent proteins in LVs and SVs, however the effects were more robust in case of SVs. To examine the potential role of rafts and vesicles in pathogenicity, Giardia-infected mice were treated with oseltamivir (1.5 mg/kg and 3.0 mg/kg) and the shedding of cysts were monitored. It was observed that this drug was significantly effective in reducing the parasite load in mice. My results suggest that virulent factors accumulated in gLRs and secretes via SVs and LVs participate in spreading giardiasis and could be targeted for drug development in the future. I have proposed two Specific Aims in my dissertation. In Aim-1, I have proposed to determine if the lipid rafts and vesicles share proteins including the virulent proteins of Giardia. The goal of Specific Aim-2 is to examine if raft disintegrating compounds and their derivatives can be used as potential anti-giardial agents.




Recieved from ProQuest

File Size

117 p.

File Format


Rights Holder

Brian Ivan Grajeda