Date of Award
Doctor of Philosophy (PhD)
Lymphatic filariasis (LF) is a neglected tropical disease caused by the nematode parasites Wuchereria bancrofti, Brugia malayi and B. timori. The primary tool used by the Global Program to Eliminate LF is mass drug administration (MDA), and some 500 million people take the medications each year. Mild to moderate adverse events (AEs) are common after LF treatment, and these pose a major challenge for the LF elimination program. To better understand the pathogenesis of AEs, we studied patients from LF treatment trials in Côte d’Ivoire and Papua New Guinea, where plasma and leucocytes were collected pre and post-treatment and subjects were monitored for AEs. We found that plasma levels of filarial antigen and DNA increased post-treatment in individuals with AEs. We discovered that a whole range of filarial antigens with the AD12 epitope circulate in the bloodstream 24 hours after treatment, in contrasts to the widely accepted notion that the high molecular weight Circulating Filarial Antigen (CFA) is the only antigen present the blood of W. bancrofti-infected individuals. We then investigated the cytokine response during AEs by measuring 27 cytokines pre and post-treatment. We identified 11-16 cytokines that increased post-treatment in individuals with AEs. This complex cytokine response could be consistent with a LPS-like response (caused by exposure to Wolbachia lipoprotein) with increases in TNF-α, IL-1β, IL-6, IL-1RA and IL-10. To further delineate the host response during AEs, a transcriptomic analysis was completed. Global RNA sequencing was performed for 9 individuals with systemic AEs and for 9 matched controls without AEs. Differential gene expression analysis identified a significant transcriptional signature associated with post-treatment AEs; 744 genes were significantly upregulated in the AE group (post versus pre-treatment, paired). These genes were enriched for many biological pathways, including pro-inflammatory pathways such as TLR and NF-kappa B signaling. A machine-learning tool was used to prioritize the genes up-regulated post-treatment in individuals with AEs, in order to identify the genes that had the best correlation between expression levels and AE classification, and in order to identify a subset of genes to validate with RT-qPCR. Increased expression of seven out of the top eight genes identified were validated with RT-qPCR. TLR2 was identified by the machine-learning tool to be highly correlated to the development of AEs, and this gene was confirmed to increase post-treatment in individuals with AEs by RT-qPCR. These results suggest that Wolbachia lipoprotein is involved in AE development because it is known to signal though TLR2-TLR6 and activate downstream NFkappa B. Additional support for this hypothesis was the discovery that LPS Binding Protein (LBP) increased post-treatment in individuals with AEs, because LBP can shuttle lipoproteins to TLR2. Improved understanding of the pathogenesis of AEs may lead to improved management or prevention that could increase MDA compliance and hasten LF elimination.
Chair and Committee
Gary J. Weil
Peter U. Fischer, John P. Atkinson, Makedonka Mitreva, Audrey R. Odom John,
Andersen, Britt Juul, "Lymphatic Filariasis: Host and Parasite Factors and the Pathogenesis of Systemic Adverse Events Following Treatment" (2020). Arts & Sciences Electronic Theses and Dissertations. 2160.