THE CONSEQUENCE OF CO-CIRCULATING PARASITES FOR VECTOR-BORNE PATHOGEN TRANSMISSION A Dissertation by ANDREW JOHN GOLNAR Submitted to the Office of Graduate and Professional Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Chair of Committee, Gabriel Lee Hamer Committee Members, Michel Slotman Micky Eubanks Jay Walton Head of Department, Pete Teel August 2019 Major Subject: Entomology Copyright 2019 Andrew John Golnar ABSTRACT The unprecedented rates of vector-borne pathogen emergence and re-emergence highlights the necessity to identify ecological drivers of transmission heterogeneity. Mosquitoes ingest a variety of viruses, protozoan, and macroparasites that circulate among avian and mammalian hosts. The consequence of these co-circulating parasites for vector-borne pathogen population dynamics remains largely unknown. In this dissertation, field research, controlled laboratory transmission experiments, and mathematical modeling techniques are combined to assess how polyparasitism may influence vector-borne pathogen transmission dynamics. Field techniques used in this dissertation highlight a community of blood-parasites in the Great-tailed grackle (Quiscalus mexicanus), results that document the propensity of co-circulating parasites to influence zoonotic vector-borne pathogen systems. Additionally, two compartmental models that describe the dynamics of vector-borne pathogen transmission structured by host and vector co- infection status were constructed, analyzed, and parameterized in an effort to define a quantitative framework of use for evaluating the impact of polyparasitism on vector-borne pathogen population dynamics. Importantly, results quantitatively illustrate that avian malaria parasites may simultaneously increase and decrease the reproductive number of WNV through multiple mechanisms of interaction. Finally, numerous experimental transmission assays were completed to evaluate how Plasmodium influence rates of midgut infection and dissemination in mosquitoes simultaneously infected with West Nile and Plasmodium parasites and sequentially infected with Plasmodium and then West Nile virus during a subsequent bloodmeal. Results suggest there are no patterns driving Plasmodium-induced changes in rates of infection and dissemination, suggesting Plasmodium parasites may not be a key driver of natural WNV transmission heterogeneity. Overall, results of this dissertation stress a need to empirically and ii analytically evaluate the impact of polyparasitism on transmission dynamics as a compounding consequence of multiple ecological and biological mechanisms. Although complex, enhancing our understanding of how patterns of polyparasitism impact zoonotic pathogens can help elucidate novel mechanisms of disease control and surveillance. iii DEDICATION This dissertation is dedicated to all my friends and family that showed patience as I adapted to the lifestyle of a scientist. Additionally, this is dedicated to all the canaries and great- tailed grackles that lost their lives in the pursuit of science. iv ACKNOWLEDGEMENTS I would like to acknowledge Dr. Gabriel Hamer for his guidance in almost seven years of graduate study. His unwavering support and trust created a positive training experience I hope to emulate in future mentorship opportunities. In short, I am incredibly grateful to receive his mentorship and look forward to our future as colleagues and friends. I also like to thank my lab members (both old and new) for their amazing support (in no particular order): Estelle Martin, Elaine Chu, Cierra Briggs, Helena Hopson, Dayvion Adams, Karen Poh, Matthew Medeiros, Mark Olson, Jose (Willy) Juarez, Emily Boothe, Alyssa Meyers, Carolyn Hodo, Rachel Curtis-Robles, Miranda Bertram, Italo Zecca, Justin Bejcek, Chris Downs, Wendy Tang, Jillian Wormington, Lisa Auckland, and Sarah Hamer. Finally, I would like to acknowledge my incredible support group through friends and family - especially those who have resided in College Station, Texas and understand it takes a bit of ingenuity to live as the 2% in Aggieland. v CONTRIBUTORS AND FUNDING SOURCES This work was supervised by a dissertation committee consisting of Dr. Gabriel L. Hamer (advisor) of the Department of Entomology and Dr. Micky Eubanks of the Department of Entomology, Dr. Michel Slotman of the Department of Entomology, Dr. Jay Walton of the Department of Mathematics, and Dr. Matthew Medeiros of the Pacific Biosciences Research Center in the University of Hawai’i at Manoa. Additional collaborators included Dr. Sarah Hamer, Dr. Estelle M. Martin, Mrs. Lisa Auckland, Dr. Wendy Tang, Dr. Rocio Marilyn Caja Rivera, Justin Bejcek, Katlyn Rosenbaum, Dr. Carter Atkinson, and Dr. Richard Eastman. Many individuals assisted in data management and laboratory work associated with these projects, including in no particular order: Elaine Chu, Cierra Briggs, Victoria Kamilar, James Sanchez, Chris Terrand, Dayvion Adams, Helena Hopson, and Andrew Evans. All other work for the dissertation was completed independently by the student. I am extremely thankful for funding provided through the National Science Foundation Graduate Research Fellowship, which provided countless opportunities throughout my graduate career. I am also thankful for departmental funding through the Knipling-Bushland-Swahrf Graduate Student Scholarship awarded in 2018 and J.H. Benedict, Sr. Memorial Graduate Student Scholarship awarded in 2017. I also appreciate other funding sources, such as the Office of Graduate and Professional Studies travel grant which provided funds to attend a conference in the United Kingdom, The One Health Research Student Travel Award that allowed me to attend American Society of Tropical Medicine and Hygiene in 2017, and the National Science Fellowship GROW with United States Agency for International Development Research and Innovation vi Fellowship program that took a chance on graduate students to fund high-risk/high-impact studies abroad. vii NOMENCLATURE BCS Bryan/College Station, Texas CDC Center for Disease Control and Prevention C.I. Confidence Interval DFE Disease-free Equilibrium DMEM Dulbecco’s Modified Eagle Media DNA Deoxyribonucleic acid FBS Fetal Bovine Serum GTGR Great-tailed Grackle HIV-1 Human Immunodeficiency virus NCBI National Center for Biotechnology Information ODE Ordinary Differential Equation PBS Phosphate Buffer Solution PCR Polymerase Chain Reaction PRCC Partial Rank Correlation Coefficient rcf relative centrifugal force R0 Basic Reproductive Number RVFV Rift Valley fever virus TB Tuberculosis USA United States of America WNV West Nile virus viii TABLE OF CONTENTS Page ABSTRACT ............................................................................................................................... ii DEDICATION ........................................................................................................................... iv ACKNOWLEDGEMENTS ........................................................................................................ v CONTRIBUTORS AND FUNDING SOURCES ........................................................................ vi NOMENCLATURE ................................................................................................................ viii TABLE OF CONTENTS ........................................................................................................... ix LIST OF FIGURES .................................................................................................................... xi LIST OF TABLES .................................................................................................................... xii CHAPTER I INTRODUCTION.................................................................................................. 1 1.1 Synopsis ............................................................................................................................ 1 1.2 Introduction ....................................................................................................................... 2 1.3 References......................................................................................................................... 6 CHAPTER II VECTOR-BORNE BLOOD-PARASITES OF THE GREAT-TAILED GRACKLE (QUISCALUS MEXICANUS) IN EAST-CENTRAL, TEXAS ................................ 12 2.1 Synopsis .......................................................................................................................... 12 2.2 Introduction ..................................................................................................................... 12 2.3 Methods .......................................................................................................................... 15 2.4 Results ............................................................................................................................ 19 2.5 Discussion ....................................................................................................................... 24 2.6 References....................................................................................................................... 27 CHAPTER III THE CONSEQUENCE OF CO-CIRCULATING PARASITES FOR VECTOR-BORNE PATHOGEN TRANSMISSION................................................................. 35 3.1 Synopsis .......................................................................................................................... 35 3.2 Introduction