INVESTIGATION OF THE MIALOME OF IXODES SCAPULARIS REPLETE TICKS AND UNDERSTANDING THE POPULATION GENOMIC STRUCTURE OF IXODES PACIFICUS TICKS
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Authors
Reyes, Jeremiah Baptist
Issue Date
2022
Type
Dissertation
Language
Keywords
Alternative Title
Abstract
Ticks are blood-feeding arthropod ectoparasites that transmit disease-causing pathogens to humans and animals worldwide. Research on vaccine development to protect humans, companion animals, and livestock from ticks and tick-transmitted pathogens has accelerated by using proteomic and transcriptomic analyses. Immunization of hosts with targeted anti-tick vaccines would ideally lead to a reduction in tick numbers and prevent transmission of tick-borne pathogens. Vaccines using cattle tick antigens (anti-tick vaccine) have proven to be cost-effective and environmentally friendly for the control of cattle tick infestations and pathogen infection and transmission. However, new strategies are needed to identify tick protective antigens for development of vaccines for tick species of human significance. Ticks are obligatory blood feeders. Blood meals are stored and digested in the midguts. Blood digestion is complex, and many proteins are involved. These tick-derived proteins in the midgut may be useful for anti-tick vaccines. Therefore, midguts were examined using transcriptome and proteome of unfed, partially engorged, and replete female Ixodes scapularis, previously uncharacterized for this species. The function of identified midgut proteins varied from nutrient transportation, anti-coagulation, erythrocyte lysis, detoxification, lipid metabolism, and immunization. Functional characterization of promising antigen targets for an anti-tick vaccine resulted in several putative candidates for further analysis (Chapter 2). In Chapter 3, function of three highly expressed serine proteases (identified in chapter 2) in blood digestion was determined. In Chapter 3, we showed that the serine proteases are indeed active in blood digestion in fully engorged females. These findings advance our understanding of tick digestive mechanisms and provide a panel for screening of vaccine candidates.
In addition, we began to determine the genetic structure of the primary vector for Lyme Disease in California, Ixodes pacificus (Chapter 4). Due to the broad host range of I. pacificus, especially large mammals and birds which have the capability of traveling long distances, it is proposed that the ticks will migrate and may establish in new areas. We collected ticks from 10 counties, prepped a restriction-associated DNA sequencing (RADseq) library, and conducted genome-wide single nucleotide polymorphism (SNP) analysis. Our data suggest two ancestral population of I. pacificus and high gene flow among populations. Our data also agrees with current pathogen prevalence data and suggests higher transmission rates in some counties than others. Once complete, these data will greatly increase our knowledge of tick migration and vector-pathogen relationships.