University of SaskatchewanHARVEST
  • Login
  • Submit Your Work
  • About
    • About HARVEST
    • Guidelines
    • Browse
      • All of HARVEST
      • Communities & Collections
      • By Issue Date
      • Authors
      • Titles
      • Subjects
      • This Collection
      • By Issue Date
      • Authors
      • Titles
      • Subjects
    • My Account
      • Login
      JavaScript is disabled for your browser. Some features of this site may not work without it.
      View Item 
      • HARVEST
      • Electronic Theses and Dissertations
      • Graduate Theses and Dissertations
      • View Item
      • HARVEST
      • Electronic Theses and Dissertations
      • Graduate Theses and Dissertations
      • View Item

      Genetic diversity and phylogeography of the blacklegged tick, Ixodes scapularis, and an associated bacterium, Anaplasma phagocytophilum

      Thumbnail
      View/Open
      KRAKOWETZ,CN_PHD_THESIS.pdf (9.652Mb)
      Date
      2015-09-22
      Author
      Krakowetz, Chantel 1986-
      Type
      Thesis
      Degree Level
      Doctoral
      Metadata
      Show full item record
      Abstract
      Climate change is altering the geographical distributions of arthropod vectors (e.g., mosquitoes and ticks) and their associated microorganisms, some of which are pathogenic to humans and/or animals. It is important to determine the origin(s) of vectors in newly established populations, particularly if there are geographical differences in the species and strains of pathogens they carry. The blacklegged tick, Ixodes scapularis, is a key vector of pathogens in the U.S.A., and its distributional range continues to expand within Canada. The aim of my Ph.D. research was to genetically characterize I. scapularis individuals and an associated bacterium, Anaplasma phagocytophilum (i.e., the causative agent of human granulocytic anaplasmosis (HGA)), and to infer the geographical origins of the different populations of this tick species in Canada. Several genetic markers were used to characterize blacklegged ticks collected from different localities in Canada and the U.S.A. and to determine the phylogeographical relationships among different sequence variants (i.e., haplotypes). A major discovery was that the genetic variability in I. scapularis was much greater than previously reported. There were also major differences in the occurrence of many haplotypes among geographical regions, suggesting different geographical origins for some tick populations in Canada. These differences may be associated with the different major migratory flyways that passerines, which transport large numbers of immature I. scapularis from the U.S.A. into Canada, use each spring. A shallow phylogeographical pattern was observed for I. scapularis, which was consistent with the life history of a generalist tick species that is dispersed over large geographical areas by migratory birds. The phylogeographical data also suggested that I. scapularis populations in Manitoba likely originated from those in Minnesota, whereas tick populations in southeastern Ontario probably originated from those in neighbouring states of the Northeast, U.S.A. Thus, ticks in the Midwest, U.S.A. (e.g., Minnesota) may be transporting different species and strains of pathogens into Canada than those in the Northeast (e.g., Rhode Island). Molecular assays targeting the 16S rRNA gene of A. phagocytophilum from infected ticks detected both the strain associated with HGA (i.e., Ap-ha), and a strain not associated with human infection (i.e., Ap-variant 1). PCR-based assays were developed to discriminate between the two strains, which enhances the ability of public health officials to assess the risk of exposure of Canadians to HGA. The proportion of infected ticks that contained the Ap-ha strain was higher in Manitoba than in more eastern provinces of Canada, suggesting that the risk of human exposure to the Ap-ha strain differs among geographical areas. Phylogenetic and phylogeographical analyses of DNA sequences of the ankyrin (ankA) gene of A. phagocytophilum revealed deep genetic structure, but common lineages were sympatric over a large geographical area. Thus, the phylogeographical patterns observed for A. phagocytophilum were incongruous with that for I. scapularis, suggesting that genetic variants of I. scapularis cannot be used to infer or predict where particular strains of A. phagocytophilum are likely to occur in Canada. However, the most common ankA strains of A. phagocytophilum varied among geographical regions, possibly in accordance with the different flyways used by the migratory passerines that are transporting blacklegged ticks, supporting the hypothesis of different origins for some tick populations in Canada. In conclusion, the work conducted herein makes a valuable contribution to our understanding of the population genetics of I. scapularis, and the phylogeographical relationships among different sequence variants of I. scapularis and A. phagocytophilum in Canada. The findings of this thesis may also have implications for studies on other arthropod vectors and their associated pathogens whose distributional ranges may also be changing in response to climate change.
      Degree
      Doctor of Philosophy (Ph.D.)
      Department
      Biology
      Program
      Biology
      Committee
      Chilton, Neil B; Todd, Christopher D; McLoughlin, Philip D; McQuillan, Ian; Lindsay, Leslie R
      Copyright Date
      August 2015
      URI
      http://hdl.handle.net/10388/12622
      Subject
      single-strand conformation polymorphism
      secondary structure
      fungal contamination
      Anaplasma phagocytophilum
      human granulocytic anaplasmosis
      PCR-RFLP
      SNP
      ankA
      DNA sequences
      amino acid sequences
      sequence concatenation
      geographical origins
      Canada
      USA
      North America
      arthropod vectors
      microorganisms
      genetic diversity
      phylogeography
      population genetics
      Ixodes scapularis
      blacklegged tick
      established populations
      adventitious ticks
      mitochondrial genes
      16S rRNA
      12S rRNA
      tRNAVal
      large subunit rRNA gene
      small subunit rRNA gene
      nuclear genes
      D3 domain
      Ixodid ticks
      Collections
      • Graduate Theses and Dissertations
      University of Saskatchewan

      University Library

      The University of Saskatchewan's main campus is situated on Treaty 6 Territory and the Homeland of the Métis.

      © University of Saskatchewan
      Contact Us | Disclaimer | Privacy