Title page for ETD etd-04192011-205428

Type of Document Dissertation
Author Sunyakumthorn, Piyanate
URN etd-04192011-205428
Title The Tick Response to Rickettsial Dissemination during Typical and Atypical Rickettsial Infection
Degree Doctor of Philosophy (Ph.D.)
Department Pathobiological Sciences (Veterinary Medical Sciences)
Advisory Committee
Advisor Name Title
Macaluso, Kevin Committee Chair
Foil, Lane Committee Member
Miller, James Committee Member
Mores, Christopher Committee Member
Brumfield, Robb Dean's Representative
  • capillary feeding technique
  • Kunitz protease inhibitor
  • lysozyme
  • defensin
  • interference phenomenon
  • rickettsial internalization
  • tick immunity
  • RNA interfence
Date of Defense 2011-04-05
Availability unrestricted
Ticks are the only disease vectors for spotted fever group (SFG) Rickettsia which are obligate intracellular bacteria belonging to the genus Rickettsia. In nature, ticks maintain the infection of SFG Rickettsia via vertical and horizontal transmission. However, the prevalence of rickettsial transmission is limited to certain species of ticks, and this limitation is known as a specific tick/Rickettsia relationship. Due to the continuous increase of tick-borne rickettsial disease cases in the United States, which contrasts with very low prevalence of Rickettsia in tick vectors, the study of vector competence of tick to Rickettsia is needed in order to understand the ecology and epidemiology of tick-borne rickettsioses. Here we characterized the role of Dermacentor variabilis -catenin during rickettsial infection in tick ovaries suggesting a role in rickettsial infection in tick ovaries. We demonstrated that the typical nonpathogenic (R. montanensis) and typical pathogenic (R. rickettsii) Rickettsia persistently infect Dermacentor variabilis compared to atypical Rickettsia (R. amblyommii), and only R. montanensis is able to disseminate to tick ovaries. D. variabilis glutathione S-transferase1 (DvGST1) has been identified as a tick immune-like molecule that specifically responds to atypical rickettsial challenge in tick midguts suggesting a role in controlling atypical rickettsial infection in tick midguts. DvGST1 is highly upregulated in tick midguts during bloodmeal acquisition. The function of GST is known to be involved with detoxification and oxidative stress reduction, and acaricide resistance in ticks. Silencing of DvGST1 gene demonstrates significant reduction of mRNA and enzyme activity of DvGST1 in tick midguts; however, further characterization of DvGST1 is needed due to the off-target effect of negative control dsRNA. Continued study on the tick/Rickettsia interaction influencing tick vector competence for Rickettsia will lead to a better understanding of ecology and epidemiology of tick-borne rickettsioses.
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