Doctor of Philosophy (PhD)


Veterinary Medical Sciences - Pathobiological Sciences

Document Type



Ticks are important worldwide as vectors of bacteria, viruses, and parasites. Pathogenic and non-pathogenic Spotted fever group (SFG) Rickettsia are maintained and transmitted by ticks with specific hard tick-Rickettsia pairings evident in nature. The pathogenic SFG Rickettsia rickettsii is transmitted by the hard tick Dermacentor variabilis. In response to infection, D. variabilis is known differentially respond to SFG Rickettsia infection. The mechanisms of differential immune induction are currently unknown, and are likely involved in the establishment of specific tick-SFG Rickettsia pairings. It was hypothesized that the level of response by D. variabilis to SFG Rickettsia occurs in a species-specific manner, and that this response drives vector competence. To this end, we report the isolation of an mRNA transcript, dvrelish, using RACE-PCR. Conserved domain analysis of dvrelish identified a Rel-homolgy domain, allowing for its identification as encoding a putative Relish-type NF-κB protein. DvRelish was identified via Western blot, immunofluorescence assay and MALDI-TOF/TOF mass-spectrometry. Tick infection assays were performed using microinjection and capillary feeding technique methodologies to identify dvrelish expression in response to SFG Rickettsia infection. Microinjection of 107 R. rickettsii induced the increased expression of dvrelish in hemocytes at 1 hour post injection, and in combined tissues at 6 hours post injected. Injection with similar and lower doses of P. aeruginosa and Rickettsia parkeri did not significantly change dvrelish expression. When capillary fed R. rickettsii, dvrelish expression increased in hemocytes after 1 hour exposure and decreased after a 3 hour exposure. Together, the expression of dvrelish was dose and tissues specific in response to SFG Rickettsia challenge. Understanding the molecular regulation of immunological response to rickettsial infection in ticks may better define the mechanisms of vector competence and the epidemiology of SFG rickettsioses.



Document Availability at the Time of Submission

Student has submitted appropriate documentation to restrict access to LSU for 365 days after which the document will be released for worldwide access.

Committee Chair

Macaluso, Kevin R.