Masters Thesis

Characterizing Ticks and Tick-Borne Pathogens in Fresno and Madera Counties

Tick-borne relapsing fever (TBRF) is a serious and understudied disease that is endemic to California. The distribution of the soft-tick vector of TBRF (Argasidae: Ornithodoros) and the prevalence of the pathogen are poorly understood in the foothills and mountains of Fresno and Madera Counties. This study attempts to characterize the range of Ornithodoros species by direct collection using large-scale trapping methods. The prevalence of TBRF was examined using conventional polymerase chain reaction to detect Borrelia spp., the causative bacterial agent of relapsing fever. A restriction fragment length polymorphism assay was successfully developed to discern between multiple species of relapsing fever Borrelia without the need for DNA sequencing or immunofluorescent assays. DNA sequencing was used to better understand ambiguous results, such as the species identification of O. parkeri that were collected from recreational locations in both Fresno and Madera. While no ticks in our collection were found to be positive for Borrelia, a group of O. parkeri from Millerton Lake were positive for Rickettsia. This Rickettsia species was determined to be a non-pathogenic endosymbiont which had not previously been described in this species of tick. These findings should better inform public health officials with the potential risks to humans visiting local parks and campgrounds in Fresno and Madera.

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