Graduation Date

Fall 2022

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

Jianmin Zhong

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Richard Brown

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Allison Bronson

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Jeremy Corrigan

Fourth Committee Member Affiliation

Community Member or Outside Professional

Subject Categories



Back in 2011 an unknown Rickettsia species was discovered in adult Ixodes pacificus and became known as Rickettsiaspecies phylotype G022. Preliminary analyses placed it among the Spotted Fever Group Rickettsia, indicating unknown pathogenicity. Another Rickettsia species previously found in I. pacificus, R. tillamookensis, was only recently the subject of research efforts after its original discovery in the 1960s. The main focus of this research was to determine the prevalence of phylotype G022 in nymphal I. pacificus to gain further insight into this tick-Rickettsia relationship. The prevalence of R. tillamookensis was also a topic of this research to add more California counties to the data. For this study, nymphal I. pacificus were collected from Humboldt, Contra Costa, Napa, Mendocino, Sonoma, and Santa Cruz counties in California and real-time PCR was used to determine the prevalence of phylotype G022 and R. tillamookensis. The prevalence of phylotype G022 in I. pacificus nymphs is 5.27% and the prevalence of R. tillamookensis is 1.59%. The co-infection rate between R. monacensis str. Humboldt and phylotype G022 was 31.87% and for R. tillamookensis it was 7.69%. None of the nymphs were infected with all three Rickettsia species. Spearman’s rank correlation test conveyed that there was either a weak or absent statistically significant correlation between the endosymbiont and either of the two Rickettsia species. This research showed that phylotype G022 can inhabit nymphal I. pacificus, with the prevalence possibly influenced by temperature. The low prevalence of this rickettsia within adults and nymphs contributes to the thought that this species is pathogenic, with the presence of G022 in nymphs showing that this rickettsiae is transstadially transmitted.


This data belongs to Erin R. Trent and Jianmin Zhong and any usage or reference to this research must be properly cited to give credit to these individuals.

Citation Style


Available for download on Friday, November 21, 2025


Thesis/Project Location