Graduation Date
Spring 2026
Document Type
Thesis
Program
Master of Science degree with a major in Biology
Committee Chair Name
Jianmin Zhong
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
Dr. Xinru Wang
Second Committee Member Affiliation
Community Member or Outside Professional
Third Committee Member Name
Brigitte Blackman
Third Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Fourth Committee Member Name
Karen Kiemnec-Tyburczy
Fourth Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Keywords
California, Ticks, Bacteria, Rickettsia, Transovarial transmission, Ixodes pacificus
Subject Categories
Biology
Abstract
The western black-legged tick, Ixodes pacificus Cooley & Kohls (Acari: Ixodidae), is a vector and host of a variety of bacteria including two Rickettsia species, Rickettsia species phylotype G022 and Rickettsia tillamookensis. Prior to this study, it was unknown whether I. pacificus larvae could be infected with these Rickettsia species, and while data suggested that transstadial passage occurs, their transovarial transmission potential had yet to be studied. The objective of this study was to determine the prevalence of both Rickettsia in adult and larval I. pacificus, evaluated G022 infection in ISE6 tick cells, and assess the presence of bacterial DNA in larvae as indirect evidence of transovarial transmission. 156 adult I. pacificus were collected and tested from Humboldt County while 90 larvae were collected across 5 different California counties: Amador, Butte, El Dorado, Humboldt, and Nevada. Real-time PCR, nested PCR, and sequencing analyses of G022 showed a prevalence of 1.3% (95% CI=0.4%-4.6%) in adult I. pacificus and 10% (95% CI=5.2%-18.1%) in larval I. pacificus. G022 was detected in three California counties: Butte, Humboldt, and Nevada. While in R. tillamookensis it showed a prevalence of 2.5% (95% CI=0.69%-8.73%) in larval I. pacificus and was detected in Butte and Humboldt County. The detection of both Rickettsia in I. pacificus larvae suggests possible transovarial transmission. Real-time PCR confirmed successful establishment of G022 infection in an ISE6 cell line. These results provide a foundation for future research on transmission routes within I. pacificus as well as for the eventual isolation, characterization, and taxonomic classification of G022.
Citation Style
Ticks and Tick-borne Diseases
Recommended Citation
King, Ashley, "Transovarial transmission of Rickettsia species phylotype G022 in larval Ixodes pacificus and detection of phylotype G022 from ISE6 tick cells" (2026). Cal Poly Humboldt theses and projects. 2547.
https://digitalcommons.humboldt.edu/etd/2547