A One Health Approach to Surveillance of Pathogenic and Emerging Rickettsia in Mammals, Ticks, and Fleas of Northwestern California - PROJECT SUMMARY Nearly one-third of emerging zoonotic diseases reported in the past decade have involved arthropod vectors such as fleas and ticks. Rickettsia species are responsible for many of these infections and continue to expand in prevalence and geographic distribution, highlighting the urgent need for ecological surveillance. In California, recognized human rickettsial pathogens include Rickettsia rickettsii, R. rickettsii subsp. californica, and R. lanei, while species of unknown pathogenic potential include Rickettsia sp. phylotype G022 (G022) and R. tillamookensis in Ixodes pacificus. Although these rickettsial agents occur at low prevalence in ticks (0.3– 9%, depending on species, stage, and region), their vertebrate hosts are largely unknown or poorly understood, contributing to the underdiagnosis and misclassification of infections. We hypothesize that small mammals, gray foxes, deer, and elk contribute to the maintenance of both established and emerging Rickettsia in northwestern California, supporting their circulation in vectors and wild animals and shaping human exposure risk. To address these gaps, we will employ field sampling, real-time PCR, nested PCR, and sequencing to achieve species-level resolution across three aims. Aim 1: Determine the prevalence of five Rickettsia species mentioned above in small mammals and their ectoparasites to identify host-pathogen (or microbe) associations and provide insights into their transmission cycle. Aim 2: Determine the prevalence of the five targeted Rickettsia species in gray foxes and their ectoparasites, and evaluate the role of this mesocarnivore as a potential amplifying hosts contributing to pathogen maintenance. Aim 3: Characterize pathogen/microbe diversity in deer and elk, animals of cultural and nutritional importance to the Karuk Tribe, and determine the prevalence of Rickettsia and six additional tick-borne pathogens (Anaplasma phagocytophilum, Babesia duncani, Borrelia burgdorferi sensu lato, B. hermsii, B. miyamotoi, and Ehrlichia chaffeensis) to expand host- focused surveillance and inform Tribal public health priorities. Together, these aims apply a One Health framework that integrates wildlife and vectors to better understand the role of wild animals in the ecology of these bacteria and to identify host taxa and their susceptibility to Rickettsia and six other tick-borne pathogens. This proposal represents the first tick-borne pathogen molecular surveillance on Karuk Tribal lands, directly supporting Karuk public health priorities. It will generate the first dataset identifying potential amplifying hosts for R. lanei, R. tillamookensis, and G022, and expand molecular surveillance of pathogens in gray fox. It will also establish a scalable model for vector-borne disease surveillance that includes wild animals, ticks, and fleas in underserved communities. By generating baseline data on the presence and prevalence of 11 vector- borne pathogens and microbes in wild animals, this study will advance understanding of their ecology within transmission cycles and geographic distribution in northwestern California, and inform assessments of pathogen transmission risk to humans and domestic species for the Karuk Tribe.
