Date of Award


Degree Name

MS in Biological Sciences


Biological Sciences


Larisa Vredevoe


Despite the fact that eight cases of Lyme disease were diagnosed in San Luis Obispo County between 2005-2013, the identity of wildlife hosts serving as sources for tick infection in this region remained unidentified. The primary cause of Lyme disease in the U.S. is the spirochetal bacterium Borrelia burgdorferi sensu stricto, and this agent had not been previously isolated from the region. Borrelia bissettii, a related species that has not been implicated as a common causative agent of Lyme disease, was isolated in small rodents inhabiting coastal scrub and chaparral habitats in a previous San Luis Obispo County study. However, B. burgdorferi was not detected. In northwestern California, B. burgdorferi has been primarily associated with high populations of the tick vector Ixodes pacificus in dense woodlands or hardwood-conifer habitats, particularly in the western gray squirrel reservoir host, Sciurus griseus. My study investigated the role of S. griseus and other associated rodents as potential reservoirs for B. burgdorferi in central coastal California woodland habitats. Rodents were live-trapped at four sites in San Luis Obispo County in oak and mixed woodland. Rodent ear samples were tested for B. burgdorferi genospecies by bacterial culture and PCR. Ticks were collected from captured rodents and surrounding environments and tested by PCR for the presence of Borrelia. Of 119 captured rodents, seven were positive for Borrelia infection (5.9%) and of these, six were positive for B. burgdorferi (5.0%). There were multiple infected rodent species that included two western gray squirrels, three deer mice (Peromyscus maniculatus), and one brush mouse (P. boylii). Borrelia spp. were not detected by PCR from the 81 ticks recovered from the environment and rodents. Here, for the first time, we verify the presence of B. burgdorferi sensu stricto in San Luis Obispo county rodents. However, in contrast to previous Northern California studies, the western gray squirrel may not be the primary reservoir host for B. burgdorferi in this region. Multiple rodent species in oak woodlands may be involved in spirochete maintenance in San Luis Obispo County.

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