Tick-borne Pathogens in Northwestern California, USA

To the Editor: In northwestern California, USA, the western black-legged tick, Ixodes pacificus, is a known vector of Borrelia burgdor-feri, the spirochete that causes Lyme disease. B. miyamotoi, which is more closely related to spirochetes that cause relapsing fever, has also been detected in 2 locations in California (1,2) and has recently been implicated as a human pathogen in the northeastern United States (3,4). Other studies may have unintentionally included B. miyamotoi infections among measures of B. burgdorferi if the diagnos-tics were for spirochetes (e.g., direct fluorescent antibody tests or dark-field microscopy) or genetically targeted for Borrelia spp. (5). To investigate Borrelia spp. ecology in California, we collected adult I. pacificus ticks by dragging a 1-m 2 white flannel blanket along vegetation and/or leaf litter in 12 recreational areas in the San Francisco Bay area during January–May 2012 (Table). Habitat varied from chaparral and grassland to coastal live oak woodland. Ticks were pooled for examination by quantitative PCR (qPCR) for the presence of Borrelia spp. We interpreted the prevalence of Borrelia spp. from positive pools as the minimum infection prevalence (i.e., assuming 1 positive tick/positive pool). DNA was extracted from ticks by using the DNeasy Blood and Tissue Kit (QIAGEN, Va-lencia, CA, USA) according to the manufacturer's protocols and then stored at –20°C until use. DNA was analyzed by qPCR, with use of primer and fluorescent hybridization probes previously developed to differentiate Borrelia spp. spirochetes (5). To identify the Borrelia spp. genotype, we attempted to sequence the 16S–23S (rrs-rrlA) intergenic spacer of each sample positive by qPCR (8). The nested PCR product was further purified by using the QIAquick Kit (QIAGEN) and then Blast.cgi) was used to compare each sequence to other Borrelia spp. sequences available from GenBank. From a total of 1,180 adult ticks, we found 43 samples positive for Bor-relia spp., resulting in a minimum infection prevalence of 3.6% (Table). We obtained intergenic spacer sequence data for 27 of the positive samples; 6 samples were B. burgdorferi sensu stricto, 7 were B. burgdorferi sensu lato (both on the basis of alignments of 816 bp), and 14 were B. miyamotoi (on the basis of alignments of 503 bp). The B. miyamotoi sequences for our samples from California and those for isolates from the eastern United States (9) and Japan (8) formed a monophyletic clade that was oriented as a sister clade to the 3 Borrelia spp. that cause tick-borne …