Unique Strain of Borrelia miyamotoi in Ixodes pacificus Ticks, California, USA

To the Editor: Borrelia miyamotoi causes a recently recognized tickborne zoonosis in Eurasia and North America (1).The species has been detected in Ixodes persulcatus ticks in Asia and Russia, I. ricinus ticks in Europe, and I. scapularis and I. pacificus ticks in North America.In most of these regions, B. miyamotoi is sympatric with Lyme disease agents, such as B. burgdorferi, and both pathogens are transmitted locally by the same species of Ixodes ticks.B. miyamotoi generally is less prevalent than B. burgdorferi in nymphs and adults in North America (2), except in California, where the prevalences of the 2 species in populations of nymphal and adult I. pacificus ticks are similar (3-6).Genomes of isolates of B. miyamotoi from I. persulcatus and I. scapularis ticks have been sequenced (7).Comparatively less was known about B. miyamotoi in I. pacificus ticks.Limited sequence data of 16S ribosomal RNA and flagellin genes and the 16S-23S intergenic spacer (IGS) were sufficient to identify the I. pacificus-borne spirochete as a sister taxon to B. miyamotoi from elsewhere (3,4).Until B. miyamotoi is isolated from I. pacificus ticks, determination of additional sequences from I. pacficus ticks from California addresses 2 issues of phylogeographic and potential epidemiologic importance: Is the California population of B. miyamotoi more akin to the strain across the Pacific Rim or to the strain thousands of kilometers to the east in North America?Will the noted pattern of exclusive association between the genotype of B. miyamotoi and the species of Ixodes vector continue to hold (1)?We evaluated DNA extracts of B. miyamotoi-infected I. pacificus ticks collected by and stored at 2 laboratories in the San Francisco Bay area of California.Ticks had been collected while questing either on low vegetation or in leaf litter.To confirm B. miyamotoi in candidate extracts and to exclude extracts that also contained B. burgdorferi sensu lato, we used a quantitative PCR, which differentiates relapsing fever and Lyme disease group species (2).Two extracts that met these criteria were Sonom53 from