Buruli ulcer in Liberia, 2012.

494 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 20, No. 3, March 2014 sensu stricto or B. burgdorferi sensu lato was detected (4/12 sites each), prevalence was 0.6%–2.2% and 0.7%– 2.5%, respectively. B. miyamotoi was detected at 7/12 sites, and prevalence ranged from 0.7% to 7.5%. A previous survey of B. burgdorferi in nearby Santa Cruz County recreational areas reported an infection prevalence of ≈6% among adult I. pacificus ticks (6); the study did not, however, differentiate between Borrelia spp. and therefore may have included B. miyamotoi among its prevalence measures (5). In our study, B. burgdorferi was found more frequently in woodland habitats, but it was also detected in a grassland–chaparral habitat several hundred meters from the nearest woodland. We did not detect B. bissettii, a species recently implicated as a human pathogen in Mendocino County, California (10). The high level of habitat variation in northwestern California presents a varied risk for Borrelia-associated tick-borne disease in humans because of diverse variations in vertebrate reservoir ecology, tick abundance, and human exposure to ticks. This variation emphasizes the need to understand the local epidemiology and ecology of a disease. In adult I. pacificus ticks in the San Francisco Bay area, B. miyamotoi is as abundant as its congener B. burgdorferi. Human disease caused by B. miyamotoi infection has not been reported in California, and transmission efficiency of B. miyamotoi by I. pacificus ticks is unknown. However, it is possible that B. miyamotoi infections in ticks and humans have not been accurately diagnosed. We advocate for increased scrutiny of the eco-epidemiology of B. miyamotoi in human, tick, and possible vertebrate host populations in northwestern California.