Volume 95, Issue 1
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



In California, the agent of human granulocytic anaplasmosis (HGA), , is transmitted by western black-legged ticks (). Cases of HGA are infrequent in California but do occur annually. We investigated nymphal and adult western black-legged tick populations in 20 recreational areas in California's San Francisco Bay Area (Marin, Napa, San Mateo, Santa Clara, Santa Cruz, and Sonoma counties). Overall, prevalence of in adult ticks was 0.8% (11/1,465), and in nymphal ticks was 4.2% (24/568), though presence was patchy and prevalence varied locally. We detected significant sequence variation in our quantitative polymerase chain reaction (qPCR)–positive samples. This included four sequences that grouped within a clade that contains clinical human and veterinary isolates as well as four others that grouped with sequences from PCR-positive lizards from northern California. Tick populations in our study sites harbor genetically diverse strains of , which may influence potential risk in the region.


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  • Received : 28 Sep 2015
  • Accepted : 17 Feb 2016
  • Published online : 06 Jul 2016

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