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Applied and Environmental Microbiology, November 2009, p. 7243-7252, Vol. 75, No. 22
0099-2240/09/$08.00+0 doi:10.1128/AEM.01704-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Population Structure of the Lyme Borreliosis Spirochete Borrelia burgdorferi in the Western Black-Legged Tick (Ixodes pacificus) in Northern California 
Yvette A. Girard,1*
Bridgit Travinsky,2
Anna Schotthoefer,3
Natalia Fedorova,1
Rebecca J. Eisen,3
Lars Eisen,4
Alan G. Barbour,2 and
Robert S. Lane1
Department of Environmental Science, Policy and Management, University of California Berkeley, 137 Mulford Hall, Berkeley, California 94720-3114,1 Departments of Microbiology and Molecular Genetics and Medicine, University of California Irvine, 3012 Hewitt Hall, Irvine, California 92697,2 Division of Vector-Borne Infectious Diseases, National Center for Zoonotic, Vector-Borne and Enteric Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado 80522,3 Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado 805234
Received 17 July 2009/ Accepted 18 September 2009
Factors potentially contributing to the lower incidence of Lyme borreliosis (LB) in the far-western than in the northeastern United States include tick host-seeking behavior resulting in fewer human tick encounters, lower densities of Borrelia burgdorferi-infected vector ticks in peridomestic environments, and genetic variation among B. burgdorferi spirochetes to which humans are exposed. We determined the population structure of B. burgdorferi in over 200 infected nymphs of the primary bridging vector to humans, Ixodes pacificus, collected in Mendocino County, CA. This was accomplished by sequence typing the spirochete lipoprotein ospC and the 16S-23S rRNA intergenic spacer (IGS). Thirteen ospC alleles belonging to 12 genotypes were found in California, and the two most abundant, ospC genotypes H3 and E3, have not been detected in ticks in the Northeast. The most prevalent ospC and IGS biallelic profile in the population, found in about 22% of ticks, was a new B. burgdorferi strain defined by ospC genotype H3. Eight of the most common ospC genotypes in the northeastern United States, including genotypes I and K that are associated with disseminated human infections, were absent in Mendocino County nymphs. ospC H3 was associated with hardwood-dominated habitats where western gray squirrels, the reservoir host, are commonly infected with LB spirochetes. The differences in B. burgdorferi population structure in California ticks compared to the Northeast emphasize the need for a greater understanding of the genetic diversity of spirochetes infecting California LB patients.
* Corresponding author. Mailing address: University of California—Berkeley, Department of Environmental Science, Policy and Management, 137 Mulford Hall #3114, Berkeley, CA 94720-3114. Phone: (510) 643-8060. Fax: (510) 642-7428. E-mail: yagirard{at}nature.berkeley.edu
Published ahead of print on 25 September 2009.
Applied and Environmental Microbiology, November 2009, p. 7243-7252, Vol. 75, No. 22
0099-2240/09/$08.00+0 doi:10.1128/AEM.01704-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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