D3197: Characterization of OspA genetic diversity in the West Coast

Lyme borreliosis is a global tick-borne disease caused by pathogenic strains within the Borrelia burgdorfei senso lato complex. The senso lato complex comprises three common strains that cause human disease: B. burgdorfei senso stricto (Bbss) in the U.S., B. afezlii and B. garinii in Europe. In the western U.S., Bbss is vectored by the tick Ixodes pacificus. Outer surface protein A, Osp A, is one of the major classes of OSPs on the Borrelia pathogen spirochete and plays a role in pathogen colonization of the tick vector, and is a major target for Lyme vaccines. Yet, our understanding of Osp A genetic diversity on the West Coast is limited. Thus, the goal of this study is to identify and characterize the genetic diversity of Osp A found in the Western U.S. Lyme disease system. Questing nymphal I. pacificus ticks were collected from 14 field sites in and around the San Francisco Bay Area. Ticks were initially screened for Bbss infection, and further nested PCR amplification occurred on PCR-positive samples targeting Osp A.

Sequencing and consensus alignments in Geneious revealed high similarity between all the sequences. Preliminary phylogenetic analysis showed distinct clades, suggesting genetic variability in the Osp A gene. There was sequence similarity between our samples and Osp A senso stricto in U.S. To ensure effective vaccines, all strains of Osp A need to be targeted. This study will help to shed light on possible vaccine candidates and prompt further study into Osp A genetics.