Prevalence of Borrelia burgdorferi and diversity of its outer surface protein C (ospC) alleles in blacklegged ticks (Ixodes scapularis) in Delaware

<p>Characterizing the diversity of genes associated with virulence and transmission of a pathogen across the pathogen's distribution can inform our understanding of host infection risk. <em>Borrelia burgdorferi</em> is a vector-borne bacterium that causes Lyme disease in humans and is common in the United States. The outer surface protein C (<em>ospC</em>) gene of <em>B</em>. <em>burgdorferi</em> exhibits substantial genetic variation across the pathogen's distribution and plays a critical role in virulence and transmission in vertebrate hosts. In fact, <em>B. burgdorferi </em>infections that disseminate across host tissues in humans are associated with only a subset of <em>ospC</em> alleles. Delaware has a high incidence of Lyme disease, but the diversity of <em>ospC</em> in <em>B. burgdorferi</em> in the state has not been evaluated. We used PCR to amplify <em>ospC</em> in <em>B. burgdorferi</em>-infected blacklegged ticks (<em>Ixodes</em> <em>scapularis</em>) in sites statewide and used short-read sequencing to identify <em>ospC</em> alleles. <em>B. burgdorferi</em> prevalence in blacklegged ticks varied across sites, but not significantly so. We identified 15 previously characterized <em>ospC</em> alleles accounting for nearly all of the expected diversity of alleles across the sites as estimated using the Chao1 index. Nearly 40% of sequenced infections (23/58) had more than one <em>ospC</em> allele present suggesting mixed strain infections and the relative frequencies of alleles in single infections were positively correlated with their relative frequencies in mixed infections. Turnover of ospC alleles was positively related to distance between sites with closer sites having more similar allele compositions than more distant sites. This suggests a degree of <em>B. burgdorferi</em> dispersal limitation or habitat specialization. <em>OspC</em> alleles known to cause disseminated infections in humans were found at the highest frequencies across sites, corresponding to Delaware's high incidence of Lyme disease.</p>