Ecological correlates of genetic diversity in Borrelia burgdorferi, the lyme disease bacterium.

摘要

Lyme disease is the number one reported vector-borne disease in the United States, and this disease continues to spread in the Northeast and Midwest. Lyme disease is caused by Borrelia burgdorferi, a bacterium that circulates among vertebrate host species and transmitted among hosts by the black-legged tick (Ixodes scapularis). The bacterium has high genetic variation at the outer surface protein C ( ospC) locus, and past studies suggests that hosts act as ecological niches to the ospC genotypes. In particular, five types are known to be human invasive (HIS), making it essential to examine disease risk at the genotypic level. My studies focus on understanding the ecological drivers of ospC diversity and frequency profile at the individual, community, and landscape scales. In chapter one, I found that endemic areas of New York State have higher ospC richness and diversity than newly invaded areas, and that HIS types are relatively common across the landscape. There is high turnover of genotypes from one population to another population along the invasion scale. In chapter two, host community composition matters when examining ospC diversity, and that host composition and host diversity are important in predicting HIS infection prevalence. Contrasting important predictors between years 2006 and 2009 could be a result of annual variation and/or site variation, since the majority of sites were not sampled in both years. Obtaining better inclusive host community composition and diversity estimates could help with the predictive powers of these metrics on the ospC frequency profile, especially with HIS types. In chapter three, variation among nine host species and their associated ospC genotype frequency profiles supports the host-niche concept. Short-tailed shrews (Blarina brevicauda) and American robins (Turdus migratorius) have high proportions of HIS to non-HIS, suggesting they could help contribute to higher disease risk. Lastly, there is support for a trade-off between occurrence frequency and transmission efficiencies of ospC types from hosts to ticks feeding on these individuals. This research sheds new light on how host composition and diversity influences disease risk, that HIS types infect all nine host species, and that HIS types occur commonly across NY State.