Local Distribution and Genetic Structure of Tick-borne Pathogens: an Example Involving the Marine Cycle of Lyme Disease

Despite the potential importance of the local structure of micropathogen populations for the epidemiology of vector‐borne diseases, the spatial and temporal heterogeneity of these populations is often neglected. This variability may have strong effects on micropathogen transmission, and therefore needs to be considered more explicitly to understand disease dynamics. Here, we examine the effects of time (years) and space (cliffs) on the local distribution and genetic structure of Lyme disease bacteria Borrelia burgdorferi sensu lato in the marine system involving seabirds and the tick Ixodes uriae. We tested for the presence of Borrelia spp. in 351 ticks collected from Black‐legged kittiwakes (Rissa tridactyla) within a large seabird colony by amplification of the flaB gene. Overall, the prevalence was 11% (±2%) and varied among sub‐colonies (i.e., cliffs), but not among years. Direct sequencing of the amplified products revealed the presence of three species of Borrelia burgdorferi s.l.: B. garinii, B. burgdorferi sensu stricto and B. afzelii. This is the first record of B. afzelii in the marine system. Isolates of B. garinii, the most abundant bacterial species, were genetically structured among cliffs, but did not change significantly over time. Our findings indicate that LB spirochetes circulating in the marine cycle are highly diverse, even at a local scale, and that the spatial structure revealed by our data should be considered more widely in this system and in epidemiological studies of Lyme disease in general. For example, adequate sampling designs to reliably estimate parameters such as local prevalence, abundance and diversity will need to take this heterogeneity into account.