Blood meal analysis reveals sources of tick-borne pathogens and differences in host utilization of juvenile Ixodes ricinus across urban and sylvatic habitats.

Abstract

Urban green spaces are locations of maximal human activity, forming areas of enhanced risk for tick-borne disease (TBD) transmission. Being also limited in spatial scale, green spaces form prime targets for control schemes aiming to reduce TBD risk. However, for effective control, the key species maintaining local tick and tick-borne pathogen (TBP) populations must be identified. To determine how patterns of host utilization vary spatially, we utilized blood meal analysis to study the contributions of voles, shrews, squirrels, leporids and cervids towards blood meals and the acquisition of TBPs of juvenile Ixodes ricinus in urban and sylvatic areas in Finland. A total of 1084 nymphs were collected from the capital city of Finland, Helsinki and from a sylvatic island in southwestern Finland, and subjected to qPCR analysis to identify DNA remnants of the previous host. We found significant differences in host contributions between urban and sylvatic environments. Specifically, squirrels and leporids were more common hosts in urban habitats, whereas cervids and voles were more common in sylvatic habitats. In addition to providing 18.4% of larval blood meals in urban habitats, red squirrels were identified as the source of 28.6% (n = 48) of Borrelia afzelii detections and 58.1% (n = 18) of Borrelia burgdorferi sensu stricto detections, indicating an important role for local enzootic cycles. Our study highlights that the key hosts maintaining tick and TBP populations may be different in urban and sylvatic habitats. Likewise, hosts generally perceived as important for upkeep may have limited importance in urban environments. Consequently, targeting control schemes based on off-site data of host importance may lead to suboptimal results.