Asynchronous local differences in Lyme disease environmental hazard driven by variation in tick abundance and Borrelia burgdorferi infection prevalence

Background The tick-borne disease Lyme borreliosis (LB) is a clear and increasing public health threat across the temperate regions of the northern hemisphere, including the United Kingdom. The epidemiology of LB is shaped by the environmental hazard posed by its causative agent Borrelia burgdorferi sensu lato, which is frequently quantified in terms of the density of infected nymphal ticks (DIN). Methods We report quantification of the dynamics of DIN at three sites in close proximity to one another in Cumbria, a region of the UK where LB is frequently reported, through monthly surveys of questing Ixodes ricinus nymphs over a 33-month period. Results Despite the proximity of study sites, we observed significant spatial variation in DIN between them. We also observed significant temporal variation in DIN at all three sites, but this variation was asynchronous. Changes in both tick abundance and B. burgdorferi infection prevalence underlay this variation. Conclusions These observations suggest very local key ecological determinants of DIN and that meaningful estimation/prediction of LB risk on a national or regional scale is extremely challenging.