The niche of Borrelia burgdorferi sensu lato in Europe is predictable and mappable

Classic environmental niche modelling to examine the distribution of the causative agent of Lyme borreliosis <i>Borrelia burgdorferi</i> sensu lato (<i>Bb</i>) in the Western Palearctic, is often inadequate because it depends on both its tick vector(s), like <i>Ixodes ricinus</i>, and vertebrate reservoirs. We aimed to better determine, identify, and map the geographic distribution of <i>Bb</i> genospecies compiling data from 15,032 <i>I. ricinus</i> samples and over 6.5 million vertebrate records across 103 genera. We leveraged Species Stacking Distribution Modelling and Principal Components Analysis to identify communities of co-occurring vertebrates and their associations between <i>Bb</i> prevalence in host-seeking <i>Ixodes</i> nymphs and. Four vertebrate communities were revealed, with one strongly linked as primary reservoirs to <i>Bb</i> geographic range. Distribution of <i>Bb</i> in southern Europe was limited by the absence of <i>I. ricinus</i> despite suitable reservoirs, while in northern regions, a lack of competent reservoirs restricts its spread. The <i>Bb</i> prevalence in questing ticks correlates significantly (R² = 0.89) with the presence of key reservoirs rather than overall vertebrate diversity which suggests the <i>Bb</i> niche is predictable and tied to specific vertebrate-tick co-occurrences. We compiled a dataset with the climate, vegetation, and vertebrate-derived variables linked to the transmission pressure of <i>Bb</i> to humans for the complete European territory, aiming for the prevention of infection in humans. This research underscores the importance of integrating reservoir species and tick distribution data to better map and predict <i>Bb</i> spread. By capturing the effects of climate and community composition on the occurrence of <i>Bb</i> in Europe, this framework provides insights for tracking Lyme borreliosis at a continental-level.