Abstract
Spillback—where non‐native species increase native pathogen prevalence—is potentially an important mechanism by which non‐natives contribute to zoonotic disease emergence. However, spillback has not yet been directly demonstrated because it is difficult to disentangle from confounding factors which correlate with non‐native species abundance and native pathogen prevalence. Here, we capitalise on replicated, quasi‐experimental releases of non‐native pheasants ( Phasianus colchicus ) to compare vector abundance and native pathogen prevalence between sites with similar local conditions but different non‐native densities. Prevalence of Borrelia spp. (the causative agent of Lyme disease) in questing ticks was almost 2.5x higher in woods where pheasants are released compared to control woods, with a particularly strong effect on Borrelia garinii , a bird specialist genospecies. Furthermore, adult (but not nymphal) ticks tended to be more abundant at pheasant‐release woods. This work provides evidence that non‐native species can impact zoonotic pathogen prevalence via spillback in ecologically relevant contexts.