Bird–Borrelia Interactions: A Historical Review and Their Significance for Human Disease Ecology

Research increasingly identifies wild birds, particularly long-distance migratory species, as epidemiologically relevant hosts and vectors for tick-borne Borrelia species that pose risks to both avian and human health. This review contextualizes avian-associated Borrelia research historically and microbiologically, showing the role of avian hosts in the ecology of agents causing relapsing fever and Lyme borreliosis. We identify key publications that trace the evolution of Borrelia research—from early microscopic observations of spirochetes to the modern molecular and serological evidence. The review collects literature on the process by which Borrelia gained early scientific attention due to its characteristic morphology and elevated bloodstream concentrations during septicemic phases, which enabled early etiological links between the microbe and disease. It follows the recognition of avian spirochetosis caused by Borrelia anserina and charts the shift in focus after the discovery of Borrelia burgdorferi sensu lato (Subgen. novum recomm. Borreliella, Lyme-group Borrelia). Publications listed show that birds can transport infected human-parasitic ticks over long distances and, in certain bird species, selectively amplify Lyme-group Borrelia species, especially Borrelia garinii, which has the highest temperature tolerance and is thus potentially viable in avian hosts. The literature supports the role of birds in maintaining and disseminating Borrelia infections and infected ticks across continents.