A Lyme borreliosis cycle in seabirds and Ixodes uriae ticks.

The Lyme disease spirochaete, Borrelia burgdorferi s.l., is the only Borrelia known to infect both mammals and birds. The main vertebrate reservoirs of B. burgdorferi are thought to be various small and intermediate size mammals, but the importance of birds as a reservoir has not been thoroughly explored. In the Northern and Southern Hemispheres the seabird tick, Ixodes uriae, is prevalent and closely associated with many species of colony-nesting marine birds. Here we report the presence of spirochaetes, demonstrated by immunofluorescent assay, by polymerase chain reaction and in culture, in I. uriae infesting razorbills on an island in the Baltic Sea. This island is free from mammals. The protein profile of the spirochaetes and the sequences of their flagellin and ospA genes are identical to those of the Lyme disease spirochaete, Borrelia burgdorferi s.l., previously isolated from I. ricinus on a nearby island. In biopsies from the foot web of razorbills, B. burgdorferi-specific DNA was detected after amplification by polymerase chain reaction. Our results suggest that birds play an important part in the maintenance of B. burgdorferi and that mammals may not be a prerequisite for its life cycle.