ABSTRACTThis is the first report on the isolation of Lyme diseaseBorreliafrom seabirds on the Faeroe Islands and the characteristics of its enzootic cycle. The major components of theBorreliacycle include the puffin (Fratercula arctica) as the reservoir andIxodes uriaeas the vector. The importance of this cycle and its impact on the spread of human Lyme borreliosis have not yet been established.Borreliaspirochetes isolated from 2 of 102 sampled puffins were compared to the borreliae previously obtained from seabird ticks,I. uriae. Therrf-rrlintergenic spacer and therrsand theospCgenes were sequenced and a series of phylogenetic trees were constructed. Sequence data and restriction fragment length polymorphism analysis grouped the strains together withBorrelia garinii. In a seroepidemiological survey performed with residents involved in puffin hunting on the Faeroe Islands, 3 of 81 serum samples were found to be positive by two commonly used clinical tests: a flagellin-based enzyme-linked immunosorbent assay (ELISA) and Western blotting. These three positive serum samples also had high optical density values in a whole-cell ELISA. The finding of seropositive Faeroe Islanders who are regularly exposed toI. uriaeindicate that there may be a transfer ofB. gariniiby this tick species to humans.