First isolations of Borrelia burgdorferi from rodents collected in northern Europe.

Spirochetes were found in 13% of Ixodes ricinus collected from an island, near Stockholm where human borreliosis is endemic. Borrelia burgdorferi was cultivated from the kidney and/or spleen of wild rodents (Clethrionomys glareolus and Apodemus flavicollis) from the same island. Spirochetes were identified as Borrelia burgdorferi by indirect immunofluorescence assays using species and genus specific monoclonal antibodies. In these tests the spirochetes could not be differentiated from strains previously cultured from Swedish patients with Ixodes-borne borreliosis. The results show that small rodents in Europe may harbour borreliae and indicate that C. glareolus and A. flavicollis may be important reservoirs for the spirochetes causing Ixodes-borne borreliosis in humans and domestic animals in Europe.