Lyme disease spirochetes in Japan: enzootic transmission cycles in birds, rodents, and Ixodes persulcatus ticks.

The ixodid tick, Ixodes persulcatus, serves as a vector of Borrelia species associated with Lyme disease in Hokkaido, Japan. The migratory birds of genera Emberiza and Turdus and the woodland rodents of genera Apodemus and Clethrionomys are the wildlife reservoirs. To systemize the enzootic transmission cycles, borreliae isolates were classified by ribosomal RNA gene restriction fragment length polymorphism (RFLP) analysis. Most (> 60%) isolates from the bird-feeding I. persulcatus larvae belonged to Borrelia garinii; the rest were classified as RFLP ribotype group IV (unknown species). In contrast, no B. garinii were found among isolates from rodent-feeding I. persulcatus larvae. These isolates were classified as Borrelia afzelii, group IV, and group V (unknown species). These observations suggest that two enzootic cycles in nature (bird-tick and rodent-tick) maintain borreliae specifically. The group IV species, which was predominant among clinical isolates from Lyme disease patients in Hokkaido, appears to be the most important pathogen for humans.