Reservoir competence of the wood mouse, Apodemus speciosus ainu, for the Lyme disease spirochete, Borrelia burgdorferi, in Hokkaido, Japan

Abstract

To evaluate the reservoir competence of feral rodents for the Lyme disease spirochete Borrelia burgdorferi transmitted by the ixodid tick Ixodes persulcatus, 523 rodents of 4 species were captured from 2 endemic sites in Furano and Nemuro, Hokkaido, during 1991. A total of 581 larvae and 144 nymphs of I. persulcatus were collected from these rodent specimens. The principal host of I. persulcatus immatures was the wood mouse Apodemus speciosus ainu. The immature ticks collected were examined for spirochetal infections by culturing their internal tissues in BSK medium. The spirochetes were isolated from 35 (20.6%) of 170 I. persulcatus larvae derived from 53 A. speciosus ainu in Furano, and 82 (69.5%) of 118 I. persulcatus larvae derived from 26 A. speciosus ainu in Nemuro. We also demonstrated the transstadial infections in I. persulcatus nymphs that had fed as larvae on A. speciosus ainu in Nemuro. Xenodiagnosis indicated that the mice retained the long-term infectivity for the vector ticks. The laboratory experiment was conducted to determine whether the infected nymphs of I. persulcatus transmit spirochetes to the uninfected A. speciosus ainu. The mice readily became infected by nymphal feeding and showed no morbidity during the infection. These data clearly indicate that A. speciosus ainu is a suitable reservoir host for B. burgdorferi transmitted by I. persulcatus in Hokkaido.