To determine whether rabbits may serve as reservoir hosts for Lyme disease spirochaetes in Europe, we compared their competence as hosts for Borrelia afzelii, one of the most prevalent European spirochaetal variants, with that of the Mongolian jird. To infect rabbits or jirds, at least 3 nymphal or adult Ixodes ricinus ticks infected with spirochaetes fed to repletion on each animal. Whereas jirds readily acquired tick-borne Lyme disease spirochaetes and subsequently infected vector ticks, rabbits exposed to tick-borne spirochaetes rarely became infectious to ticks. Only the rabbit that was infectious to ticks developed an antibody response. To the extent that I. ricinus ticks feed on European rabbits, these mammals may be zooprophylactic by diverting vector ticks from more suitable reservoir competent hosts.

To define conditions promoting inherited infection by Lyme disease spirochetes in Ixodes ticks, we variously infected ticks with Borrelia afzelii and examined their progenies by dark-field microscopy, immunofluorescence, PCR, and serial passage. No episode of inherited infection was evident, regardless of instar or gender infected or frequency of exposure. We suggest that these spirochetes rarely, if ever, are inherited by vector ticks.

We determined whether the genospecies diversity of Lyme disease spirochetes in vector ticks questing on a subtropical island is as broad as that in Central Europe. Although spirochetes infected <1% of the ticks sampled on Madeira Island, these infections included all three genospecies implicated in human disease. Therefore, spirochetal diversity is as great at the southern margin as it is in the center of this pathogen’s range.