Diversionary role of hoofed game in the transmission of Lyme disease spirochetes.

To determine whether the presence of ungulates may inhibit transmission of the agent of Lyme disease (Borrelia burgdorferi) while promoting the abundance of its European vector tick (Ixodes ricinus), we compared the feeding density of subadult ticks on roe deer (Capreolus capreolus), red deer (Cervus elaphus), fallow deer (Dama dama), and wild sheep (Ovis ammon) near Berlin and in Brandenburg State, Germany. The prevalence of spirochetal infection in these ticks was compared with that in ticks swept from nearby vegetation. Spirochetes are present in nearly one-fifth of nonfed, questing nymphal and adult wood ticks in the region. Many ungulates in this intensely enzootic region fail to mount a detectable humoral response against the agent of Lyme disease, even when exposed to numerous infected ticks. During the height of the summer, each ungulate may support the feeding of hundreds of subadult ticks. Larvae feed lower on the bodies of hoofed game than do nymphs. Few ticks retain infection by the Lyme disease spirochete after feeding on hoofed game animals. We conclude that numerous I. ricinus ticks feed on ungulates, but that such host-contact fails to infect these ticks while eliminating pre-existing spirochetal infection.