Infestation of Peromyscus leucopus and Tamias striatus by Ixodes scapularis (Acari : Ixodidae) in relation to the abundance of hosts and parasites

The risk of humans acquiring Lyme disease is a function of the local densit y of nymphal and adult ticks that are infected with Lyme disease spirochete s. This in rum, will be related to host-use patterns of ticks and to the de nsities of both juvenile ticks and their hosts. At a forested site in Dutch ess County, NY, we quantified host-use patterns of larval and nymphal Ixode s scapularis Say infesting the 2 dominant vertebrate hosts, white-footed mi ce and eastern chipmunks, during a 3-yr period. Larval tick burdens were 2- 3 times higher on mice than they were on chipmunks, whereas nymphal tick bu rdens were >3 times higher on chipmunks than they were on mice. We used mul tiple I egression analysis to examine juvenile tick and host densities as i ndependent variables influencing tick burdens. The density of questing lan al ticks was positively correlated with larval tick burdens on mice, wherea s the density of questing nymphs was weakly related to nymphal burdens on e ither host. Effects of the densities of mice and chipmunks on tick burdens were strong in some years, but weak in others. Moreover, the sign of the re gression coefficients changed from one year to the next. We argue that thes e results are inconsistent with a passive encounter model of host selection , and suggest instead that either rick behavior or host responses cause str ong biases in the distribution of juvenile ticks on their hosts.