Limited Capacity of Deer To Serve as Zooprophylactic Hosts for Borrelia burgdorferi in the Northeastern United States.

Because deer are considered to be incompetent reservoirs of the agent of Lyme disease (Borrelia burgdorferi sensu stricto) in the northeastern United States, they may serve as zooprophylactic or "dilution" hosts if larvae of the deer tick vector (Ixodes dammini, "northern" clade of Ixodes scapularis) frequently feed on them. To determine whether host-seeking nymphal deer ticks commonly feed on deer as larvae, we used a real-time PCR host bloodmeal remnant identification assay to identify the host on which these ticks had fed. Nymphal lone star ticks (Amblyomma americanum) were collected simultaneously in our sites and provided an index of the availability of deer in these sites. At 3 of the 4 sites, Ixodes nymphs had fed as larvae on a variety of hosts, including mice, birds, and shrews, but rarely on deer (<6% for all sites); in contrast, lone star tick nymphs had commonly fed on deer (31 to 78%). Deer were common larval hosts for Ixodes ticks (39% of bloodmeals) in only one site. The prevalence of B. burgdorferi in host-seeking nymphal deer ticks was associated with mouse-fed ticks (P = 0.007), but there was no association with deer-fed ticks (P = 0.5). The diversity and prevalence of hosts that were identified differed between deer ticks and lone star ticks that were collected simultaneously, demonstrating that there is no confounding of host bloodmeal identification by contaminating environmental DNA (eDNA). We conclude that deer were not common hosts for larval deer ticks, thus limiting their zooprophylactic role in our sites. IMPORTANCE Because deer are incompetent reservoirs for B. burgdorferi, their presence may modulate the force of enzootic transmission by serving as zooprophylactic or "dilution" hosts. Such an effect would depend on the extent to which subadult deer ticks feed on other hosts. We used bloodmeal analysis on nymphal deer ticks to identify the host upon which larvae had fed. We found that lone star ticks collected at the same time as deer ticks commonly fed on deer, but deer ticks did not. We conclude that deer are not a preferred host for larval deer ticks and, thus, are not necessarily zooprophylactic.