Ecological and Epidemiological Consequences of Tick-Control Interventions in Residential Neighborhoods: A Synthesis of The Tick Project.

Controlling populations of Ixodes ticks has emerged as a core strategy for reducing human exposure to tick-borne infections. Several means of reducing the size of the tick population using chemical and biological acaricides show promise in field trials and are frequently used commercially in North America and Europe. The Tick Project (TTP) assessed whether the use of two commercially available methods of reducing the abundance of host-seeking blacklegged ticks (Ixodes scapularis) reduced encounters with ticks and reported cases of tick-borne disease in humans and their outdoor pets. Residential neighborhoods were the units of replication. Here, we synthesize the results of this large-scale, long-term ecological and epidemiological study and integrate them with comparable literature to assess: (1) the peridomestic risk factors linked to tick encounters and cases of tick-borne disease; (2) the spatial scale of these risk and response factors; (3) discordance between ecological consequences of tick control (strongly reduced tick abundance) and weak or undetectable epidemiological responses; (4) possible causes of the failure of tick control to reduce disease incidence; and (5) future approaches to preventing tick-borne disease with environmentally- and behaviorally-based interventions. We conclude that the low efficacy of tick control in reducing cases of tick-borne disease observed to date could be improved with greater attention to human behaviors that affect exposure risk.