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Does tick control provide health protection? Insights from The Tick Project

Speaker: Dr. Richard Ostfeld, Cary Institute

To reduce the impact of tick-borne diseases on people, scientists seek to improve diagnosis, treatment, and prevention. A hallmark of prevention is tick control. Several chemical and biological agents lethal to ticks (acaricides) have shown promise in reducing tick abundance. The expectation has been that human encounters with ticks and incidence of tick-borne disease would decline as a result of lower tick abundance.

The Tick Project was designed to test whether two acaricidal treatments, deployed at the level of residential neighborhoods within a Lyme-disease endemic area, would reduce cases of tick-borne disease and human encounters with ticks. We deployed TCS bait boxes, which apply chemical acaricide to small-mammal hosts, and Met52, a fungal acaricide sprayed on vegetation, separately and together, using a double-masked, placebo-controlled, randomized design. Twenty-four neighborhoods, each consisting of roughly 100 properties, in Dutchess County, NY, comprised the study sites.

Although active TCS bait boxes were associated with a ~50% reduction in abundance of host-seeking blacklegged ticks, we observed no significant effects on either human encounters with ticks or cases of tick-borne disease. As a follow-up, we compared the results of published studies that did or did not use masking, placebo controls, and random assignment of treatment categories. We found that studies with masking, placebo controls, and randomization tended to have considerably smaller effect sizes and also tended to show no epidemiological impact. These results suggest that the public health efficacy of tick control in residential areas has not been demonstrated. Funding levels sufficient to reduce serious constraints on experimental design will be important in determining whether tick control will prevent cases of tick-borne disease.