The United States is facing an increased risk for Lyme disease and other tick-borne diseases due to the widespread distribution of the blacklegged tick Ixodes scapularis in the northeastern and upper midwestern states. Successful tick population management requires integrated use of various tick management tools or products, such as area spray of acaricides and host-targeted tick control products. However, there is only a limited number of commercial host-targeted tick control products available on the market. The goal of this study was to develop an oral bait formulation of ivermectin and evaluate its efficacy against I. scapularis through in vitro capillary feeding and in vivo efficacy trials using laboratory-bred C3H and Peromyscus leucopus species under laboratory conditions. Tick capillary feeding experiments were performed to ascertain necessary ivermectin plasma levels to kill feeding ticks. An ivermectin-treated bait was then fed to mice to show resulting pharmacokinetic properties and resulting ivermectin concentrations via HPLC. Subsequent tick-challenge trials were conducted to ascertain ivermectin impact on feeding and engorgement and impact on mouse morbidity. Results indicate ivermectin can kill feeding ticks effectively in the capillary feeding studies. However, in vivo study animal models, ivermectin was most effective in killing ticks when ingested by mice prior to tick challenge (i.e., 24-hours). While ivermectin has shown some efficacy in controlling tick feeding in P. leucopus on a temporally limited basis, which in turn impacts the amount of ivermectin that must be applied in a given area for a reasonable knockdown of ticks. This can raise environmental concerns and impact programmatic costs. Based on the results from this study, continuing product development is not recommended.

In vitro and in vivo acaricidal properties of orally delivered ivermectin against the black-legged tick Ixodes scapularis

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ACS Fall 2022

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